SLOVAK UNIVERSITY OF TECHNOLOGY IN BRATISLAVA
FACULTY OF CHEMICAL AND FOOD TECHNOLOGY
Institute of Organic Chemistry, Catalysis and Petrochemistry
ORGANIC TECNOLOGY
AND
PETROCHEMISTRY
REPORT ON TRAINING VISIT
In the frame work of the project
No. SAMRS 2010/12/10
“Development of human resource capacity of Kabul polytechnic university”
Funded by
Bratislava 2010
Pro.Phd.hasani
1
Acknowledgement:
The author would like to express his appreciation for the Scientific Training Program to
Institute of Chemical and Environmental Engineering, Faculty of Chemical and Food
Technology of the Slovak University of Technology and Slovak Aid program for financial
support of this project. I would like to say my hearth thank to Assoc. Prof. Alexander
Kaszonyi, PhD.. for his guidance and assistance during the all time of my training visit. My
thank belongs also to Assoc. Prof. Ing. Juma Haydary, PhD. the coordinator of the project
SMARS/2010/12/10 in the frame work of which my visit was realized.
2
VISITING REPORT
FROM
FACULTY OF CHIMICAL TECHNOLOGY
OF
SLOVAK UNIVERSITY OF TECHNOLOGY
IN BRATISLOVA
This visit was organized for exchanging knowledgical views and
advices between us (professors of Kabul Poly Technical
University) and professors of this faculty.
My visit was especially organized to the departments of organic
chemistry and technology of organic materials.
I did following activities in this period that includes in 3 parts:
1.Pedagogic area
2.Researches
3.Practical activities
Each part is described as following:
1. PEDAGOGIC AREA: - I attended to the lectures of the professors
and, saw the methods of the lectures and teachings, I also visit
the classes and sow the students and their activities, besides of
these I also participated to the Conferences and Seminars
presented by the professors and students.
2. RESEARCHES: - I researched about petroleum and its derivatives
that is the most important factor and skeleton for economical
development of a human being society and a country and
especially in our country that it is the hot view of point now a
days. During this period I prepared a knowledgical article which
is included.
3
3. PRACTICAL ACTIVITIES:- I did some syntheses of glycerol
products under deferent conventions and deferent parameters
and then these products were checked and evaluated by
physical chemical methods that were satisfy able. These
activities were done independently and with the aspirants of
this faculty as well in the Technology of Organical materials’
department. These activities are written in an additional report
which is included.
4
PREFACE
This visit was organized for exchanging knowledgical views
and advices between us (professor of Kabul Poly Technic
University and professors of faculty of Chemical Technology
specially departments of Technology of Organic Materials and
Organic Chemistry).
As we know that chemistry is one part of scientific
Knowledge and Organic chemistry is the most important part of
it, that products of it are used in all parts of life. Due to fast
increasing inhabitance of humanity on the earth we feel more
necessity for fast improving of this technology and its products,
especially after discovering of petroleum and its derivatives that
cover all fields of our life. For this reason all scientist and
researchers of chemistry and Technology of Chemistry are
interested to this field of science,
Fortunately our country has a lot of rich natural minds, to educts
and use these minds is needed modern technology, of course this
might have improve the national economy stage and prepare
good situation for the life of human being.
To reach to this aim needs to learn and use the new and modern
methods and technology.
During this visiting we met new and modern methods and
technology of chemistry that are very useful for our students and
we will teach them too.
5
Organic Technology and Petrochemistry
6
7
8
9
10
11
12
Petrochemical
Petrochemicals are chemical products made from raw materials of petroleum or other
hydrocarbon origin. Although some of the chemical compounds that originate from petroleum
may also be derived from coal and natural gas, petroleum is the major source. The largest
petrochemical industries are to be found in the USA and Western Europe, though the major
growth in new production capacity is in the Middle East and Asia. There is a substantial interregional trade in petrochemicals of all kinds. World production of ethylene is around 110
million tons per year, of propylene 65 million tons, and of aromatic raw materials 70 million
tons.
The following is a partial list of the major commercial petrochemicals and their derivatives:
•
•
ethylene - the simplest olefin; used as a ripening hormone, a monomer and a chemical
feedstock
o polyethylenes - polymerized ethylene
o ethanol - made by hydration (chemical reaction adding water) of ethylene
o ethylene oxide - sometimes called oxirane; can be made by oxidation of
ethylene
 ethylene glycol - from hydration of ethylene oxide or oxidation of
ethylene
 engine coolant - contains ethylene glycol
 polyesters - any of several polymers with ester linkages in the
backbone chain
 glycol ethers - from condensation of glycols
 ethoxylates
o vinyl acetate
o 1,2-dichloroethane
 trichloroethylene
 tetrachloroethylene - also called perchloroethylene; used as a dry
cleaning solvent and degreaser
 vinyl chloride - monomer for polyvinyl chloride
 polyvinyl chloride (PVC) - type of plastic used for piping,
tubing, other things
propylene - used as a monomer and a chemical feedstock
o isopropyl alcohol - 2-propanol; often used as a solvent or rubbing alcohol
o acrylonitrile - useful as a monomer in forming Orlon, ABS
o polypropylene - polymerized propylene
o propylene oxide
 propylene glycol - sometimes used in engine coolant
 glycol ethers - from condensation of glycols
o isomers of butylene - useful as monomers or co-monomers
 isobutylene - feed for making methyl tert-butyl ether (MTBE) or
monomer for copolymerization with a low percentage of isoprene to
make butyl rubber
o 1,3-butadiene - a diene often used as a monomer or co-monomer for
polymerization to elastomers such as polybutadiene or a plastic such as
acrylonitrile-butadiene-styrene (ABS)
 synthetic rubbers - synthetic elastomers made of any one or more of
several petrochemical (usually) monomers such as 1,3-butadiene,
styrene, isobutylene, isoprene, chloroprene; elastomeric polymers are
13
often made with a high percentage of conjugated diene monomers such
as 1,3-butadiene, isoprene, or chloroprene
o higher olefins
 polyolefins such poly-alpha-olefins which are used as lubricants
 alpha-olefins - used as monomers, co-monomers, and other chemical
precursors. For example, a small amount of 1-hexene can be
copolymerized with ethylene into a more flexible form of polyethylene.
 other higher olefins
 detergent alcohols
o acrylic acid
 acrylic polymers
o allyl chloride  epichlorohydrin - chloro-oxirane; used in epoxy resin formation
 epoxy resins - a type of polymerizing glue from bisphenol A,
epichlorohydrin, and some amine
•
benzene - the simplest aromatic hydrocarbon
o ethylbenzene - made from benzene and ethylene
 styrene made by dehydrogenation of ethylbenzene; used as a monomer
 polystyrenes - polymers with styrene as a monomer
o cumene - isopropylbenzene; a feedstock in the cumene process
 phenol - hydroxybenzene; often made by the cumene process
 acetone - dimethyl ketone; also often made by the cumene process
 bisphenol A - a type of "double" phenol used in polymerization in
epoxy resins and making a common type of polycarbonate
 epoxy resins - a type of polymerizing glue from bisphenol A,
epichlorohydrin, and some amine
 polycarbonate - a plastic polymer made from bisphenol A and
phosgene (carbonyl dichloride)
 solvents - liquids used for dissolving materials; examples often made
from petrochemicals include ethanol, isopropyl alcohol, acetone,
benzene, toluene, xylenes
o cyclohexane - a 6-carbon aliphatic cyclic hydrocarbon sometimes used as a
non-polar solvent
 adipic acid - a 6-carbon dicarboxylic acid which can be a precursor
used as a co-monomer together with a diamine to form an alternating
copolymer form of nylon.
 nylons - types of polyamides, some are alternating copolymers
formed from copolymerizing dicarboxylic acid or derivatives
with diamines
 caprolactam - a 6-carbon cyclic amide
 nylons - types of polyamides, some are from polymerizing
caprolactam
o nitrobenzene - can be made by single nitration of benzene
 aniline - aminobenzene
 methylene diphenyl diisocyanate (MDI) - used as a comonomer with diols or polyols to form polyurethanes or with
di- or polyamines to form polyureas
 polyurethanes
o alkylbenzene - a general type of aromatic hydrocarbon which can be used as a
presursor for a sulfonate surfactant (detergent)
14

•
•
detergents - often include surfactants types such as
alkylbenzenesulfonates and nonylphenol ethoxylates
o chlorobenzene
toluene - methylbenzene; can be a solvent or precursor for other chemicals
o benzene
o toluene diisocyanate (TDI) - used as co-monomers with diols or polyols to
form polyurethanes or with di- or polyamines to form polyureas
 polyurethanes - a polymer formed from diisocyanates and diols or
polyols
o benzoic acid - carboxybenzene
 caprolactam
 nylon
mixed xylenes - any of three dimethylbenzene isomers, could be a solvent but more
often precursor chemicals
o ortho-xylene - both methyl groups can be oxidized to form (ortho-)phthalic
acid
 phthalic anhydride
o para-xylene - both methyl groups can be oxidized to form terephthalic acid
 dimethyl terephthalate - can be copolymerized to form certain
polyesters
 polyesters - although there can be many types, polyethylene
terephthalate is made from petrochemical products and is very
widely used.
 purified terephthalic acid - often copolymerized to form polyethylene
terephthalate
 polyesters
Modern Refining
Petroleum refineries are marvels of modern engineering. Within them a maze of pipes,
distillation columns, and chemical reactors turn crude oil into valuable products. Large
refineries cost billions of dollars, employ several thousand workers, operate around the clock,
and occupy the same area as several hundred football stadiums. The U.S. has about 300
refineries that can process anywhere between 40 and 400,000 barrels of oil a day. These
refineries turn out the gasoline and chemical feedstocks that keep the country running.
Locating an oil field is the first obstacle to be overcome. The first explorers used Y-shaped
devining rods and other supernatural, but ineffective, means of locating petroleum. Today
geologists and petroleum engineers employ more tried and true methods. Instruments to aid
the search include; geophones (uses sound), gravimeters (uses gravity), and magnetometers
(uses the Earth's magnet field). While these methods narrow the search tremendously, a
person still has to drill a exploratory well, or wildcat well, to see if the oil actually exists.
Success brings visions of gushers soaring skyward, however today wells are capped before
this happens.
Drilling
There are three main types of drilling operations; cable-tool, rotary, and off-shore. Cabletool drilling involves a jack-hammer approach were a chisel dislodges earth and hauls up the
loose sediment. Rotary drilling works at much greater depths, and involve sinking a drill
15
pipe with a rotating steel bit in the middle. Off-shore drilling involves huge
semisubmersible platforms which lower a shaft to the ocean floor, containing any oil which
is located.
All crude oil contains some amount of methane or other gases dissolved in it. Once the
drilling shaft makes contact with the oil it releases the pressure in the underground reservoir.
Just like opening a can of soda pop, the dissolved gases fizz out of solution pushing crude
oil to the surface. The dissolved gases will allow about 20% recovery of oil. To get better
recovery water is often pumped into the well, this forces the lighter oil to the surface. Water
flooding allows recoveries of about 50%. The addition of surfactant allows even more oil to
be recovered by preventing much of it from getting trapped in nooks and crannies. Yet, it is
impossible to get all of the oil out of a well.
Transportation
Because crude oil is a liquid it is much easier to move than natural gas or coal. Coal is nice
and dense, so it does not require large holding containers, but it cannot be pumped.
Conveyor belts and cranes cannot compete with pipelines for economic efficiency. Natural
gas can be pumped using expensive compressors, but it requires enormous holding tanks. A
recent trick has been to inject huge amounts of water into salt strata. The water dissolves the
salt, leaving truly enormous caverns. The natural gas is then pumped in and stored until
needed. The ease in transporting oil is one of the reasons we have become so dependent
upon it. Pound for pound natural gas and coal just cannot compete.
Reserves
The proven reserves of crude oil within the U.S. are about 3.9 billion cubic meters. This
could cover the state of Minnesota with a layer one half inch thick. A reasonable value for
the total amount of crude oil obtainable using current methods from around the world is 350
billion cubic meters. This could cover Minnesota with a layer of oil four and a half feet
thick. Yet, at the rate we are consuming oil, the nation's reserves will be depleted by 2010,
and the world's reserves will be depleted by the end of the 21st Century.
Chemistry
Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly
found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons, or
more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of
molecules, which define its physical and chemical properties, like color and viscosity.
The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched
chains which contain only carbon and hydrogen and have the general formula CnH2n+2 They
generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or
longer molecules may be present in the mixture.
The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline (petrol), the
ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel and kerosene (primary
component of many types of jet fuel), and the ones from hexadecane upwards into fuel oil and
lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately
25 carbon atoms, while asphalt has 35 and up, although these are usually cracked by modern
refineries into more valuable products. The shortest molecules, those with four or fewer
16
carbon atoms, are in a gaseous state at room temperature. They are the petroleum gases.
Depending on demand and the cost of recovery, these gases are either flared off, sold as
liquified petroleum gas under pressure, or used to power the refinery's own burners. During
the winter, Butane (C4H10), is blended into the gasoline pool at high rates, because butane's
high vapor pressure assists with cold starts. Liquified under pressure slightly above
atmospheric, it is best known for powering cigarette lighters, but it is also a main fuel source
for many developing countries. Propane can be liquified under modest pressure, and is
consumed for just about every application relying on petroleum for energy, from cooking to
heating to transportation.
The cycloalkanes, also known as naphthenes, are saturated hydrocarbons which have one or
more carbon rings to which hydrogen atoms are attached according to the formula CnH2n.
Cycloalkanes have similar properties to alkanes but have higher boiling points.
The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar
six-carbon rings called benzene rings, to which hydrogen atoms are attached with the formula
CnHn. They tend to burn with a sooty flame, and many have a sweet aroma. Some are
carcinogenic.
These different molecules are separated by fractional distillation at an oil refinery to produce
gasoline, jet fuel, kerosene, and other hydrocarbons. For example 2,2,4-trimethylpentane
(isooctane), widely used in gasoline, has a chemical formula of C8H18 and it reacts with
oxygen exothermically:[11]
Incomplete combustion of petroleum or gasoline results in production of toxic byproducts.
Too little oxygen results in carbon monoxide. Due to the high temperatures and high pressures
involved, exhaust gases from gasoline combustion in car engines usually include nitrogen
oxides which are responsible for creation of photochemical smog.
Formation
Geologists view crude oil and natural gas as the product of compression and heating of
ancient organic materials (i.e. kerogen) over geological time. Formation of petroleum occurs
from hydrocarbon pyrolysis, in a variety of mostly endothermic reactions at high temperature
and/or pressure.[13] Today's oil formed from the preserved remains of prehistoric zooplankton
and algae, which had settled to a sea or lake bottom in large quantities under anoxic
conditions (the remains of prehistoric terrestrial plants, on the other hand, tended to form
coal). Over geological time the organic matter mixed with mud, and was buried under heavy
layers of sediment resulting in high levels of heat and pressure (known as diagenesis). This
caused the organic matter to chemically change, first into a waxy material known as kerogen
which is found in various oil shales around the world, and then with more heat into liquid and
gaseous hydrocarbons in a process known as catagenesis.
Geologists often refer to the temperature range in which oil forms as an "oil window"[14]—
below the minimum temperature oil remains trapped in the form of kerogen, and above the
maximum temperature the oil is converted to natural gas through the process of thermal
cracking. Although this temperature range is found at different depths below the surface
throughout the world, a typical depth for the oil window is 4–6 km. Sometimes, oil which is
formed at extreme depths may migrate and become trapped at much shallower depths than
where it was formed. The Athabasca Oil Sands is one example of this.
17
Crude oil reservoirs
Hydrocarbon trap.
Three conditions must be present for oil reservoirs to form: a source rock rich in hydrocarbon
material buried deep enough for subterranean heat to cook it into oil; a porous and permeable
reservoir rock for it to accumulate in; and a cap rock (seal) or other mechanism that prevents
it from escaping to the surface. Within these reservoirs, fluids will typically organize
themselves like a three-layer cake with a layer of water below the oil layer and a layer of gas
above it, although the different layers vary in size between reservoirs. Because most
hydrocarbons are lighter than rock or water, they often migrate upward through adjacent rock
layers until either reaching the surface or becoming trapped within porous rocks (known as
reservoirs) by impermeable rocks above. However, the process is influenced by underground
water flows, causing oil to migrate hundreds of kilometres horizontally or even short
distances downward before becoming trapped in a reservoir. When hydrocarbons are
concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling
and pumping.
The reactions that produce oil and natural gas are often modeled as first order breakdown
reactions, where hydrocarbons are broken down to oil and natural gas by a set of parallel
reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter
set is regularly used in petrochemical plants and oil refineries.
Non-conventional oil reservoirs
Oil-eating bacteria biodegrades oil that has escaped to the surface. Oil sands are reservoirs of
partially biodegraded oil still in the process of escaping and being biodegraded, but they
contain so much migrating oil that, although most of it has escaped, vast amounts are still
present—more than can be found in conventional oil reservoirs. The lighter fractions of the
crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of
crude oil, called crude bitumen in Canada, or extra-heavy crude oil in Venezuela. These two
countries have the world's largest deposits of oil sands.
On the other hand, oil shales are source rocks that have not been exposed to heat or pressure
long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil
shales are not really shales and do not really contain oil, but are usually relatively hard rocks
called marls containing a waxy substance called kerogen. The kerogen trapped in the rock can
be converted into crude oil using heat and pressure to simulate natural processes. The method
has been known for centuries and was patented in 1694 under British Crown Patent No. 330
covering, "A way to extract and make great quantityes of pitch, tarr, and oyle out of a sort of
stone." Although oil shales are found in many countries, the United States has the world's
largest deposits.[15]
Classification
The petroleum industry generally classifies crude oil by the geographic location it is produced
in (e.g. West Texas, Brent, or Oman), its API gravity (an oil industry measure of density), and
by its sulfur content. Crude oil may be considered light if it has low density or heavy if it has
18
high density; and it may be referred to as sweet if it contains relatively little sulfur or sour if it
contains substantial amounts of sulfur.
The geographic location is important because it affects transportation costs to the refinery.
Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline,
while sweet oil commands a higher price than sour oil because it has fewer environmental
problems and requires less refining to meet sulfur standards imposed on fuels in consuming
countries. Each crude oil has unique molecular characteristics which are understood by the
use of crude oil assay analysis in petroleum laboratories.
Barrels from an area in which the crude oil's molecular characteristics have been determined
and the oil has been classified are used as pricing references throughout the world. Some of
the common reference crudes are:
•
•
•
•
•
•
West Texas Intermediate (WTI), a very high-quality, sweet, light oil delivered at
Cushing, Oklahoma for North American oil
Brent Blend, comprising 15 oils from fields in the Brent and Ninian systems in the
East Shetland Basin of the North Sea. The oil is landed at Sullom Voe terminal in the
Shetlands. Oil production from Europe, Africa and Middle Eastern oil flowing West
tends to be priced off this oil, which forms a benchmark
Dubai-Oman, used as benchmark for Middle East sour crude oil flowing to the AsiaPacific region
Tapis (from Malaysia, used as a reference for light Far East oil)
Minas (from Indonesia, used as a reference for heavy Far East oil)
The OPEC Reference Basket, a weighted average of oil blends from various OPEC
(The Organization of the Petroleum Exporting Countries) countries
A Few Terms
The petroleum industry, like other chemical industries, has a plethora of terms designed to
scare off anyone who wants to understand exactly what is going on. Mastering this
nomenclature is one of the main tasks facing chemistry and chemical engineering
students. Here are a few commonly used terms, but be forewarned; because of the complexity
of compounds in the petroleum industry some of these terms are very vague.
Hydrocarbons are chemical compounds made mainly of carbon and hydrogen. Both
petroleum and coal contain many different hydrocarbons. Methane, ethanol, and benzene are
examples of hydrocarbons, though there are many many others.
Bitumen is another term for hydrocarbons. Both petroleum and coal are sometimes referred
to as Bituminous.
Organic compounds are chemicals made of carbon (although the classification is not totally
consistent and some carbon compounds, like carbon dioxide, are not considered organic).
Hydrocarbons are commonly referred to as organic compounds, and it is fair to think of the
two as equivalent. Carbohydrates, proteins, and urea (found in urine) are examples or organic
compounds. It was once thought that organic compounds could only be produced from
organic sources. Because of their usefulness, a huge chemical industry developed around
organic chemicals during the 19th Century. Dyes and pharmaceuticals where products of this
industry. As chemists increased their skills they found that organic compounds could be
synthesized from inorganic sources. However, by this time the classification had been firmly
rooted in industry and universities and so it remains today.
19
Inorganic compounds include everything that is not considered organic (every compound
in the world is ether organic or inorganic).
Aromatic compounds are organic compounds which always have a benzene ring in them.
Because of this they can be quite reactive and have some interesting properties. The dye
and pharmaceutical industries depend heavily on aromatic compounds.
Aliphatic compounds are organic compounds which are not aromatic. They include single
bonded (ethane, propane, butane), double bonded (ethene or called ethylene, propene, butene),
and triple bonded (ethyne or called acetylene, propyne, butyne) straight chain hydrocarbons as
well as cyclic non-benzene structures (cyclopentane, cyclobutane) (every organic compound
in the world is either aromatic or aliphatic).
A Barrel (bbl.) of crude contains 42 gallons or 158.8 liters. No one actually ships petroleum
in barrels anymore because they are too small, but the term is still used to describe a defined
volume.
Petroleum literally means "rock oil". It is a very broad word referring to all liquid
hydrocarbons which can be collected from the ground. Even natural gas and solid
hydrocarbons are sometimes referred to as petroleum. When petroleum first comes from the
ground it is called crude oil. Later it is usually just referred to as oil. It can flow like water or
be as viscous as peanut butter. It can be yellow, red, green, brown, or black.
Fractions are complex mixtures of chemical compounds that all have a similar boiling
point. Light and heavy fractions refer to a compound's boiling point and not their actual
density (these are two entirely different things). Light fractions can be very heavy (dense),
and heavy fractions can be very light (go figure)!
Isomers are chemicals which have the same number and type of atoms but have them
arranged in a different way. Methane (CH4), ethane (C2H6), and propane (C3H8) have no
isomers because their is only one way the carbons can hook together. Butane (C4H10) has
two isomers (n-butane and isobutane). Decane (C10H22) has seventy five isomers, and a
molecule with 20 carbon atoms (C20H42) has over 100,000 isomers. Crude oil contains
molecules having 1 to 100+ carbon atoms. Naming these compounds based upon normal
chemical rhetoric would be hell on earth! The huge number of possible molecular
arrangements is why people talk of fractions instead of using proper chemical nomenclature.
Natural Gas is a mixture of very low boiling hydrocarbons. Natural gas can only be
liquefied under extremely high pressures and very low temperatures. It is called "dry" when
methane (CH4) is the primary component, and "wet" if it contains higher boiling
20
hydrocarbons. If it smells bad, because of sulfur compounds, it is called "sour". Otherwise, it
is called "sweet".
Liquefied Petroleum Gas (LPG) is a very light fraction of petroleum. It is also a fairly
simple fraction containing mainly propane and butane. First, it should be noted that under
normal pressures LPG is actually a gas, unlike gasoline (often just called "gas") which is
really a liquid (ugh). However, under modestly high pressures these compounds can be
converted to a liquid (hence their name). Being able to store them as a liquid reduces the
container size by a factor of a hundred. This is no doubt why propane stoves are so popular.
As cracking methods have evolved more and more LPG has been produced by refineries.
Gasoline is a light fraction of petroleum which is quite volatile and burns rapidly. Straight
run gasoline refers to gasoline produced by distillation instead of cracking, although it really
doesn't make a difference. Gasoline is often just called "gas", however it is a liquid at
typical pressures. This confusing state of affairs developed because the first internal
combustion engines ran on town gas (a mixture of carbon monoxide, CO, and hydrogen,
H2, both actual gases). These engines were therefore called "gas engines". When gasoline
replaced town gas people still called the motors "gas engines" and also started calling gasoline
"gas". Today, the average American uses 450 gallons of gasoline a year.
Octane Number rates a fuel's ability to avoid premature ignition called knock. Premature
ignition reduces an engine's power and quickly wares it out. The octane scale arbitrarily
defines n-heptane a value of 0, and isooctane (2, 2, 4-trimethyl pentane) an octane number of
100. Isooctane is then added to heptane until the mixture has the same knock characteristics as
the fuel being tested, and the percent isooctane is taken as the unknown fuels octane number.
Tetraethyl lead used to be a common anti-knock additive which would raise a fuels octane
number. High octane fuel can be used in engines with high compression ratios which in
turn produce much more power. However, the additive is no longer used because of concerns
over lead pollution.
Naphtha is a light fraction of petroleum used to make gasoline. Naphtha also produces
solvents and feedstocks for the petrochemical industry.
Kerosene was the first important petroleum fraction, replacing whale oils in lamps over a
hundred years ago. Some unscrupulous refiners failed to distill off all the naphtha from the
kerosene fraction thereby increasing the volume of their final product. This lead to many lamp
explosions and fires.
Diesel fuels find use in the fleet of trucks which transport the nations goods. Diesel engines
power these larger engines, and use higher compression ratios (and temperatures) than their
gasoline cousins. They are therefore more efficient. It is also interesting to note that diesel
engines have no spark plugs, instead the fuel-air mixture is ignited by the rising
temperatures and pressures during the compression stroke.
Gas Oil (or fuel oils) are used for domestic heating. In the winter refineries produce more
gas oil, whereas during the summer driving months they produce more gasoline.
Heavy Fuel Oil is often blended with gas oils for easier use in industry. Ships burn heavy
fuel oils but they call it bunker oil.
Atmospheric Residual is everything that cannot be vaporized under normal pressures.
Atmospheric residual is fed into another distillation column, operating at lower pressures,
21
which can separate out some of the lighter compounds. Lubricants and waxes reside in this
fraction.
Paraffins
30%
15 to 60%
Asphaltics
6%
remainder
Vacuum Residual
is the bottom of
the barrel. It
includes asphalt
and some coke.
Pitch is a thick, black, sticky material. It is left behind when the lighter components of coal
tar or petroleum are distilled off. Pitch is a "natural" form of asphalt.
Asphalt is a high boiling component of crude oil. It is therefore found at the "bottom of the
barrel" when petroleum is distilled.
Tars are byproducts formed when coke is made from coal or charcoal is made from wood.
It is a thick, complex, oily black mixture of heavy organic compounds very similar to pitch or
asphalt, though from a different source.
Composition
The proportion of hydrocarbons in the mixture is highly variable and ranges from as much as
97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.
The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic
hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and
trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular
composition varies widely from formation to formation but the proportion of chemical
elements vary over fairly narrow limits as follows:[2]
Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of
each varies from oil to oil, determining the
22
1. desalting
Why Desalt Crude?
•
•
•
•
•
The salts that are most frequently present in crude oil are Calcium,Sodium and
Magnesium Chlorides. If these compounds are not removed from the oil several
problems arise in the refining process. The high temperatures that occur downstream
in the process could cause water hydrolysis, which in turn allows the formation of
hydrochloric acid.
Sand, Silts, Salt deposit and Foul Heat Exchangers
Water Heat of Vaporization reduces crude Pre-Heat capacity
Sodium, Arsenic and Other Metals can poison Catalysts
Environmental Compliance, i.e., By removing the suspended solids, which might
otherwise become an issue in flue gas opacity norms, etc.,
Distillation
Which Fraction to Make?
Various fractions are more important at different times of year. During the summer
driving months, the public consumes vast amounts of gasoline, whereas during the winter
more fuel oil is consumed. These demands also vary depending upon whether you live in the
frigid north, or the humid south. Modern refineries are able to alter the ratios of the
different fractions to meet demand, and maximize profit.
Design and operation of a distillation column depends on the feed and desired products. Given
a simple, binary component feed, analytical methods such as the McCabe-Thiele
method[5][6][7] or the Fenske equation[5] can be used to assist in the design. For a multicomponent feed, computerized simulation models are used both for design and subsequently
in operation of the column as well. Modeling is also used to optimize already erected columns
for the distillation of mixtures other than those the distillation equipment was originally
designed for.
23
When a continuous distillation column is in operation, it has to be closely monitored for
changes in feed composition, operating temperature and product composition. Many of these
tasks are performed using advanced computer control equipment.
Column feed
The column can be fed in different ways. If the feed is from a source at a pressure higher than
the distillation column pressure, it is simply piped into the column. Otherwise, the feed is
pumped or compressed into the column. The feed may be a superheated vapor, a saturated
vapor, a partially vaporized liquid-vapor mixture, a saturated liquid (i.e., liquid at its boiling
point at the column's pressure), or a sub-cooled liquid. If the feed is a liquid at a much higher
pressure than the column pressure and flows through a pressure let-down valve just ahead of
the column, it will immediately expand and undergo a partial flash vaporization resulting in a
liquid-vapor mixture as it enters the distillation column.
Improving separation
Although small size units, mostly made of glass, can be used in laboratories, industrial units
are large, vertical, steel vessels (see images 1 and 2) known as "distillation towers" or
"distillation columns". To improve the separation, the tower is normally provided inside with
horizontal plates or trays as shown in image 5, or the column is packed with a packing
material. To provide the heat required for the vaporization involved in distillation and also to
compensate for heat loss, heat is most often added to the bottom of the column by a reboiler,
and the purity of the top product can be improved by recycling some of the externally
condensed top product liquid as reflux. Depending on their purpose, distillation columns may
have liquid outlets at intervals up the length of the column as shown in image 4.
Reflux
Large-scale industrial fractionation towers use reflux to achieve more efficient separation of
products.[3][5] Reflux refers to the portion of the condensed overhead liquid product from a
distillation tower that is returned to the upper part of the tower as shown in images 3 and 4.
Inside the tower, the downflowing reflux liquid provides cooling and partial condensation of
the upflowing vapors, thereby increasing the efficacy of the distillation tower. The more
reflux that is provided, the better is the tower's separation of the lower boiling from the higher
boiling components of the feed. A balance of heating with a reboiler at the bottom of a
column and cooling by condensed reflux at the top of the column maintains a temperature
gradient (or gradual temperature difference) along the height of the column to provide good
conditions for fractionating the feed mixture. Reflux flows at the middle of the tower are
called pumparounds.
Changing the reflux (in combination with changes in feed and product withdrawal) can also
be used to improve the separation properties of a continuous distillation column while in
operation (in contrast to adding plates or trays, or changing the packing, which would, at a
minimum, require quite significant downtime).
Plates or trays
Image 5: Cross-sectional diagram of a binary fractional distillation tower with bubble-cap
trays. (See theoretical plate for enlarged tray image.)
24
Distillation towers (such as in images 3 and 4) use various vapor and liquid contacting
methods to provide the required number of equilibrium stages. Such devices are commonly
known as "plates" or "trays".[8] Each of these plates or trays is at a different temperature and
pressure. The stage at the tower bottom has the highest pressure and temperature. Progressing
upwards in the tower, the pressure and temperature decreases for each succeeding stage. The
vapor-liquid equilibrium for each feed component in the tower reacts in its unique way to the
different pressure and temperature conditions at each of the stages. That means that each
component establishes a different concentration in the vapor and liquid phases at each of the
stages, and this results in the separation of the components. Some example trays are depicted
in image 5. A more detailed, expanded image of two trays can be seen in the theoretical plate
article. The reboiler often acts as an additional equilibrium stage.
If each physical tray or plate were 100% efficient, than the number of physical trays needed
for a given separation would equal the number of equilibrium stages or theoretical plates.
However, that is very seldom the case. Hence, a distillation column needs more plates than
the required number of theoretical vapor-liquid equilibrium stages.
Fractionation Research, Inc. (commonly known as FRI) has performed research on all types
of trays measuring their capacity, pressure drop and efficiency in hydrocarbon systems from
full vacuum to 500 psia.[9]
Packing
Another way of improving the separation in a distillation column is to use a packing material
instead of trays. These offer the advantage of a lower pressure drop across the column (when
compared to plates or trays), beneficial when operating under vacuum. If a distillation tower
uses packing instead of trays, the number of necessary theoretical equilibrium stages is first
determined and then the packing height equivalent to a theoretical equilibrium stage, known
as the height equivalent to a theoretical plate (HETP), is also determined. The total packing
height required is the number theoretical stages multiplied by the HETP.
This packing material can either be random dumped packing such as Raschig rings or
structured sheet metal. Liquids tend to wet the surface of the packing and the vapors pass
across this wetted surface, where mass transfer takes place. Unlike conventional tray
distillation in which every tray represents a separate point of vapor-liquid equilibrium, the
vapor-liquid equilibrium curve in a packed column is continuous. However, when modeling
packed columns it is useful to compute a number of theoretical plates to denote the separation
efficiency of the packed column with respect to more traditional trays. Differently shaped
packings have different surface areas and void space between packings. Both of these factors
affect packing performance.
Another factor in addition to the packing shape and surface area that affects the performance
of random or structured packing is liquid and vapor distribution entering the packed bed. The
number of theoretical stages required to make a given separation is calculated using a specific
vapor to liquid ratio. If the liquid and vapor are not evenly distributed across the superficial
tower area as it enters the packed bed, the liquid to vapor ratio will not be correct in the
packed bed and the required separation will not be achieved. The packing will appear to not
be working properly. The height equivalent to a theoretical plate (HETP) will be greater than
expected. The problem is not the packing itself but the mal-distribution of the fluids entering
the packed bed. Liquid mal-distribution is more frequently the problem than vapor. The
design of the liquid distributors used to introduce the feed and reflux to a packed bed is
critical to making the packing perform at maximum efficiency. Methods of evaluating the
25
effectiveness of a liquid distributor can be found in references..[10][11] Considerable work as
been done on this topic by Fractionation Research, Inc.[12]
Overhead system arrangements
Images 4 and 5 assume an overhead stream that is totally condensed into a liquid product
using water or air-cooling. However, in many cases, the tower overhead is not easily
condensed totally and the reflux drum must include a vent gas outlet stream. In yet other
cases, the overhead stream may also contain water vapor because either the feed stream
contains some water or some steam is injected into the distillation tower (which is the case in
the crude oil distillation towers in oil refineries). In those cases, if the distillate product is
insoluble in water, the reflux drum may contain a condensed liquid distillate phase, a
condensed water phase and a non-condensible gas phase, which makes it necessary that the
reflux drum also have a water outlet stream.
Examples
Continuous distillation of crude oil
Petroleum crude oils contain hundreds of different hydrocarbon compounds: paraffins,
naphthenes and aromatics as well as organic sulfur compounds, organic nitrogen compounds
and some oxygen containing hydrocarbons such as phenols. Although crude oils generally do
not contain olefins, they are formed in many of the processes used in a petroleum refinery.[13]
The crude oil fractionator does not produce products having a single boiling point, rather, it
produces fractions having boiling ranges.[13][14] For example, the crude oil fractionator
produces an overhead fraction called "naphtha" which becomes a gasoline component after it
is further processed through a catalytic hydrodesulfurizer to remove sulfur and a catalytic
reformer to reform its hydrocarbon molecules into more complex molecules with a higher
octane rating value.
The naphtha cut, as that fraction is called, contains many different hydrocarbon compounds.
Therefore it has an initial boiling point of about 35 °C and a final boiling point of about
200 °C. Each cut produced in the fractionating columns has a different boiling range. At some
distance below the overhead, the next cut is withdrawn from the side of the column and it is
usually the jet fuel cut, also known as a kerosene cut. The boiling range of that cut is from an
initial boiling point of about 150 °C to a final boiling point of about 270 °C, and it also
contains many different hydrocarbons. The next cut further down the tower is the diesel oil
cut with a boiling range from about 180 °C to about 315 °C. The boiling ranges between any
cut and the next cut overlap because the distillation separations are not perfectly sharp. After
these come the heavy fuel oil cuts and finally the bottoms product, with very wide boiling
ranges. All these cuts are processed further in subsequent refining processes.
Additional information from internet:
For example:
Oil refinery From Wikipedia, the free encyclopedia
26
An oil refinery is an industrial process plant where crude oil is processed and refined into
more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil,
kerosene, and liquefied petroleum gas.[1][2] Oil refineries are typically large sprawling
industrial complexes with extensive piping running throughout, carrying streams of fluids
between large chemical processing units.
