INDUSTRIAL CHEMISTRY
THE PRODUCTION OF ETHENE
Many reactions proceed too slowly under normal conditions of temperature and pressure.
Some reactions proceed at very fast rates but produce very small quantities of product.
In order to maximise profits and to reduce costs to consumers, industries aim to minimise
the costs of industrial processes. This involves a consideration of yields and rates.
The reactions that cause greatest concerns to industries include:

Reactions with low equilibrium constants. Low equilibrium constants result in low yields
of product.
For example: The production of ammonia, nitric acid and sulfuric acid.

Reactions with slow reaction rates.

Exothermic processes.
Lower temperatures are required to increase yields, however, this results in slower
reaction rates. Industries will generally employ lower temperatures and use catalysts to
compromise on the decreased reaction rates.
For example: The production of sulfuric acid, nitric acid and ammonia.
THE GREATEST COSTS ASSOCIATED WITH
INDUSTRIAL PROCESSES INCLUDE:

The costs of raw materials.
To maximise profits, yields are maximised.

Generating high pressures.
Industries avoid using extremes of pressure to maximise the yield of product as high
pressures require very powerful and expensive pumping equipment together with
vessels that can withstand the high pressures. These added costs may not justify the
use of higher pressures, and in many cases, it is more profitable to lower the pressure
and obtain a lower yield of product.

Generating high temperatures.
Industries decrease these costs by using heat evolved in exothermic processes to fuel
other reactions in the plant.

The time required to produce the product.
Rates are increased by using appropriate catalysts.
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Unit 4 Chemistry – The Production of Ethene
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Note:
Industries use processes that use less energy to decrease costs and preserve finite sources.
For example:

The heat produced in one stage of a chemical process is frequently recycled and used
to heat other stages of the process.

The heat exchangers which remove and recycle heat operate 24 hours per day so that
the enormous costs associated with warming up equipment are avoided.

Industries often exist as integrated complexes i.e. A collection of related industries are
located within a close proximity of one another. The by products of one industry
(eg. heat) can then be used as a raw material for another industry, reducing wastage,
environmental pollution and costs.

If sufficient thermal energy is produced, it may be possible to convert it to electrical
energy for use in the plant. In some cases, excess supplies are sold to an electricity
supply grid.
MAXIMISING YIELDS
Industries will attempt to maximise yields by manipulating Le Chatelier’s Principle.
Yields may be cost effectively increased by changing the following reaction conditions:

Adding an excess amount of the cheaper reactant.

Periodically removing products.

Changing the temperature and pressure of the reaction system.
MAXIMISING RATES
As time has a significant impact on the cost of products and staff, industries will also attempt
to maximise the speed or time taken to produce a product.
Conditions that favour fast reaction rates include:

High reactant concentrations.

High pressures.

High temperatures.

High surface areas.

Use of catalysts.
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Unit 4 Chemistry – The Production of Ethene
Page 2
FACTORS INFLUENCING THE METHOD IN WHICH
A CHEMICAL IS PRODUCED
The operating conditions and any compromises that are required are determined by running
small scale experiments, and choosing the set of conditions that will maximise profits i.e.
those conditions that result in the highest possible yield of product in the shortest possible
time.
Other considerations include:

Raw materials – cost, availability, purity, safety.

Environmental impact – pollution, storage/hazards of waste products, use of water
bodies to cool equipment.

Transporting of raw materials and product.

Location of plant.

Availability of necessary technology.

Availability of appropriately qualified staff.
TYPES OF CHEMICAL PROCESSES
Batch Processing
In this process, fixed amounts of reactants are mixed to produce fixed amounts products.
This method is usually reserved for the production of small amounts of product and/or
reactions that display high equilibrium constants.
Continuous Flow Processing
In this process, reactants are continuously supplied at one end, to produce a continual
supply of products, which are then removed at the other end of the processing line. This
process is only cost effective if sufficient demand exists for the large amounts of products
derived via the process. Continuous flow processing also allows for greater control over
reaction conditions, making it the preferred technique for many large scale operations.
Reactants may be added or products removed at any stage of a process to increase product
yields.
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Unit 4 Chemistry – The Production of Ethene
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PLANT LOCATION AND STRUCTURE
Factors to Consider:

Accessibility to raw materials.

Transportation costs.

Availability of energy/power sources.

The price of land.

Availability of water supplies.

Storage of raw materials and waste products.

Disposal of waste products.

Pollution and its effects on the environment.

Recycling energy, water and waste products.
GREEN CHEMISTRY
Green chemistry involves the design of chemical processes and products that reduce or
eliminate the use and generation of hazardous substances in the manufacture and
application of the products. By eliminating and reducing waste from chemical processes,
green chemistry aims to develop a sustainable approach to a cleaner environment that is
beneficial to both our society and the economy.
The hazards that green chemistry aims to avoid completely include:




Toxicity.
Physical hazards like explosions.
Impact on global climate change.
Depletion of resources.
The major difference between green and environmental chemistry is that environmental
chemistry focuses on pollution control once the pollutants have been produced whereas
green chemistry aims to avoid pollution in the first place.
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Unit 4 Chemistry – The Production of Ethene
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THE 12 PRINCIPLES OF GREEN CHEMISTRY
Taken From Heinemann Chemistry 2
1.
Prevent waste
It is better to design chemical processes to prevent waste than to treat waste or clean it
up after it is formed.
2.
Design safer chemicals and products
Design chemical products to be fully effective, yet have little or no toxicity.
3.
Design less hazardous chemical syntheses
Methods should be designed that use and generate substances with little or no toxicity
to humans and the environment.
4.
Use renewable raw materials
Use starting materials that are derived from renewable resources such as plant
material rather than those such as from fossil fuels that will eventually run out.
5.
Use catalysts, not stoichiometric reagents
Minimise waste by using catalysts in small amounts that can carry out a single reaction
many times. They are preferable to stoichiometric reagents, which are used in excess
and work only once.
6.
Avoid chemical derivatives
Avoid using blocking or protecting groups or any temporary modifications if possible.
Derivatives use additional reagents and generate waste.
7.
Maximise atom economy
Design syntheses so that the final product contains the maximum proportion of the
starting materials. There should be few, if any, wasted atoms.
8.
Use safer solvents and reaction conditions
Avoid using toxic solvents to dissolve reactants or extract products.
9.
Increase energy efficiency
Energy requirements should be minimised. Run chemical reactions at room
temperature and pressure whenever possible.
10. Design for degradation
Chemical products should be designed to break down to harmless substances after
use so that they do not accumulate in the environment.
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Unit 4 Chemistry – The Production of Ethene
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11. Analyse in real time to prevent pollution
Include continuous monitoring and control during process to minimise or eliminate the
formation of by-products.
12. Minimise the potential for accidents
Design chemicals and their forms (solid, liquid or gas) to minimise the potential for
chemical accidents including explosions, fires and releases to the environment.
BENEFITS OF GREEN CHEMISTRY
Some of the many benefits of a green chemistry approach include:

Higher atom economy.

Advocating energy efficient processes.

Lowers cost of production and regulation.

Less wastes.

Safer products.

Healthier workplaces and communities.

Protects human health (end-users) and the environment.

Offers businesses a competitive advantage in the market place.

Economical stimulus.
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Unit 4 Chemistry – The Production of Ethene
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YIELD VERSUS ATOM ECONOMY
The yield of a reaction tells us how efficient a reaction is in terms of the amount of product
we obtain, relative to the maximum we could get from the amount of reactants we used.
It is calculated using the formula:
% Yield
=
mass of product obtained (g) x 100
theoretical yield (g)
However, it does not take into account the waste products.
Efficient chemical processes have high atom economy, and are important for sustainable
development. Atom economy is determined by measuring the amount of starting materials
that are incorporated into the desired products, and distinguishing them from those that are
wasted (incorporated into undesirable products). Atom economy can be calculated by:
% Atom economy =
Relative Molar Mass of Desired Product
X 100
Sum of Relative Molar Masses of all Products
A given chemical reaction might have high yield but low atom economy, hence not be seen
as a adhering to green chemistry guidelines.
WORKED EXAMPLE 1
(a)
Calculate the percentage atom economy of CH 2Cl2 , which is formed according to the
following chemical equation: CH 4( g )  2Cl2( g )  CH 2Cl2( aq )  2 HCl( aq )
% Atom economy 
(b)
85
100  53.8%
85  36.6
Would this method of CH 2Cl2 production be considered as a “Green” process?
Give a reason for your answer.
An atom economy of 53.8% is particularly poor, and this is a very wasteful process.
This would not be considered a green process, as one the key principles of green
chemistry is that it is better to develop reactions with fewer waste products than to have
to clean up the waste (eg. achieve high atom economy).
(c)
How could a chemical company maximise their profits from this chemical process?
Use waste products in other chemical reactions. The by-product is hydrogen chloride,
which can be sold as a gas or made into hydrochloric acid. These useful substances
can then be sold, reducing the potential wastage from the initial process. Alternatively,
waste products that are non-toxic and biodegradable are favourable.
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Unit 4 Chemistry – The Production of Ethene
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WASTE MANAGEMENT AND POLLUTION
IN THE CHEMICAL INDUSTRY
A waste product is an unusable or unwanted substance produced during or as a result of a
chemical process.
Chemical waste is generated in many chemical processes and if not managed correctly, can
impose adverse effects on human health and the environment.
Responsible industries therefore practise sound waste management by implementing the
following actions:
1.
Prevention
2.
Elimination
3.
Reduction
4.
Recycling
5.
Treatment
6.
Disposal
WASTE TREATMENT
There are many different forms of waste treatment including:

Landfill

Dumping at sea

Dispersion in controlled amounts in water or air

Vitrification (sealing in molten slag)

High-temperature incineration ( 1100o C )

Removal of pollutants from waste gases and liquids

Storage in sealed drums in secure locations

High-temperature steam and water treatments
Which treatment process is used by industries depends upon:

The physical form of the waste

The hazardness of the waste

Threats to animals, people and the environment

The cost of the process
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Unit 4 Chemistry – The Production of Ethene
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PRODUCTION OF ETHENE
Ethene or ethylene (C 2 H 4 ) is the first member of the alkene series. These molecules are
characterised by the presence of one or more double bonds between carbon atoms, and
therefore, ethene is referred to as an unsaturated hydrocarbon.
PROPERTIES OF ETHENE

Ethene is a non polar molecule.

Ethene is a flammable gas.

Due to the weak dispersion forces acting between molecules,
ethene displays a low boiling temperature ( -1040 C ).
USES OF ETHENE
Ethene is the leading synthetic organic chemical in the world in terms of scale of production.
Although ethene is widely used as a starting material in the production of many chemicals
and products, most of the ethene produced in Australia (about 60%) is used to make
polyethene, which is used to produce:

Plastic equipment eg. bowls, buckets, bins, glad wrap.

Covers for metal containers eg. piping that is susceptible to corrosion.

Insulating materials.
Other uses of ethene include:

The production of ethanol, which is used as:

Solvents such as methylated spirits.

Solvents in cosmetics, drugs and perfumes.

A raw material in the manufacture of other chemicals.

Herbicides.

The production of ethylene glycol which is used as an antifreeze solution.

The production of teflon which is used to make “