Operation
Crude oil is separated into fractions by fractional distillation. The fractions at the top of the
fractionating column have lower boiling points than the fractions at the bottom. The heavy
bottom fractions are often cracked into lighter, more useful products. All of the fractions are
processed further in other refining units.
Raw or unprocessed crude oil is not generally useful in its raw or unprocessed form, as it
comes out of the ground. Although "light, sweet" (low viscosity, low sulfur) crude oil has
been used directly as a burner fuel for steam vessel propulsion, the lighter elements form
explosive vapors in the fuel tanks and so it was quite dangerous, especially in warships.
Instead, the hundreds of different hydrocarbon molecules in crude oil are separated in a
refinery into components that can be used as fuels, lubricants, and as feedstock in
petrochemical processes that manufacture such products as plastics, detergents, solvents,
elastomers and fibers such as nylon and polyesters. Petroleum fossil fuels are burned in
internal combustion engines in order to provide power to operate ships, automobiles, aircraft
engines, lawn-mowers, chainsaws, and other pieces of power equipment. These different
hydrocarbons have different boiling points, which means they can be separated by distillation.
Since the lighter liquid products are in great demand for use in internal combustion engines, a
modern refinery will convert heavy hydrocarbons and lighter gaseous elements into these
higher value products.
Oil can be used in so many ways because it contains hydrocarbons of varying molecular
masses, forms and lengths such as paraffins, aromatics, naphthenes (or cycloalkanes), alkenes,
dienes, and alkynes. While the molecules in crude oil include many different atoms such as
sulfur and nitrogen, the most plentiful molecules are the hydrocarbons, which are molecules
of varying length and complexity made of hydrogen and carbon atoms, and a small number of
oxygen atoms. The differences in the structure of these molecules is what confers upon them
their varying physical and chemical properties, and it is this variety that makes crude oil so
useful in such a broad range of applications.
Once separated and purified of any contaminants and impurities, the fuel or lubricant can be
sold without any further processing. Smaller molecules such as isobutane and propylene or
butylenes can be recombined to meet specific octane requirements of fuels by processes such
as alkylation or less commonly, dimerization. Octane grade of gasoline can also be improved
by catalytic reforming, which strips hydrogen out of hydrocarbons to produce aromatics,
which have much higher octane ratings. Intermediate products such as gasoils can even be
reprocessed to break a heavy, long-chained oil into a lighter short-chained one, by various
forms of cracking such as fluid catalytic cracking, thermal cracking, and hydrocracking. The
final step in gasoline production is the blending of fuels with different octane ratings, vapor
pressures, and other properties to meet product specifications.
Oil refineries are large scale plants, processing from about a hundred thousand to several
hundred thousand barrels of crude oil per day. Because of the high capacity, many of the units
27
are operated continuously (as opposed to processing in batches) at steady state or
approximately steady state for long periods of time (months to years). This high capacity also
makes process optimization and advanced process control very desirable.
Major products of oil refineries
Most products of oil processing are usually grouped into three categories: light distillates
(LPG, gasoline, naphtha), middle distillates (kerosene, diesel), heavy distillates and residuum
(fuel oil, lubricating oils, wax, tar). This classification is based on the way crude oil is
distilled and separated into fractions (called distillates and residuum) as can be seen in the
above drawing.[2]
Common process units found in a refinery
The number and nature of the process units in a refinery determine its complexity index.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Desalter unit washes out salt from the crude oil before it enters the atmospheric
distillation unit.
Atmospheric Distillation unit distills crude oil into fractions. See Continuous
distillation.
Vacuum Distillation unit further distills residual bottoms after atmospheric distillation.
Naphtha Hydrotreater unit uses hydrogen to desulfurize naphtha from atmospheric
distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer unit.
Catalytic Reformer unit is used to convert the naphtha-boiling range molecules into
higher octane reformate (reformer product). The reformate has higher content of
aromatics and cyclic hydrocarbons). An important byproduct of a reformer is
hydrogen released during the catalyst reaction. The hydrogen is used either in the
hydrotreaters or the hydrocracker.
Distillate Hydrotreater unit desulfurizes distillates (such as diesel) after atmospheric
distillation.
Fluid Catalytic Cracker (FCC) unit upgrades heavier fractions into lighter, more
valuable products.
Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more
valuable products.
Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter,
more valuable reduced viscosity products.
Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic
disulfides.
Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual
oils into gasoline and diesel fuel, leaving petroleum coke as a residual product.
Alkylation unit produces high-octane component for gasoline blending.
Dimerization unit converts olefins into higher-octane gasoline blending components.
For example, butenes can be dimerized into isooctene which may subsequently be
hydrogenated to form isooctane. There are also other uses for dimerization.
Isomerization unit converts linear molecules to higher-octane branched molecules for
blending into gasoline or feed to alkylation units.
Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker.
Liquified gas storage units for propane and similar gaseous fuels at pressure sufficient
to maintain in liquid form. These are usually spherical vessels or bullets (horizontal
vessels with rounded ends.
28
•
•
•
•
•
•
Storage tanks for crude oil and finished products, usually cylindrical, with some sort
of vapor emission control and surrounded by an earthen berm to contain spills.
Amine gas treater, Claus unit, and tail gas treatment for converting hydrogen sulfide
from hydrodesulfurization into elemental sulfur.
Utility units such as cooling towers for circulating cooling water, boiler plants for
steam generation, instrument air systems for pneumatically operated control valves
and an electrical substation.
Wastewater collection and treating systems consisting of API separators, dissolved air
flotation (DAF) units and some type of further treatment (such as an activated sludge
biotreater) to make such water suitable for reuse or for disposal.[3]
Solvent refining units use solvent such as cresol or furfural to remove unwanted,
mainly asphaltenic materials from lubricating oil stock (or diesel stock).
Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum
distillation products.
Flow diagram of typical refinery
The image below is a schematic flow diagram of a typical oil refinery that depicts the various
unit processes and the flow of intermediate product streams that occurs between the inlet
crude oil feedstock and the final end products. The diagram depicts only one of the literally
hundreds of different oil refinery configurations. The diagram also does not include any of the
usual refinery facilities providing utilities such as steam, cooling water, and electric power as
well as storage tanks for crude oil feedstock and for intermediate products and end
products.[1][4][5][6]
The Five Pillars of Refining
While distillation can separate oil into fractions, chemical reactors are required to create
more of the products that are in high demand. Refineries rely on four major processing steps
to alter the ratios of the different fractions. They are; Catalytic Reforming, Alkylation,
Catalytic Cracking, and Hydroprocessing. Each of these methods involves feeding
reactants to a reactor where they will be partly converted into products. The unreacted
reactants are then separated from the products with a distillation column. The unreacted
reactants are recycled for another pass, while the products are further separated and mixed
with existing streams. In this way complete conversion of reactants can be obtained, even
though not all of the reactants are converted on a given pass through the reactor. The four
processing methods, along with distillation, are the pillars of petroleum refining.
Catalytic Reforming
Catalytic Reforming produces high octane gasoline for today’s automobiles. Gasoline and
naphtha feedstocks are heated to 500 degrees Celsius and flow through a series of fixed-bed
catalytic reactors. Because the reactions which produce higher octane compounds (aliphatic
in this case) are endothermic (absorb heat) additional heaters are installed between reactors
to keep the reactants at the proper temperature. The catalyst is a platinum (Pt) metal on an
alumina (Al2O3) base. While catalysts are never consumed in chemical reactions, they can be
fouled, making them less effective over time. The series of reactors used in Catalytic
Reforming are therefore designed to be disconnected, and swiveled out of place, so the
catalyst can be regenerated.
29
Alkylation
Alkylation is another process for producing high octane gasoline. The reaction requires an
acid catalyst (sulfuric acid, H2SO4 or hydrofluoric acid, HF) at low temperatures (1-40
degrees Celsius) and low pressures (1-10 atmospheres). The acid composition is usually kept
at about 50% making the mixture very corrosive.
Fluidized Catalytic Cracking
Catalytic Cracking takes long molecules and breaks them into much smaller molecules. The
cracking reaction is very endothermic, and requires a large amount of heat. Another
problem is that reaction quickly fouls the Silica (SiO2) and alumina (Al2O3) catalyst by
forming coke on its surface. However, by using a fluidized bed to slowly carry the catalyst
upwards, and then sending it to a regenerator where the coke can be burned off, the catalyst
is continuously regenerated. This system has the additional benefit of using the large
amounts of heat liberated in the exothermic regeneration reaction to heat the cracking
reactor. The FCC system is a brilliant reaction scheme, which turns two negatives (heating
and fouling) into a positive, thereby making the process extremely economical.
Hydroprocessing
Hydroprocessing includes both hydrocracking and hydrotreating techniques. Hydrotreating
involves the addition of hydrogen atoms to molecules without actually breaking the molecule
into smaller pieces. Hydrotreating involves temperatures of about 325 degrees Celsius and
pressures of about 50 atmospheres. Many catalysts will work, including; nickel, palladium,
platinum, cobalt, and iron. Hydrocracking breaks longer molecules into smaller ones.
Hydrocracking involves temperatures over 350 degrees Celsius and pressures up to 200
atmospheres. In both cases, very long residence times (about an hour) are required because
of the slow nature of the reactions.
Catalytic reforming is a chemical process used to convert petroleum refinery naphthas,
typically having low octane ratings, into high-octane liquid products called reformates which
are components of high-octane gasoline (also known as petrol). Basically, the process rearranges or re-structures the hydrocarbon molecules in the naphtha feedstocks as well as
breaking some of the molecules into smaller molecules. The overall effect is that the product
reformate contains hydrocarbons with more complex molecular shapes having higher octane
values than the hydrocarbons in the naphtha feedstock. In so doing, the process separates
hydrogen atoms from the hydrocarbon molecules and produces very significant amounts of
byproduct hydrogen gas for use in a number of the other processes involved in a modern
petroleum refinery. Other byproducts are small amounts of methane, ethane, propane and
butanes.
This process is quite different from and not to be confused with the catalytic steam reforming
process used industrially to produce various products such as hydrogen, ammonia and
methanol from natural gas, naphtha or other petroleum-derived feedstocks. Nor is this process
30
to be confused with various other catalytic reforming processes that use methanol or biomassderived feedstocks to produce hydrogen for fuel cells or other uses.
History
Universal Oil Products (also known as UOP) is a multi-national company developing and
delivering technology to the petroleum refining, natural gas processing, petrochemical
production and other manufacturing industries. In the 1940s, an eminent research chemist
named Vladimir Haensel[1] working for UOP developed a catalytic reforming process using a
catalyst containing platinum. Haensel's process was subsequently commercialized by UOP in
1949 for producing a high octane gasoline from low octane naphthas and the UOP process
become known as the Platforming process.[2] The first Platforming unit was built in 1949 at
the refinery of the Old Dutch Refining Company in Muskegon, Michigan.
In the years since then, many other versions of the process have been developed by some of
the major oil companies and other organizations. Today, the large majority of gasoline
produced worldwide is derived from the catalytic reforming process.
To name a few of the other catalytic reforming versions that were developed, all of which
utilized a platinum and/or a rhenium catalyst:
•
•
•
•
•
•
•
Rheniforming: Developed by Chevron Oil Company.
Powerforming: Developed by Esso Oil Company, now known as ExxonMobil.
Magnaforming: Developed by Englehard Catalyst Company and Atlantic Richfield Oil
Company.
Ultraforming: Developed by Standard Oil of Indiana, now a part of the British
Petroleum Company.
Houdriforming: Developed by the Houdry Process Corporation.
CCR Platforming: A Platforming version, designed for continuous catalyst
regeneration, developed by UOP.
Octanizing: A catalytic reforming version developed by Axens, a subsidiary of Institut
francais du petrole (IFP), designed for continuous catalyst regeneration.
Chemistry
Before describing the reaction chemistry of the catalytic reforming process as used in
petroleum refineries, the typical naphthas used as catalytic reforming feedstocks will be
discussed.
Typical naphtha feedstocks
A petroleum refinery includes many unit operations and unit processes. The first unit
operation in a refinery is the continuous distillation of the petroleum crude oil being refined.
The overhead liquid distillate is called naphtha and will become a major component of the
refinery's gasoline (petrol) product after it is further processed through a catalytic
hydrodesulfurizer to remove sulfur-containing hydrocarbons and a catalytic reformer to
reform its hydrocarbon molecules into more complex molecules with a higher octane rating
value. The naphtha is a mixture of very many different hydrocarbon compounds. It has an
initial boiling point of about 35 °C and a final boiling point of about 200 °C, and it contains
paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons ranging from those
containing 4 carbon atoms to those containing about 10 or 11 carbon atoms.
31
The naphtha from the crude oil distillation is often further distilled to produce a "light"
naphtha containing most (but not all) of the hydrocarbons with 6 or less carbon atoms and a
"heavy" naphtha containing most (but not all) of the hydrocarbons with more than 6 carbon
atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final
boiling point of about 190 to 205 °C. The naphthas derived from the distillation of crude oils
are referred to as "straight-run" naphthas.
It is the straight-run heavy naphtha that is usually processed in a catalytic reformer because
the light naphtha has molecules with 6 or less carbon atoms which, when reformed, tend to
crack into butane and lower molecular weight hydrocarbons which are not useful as highoctane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form
aromatics which is undesirable because governmental environmental regulations in a number
of countries limit the amount of aromatics (most particularly benzene) that gasoline may
contain.[3][4][5]
It should be noted that there are a great many petroleum crude oil sources worldwide and each
crude oil has its own unique composition or "assay". Also, not all refineries process the same
crude oils and each refinery produces its own straight-run naphthas with their own unique
initial and final boiling points. In other words, naphtha is a generic term rather than a specific
term.
The table just below lists some fairly typical straight-run heavy naphtha feedstocks, available
for catalytic reforming, derived from various crude oils. It can be seen that they differ
significantly in their content of paraffins, naphthenes and aromatics:
Typical Heavy Naphtha Feedstocks
Crude oil name
Location
Barrow Island
Australia[6]
Initial boiling
point, °C
149
Final boiling
point, °C
204
Mutineer-Exeter CPC Blend
Australia[7]
Kazakhstan[8]
140
149
190
204
32
150
180
Draugen
North Sea[9]
Paraffins,
liquid
volume %
Naphthenes,
liquid
volume %
46
42
Aromatics,
12
liquid volume %
62
57
32
38
27
6
45
16
17
Some refinery naphthas include olefinic hydrocarbons, such as naphthas derived from the
fluid catalytic cracking and coking processes used in many refineries. Some refineries may
also desulfurize and catalytically reform those naphthas. However, for the most part, catalytic
reforming is mainly used on the straight-run heavy naphthas, such as those in the above table,
derived from the distillation of crude oils.
The reaction chemistry
There are a good many chemical reactions that occur in the catalytic reforming process, all of
which occur in the presence of a catalyst and a high partial pressure of hydrogen. Depending
upon the type or version of catalytic reforming used as well as the desired reaction severity,
the reaction conditions range from temperatures of about 495 to 525 °C and from pressures of
about 5 to 45 atm.[10]
The commonly used catalytic reforming catalysts contain noble metals such as platinum
and/or rhenium, which are very susceptible to poisoning by sulfur and nitrogen compounds.
Therefore, the naphtha feedstock to a catalytic reformer is always pre-processed in a
hydrodesulfurization unit which removes both the sulfur and the nitrogen compounds.
The four major catalytic reforming reactions are:[11]
1: The dehydrogenation of naphthenes to convert them into aromatics as exemplified in the
conversion methylcyclohexane (a naphthene) to toluene (an aromatic), as shown below:
2: The isomerization of normal paraffins to isoparaffins as exemplified in the conversion of
normal octane to 2,5-Dimethylhexane (an isoparaffin), as shown below:
33
3: The dehydrogenation and aromatization of paraffins to aromatics (commonly called
dehydrocyclization) as exemplified in the conversion of normal heptane to toluene, as shown
below:
4: The hydrocracking of paraffins into smaller molecules as exemplified by the cracking of
normal heptane into isopentane and ethane, as shown below:
The hydrocracking of paraffins is the only one of the above four major reforming reactions
that consumes hydrogen. The isomerization of normal paraffins does not consume or produce
hydrogen. However, both the dehydrogenation of naphthenes and the dehydrocyclization of
paraffins produce hydrogen. The overall net production of hydrogen in the catalytic reforming
of petroleum naphthas ranges from about 50 to 200 cubic meters of hydrogen gas (at 0 °C and
1 atm) per cubic meter of liquid naphtha feedstock. In the United States customary units, that
is equivalent to 300 to 1200 cubic feet of hydrogen gas (at 60 °F and 1 atm) per barrel of
liquid naphtha feedstock.[12] In many petroleum refineries, the net hydrogen produced in
catalytic reforming supplies a significant part of the hydrogen used elsewhere in the refinery
(for example, in hydrodesulfurization processes). The hydrogen is also necessary in order to
hydrogenolyze any polymers that form on the catalyst.
Process description
The most commonly used type of catalytic reforming unit has three reactors, each with a fixed
bed of catalyst, and all of the catalyst is regenerated in situ during routine catalyst
regeneration shutdowns which occur approximately once each 6 to 24 months. Such a unit is
referred to as a semi-regenerative catalytic reformer (SRR).
Some catalytic reforming units have an extra spare or swing reactor and each reactor can be
individually isolated so that any one reactor can be undergoing in situ regeneration while the
other reactors are in operation. When that reactor is regenerated, it replaces another reactor
which, in turn, is isolated so that it can then be regenerated. Such units, referred to as cyclic
catalytic reformers, are not very common. Cyclic catalytic reformers serve to extend the
period between required shutdowns.
The latest and most modern type of catalytic reformers are called continuous catalyst
regeneration reformers (CCR). Such units are characterized by continuous in-situ regeneration
of part of the catalyst in a special regenerator, and by continuous addition of the regenerated
catalyst to the operating reactors. As of 2006, two CCR versions available: UOP's CCR
Platformer process[13] and Axen's Octanizing process.[14] The installation and use of CCR
units is rapidly increasing.
Many of the earliest catalytic reforming units (in the 1950s and 1960's) were non-regenerative
in that they did not perform in situ catalyst regeneration. Instead, when needed, the aged
catalyst was replaced by fresh catalyst and the aged catalyst was shipped to catalyst
manufacturer's to be either regenerated or to recover the platinum content of the aged catalyst.
Very few, if any, catalytic reformers currently in operation are non-regenerative.
The process flow diagram below depicts a typical semi-regenerative catalytic reforming unit.
34
Schematic diagram of a typical semi-regenerative catalytic reformer unit in a petroleum
refinery
The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5 to
45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas
mixture is preheated by flowing through a heat exchanger. The preheated feed mixture is then
totally vaporized and heated to the reaction temperature (495 to 520 °C) before the vaporized
reactants enter the first reactor. As the vaporized reactants flow through the fixed bed of
catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromatics
(as described earlier herein) which is highly endothermic and results in a large temperature
decrease between the inlet and outlet of the reactor. To maintain the required reaction
temperature and the rate of reaction, the vaporized stream is reheated in the second fired
heater before it flows through the second reactor. The temperature again decreases across the
second reactor and the vaporized stream must again be reheated in the third fired heater before
it flows through the third reactor. As the vaporized stream proceeds through the three reactors,
the reaction rates decrease and the reactors therefore become larger. At the same time, the
amount of reheat required between the reactors becomes smaller. Usually, three reactors are
all that is required to provide the desired performance of the catalytic reforming unit.
Some installations use three separate fired heaters as shown in the schematic diagram and
some installations use a single fired heater with three separate heating coils.
The hot reaction products from the third reactor are partially cooled by flowing through the
heat exchanger where the feed to the first reactor is preheated and then flow through a watercooled heat exchanger before flowing through the pressure controller (PC) into the gas
separator.
Most of the hydrogen-rich gas from the gas separator vessel returns to the suction of the
recycle hydrogen gas compressor and the net production of hydrogen-rich gas from the
reforming reactions is exported for use in other the other refinery processes that consume
hydrogen (such as hydrodesulfurization units and/or a hydrocracker unit).
The liquid from the gas separator vessel is routed into a fractionating column commonly
called a stabilizer. The overhead offgas product from the stabilizer contains the byproduct
methane, ethane, propane and butane gases produced by the hydrocracking reactions as
explained in the above discussion of the reaction chemistry of a catalytic reformer, and it may
also contain some small amount of hydrogen. That offgas is routed to the refinery's central gas
processing plant for removal and recovery of propane and butane. The residual gas after such
processing becomes part of the refinery's fuel gas system.
The bottoms product from the stabilizer is the high-octane liquid reformate that will become a
component of the refinery's product gasoline.
Catalysts and mechanisms
Most catalytic reforming catalysts contain platinum or rhenium on a silica or silica-alumina
support base, and some contain both platinum and rhenium. Fresh catalyst is chlorided
(chlorinated) prior to use.
35
The noble metals (platinum and rhenium) are considered to be catalytic sites for the
dehydrogenation reactions and the chlorinated alumina provides the acid sites needed for
isomerization, cyclization and hydrocracking reactions.[11]
The activity (i.e., effectiveness) of the catalyst in a semi-regenerative catalytic reformer is
reduced over time during operation by carbonaceous coke deposition and chloride loss. The
activity of the catalyst can be periodically regenerated or restored by in situ high temperature
oxidation of the coke followed by chlorination. As stated earlier herein, semi-regenerative
catalytic reformers are regenerated about once per 6 to 24 months.
Normally, the catalyst can be regenerated perhaps 3 or 4 times before it must be returned to
the manufacturer for reclamation of the valuable platinum and/or rhenium content.[11]
Alkylation
In a standard oil refinery process, isobutane is alkylated with low-molecular-weight alkenes
(primarily a mixture of propylene and butylene) in the presence of a strong acid catalyst,
either sulfuric acid or hydrofluoric acid. In an oil refinery it is referred to as a sulfuric acid
alkylation unit (SAAU) or a hydrofluoric alkylation unit, (HFAU). However, oil refinery
employees may simply refer to the unit as the Alkyl or Alky unit. The catalyst is able to
protonate the alkenes (propylene, butylene) to produce reactive carbocations, which alkylate
isobutane. The reaction is carried out at mild temperatures (0 and 30 °C) in a two-phase
reaction. It is important to keep a high ratio of isobutane to alkene at the point of reaction to
prevent side reactions that lead to a lower octane product, so the plants have a high recycle of
isobutane back to feed. The phases separate spontaneously, so the acid phase is vigoriously
mixed with the hydrocarbon phase to create sufficient contact surface.
The product is called alkylate and is composed of a mixture of high-octane, branched-chain
paraffinic hydrocarbons (mostly isopentane and isooctane). Alkylate is a premium gasoline
blending stock because it has exceptional antiknock properties and is clean burning. Alkylate
is also a key component of avgas. The octane number of the alkylate depends mainly upon the
kind of alkenes used and upon operating conditions. For example, isooctane results from
combining butylene with isobutane and has an octane rating of 100 by definition. There are
other products in the alkylate, so the octane rating will vary accordingly.
Most crude oils contain only 10 to 40 percent of their hydrocarbon constituents in the gasoline
range, so refineries use a fluid catalytic cracking process to convert high molecular weight
hydrocarbons into smaller and more volatile compounds. Polymerization converts gaseous
alkenes into liquid gasoline-size hydrocarbons. Alkylation processes transform low
molecular-weight alkenes and iso-paraffin molecules into larger iso-paraffins with a high
octane number.
Combining cracking, polymerization, and alkylation can result in a gasoline yield representing
70 percent of the starting crude oil. More advanced processes, such as cyclicization of
paraffins and dehydrogenation of naphthenes to form aromatic hydrocarbons in a catalytic
reformer, have also been developed to increase the octane rating of gasoline. Modern refinery
operation can be shifted to produce almost any fuel type with specified performance criteria
from a single crude feedstock.
36
In the entire range of refinery processes, alkylation is a very important process that enhances
the yield of high-octane gasoline. However, not all refineries have an alkylation plant. The oil
and gas journal annual survey of worldwide refining capacities for January 2007 lists many
countries with no alkylation plants at their refineries.
A primary factor in deciding to install alkylation is usually economics. Refinery alkylation
units are complex and there is substantial economy of scale. In addition to a suitable quantity
of feedstock, the price spread between the value of alkylate product and alternate feedstock
disposition value must be large enough to justify the plant. Alternative outlets for refinery
alklylation feedstocks include sales as LPG, blending of C4 streams directly into gasoline and
feedstocks for chemical plants. Local market conditions vary widely between plants.
Variation in the RVP specification for gasoline between countries and between seasons
dramatically impacts the amount of butane streams that can be blended directly into gasoline.
The transportation of specific types of LPG streams can be expensive so local disparities in
economic conditions are often not fully mitigated by cross market movements of alkylation
feedstocks.
Another factor in the decision to build an alkylation plant concerns the availability of a
suitable catalyst. If sulfuric acid is used, significant volumes are needed. This requires access
to a suitable plant for the supply of fresh acid and the disposition of spent acid. If a sulfuric
acid plant must be constructed specifically to support an alkylation unit, this will have a
significant impact on both the initial capital requirements and ongoing operating costs. The
second main catalyst option is hydrofluoric acid. Consumption rates for HF acid in alkylation
plants are much lower than for sulfuric acid. HF acid plants can process a wider range of
feedstock mix with proplyenes and butylenes. HF plants also produce alklyate with better
octane than sulfuric plants. However, due to the hazardous nature of the material, HF acid is
produced at very few locations and transportation must be managed rigorously.
Thermal cracking
William Merriam Burton developed one of the earliest thermal cracking processes in 1912
which operated at 700-750 °F (370-400 °C) and an absolute pressure of 90 psia (620 kPa) and
was known as the Burton process. Shortly thereafter, in 1921, C.P. Dubbs, an employee of the
Universal Oil Products Company, developed a somewhat more advanced thermal cracking
process which operated at 750-860 °F (400-460 °C) and was known as the Dubbs process.[9]
The Dubbs process was used extensively by many refineries until the early 1940's when
catalytic cracking came into use.
Modern high-pressure thermal cracking operates at absolute pressures of about 7,000 kPa. An
overall process of disproportionation can be observed, where "light", hydrogen-rich products
are formed at the expense of heavier molecules which condense and are depleted of hydrogen.
The actual reaction is known as homolytic fission and produces alkenes, which are the basis
for the economically important production of polymers.
A large number of chemical reactions take place during steam cracking, most of them based
on free radicals. Computer simulations aimed at modeling what takes place during steam
cracking have included hundreds or even thousands of reactions in their models. The main
reactions that take place include:
Initiation reactions, where a single molecule breaks apart into two free radicals. Only a small
fraction of the feed molecules actually undergo initiation, but these reactions are necessary to
37
produce the free radicals that drive the rest of the reactions. In steam cracking, initiation
usually involves breaking a chemical bond between two carbon atoms, rather than the bond
between a carbon and a hydrogen atom.
CH3CH3 → 2 CH3•
Hydrogen abstraction, where a free radical removes a hydrogen atom from another molecule,
turning the second molecule into a free radical.
CH3• + CH3CH3 → CH4 + CH3CH2•
Radical decomposition, where a free radical breaks apart into two molecules, one an alkene,
the other a free radical. This is the process that results in the alkene products of steam
cracking.
CH3CH2• → CH2=CH2 + H•
Radical addition, the reverse of radical decomposition, in which a radical reacts with an
alkene to form a single, larger free radical. These processes are involved in forming the
aromatic products that result when heavier feedstocks are used.
CH3CH2• + CH2=CH2 → CH3CH2CH2CH2•
Termination reactions, which happen when two free radicals react with each other to produce
products that are not free radicals. Two common forms of termination are recombination,
where the two radicals combine to form one larger molecule, and disproportionation, where
one radical transfers a hydrogen atom to the other, giving an alkene and an alkane.
CH3• + CH3CH2• → CH3CH2CH3
CH3CH2• + CH3CH2• → CH2=CH2 + CH3CH3
Thermal cracking is an example of a reaction whose energetics are dominated by entropy
(∆S°) rather than by enthalpy (∆H°) in the Gibbs Free Energy equation ∆G°=∆H°-T∆S°.
Although the bond dissociation energy D for a carbon-carbon single bond is relatively high
(about 375 kJ/mol) and cracking is highly endothermic, the large positive entropy change
resulting from the fragmentation of one large molecule into several smaller pieces, together
with the extremely high temperature, makes T∆S° term larger than the ∆H° term, thereby
favoring the cracking reaction.
Here is an example of cracking with butane CH3-CH2-CH2-CH3
•
1st possibility (48%): breaking is done on the CH3-CH2 bond.
CH3* / *CH2-CH2-CH3
after a certain number of steps, we will obtain an alkane and an alkene: CH4 + CH2=CH-CH3
•
2nd possibility (38%): breaking is done on the CH2-CH2 bond.
CH3-CH2* / *CH2-CH3
38
after a certain number of steps, we will obtain an alkane and an alkene from different types:
CH3-CH3 + CH2=CH2
•
3rd possibility (14%): breaking of a C-H bond
after a certain number of steps, we will obtain an alkene and hydrogen gas: CH2=CH-CH2CH3 + H2 this is very useful since the catalyst can be recycled.
Fluid catalytic cracking
From Wikipedia, the free encyclopedia
Fluid catalytic cracking (FCC) is the most important conversion process used in petroleum
refineries. It is widely used to convert the high-boiling hydrocarbon fractions of petroleum
crude oils to more valuable gasoline, olefinic gases and other products.[1][2][3] Cracking of
petroleum hydrocarbons was originally done by thermal cracking which has been almost
completely replaced by catalytic cracking because it produces more gasoline with a higher
octane rating. It also produces byproduct gases that are more olefinic, and hence more
valuable, than those produced by thermal cracking.
The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point
of 340 °C or higher at atmospheric pressure and an average molecular weight ranging from
about 200 to 600 or higher. The FCC process vaporizes and breaks the long-chain molecules
of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the
feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst.
In effect, refineries use fluid catalytic cracking to correct the imbalance between the market
demand for gasoline and the excess of heavy, high boiling range products resulting from the
distillation of crude oil.
As of 2006, FCC units were in operation at 400 petroleum refineries worldwide and about
one-third of the crude oil refined in those refineries is processed in an FCC to produce highoctane gasoline and fuel oils.[2][4] During 2007, the FCC units in the United States processed a
total of 5,300,000 barrels (834,300,000 litres) per day of feedstock[5] and FCC units
worldwide processed about twice that amount.
Flow diagram and process description
The modern FCC units are all continuous processes which operate 24 hours a day for as much
as 2 to 3 years between shutdowns for routine maintenance.
There are a number of different proprietary designs that have been developed for modern FCC
units. Each design is available under a license that must be purchased from the design
developer by any petroleum refining company desiring to construct and operate an FCC of a
given design.
39
Basically, there are two different configurations for an FCC unit: the "stacked" type where the
reactor and the catalyst regenerator are contained in a single vessel with the reactor above the
catalyst regenerator and the "side-by-side" type where the reactor and catalyst regenerator are
in two separate vessels. These are the major FCC designers and licensors:[1][3][4][6]
Reactor and Regenerator
The schematic flow diagram of a typical modern FCC unit in Figure 1 below is based upon
the "side-by-side" configuration. The preheated high-boiling petroleum feedstock (at about
315 to 430 °C) consisting of long-chain hydrocarbon molecules is combined with recycle
slurry oil from the bottom of the distillation column and injected into the catalyst riser where
it is vaporized and cracked into smaller molecules of vapor by contact and mixing with the
very hot powdered catalyst from the regenerator. All of the cracking reactions take place in
the catalyst riser. The hydrocarbon vapors "fluidize" the powdered catalyst and the mixture of
hydrocarbon vapors and catalyst flows upward to enter the reactor at a temperature of about
535 °C and a pressure of about 1.72 barg.
The reactor is in fact merely a vessel in which the cracked product vapors are: (a) separated
from the so-called spent catalyst by flowing through a set of two-stage cyclones within the
reactor and (b) the spent catalyst flows downward through a steam stripping section to
remove any hydrocarbon vapors before the spent catalyst returns to the catalyst regenerator.
The flow of spent catalyst to the regenerator is regulated by a slide valve in the spent catalyst
line.
Since the cracking reactions produce some carbonaceous material (referred to as coke) that
deposits on the catalyst and very quickly reduces the catalyst reactivity, the catalyst is
regenerated by burning off the deposited coke with air blown into the regenerator. The
regenerator operates at a temperature of about 715 °C and a pressure of about 2.41 barg. The
combustion of the coke is exothermic and it produces a large amount of heat that is partially
absorbed by the regenerated catalyst and provides the heat required for the vaporization of the
feedstock and the endothermic cracking reactions that take place in the catalyst riser. For that
reason, FCC units are often referred to as being heat balanced.
The hot catalyst (at about 715 °C) leaving the regenerator flows into a catalyst withdrawal
well where any entrained combustion flue gases are allowed to escape and flow back into the
upper part to the regenerator. The flow of regenerated catalyst to the feedstock injection point
below the catalyst riser is regulated by a slide valve in the regenerated catalyst line. The hot
flue gas exits the regenerator after passing through multiple sets of two-stage cylones that
remove entrained catalyst from the flue gas,
The amount of catalyst circulating between the regenerator and the reactor amounts to about 5
kg per kg of feedstock which is equivalent to about 4.66 kg per litre of feedstock.[1][7] Thus, an
FCC unit processing 75,000 barrels/day (12,000,000 litres/day) will circulate about 55,900
metric tons per day of catalyst.
Chemistry
Before delving into the chemistry involved in catalytic cracking, it will be helpful to briefly
discuss the composition of petroleum crude oil.
40
Table 1
Petroleum crude oil consists primarily of a mixture of hydrocarbons with small amounts of
other organic compounds containing sulfur, nitrogen and oxygen. The crude oil also contains
small amounts of metals such as copper, iron, nickel and vanadium.[2]
Carbon 83-87%
Nitroge 0.1-2%
n
Sulfur
0.5-6%
Metals
< 0.1%
Hydrogen
10-14%
Oxygen
0.1-1.5%
The elemental composition ranges of crude oil are summarized in Table 1 and the
hydrocarbons in the crude oil can be classified into three types:[1][2]
•
•
•
Paraffins or alkanes: saturated straight-chain or branched hydrocarbons, without any
ring structures
Naphthenes or cycloalkanes: saturated hydrocarbons having one or more ring
structures with one or more side-chain paraffins
Aromatics: hydrocarbons having one or more unsaturated ring structures such as
benzene or unsaturated polycyclic ring structures such as naphthalene or
phenanthrene, any of which may also have one or more side-chain paraffins.
Figure 2 : A schematic flow diagram of a Fluid Catalytic Cracking unit as used in petroleum
refineries
Olefins or alkenes, which are unsaturated straight-chain or branched hydrocarbons, do not
occur naturally in crude oil.
Figure : Diagrammatic example of the catalytic cracking of petroleum hydrocarbons
In plain language, the fluid catalytic cracking process breaks large hydrocarbon molecules
into smaller molecules by contacting them with powdered catalyst at a high temperature and
moderate pressure which first vaporizes the hydrocarbons and then breaks them. The cracking
reactions occur in the vapor phase and start immediately when the feedstock is vaporized in
the catalyst riser.
Figure 2 is a very simplified schematic diagram that exemplifies how the process breaks high
boiling, straight-chain alkane (paraffin) hydrocarbons into smaller straight-chain alkanes as
well as branched-chain alkanes, branched alkenes (olefins) and cycloalkanes (naphthenes).[9]
41
The breaking of the large hydrocarbon molecules into smaller molecules is more technically
referred to by organic chemists as scission of the carbon-to-carbon bonds.
As depicted in Figure 2, some of the smaller alkanes are then broken and converted into even
smaller alkenes and branched alkenes such as the gases ethylene, propylene, butylenes and
isobutylenes. Those olefinic gases are valuable for use as petrochemical feedstocks. The
propylene, butylene and isobutylene are also valuable feedstocks for certain petroleum
refining processes that convert them into high-octane gasoline blending components.
As also depicted in Figure 2, the cycloalkanes (naphthenes) formed by the initial breakup of
the large molecules are further converted to aromatics such as benzene, toluene and xylenes
which boil in the gasoline boiling range and have much higher octane ratings than alkanes.
By no means does Figure 2 include all the chemistry of the primary and secondary reactions
taking place in the fluid catalytic process. There are a great many other reactions involved.
However, a full discussion of the highly technical details of the various catalytic cracking
reactions is beyond the scope of this article and can be found in the technical
literature.[1][2][3][4]
Catalysts
Modern FCC catalysts are fine powders with a bulk density of 0.80 to 0.96 g/cc and having a
particle size distribution ranging from 10 to 150 μm and an average particle size of 60 to 100
μm.[10][11] The design and operation of an FCC unit is largely dependent upon the chemical
and physical properties of the catalyst. The desirable properties of an FCC catalyst are:
•
•
•
•
•
Good stability to high temperature and to steam
High activity
Large pore sizes
Good resistance to attrition
Low coke production
A modern FCC catalyst has four major components: crystalline zeolite, matrix, binder and
filler. Zeolite is the primary active component and can range from about 15 to 50 weight
percent of the catalyst. The zeolite used in FCC catalysts is referred to as faujasite or as Type
Y and is comprised of silica and alumina tetrahedra with each tetrahedron having either an
aluminum or a silicon atom at the center and four oxygen atoms at the corners. It is a
molecular sieve with a distinctive lattice structure that allows only a certain size range of
hydrocarbon molecules to enter the lattice. In general, the zeolite does not allow molecules
larger than 8 to 10 nm (i.e., 80 to 90 angstroms) to enter the lattice.[10][11]
The catalytic sites in the zeolite are strong acids (equivalent to 90% sulfuric acid) and provide
most of the catalytic activity. The acidic sites are provided by the alumina tetrahedra. The
aluminum atom at the center of each alumina tetrahedra is at a +3 oxidation state surrounded
by four oxygen atoms at the corners which are shared by the neighboring tetrahedra. Thus, the
net charge of the alumina tetrahedra is -1 which is balanced by a sodium ion during the
production of the catalyst. The sodium ion is later replaced by an ammonium ion which is
vaporized when the catalyst is subsequently dried, resulting in the formation of Lewis and
Brønsted acidic sites. In some FCC catalysts, the Brønsted sites may be later replaced by rare
earth metals such as cerium and lanthanum to provide alternative activity and stability
levels.[10][11]
42
The matrix component of an FCC catalyst contains amorphous alumina which also provides
catalytic activity sites and in larger pores that allows entry for larger molecules than does the
zeolite. That enables the cracking of higher-boiling, larger feedstock molecules than are
cracked by the zeolite.
The binder and filler components provide the physical strength and integrity of the catalyst.
The binder is usually silica sol and the filler is usually a clay (kaolin).
Hydrocracking
In 1920 a plant for the commercial hydrogenation of brown coal is commissioned at Leuna in
Germany[8].
Hydrocracking is a catalytic cracking process assisted by the presence of an elevated partial
pressure of hydrogen gas. Similar to the hydrotreater, the function of hydrogen is the
purification of the hydrocarbon stream from sulfur and nitrogen hetero-atoms.
The products of this process are saturated hydrocarbons; depending on the reaction conditions
(temperature, pressure, catalyst activity) these products range from ethane, LPG to heavier
hydrocarbons comprising mostly of isoparaffins. Hydrocracking is normally facilitated by a bi
functional catalyst that is capable of rearranging and breaking hydrocarbon chains as well as
adding hydrogen to aromatics and olefins to produce naphthenes and alkanes.
Major products from hydrocracking are jet fuel and diesel, while also relatively high octane
rating gasoline fractions and LPG are produced. All these products have a very low content of
sulfur and other contaminants.
It is very common in India, Europe and Asia because those regions have high demand for
diesel and kerosene. In the US, Fluid Catalytic Cracking is more common because the
demand for gasoline is higher.
43
Case Study: Petroleum
Origins of the Industry
The American chemical engineer and the American petroleum industry developed side by
side over the past century. The petroleum industry began when Edwin L. Drake drilled a
successful oil well at Titusville Pennsylvania in 1859. Others quickly followed his lead, and
before long oil wells covered the countryside. Just ten years after California's Gold Rush,
Pennsylvania had developed its own brand of "gold fever". Some, like John D. Rockefeller,
accumulated vast fortunes from this "black gold", while others like Mr. Drake died broke.
The difference between success and failure was often a fine line.
"Enough already...go to the end."
Ancient, and Less Ancient, Times
Small amounts of petroleum have been used throughout history. The Egyptians coated
mummies and sealed their mighty Pyramids with pitch. The Babylonians, Assyrians, and
Persians used it to pave their streets and hold their walls and buildings together. Boats
along the Euphrates were constructed with woven reeds and sealed with pitch. The Chinese
also came across it while digging holes for brine (salt water) and used the petroleum for
heating. The Bible even claims that Noah used it to make his Ark seaworthy.
American Indians used petroleum for paint, fuel, and medicine. Desert nomads used it to
treat camels for mange, and the Holy Roman Emperor, Charles V, used petroleum it to treat
his gout. Ancient Persians and Sumatrans also believed petroleum had medicinal value.
This seemed a popular idea, and up through the 19th Century jars of petroleum were sold as
miracle tonic able to cure whatever ailed you. People who drank this "snake oil" discovered
that petroleum doesn't taste very good!
The Search for Oil
Yet despite its usefulness, for thousands of years petroleum was very scarce. People
collected it when it bubbled to the surface or seeped into wells. For those digging wells to get
drinking water the petroleum was seen as a nuisance. However, some thought the oil might
have large scale economic value. George Bissell, a lawyer, thought that petroleum might be
converted into kerosene for use in lamps. An analysis by Benjamin Silliman, Jr., a Yale
chemistry and geology professor, confirmed his hunch.
In 1854 Bissell and a friend formed the unsuccessful Pennsylvania Rock Oil Company. Not
one to be easily dismayed, in 1858 Bissell and a group of business men formed the Seneca
Oil Company. They hired an ex-railroad conductor named Edwin Drake to drill for oil along
a secluded creek in Titusville Pennsylvania. They soon dubbed him "Colonel" Drake to
impress the locals. But the "Colonel" needed help so he hired Uncle Billy Smith and his two
sons who had experience with drilling salt wells. In 1859 this motley crew found oil at a
depth of 69 ˝ feet.
Pennsylvania's "Black Gold"
44
Drake's well produced only thirty-five barrels a day, however he could sell it for $20 a
barrel. News of the well quickly spread and brought droves of fortune seekers. Soon the
hills were covered with prospectors trying to decide where to dig their wells. Some used Yshaped devining rods to guide them. Others followed Drake's lead and drilled close to
water, a technique that was dubbed "creekology". Many found oil, but usually at 4 or 5
hundred feet below the surface. Drake had just been lucky to find oil so high up!
To dig the wells six-inch wide cast iron pipes were sunk down to the bedrock. A screw
like drill was then used to scoop out dirt and rock from the middle. Many discovered to their
dismay that once they hit oil they had no way to contain all of it. Until caps were added to the
wells vast quantities of oil flowed into the appropriately named Oil Creek.
The First Pipeline
Transporting the oil was also a problem. In 1865 Samuel Van Syckel, an oil buyer, began
construction on a two-inch wide pipeline designed to span the distance to the railroad depot
five miles away. The teamsters, who had previously transported the oil, didn't take to kindly
to Syckel's plan, and they used pickaxes to break apart the line. Eventually Van Syckel
brought in armed guards, finished the pipeline, and made a ton-o-money. By 1865 wooden
derricks were bled 3.5 million barrels a year out of the ground. (Giddens) Such large scale
production caused the price of crude oil to plummet to ten cents a barrel.
How Much Oil?
Andrew Carnegie was a large stockholder in the Columbia Oil Company. Carnegie
believed that the oil fields would quickly run dry because of all the drilling. He persuaded
Columbia Oil to dig a huge hole to store 100,000 barrels of oil so that they could make a
killing when the country's wells went dry. Luckily there was more oil than they thought!
But don't feel too sorry for Carnegie, he didn't let the setback slow him down very much, and
went on to make his millions in the steel industry.
In contrast, "Colonel" Drake was committed to the oil business. He scoured the country
looking for customers willing to buy his crude oil. However, the bad smell, muddy black
color, and highly volatile component, called naphtha, caused few sales. It became obvious
that one would have to refine the oil to find a market.
Early Refining
By 1860 there were 15 refineries in operation. Known as "tea kettle" stills, they consisted of
a large iron drum and a long tube which acted as a condenser. Capacity of these stills ranged
from 1 to 100 barrels a day. A coal fire heated the drum, and three fractions were obtained
during the distillation process. The first component to boil off was the highly volatile
naphtha. Next came the kerosene, or "lamp oil", and lastly came the heavy oils and tar
which were simply left in the bottom of the drum. These early refineries produced about 75%
kerosene, which could be sold for high profits. (Giddens, p.14)
Kerosene was so valuable because of a whale shortage that had began in 1845 due to heavy
hunting. Sperm oil had been the main product of the whaling industry and was used in
lamps. Candles were made with another whale product called "spermaceti". This shortage of
natural sources meant that kerosene was in great demand. Almost all the families across the
country started using kerosene to light their homes. However, the naphtha and tar
45
fractions were seen as valueless and were simply dumped into Oil Creek. (I would like to
point out that these first refineries were not operated by chemical engineers!)
Later these waste streams were converted into valuable products. In 1869 Robert
Chesebrough discovered how to make petroleum jelly and called his new product Vaseline.
The heavy components began being used as lubricants, or as waxes in candles and chewing
gum. Tar was used as a roofing material. But the more volatile components were still
without much value. Limited success came in using gasoline as a local anesthetic and
liquid petroleum gas (LPG) in a compression cycle to make ice. The success in refined
petroleum products greatly spread the technique. By 1865 there were 194 refineries in
operation.
John D. Rockefeller
In 1862 John D. Rockefeller financed his first refinery as a side investment. He soon
discovered that he liked the petroleum industry, and devoted himself to it full time. As a
young bookkeeper Rockefeller had come to love the order of a well organized ledger.
However, he was appalled by the disorder and instability of the oil industry. Anyone could
drill a well, and overproduction plagued the early industry. At times this overproduction
meant that the crude oil was cheaper than water. Rockefeller saw early on, that refining
and transportation, as opposed to production, were the keys to taking control of the
industry. And control the industry he did!
In 1870 he established Standard Oil, which then controlled 10% of the refining capacity in
the country. Transportation often encompassed 20% of the total production cost and
Rockefeller made under-the-table deals with railroads to give him secret shipping rebates.
This cheap transportation allowed Standard to undercut its competitors and Rockefeller
expanded aggressively, buying out competitors left and right. Soon standard built a network
of "iron arteries" which delivered oil across the Eastern U.S. This pipeline system relieved
Standard's dependence upon the railroads and reduced its transportation costs even more. By
1880 Standard controlled 90% of the country's refining capacity. Because of its massive
size, it brought security and stability to the oil business, guaranteeing continuous profits.
With Standard Oil, John D. Rockefeller became the richest person in the World.
So What?
But what came out of all this activity? In short the early petroleum industry:
Brought a revolution in lighting with kerosene.
Helped keep machines in good conditions with lubricants. (it was the "Machine Age" after
all)
Provided a new source of national wealth (in 1865 it was the countries 6th largest export).
Aided the Union in the Civil War by strengthening the economy (also petroleum was used to
treat wounded soldiers at the battle of Gettysburg).
46
Modern Refining
Petroleum refineries are marvels of modern engineering. Within them a maze of pipes,
distillation columns, and chemical reactors turn crude oil into valuable products. Large
refineries cost billions of dollars, employ several thousand workers, operate around the clock,
and occupy the same area as several hundred football stadiums. The U.S. has about 300
refineries that can process anywhere between 40 and 400,000 barrels of oil a day. These
refineries turn out the gasoline and chemical feedstocks that keep the country running.
The Search
Locating an oil field is the first obstacle to be overcome. The first explorers used Y-shaped
devining rods and other supernatural, but ineffective, means of locating petroleum. Today
geologists and petroleum engineers employ more tried and true methods. Instruments to aid
the search include; geophones (uses sound), gravimeters (uses gravity), and magnetometers
(uses the Earth's magnet field). While these methods narrow the search tremendously, a
person still has to drill a exploratory well, or wildcat well, to see if the oil actually exists.
Success brings visions of gushers soaring skyward, however today wells are capped before
this happens.
Drilling
There are three main types of drilling operations; cable-tool, rotary, and off-shore. Cabletool drilling involves a jack-hammer approach were a chisel dislodges earth and hauls up the
loose sediment. Rotary drilling works at much greater depths, and involve sinking a drill
pipe with a rotating steel bit in the middle. Off-shore drilling involves huge
semisubmersible platforms which lower a shaft to the ocean floor, containing any oil which
is located.
All crude oil contains some amount of methane or other gases dissolved in it. Once the
drilling shaft makes contact with the oil it releases the pressure in the underground reservoir.
Just like opening a can of soda pop, the dissolved gases fizz out of solution pushing crude
oil to the surface. The dissolved gases will allow about 20% recovery of oil. To get better
recovery water is often pumped into the well, this forces the lighter oil to the surface. Water
flooding allows recoveries of about 50%. The addition of surfactant allows even more oil to
be recovered by preventing much of it from getting trapped in nooks and crannies. Yet, it is
impossible to get all of the oil out of a well.
Transportation
Because crude oil is a liquid it is much easier to move than natural gas or coal. Coal is nice
and dense, so it does not require large holding containers, but it cannot be pumped.
Conveyor belts and cranes cannot compete with pipelines for economic efficiency. Natural
gas can be pumped using expensive compressors, but it requires enormous holding tanks. A
recent trick has been to inject huge amounts of water into salt strata. The water dissolves the
salt, leaving truly enormous caverns. The natural gas is then pumped in and stored until
needed. The ease in transporting oil is one of the reasons we have become so dependent
upon it. Pound for pound natural gas and coal just cannot compete.
47
Reserves
The proven reserves of crude oil within the U.S. are about 3.9 billion cubic meters. This
could cover the state of Minnesota with a layer one half inch thick. A reasonable value for
the total amount of crude oil obtainable using current methods from around the world is 350
billion cubic meters. This could cover Minnesota with a layer of oil four and a half feet
thick. Yet, at the rate we are consuming oil, the nation's reserves will be depleted by 2010,
and the world's reserves will be depleted by the end of the 21st Century.
Yet, oil is not the only source of hydrocarbons. Natural gas and coal are both available in
much greater amounts (see Distillation Figure). However, we may decide that it is not such a
good idea to burn all of these hydrocarbons. Carbon dioxide is a strong greenhouse gas
(along with water and methane), and the results to the global environment could be
catastrophic to human life. Nuclear fission, solar power, hydroelectric power, and geothermal
power offer immediate alternatives, however energy produced by these methods would be
more expensive than burning oil, coal, or natural gas. The holy grail of power production,
nuclear fusion, continues to elude scientists and engineers. In any case, refining techniques
will remain vital to produce not only fuels but raw materials for petrochemical industries
(plastics, pharmaceuticals, agrochemicals, etc.).
"The Kingdom of Heaven runs on righteousness, but the Kingdom of Earth
runs on OIL!"
Quote by Ernest Bevin at the British Parliament during a heated discussion concerning the
Middle East.
Chemistry
Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly
found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons, or
more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of
molecules, which define its physical and chemical properties, like color and viscosity.
The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched
chains which contain only carbon and hydrogen and have the general formula CnH2n+2 They
generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or
longer molecules may be present in the mixture.
The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline (petrol), the
ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel and kerosene (primary
component of many types of jet fuel), and the ones from hexadecane upwards into fuel oil and
lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately
25 carbon atoms, while asphalt has 35 and up, although these are usually cracked by modern
refineries into more valuable products. The shortest molecules, those with four or fewer
carbon atoms, are in a gaseous state at room temperature. They are the petroleum gases.
Depending on demand and the cost of recovery, these gases are either flared off, sold as
liquified petroleum gas under pressure, or used to power the refinery's own burners. During
the winter, Butane (C4H10), is blended into the gasoline pool at high rates, because butane's
high vapor pressure assists with cold starts. Liquified under pressure slightly above
atmospheric, it is best known for powering cigarette lighters, but it is also a main fuel source
for many developing countries. Propane can be liquified under modest pressure, and is
48
consumed for just about every application relying on petroleum for energy, from cooking to
heating to transportation.
The cycloalkanes, also known as naphthenes, are saturated hydrocarbons which have one or
more carbon rings to which hydrogen atoms are attached according to the formula CnH2n.
Cycloalkanes have similar properties to alkanes but have higher boiling points.
The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar
six-carbon rings called benzene rings, to which hydrogen atoms are attached with the formula
CnHn. They tend to burn with a sooty flame, and many have a sweet aroma. Some are
carcinogenic.
These different molecules are separated by fractional distillation at an oil refinery to produce
gasoline, jet fuel, kerosene, and other hydrocarbons. For example 2,2,4-trimethylpentane
(isooctane), widely used in gasoline, has a chemical formula of C8H18 and it reacts with
oxygen exothermically:[11]
The amount of various molecules in an oil sample can be determined in laboratory. The
molecules are typically extracted in a solvent, then separated in a gas chromatograph, and
finally determined with a suitable detector, such as a flame ionization detector or a mass
spectrometer[12].
Incomplete combustion of petroleum or gasoline results in production of toxic byproducts.
Too little oxygen results in carbon monoxide. Due to the high temperatures and high pressures
involved, exhaust gases from gasoline combustion in car engines usually include nitrogen
oxides which are responsible for creation of photochemical smog.
Formation
Geologists view crude oil and natural gas as the product of compression and heating of
ancient organic materials (i.e. kerogen) over geological time. Formation of petroleum occurs
from hydrocarbon pyrolysis, in a variety of mostly endothermic reactions at high temperature
and/or pressure.[13] Today's oil formed from the preserved remains of prehistoric zooplankton
and algae, which had settled to a sea or lake bottom in large quantities under anoxic
conditions (the remains of prehistoric terrestrial plants, on the other hand, tended to form
coal). Over geological time the organic matter mixed with mud, and was buried under heavy
layers of sediment resulting in high levels of heat and pressure (known as diagenesis). This
caused the organic matter to chemically change, first into a waxy material known as kerogen
which is found in various oil shales around the world, and then with more heat into liquid and
gaseous hydrocarbons in a process known as catagenesis.
Geologists often refer to the temperature range in which oil forms as an "oil window"[14]—
below the minimum temperature oil remains trapped in the form of kerogen, and above the
maximum temperature the oil is converted to natural gas through the process of thermal
cracking. Although this temperature range is found at different depths below the surface
throughout the world, a typical depth for the oil window is 4–6 km. Sometimes, oil which is
formed at extreme depths may migrate and become trapped at much shallower depths than
where it was formed. The Athabasca Oil Sands is one example of this.
49
Crude Oil
Crude oil reservoirs
Hydrocarbon trap.
Three conditions must be present for oil reservoirs to form: a source rock rich in hydrocarbon
material buried deep enough for subterranean heat to cook it into oil; a porous and permeable
reservoir rock for it to accumulate in; and a cap rock (seal) or other mechanism that prevents
it from escaping to the surface. Within these reservoirs, fluids will typically organize
themselves like a three-layer cake with a layer of water below the oil layer and a layer of gas
above it, although the different layers vary in size between reservoirs. Because most
hydrocarbons are lighter than rock or water, they often migrate upward through adjacent rock
layers until either reaching the surface or becoming trapped within porous rocks (known as
reservoirs) by impermeable rocks above. However, the process is influenced by underground
water flows, causing oil to migrate hundreds of kilometres horizontally or even short
distances downward before becoming trapped in a reservoir. When hydrocarbons are
concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling
and pumping.
The reactions that produce oil and natural gas are often modeled as first order breakdown
reactions, where hydrocarbons are broken down to oil and natural gas by a set of parallel
reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter
set is regularly used in petrochemical plants and oil refineries.
[Non-conventional oil reservoirs
Oil-eating bacteria biodegrades oil that has escaped to the surface. Oil sands are reservoirs of
partially biodegraded oil still in the process of escaping and being biodegraded, but they
contain so much migrating oil that, although most of it has escaped, vast amounts are still
present—more than can be found in conventional oil reservoirs. The lighter fractions of the
crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of
crude oil, called crude bitumen in Canada, or extra-heavy crude oil in Venezuela. These two
countries have the world's largest deposits of oil sands.
On the other hand, oil shales are source rocks that have not been exposed to heat or pressure
long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil
shales are not really shales and do not really contain oil, but are usually relatively hard rocks
called marls containing a waxy substance called kerogen. The kerogen trapped in the rock can
be converted into crude oil using heat and pressure to simulate natural processes. The method
has been known for centuries and was patented in 1694 under British Crown Patent No. 330
covering, "A way to extract and make great quantityes of pitch, tarr, and oyle out of a sort of
stone." Although oil shales are found in many countries, the United States has the world's
largest deposits.[15]
Abiogenic origin
Main article: Abiogenic petroleum origin
50
A number of geologists in Russia adhere to the abiogenic petroleum origin hypothesis and
maintain that hydrocarbons of purely inorganic origin exist within Earth's interior.
Astronomer Thomas Gold championed the theory in the Western world by supporting the
work done by Nikolai Kudryavtsev in the 1950s. It is currently supported primarily by
Kenney and Krayushkin.[16]
The abiogenic origin hypothesis lacks scientific support, and all current oil reserves have
biological origin. It also has not been successfully used in uncovering oil deposits by
geologists.[17]
Classification
See also: Benchmark (crude oil)
A sample of medium heavy crude oil
The petroleum industry generally classifies crude oil by the geographic location it is produced
in (e.g. West Texas, Brent, or Oman), its API gravity (an oil industry measure of density), and
by its sulfur content. Crude oil may be considered light if it has low density or heavy if it has
high density; and it may be referred to as sweet if it contains relatively little sulfur or sour if it
contains substantial amounts of sulfur.
The geographic location is important because it affects transportation costs to the refinery.
Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline,
while sweet oil commands a higher price than sour oil because it has fewer environmental
problems and requires less refining to meet sulfur standards imposed on fuels in consuming
countries. Each crude oil has unique molecular characteristics which are understood by the
use of crude oil assay analysis in petroleum laboratories.
Barrels from an area in which the crude oil's molecular characteristics have been determined
and the oil has been classified are used as pricing references throughout the world. Some of
the common reference crudes are:
•
•
•
•
•
•
West Texas Intermediate (WTI), a very high-quality, sweet, light oil delivered at
Cushing, Oklahoma for North American oil
Brent Blend, comprising 15 oils from fields in the Brent and Ninian systems in the
East Shetland Basin of the North Sea. The oil is landed at Sullom Voe terminal in the
Shetlands. Oil production from Europe, Africa and Middle Eastern oil flowing West
tends to be priced off this oil, which forms a benchmark
Dubai-Oman, used as benchmark for Middle East sour crude oil flowing to the AsiaPacific region
Tapis (from Malaysia, used as a reference for light Far East oil)
Minas (from Indonesia, used as a reference for heavy Far East oil)
The OPEC Reference Basket, a weighted average of oil blends from various OPEC
(The Organization of the Petroleum Exporting Countries) countries
There are declining amounts of these benchmark oils being produced each year, so other oils
are more commonly what is actually delivered. While the reference price may be for West
Texas Intermediate delivered at Cushing, the actual oil being traded may be a discounted
51
Canadian heavy oil delivered at Hardisty, Alberta, and for a Brent Blend delivered at the
Shetlands, it may be a Russian Export Blend delivered at the port of Primorsk.[18]
Petroleum industry
Main article: Petroleum industry
NYMEX Light Sweet Crude prices 1994 2005 to Nov 2008
to Mar 2008
The petroleum industry is involved in the global processes of exploration, extraction, refining,
transporting (often with oil tankers and pipelines), and marketing petroleum products. The
largest volume products of the industry are fuel oil and gasoline (petrol). Petroleum is also the
raw material for many chemical products, including pharmaceuticals, solvents, fertilizers,
pesticides, and plastics. The industry is usually divided into three major components:
upstream, midstream and downstream. Midstream operations are usually included in the
downstream category.
Petroleum is vital to many industries, and is of importance to the maintenance of
industrialized civilization itself, and thus is critical concern to many nations. Oil accounts for
a large percentage of the world’s energy consumption, ranging from a low of 32% for Europe
and Asia, up to a high of 53% for the Middle East. Other geographic regions’ consumption
patterns are as follows: South and Central America (44%), Africa (41%), and North America
(40%). The world at large consumes 30 billion barrels (4.8 km³) of oil per year, and the top oil
consumers largely consist of developed nations. In fact, 24% of the oil consumed in 2004
went to the United States alone.[19] The production, distribution, refining, and retailing of
petroleum taken as a whole represent the single largest industry in terms of dollar value on
earth.
In the US, in the states of Arizona, California, Hawaii, Nevada, Oregon and Washington, the
Western States Petroleum Association (WSPA) is responsible for producing, distributing,
refining, transporting and marketing petroleum. This is non-profit trade association that was
founded in 1907, and is the oldest petroleum trade association in the United States.[20]
History
Kerosene lamp
Ignacy Łukasiewicz - creator of the process of refining of kerosene from crude oil.
Oil derrick in Okemah, Oklahoma, 1922
Oil field in California, 1938.
52
Petroleum, in one form or another, is not a recent discovery. More than four thousand years
ago, according to Herodotus and confirmed by Diodorus Siculus, asphalt was employed in the
construction of the walls and towers of Babylon; there were oil pits near Ardericca (near
Babylon), and a pitch spring on Zacynthus.[21] Great quantities of it were found on the banks
of the river Issus, one of the tributaries of the Euphrates. Ancient Persian tablets indicate the
medicinal and lighting uses of petroleum in the upper levels of their society.
Oil was exploited in the Roman province of Dacia, now in Romania, where it was called
picula.
The earliest known oil wells were drilled in China in 347 CE or earlier. They had depths of up
to about 800 feet (240 m) and were drilled using bits attached to bamboo poles.[22] The oil was
burned to evaporate brine and produce salt. By the 10th century, extensive bamboo pipelines
connected oil wells with salt springs. The ancient records of China and Japan are said to
contain many allusions to the use of natural gas for lighting and heating. Petroleum was
known as burning water in Japan in the 7th century.[21] In his book Dream Pool Essays
written in 1088, the polymathic scientist and statesman Shen Kuo of the Song Dynasty coined
the word 石油 (Shíyóu, literally "rock oil") for petroleum, which remains the term used in
contemporary Chinese.
The first streets of Baghdad were paved with tar, derived from petroleum that became
accessible from natural fields in the region. In the 9th century, oil fields were exploited in the
area around modern Baku, Azerbaijan, to produce naphtha. These fields were described by the
Arab geographer Abu al-Hasan 'Alī al-Mas'ūdī in the 10th century, and by Marco Polo in the
13th century, who described the output of those wells as hundreds of shiploads. Petroleum
was distilled by the Persian alchemist Muhammad ibn Zakarīya Rāzi (Rhazes) in the 9th
century, producing chemicals such as kerosene in the alembic (al-ambiq),[23] and which was
mainly used for kerosene lamps.[24] Arab and Persian chemists also distilled crude oil in order
to produce flammable products for military purposes. Through Islamic Spain, distillation
became available in Western Europe by the 12th century.[25] It has also been present in
Romania since the 13th century, being recorded as păcură.[26]
The earliest mention of petroleum in the Americas occurs in Sir Walter Raleigh's account of
the Trinidad Pitch Lake in 1595; whilst thirty-seven years later, the account of a visit of a
Franciscan, Joseph de la Roche d'Allion, to the oil springs of New York was published in
Sagard's Histoire du Canada. A Russian traveller, Peter Kalm, in his work on America
published in 1748 showed on a map the oil springs of Pennsylvania.[21]
In 1710 or 1711 (sources vary) the Russian-born Swiss physician and Greek teacher Eyrini
d’Eyrinis (also spelled as Eirini d'Eirinis) discovered asphaltum at Val-de-Travers,
(Neuchâtel). He established a bitumen mine de la Presta there in 1719 that operated until
1986.[27][28][29][30]
Oil sands were mined from 1745 in Merkwiller-Pechelbronn, Alsace under the direction of
Louis Pierre Ancillon de la Sablonnière, by special appointment of Louis XV.[31] The
Pechelbronn oil field was active until 1970, and was the birth place of companies like Antar
and Schlumberger. The first modern refinery was built there in 1857.[31]
The modern history of petroleum began in 1846 with the discovery of the process of refining
kerosene from coal by Nova Scotian Abraham Pineo Gesner. Ignacy Łukasiewicz improved
Gesner's method to develop a means of refining kerosene from the more readily available
"rock oil" ("petr-oleum") seeps in 1852 and the first rock oil mine was built in Bóbrka, near
53
Krosno in Galicia(Poland/Ukraine) in the following year. In 1854, Benjamin Silliman, a
science professor at Yale University in New Haven, was the first to fractionate petroleum by
distillation. These discoveries rapidly spread around the world, and Meerzoeff built the first
Russian refinery in the mature oil fields at Baku in 1861. At that time Baku produced about
90% of the world's oil.
The first commercial oil well in Romania was drilled in 1857, and the world's first oil refinery
opened at Ploiesti, Romania being the first country in the world with a crude oil output
officially recorded in international statistics, namely 275 tonnes[32][33]. The first oil well in
North America was in Oil Springs, Ontario, Canada in 1858, dug by James Miller Williams.
The US petroleum industry began with Edwin Drake's drilling of a 69-foot (21 m) oil well in
1859, on Oil Creek near Titusville, Pennsylvania, for the Seneca Oil Company (originally
yielding 25 barrels per day (4.0 m³/d), by the end of the year output was at the rate of
15 barrels per day (2.4 m³/d)). The industry grew through the 1800s, driven by the demand for
kerosene and oil lamps. It became a major national concern in the early part of the 20th
century; the introduction of the internal combustion engine provided a demand that has
largely sustained the industry to this day. Early "local" finds like those in Pennsylvania and
Ontario were quickly outpaced by demand, leading to "oil booms" in Texas, Oklahoma, and
California.
Early production of crude petroleum in the United States:[21]
•
•
•
•
•
•
1859: 2,000 barrels (~270 t)
1869: 4,215,000 barrels (~5.750×105 t)
1879: 19,914,146 barrels (~2.717×106 t)
1889: 35,163,513 barrels (~4.797×106 t)
1899: 57,084,428 barrels (~7.788×106 t)
1906: 126,493,936 barrels (~1.726×107 t)
By 1910, significant oil fields had been discovered in Canada (specifically, in the province of
Alberta), the Dutch East Indies (1885, in Sumatra), Iran (1908, in Masjed Soleiman), (1863,
in Zorritos District) Peru, Venezuela, and Mexico, and were being developed at an industrial
level.
During World War II, oil facilities were a major strategic asset and were extensively bombed.
Even until the mid-1950s, coal was still the world's foremost fuel, but oil quickly took over.
Following the 1973 energy crisis and the 1979 energy crisis, there was significant media
coverage of oil supply levels. This brought to light the concern that oil is a limited resource
that will eventually run out, at least as an economically viable energy source. At the time, the
most common and popular predictions were quite dire. However, a period of increased
production and reduced demand caused an oil glut in the 1980s.
Today, about 90% of vehicular fuel needs are met by oil. Petroleum also makes up 40% of
total energy consumption in the United States, but is responsible for only 2% of electricity
generation. Petroleum's worth as a portable, dense energy source powering the vast majority
of vehicles and as the base of many industrial chemicals makes it one of the world's most
important commodities. Access to it was a major factor in several military conflicts of the late
twentieth and early twenty-first centuries, including World War II[34] and the Persian Gulf
Wars (Iran–Iraq War, Operation Desert Storm, and the Iraq War)[35]. The top three oil
producing countries are Saudi Arabia, Russia, and the United States.[36] About 80% of the
world's readily accessible reserves are located in the Middle East, with 62.5% coming from
54
the Arab 5: Saudi Arabia (12.5%), UAE, Iraq, Qatar and Kuwait. However, with high oil
prices, (above $100/barrel) Venezuela has larger reserves than Saudi Arabia due to crude
reserves derived from bitumen.
Oil contains a complex mixture of hydrocarbons. The first step in obtaining something of
value from this muck is to de-salt and de-water it. Then the oil is heated and sent into a huge
distillation column operating at atmospheric pressure. Heat is added at the reboiler, and
removed at the condenser, thereby separating the oil into fractions based upon boiling
point. A typical atmospheric column can separate about 4,000 cubic meters (25,000 barrels)
of oil per day. The bottom fraction is sent to another column operating at a pressure of about
75 mm Hg (one tenth of an atmosphere). This column can separate the heaviest fraction
without thermally degrading (cracking) it. Whereas atmospheric columns are thin at tall,
vacuum columns are thick and short, to minimize pressure fluctuations along the column.
Vacuum columns can be over 40 feet in diameter!
Which Fraction to Make?
Various fractions are more important at different times of year. During the summer
driving months, the public consumes vast amounts of gasoline, whereas during the winter
more fuel oil is consumed. These demands also vary depending upon whether you live in the
frigid north, or the humid south. Modern refineries are able to alter the ratios of the
different fractions to meet demand, and maximize profit.
Petroleum: Origins of the Industry
A Few Terms
The petroleum industry, like other chemical industries, has a plethora of terms designed to
scare off anyone who wants to understand exactly what is going on. Mastering this
nomenclature is one of the main tasks facing chemistry and chemical engineering
students. Here are a few commonly used terms, but be forewarned; because of the complexity
of compounds in the petroleum industry some of these terms are very vague.
Hydrocarbons are chemical compounds made mainly of carbon and hydrogen. Both
petroleum and coal contain many different hydrocarbons. Methane, ethanol, and benzene are
examples of hydrocarbons, though there are many many others.
Bitumen is a another term for hydrocarbons. Both petroleum and coal are sometimes
referred to as Bituminous.
Organic compounds are chemicals made of carbon (although the classification is not totally
consistent and some carbon compounds, like carbon dioxide, are not considered organic).
Hydrocarbons are commonly referred to as organic compounds, and it is fair to think of the
two as equivalent. Carbohydrates, proteins, and urea (found in urine) are examples or organic
compounds. It was once thought that organic compounds could only be produced from
organic sources. Because of their usefulness, a huge chemical industry developed around
55
February 2009
Distillation
organic chemicals during the 19th Century. Dyes and pharmaceuticals where products of this
industry. As chemists increased their skills they found that organic compounds could be
synthesized from inorganic sources. However, by this time the classification had been firmly
rooted in industry and universities and so it remains today.
Inorganic compounds include everything that is not considered organic (every compound
in the world is ether organic or inorganic).
Aromatic compounds are organic compounds which always have a benzene ring in them.
Because of this they can be quite reactive and have some interesting properties. The dye
and pharmaceutical industries depend heavily on aromatic compounds.
Aliphatic compounds are organic compounds which are not aromatic. They include single
bonded (ethane, propane, butane), double bonded (ethene or called ethylene, propene, butene),
and triple bonded (ethyne or called acetylene, propyne, butyne) straight chain hydrocarbons as
well as cyclic non-benzene structures (cyclopentane, cyclobutane) (every organic compound
in the world is either aromatic or aliphatic).
A Barrel (bbl.) of crude contains 42 gallons or 158.8 liters. No one actually ships petroleum
in barrels anymore because they are too small, but the term is still used to describe a defined
volume.
Petroleum literally means "rock oil". It is a very broad word referring to all liquid
hydrocarbons which can be collected from the ground. Even natural gas and solid
hydrocarbons are sometimes referred to as petroleum. When petroleum first comes from the
ground it is called crude oil. Later it is usually just referred to as oil. It can flow like water or
be as viscous as peanut butter. It can be yellow, red, green, brown, or black.
Fractions are complex mixtures of chemical compounds that all have a similar boiling
point. Light and heavy fractions refer to a compound's boiling point and not their actual
density (these are two entirely different things). Light fractions can be very heavy (dense),
and heavy fractions can be very light (go figure)!
Isomers are chemicals which have the same number and type of atoms but have them
arranged in a different way. Methane (CH4), ethane (C2H6), and propane (C3H8) have no
isomers because their is only one way the carbons can hook together. Butane (C4H10) has
56
two isomers (n-butane and isobutane). Decane (C10H22) has seventy five isomers, and a
molecule with 20 carbon atoms (C20H42) has over 100,000 isomers. Crude oil contains
molecules having 1 to 100+ carbon atoms. Naming these compounds based upon normal
chemical rhetoric would be hell on earth! The huge number of possible molecular
arrangements is why people talk of fractions instead of using proper chemical nomenclature.
Natural Gas is a mixture of very low boiling hydrocarbons. Natural gas can only be
liquefied under extremely high pressures and very low temperatures. It is called "dry" when
methane (CH4) is the primary component, and "wet" if it contains higher boiling
hydrocarbons. If it smells bad, because of sulfur compounds, it is called "sour". Otherwise, it
is called "sweet".
Liquefied Petroleum Gas (LPG) is a very light fraction of petroleum. It is also a fairly
simple fraction containing mainly propane and butane. First, it should be noted that under
normal pressures LPG is actually a gas, unlike gasoline (often just called "gas") which is
really a liquid (ugh). However, under modestly high pressures these compounds can be
converted to a liquid (hence their name). Being able to store them as a liquid reduces the
container size by a factor of a hundred. This is no doubt why propane stoves are so popular.
As cracking methods have evolved more and more LPG has been produced by refineries.
Gasoline is a light fraction of petroleum which is quite volatile and burns rapidly. Straight
run gasoline refers to gasoline produced by distillation instead of cracking, although it really
doesn't make a difference. Gasoline is often just called "gas", however it is a liquid at
typical pressures. This confusing state of affairs developed because the first internal
combustion engines ran on town gas (a mixture of carbon monoxide, CO, and hydrogen,
H2, both actual gases). These engines were therefore called "gas engines". When gasoline
replaced town gas people still called the motors "gas engines" and also started calling gasoline
"gas". Today, the average American uses 450 gallons of gasoline a year.
Octane Number rates a fuel's ability to avoid premature ignition called knock. Premature
ignition reduces an engine's power and quickly wares it out. The octane scale arbitrarily
defines n-heptane a value of 0, and isooctane (2,2,4-trimethyl pentane) an octane number of
100. Isooctane is then added to heptane until the mixture has the same knock characteristics as
the fuel being tested, and the percent isooctane is taken as the unknown fuels octane number.
Tetraethyl lead used to be a common anti-knock additive which would raise a fuels octane
number. High octane fuel can be used in engines with high compression ratios which in
turn produce much more power. However, the additive is no longer used because of concerns
over lead pollution.
Naphtha is a light fraction of petroleum used to make gasoline. Naphtha also produces
solvents and feedstocks for the petrochemical industry.
Kerosene was the first important petroleum fraction, replacing whale oils in lamps over a
hundred years ago. Some unscrupulous refiners failed to distill off all the naphtha from the
kerosene fraction thereby increasing the volume of their final product. This lead to many lamp
explosions and fires.
Diesel fuels find use in the fleet of trucks which transport the nations goods. Diesel engines
power these larger engines, and use higher compression ratios (and temperatures) than their
gasoline cousins. They are therefore more efficient. It is also interesting to note that diesel
57
engines have no spark plugs, instead the fuel-air mixture is ignited by the rising
temperatures and pressures during the compression stroke.
Gas Oil (or fuel oils) are used for domestic heating. In the winter refineries produce more
gas oil, whereas during the summer driving months they produce more gasoline.
Heavy Fuel Oil is often blended with gas oils for easier use in industry. Ships burn heavy
fuel oils but they call it bunker oil.
Atmospheric Residual is everything that cannot be vaporized under normal pressures.
Atmospheric residual is fed into another distillation column, operating at lower pressures,
which can separate out some of the lighter compounds. Lubricants and waxes reside in this
fraction.
Vacuum Residual is the bottom of the barrel. It includes asphalt and some coke.
Pitch is a thick, black, sticky material. It is left behind when the lighter components of coal
tar or petroleum are distilled off. Pitch is a "natural" form of asphalt.
Asphalt is a high boiling component of crude oil. It is therefore found at the "bottom of the
barrel" when petroleum is distilled.
Tars are byproducts formed when coke is made from coal or charcoal is made from wood.
It is a thick, complex, oily black mixture of heavy organic compounds very similar to pitch or
asphalt, though from a different source.
Composition
The proportion of hydrocarbons in the mixture is highly variable and ranges from as much as
97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.
The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic
hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and
trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular
composition varies widely from formation to formation but the proportion of chemical
elements vary over fairly narrow limits as follows:[2]
Co
mp
osit
ion
by
wei
ght
Element Percent range
Carbon
83 to 87%
58
Hydrogen 10 to 14%
Nitrogen 0.1 to 2%
Oxygen
0.1 to 1.5%
Sulfur
0.5 to 6%
Metals
less than 1000 ppm
Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of
each varies from oil to oil, determining the properties of each oil.[3]
Composition by weight
Hydrocarbon Average Range
Paraffins
30%
15 to 60%
Naphthenes
49%
30 to 60%
Aromatics
15%
3 to 30%
Asphaltics
6%
remainder
Most of the world's oils are non-conventional.[4]
Crude oil varies greatly in appearance depending on its composition. It is usually black or
dark brown (although it may be yellowish or even greenish). In the reservoir it is usually
found in association with natural gas, which being lighter forms a gas cap over the petroleum,
and saline water which, being heavier than most forms of crude oil, generally sinks beneath it.
Crude oil may also be found in semi-solid form mixed with sand and water, as in the
Athabasca oil sands in Canada, where it is usually referred to as crude bitumen. In Canada,
bitumen is considered a sticky, tar-like form of crude oil which is so thick and heavy that it
must be heated or diluted before it will flow.[5] Venezuela also has large amounts of oil in the
Orinoco oil sands, although the hydrocarbons trapped in them are more fluid than in Canada
and are usually called extra heavy oil. These oil sands resources are called non-conventional
oil to distinguish them from oil which can be extracted using traditional oil well methods.
Between them, Canada and Venezuela contain an estimated 3.6 trillion barrels (570×109 m3)
of bitumen and extra-heavy oil, about twice the volume of the world's reserves of
conventional oil.[6]
Petroleum is used mostly, by volume, for producing fuel oil and gasoline (petrol), both
important "primary energy" sources.[7] 84% by volume of the hydrocarbons present in
petroleum is converted into energy-rich fuels (petroleum-based fuels), including gasoline,
diesel, jet, heating, and other fuel oils, and liquefied petroleum gas.[8] The lighter grades of
crude oil produce the best yields of these products, but as the world's reserves of light and
medium oil are depleted, oil refineries are increasingly having to process heavy oil and
bitumen, and use more complex and expensive methods to produce the products required.
Because heavier crude oils have too much carbon and not enough hydrogen, these processes
generally involve removing carbon from or adding hydrogen to the molecules, and using fluid
catalytic cracking to convert the longer, more complex molecules in the oil to the shorter,
simpler ones in the fuels.
59
Due to its high energy density, easy transportability and relative abundance, oil has become
the world's most important source of energy since the mid-1950s. Petroleum is also the raw
material for many chemical products, including pharmaceuticals, solvents, fertilizers,
pesticides, and plastics; the 16% not used for energy production is converted into these other
materials.
Petroleum is found in porous rock formations in the upper strata of some areas of the Earth's
crust. There is also petroleum in oil sands (tar sands). Known reserves of petroleum are
typically estimated at around 190 km3 (1.2 trillion (short scale) barrels) without oil sands,[9] or
595 km3 (3.74 trillion barrels) with oil sands.[10] Consumption is currently around 84 million
barrels (13.4×106 m3) per day, or 4.9 km3 per year. Because the energy return over energy
invested (EROEI) ratio of oil is constantly falling (due to physical phenomena such as
residual oil saturation, and the economic factor of rising marginal extraction costs),
recoverable oil reserves are significantly less than total oil in place. At current consumption
levels, and assuming that oil will be consumed only from reservoirs, known recoverable
reserves would be gone around 2039, potentially leading to a global energy crisis. However,
there are factors which may extend or reduce this estimate, including the rapidly increasing
demand for petroleum in China, India, and other developing nations; new discoveries; energy
conservation and use of alternative energy sources; and new economically viable exploitation
of non-conventional oil sources.
Image 1: Typical industrial distillation towers
2. desalting
Why Desalt Crude?
•
•
•
•
•
The salts that are most frequently present in crude oil are Calcium,Sodium and
Magnesium Chlorides. If these compounds are not removed from the oil several
problems arise in the refining process. The high temperatures that occur downstream
in the process could cause water hydrolysis, which in turn allows the formation of
hydrochloric acid.
Sand, Silts, Salt deposit and Foul Heat Exchangers
Water Heat of Vaporization reduces crude Pre-Heat capacity
Sodium, Arsenic and Other Metals can poison Catalysts
Environmental Compliance, i.e., By removing the suspended solids, which might
otherwise become an issue in flue gas opacity norms, etc.,
60
Design and operation
Design and operation of a distillation column depends on the feed and desired products. Given
a simple, binary component feed, analytical methods such as the McCabe-Thiele
method[5][6][7] or the Fenske equation[5] can be used to assist in the design. For a multicomponent feed, computerized simulation models are used both for design and subsequently
in operation of the column as well. Modeling is also used to optimize already erected columns
for the distillation of mixtures other than those the distillation equipment was originally
designed for.
When a continuous distillation column is in operation, it has to be closely monitored for
changes in feed composition, operating temperature and product composition. Many of these
tasks are performed using advanced computer control equipment.
Column feed
The column can be fed in different ways. If the feed is from a source at a pressure higher than
the distillation column pressure, it is simply piped into the column. Otherwise, the feed is
pumped or compressed into the column. The feed may be a superheated vapor, a saturated
vapor, a partially vaporized liquid-vapor mixture, a saturated liquid (i.e., liquid at its boiling
point at the column's pressure), or a sub-cooled liquid. If the feed is a liquid at a much higher
pressure than the column pressure and flows through a pressure let-down valve just ahead of
the column, it will immediately expand and undergo a partial flash vaporization resulting in a
liquid-vapor mixture as it enters the distillation column.
Improving separation
Although small size units, mostly made of glass, can be used in laboratories, industrial units
are large, vertical, steel vessels (see images 1 and 2) known as "distillation towers" or
"distillation columns". To improve the separation, the tower is normally provided inside with
horizontal plates or trays as shown in image 5, or the column is packed with a packing
material. To provide the heat required for the vaporization involved in distillation and also to
compensate for heat loss, heat is most often added to the bottom of the column by a reboiler,
and the purity of the top product can be improved by recycling some of the externally
61
condensed top product liquid as reflux. Depending on their purpose, distillation columns may
have liquid outlets at intervals up the length of the column as shown in image 4.
Reflux
Large-scale industrial fractionation towers use reflux to achieve more efficient separation of
products.[3][5] Reflux refers to the portion of the condensed overhead liquid product from a
distillation tower that is returned to the upper part of the tower as shown in images 3 and 4.
Inside the tower, the downflowing reflux liquid provides cooling and partial condensation of
the upflowing vapors, thereby increasing the efficacy of the distillation tower. The more
reflux that is provided, the better is the tower's separation of the lower boiling from the higher
boiling components of the feed. A balance of heating with a reboiler at the bottom of a
column and cooling by condensed reflux at the top of the column maintains a temperature
gradient (or gradual temperature difference) along the height of the column to provide good
conditions for fractionating the feed mixture. Reflux flows at the middle of the tower are
called pumparounds.
Changing the reflux (in combination with changes in feed and product withdrawal) can also
be used to improve the separation properties of a continuous distillation column while in
operation (in contrast to adding plates or trays, or changing the packing, which would, at a
minimum, require quite significant downtime).
Plates or trays
Image 5: Cross-sectional diagram of a binary fractional distillation tower with bubble-cap
trays. (See theoretical plate for enlarged tray image.)
Distillation towers (such as in images 3 and 4) use various vapor and liquid contacting
methods to provide the required number of equilibrium stages. Such devices are commonly
known as "plates" or "trays".[8] Each of these plates or trays is at a different temperature and
pressure. The stage at the tower bottom has the highest pressure and temperature. Progressing
upwards in the tower, the pressure and temperature decreases for each succeeding stage. The
vapor-liquid equilibrium for each feed component in the tower reacts in its unique way to the
different pressure and temperature conditions at each of the stages. That means that each
component establishes a different concentration in the vapor and liquid phases at each of the
stages, and this results in the separation of the components. Some example trays are depicted
in image 5. A more detailed, expanded image of two trays can be seen in the theoretical plate
article. The reboiler often acts as an additional equilibrium stage.
If each physical tray or plate were 100% efficient, than the number of physical trays needed
for a given separation would equal the number of equilibrium stages or theoretical plates.
However, that is very seldom the case. Hence, a distillation column needs more plates than
the required number of theoretical vapor-liquid equilibrium stages.
Fractionation Research, Inc. (commonly known as FRI) has performed research on all types
of trays measuring their capacity, pressure drop and efficiency in hydrocarbon systems from
full vacuum to 500 psia.[9]
62
Packing
Another way of improving the separation in a distillation column is to use a packing material
instead of trays. These offer the advantage of a lower pressure drop across the column (when
compared to plates or trays), beneficial when operating under vacuum. If a distillation tower
uses packing instead of trays, the number of necessary theoretical equilibrium stages is first
determined and then the packing height equivalent to a theoretical equilibrium stage, known
as the height equivalent to a theoretical plate (HETP), is also determined. The total packing
height required is the number theoretical stages multiplied by the HETP.
This packing material can either be random dumped packing such as Raschig rings or
structured sheet metal. Liquids tend to wet the surface of the packing and the vapors pass
across this wetted surface, where mass transfer takes place. Unlike conventional tray
distillation in which every tray represents a separate point of vapor-liquid equilibrium, the
vapor-liquid equilibrium curve in a packed column is continuous. However, when modeling
packed columns it is useful to compute a number of theoretical plates to denote the separation
efficiency of the packed column with respect to more traditional trays. Differently shaped
packings have different surface areas and void space between packings. Both of these factors
affect packing performance.
Another factor in addition to the packing shape and surface area that affects the performance
of random or structured packing is liquid and vapor distribution entering the packed bed. The
number of theoretical stages required to make a given separation is calculated using a specific
vapor to liquid ratio. If the liquid and vapor are not evenly distributed across the superficial
tower area as it enters the packed bed, the liquid to vapor ratio will not be correct in the
packed bed and the required separation will not be achieved. The packing will appear to not
be working properly. The height equivalent to a theoretical plate (HETP) will be greater than
expected. The problem is not the packing itself but the mal-distribution of the fluids entering
the packed bed. Liquid mal-distribution is more frequently the problem than vapor. The
design of the liquid distributors used to introduce the feed and reflux to a packed bed is
critical to making the packing perform at maximum efficiency. Methods of evaluating the
effectiveness of a liquid distributor can be found in references..[10][11] Considerable work as
been done on this topic by Fractionation Research, Inc.[12]
Overhead system arrangements
Images 4 and 5 assume an overhead stream that is totally condensed into a liquid product
using water or air-cooling. However, in many cases, the tower overhead is not easily
condensed totally and the reflux drum must include a vent gas outlet stream. In yet other
cases, the overhead stream may also contain water vapor because either the feed stream
contains some water or some steam is injected into the distillation tower (which is the case in
the crude oil distillation towers in oil refineries). In those cases, if the distillate product is
insoluble in water, the reflux drum may contain a condensed liquid distillate phase, a
condensed water phase and a non-condensible gas phase, which makes it necessary that the
reflux drum also have a water outlet stream.
Examples
Image 2: A crude oil vacuum distillation column as used in oil refineries
63
Continuous distillation of crude oil
Petroleum crude oils contain hundreds of different hydrocarbon compounds: paraffins,
naphthenes and aromatics as well as organic sulfur compounds, organic nitrogen compounds
and some oxygen containing hydrocarbons such as phenols. Although crude oils generally do
not contain olefins, they are formed in many of the processes used in a petroleum refinery.[13]
The crude oil fractionator does not produce products having a single boiling point, rather, it
produces fractions having boiling ranges.[13][14] For example, the crude oil fractionator
produces an overhead fraction called "naphtha" which becomes a gasoline component after it
is further processed through a catalytic hydrodesulfurizer to remove sulfur and a catalytic
reformer to reform its hydrocarbon molecules into more complex molecules with a higher
octane rating value.
The naphtha cut, as that fraction is called, contains many different hydrocarbon compounds.
Therefore it has an initial boiling point of about 35 °C and a final boiling point of about
200 °C. Each cut produced in the fractionating columns has a different boiling range. At some
distance below the overhead, the next cut is withdrawn from the side of the column and it is
usually the jet fuel cut, also known as a kerosene cut. The boiling range of that cut is from an
initial boiling point of about 150 °C to a final boiling point of about 270 °C, and it also
contains many different hydrocarbons. The next cut further down the tower is the diesel oil
cut with a boiling range from about 180 °C to about 315 °C. The boiling ranges between any
cut and the next cut overlap because the distillation separations are not perfectly sharp. After
these come the heavy fuel oil cuts and finally the bottoms product, with very wide boiling
ranges. All these cuts are processed further in subsequent refining processes.
Oil refinery
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Anacortes Refinery (Tesoro), on the north end of March Point southeast of Anacortes,
Washington
An oil refinery is an industrial process plant where crude oil is processed and refined into
more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil,
kerosene, and liquefied petroleum gas.[1][2] Oil refineries are typically large sprawling
64
industrial complexes with extensive piping running throughout, carrying streams of fluids
between large chemical processing units.
Operation
Crude oil is separated into fractions by fractional distillation. The fractions at the top of the
fractionating column have lower boiling points than the fractions at the bottom. The heavy
bottom fractions are often cracked into lighter, more useful products. All of the fractions are
processed further in other refining units.
Raw or unprocessed crude oil is not generally useful in its raw or unprocessed form, as it
comes out of the ground. Although "light, sweet" (low viscosity, low sulfur) crude oil has
been used directly as a burner fuel for steam vessel propulsion, the lighter elements form
explosive vapors in the fuel tanks and so it was quite dangerous, especially in warships.
Instead, the hundreds of different hydrocarbon molecules in crude oil are separated in a
refinery into components that can be used as fuels, lubricants, and as feedstock in
petrochemical processes that manufacture such products as plastics, detergents, solvents,
elastomers and fibers such as nylon and polyesters. Petroleum fossil fuels are burned in
internal combustion engines in order to provide power to operate ships, automobiles, aircraft
engines, lawn-mowers, chainsaws, and other pieces of power equipment. These different
hydrocarbons have different boiling points, which means they can be separated by distillation.
Since the lighter liquid products are in great demand for use in internal combustion engines, a
modern refinery will convert heavy hydrocarbons and lighter gaseous elements into these
higher value products.
Oil can be used in so many ways because it contains hydrocarbons of varying molecular
masses, forms and lengths such as paraffins, aromatics, naphthenes (or cycloalkanes), alkenes,
dienes, and alkynes. While the molecules in crude oil include many different atoms such as
sulfur and nitrogen, the most plentiful molecules are the hydrocarbons, which are molecules
of varying length and complexity made of hydrogen and carbon atoms, and a small number of
oxygen atoms. The differences in the structure of these molecules is what confers upon them
their varying physical and chemical properties, and it is this variety that makes crude oil so
useful in such a broad range of applications.
Once separated and purified of any contaminants and impurities, the fuel or lubricant can be
sold without any further processing. Smaller molecules such as isobutane and propylene or
butylenes can be recombined to meet specific octane requirements of fuels by processes such
as alkylation or less commonly, dimerization. Octane grade of gasoline can also be improved
by catalytic reforming, which strips hydrogen out of hydrocarbons to produce aromatics,
which have much higher octane ratings. Intermediate products such as gasoils can even be
reprocessed to break a heavy, long-chained oil into a lighter short-chained one, by various
forms of cracking such as fluid catalytic cracking, thermal cracking, and hydrocracking. The
final step in gasoline production is the blending of fuels with different octane ratings, vapor
pressures, and other properties to meet product specifications.
Oil refineries are large scale plants, processing from about a hundred thousand to several
hundred thousand barrels of crude oil per day. Because of the high capacity, many of the units
are operated continuously (as opposed to processing in batches) at steady state or
approximately steady state for long periods of time (months to years). This high capacity also
makes process optimization and advanced process control very desirable.
65
Major products of oil refineries
Most products of oil processing are usually grouped into three categories: light distillates
(LPG, gasoline, naphtha), middle distillates (kerosene, diesel), heavy distillates and residuum
(fuel oil, lubricating oils, wax, tar). This classification is based on the way crude oil is
distilled and separated into fractions (called distillates and residuum) as can be seen in the
above drawing.[2]
Common process units found in a refinery
The number and nature of the process units in a refinery determine its complexity index.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Desalter unit washes out salt from the crude oil before it enters the atmospheric
distillation unit.
Atmospheric Distillation unit distills crude oil into fractions. See Continuous
distillation.
Vacuum Distillation unit further distills residual bottoms after atmospheric distillation.
Naphtha Hydrotreater unit uses hydrogen to desulfurize naphtha from atmospheric
distillation. Must hydrotreat the naphtha before sending to a Catalytic Reformer unit.
Catalytic Reformer unit is used to convert the naphtha-boiling range molecules into
higher octane reformate (reformer product). The reformate has higher content of
aromatics and cyclic hydrocarbons). An important byproduct of a reformer is
hydrogen released during the catalyst reaction. The hydrogen is used either in the
hydrotreaters or the hydrocracker.
Distillate Hydrotreater unit desulfurizes distillates (such as diesel) after atmospheric
distillation.
Fluid Catalytic Cracker (FCC) unit upgrades heavier fractions into lighter, more
valuable products.
Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more
valuable products.
Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter,
more valuable reduced viscosity products.
Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic
disulfides.
Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual
oils into gasoline and diesel fuel, leaving petroleum coke as a residual product.
Alkylation unit produces high-octane component for gasoline blending.
Dimerization unit converts olefins into higher-octane gasoline blending components.
For example, butenes can be dimerized into isooctene which may subsequently be
hydrogenated to form isooctane. There are also other uses for dimerization.
Isomerization unit converts linear molecules to higher-octane branched molecules for
blending into gasoline or feed to alkylation units.
Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker.
Liquified gas storage units for propane and similar gaseous fuels at pressure sufficient
to maintain in liquid form. These are usually spherical vessels or bullets (horizontal
vessels with rounded ends.
Storage tanks for crude oil and finished products, usually cylindrical, with some sort
of vapor emission control and surrounded by an earthen berm to contain spills.
Amine gas treater, Claus unit, and tail gas treatment for converting hydrogen sulfide
from hydrodesulfurization into elemental sulfur.
66
•
•
•
•
Utility units such as cooling towers for circulating cooling water, boiler plants for
steam generation, instrument air systems for pneumatically operated control valves
and an electrical substation.
Wastewater collection and treating systems consisting of API separators, dissolved air
flotation (DAF) units and some type of further treatment (such as an activated sludge
biotreater) to make such water suitable for reuse or for disposal.[3]
Solvent refining units use solvent such as cresol or furfural to remove unwanted,
mainly asphaltenic materials from lubricating oil stock (or diesel stock).
Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum
distillation products.
Flow diagram of typical refinery
The image below is a schematic flow diagram of a typical oil refinery that depicts the various
unit processes and the flow of intermediate product streams that occurs between the inlet
crude oil feedstock and the final end products. The diagram depicts only one of the literally
hundreds of different oil refinery configurations. The diagram also does not include any of the
usual refinery facilities providing utilities such as steam, cooling water, and electric power as
well as storage tanks for crude oil feedstock and for intermediate products and end
products.[1][4][5][6]
The Five Pillars of Refining
While distillation can separate oil into fractions, chemical reactors are required to create
more of the products that are in high demand. Refineries rely on four major processing steps
to alter the ratios of the different fractions. They are; Catalytic Reforming, Alkylation,
Catalytic Cracking, and Hydroprocessing. Each of these methods involves feeding
reactants to a reactor where they will be partly converted into products. The unreacted
reactants are then separated from the products with a distillation column. The unreacted
reactants are recycled for another pass, while the products are further separated and mixed
with existing streams. In this way complete conversion of reactants can be obtained, even
though not all of the reactants are converted on a given pass through the reactor. The four
processing methods, along with distillation, are the pillars of petroleum refining.
Catalytic Reforming
Catalytic Reforming produces high octane gasoline for today’s automobiles. Gasoline and
naphtha feedstocks are heated to 500 degrees Celsius and flow through a series of fixed-bed
catalytic reactors. Because the reactions which produce higher octane compounds (aliphatic
in this case) are endothermic (absorb heat) additional heaters are installed between reactors
to keep the reactants at the proper temperature. The catalyst is a platinum (Pt) metal on an
alumina (Al2O3) base. While catalysts are never consumed in chemical reactions, they can be
fouled, making them less effective over time. The series of reactors used in Catalytic
67
Reforming are therefore designed to be disconnected, and swiveled out of place, so the
catalyst can be regenerated.
Alkylation
Alkylation is another process for producing high octane gasoline. The reaction requires an
acid catalyst (sulfuric acid, H2SO4 or hydrofluoric acid, HF) at low temperatures (1-40
degrees Celsius) and low pressures (1-10 atmospheres). The acid composition is usually kept
at about 50% making the mixture very corrosive.
Fluidized Catalytic Cracking
Catalytic Cracking takes long molecules and breaks them into much smaller molecules. The
cracking reaction is very endothermic, and requires a large amount of heat. Another
problem is that reaction quickly fouls the Silica (SiO2) and alumina (Al2O3) catalyst by
forming coke on its surface. However, by using a fluidized bed to slowly carry the catalyst
upwards, and then sending it to a regenerator where the coke can be burned off, the catalyst
is continuously regenerated. This system has the additional benefit of using the large
amounts of heat liberated in the exothermic regeneration reaction to heat the cracking
reactor. The FCC system is a brilliant reaction scheme, which turns two negatives (heating
and fouling) into a positive, thereby making the process extremely economical.
Hydroprocessing
Hydroprocessing includes both hydrocracking and hydrotreating techniques. Hydrotreating
involves the addition of hydrogen atoms to molecules without actually breaking the molecule
into smaller pieces. Hydrotreating involves temperatures of about 325 degrees Celsius and
pressures of about 50 atmospheres. Many catalysts will work, including; nickel, palladium,
platinum, cobalt, and iron. Hydrocracking breaks longer molecules into smaller ones.
Hydrocracking involves temperatures over 350 degrees Celsius and pressures up to 200
atmospheres. In both cases, very long residence times (about an hour) are required because
of the slow nature of the reactions.
Catalytic reforming is a chemical process used to convert petroleum refinery naphthas,
typically having low octane ratings, into high-octane liquid products called reformates which
are components of high-octane gasoline (also known as petrol). Basically, the process rearranges or re-structures the hydrocarbon molecules in the naphtha feedstocks as well as
68
breaking some of the molecules into smaller molecules. The overall effect is that the product
reformate contains hydrocarbons with more complex molecular shapes having higher octane
values than the hydrocarbons in the naphtha feedstock. In so doing, the process separates
hydrogen atoms from the hydrocarbon molecules and produces very significant amounts of
byproduct hydrogen gas for use in a number of the other processes involved in a modern
petroleum refinery. Other byproducts are small amounts of methane, ethane, propane and
butanes.
This process is quite different from and not to be confused with the catalytic steam reforming
process used industrially to produce various products such as hydrogen, ammonia and
methanol from natural gas, naphtha or other petroleum-derived feedstocks. Nor is this process
to be confused with various other catalytic reforming processes that use methanol or biomassderived feedstocks to produce hydrogen for fuel cells or other uses.
History
Universal Oil Products (also known as UOP) is a multi-national company developing and
delivering technology to the petroleum refining, natural gas processing, petrochemical
production and other manufacturing industries. In the 1940s, an eminent research chemist
named Vladimir Haensel[1] working for UOP developed a catalytic reforming process using a
catalyst containing platinum. Haensel's process was subsequently commercialized by UOP in
1949 for producing a high octane gasoline from low octane naphthas and the UOP process
become known as the Platforming process.[2] The first Platforming unit was built in 1949 at
the refinery of the Old Dutch Refining Company in Muskegon, Michigan.
In the years since then, many other versions of the process have been developed by some of
the major oil companies and other organizations. Today, the large majority of gasoline
produced worldwide is derived from the catalytic reforming process.
To name a few of the other catalytic reforming versions that were developed, all of which
utilized a platinum and/or a rhenium catalyst:
•
•
•
•
•
•
•
Rheniforming: Developed by Chevron Oil Company.
Powerforming: Developed by Esso Oil Company, now known as ExxonMobil.
Magnaforming: Developed by Englehard Catalyst Company and Atlantic Richfield Oil
Company.
Ultraforming: Developed by Standard Oil of Indiana, now a part of the British
Petroleum Company.
Houdriforming: Developed by the Houdry Process Corporation.
CCR Platforming: A Platforming version, designed for continuous catalyst
regeneration, developed by UOP.
Octanizing: A catalytic reforming version developed by Axens, a subsidiary of Institut
francais du petrole (IFP), designed for continuous catalyst regeneration.
Chemistry
Before describing the reaction chemistry of the catalytic reforming process as used in
petroleum refineries, the typical naphthas used as catalytic reforming feedstocks will be
discussed.
Typical naphtha feedstocks
69
A petroleum refinery includes many unit operations and unit processes. The first unit
operation in a refinery is the continuous distillation of the petroleum crude oil being refined.
The overhead liquid distillate is called naphtha and will become a major component of the
refinery's gasoline (petrol) product after it is further processed through a catalytic
hydrodesulfurizer to remove sulfur-containing hydrocarbons and a catalytic reformer to
reform its hydrocarbon molecules into more complex molecules with a higher octane rating
value. The naphtha is a mixture of very many different hydrocarbon compounds. It has an
initial boiling point of about 35 °C and a final boiling point of about 200 °C, and it contains
paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons ranging from those
containing 4 carbon atoms to those containing about 10 or 11 carbon atoms.
The naphtha from the crude oil distillation is often further distilled to produce a "light"
naphtha containing most (but not all) of the hydrocarbons with 6 or less carbon atoms and a
"heavy" naphtha containing most (but not all) of the hydrocarbons with more than 6 carbon
atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final
boiling point of about 190 to 205 °C. The naphthas derived from the distillation of crude oils
are referred to as "straight-run" naphthas.
It is the straight-run heavy naphtha that is usually processed in a catalytic reformer because
the light naphtha has molecules with 6 or less carbon atoms which, when reformed, tend to
crack into butane and lower molecular weight hydrocarbons which are not useful as highoctane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form
aromatics which is undesirable because governmental environmental regulations in a number
of countries limit the amount of aromatics (most particularly benzene) that gasoline may
contain.[3][4][5]
It should be noted that there are a great many petroleum crude oil sources worldwide and each
crude oil has its own unique composition or "assay". Also, not all refineries process the same
crude oils and each refinery produces its own straight-run naphthas with their own unique
initial and final boiling points. In other words, naphtha is a generic term rather than a specific
term.
The table just below lists some fairly typical straight-run heavy naphtha feedstocks, available
for catalytic reforming, derived from various crude oils. It can be seen that they differ
significantly in their content of paraffins, naphthenes and aromatics:
Some refinery naphthas include olefinic hydrocarbons, such as naphthas derived from the
fluid catalytic cracking and coking processes used in many refineries. Some refineries may
also desulfurize and catalytically reform those naphthas. However, for the most part, catalytic
reforming is mainly used on the straight-run heavy naphthas, such as those in the above table,
derived from the distillation of crude oils.
The reaction chemistry
There are a good many chemical reactions that occur in the catalytic reforming process, all of
which occur in the presence of a catalyst and a high partial pressure of hydrogen. Depending
upon the type or version of catalytic reforming used as well as the desired reaction severity,
the reaction conditions range from temperatures of about 495 to 525 °C and from pressures of
about 5 to 45 atm.[10]
The commonly used catalytic reforming catalysts contain noble metals such as platinum
and/or rhenium, which are very susceptible to poisoning by sulfur and nitrogen compounds.
70
Therefore, the naphtha feedstock to a catalytic reformer is always pre-processed in a
hydrodesulfurization unit which removes both the sulfur and the nitrogen compounds.
The four major catalytic reforming reactions are:[11]
1: The dehydrogenation of naphthenes to convert them into aromatics as exemplified in the
conversion methylcyclohexane (a naphthene) to toluene (an aromatic), as shown below:
2: The isomerization of normal paraffins to isoparaffins as exemplified in the conversion of
normal octane to 2,5-Dimethylhexane (an isoparaffin), as shown below:
3: The dehydrogenation and aromatization of paraffins to aromatics (commonly called
dehydrocyclization) as exemplified in the conversion of normal heptane to toluene, as shown
below:
4: The hydrocracking of paraffins into smaller molecules as exemplified by the cracking of
normal heptane into isopentane and ethane, as shown below:
The hydrocracking of paraffins is the only one of the above four major reforming reactions
that consumes hydrogen. The isomerization of normal paraffins does not consume or produce
hydrogen. However, both the dehydrogenation of naphthenes and the dehydrocyclization of
paraffins produce hydrogen. The overall net production of hydrogen in the catalytic reforming
of petroleum naphthas ranges from about 50 to 200 cubic meters of hydrogen gas (at 0 °C and
1 atm) per cubic meter of liquid naphtha feedstock. In the United States customary units, that
is equivalent to 300 to 1200 cubic feet of hydrogen gas (at 60 °F and 1 atm) per barrel of
liquid naphtha feedstock.[12] In many petroleum refineries, the net hydrogen produced in
catalytic reforming supplies a significant part of the hydrogen used elsewhere in the refinery
(for example, in hydrodesulfurization processes). The hydrogen is also necessary in order to
hydrogenolyze any polymers that form on the catalyst.
Process description
The most commonly used type of catalytic reforming unit has three reactors, each with a fixed
bed of catalyst, and all of the catalyst is regenerated in situ during routine catalyst
regeneration shutdowns which occur approximately once each 6 to 24 months. Such a unit is
referred to as a semi-regenerative catalytic reformer (SRR).
Some catalytic reforming units have an extra spare or swing reactor and each reactor can be
individually isolated so that any one reactor can be undergoing in situ regeneration while the
other reactors are in operation. When that reactor is regenerated, it replaces another reactor
which, in turn, is isolated so that it can then be regenerated. Such units, referred to as cyclic
catalytic reformers, are not very common. Cyclic catalytic reformers serve to extend the
period between required shutdowns.
71
The latest and most modern type of catalytic reformers are called continuous catalyst
regeneration reformers (CCR). Such units are characterized by continuous in-situ regeneration
of part of the catalyst in a special regenerator, and by continuous addition of the regenerated
catalyst to the operating reactors. As of 2006, two CCR versions available: UOP's CCR
Platformer process[13] and Axen's Octanizing process.[14] The installation and use of CCR
units is rapidly increasing.
Many of the earliest catalytic reforming units (in the 1950s and 1960's) were non-regenerative
in that they did not perform in situ catalyst regeneration. Instead, when needed, the aged
catalyst was replaced by fresh catalyst and the aged catalyst was shipped to catalyst
manufacturer's to be either regenerated or to recover the platinum content of the aged catalyst.
Very few, if any, catalytic reformers currently in operation are non-regenerative.
The process flow diagram below depicts a typical semi-regenerative catalytic reforming unit.
Schematic diagram of a typical semi-regenerative catalytic reformer unit in a petroleum
refinery
The liquid feed (at the bottom left in the diagram) is pumped up to the reaction pressure (5 to
45 atm) and is joined by a stream of hydrogen-rich recycle gas. The resulting liquid-gas
mixture is preheated by flowing through a heat exchanger. The preheated feed mixture is then
totally vaporized and heated to the reaction temperature (495 to 520 °C) before the vaporized
reactants enter the first reactor. As the vaporized reactants flow through the fixed bed of
catalyst in the reactor, the major reaction is the dehydrogenation of naphthenes to aromatics
(as described earlier herein) which is highly endothermic and results in a large temperature
decrease between the inlet and outlet of the reactor. To maintain the required reaction
temperature and the rate of reaction, the vaporized stream is reheated in the second fired
heater before it flows through the second reactor. The temperature again decreases across the
second reactor and the vaporized stream must again be reheated in the third fired heater before
it flows through the third reactor. As the vaporized stream proceeds through the three reactors,
the reaction rates decrease and the reactors therefore become larger. At the same time, the
amount of reheat required between the reactors becomes smaller. Usually, three reactors are
all that is required to provide the desired performance of the catalytic reforming unit.
Some installations use three separate fired heaters as shown in the schematic diagram and
some installations use a single fired heater with three separate heating coils.
The hot reaction products from the third reactor are partially cooled by flowing through the
heat exchanger where the feed to the first reactor is preheated and then flow through a watercooled heat exchanger before flowing through the pressure controller (PC) into the gas
separator.
Most of the hydrogen-rich gas from the gas separator vessel returns to the suction of the
recycle hydrogen gas compressor and the net production of hydrogen-rich gas from the
reforming reactions is exported for use in other the other refinery processes that consume
hydrogen (such as hydrodesulfurization units and/or a hydrocracker unit).
The liquid from the gas separator vessel is routed into a fractionating column commonly
called a stabilizer. The overhead offgas product from the stabilizer contains the byproduct
methane, ethane, propane and butane gases produced by the hydrocracking reactions as
72
explained in the above discussion of the reaction chemistry of a catalytic reformer, and it may
also contain some small amount of hydrogen. That offgas is routed to the refinery's central gas
processing plant for removal and recovery of propane and butane. The residual gas after such
processing becomes part of the refinery's fuel gas system.
The bottoms product from the stabilizer is the high-octane liquid reformate that will become a
component of the refinery's product gasoline.
Catalysts and mechanisms
Most catalytic reforming catalysts contain platinum or rhenium on a silica or silica-alumina
support base, and some contain both platinum and rhenium. Fresh catalyst is chlorided
(chlorinated) prior to use.
The noble metals (platinum and rhenium) are considered to be catalytic sites for the
dehydrogenation reactions and the chlorinated alumina provides the acid sites needed for
isomerization, cyclization and hydrocracking reactions.[11]
The activity (i.e., effectiveness) of the catalyst in a semi-regenerative catalytic reformer is
reduced over time during operation by carbonaceous coke deposition and chloride loss. The
activity of the catalyst can be periodically regenerated or restored by in situ high temperature
oxidation of the coke followed by chlorination. As stated earlier herein, semi-regenerative
catalytic reformers are regenerated about once per 6 to 24 months.
Normally, the catalyst can be regenerated perhaps 3 or 4 times before it must be returned to
the manufacturer for reclamation of the valuable platinum and/or rhenium content.[11]
Alkylation
In a standard oil refinery process, isobutane is alkylated with low-molecular-weight alkenes
(primarily a mixture of propylene and butylene) in the presence of a strong acid catalyst,
either sulfuric acid or hydrofluoric acid. In an oil refinery it is referred to as a sulfuric acid
alkylation unit (SAAU) or a hydrofluoric alkylation unit, (HFAU). However, oil refinery
employees may simply refer to the unit as the Alkyl or Alky unit. The catalyst is able to
protonate the alkenes (propylene, butylene) to produce reactive carbocations, which alkylate
isobutane. The reaction is carried out at mild temperatures (0 and 30 °C) in a two-phase
reaction. It is important to keep a high ratio of isobutane to alkene at the point of reaction to
prevent side reactions that lead to a lower octane product, so the plants have a high recycle of
isobutane back to feed. The phases separate spontaneously, so the acid phase is vigoriously
mixed with the hydrocarbon phase to create sufficient contact surface.
The product is called alkylate and is composed of a mixture of high-octane, branched-chain
paraffinic hydrocarbons (mostly isopentane and isooctane). Alkylate is a premium gasoline
blending stock because it has exceptional antiknock properties and is clean burning. Alkylate
is also a key component of avgas. The octane number of the alkylate depends mainly upon the
kind of alkenes used and upon operating conditions. For example, isooctane results from
combining butylene with isobutane and has an octane rating of 100 by definition. There are
other products in the alkylate, so the octane rating will vary accordingly.
Most crude oils contain only 10 to 40 percent of their hydrocarbon constituents in the gasoline
range, so refineries use a fluid catalytic cracking process to convert high molecular weight
73
hydrocarbons into smaller and more volatile compounds. Polymerization converts gaseous
alkenes into liquid gasoline-size hydrocarbons. Alkylation processes transform low
molecular-weight alkenes and iso-paraffin molecules into larger iso-paraffins with a high
octane number.
Combining cracking, polymerization, and alkylation can result in a gasoline yield representing
70 percent of the starting crude oil. More advanced processes, such as cyclicization of
paraffins and dehydrogenation of naphthenes to form aromatic hydrocarbons in a catalytic
reformer, have also been developed to increase the octane rating of gasoline. Modern refinery
operation can be shifted to produce almost any fuel type with specified performance criteria
from a single crude feedstock.
In the entire range of refinery processes, alkylation is a very important process that enhances
the yield of high-octane gasoline. However, not all refineries have an alkylation plant. The oil
and gas journal annual survey of worldwide refining capacities for January 2007 lists many
countries with no alkylation plants at their refineries.
A primary factor in deciding to install alkylation is usually economics. Refinery alkylation
units are complex and there is substantial economy of scale. In addition to a suitable quantity
of feedstock, the price spread between the value of alkylate product and alternate feedstock
disposition value must be large enough to justify the plant. Alternative outlets for refinery
alklylation feedstocks include sales as LPG, blending of C4 streams directly into gasoline and
feedstocks for chemical plants. Local market conditions vary widely between plants.
Variation in the RVP specification for gasoline between countries and between seasons
dramatically impacts the amount of butane streams that can be blended directly into gasoline.
The transportation of specific types of LPG streams can be expensive so local disparities in
economic conditions are often not fully mitigated by cross market movements of alkylation
feedstocks.
Another factor in the decision to build an alkylation plant concerns the availability of a
suitable catalyst. If sulfuric acid is used, significant volumes are needed. This requires access
to a suitable plant for the supply of fresh acid and the disposition of spent acid. If a sulfuric
acid plant must be constructed specifically to support an alkylation unit, this will have a
significant impact on both the initial capital requirements and ongoing operating costs. The
second main catalyst option is hydrofluoric acid. Consumption rates for HF acid in alkylation
plants are much lower than for sulfuric acid. HF acid plants can process a wider range of
feedstock mix with proplyenes and butylenes. HF plants also produce alklyate with better
octane than sulfuric plants. However, due to the hazardous nature of the material, HF acid is
produced at very few locations and transportation must be managed rigorously.
Thermal cracking
William Merriam Burton developed one of the earliest thermal cracking processes in 1912
which operated at 700-750 °F (370-400 °C) and an absolute pressure of 90 psia (620 kPa) and
was known as the Burton process. Shortly thereafter, in 1921, C.P. Dubbs, an employee of the
Universal Oil Products Company, developed a somewhat more advanced thermal cracking
process which operated at 750-860 °F (400-460 °C) and was known as the Dubbs process.[9]
The Dubbs process was used extensively by many refineries until the early 1940's when
catalytic cracking came into use.
74
Modern high-pressure thermal cracking operates at absolute pressures of about 7,000 kPa. An
overall process of disproportionation can be observed, where "light", hydrogen-rich products
are formed at the expense of heavier molecules which condense and are depleted of hydrogen.
The actual reaction is known as homolytic fission and produces alkenes, which are the basis
for the economically important production of polymers.
A large number of chemical reactions take place during steam cracking, most of them based
on free radicals. Computer simulations aimed at modeling what takes place during steam
cracking have included hundreds or even thousands of reactions in their models. The main
reactions that take place include:
Initiation reactions, where a single molecule breaks apart into two free radicals. Only a small
fraction of the feed molecules actually undergo initiation, but these reactions are necessary to
produce the free radicals that drive the rest of the reactions. In steam cracking, initiation
usually involves breaking a chemical bond between two carbon atoms, rather than the bond
between a carbon and a hydrogen atom.
CH3CH3 → 2 CH3•
Hydrogen abstraction, where a free radical removes a hydrogen atom from another molecule,
turning the second molecule into a free radical.
CH3• + CH3CH3 → CH4 + CH3CH2•
Radical decomposition, where a free radical breaks apart into two molecules, one an alkene,
the other a free radical. This is the process that results in the alkene products of steam
cracking.
CH3CH2• → CH2=CH2 + H•
Radical addition, the reverse of radical decomposition, in which a radical reacts with an
alkene to form a single, larger free radical. These processes are involved in forming the
aromatic products that result when heavier feedstocks are used.
CH3CH2• + CH2=CH2 → CH3CH2CH2CH2•
Termination reactions, which happen when two free radicals react with each other to produce
products that are not free radicals. Two common forms of termination are recombination,
where the two radicals combine to form one larger molecule, and disproportionation, where
one radical transfers a hydrogen atom to the other, giving an alkene and an alkane.
CH3• + CH3CH2• → CH3CH2CH3
CH3CH2• + CH3CH2• → CH2=CH2 + CH3CH3
Thermal cracking is an example of a reaction whose energetics are dominated by entropy
(∆S°) rather than by enthalpy (∆H°) in the Gibbs Free Energy equation ∆G°=∆H°-T∆S°.
Although the bond dissociation energy D for a carbon-carbon single bond is relatively high
(about 375 kJ/mol) and cracking is highly endothermic, the large positive entropy change
resulting from the fragmentation of one large molecule into several smaller pieces, together
with the extremely high temperature, makes T∆S° term larger than the ∆H° term, thereby
favoring the cracking reaction.
75
Here is an example of cracking with butane CH3-CH2-CH2-CH3
•
1st possibility (48%): breaking is done on the CH3-CH2 bond.
CH3* / *CH2-CH2-CH3
after a certain number of steps, we will obtain an alkane and an alkene: CH4 + CH2=CH-CH3
•
2nd possibility (38%): breaking is done on the CH2-CH2 bond.
CH3-CH2* / *CH2-CH3
after a certain number of steps, we will obtain an alkane and an alkene from different types:
CH3-CH3 + CH2=CH2
•
3rd possibility (14%): breaking of a C-H bond
after a certain number of steps, we will obtain an alkene and hydrogen gas: CH2=CH-CH2CH3 + H2 this is very useful since the catalyst can be recycled.
Fluid catalytic cracking
From Wikipedia, the free encyclopedia
Fluid catalytic cracking (FCC) is the most important conversion process used in petroleum
refineries. It is widely used to convert the high-boiling hydrocarbon fractions of petroleum
crude oils to more valuable gasoline, olefinic gases and other products.[1][2][3] Cracking of
petroleum hydrocarbons was originally done by thermal cracking which has been almost
completely replaced by catalytic cracking because it produces more gasoline with a higher
octane rating. It also produces byproduct gases that are more olefinic, and hence more
valuable, than those produced by thermal cracking.
The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point
of 340 °C or higher at atmospheric pressure and an average molecular weight ranging from
about 200 to 600 or higher. The FCC process vaporizes and breaks the long-chain molecules
of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the
feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst.
In effect, refineries use fluid catalytic cracking to correct the imbalance between the market
demand for gasoline and the excess of heavy, high boiling range products resulting from the
distillation of crude oil.
As of 2006, FCC units were in operation at 400 petroleum refineries worldwide and about
one-third of the crude oil refined in those refineries is processed in an FCC to produce highoctane gasoline and fuel oils.[2][4] During 2007, the FCC units in the United States processed a
total of 5,300,000 barrels (834,300,000 litres) per day of feedstock[5] and FCC units
worldwide processed about twice that amount.
76
Flow diagram and process description
The modern FCC units are all continuous processes which operate 24 hours a day for as much
as 2 to 3 years between shutdowns for routine maintenance.
There are a number of different proprietary designs that have been developed for modern FCC
units. Each design is available under a license that must be purchased from the design
developer by any petroleum refining company desiring to construct and operate an FCC of a
given design.
Basically, there are two different configurations for an FCC unit: the "stacked" type where the
reactor and the catalyst regenerator are contained in a single vessel with the reactor above the
catalyst regenerator and the "side-by-side" type where the reactor and catalyst regenerator are
in two separate vessels. These are the major FCC designers and licensors:[1][3][4][6]
Stacked configuration:
Each of the proprietary design licensors claims to have unique features and advantages. A
complete discussion of the relative advantages of each of the processes is well beyond the
scope of this article. Suffice it to say that all of the licensors have designed and constructed
FCC units that have operated quite satisfactorily.
Reactor and Regenerator
The schematic flow diagram of a typical modern FCC unit in Figure 1 below is based upon
the "side-by-side" configuration. The preheated high-boiling petroleum feedstock (at about
315 to 430 °C) consisting of long-chain hydrocarbon molecules is combined with recycle
slurry oil from the bottom of the distillation column and injected into the catalyst riser where
it is vaporized and cracked into smaller molecules of vapor by contact and mixing with the
very hot powdered catalyst from the regenerator. All of the cracking reactions take place in
the catalyst riser. The hydrocarbon vapors "fluidize" the powdered catalyst and the mixture of
hydrocarbon vapors and catalyst flows upward to enter the reactor at a temperature of about
535 °C and a pressure of about 1.72 barg.
The reactor is in fact merely a vessel in which the cracked product vapors are: (a) separated
from the so-called spent catalyst by flowing through a set of two-stage cyclones within the
reactor and (b) the spent catalyst flows downward through a steam stripping section to
remove any hydrocarbon vapors before the spent catalyst returns to the catalyst regenerator.
The flow of spent catalyst to the regenerator is regulated by a slide valve in the spent catalyst
line.
Since the cracking reactions produce some carbonaceous material (referred to as coke) that
deposits on the catalyst and very quickly reduces the catalyst reactivity, the catalyst is
regenerated by burning off the deposited coke with air blown into the regenerator. The
regenerator operates at a temperature of about 715 °C and a pressure of about 2.41 barg. The
combustion of the coke is exothermic and it produces a large amount of heat that is partially
absorbed by the regenerated catalyst and provides the heat required for the vaporization of the
77
feedstock and the endothermic cracking reactions that take place in the catalyst riser. For that
reason, FCC units are often referred to as being heat balanced.
The hot catalyst (at about 715 °C) leaving the regenerator flows into a catalyst withdrawal
well where any entrained combustion flue gases are allowed to escape and flow back into the
upper part to the regenerator. The flow of regenerated catalyst to the feedstock injection point
below the catalyst riser is regulated by a slide valve in the regenerated catalyst line. The hot
flue gas exits the regenerator after passing through multiple sets of two-stage cylones that
remove entrained catalyst from the flue gas,
The amount of catalyst circulating between the regenerator and the reactor amounts to about 5
kg per kg of feedstock which is equivalent to about 4.66 kg per litre of feedstock.[1][7] Thus, an
FCC unit processing 75,000 barrels/day (12,000,000 litres/day) will circulate about 55,900
metric tons per day of catalyst.
Figure 1: A schematic flow diagram of a Fluid Catalytic Cracking unit as used in petroleum
refineries
Distillation column
The reaction product vapors (at 535 °C and a pressure of 1.72 barg) flow from the top of the
reactor to the bottom section of the distillation column (commonly referred to as the main
fractionator) where they are distilled into the FCC end products of cracked naphtha, fuel oil
and offgas. After further processing for removal of sulfur compounds, the cracked naphtha
becomes a high-octane component of the refinery's blended gasolines.
The main fractionator offgas is sent to what is called a gas recovery unit where it is separated
into butanes and butylenes, propane and propylene, and lower molecular weight gases
(hydrogen, methane, ethylene and ethane). Some FCC gas recovery units may also separate
out some of the ethane and ethylene.
Although the schematic flow diagram above depicts the main fractionator as having only one
sidecut stripper and one fuel oil product, many FCC main fractionators have two sidecut
strippers and produce a light fuel oil and a heavy fuel oil. Likewise, many FCC main
fractionators produce a light cracked naphtha and a heavy cracked naphtha. The terminology
light and heavy in this context refers to the product boiling ranges, with light products having
a lower boiling range than heavy products.
The bottom product oil from the main fractionator contains residual catalyst particles which
were not completely removed by the cyclones in the top of the reactor. For that reason, the
bottom product oil is referred to as a slurry oil. Part of that slurry oil is recycled back into the
main fractionator above the entry point of the hot reaction product vapors so as to cool and
partially condense the reaction product vapors as they enter the main fractionator. The
remainder of the slurry oil is pumped through a slurry settler. The bottom oil from the slurry
settler contains most of the slurry oil catalyst particles and is recycled back into the catalyst
riser by combining it with the FCC feedstock oil. The so-called clarified slurry oil or decant
oil, DCO is withdrawn from the top of slurry settler for use elsewhere in the refinery or as a
heavy fuel oil blending component.
78
Regenerator flue gas
Depending on the choice of FCC design, the combustion in the regenerator of the coke on the
spent catalyst may or may not be complete combustion to carbon dioxide (CO2). The
combustion air flow is controlled so as to provide the desired ratio of carbon monoxide (CO)
to carbon dioxide for each specific FCC design.[1] [4]
In the design shown in Figure 1, the coke has only been partially combusted to CO2. The
combustion flue gas (containing CO and CO2) at 715 °C and at a pressure of 2.41 barg is
routed through a secondary catalyst separator containing swirl tubes designed to remove 70 to
90 percent of the particulates in the flue gas leaving the regenerator.[8] This is required to
prevent erosion damage to the blades in the turbo-expander that the flue gas is next routed
through.
The expansion of flue gas through a turbo-expander provides sufficient power to drive the
regenerator's combustion air compressor. The electrical motor-generator can consume or
produce electrical power. If the expansion of the flue gas does not provide enough power to
drive the air compressor, the electric motor/generator provides the needed additional power. If
the flue gas expansion provides more power than needed to drive the air compressor, than the
electric motor/generator converts the excess power into electric power and exports it to the
refinery's electrical system.[3]
The expanded flue gas is then routed through a steam-generating boiler (referred to as a CO
boiler) where the carbon monoxide in the flue gas is burned as fuel to provide steam for use in
the refinery as well as to comply with any applicable environmental regulatory limits on
carbon monoxide emissions.[3]
The flue gas is finally processed through an electrostatic precipitator (ESP) to remove residual
particulate matter to comply with any applicable environmental regulations regarding
particulate emissions. The ESP removes particulates in the size range of 2 to 20 microns from
the flue gas.[3]
The steam turbine in the flue gas processing system (shown in the above diagram) is used to
drive the regenerator's combustion air compressor during start-ups of the FCC unit until there
is sufficient combustion flue gas to take over that task.
Chemistry
Before delving into the chemistry involved in catalytic cracking, it will be helpful to briefly
discuss the composition of petroleum crude oil.
Petroleum crude oil consists primarily of a mixture of hydrocarbons with small amounts of
other organic compounds containing sulfur, nitrogen and oxygen. The crude oil also contains
small amounts of metals such as copper, iron, nickel and vanadium.[2]
Table 1
Carbon
83-87%
Hydrogen 10-14%
Nitrogen 0.1-2%
Oxygen
79
0.1-1.5%
The elemental composition ranges of crude oil are summarized in Table Sulfur
1 and the hydrocarbons in the crude oil can be classified into three
Metals
types:[1][2]
•
•
•
0.5-6%
< 0.1%
Paraffins or alkanes: saturated straight-chain or branched hydrocarbons, without any
ring structures
Naphthenes or cycloalkanes: saturated hydrocarbons having one or more ring
structures with one or more side-chain paraffins
Aromatics: hydrocarbons having one or more unsaturated ring structures such as
benzene or unsaturated polycyclic ring structures such as naphthalene or
phenanthrene, any of which may also have one or more side-chain paraffins.
Olefins or alkenes, which are unsaturated straight-chain or branched hydrocarbons, do not
occur naturally in crude oil.
Figure 2: Diagrammatic example of the catalytic cracking of petroleum hydrocarbons
In plain language, the fluid catalytic cracking process breaks large hydrocarbon molecules
into smaller molecules by contacting them with powdered catalyst at a high temperature and
moderate pressure which first vaporizes the hydrocarbons and then breaks them. The cracking
reactions occur in the vapor phase and start immediately when the feedstock is vaporized in
the catalyst riser.
Figure 2 is a very simplified schematic diagram that exemplifies how the process breaks high
boiling, straight-chain alkane (paraffin) hydrocarbons into smaller straight-chain alkanes as
well as branched-chain alkanes, branched alkenes (olefins) and cycloalkanes (naphthenes).[9]
The breaking of the large hydrocarbon molecules into smaller molecules is more technically
referred to by organic chemists as scission of the carbon-to-carbon bonds.
As depicted in Figure 2, some of the smaller alkanes are then broken and converted into even
smaller alkenes and branched alkenes such as the gases ethylene, propylene, butylenes and
isobutylenes. Those olefinic gases are valuable for use as petrochemical feedstocks. The
propylene, butylene and isobutylene are also valuable feedstocks for certain petroleum
refining processes that convert them into high-octane gasoline blending components.
As also depicted in Figure 2, the cycloalkanes (naphthenes) formed by the initial breakup of
the large molecules are further converted to aromatics such as benzene, toluene and xylenes
which boil in the gasoline boiling range and have much higher octane ratings than alkanes.
By no means does Figure 2 include all the chemistry of the primary and secondary reactions
taking place in the fluid catalytic process. There are a great many other reactions involved.
However, a full discussion of the highly technical details of the various catalytic cracking
reactions is beyond the scope of this article and can be found in the technical
literature.[1][2][3][4]
Catalysts
80
Modern FCC catalysts are fine powders with a bulk density of 0.80 to 0.96 g/cc and having a
particle size distribution ranging from 10 to 150 μm and an average particle size of 60 to 100
μm.[10][11] The design and operation of an FCC unit is largely dependent upon the chemical
and physical properties of the catalyst. The desirable properties of an FCC catalyst are:
•
•
•
•
•
Good stability to high temperature and to steam
High activity
Large pore sizes
Good resistance to attrition
Low coke production
A modern FCC catalyst has four major components: crystalline zeolite, matrix, binder and
filler. Zeolite is the primary active component and can range from about 15 to 50 weight
percent of the catalyst. The zeolite used in FCC catalysts is referred to as faujasite or as Type
Y and is comprised of silica and alumina tetrahedra with each tetrahedron having either an
aluminum or a silicon atom at the center and four oxygen atoms at the corners. It is a
molecular sieve with a distinctive lattice structure that allows only a certain size range of
hydrocarbon molecules to enter the lattice. In general, the zeolite does not allow molecules
larger than 8 to 10 nm (i.e., 80 to 90 angstroms) to enter the lattice.[10][11]
The catalytic sites in the zeolite are strong acids (equivalent to 90% sulfuric acid) and provide
most of the catalytic activity. The acidic sites are provided by the alumina tetrahedra. The
aluminum atom at the center of each alumina tetrahedra is at a +3 oxidation state surrounded
by four oxygen atoms at the corners which are shared by the neighboring tetrahedra. Thus, the
net charge of the alumina tetrahedra is -1 which is balanced by a sodium ion during the
production of the catalyst. The sodium ion is later replaced by an ammonium ion which is
vaporized when the catalyst is subsequently dried, resulting in the formation of Lewis and
Brønsted acidic sites. In some FCC catalysts, the Brønsted sites may be later replaced by rare
earth metals such as cerium and lanthanum to provide alternative activity and stability
levels.[10][11]
The matrix component of an FCC catalyst contains amorphous alumina which also provides
catalytic activity sites and in larger pores that allows entry for larger molecules than does the
zeolite. That enables the cracking of higher-boiling, larger feedstock molecules than are
cracked by the zeolite.
The binder and filler components provide the physical strength and integrity of the catalyst.
The binder is usually silica sol and the filler is usually a clay (kaolin).
Nickel, vanadium, iron, copper and other metal contaminants, present in FCC feedstocks in
the parts per million range, all have detrimental effects on the catalyst activity and
performance. Nickel and vanadium are particularly troublesome. There are a number of
methods for mitigating the effects of the contaminant metals:[12][13]
•
•
•
Avoid feedstocks with high metals content: This seriously hampers a refinery's
flexibility to process various crude oils or purchased FCC feedstocks.
Feedstock feed pretreatment: Hydrodesulfurization of the FCC feedstock removes
some of the metals and also reduces the sulfur content of the FCC products. However,
this is quite a costly option.
Increasing fresh catalyst addition: All FCC units withdraw some of the circulating
equilibrium catalyst as spent catalyst and replaces it with fresh catalyst in order to
maintain a desired level of activity. Increasing the rate of such exchange lowers the
81
•
•
level of metals in the circulating equilibrium catalyst, but this is also quite a costly
option.
Demetallization: The commercial proprietary Demet Process removes nickel and
vanadium from the withdrawn spent catalyst. The nickel and vanadium are converted
to chlorides which are then washed out of the catalyst. After drying, the demetallized
catalyst is recycled into the circulating catalyst. Removals of about 95 percent nickel
removal and 67 to 85 percent vanadium have been reported. Despite that, the use of
the Demet process has not become widespread, perhaps because of the high capital
expenditure required.
Metals passivation: Certain materials can be used as additives which can be
impregnated into the catalyst or added to the FCC feedstock in the form of metalorganic compounds. Such materials react with the metal contaminants and passivate
the contaminants by forming less harmful compounds that remain on the catalyst. For
example, antimony and bismuth are effective in passivating nickel and tin is effective
in passivating vanadium. A number of proprietary passivation processes are available
and fairly widely used.
The major suppliers of FCC catalysts worldwide include Albemarle Corporation, W.R. Grace
Company and BASF Catalysts (formerly Engelhard).
History
The first commercial use of catalytic cracking occurred in 1915 when Almer M. McAfee of
the Gulf Refining Company developed a batch process using aluminum chloride (a Friedel
Crafts catalyst known since 1877) to catalytically crack heavy petroleum oils. However, the
prohibitive cost of the catalyst prevented the widespread use of McAfee's process at that
time.[2][14]
In 1922, a French mechanical engineer named Eugene Jules Houdry and a French pharmacist
named E.A. Prudhomme set up a laboratory near Paris to develop a catalytic process for
converting lignite coal to gasoline. Supported by the French government, they built a small
demonstration plant in 1929 that processed about 60 tons per day of lignite coal. The results
indicated that the process was not economically viable and it was subsequently
shutdown.[15][16][17]
Houdry had found that Fuller's Earth, a clay mineral containing aluminosilicate (Al2SiO6),
could convert oil derived from the lignite to gasoline. He then began to study the catalysis of
petroleum oils and had some success in converting vaporized petroleum oil to gasoline. In
1930, the Vacuum Oil Company invited him to come to the United States and he moved his
laboratory to Paulsboro, New Jersey.
In 1931, the Vacuum Oil Company merged with Standard Oil of New York (Socony) to form
the Socony-Vacuum Oil Company. In 1933, a small Houdry process unit processing 200
barrels per day (32,000 litres per day) of petroleum oil. Because of the economic depression
of the early 1930's, Socony-Vacuum was no longer able to support Houdry's work and gave
him permission to seek help elsewhere.
In 1933, Houdry and Socony-Vacuum joined with Sun Oil Company in developing the
Houdry process. Three years later, in 1936, Socony-Vacuum converted an older thermal
cracking unit in their Paulsboro refinery in New Jersey to a small demonstration unit using the
Houdry process to catalytically crack 2,000 barrels per day (318,000 litres per day) of
petroleum oil.
82
In 1937, Sun Oil began operation of a new Houdry unit processing 12,000 barrels per day
(2,390,000 litres per day) in their Marcus Hook refinery in Pennsylvania. The Houdry process
at that time used reactors with a fixed bed of catalyst and was a semi-batch operation
involving multiple reactors with some of the reactors in operation while other reactors were in
various stages of regenerating the catalyst. Motor-driven valves were used to switch the
reactors between online operation and offline regeneration and a cycle timer managed the
switching. Almost 50 percent of the cracked product was gasoline as compared with about 25
percent from the thermal cracking processes.[15][16][17]
By 1938, when the Houdry process was publicly announced, Socony-Vacuum had eight
additional units under construction. Licensing the process to other companies also began and
by 1940 there were 14 Houdry units in operation processing 140,000 barrels per day
(22,300,000 litres per day).
The next major step was to develop a continuous process rather than the semi-batch Houdry
process. That step was implemented by advent of the moving-bed process known as the
Thermafor Catalytic Cracking (TCC) process which used a bucket conveyor-elevator to move
the catalyst from the regeneration kiln to the separate reactor section. A small demonstration
TCC unit was built in Socony-Vacuum's Paulsboro refinery in 1941 and operated
successfully. Then a full-scale commercial TCC unit processing 10,000 barrels per day
(1,590,000 litres per day) began operation in 1943 at the Beaumont, Texas refinery of
Magnolia Oil Company, an affiliate of Socony-Vacuum. By the end of World War II in 1945,
the processing capacity of the TCC units in operation was about 300,000 barrels per day
(47,700,000 litres per day).
It is said that the Houdry and TCC units were a major factor in the winning of World War II
by supplying the high-octane gasoline needed by the air forces of Great Britain and the United
States.[15][16][17]
In the years immediately after World War II, the Houdriflow process and the air-lift TCC
process were developed as improved variations on the moving-bed theme. Just like Houdry's
fixed-bed reactors, the moving-bed designs were prime examples of good engineering by
developing a method of continuously moving the catalyst between the reactor and
regeneration sections.
This fluid catalytic cracking process had first been investigated in the 1920s by Standard Oil
of New Jersey, but research on it was abandoned during the economic depression years of
1929 to 1939. In 1938, when the success of Houdry’s process had become apparent, Standard
Oil of New Jersey resumed the project as part of a consortium of that include five oil
companies (Standard Oil of New Jersey, Standard Oil of Indiana, Anglo-Iranian Oil, Texas
Oil and Dutch Shell), two engineering-construction companies (M.W. Kellogg and Universal
Oil Products) and a German chemical company (I.G. Farben). The consortium was called
Catalytic Research Associates (CRA) and its purpose was to develop a catalytic cracking
process which would not impinge on Houdry's patents.[15][16][18]
Chemical engineering professors Warren K. Lewis and Edwin R. Gilliland of the
Massachusetts Institute of Technology (MIT) suggested to the CRA researchers that a low
velocity gas flow through a powder might "lift" it enough to cause it to flow in a manner
similar to a liquid. Focused on that idea of a fluidized catalyst, researchers Donald Campbell,
Homer Martin, Eger Murphree and Charles Tyson of the Standard Oil of New Jersey (now
Exxon-Mobil Company) developed the first fluidized catalytic cracking unit. Their U.S.
Patent No. 2,451,804, A Method of and Apparatus for Contacting Solids and Gases, describes
83
their milestone invention. Based on their work, M. W. Kellogg Company constructed a large
pilot plant in the Baton Rouge, Louisiana refinery of the Standard Oil of New Jersey. The
pilot plant began operation in May of 1940.
Based on the success of the pilot plant, the first commercial fluid catalytic cracking plant
(known as the Model I FCC) began processing 13,000 barrels per day (2,070,000 litres per
day) of petroleum oil in the Baton Rouge refinery on May 25, 1942, just four years after the
CRA consortium was formed and in the midst of World War II. A little more than a month
later, in July 1942, it was processing 17,000 barrels per day (2,700,000 litres per day). In
1963, that first Model I FCC unit was shut down after 21 years of operation and subsequently
dismantled.[15][16][18][19]
In the many decades since the Model I FCC unit began operation, the fixed bed Houdry units
have all been shut down as have most of the moving bed units (such as the TCC units) while
hundreds of FCC units have been built. During those decades, many improved FCC designs
have evolved and cracking catalysts have been greatly improved, but the modern FCC units
are essentially the same as that first Model I FCC unit.
Hydrocracking
In 1920 a plant for the commercial hydrogenation of brown coal is commissioned at Leuna in
Germany[8].
Hydrocracking is a catalytic cracking process assisted by the presence of an elevated partial
pressure of hydrogen gas. Similar to the hydrotreater, the function of hydrogen is the
purification of the hydrocarbon stream from sulfur and nitrogen hetero-atoms.
The products of this process are saturated hydrocarbons; depending on the reaction conditions
(temperature, pressure, catalyst activity) these products range from ethane, LPG to heavier
hydrocarbons comprising mostly of isoparaffins. Hydrocracking is normally facilitated by a bi
functional catalyst that is capable of rearranging and breaking hydrocarbon chains as well as
adding hydrogen to aromatics and olefins to produce naphthenes and alkanes.
Major products from hydrocracking are jet fuel and diesel, while also relatively high octane
rating gasoline fractions and LPG are produced. All these products have a very low content of
sulfur and other contaminants.
It is very common in India, Europe and Asia because those regions have high demand for
diesel and kerosene. In the US, Fluid Catalytic Cracking is more common because the
demand for gasoline is higher.
84
Mass spectrometry
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of
charged particles.[1] It is used for determining masses of particles, for determining the
elemental composition of a sample or molecule, and for elucidating the chemical structures of
molecules, such as peptides and other chemical compounds. The MS principle consists of
ionizing chemical compounds to generate charged molecules or molecule fragments and
measurement of their mass-to-charge ratios.[1] In a typical MS procedure:
1. A sample is loaded onto the MS instrument, and undergoes vaporization
2. The components of the sample are ionized by one of a variety of methods (e.g., by
impacting them with an electron beam), which results in the formation of charged
particles (ions)
3. The ions are separated according to their mass-to-charge ratio in an analyzer by
electromagnetic fields
4. The ions are detected, usually by a quantitative method
5. The ion signal is processed into mass spectra
MS instruments consist of three modules:
•
•
•
An ion source, which can convert gas phase sample molecules into ions (or, in the
case of electrospray ionization, move ions that exist in solution into the gas phase)
A mass analyzer, which sorts the ions by their masses by applying electromagnetic
fields
A detector, which measures the value of an indicator quantity and thus provides data
for calculating the abundances of each ion present
The technique has both qualitative and quantitative uses. These include identifying unknown
compounds, determining the isotopic composition of elements in a molecule, and determining
the structure of a compound by observing its fragmentation. Other uses include quantifying
the amount of a compound in a sample or studying the fundamentals of gas phase ion
chemistry (the chemistry of ions and neutrals in a vacuum). MS is now in very common use in
analytical laboratories that study physical, chemical, or biological properties of a great variety
of compounds.
Etymology
The word spectrograph has been used since 1884 as an "International Scientific
Vocabulary".[2][3] The linguistic roots are a combination and removal of bound morphemes
and free morphemes which relate to the terms spectr-um and phot-ograph-ic plate.[4] Early
spectrometry devices that measured the mass-to-charge ratio of ions were called mass
spectrographs which consisted of instruments that recorded a spectrum of mass values on a
photographic plate.[5][6] A mass spectroscope is similar to a mass spectrograph except that the
beam of ions is directed onto a phosphor screen.[7] A mass spectroscope configuration was
85
used in early instruments when it was desired that the effects of adjustments be quickly
observed. Once the instrument was properly adjusted, a photographic plate was inserted and
exposed. The term mass spectroscope continued to be used even though the direct
illumination of a phosphor screen was replaced by indirect measurements with an
oscilloscope.[8] The use of the term mass spectroscopy is now discouraged due to the
possibility of confusion with light spectroscopy.[1][1][9] Mass spectrometry is often abbreviated
as mass-spec or simply as MS.[1] Thomson has also noted that a mass spectroscope is similar
to a mass spectrograph except that the beam of ions is directed onto a phosphor screen.[10] ]
The suffix -scope here denotes the direct viewing of the spectra (range) of masses.
History
For more details on this topic, see History of mass spectrometry.
Replica of an early mass spectrometer
Francis William Aston won the 1922 Nobel Prize in Chemistry for his work in mass
spectrometry
In 1886, Eugen Goldstein observed rays in gas discharges under low pressure that traveled
away from the anode and through channels in a perforated cathode, opposite to the direction
of negatively charged cathode rays (which travel from cathode to anode). Goldstein called
these positively charged anode rays "Kanalstrahlen"; the standard translation of this term into
English is "canal rays". Wilhelm Wien found that strong electric or magnetic fields deflected
the canal rays and, in 1899, constructed a device with parallel electric and magnetic fields that
separated the positive rays according to their charge-to-mass ratio (Q/m). Wien found that the
charge-to-mass ratio depended on the nature of the gas in the discharge tube. English scientist
J.J. Thomson later improved on the work of Wien by reducing the pressure to create a mass
spectrograph.
The first application of mass spectrometry to the analysis of amino acids and peptides was
reported in 1958.[11] Carl-Ove Andersson highlighted the main fragment ions observed in the
ionization of methyl esters.[12]
Some of the modern techniques of mass spectrometry were devised by Arthur Jeffrey
Dempster and F.W. Aston in 1918 and 1919 respectively. In 1989, half of the Nobel Prize in
Physics was awarded to Hans Dehmelt and Wolfgang Paul for the development of the ion trap
technique in the 1950s and 1960s. In 2002, the Nobel Prize in Chemistry was awarded to John
Bennett Fenn for the development of electrospray ionization (ESI) and Koichi Tanaka for the
development of soft laser desorption (SLD) and their application to the ionization of
biological macromolecules, especially proteins.[13]
Simplified example
Schematics of a simple mass spectrometer with sector type mass analyzer. This one is for the
measurement of Carbon dioxide isotope ratios (IRMS) as in the carbon-13 urea breath test
The following example describes the operation of a spectrometer mass analyzer, which is of
the sector type. (Other analyzer types are treated below.) Consider a sample of sodium
86
chloride (table salt). In the ion source, the sample is vaporized (turned into gas) and ionized
(transformed into electrically charged particles) into sodium (Na+) and chloride (Cl-) ions.
Sodium atoms and ions are monoisotopic, with a mass of about 23 amu. Chloride atoms and
ions come in two isotopes with masses of approximately 35 amu (at a natural abundance of
about 75 percent) and approximately 37 amu (at a natural abundance of about 25 percent).
The analyzer part of the spectrometer contains electric and magnetic fields, which exert forces
on ions traveling through these fields. The speed of a charged particle may be increased or
decreased while passing through the electric field, and its direction may be altered by the
magnetic field. The magnitude of the deflection of the moving ion's trajectory depends on its
mass-to-charge ratio. Lighter ions get deflected by the magnetic force more than heavier ions
(based on Newton's second law of motion, F = ma). The streams of sorted ions pass from the
analyzer to the detector, which records the relative abundance of each ion type. This
information is used to determine the chemical element composition of the original sample (i.e.
that both sodium and chlorine are present in the sample) and the isotopic composition of its
constituents (the ratio of 35Cl to 37Cl).
Instrumentation
Ion source technologies
Main article: Ion source
The ion source is the part of the mass spectrometer that ionizes the material under analysis
(the analyte). The ions are then transported by magnetic or electric fields to the mass analyzer.
Techniques for ionization have been key to determining what types of samples can be
analyzed by mass spectrometry. Electron ionization and chemical ionization are used for
gases and vapors. In chemical ionization sources, the analyte is ionized by chemical ionmolecule reactions during collisions in the source. Two techniques often used with liquid and
solid biological samples include electrospray ionization (invented by John Fenn[14]) and
matrix-assisted laser desorption/ionization (MALDI, developed by K. Tanaka[15] and
separately by M. Karas and F. Hillenkamp[16]).
Inductively coupled plasma (ICP) sources are used primarily for cation analysis of a wide
array of sample types. In this type of Ion Source Technology, a 'flame' of plasma that is
electrically neutral overall, but that has had a substantial fraction of its atoms ionized by high
temperature, is used to atomize introduced sample molecules and to further strip the outer
electrons from those atoms. The plasma is usually generated from argon gas, since the first
ionization energy of argon atoms is higher than the first of any other elements except He, O, F
and Ne, but lower than the second ionization energy of all except the most electropositive
metals. The heating is achieved by a radio-frequency current passed through a coil
surrounding the plasma.
Ion Attachment Ionization is a newer soft ionization technique that allows for fragmentation
free analysis.
Mass analyzer technologies
Mass analyzers separate the ions according to their mass-to-charge ratio. The following two
laws govern the dynamics of charged particles in electric and magnetic fields in vacuum:
87
(Lorentz force law);
(Newton's second law of motion in non-relativistic case, i.e. valid only at ion velocity
much lower than the speed of light).
Here F is the force applied to the ion, m is the mass of the ion, a is the acceleration, Q is the
ion charge, E is the electric field, and v x B is the vector cross product of the ion velocity and
the magnetic field
Equating the above expressions for the force applied to the ion yields:
This differential equation is the classic equation of motion for charged particles. Together
with the particle's initial conditions, it completely determines the particle's motion in space
and time in terms of m/Q. Thus mass spectrometers could be thought of as "mass-to-charge
spectrometers". When presenting data, it is common to use the (officially) dimensionless m/z,
where z is the number of elementary charges (e) on the ion (z=Q/e). This quantity, although it
is informally called the mass-to-charge ratio, more accurately speaking represents the ratio of
the mass number and the charge number, z.
There are many types of mass analyzers, using either static or dynamic fields, and magnetic or
electric fields, but all operate according to the above differential equation. Each analyzer type
has its strengths and weaknesses. Many mass spectrometers use two or more mass analyzers
for tandem mass spectrometry (MS/MS). In addition to the more common mass analyzers
listed below, there are others designed for special situations.
Sector
For more details on this topic, see sector instrument.
A sector field mass analyzer uses an electric and/or magnetic field to affect the path and/or
velocity of the charged particles in some way. As shown above, sector instruments bend the
trajectories of the ions as they pass through the mass analyzer, according to their mass-tocharge ratios, deflecting the more charged and faster-moving, lighter ions more. The analyzer
can be used to select a narrow range of m/z or to scan through a range of m/z to catalog the
ions present.[18]
Time-of-flight
For more details on this topic, see time-of-flight mass spectrometry.
The time-of-flight (TOF) analyzer uses an electric field to accelerate the ions through the
same potential, and then measures the time they take to reach the detector. If the particles all
have the same charge, the kinetic energies will be identical, and their velocities will depend
only on their masses. Lighter ions will reach the detector first.[19]
Quadrupole mass filter
For more details on this topic, see Quadrupole mass analyzer.
Quadrupole mass analyzers use oscillating electrical fields to selectively stabilize or
destabilize the paths of ions passing through a radio frequency (RF) quadrupole field created
between 4 parallel rods. Only the ions in a certain range of mass/charge ratio are passed
through the system at any time, but changes to the potentials on the rods allow a wide range of
88
m/z values to be swept rapidly, either continuously or in a succession of discrete hops. A
quadrupole mass analyzer acts as a mass-selective filter and is closely related to the
quadrupole ion trap, particularly the linear quadrupole ion trap except that it is designed to
pass the untrapped ions rather than collect the trapped ones, and is for that reason referred to
as a transmission quadrupole. A common variation of the quadrupole is the triple quadrupole.
Triple quadrupole mass spectrometers have three consecutive quadrupoles arranged in series
to incoming ions. The first quadrupole acts as a mass filter. The second quadrupole acts as a
collision cell where selected ions are broken into fragments. The resulting fragments are
analyzed by the third quadrupole.
Three-dimensional quadrupole ion trap
For more details on this topic, see quadrupole ion trap.
The quadrupole ion trap works on the same physical principles as the quadrupole mass
analyzer, but the ions are trapped and sequentially ejected. Ions are trapped in a mainly
quadrupole RF field, in a space defined by a ring electrode (usually connected to the main RF
potential) between two endcap electrodes (typically connected to DC or auxiliary AC
potentials). The sample is ionized either internally (e.g. with an electron or laser beam), or
externally, in which case the ions are often introduced through an aperture in an endcap
electrode.
There are many mass/charge separation and isolation methods but the most commonly used is
the mass instability mode in which the RF potential is ramped so that the orbit of ions with a
mass a > b are stable while ions with mass b become unstable and are ejected on the z-axis
onto a detector. There are also non-destructive analysis methods.
Ions may also be ejected by the resonance excitation method, whereby a supplemental
oscillatory excitation voltage is applied to the endcap electrodes, and the trapping voltage
amplitude and/or excitation voltage frequency is varied to bring ions into a resonance
condition in order of their mass/charge ratio.[20][21]
The cylindrical ion trap mass spectrometer is a derivative of the quadrupole ion trap mass
spectrometer.
Linear quadrupole ion trap
A linear quadrupole ion trap is similar to a quadrupole ion trap, but it traps ions in a two
dimensional quadrupole field, instead of a three-dimensional quadrupole field as in a 3D
quadrupole ion trap. Thermo Fisher's LTQ ("linear trap quadrupole") is an example of the
linear ion trap.[22]
Fourier transform ion cyclotron resonance
An FT-ICR mass spectrometer
For more details on this topic, see Fourier transform mass spectrometry.
Fourier transform mass spectrometry (FTMS), or more precisely Fourier transform ion
cyclotron resonance MS, measures mass by detecting the image current produced by ions
cyclotroning in the presence of a magnetic field. Instead of measuring the deflection of ions
with a detector such as an electron multiplier, the ions are injected into a Penning trap (a static
89
electric/magnetic ion trap) where they effectively form part of a circuit. Detectors at fixed
positions in space measure the electrical signal of ions which pass near them over time,
producing a periodic signal. Since the frequency of an ion's cycling is determined by its mass
to charge ratio, this can be deconvoluted by performing a Fourier transform on the signal.
FTMS has the advantage of high sensitivity (since each ion is "counted" more than once) and
much higher resolution and thus precision.[23][24]
Ion cyclotron resonance (ICR) is an older mass analysis technique similar to FTMS except
that ions are detected with a traditional detector. Ions trapped in a Penning trap are excited by
an RF electric field until they impact the wall of the trap, where the detector is located. Ions of
different mass are resolved according to impact time.
Orbitrap
For more details on this topic, see Orbitrap.
Very similar nonmagnetic FTMS has been performed, where ions are electrostatically trapped
in an orbit around a central, spindle shaped electrode. The electrode confines the ions so that
they both orbit around the central electrode and oscillate back and forth along the central
electrode's long axis. This oscillation generates an image current in the detector plates which
is recorded by the instrument. The frequencies of these image currents depend on the mass to
charge ratios of the ions. Mass spectra are obtained by Fourier transformation of the recorded
image currents.
Similar to Fourier transform ion cyclotron resonance mass spectrometers, Orbitraps have a
high mass accuracy, high sensitivity and a good dynamic range.[25]
Toroidal Ion Trap
The toroidal ion trap is visualized as a linear quadrupole curved around and connected at the
ends or as a cross section of a 3D ion trap rotated on edge to form the toroid, donut shaped
trap. The trap can store large volumes of ions by distributing them throughout the ring-like
trap structure. This toroidal shaped trap is a configuration that allows the increased
miniaturization of an ion trap mass analyzer. Additionally all ions are stored in the same
trapping field and ejected together simplifying detection that can be complicated with array
configurations due to variations in detector alignment and machining of the arrays.[26]
Detector
A continuous dynode particle multiplier detector.
The final element of the mass spectrometer is the detector. The detector records either the
charge induced or the current produced when an ion passes by or hits a surface. In a scanning
instrument, the signal produced in the detector during the course of the scan versus where the
instrument is in the scan (at what m/Q) will produce a mass spectrum, a record of ions as a
function of m/Q.
Typically, some type of electron multiplier is used, though other detectors including Faraday
cups and ion-to-photon detectors are also used. Because the number of ions leaving the mass
analyzer at a particular instant is typically quite small, considerable amplification is often
90
necessary to get a signal. Microchannel plate detectors are commonly used in modern
commercial instruments.[27] In FTMS and Orbitraps, the detector consists of a pair of metal
surfaces within the mass analyzer/ion trap region which the ions only pass near as they
oscillate. No DC current is produced, only a weak AC image current is produced in a circuit
between the electrodes. Other inductive detectors have also been used.[28]
Analysers characteristics
Mass resolving power
Main article: Resolution (mass spectrometry)
The mass resolving power is the measure of the ability to distinguish two peaks of slightly
different m/z.
Mass accuracy
The mass accuracy is the ratio of the m/z measurement error to the true m/z. Usually
measured in ppm or milli mass units.
Mass range
The mass range is the range of m/z amenable to analysis by a given analyzer.
Linear dynamic range
The linear dynamic range is the range over which ion signal is linear with analyte
concentration.
Speed
Speed refers to the time frame of the experiment and ultimately is used to determine the
number of spectra per unit time that can be generated.
Tandem mass spectrometry
Main article: Tandem mass spectrometry
A tandem mass spectrometer is one capable of multiple rounds of mass spectrometry, usually
separated by some form of molecule fragmentation. For example, one mass analyzer can
isolate one peptide from many entering a mass spectrometer. A second mass analyzer then
stabilizes the peptide ions while they collide with a gas, causing them to fragment by
collision-induced dissociation (CID). A third mass analyzer then sorts the fragments produced
from the peptides. Tandem MS can also be done in a single mass analyzer over time, as in a
quadrupole ion trap. There are various methods for fragmenting molecules for tandem MS,
including collision-induced dissociation (CID), electron capture dissociation (ECD), electron
transfer dissociation (ETD), infrared multiphoton dissociation (IRMPD) and blackbody
infrared radiative dissociation (BIRD). An important application using tandem mass
spectrometry is in protein identification.[29]
Tandem mass spectrometry enables a variety of experimental sequences. Many commercial
mass spectrometers are designed to expedite the execution of such routine sequences as
91
selected reaction monitoring (SRM), multiple reaction monitoring (MRM), and precursor ion
scan. In SRM, the first analyzer allows only a single mass through and the second analyzer
monitors for a single user defined fragment ion. MRM allows for multiple user defined
fragment ions. SRM and MRM are most often used with scanning instruments where the
second mass analysis event is duty cycle limited. These experiments are used to increase
specificity of detection of known molecules, notably in pharmacokinetic studies. Precursor
ion scan refers to monitoring for a specific loss from the precursor ion. The first and second
mass analyzers scan across the spectrum as partitioned by a user defined m/z value. This
experiment is used to detect specific motifs within unknown molecules.
Another type of tandem mass spectrometry used for radiocarbon dating is Accelerator Mass
Spectrometry (AMS), which uses very high voltages, usually in the mega-volt range, to
accelerate negative ions into a type of tandem mass spectrometer.
Common mass spectrometer configurations and techniques
When a specific configuration of source, analyzer, and detector becomes conventional in
practice, often a compound acronym arises to designate it, and the compound acronym may
be better known among nonspectrometrists than the component acronyms. The epitome of this
is MALDI-TOF, which simply refers to combining a matrix-assisted laser
desorption/ionization source with a time-of-flight mass analyzer. The MALDI-TOF moniker
is more widely recognized by the non-mass spectrometrists than MALDI or TOF individually.
Other examples include inductively coupled plasma-mass spectrometry (ICP-MS), accelerator
mass spectrometry (AMS), Thermal ionization-mass spectrometry (TIMS) and spark source
mass spectrometry (SSMS). Sometimes the use of the generic "MS" actually connotes a very
specific mass analyzer and detection system, as is the case with AMS, which is always sector
based.
Certain applications of mass spectrometry have developed monikers that although strictly
speaking would seem to refer to a broad application, in practice have come instead to connote
a specific or a limited number of instrument configurations. An example of this is isotope
ratio mass spectrometry (IRMS), which refers in practice to the use of a limited number of
sector based mass analyzers; this name is used to refer to both the application and the
instrument used for the application.
Chromatographic techniques combined with mass spectrometry
An important enhancement to the mass resolving and mass determining capabilities of mass
spectrometry is using it in tandem with chromatographic separation techniques.
Gas chromatography
A gas chromatograph (right) directly coupled to a mass spectrometer (left)
See also: Gas chromatography-mass spectrometry
A common combination is gas chromatography-mass spectrometry (GC/MS or GC-MS). In
this technique, a gas chromatograph is used to separate different compounds. This stream of
separated compounds is fed online into the ion source, a metallic filament to which voltage is
applied. This filament emits electrons which ionize the compounds. The ions can then further
92
fragment, yielding predictable patterns. Intact ions and fragments pass into the mass
spectrometer's analyzer and are eventually detected.[30]
Liquid chromatography
See also: Liquid chromatography-mass spectrometry
Similar to gas chromatography MS (GC/MS), liquid chromatography mass spectrometry
(LC/MS or LC-MS) separates compounds chromatographically before they are introduced to
the ion source and mass spectrometer. It differs from GC/MS in that the mobile phase is
liquid, usually a mixture of water and organic solvents, instead of gas and the ions fragments
cannot yield predictable patterns. Most commonly, an electrospray ionization source is used
in LC/MS. There are also some newly developed ionization techniques like laser spray.
Ion mobility
See also: Ion mobility spectrometry-mass spectrometry
Ion mobility spectrometry/mass spectrometry (IMS/MS or IMMS) is a technique where ions
are first separated by drift time through some neutral gas under an applied electrical potential
gradient before being introduced into a mass spectrometer.[31] Drift time is a measure of the
radius relative to the charge of the ion. The duty cycle of IMS (the time over which the
experiment takes place) is longer than most mass spectrometric techniques, such that the mass
spectrometer can sample along the course of the IMS separation. This produces data about the
IMS separation and the mass-to-charge ratio of the ions in a manner similar to LC/MS.[32]
The duty cycle of IMS is short relative to liquid chromatography or gas chromatography
separations and can thus be coupled to such techniques, producing triple modalities such as
LC/IMS/MS.[33]
Data and analysis
Mass spectrum of a peptide showing the isotopic distribution
Data representations
See also: Mass spectrometry data format
Mass spectrometry produces various types of data. The most common data representation is
the mass spectrum.
Certain types of mass spectrometry data are best represented as a mass chromatogram. Types
of chromatograms include selected ion monitoring (SIM), total ion current (TIC), and selected
reaction monitoring chromatogram (SRM), among many others.
Other types of mass spectrometry data are well represented as a three-dimensional contour
map. In this form, the mass-to-charge, m/z is on the x-axis, intensity the y-axis, and an
additional experimental parameter, such as time, is recorded on the z-axis.
Data analysis
93
Basics
Mass spectrometry data analysis is a complicated subject that is very specific to the type of
experiment producing the data. There are general subdivisions of data that are fundamental to
understanding any data.
Many mass spectrometers work in either negative ion mode or positive ion mode. It is very
important to know whether the observed ions are negatively or positively charged. This is
often important in determining the neutral mass but it also indicates something about the
nature of the molecules.
Different types of ion source result in different arrays of fragments produced from the original
molecules. An electron ionization source produces many fragments and mostly single-charged
(1-) radicals (odd number of electrons), whereas an electrospray source usually produces nonradical quasimolecular ions that are frequently multiply charged. Tandem mass spectrometry
purposely produces fragment ions post-source and can drastically change the sort of data
achieved by an experiment.
By understanding the origin of a sample, certain expectations can be assumed as to the
component molecules of the sample and their fragmentations. A sample from a
synthesis/manufacturing process will probably contain impurities chemically related to the
target component. A relatively crudely prepared biological sample will probably contain a
certain amount of salt, which may form adducts with the analyte molecules in certain
analyses.
Results can also depend heavily on how the sample was prepared and how it was
run/introduced. An important example is the issue of which matrix is used for MALDI
spotting, since much of the energetics of the desorption/ionization event is controlled by the
matrix rather than the laser power. Sometimes samples are spiked with sodium or another ioncarrying species to produce adducts rather than a protonated species.
The greatest source of trouble when non-mass spectrometrists try to conduct mass
spectrometry on their own or collaborate with a mass spectrometrist is inadequate definition
of the research goal of the experiment. Adequate definition of the experimental goal is a
prerequisite for collecting the proper data and successfully interpreting it. Among the
determinations that can be achieved with mass spectrometry are molecular mass, molecular
structure, and sample purity. Each of these questions requires a different experimental
procedure. Simply asking for a "mass spec" will most likely not answer the real question at
hand.
Interpretation of mass spectra
Main article: Mass spectrum analysis
Since the precise structure or peptide sequence of a molecule is deciphered through the set of
fragment masses, the interpretation of mass spectra requires combined use of various
techniques. Usually the first strategy for identifying an unknown compound is to compare its
experimental mass spectrum against a library of mass spectra. If the search comes up empty,
then manual interpretation[34] or software assisted interpretation of mass spectra are
performed. Computer simulation of ionization and fragmentation processes occurring in mass
spectrometer is the primary tool for assigning structure or peptide sequence to a molecule. An
a priori structural information is fragmented in silico and the resulting pattern is compared
94
with observed spectrum. Such simulation is often supported by a fragmentation library[35] that
contains published patterns of known decomposition reactions. Software taking advantage of
this idea has been developed for both small molecules and proteins.
Another way of interpreting mass spectra involves spectra with accurate mass. A mass-tocharge ratio value (m/z) with only integer precision can represent an immense number of
theoretically possible ion structures. More precise mass figures significantly reduce the
number of candidate molecular formulas, albeit each can still represent large number of
structurally diverse compounds. A computer algorithm called formula generator calculates all
molecular formulas that theoretically fit a given mass with specified tolerance.
A recent technique for structure elucidation in mass spectrometry, called precursor ion
fingerprinting identifies individual pieces of structural information by conducting a search of
the tandem spectra of the molecule under investigation against a library of the product-ion
spectra of structurally characterized precursor ions.
Applications
Isotope ratio MS: isotope dating and tracking
Mass spectrometer to determine the 16O/18O and 12C/13C isotope ratio on biogenous carbonate
Main article: Isotope ratio mass spectrometry
Mass spectrometry is also used to determine the isotopic composition of elements within a
sample. Differences in mass among isotopes of an element are very small, and the less
abundant isotopes of an element are typically very rare, so a very sensitive instrument is
required. These instruments, sometimes referred to as isotope ratio mass spectrometers (IRMS), usually use a single magnet to bend a beam of ionized particles towards a series of
Faraday cups which convert particle impacts to electric current. A fast on-line analysis of
deuterium content of water can be done using Flowing afterglow mass spectrometry, FA-MS.
Probably the most sensitive and accurate mass spectrometer for this purpose is the accelerator
mass spectrometer (AMS). Isotope ratios are important markers of a variety of processes.
Some isotope ratios are used to determine the age of materials for example as in carbon
dating. Labeling with stable isotopes is also used for protein quantification. (see protein
characterization below)
Trace gas analysis
Several techniques use ions created in a dedicated ion source injected into a flow tube or a
drift tube: selected ion flow tube (SIFT-MS), and proton transfer reaction (PTR-MS), are
variants of chemical ionization dedicated for trace gas analysis of air, breath or liquid
headspace using well defined reaction time allowing calculations of analyte concentrations
from the known reaction kinetics without the need for internal standard or calibration.
Atom probe
Main article: Atom probe
95
An atom probe is an instrument that combines time-of-flight mass spectrometry and field ion
microscopy (FIM) to map the location of individual atoms.
Pharmacokinetics
Main article: Pharmacokinetics
Pharmacokinetics is often studied using mass spectrometry because of the complex nature of
the matrix (often blood or urine) and the need for high sensitivity to observe low dose and
long time point data. The most common instrumentation used in this application is LC-MS
with a triple quadrupole mass spectrometer. Tandem mass spectrometry is usually employed
for added specificity. Standard curves and internal standards are used for quantitation of
usually a single pharmaceutical in the samples. The samples represent different time points as
a pharmaceutical is administered and then metabolized or cleared from the body. Blank or t=0
samples taken before administration are important in determining background and insuring
data integrity with such complex sample matrices. Much attention is paid to the linearity of
the standard curve; however it is not uncommon to use curve fitting with more complex
functions such as quadratics since the response of most mass spectrometers is less than linear
across large concentration ranges.[36][37][38]
There is currently considerable interest in the use of very high sensitivity mass spectrometry
for microdosing studies, which are seen as a promising alternative to animal experimentation.
Protein characterization
Main article: Protein mass spectrometry
Mass spectrometry is an important emerging method for the characterization of proteins. The
two primary methods for ionization of whole proteins are electrospray ionization (ESI) and
matrix-assisted laser desorption/ionization (MALDI). In keeping with the performance and
mass range of available mass spectrometers, two approaches are used for characterizing
proteins. In the first, intact proteins are ionized by either of the two techniques described
above, and then introduced to a mass analyzer. This approach is referred to as "top-down"
strategy of protein analysis. In the second, proteins are enzymatically digested into smaller
peptides using proteases such as trypsin or pepsin, either in solution or in gel after
electrophoretic separation. Other proteolytic agents are also used. The collection of peptide
products are then introduced to the mass analyzer. When the characteristic pattern of peptides
is used for the identification of the protein the method is called peptide mass fingerprinting
(PMF), if the identification is performed using the sequence data determined in tandem MS
analysis it is called de novo sequencing. These procedures of protein analysis are also referred
to as the "bottom-up" approach.
Glycan Analysis
Mass spectrometry (MS), with its low sample requirement and high sensitivity, has been the
predominantly used in glycobiology for characterization and elucidation of glycan structures.
[39]
Mass spectrometry provides a complementary method to HPLC for the analysis of
glycans. Intact glycans may be detected directly as singly charged ions by matrix-assisted
laser desorption/ionization mass spectrometry (MALDI-MS) or, following permethylation or
peracetylation, by fast atom bombardment mass spectrometry (FAB-MS).[40] Electrospray
ionization mass spectrometry (ESI-MS) also gives good signals for the smaller glycans.[41]
96
Various free and commercial software are now available which interpret MS data and aid in
Glycan structure characterization.
Space exploration
As a standard method for analysis, mass spectrometers have reached other planets and moons.
Two were taken to Mars by the Viking program. In early 2005 the Cassini-Huygens mission
delivered a specialized GC-MS instrument aboard the Huygens probe through the atmosphere
of Titan, the largest moon of the planet Saturn. This instrument analyzed atmospheric samples
along its descent trajectory and was able to vaporize and analyze samples of Titan's frozen,
hydrocarbon covered surface once the probe had landed. These measurements compare the
abundance of isotope(s) of each particle comparatively to earth's natural abundance.[42] Also
onboard the Cassini-Huygens spacecraft is an ion and neutral mass spectrometer which has
been taking measurements of Titan's atmospheric composition as well as the composition of
Enceladus' plumes. A Thermal and Evolved Gas Analyzer mass spectrometer was carried by
the Mars Phoenix Lander launched in 2007.[43]
Mass spectrometers are also widely used in space missions to measure the composition of
plasmas. For example, the Cassini spacecraft carries the Cassini Plasma Spectrometer
(CAPS),[44] which measures the mass of ions in Saturn's magnetosphere.
Respired gas monitor
Mass spectrometers were used in hospitals for respiratory gas analysis beginning around 1975
through the end of the century. Some are probably still in use but none are currently being
manufactured.[45]
Found mostly in the operating room, they were a part of a complex system, in which respired
gas samples from patients undergoing anesthesia were drawn into the instrument through a
valve mechanism designed to sequentially connect up to 32 rooms to the mass spectrometer.
A computer directed all operations of the system. The data collected from the mass
spectrometer was delivered to the individual rooms for the anesthesiologist to use.
The uniqueness of this magnetic sector mass spectrometer may have been the fact that a plane
of detectors, each purposely positioned to collect all of the ion species expected to be in the
samples, allowed the instrument to simultaneously report all of the gases respired by the
patient. Although the mass range was limited to slightly over 120 u, fragmentation of some of
the heavier molecules negated the need for a higher detection limit.[46]
References
1. ^ a b c d e Sparkman, O. David (2000). Mass spectrometry desk reference. Pittsburgh:
Global View Pub. ISBN 0-9660813-2-3.
2. ^ "Definition of spectrograph." Merriam Webster. Accessed 13 June 2008.
3. ^ KM Downard (2007). "William Aston - the man behind the mass spectrograph".
European Journal of Mass Spectrometry 13 (3): 177–190. doi:10.1255/ejms.878.
PMID 17881785.
4. ^ Harper, Douglas. "Spectrum." Online Etymology Dictionary. Nov. 2001. Accessed
07-12-2007. Note: This part of the article only makes descriptive claims about the
information found in the primary source, the accuracy and applicability of which is
97
easily verifiable by any reasonable, educated person without specialist knowledge.
(See WP:PSTS)
5. ^ Squires, Gordon (1998). "Francis Aston and the mass spectrograph". Dalton
Transactions: 3893–3900. doi:10.1039/a804629h.
6. ^ KM Downard (2007). "Francis William Aston - the man behind the mass
spectrograph". European Journal of Mass Spectrometry 13 (3): 177–190.
doi:10.1255/ejms.878. PMID 17881785.
7. ^ Thomson, J.J. (1913). Rays Of Positive Electricity and Their Application to
Chemical Analysis. London: Longman's Green and Company.
http://www.archive.org/details/RaysOfPositiveElectricity.
8. ^ Siri, William (1947). "Mass spectroscope for analysis in the low-mass range".
Review of Scientific Instruments 18 (8): 540–545. doi:10.1063/1.1740998.
9. ^ Price, Phil (1991). "Standard definitions of terms relating to mass spectrometry. A
report from the Committee on Measurements and Standards of the American Society
for Mass Spectrometry". Journal of the American Society for Mass Spectrometry 2 (4):
336–348. doi:10.1016/1044-0305(91)80025-3.
10. ^ J.J., Thomson (1913). Rays Of Positive Electricity and Their Application to
Chemical Analysis. London: Longman's Green and Company.
http://www.archive.org/details/RaysOfPositiveElectricity.
11. ^ Carl-Ove Andersson, Acta. Chem. Scand. 1958, 12, 1353
12. ^ Mass Spec Anniversary, Chemical & Engineering News, 87, 6 (9 Feb. 2009), p. 4
13. ^ "The Nobel Prize in Chemistry 2002: Information for the Public". The Nobel
Foundation. 9 October 2002.
http://nobelprize.org/nobel_prizes/chemistry/laureates/2002/public.html. Retrieved
2007-08-29.
14. ^ Fenn, J. B.; Mann, M.; Meng, C. K.; Wong, S. F.; Whitehouse, C. M. (1989).
"Electrospray ionization for mass spectrometry of large biomolecules". Science 246
(4926): 64–71. doi:10.1126/science.2675315. PMID 2675315.
15. ^ Tanaka, K.; Waki, H.; Ido, Y.; Akita, S.; Yoshida, Y.; Yoshida, T. (1988). "Protein
and Polymer Analyses up to m/z 100 000 by Laser Ionization Time-of flight Mass
Spectrometry". Rapid Commun Mass Spectrom 2 (20): 151–3.
doi:10.1002/rcm.1290020802.
16. ^ Karas, M.; Bachman, D.; Bahr, U.; Hillenkamp, F. (1987). "Matrix-Assisted
Ultraviolet Laser Desorption of Non-Volatile Compounds". Int J Mass Spectrom Ion
Proc 78: 53–68. doi:10.1016/0168-1176(87)87041-6.
17. ^ A. P. Bruins (1991). "Mass spectrometry with ion sources operating at atmospheric
pressure". Mass Spectrometry Reviews 10 (1): 53–77. doi:10.1002/mas.1280100104.
18. ^ John S Cottrell, Roger J Greathead (1986). "Extending the Mass Range of a Sector
Mass Spectrometer". Mass Spectrometry Reviews 5: 215–247.
doi:10.1002/mas.1280050302.
19. ^ Wollnik, H. (1993). "Time-of-flight mass analyzers". Mass Spectrometry Reviews
12: 89. doi:10.1002/mas.1280120202.
20. ^ Paul W., Steinwedel H. (1953). "Ein neues Massenspektrometer ohne Magnetfeld".
Zeitschrift für Naturforschung A 8 (7): 448–450. Bibcode: 1953ZNatA...8..448P.
21. ^ R. E. March (2000). "Quadrupole ion trap mass spectrometry: a view at the turn of
the century". International Journal of Mass Spectrometry 200 (1-3): 285–312.
doi:10.1016/S1387-3806(00)00345-6.
22. ^ Schwartz, Jae C.; Michael W. Senko and John E. P. Syka (2002). "A twodimensional quadrupole ion trap mass spectrometer". Journal of the American Society
for Mass Spectrometry 13 (6): 659–669. doi:10.1016/S1044-0305(02)00384-7.
PMID 12056566.
98
23. ^ M. B. Comisarow and A. G. Marshall (1974). "Fourier transform ion cyclotron
resonance spectroscopy". Chemical Physics Letters 25 (2): 282–283.
doi:10.1016/0009-2614(74)89137-2.
24. ^ Marshall, A. G.; Hendrickson, C. L.; Jackson, G. S. (1998). "Fourier transform ion
cyclotron resonance mass spectrometry: a primer". Mass Spectrometry Reviews 17 (1):
1–34. doi:10.1002/(SICI)1098-2787(1998)17:1<1::AID-MAS1>3.0.CO;2-K.
25. ^ Q. Hu, R. J. Noll, H. Li, A. Makarov, M. Hardman and R. G. Cooks (2005). "The
Orbitrap: a new mass spectrometer". Journal of Mass Spectrometry 40 (4): 430–443.
doi:10.1002/jms.856. PMID 15838939.
26. ^ Lammert SA, Rockwood AA, Wang M, and ML Lee (2006). "Miniature Toroidal
Radio Frequency Ion Trap Mass Analyzer". Journal of the American Society for Mass
Spectrometry 17 (7): 916–922. doi:10.1016/j.jasms.2006.02.009. PMID 16697659.
27. ^ F. Dubois, R. Knochenmuss, R. Zenobi, A. Brunelle, C. Deprun and Y. L. Beyec
(1999). "A comparison between ion-to-photon and microchannel plate detectors".
Rapid Communications in Mass Spectrometry 13 (9): 786–791.
doi:10.1002/(SICI)1097-0231(19990515)13:9<786::AID-RCM566>3.0.CO;2-3.
28. ^ M. A. Park, J. H. Callahan and A. Vertes (1994). "An inductive detector for time-offlight mass spectrometry". Rapid Communications in Mass Spectrometry 8 (4): 317–
322. doi:10.1002/rcm.1290080407.
29. ^ Robert K. Boyd (1994). "Linked-scan techniques for MS/MS using tandem-in-space
instruments". Mass Spectrometry Reviews 13 (5-6): 359–410.
doi:10.1002/mas.1280130502.
30. ^ Eiceman, G.A. (2000). Gas Chromatography. In R.A. Meyers (Ed.), Encyclopedia of
Analytical Chemistry: Applications, Theory, and Instrumentation, pp. 10627.
Chichester: Wiley. ISBN 0-471-97670-9
31. ^ Verbeck, GF and Ruotolo, BT and Sawyer, HA and Gillig, KJ and Russell, DH, G;
Ruotolo, B; Sawyer, H; Gillig, K; Russell, D (2002). "A fundamental introduction to
ion mobility mass spectrometry applied to the analysis of biomolecules". J Biomol
Tech 13 (2): 56–61. PMID 19498967. PMC 2279851.
http://jbt.highwire.org/cgi/content/abstract/13/2/56.
32. ^ L. M. Matz, G. R. Asbury and H. H. Hill (2002). "Two-dimensional separations
with electrospray ionization ambient pressure high-resolution ion mobility
spectrometry/quadrupole mass spectrometry". Rapid Communications in Mass
Spectrometry 16 (7): 670–675. doi:10.1002/rcm.623. PMID 11921245.
33. ^ Rena A. Sowell, Stormy L. Koeniger, Stephen J. Valentine, Myeong Hee Moon and
David E. Clemmer (2004). "Nanoflow LC/IMS-MS and LC/IMS-CID/MS of Protein
Mixtures". Journal of the American Society for Mass Spectrometry 15 (9): 1341–1353.
doi:10.1016/j.jasms.2004.06.014. PMID 15337515.
34. ^ Tureček, František; McLafferty, Fred W. (1993). Interpretation of mass spectra.
Sausalito: University Science Books. ISBN 0-935702-25-3.
http://books.google.com/?id=xQWk5WQfMQAC&printsec=frontcover.
35. ^ Mistrik, R.(2004). A New Concept for the Interpretation of Mass Spectra Based on a
Combination of a Fragmentation Mechanism Database and a Computer Expert
System. in Ashcroft, A.E., Brenton, G., Monaghan,J.J. (Eds.), Advances in Mass
Spectrometry, Elsevier, Amsterdam, vol. 16, pp. 821.
36. ^ Hsieh, Yunsheng; Korfmacher, WA (2006). "Systems for Drug Metabolism and
Pharmacokinetic Screening, Y. Hsieh and W.A. Korfmacher, Current Drug
Metabolism". Current Drug Metabolism 7 (5): 479–489.
doi:10.2174/138920006777697963. PMID 16787157.
37. ^ Covey, T.R.; Lee, E.D.; Henion, J.D. (1986). "Mass Spectrometry for the
Determination of Drugs in Biological Samples". Anal. Chem. 58: 2453–2460.
doi:10.1021/ac00125a022.
99
38. ^ Covey, Tom R.; Crowther, Jonathan B.; Dewey, Elizabeth A.; Henion, Jack D.
(1985). "Mass Spectrometry Determination of Drugs and Their Metabolites in
Biological Fluids". Anal. Chem. 57 (2): 474–81. doi:10.1021/ac50001a036.
39. ^ Apte, A.; Meitei, N.S. (2009). Bioinformatics in Glycomics: Glycan
Characterization with Mass Spectrometric Data Using SimGlycan™. 600. pp. 269281. doi:10.1007/978-1-60761-454-8_19.
40. ^ Harvey, D.; Rudd, P.M. (2000). Determining the Structure of Glycan Moieties by
Mass Spectrometry. pp. 12.7-12.7.15. doi:10.1002/0471140864.ps1207s43.
41. ^ Blow (2009). "Glycobiology: A spoonful of sugar". Nature: 617-620.
doi:10.1038/457617a.
42. ^ S. Petrie and D. K. Bohme (2007). "Ions in space". Mass Spectrometry Reviews 26
(2): 258–280. doi:10.1002/mas.20114. PMID 17111346.
43. ^ Hoffman, J; Chaney, R; Hammack, H (2008). "Phoenix Mars Mission—The
Thermal Evolved Gas Analyzer". Journal of the American Society for Mass
Spectrometry 19 (10): 1377. doi:10.1016/j.jasms.2008.07.015. PMID 18715800
44. ^ "Cassini Plasma Spectrometer". Southwest Research Institute.
http://caps.space.swri.edu/. Retrieved 2008-01-04.
45. ^ Riker JB, Haberman B (1976). "Expired gas monitoring by mass spectrometry in a
respiratory intensive care unit". Crit. Care Med. 4 (5): 223–9. doi:10.1097/00003246197609000-00002. PMID 975846.
46. ^ J. W. W. Gothard, C. M. Busst, M. A. Branthwaite, N. J. H. Davies and D. M.
Denison (1980). "Applications of respiratory mass spectrometry to intensive care".
Anaesthesia 35 (9): 890–895. doi:10.1111/j.1365-2044.1980.tb03950.x.
100
Infrared spectroscopy
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For a table of IR spectroscopy data, see infrared spectroscopy correlation table.
Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared
region of the electromagnetic spectrum, that is light with a longer wavelength and lower
frequency than visible light. It covers a range of techniques, mostly based on absorption
spectroscopy. As with all spectroscopic techniques, it can be used to identify and study
chemicals. A common laboratory instrument that uses this technique is a Fourier transform
infrared (FTIR) spectrometer.
The infrared portion of the electromagnetic spectrum is usually divided into three regions; the
near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher
energy near-IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite
overtone or harmonic vibrations. The mid-infrared, approximately 4000–400 cm−1 (2.5–
25 μm) may be used to study the fundamental vibrations and associated rotational-vibrational
structure. The far-infrared, approximately 400–10 cm−1 (25–1000 μm), lying adjacent to the
microwave region, has low energy and may be used for rotational spectroscopy. The names
and classifications of these subregions are conventions, and are only loosely based on the
relative molecular or electromagnetic properties.
Theory
Infrared spectroscopy exploits the fact that molecules absorb specific frequencies that are
characteristic of their structure. These absorptions are resonant frequencies, i.e. the frequency
of the absorbed radiation matches the frequency of the bond or group that vibrates. The
energies are determined by the shape of the molecular potential energy surfaces, the masses of
the atoms, and the associated vibronic coupling.
In particular, in the Born–Oppenheimer and harmonic approximations, i.e. when the
molecular Hamiltonian corresponding to the electronic ground state can be approximated by a
harmonic oscillator in the neighborhood of the equilibrium molecular geometry, the resonant
frequencies are determined by the normal modes corresponding to the molecular electronic
ground state potential energy surface. Nevertheless, the resonant frequencies can be in a first
approach related to the strength of the bond, and the mass of the atoms at either end of it.
Thus, the frequency of the vibrations can be associated with a particular bond type.
Number of vibrational modes
In order for a vibrational mode in a molecule to be "IR active," it must be associated with
changes in the permanent dipole.
A molecule can vibrate in many ways, and each way is called a vibrational mode. Linear
molecules have 3N – 5 degrees of vibrational modes whereas nonlinear molecules have 3N –
101
6 degrees of vibrational modes (also called vibrational degrees of freedom). As an example
H2O, a non-linear molecule, will have 3 × 3 – 6 = 3 degrees of vibrational freedom, or modes.
Simple diatomic molecules have only one bond and only one vibrational band. If the molecule
is symmetrical, e.g. N2, the band is not observed in the IR spectrum, but only in the Raman
spectrum. Unsymmetrical diatomic molecules, e.g. CO, absorb in the IR spectrum. More
complex molecules have many bonds, and their vibrational spectra are correspondingly more
complex, i.e. big molecules have many peaks in their IR spectra.
The atoms in a CH2 group, commonly found in organic compounds, can vibrate in six
different ways: symmetric and antisymmetric stretching, scissoring, rocking, wagging and
twisting:
Symmetrical Antisymmetrical
Scissoring
stretching
stretching
Ro Wa Tw
cki ggi isti
ng ng ng
(These figures do not represent the "recoil" of the C atoms, which, though necessarily present
to balance the overall movements of the molecule, are much smaller than the movements of
the lighter H atoms).
Special effects
The simplest and most important IR bands arise from the "normal modes," the simplest
distortions of the molecule. In some cases, "overtone bands" are observed. These bands arise
from the absorption of a photon that leads to a doubly excited vibrational state. Such bands
appear at approximately twice the energy of the normal mode. Some vibrations, so-called
'combination modes," involve more than one normal mode. The phenomenon of Fermi
resonance can arise when two modes are similar in energy, Fermi resonance results in an
unexpected shift in energy and intensity of the bands.
Practical IR spectroscopy
The infrared spectrum of a sample is recorded by passing a beam of infrared light through the
sample. Examination of the transmitted light reveals how much energy was absorbed at each
wavelength. This can be done with a monochromatic beam, which changes in wavelength
over time, or by using a Fourier transform instrument to measure all wavelengths at once.
From this, a transmittance or absorbance spectrum can be produced, showing at which IR
wavelengths the sample absorbs. Analysis of these absorption characteristics reveals details
about the molecular structure of the sample. When the frequency of the IR is the same as the
vibrational frequency of a bond, absorption occurs.
This technique works almost exclusively on samples with covalent bonds. Simple spectra are
obtained from samples with few IR active bonds and high levels of purity. More complex
102
molecular structures lead to more absorption bands and more complex spectra. The technique
has been used for the characterization of very complex mixtures.
Sample preparation
Gaseous samples require a sample cell with a long pathlength (typically 5–10 cm), to
compensate for the diluteness.
Liquid samples can be sandwiched between two plates of a salt (commonly sodium chloride,
or common salt, although a number of other salts such as potassium bromide or calcium
fluoride are also used).[1] The plates are transparent to the infrared light and do not introduce
any lines onto the spectra.
Solid samples can be prepared in a variety of ways. One common method is to crush the
sample with an oily mulling agent (usually Nujol) in a marble or agate mortar, with a pestle.
A thin film of the mull is smeared onto salt plates and measured. The second method is to
grind a quantity of the sample with a specially purified salt (usually potassium bromide)
finely (to remove scattering effects from large crystals). This powder mixture is then pressed
in a mechanical press to form a translucent pellet through which the beam of the spectrometer
can pass.[1] A third technique is the "cast film" technique, which is used mainly for polymeric
materials. The sample is first dissolved in a suitable, non hygroscopic solvent. A drop of this
solution is deposited on surface of KBr or NaCl cell. The solution is then evaporated to
dryness and the film formed on the cell is analysed directly. Care is important to ensure that
the film is not too thick otherwise light cannot pass through. This technique is suitable for
qualitative analysis. The final method is to use microtomy to cut a thin (20–100 µm) film
from a solid sample. This is one of the most important ways of analysing failed plastic
products for example because the integrity of the solid is preserved.
It is important to note that spectra obtained from different sample preparation methods will
look slightly different from each other due to differences in the samples' physical states.
Comparing to a reference
Schematics of a two-beam absorption spectrometer. A beam of infrared light is produced,
passed through an interferometer (not shown), and then split into two separate beams. One is
passed through the sample, the other passed through a reference. The beams are both reflected
back towards a detector, however first they pass through a splitter, which quickly alternates
which of the two beams enters the detector. The two signals are then compared and a printout
is obtained. This "two-beam" setup gives accurate spectra even if the intensity of the light
source drifts over time.
To take the infrared spectrum of a sample, it is necessary to measure both the sample and a
"reference" (or "control"). This is because each measurement is affected by not only the lightabsorption properties of the sample, but also the properties of the instrument (for example,
what light source is used, what detector is used, etc.). The reference measurement makes it
possible to eliminate the instrument influence. Mathematically, the sample transmission
spectrum is divided by the reference transmission spectrum.
103
The appropriate "reference" depends on the measurement and its goal. The simplest reference
measurement is to simply remove the sample (replacing it by air). However, sometimes a
different reference is more useful. For example, if the sample is a dilute solute dissolved in
water in a beaker, then a good reference measurement might be to measure pure water in the
same beaker. Then the reference measurement would cancel out not only all the instrumental
properties (like what light source is used), but also the light-absorbing and light-reflecting
properties of the water and beaker, and the final result would just show the properties of the
solute (at least approximately).
A common way to compare to a reference is sequentially: First measure the reference, then
replace the reference by the sample, then measure the sample. This technique is not perfectly
reliable: If the infrared lamp is a bit brighter during the reference measurement, then a bit
dimmer during the sample measurement, the measurement will be distorted. More elaborate
methods, such as a "two-beam" setup (see figure), can correct for these types of effects to give
very accurate results.
FTIR
Main article: Fourier transform infrared spectroscopy
An interferogram from an FTIR measurement. The horizontal axis is the position of the
mirror, and the vertical axis is the amount of light detected. This is the "raw data" which can
be Fourier transformed to get the actual spectrum.
Fourier transform infrared (FTIR) spectroscopy is a measurement technique that allows
one to record infrared spectra. Infrared light is guided through an interferometer and then
through the sample (or vice versa). A moving mirror inside the apparatus alters the
distribution of infrared light that passes through the interferometer. The signal directly
recorded, called an "interferogram", represents light output as a function of mirror position. A
data-processing technique called Fourier transform turns this raw data into the desired result
(the sample's spectrum): Light output as a function of infrared wavelength (or equivalently,
wavenumber). As described above, the sample's spectrum is always compared to a reference.
There is an alternate method for taking spectra (the "dispersive" or "scanning
monochromator" method), where one wavelength at a time passes through the sample. The
dispersive method is more common in UV-Vis spectroscopy, but is less practical in the
infrared than the FTIR method. One reason that FTIR is favored is called "Fellgett's
advantage" or the "multiplex advantage": The information at all frequencies is collected
simultaneously, improving both speed and signal-to-noise ratio. Another is called "Jacquinot's
Throughput Advantage": A dispersive measurement requires detecting much lower light
levels than an FTIR measurement.[2] There are other advantages, as well as some
disadvantages,[2] but virtually all modern infrared spectrometers are FTIR instruments.
Absorption bands
Main article: Infrared Spectroscopy Correlation Table
Wavenumbers listed in cm−1.
104
Uses and applications
Infrared spectroscopy is widely used in both research and industry as a simple and reliable
technique for measurement, quality control and dynamic measurement. It is also used in
forensic analysis in both criminal and civil cases, enabling identification of polymer
degradation for example.
The instruments are now small, and can be transported, even for use in field trials. With
increasing technology in computer filtering and manipulation of the results, samples in
solution can now be measured accurately (water produces a broad absorbance across the range
of interest, and thus renders the spectra unreadable without this computer treatment). Some
instruments will also automatically tell you what substance is being measured from a store of
thousands of reference spectra held in storage.
By measuring at a specific frequency over time, changes in the character or quantity of a
particular bond can be measured. This is especially useful in measuring the degree of
polymerization in polymer manufacture. Modern research instruments can take infrared
measurements across the whole range of interest as frequently as 32 times a second. This can
be done whilst simultaneous measurements are made using other techniques. This makes the
observations of chemical reactions and processes quicker and more accurate.
Infrared spectroscopy has been highly successful for applications in both organic and
inorganic chemistry. Infrared spectroscopy has also been successfully utilized in the field of
semiconductor microelectronics:[3] for example, infrared spectroscopy can be applied to
semiconductors like silicon, gallium arsenide, gallium nitride, zinc selenide, amorphous
silicon, silicon nitride, etc.
Isotope effects
The different isotopes in a particular species may give fine detail in infrared spectroscopy. For
example, the O–O stretching frequency (in reciprocal centimeters) of oxyhemocyanin is
experimentally determined to be 832 and 788 cm−1 for ν(16O–16O) and ν(18O–18O),
respectively.
By considering the O–O bond as a spring, the wavenumber of absorbance, ν can be
calculated:
where k is the spring constant for the bond, c is the speed of light, and μ is the reduced mass
of the A–B system:
(mi is the mass of atom i).
The reduced masses for 16O–16O and 18O–18O can be approximated as 8 and 9 respectively.
Thus
105
Where ν is the wavenumber; [wavenumber = frequency/(speed of light)]
The effect of isotopes, both on the vibration and the decay dynamics, has been found to be
stronger than previously thought. In some systems, such as silicon and germanium, the decay
of the anti-symmetric stretch mode of interstitial oxygen involves the symmetric stretch mode
with a strong isotope dependence. For example, it was shown that for a natural silicon sample,
the lifetime of the anti-symmetric vibration is 11.4 ps. When the isotope of one of the silicon
atoms is increased to 29Si, the lifetime increases to 19 ps. In similar manner, when the silicon
atom is changed to 30Si, the lifetime becomes 27 ps.[4]
Two-dimensional IR
Two-dimensional infrared correlation spectroscopy analysis is the application of 2D
correlation analysis on infrared spectra. By extending the spectral information of a perturbed
sample, spectral analysis is simplified and resolution is enhanced. The 2D synchronous and
2D asynchronous spectra represent a graphical overview of the spectral changes due to a
perturbation (such as a changing concentration or changing temperature) as well as the
relationship between the spectral changes at two different wavenumbers.
Main article: Two-dimensional infrared spectroscopy
Pulse Sequence used to obtain a two-dimensional Fourier transform infrared spectrum. The
time period τ1 is usually referred to as the coherence time and the second time period τ2 is
known as the waiting time. The excitation frequency is obtained by Fourier transforming
along the τ1 axis.
Nonlinear two-dimensional infrared spectroscopy[5][6] is the infrared version of correlation
spectroscopy. Nonlinear two-dimensional infrared spectroscopy is a technique that has
become available with the development of femtosecond infrared laser pulses. In this
experiment, first a set of pump pulses are applied to the sample. This is followed by a waiting
time, wherein the system is allowed to relax. The typical waiting time lasts from zero to
several picoseconds, and the duration can be controlled with a resolution of tens of
femtoseconds. A probe pulse is then applied resulting in the emission of a signal from the
sample. The nonlinear two-dimensional infrared spectrum is a two-dimensional correlation
plot of the frequency ω1 that was excited by the initial pump pulses and the frequency ω3
excited by the probe pulse after the waiting time. This allows the observation of coupling
between different vibrational modes; because of its extremely high time resolution, it can be
used to monitor molecular dynamics on a picosecond timescale. It is still a largely unexplored
technique and is becoming increasingly popular for fundamental research.
As with two-dimensional nuclear magnetic resonance (2DNMR) spectroscopy, this technique
spreads the spectrum in two dimensions and allows for the observation of cross peaks that
contain information on the coupling between different modes. In contrast to 2DNMR,
nonlinear two-dimensional infrared spectroscopy also involves the excitation to overtones.
These excitations result in excited state absorption peaks located below the diagonal and cross
peaks. In 2DNMR, two distinct techniques, COSY and NOESY, are frequently used. The
cross peaks in the first are related to the scalar coupling, while in the later they are related to
the spin transfer between different nuclei. In nonlinear two-dimensional infrared
spectroscopy, analogs have been drawn to these 2DNMR techniques. Nonlinear twodimensional infrared spectroscopy with zero waiting time corresponds to COSY, and
nonlinear two-dimensional infrared spectroscopy with finite waiting time allowing vibrational
106
population transfer corresponds to NOESY. The COSY variant of nonlinear two-dimensional
infrared spectroscopy has been used for determination of the secondary structure content
proteins.[7]
References
1. ^ a b Laurence M. Harwood, Christopher J. Moody (1989). Experimental organic
chemistry: Principles and Practice (Illustrated ed.). Wiley-Blackwell. p. 292.
ISBN 0632020172.
2. ^ a b Chromatography/Fourier transform infrared spectroscopy and its applications,
by Robert White, p7
3. ^ Lau, W.S. (1999). Infrared characterization for microelectronics. World Scientific.
ISBN 9810223528.
http://books.google.com/?id=rotNlJDFJWsC&printsec=frontcover.
4. ^ Kohli, K.; Davies, Gordon; Vinh, N.; West, D.; Estreicher, S.; Gregorkiewicz, T.;
Izeddin, I.; Itoh, K. (2006). "Isotope Dependence of the Lifetime of the 1136-cm-1
Vibration of Oxygen in Silicon". Physical Review Letters 96 (22): 225503.
doi:10.1103/PhysRevLett.96.225503. PMID 16803320.
5. ^ P. Hamm, M. H. Lim, R. M. Hochstrasser (1998). "Structure of the amide I band of
peptides measured by femtosecond nonlinear-infrared spectroscopy". J. Phys. Chem. B
102: 6123. doi:10.1021/jp9813286.
6. ^ S. Mukamel (2000). "Multidimensional Fentosecond Correlation Spectroscopies of
Electronic and Vibrational Excitations". Annual Review of Physics and Chemistry 51:
691. doi:10.1146/annurev.physchem.51.1.691. PMID 11031297.
7. ^ N. Demirdöven, C. M. Cheatum, H. S. Chung, M. Khalil, J. Knoester, A. Tokmakoff
(2004). "Two-dimensional infrared spectroscopy of antiparallel beta-sheet secondary
structure". Journal of the American Chemical Society 126 (25): 7981.
doi:10.1021/ja049811j. PMID 15212548.
107
Ultraviolet–visible spectroscopy
Beckman DU640 UV/Vis spectrophotometer.
Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry (UV-Vis or
UV/Vis) refers to absorption spectroscopy in the ultraviolet-visible spectral region. This
means it uses light in the visible and adjacent (near-UV and near-infrared (NIR)) ranges. The
absorption in the visible range directly affects the perceived color of the chemicals involved.
In this region of the electromagnetic spectrum, molecules undergo electronic transitions. This
technique is complementary to fluorescence spectroscopy, in that fluorescence deals with
transitions from the excited state to the ground state, while absorption measures transitions
from the ground state to the excited state.[1]
Applications
An example of a UV/Vis readout
UV/Vis spectroscopy is routinely used in the quantitative determination of solutions of
transition metal ions and highly conjugated organic compounds.
•
•
•
Solutions of transition metal ions can be colored (i.e., absorb visible light) because d
electrons within the metal atoms can be excited from one electronic state to another.
The colour of metal ion solutions is strongly affected by the presence of other species,
such as certain anions or ligands. For instance, the colour of a dilute solution of copper
sulfate is a very light blue; adding ammonia intensifies the colour and changes the
wavelength of maximum absorption (λmax).
Organic compounds, especially those with a high degree of conjugation, also absorb
light in the UV or visible regions of the electromagnetic spectrum. The solvents for
these determinations are often water for water soluble compounds, or ethanol for
organic-soluble compounds. (Organic solvents may have significant UV absorption;
not all solvents are suitable for use in UV spectroscopy. Ethanol absorbs very weakly
at most wavelengths.) Solvent polarity and pH can affect the absorption spectrum of
an organic compound. Tyrosine, for example, increases in absorption maxima and
molar extinction coefficient when pH increases from 6 to 13 or when solvent polarity
decreases.
While charge transfer complexes also give rise to colours, the colours are often too
intense to be used for quantitative measurement.
The Beer-Lambert law states that the absorbance of a solution is directly proportional to the
concentration of the absorbing species in the solution and the path length. Thus, for a fixed
path length, UV/Vis spectroscopy can be used to determine the concentration of the absorber
in a solution. It is necessary to know how quickly the absorbance changes with concentration.
This can be taken from references (tables of molar extinction coefficients), or more
accurately, determined from a calibration curve.
108
A UV/Vis spectrophotometer may be used as a detector for HPLC. The presence of an analyte
gives a response assumed to be proportional to the concentration. For accurate results, the
instrument's response to the analyte in the unknown should be compared with the response to
a standard; this is very similar to the use of calibration curves. The response (e.g., peak
height) for a particular concentration is known as the response factor.
The wavelengths of absorption peaks can be correlated with the types of bonds in a given
molecule and are valuable in determining the functional groups within a molecule. The
Woodward-Fieser rules, for instance, are a set of empirical observations used to predict λmax,
the wavelength of the most intense UV/Vis absorption, for conjugated organic compounds
such as dienes and ketones. The spectrum alone is not, however, a specific test for any given
sample. The nature of the solvent, the pH of the solution, temperature, high electrolyte
concentrations, and the presence of interfering substances can influence the absorption
spectrum. Experimental variations such as the slit width (effective bandwidth) of the
spectrophotometer will also alter the spectrum. To apply UV/Vis spectroscopy to analysis,
these variables must be controlled or accounted for in order to identify the substances present.
Beer-Lambert law
Main article: Beer-Lambert law
The method is most often used in a quantitative way to determine concentrations of an
absorbing species in solution, using the Beer-Lambert law:
−,
where A is the measured absorbance, I0 is the intensity of the incident light at a given
wavelength, I is the transmitted intensity, L the pathlength through the sample, and c the
concentration of the absorbing species. For each species and wavelength, ε is a constant
known as the molar absorptivity or extinction coefficient. This constant is a fundamental
molecular property in a given solvent, at a particular temperature and pressure, and has units
of 1 / M * cm or often AU / M * cm.
The absorbance and extinction ε are sometimes defined in terms of the natural logarithm
instead of the base-10 logarithm.
The Beer-Lambert Law is useful for characterizing many compounds but does not hold as a
universal relationship for the concentration and absorption of all substances. A 2nd order
polynomial relationship between absorption and concentration is sometimes encountered for
very large, complex molecules such as organic dyes (Xylenol Orange or Neutral Red, for
example).
Practical considerations
The Beer-Lambert law has implicit assumptions that must be met experimentally for it to
apply. For instance, the chemical makeup and physical environment of the sample can alter its
extinction coefficient. The chemical and physical conditions of a test sample therefore must
match reference measurements for conclusions to be valid.
109
Spectral bandwidth
A given spectrometer has a spectral bandwidth that characterizes how monochromatic the
light is. If this bandwidth is comparable to the width of the absorption features, then the
measured extinction coefficient will be altered. In most reference measurements, the
instrument bandwidth is kept below the width of the spectral lines. When a new material is
being measured, it may be necessary to test and verify if the bandwidth is sufficiently narrow.
Reducing the spectral bandwidth will reduce the energy passed to the detector and will,
therefore, require a longer measurement time to achieve the same signal to noise ratio.
Wavelength error
In liquids, the extinction coefficient usually changes slowly with wavelength. A peak of the
absorbance curve (a wavelength where the absorbance reaches a maximum) is where the rate
of change in absorbance with wavelength is smallest. Measurements are usually made at a
peak to minimize errors produced by errors in wavelength in the instrument, that is errors due
to having a different extinction coefficient than assumed.
Stray light
See also: Stray light
Another important factor is the purity of the light used. The most important factor affecting
this is the stray light level of the monochromator [2] . The detector used is broadband, it
responds to all the light that reaches it. If a significant amount of the light passed through the
sample contains wavelengths that have much lower extinction coefficients than the nominal
one, the instrument will report an incorrectly low absorbance. Any instrument will reach a
point where an increase in sample concentration will not result in an increase in the reported
absorbance, because the detector is simply responding to the stray light. In practice the
concentration of the sample or the optical path length must be adjusted to place the unknown
absorbance within a range that is valid for the instrument. Sometimes an empirical calibration
function is developed, using known concentrations of the sample, to allow measurements into
the region where the instrument is becoming non-linear.
As a rough guide, an instrument with a single monochromator would typically have a stray
light level corresponding to about 3 AU, which would make measurements above about 2 AU
problematic. A more complex instrument with a double monochromator would have a stray
light level corresponding to about 6 AU, which would therefore allow measuring a much
wider absorbance range.
Absorption flattening
At sufficiently high concentrations, the absorption bands will saturate and show absorption
flattening. The absorption peak appears to flatten because close to 100% of the light is already
being absorbed. The concentration at which this occurs depends on the particular compound
being measured. One test that can be used to test for this effect is to vary the path length of the
measurement. In the Beer-Lambert law, varying concentration and path length has an
equivalent effect—diluting a solution by a factor of 10 has the same effect as shortening the
path length by a factor of 10. If cells of different path lengths are available, testing if this
relationship holds true is one way to judge if absorption flattening is occurring.
110
Solutions that are not homogeneous can show deviations from the Beer-Lambert law because
of the phenomenon of absorption flattening. This can happen, for instance, where the
absorbing substance is located within suspended particles.[3] The deviations will be most
noticeable under conditions of low concentration and high absorbance. The reference
describes a way to correct for this deviation.
Ultraviolet-visible spectrophotometer
The instrument used in ultraviolet-visible spectroscopy is called a UV/Vis
spectrophotometer. It measures the intensity of light passing through a sample (I), and
compares it to the intensity of light before it passes through the sample (Io). The ratio I / Io is
called the transmittance, and is usually expressed as a percentage (%T). The absorbance, A, is
based on the transmittance:
A = − log(%T / 100%)
The basic parts of a spectrophotometer are a light source, a holder for the sample, a diffraction
grating or monochromator to separate the different wavelengths of light, and a detector. The
radiation source is often a Tungsten filament (300-2500 nm), a deuterium arc lamp, which is
continuous over the ultraviolet region (190-400 nm)— or more recently, light emitting diodes
(LED) and Xenon arc lamps[4] for the visible wavelengths. The detector is typically a
photodiode or a CCD. Photodiodes are used with monochromators, which filter the light so
that only light of a single wavelength reaches the detector. Diffraction gratings are used with
CCDs, which collects light of different wavelengths on different pixels.
Diagram of a single-beam UV/Vis spectrophotometer.
A spectrophotometer can be either single beam or double beam. In a single beam instrument
(such as the Spectronic 20), all of the light passes through the sample cell. Io must be
measured by removing the sample. This was the earliest design, but is still in common use in
both teaching and industrial labs.
In a double-beam instrument, the light is split into two beams before it reaches the sample.
One beam is used as the reference; the other beam passes through the sample. The reference
beam intensity is taken as 100% Transmission (or 0 Absorbance), and the measurement
displayed is the ratio of the two beam intensities. Some double-beam instruments have two
detectors (photodiodes), and the sample and reference beam are measured at the same time. In
other instruments, the two beams pass through a beam chopper, which blocks one beam at a
time. The detector alternates between measuring the sample beam and the reference beam in
synchronism with the chopper. There may also be one or more dark intervals in the chopper
cycle. In this case the measured beam intensities may be corrected by subtracting the intensity
measured in the dark interval before the ratio is taken.
Samples for UV/Vis spectrophotometry are most often liquids, although the absorbance of
gases and even of solids can also be measured. Samples are typically placed in a transparent
cell, known as a cuvette. Cuvettes are typically rectangular in shape, commonly with an
internal width of 1 cm. (This width becomes the path length, L, in the Beer-Lambert law.)
Test tubes can also be used as cuvettes in some instruments. The type of sample container
used must allow radiation to pass over the spectral region of interest. The most widely
applicable cuvettes are made of high quality fused silica or quartz glass because these are
111
transparent throughout the UV, visible and near infrared regions. Glass and plastic cuvettes
are also common, although glass and most plastics absorb in the UV, which limits their
usefulness to visible wavelengths.[5]
A complete spectrum of the absorption at all wavelengths of interest can often be produced
directly by a more sophisticated spectrophotometer. In simpler instruments the absorption is
determined one wavelength at a time and then compiled into a spectrum by the operator. A
standardized spectrum is formed by removing the concentration dependence and determining
the extinction coefficient (ε) as a function of wavelength.
Notes
1. ^ Skoog, et al. Principles of Instrumental Analysis. 6th ed. Thomson Brooks/Cole.
2007, 169-173.
2. ^ "Beer's Law - Alisdair Boraston".
http://www.brewingtechniques.com/brewingtechniques/beerslaw/boraston.html.
Retrieved 2009-02-06.
3. ^ Wittung, Pernilla; Johan Kajanus, Mikael Kubista, Bo G. Malmström (8 August
1994). "Absorption flattening in the optical spectra of liposome-entrapped substances"
(pdf). FEBS_Lett_352_37_1994.pdf (application/pdf Object).
http://www.img.cas.cz/ge/FEBS_Lett_352_37_1994.pdf. Retrieved 2009-02-06.
4. ^ Skoog, et al. Principles of Instrumental Analysis. 6th ed. Thomson Brooks/Cole.
2007, 349-351.
5. ^ Skoog, et al. Principles of Instrumental Analysis. 6th ed. Thomson Brooks/Cole.
2007, 35
NMR spectroscopy
A 900MHz NMR instrument with a 21.2 T magnet at HWB-NMR, Birmingham, UK
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy,
is the name given to a technique that exploits the magnetic properties of certain nuclei. For
details regarding this phenomenon and its origins, refer to the nuclear magnetic resonance
article. The most important applications for the organic chemist are proton NMR and carbon13 NMR spectroscopy. In principle, NMR is applicable to any nucleus possessing spin.
Many types of information can be obtained from an NMR spectrum. Much like using infrared
spectroscopy (IR) to identify functional groups, analysis of a NMR spectrum provides
information on the number and type of chemical entities in a molecule. However, NMR
provides much more information than IR.
The impact of NMR spectroscopy on the natural sciences has been substantial. It can, among
other things, be used to study mixtures of analytes, to understand dynamic effects such as
change in temperature and reaction mechanisms, and is an invaluable tool in understanding
protein and nucleic acid structure and function. It can be applied to a wide variety of samples,
both in the solution and the solid state.
112
Contents
Basic NMR techniques
The NMR sample is prepared in a thin-walled glass tube - an NMR tube.
When placed in a magnetic field, NMR active nuclei (such as 1H or 13C) absorb at a frequency
characteristic of the isotope. The resonant frequency, energy of the absorption and the
intensity of the signal are proportional to the strength of the magnetic field. For example, in a
21 tesla magnetic field, protons resonate at 900 MHz. It is common to refer to a 21 T magnet
as a 900 MHz magnet, although different nuclei resonate at a different frequency at this field
strength.
In the Earth's magnetic field the same nuclei resonate at audio frequencies. This effect is used
in Earth's field NMR spectrometers and other instruments. Because these instruments are
portable and inexpensive, they are often used for teaching and field work.
Chemical shift
Main article: Chemical shift
Depending on the local chemical environment, different protons in a molecule resonate at
slightly different frequencies. Since both this frequency shift and the fundamental resonant
frequency are directly proportional to the strength of the magnetic field, the shift is converted
into a field-independent dimensionless value known as the chemical shift. The chemical shift
is reported as a relative measure from some reference resonance frequency. (For the nuclei
1
H, 13C, and 29Si, TMS (tetramethylsilane) is commonly used as a reference.) This difference
between the frequency of the signal and the frequency of the reference is divided by
frequency of the reference signal to give the chemical shift. The frequency shifts are
extremely small in comparison to the fundamental NMR frequency. A typical frequency shift
might be 100 Hz, compared to a fundamental NMR frequency of 100 MHz, so the chemical
shift is generally expressed in parts per million (ppm).[1] To detect such small frequency
differences the applied magnetic field must be constant throughout the sample volume. High
resolution NMR spectrometers use shims to adjust the homogeneity of the magnetic field to
parts per billion (ppb) in a volume of a few cubic centimeters.
By understanding different chemical environments, the chemical shift can be used to obtain
some structural information about the molecule in a sample. The conversion of the raw data to
this information is called assigning the spectrum. For example, for the 1H-NMR spectrum for
ethanol (CH3CH2OH), one would expect three specific signals at three specific chemical
shifts: one for the CH3 group, one for the CH2 group and one for the OH group. A typical CH3
group has a shift around 1 ppm, a CH2 attached to an OH has a shift of around 4 ppm and an
OH has a shift around 2–3 ppm depending on the solvent used.
Because of molecular motion at room temperature, the three methyl protons average out
during the course of the NMR experiment (which typically requires a few ms). These protons
become degenerate and form a peak at the same chemical shift.
113
The shape and size of peaks are indicators of chemical structure too. In the example above—
the proton spectrum of ethanol—the CH3 peak would be three times as large as the OH.
Similarly the CH2 peak would be twice the size of the OH peak but only 2/3 the size of the
CH3 peak.
Modern analysis software allows analysis of the size of peaks to understand how many
protons give rise to the peak. This is known as integration—a mathematical process which
calculates the area under a curve. The analyst must integrate the peak and not measure its
height because the peaks also have width—and thus its size is dependent on its area not its
height. However, it should be mentioned that the number of protons, or any other observed
nucleus, is only proportional to the intensity, or the integral, of the NMR signal, in the very
simplest one-dimensional NMR experiments. In more elaborate experiments, for instance,
experiments typically used to obtain carbon-13 NMR spectra, the integral of the signals
depends on the relaxation rate of the nucleus, and its scalar and dipolar coupling constants.
Very often these factors are poorly known - therefore, the integral of the NMR signal is very
difficult to interpret in more complicated NMR experiments.
J-coupling
Main article: J-coupling
Some of the most useful information for structure
Multiplicity Intensity Ratio
determination in a one-dimensional NMR spectrum comes
Singlet (s)
1
from J-coupling or scalar coupling (a special case of spinDoublet (d)
1:1
spin coupling) between NMR active nuclei. This coupling
Triplet (t)
1:2:1
arises from the interaction of different spin states through the
chemical bonds of a molecule and results in the splitting of
Quartet (q)
1:3:3:1
NMR signals. These splitting patterns can be complex or
Quintet
1:4:6:4:1
simple and, likewise, can be straightforwardly interpretable or
Sextet
1:5:10:10:5:1
deceptive. This coupling provides detailed insight into the
Septet
1:6:15:20:15:6:1
connectivity of atoms in a molecule.
Coupling to n equivalent (spin ½) nuclei splits the signal into a n+1 multiplet with intensity
ratios following Pascal's triangle as described on the right. Coupling to additional spins will
lead to further splittings of each component of the multiplet e.g. coupling to two different spin
½ nuclei with significantly different coupling constants will lead to a doublet of doublets
(abbreviation: dd). Note that coupling between nuclei that are chemically equivalent (that is,
have the same chemical shift) has no effect of the NMR spectra and couplings between nuclei
that are distant (usually more than 3 bonds apart for protons in flexible molecules) are usually
too small to cause observable splittings. Long-range couplings over more than three bonds
can often be observed in cyclic and aromatic compounds, leading to more complex splitting
patterns.
For example, in the proton spectrum for ethanol described above, the CH3 group is split into a
triplet with an intensity ratio of 1:2:1 by the two neighboring CH2 protons. Similarly, the CH2
is split into a quartet with an intensity ratio of 1:3:3:1 by the three neighboring CH3 protons.
In principle, the two CH2 protons would also be split again into a doublet to form a doublet of
quartets by the hydroxyl proton, but intermolecular exchange of the acidic hydroxyl proton
often results in a loss of coupling information.
Coupling to any spin ½ nuclei such as phosphorus-31 or fluorine-19 works in this fashion
(although the magnitudes of the coupling constants may be very different). But the splitting
patterns differ from those described above for nuclei with spin greater than ½ because the spin
114
quantum number has more than two possible values. For instance, coupling to deuterium (a
spin 1 nucleus) splits the signal into a 1:1:1 triplet because the spin 1 has three spin states.
Similarly, a spin 3/2 nucleus splits a signal into a 1:1:1:1 quartet and so on.
Coupling combined with the chemical shift (and the integration for protons) tells us not only
about the chemical environment of the nuclei, but also the number of neighboring NMR
active nuclei within the molecule. In more complex spectra with multiple peaks at similar
chemical shifts or in spectra of nuclei other than hydrogen, coupling is often the only way to
distinguish different nuclei.
Second-order (or strong) coupling
The above description assumes that the coupling constant is small in comparison with the
difference in NMR frequencies between the inequivalent spins. If the shift separation
decreases (or the coupling strength increases), the multiplet intensity patterns are first
distorted, and then become more complex and less easily analyzed (especially if more than
two spins are involved). Intensification of some peaks in a multiplet is achieved at the
expense of the remainder, which sometimes almost disappear in the background noise,
although the integrated area under the peaks remains constant. In most high-field NMR,
however, the distortions are usually modest and the characteristic distortions (roofing) can in
fact help to identify related peaks.
Second-order effects decrease as the frequency difference between multiplets increases, so
that high-field (i.e. high-frequency) NMR spectra display less distortion than lower frequency
spectra. Early spectra at 60 MHz were more prone to distortion than spectra from later
machines typically operating at frequencies at 200 MHz or above.
Magnetic inequivalence
More subtle effects can occur if chemically equivalent spins (i.e. nuclei related by symmetry
and so having the same NMR frequency) have different coupling relationships to external
spins. Spins that are chemically equivalent but are not indistinguishable (based on their
coupling relationships) are termed magnetically inequivalent. For example, the 4 H sites of
1,2-dichlorobenzene divide into two chemically equivalent pairs by symmetry, but an
individual member of one of the pairs has different couplings to the spins making up the other
pair. Magnetic inequivalence can lead to highly complex spectra which can only be analyzed
by computational modeling. Such effects are more common in NMR spectra of aromatic and
other non-flexible systems, while conformational averaging about C-C bonds in flexible
molecules tends to equalize the couplings between protons on adjacent carbons, reducing
problems with magnetic inequivalence.
Correlation spectroscopy
Correlation spectroscopy is one of several types of two-dimensional nuclear magnetic
resonance (NMR) spectroscopy or 2D-NMR. This type of NMR experiment is best known by
its acronym, COSY. Other types of two-dimensional NMR include J-spectroscopy, exchange
spectroscopy (EXSY), Nuclear Overhauser effect spectroscopy (NOESY), total correlation
spectroscopy (TOCSY) and heteronuclear correlation experiments, such as HSQC, HMQC,
and HMBC. Two-dimensional NMR spectra provide more information about a molecule than
one-dimensional NMR spectra and are especially useful in determining the structure of a
molecule, particularly for molecules that are too complicated to work with using one115
dimensional NMR. The first two-dimensional experiment, COSY, was proposed by Jean
Jeener, a professor at Université Libre de Bruxelles, in 1971[citation needed]. This experiment was
later implemented by Walter P. Aue, Enrico Bartholdi and Richard R. Ernst, who published
their work in 1976.[2]
Solid-state nuclear magnetic resonance
A variety of physical circumstances does not allow molecules to be studied in solution, and at
the same time not by other spectroscopic techniques to an atomic level, either. In solid-phase
media, such as crystals, microcrystalline powders, gels, anisotropic solutions, etc., it is in
particular the dipolar coupling and chemical shift anisotropy that become dominant to the
behaviour of the nuclear spin systems. In conventional solution-state NMR spectroscopy,
these additional interactions would lead to a significant broadening of spectral lines. A variety
of techniques allows to establish high-resolution conditions, that can, at least for 13C spectra,
be comparable to solution-state NMR spectra.
Two important concepts for high-resolution solid-state NMR spectroscopy are the limitation
of possible molecular orientation by sample orientation, and the reduction of anisotropic
nuclear magnetic interactions by sample spinning. Of the latter approach, fast spinning around
the magic angle is a very prominent method, when the system comprises spin 1/2 nuclei. A
number of intermediate techniques, with samples of partial alignment or reduced mobility, is
currently being used in NMR spectroscopy.
Applications in which solid-state NMR effects occur are often related to structure
investigations on membrane proteins, protein fibrils or all kinds of polymers, and chemical
analysis in inorganic chemistry, but also include "exotic" applications like the plant leaves
and fuel cells.
NMR spectroscopy applied to proteins
Main article: Protein nuclear magnetic resonance spectroscopy
Much of the recent innovation within NMR spectroscopy has been within the field of protein
NMR, which has become a very important technique in structural biology. One common goal
of these investigations is to obtain high resolution 3-dimensional structures of the protein,
similar to what can be achieved by X-ray crystallography. In contrast to X-ray
crystallography, NMR is primarily limited to relatively small proteins, usually smaller than 35
kDa, though technical advances allow ever larger structures to be solved. NMR spectroscopy
is often the only way to obtain high resolution information on partially or wholly intrinsically
unstructured proteins. It is now a common tool for the determination of Conformation
Activity Relationships where the structure before and after interaction with, for example, a
drug candidate is compared to its known biochemical activity. Proteins are orders of
magnitude larger than the small organic molecules discussed earlier in this article, but the
basic NMR techniques and some of the NMR theory also applies. Because of the much higher
number of atoms present in a protein molecule in comparison with a small organic compound,
the basic 1D spectra become crowded with overlapping signals to an extent where direct
spectra analysis becomnes untenable. Therefore, multidimensional (2, 3 or 4D) experiments
have been devised to deal with this problem. To facilitate these experiments, it is desirable to
isotopically label the protein with 13C and 15N because the predominant naturally occurring
isotope 12C is not NMR-active, whereas the nuclear quadrupole moment of the predominant
naturally occurring 14N isotope prevents high resolution information to be obtained from this
nitrogen isotope. The most important method used for structure determination of proteins
116
utilizes NOE experiments to measure distances between pairs of atoms within the molecule.
Subsequently, the obtained distances are used to generate a 3D structure of the molecule by
solving a distance geometry problem.
117
Laboratories of Organic Chemistry
Work A
Cleaning of organic substances by crystallization
ROLE: Selecting suitable solvent for crystallization and recrystallized unknown organic
substances.
OBJECTIVE: To learn the correct technique for crystallising substances.
PRINCIPLE OF WORK: See Section 2.4 Add:
Area of life, and brief description of the crystallization properties of solvents selected for
crystallization
WORKING PROCEDURE
1. Selection of a suitable solvent for crystallization: Approximately 0.1 grams of a model
substance for crystallization is gradually mixed in tubes with 0.5 to 1 ml solvent, room
temperature (dropwise addition) and is gradually heated to boiling.
The solvent is suitable for crystallization: if the substance is dissolved in 1 ml of solvent at room temperature or under moderate
heating - if the substance is dissolved by boiling or by adding another 2 ml solvent - if the
substance is dissolved at the boiling point solvent, but after cooling exclude crystals,
respectively. is not precluded by strong supercooling (ice-NaCl-water), shaking the walls peel
rod tube below the surface of the solution
The solvent is suitable for crystallization: - if the substance is in the hot solvent-soluble and
cooling the solution, the crystals only where the substance is well soluble at room
temperature in a solvent and a minimum, may be the crystallization of this sample use a
mixture of these solvents. Solvents must be miscible with each other.
2. Build your apparatus as shown.
Fig. 1 Apparatus for the crystallization of organic substances from different solvent A - B
electric Bank - the condenser (Liebig, ball) C - D Bath - cooker
3. Practical implementation of the crystallization residue tested sample is weighed (too large
crystals are broken), transferred to a flask and add a small amount (about 10 ml) of the
selected solvent. In the crystallization of water only built on a boiling beaker. Content Bank
(after adding boiling chips) is heated (usually in a water bath), stirring occasionally until
boiling. The water level in the bath should be taking about 0.5 cm below the surface of the
solution in the bank to its walls exclude crystallized substance. If the substance in that
quantity of solvent at the boiling point to dissolve, add more gradually through the cooler
(measured) amount of solvent to obtain a saturated solution at boiling point. For reasons of
practical implementation of the crystallization is recommended that this solution slightly
diluted The de-inking, clean and clarifying solution (after it cooled very marginal) to him
Rida charcoal (1 / 50 to 1 / 20 weight of the sample). P contents of the flask boil 2-3 minutes.
Hot is filtered (through a folded filter) into a beaker and allowed to cool gradually. If that
does not exclude the filtrate from the solid, the filtrate vessel is immersed in a cooling bath
(ice-NaCl-water), scratch beneath the surface of vessel wall solution, esp. be used other ways
of crystallization (Chapter 2.4.3). r precipitated crystals are separated from the filtrate by
suction (the residue in the flask is washed first share fitr), washed on filter with cold solvent
and dried in air. L pieces over and consider the calculate the force of crystallization. If the
substance in the amount of solvent to dissolve at the boiling point, add progressively cooler
over other (measured) amount of solvent to obtain a saturated solution at boiling point. For
reasons of practical implementation of the crystallization is recommended that this solution
slightly diluted If it is necessary to crystallize the substance from a mixture of solvents
proceed as follows: For almost boiling solution of the substance in a small amount of solvent
in which the substance dissolves well, and gradually added to a permanent haze hot solvent in
which the substance is insoluble or poorly soluble. Turbidity to remove the heating, or adding
a few drops of the first reagent. Next, we proceed as in the above example by adding
activated charcoal and subsequent laboratory operations as described. R precipitated crystals
are separated from the filtrate by suction (the residue in the flask is washed first share fitr),
washed on filter with cold solvent and dried in air . L pieces over to consider and calculate
the force of crystallization. If the substance in the amount of solvent to dissolve at the boiling
point, add progressively cooler over the other (measured) amount of solvent to obtain a
saturated solution at boiling point. For reasons of practical implementation of the
crystallization is recommended that this solution slightly diluted.
4. Own knowledge at work:
Solubility of substances in different solvents
+ = Substance is soluble
- = insoluble substance
5. Evaluation work
Work B
Separation of organic substances by distillation at atmospheric pressure
ROLE: Separation of a model mixture consist of components with different boiling points.
Aim: To obtain data on boiling single fractions, the best to separate the individual
components, remains a distillation curve.
PRINCIPLE OF WORK: see chapter 2.5.1 and 2.5.3 Add: Basic terms:
Definition and mathematical expression of the parameters affecting the efficiency of
separation: see chapter 2.5.1 and 2.5.3 Complete: Basic concepts:
WORKING PROCEDURE:
1. Assemble the distillation apparatus as shown (Fig. 2)
2. Distillation flask to fill 2 / 3 (up to 3 / 4) volume of the sample. Add 2-3 boiling stones,
which will prevent bumping boil.
3. Injected into the water cooler and we start to warm up carefully (if observed var secret,
never Do not dispose of boiling stones in superheated liquids. We must remove the heat and
wait until the liquid has cooled, and then add boiling stones and continue heating. Otherwise,
the liquid contents can surge, thermometer hit of equipment and cause injury and fire)
4. When the sample begins to distil, takes the spirit after 2 ml and shares for each share
apiece its boiling point. Of
5 The record also construct a distillation curve as the dependence of boiling bjeme. On the
6th The chart TV subtract individual components and medzifrakcií NB.: A.) An important
parameter influencing the quality of the separation of components is heat. Must be a slow,
steady and controllable. To heat the distilled samples will be used heating nest, where the
temperature is gradually added under the lights on the nest. At the beginning of the heat so
we choose to give us light lit up the heating nest, light goes out once again add to the warmup, but just enough to light lit up again and so we proceed until the entire volume of distilled
evydestiluje samples. N
b.) distillatively one component of the mixture to a decrease in temperature on the
thermometer in the cooler Claisen, slowing and stopping the distillation. This applies only if
the force is sufficiently high and cutting fluids in the mixture forming azeotrope see Chap.
2.5.4). (C) distilled off after the second component of the mixture can become the third
component has such a high boiling point that exceeds the temperatures reached in the
column. In this case the distillation is interrupted, the bath was removed, the flask is cooled
and the apparatus was removed by puncture column. The paper then continues with a
simplified apparatus.
Schematic diagram of apparatus:
Fig. 2 Apparatus for fractional distillation under atmospheric pressure - flask B - puncture
column C - Claisen condenser D - E thermometer - measuring cylinder F - heating nest
EVALUATION OF THE TRIAL:
WORK C
Cleaning substances by distillation under reduced pressure
TASK: distillation of a sample with high boiling point components.
OBJECTIVE: To build the apparatus for distillation of organic substances under reduced
pressure. Capture a fraction of constant boiling point and using a nomogram to determine the
boiling temperature of the collected fractions and atmospheric pressure. Z
WORKS PRINCIPLE:i See chapter 2.5.1 and 2.5.2.2 lowering the pressure of the
rectification will reduce the boiling point of components with high boiling points, preventing
degradation of substances, and also escape the health damaging fumes in air. Distillation
under reduced pressure distillation required in comparison simple changes in an apparatus .
Basic concepts:
Sources vacuum: Safety at work: Due to work with glass sets of the apparatus under vacuum
is a real danger of implosion. Therefore throughout the work to protect your eyes or glasses.
face shield.
WORKING PROCEDURE: 1 Determine the approximate boiling point of an unknown
sample of our machinery to measure the boiling point. To the tube for that purpose by the
Pasteur pipette is spread over 0.5 cm samples, which you insert into the capillary with a
sealed end upwards. Temperature range of the device is set from 120 to 210 ° C and the
temperature gradient of 20 ° C (at a time can be measured two Samples). Detailed procedure
for measuring the BP, see the work of E. 2 Build the drawing apparatus for distillation under
reduced pressure (Fig. 3). In Tavannes forget all ground joints carefully cleaned and painted
in their fat. With the third Put on your goggles or face shield and throughout their distillation
immediately.
4. Turn on the vacuum pump and sealing apparatus investigate "dry" without pouring
samples. Failure to reach the desired pressure reduction is controlled by sealing apparatus
away from the pumps to apparatus the fifth After examining the tightness of bank fill up. to
half the volume of sample 6. Turn on the vacuum pump and observe the pressure drop gauge.
After reaching the desired vacuum begin with heating bath. Using the nomogram and around
the TV set device, we will determine at what temperature should distil our sample with a
pressure gauge shows us. Then set the bath temperature about 30 ° C or more. If the sample
of non-distilled after reaching the set temperature in the bath, gradually adding warm-up in
the bath (after 5 to 10 ° C) until the sample begins to distil.
7. During the distillation temperature monitor and check the pressure. After stabilization of
temperature and pressure Data write. S 8th After distillation heating is switched off, remove
the oil bath apparatus and gently aerate. 9th Turn off the vacuum pump 10. The resulting data
back can be determined from a monogram designed t our experimental samples.
Schematic diagram of apparatus:
Fig. 3 distillation apparatus under reduced pressure - magnetic stirrer, oil bath,
thermometer B - flask with stirrer C - D Claisen condenser - pressure reducing valve plug or
E - Thermometer F - G Alonzo vacuum - Bank of alcohol consumption - connect to the pump
The evaluation experiment: Approximate determination of BP at atmospheric pressure:
Expected BP under reduced pressure:
H donate obtained in the distillation under reduced pressure: values calculated from the
monogram:
WORK D
Steam distillation and extraction
TASK:
By steam distillation divide mixture of xylene and aniline.
OBJECTIVE: To use the apparatus for steam distillation and know it to practical use in
conjunction with a simple chemical reaction. Determine the presence of xylene and aniline
mixture model and manage methodology for extraction.
The PRINCIPLE OF WORK: see chapter 2.5.4. Steam distillation 2.7 Extraction 2.7.1.
Extraction of particulate matter 2.7.2. Extraction fluid
WORKING PROCEDURE:
1 Assemble the apparatus as shown in the steam distillation (Fig. 4)
2. We have a sample that is a model mixture of xylene and aniline. The two compounds are
insoluble in water, shall not be mixed with water, have high tv, that are suitable for steam
distillation. Our task is to separate them to each other. Before processing, we measure the
volume of sample and place it in the distilling flask.
3 Dilute hydrochloric acid (1:1), using INDICATOR PAPER acidify sample to pH 2 Xylem
with hydrochloric acid (HCl) reaction, but gives the lowland HCl anilíniumchlorid. And
Anilínium chloride is a crystalline substance in water-soluble, which doesn’t evaporate with
the steam. This allows the separation of xylene.
4. Distillation flask with the sample attached to the apparatus to an acidic environment with
steam distilled xylene by distillation receiver. Aniline in the form Aniliniumchloridu
remained in the distilling flask dissolved in water. N 5th Distillation flask and cooled slightly
by adding conc. NaOH solution (may be added solid NaOH) distillation residue basified to
pH 11 to release the aniline salt. z
6. In steam distillation continued until alkaline environment distilled into a second master
aniline. D 7 Both distilled saturated NaCl solutions, the resulting layer is separated in a
separating funnel. Of the remaining layers of water separately extracted with xylene and
aniline in ether. The simplest form of extraction is mixing and separating, it is done in a
separating funnel. Before extraction is necessary to examine the tightness of the stopper and
tap the funnel. If necessary, tap gently clean it again and then top with grease. Aqueous
solution of the substance to extract transferred to a separating funnel and add it to the
extraction solvent in an amount of 1 / 3 the volume of extracted solution (in our case only 10
ml ether). Funnel extraction hold with both hands. With one hand, adhering to the stopper and
the second tap. Mixture in the funnel shacked slightly, then turn the tap funnel topand
opening the resulting pressure will be released. Shake for 1-2 seconds then back in balance
and pressure. Repeat the process until no further stops in the funnel formed pressure. Content
separating funnel even then thoroughly shaken for a few minutes to contact the two phases
was the most perfect. Funnel with a relaxed stopper mounted in rack and let stand until the
publication of two sharply defined layers. The bottom layer is deleted from the dropping
funnel into a beaker and pour the top layer of dry-mouthed funnel into Adobe. If necessary,
the extraction is repeated with fresh portions of solvent. N 8th The combined organics
transferred to a dry flask, add the appropriate amount of drying agent (anhydrous Na2SO4),
and the bank will conclude with occasional stirring ECHAM stand 5 to 10 min. After drying
agent, filtered off. N9. Build a simple distillation apparatus at atmospheric pressure (p. 22)
with a magnetic stirrer and oil bath 10. First set the bath temperature to distillatively ether (tv
ether 37 ° C) and after ydestilovaní raise the temperature of the bath distillatively xylene
(xylene tv 139-140 ° C). At 11 Aniline processed by analogy with the difference that the
ether evaporated on a rotary evaporator and pass on aniline as the raw product.
Schematic diagram APPARATUS
Fig. 4 Apparatus for steam distillation A - B nest heating - steam generator C - core
tube with olive and D - extension to rain. By steam E - F flask - Liebig condenser G - Alonzo
H - collecting vessel
ASSESSMENT AND RECORD ATTEMPT own observations: C Elkova volume
model mixture in ml: volume in ml distilled xylene About bjem aniline after evaporation of
ether in ml: The ratio of both components in the mixture:
WORK E
Determination of physical constants and chromatography
ROLE: a.) Determine the melting point of solid b.) Determine the boiling point of liquid
unknown sample c.) analyzed by thin layer chromatography and mixture model to determine
the standards of quality organic ingredients
OBJECTIVE: a.) To master the basic methods for the determination of physicochemical
constants characterizing the chemical compound. B.) To master basic techniques of thin layer
chromatography
PRINCIPLE OF WORK: see chapter 2.8, 2.8.1, 2.8.2, 2.8.3, 3.1 and 3.2
The melting and boiling point are estimated by Büchi B-540th
Melting point measurement
Procedure P: Preparing the sample to the melting temperature: Granulated crystalline and
non-homogeneous samples were first homogenized in a mortar. Capillary for the
determination of tt to fill up 4-6 mm. To obtain comparable results it is important that the
capillary filled to the same amount, and the sample was compact. Sample is obtained by
tapping the capillary on a hard surface A
Approximate Melting temperature:
1 Turn on your device and determine the approximate melting point of our unknown sample.
Temperature range of the device is set from 80 to 200 ° C and the temperature gradient of 20
° C / min. For both samples an approximate indication tt do at once. Detailed description of
settings parameters is attached to the device.
2. Measurement start pressing START. The display device will appear graphic design during
measurement, which informs about the current phase measurement.
3 The first phase of measurement is Warm-up phase, when the device is heated to the starting
temperature (SETPOINT) from which we pursue our sample, in this case 80 ° C. Reaching
this temperature and start the next phase of the device notified beep.
4 After the beep, enter one of the samples at the respective positions of the melting
temperature of the device (middle three positions) and press START.
5. The next stage is measured by itself t temperature rises at a rate, what the temperature
gradient was determined at the beginning. In this case, 20 ° C / min. Through a magnifying
glass in the monitor device embedded with capillary samples. When the substance begins to
melt, press the corresponding button, with which the position of the first sample in a
capillary. When the sample is completely melted, press the button (with the position of the
sample) for the second time. Subsequently press STOP button. If you press Stop before it
reaches the maximum temperature (MAXPOINT) is necessary to press this button twice, the
device began to cool and the initial temperature.
6. After pressing STOP, the display appears at approximately the melting temperature of our
samples, which we will record.
The precise determination of melting point:
7. If we can determine the temperature approaching melting point, the whole measurement is
repeated so that the capillary preparing two melting temperature of one sample and
instrument parameters set so that the initial temperature (SETPOINT) will be about 50 to 10 °
C lower than the approximate determination of the melting point , temperature gradient set to
2 ° C. / min and maximum temperature (MAXPOINT) is automatically set to 15 º C above
the initial, the temperature is only confirmation. Make sure that the height of the sample in
the capillary was the same and compact
8. Furthermore, longer follow the above procedure and the same way we set the melting point
of the second sample.
Determination of BOILING TEMPERATURE
Determination of boiling by Silowopova.
Procedure : Approximate boiling point :
1 first, pulled out three thin capillaries about 10 to 12 cm long, which sealed a oniec.
2 Unknown liquid sample is placed in a microfuge up to 5-10 mm and immersed it into a
capillary to the upper end sealed. (Use a Pasteur pipette for easy filling microfuge liquid.)
3. Turn on the device to measure temperature and determine the approximate boiling point of
our unknown sample. Temperature range of the device is set from 40 to 150 ° C and the
temperature gradient of 20 ° C / min (at a time can be measured two samples, so an
approximate indication bv students can do two at once). Detailed description of the parameter
settings when the device is attached
4. Measurement start pressing START. The display device will appear graphic showing
during measurement, which informs about the current phase measurement.
5 The first phase of measurement is Warm-up phase, when the device is heated to the
starting temperature (SETPOINT) from which we pursue our sample, this case 40 ° C.
Achieving this temperature and start the next phase of the device notified beep.
6. After the beep, place a sample on one of the positions for measuring the boiling
temperature of the device (the two most extreme position) and press START. In the 7th The
next stage is determined BP itself temperature rises at a rate, what the temperature gradient
was determined at the beginning. In this case, 20 ° C / min. Through a magnifying glass
Fig. 6 Determination of boiling point
The device monitor embedded samples. The boiling point is reached when bubbles begin to
escape from the bottom of the capillary rapidly and continuously (see Fig. 6).
Fron the disply read the aproximate point
boil one and the second sample and then press STOP button. If you press Stop before it
reaches the maximum temperature (MAXPOINT), it is necessary to press this button twice,
the device began to cool initial temperature. P P as to the precise determination of boiling
point:
8. If we determine the approximate boiling point of the whole measurement is repeated so
that the preparing two microfuge our sample parameters and set the device so that the initial
temperature (SETPOINT) will be about 5 degrees lower than some specified point, boiling
point, the temperature gradient set to 2 ° C / min and maximum temperature (MAXPOINT) is
automatically set to 15 ° C higher than the initial, the temperature has only confirmed. Make
sure that the Height of liquid in the tubes was the same.
9 Furthermore, longer follow
THIN-LAYER CHROMATOGRAPHY
The qualitative analysis of the model will use a mixture of commercial thin-layer
chromatography plates for chromatography with SiO2 layer formed. The composition of the
sample can be determined for standard delivery expenses. Of operation: the above procedure.
Working procedure:
1. Prepare a solution of the sample examined in that it dissolved in 0.5 ml of ethanol
2. On silufolovej plate using a ruler and a pencil to lightly outline the regions start at a
distance of about 1.5 cm from the bottom. The distance between the sample application from
the edges of the plate should be about 0.5 to 1 cm
3. Using a fine glass capillary Streak individual samples plate so that the spots not greater
than 2-3 mm diameter. Each standard is applied special capillary.
4. Prepare a chromatography chamber, in our conditions, we will serve the beaker covered
with watch glass, which is inserted a strip of filter paper placed in a beaker and tenách after
reaching its peak.
5 Pour it into the developing solvent mixture so that the water level was about 0.5 cm from
the bottom.
6. Chromatogram of sample application put in a chromatographic chamber so that the tart
was above the solvent.
7. When rising, the solvent reaches a distance of about 1 cm from the top, chromatogram out
of the chamber, mark the solvent front in pencil (the interface between wet and dry part of the
plate) and chromatogram let air-dry
8. Separated substances in our sample are colored spots on the chromatogram without visible
detection. From the chromatogram of visual evidence of the composition of the samples and
confirm dentitu individual components of the standards by comparing their R and F values
9. RF retarding factor is calculated by the formula:
RF = a / b
a = distance from start center spots in cm
b = distance of solvent front from the start in cm
10. When we worked exactly as the standard RF and RF spots in the sample are equal.
Fig. 7 Chromatogram
A - Start
B - Solvent front
Results VALUATION:
Observations on the determination of the melting temperature: melting point samples: Sample
# 1 Sample # 2
1. .................... 1. ....................
2. .................... 2…………………….
Observation in determining the boiling point: Temperature boiling samples: Pressure:
....................... Boiling Point:
1. ....................... 2nd .......................
E VALUATION thin layer chromatography:
Drawing chromatograms:
2
1.5-Diphenyl-1 ,4-pentadiene-3-one (dibenzalacetón) is prepared by condensation of
benzaldehyde with acetone in the presence of bases.
Necessary chemicals: 2.65 g benzaldehyde (2.5 ml, 0.25 mol) acetone 0.75 g (1.0 ml, 0.013
mol) ethanol, 20 ml sodium hydroxide
Workflow:
The flask with a magnetic stirrer, mix 25 ml cold 10% solution of NaOH with 20 ml of
ethanol. Stirring on a magnetic stirrer are added sequentially 2.5 ml distilled mixture of
benzaldehyde and 1.0 ml of acetone. For 15 min. maintain the reaction mixture with stirring
at room temperature. The reaction mixture was cooled in a water bath, the precipitated
product filtered through a Buchner funnel and washed with cold water until neutral washings.
The crude product is purified by crystallization from ethanol with addition of activated
charcoal. We obtain yellow crystals with mp ~ 112 ° C.
N-Benzylidénanilín (benzanilín)
is prepared by condensation of benzaldehyde with aniline.
Necessary chemicals: benzaldehyde 3.2 g (0.03 mol) aniline 2.8 g (0.03 mol) ethanol, 5 ml
Workflow:
Banks to place a 3.2 g of benzaldehyde. Within 15 minutes, stirring constantly to it gradually
add 2.8 g distilled aniline. The reaction is exothermic. After addition of aniline reaction
mixture pour into a beaker and add to it 5 ml of ethanol. Cooling the reaction mixture in an
ice bath to exclude the product crystals, which evacuated and dried. The crude product
crystallized from ethanol. Tem of product is 52 ° C
Brombutan
is prepared by the action of a mixture of sodium bromide and sulfuric acid to butane-1-ol.
Necessary chemicals:
butane-1-ol 11.2 g (0.15 mol) NaBr 17.8 g (0.17 mol) of sulfuric acid concentration. 15 ml
NaHCO3, Na2SO4
Preparation:
The Bank NaBr Dissolve 17.8 g in 20 ml of water and add to it distilled butane-1-ol. Stirring
slowly add 15 ml conc. sulfuric acid when the reaction temperature rises above 90 ° C,
contents of the flask cool down in a water bath. After adding the whole amount, we will give
the bank a magnetic stirring bar and reflux with continuous vigorous stirring the mixture is
heated in an oil bath at t reaction mixture (about 130 ° C in bath) for 1 hour. If we do not
work in the hood, we modify the apparatus so that the unreacted bromo-hydrogen leaking
into the air. On the upper end of the radiator hose to water the funnel, the extended part is
immersed in a beaker of water, just below the surface. After an hour of heating contents of
the flask cool down, reversing the downward and the mixture distilled until oily droplets of
the crude product (about 30 min). Destilávlejeme into a separating funnel, add to it 30 ml of
ether and shaken obsalievika well. Funnel mounted on the stand Let stand, sour appears sharp
interface between layers. Separate the ether layer gradually in a separating funnel Wash the
water, conc. HCI (2-3 ml), water, 5% sodium bicarbonate solution and finally IR
again with water. For use after washing 10 ml of water and other reagents except conc. HCl.
After separating the aqueous layer éterickpodiel Dry the small amount of crack. Sodium
sulphate is filtered to Claisen distillation flask. After the first completisation of apparatues
ether distilled from the reaction mixture at given temperature oil bath and subsequently raise
the temperature of bath and we distillate the product. We capture share in the 100 to 103 ° C.
4-Phenyl-3-butene-2-one (benzalacetón)
Preparing Claisen-Schmidt reaction of benzaldehyde with acetone.
Necessary chemicals:
benzaldehyde 4.2 g (4.0 ml, 0.04 mol) acetone 6.7 g (8.5 ml, 0.115 mol) NaOH 10%
Solution for crack. Na2SO4, ether (diethyl ether), HCl
Workflow:
The round bottom flask, mix 4 ml distilled benzaldehyde, 8.5 ml of acetone and 1 ml of 10%
NaOH. Contents of the flask while stirring on a magnetic stirrer was heated in an oil bath at
25-30 ° C for 1.5 hours. Then the solution is acidified with dilute HCl 1:1 to the indicator
paper and pour into a separating funnel. The organic layer is separated, the aqueous layer
extract 5-10 ml ether. Add to extract the organic layer. Wash the combined organic layers
with a little water and dried crack. sodium sulfate. Drying agent was filtered, the filtrate
distilled ether and distilled under reduced pressure lujeme. We capture fraction distilling at
133-134 ° C and pressure 2.13 kPa, or at a temperature of 100-108 ° C and pressure 0:26 kPa.
Properly distilled benzalacetón solidifies and has mp 38-39 ° C. Crystallization from
petroleum ether mp increased to 42 ° C.
2-nitrophenol and 4-nitrophenol
They are prepared phenol nitration with dilute nitric acid. After reaction, the 2-isomer is
distilled from the reaction mixture with water vapor and 4-isomer remains in the distillation
residue.
Necessary chemicals:
Phenol 9.4 g (0.1 mol)
HNO3 19.0 g (14.5 ml, 0.3 mol)
Preparation:
Combine 14.5 ml HNO3 with 40 ml of water. To establish a small beaker 9.4 g of molten
phenol and add to it 2 ml of water to remain liquid. (Phenol liquefies immersing the container
in which it is located in a warm water bath). Prepared dilute nitric acid to pour 500 ml flask
and add 2 ml of phenol. Components begin to react, resulting dims and heating solution.
Phenol add further so that the reaction temperature remained in the game-destroying 45-55 °
C. After adding the whole amount of phenol (about 5 min), the contents of the flask cooled,
the mixture of nitrophenol resin was washed with 2x100 ml of ice-cold water to remove acid
residues. Oily layer containing nitrate next product also decomposition products of oxidation,
is subjected to steam distillation. Distillation is finished after separating the 2-isomer share
(so we find that
cooler has condensation 2-nitrophenol and distilled water only). If the 2-isomer (mp 45 ° C)
in the distillate solidifies, it is cool spirit. Conversely, if already starts to solidify in the
condenser during the distillation, it is occasionally shut down the supply of cooling water.
The alcohol 2-nitrophenol evacuated between filter paper and dried thoroughly and complete
drying in air. 4-nitrophenol evaporate with the steam and remained in the distillation flask.
The contents of the flask charcoal, warm up to boiling and filtered through a folded filter.
Beaker containing 400 ml plunge into ice bath. Pour into it a few ml of hot filtrate. Solution
was stirred until the rod is eliminated by the crystals of 4-nitrophenol. Add another portion (2
ml) and the filtrate again quickly blended. Thus the whole process a filtrate. Excluded
odsajeme crystals and dried. Tt 4-nitrophenol
Cooler has condensation 2-nitrophenol and distilled water only).
If the 2-isomer (mp 45 ° C) in the distillate solidifies, it is cool spirit. Conversely, if already
starts to solidify in the condenser during the distillation, it is occasionally shut down supply
Fenylamid cN-acetic acid (acetanilide) is prepared by condensation of aniline with acetic
anhydride.
Necessary chemicals:
aniline 4.6 g (4.5 ml, 0.05 mol)
acetic anhydride 7.2 g (6.6 ml, 0.07 mol)
activated charcoal
Working procedure: The Erlenmeyer flask mix aniline with 40 ml of water if the suspension
under vigorous stirring often added acetic anhydride. After adding all the acetic anhydride,
the reaction was shaken for 10 min, the reaction can be observed spontaneous secretion of
crystalline product. On completion of the reaction the reaction mixture was allowed to stand
for 30 min. Excluded crystals on a Buchner funnel, filter cake from the mother liquor and
print it Wash the can with a little cold water. The next reaction use 5 grams of crude
acetanilide well washed and the residue crystallized from water using activated carbon. In the
event of dissolution in hot water to create a layer of oily, it is necessary to add small doses of
hot water while stirring rod until the layer disappears. Product was dried at room temperature
(mp = 113-114 ° C)
Note: Acetic anhydride is irritating to eyes and skin. We work in the hood with protective
gloves.
4-nitroaniline, 4-nitroacetanilid
Preparing nitration of acetanilide, followed by acid hydrolysis intermediate.
Necessary chemicals:
acetanilid 4 g (0.03 mol)
HNO3 (65%) 2.9 g (2.2 ml, 0.03 mol) conc
. H2SO4, conc. HCl, NH3 (aq)
Working procedure: The Erlenmeyer flask mix 5 g of crude acetanilide (See note.) With
conc. H2SO4 (9 ml). After the dissolution of almost all the contents of the flask cooled
acetanilide and carefully added dropwise nitration mixture prepared by carefully mixing 2.2
ml 65% HNO3 with 2.2 ml conc. H2SO4. The reaction mixture vigorously stirred. Nitration
maintain the temperature below 35 ° C. After adding the entire volume of the nitration
mixture flask from the cooling bath and let stand at room temperature 10 minutes. Then pour
the reaction mixture to quadruple the volume of ice and water. 4-nitroacetanilid precipitated
after mixing Wash the filtered and little water. Intermediate wet transferred to the boiling
flask, add 30 ml water and 20 ml conc. HCl, fit a reflux condenser and the reaction mixture is
heated to the boiling sky bath 30 minutes. The resulting solution pour into a beaker with 30 g
of ice. 4-Nitroaniline isolate the mixture basified with ammonia water. The precipitated 4nitroaniline is evacuated on a Buchner funnel and dried. The product after crystallization
from ethanol forms yellow needles with mp
Note:
Raw acetanilide use of the previous reaction. It is a raw and wet acetanilid, so use it in
excess (5 g), approximately 4 g of pure, dry acetanilide.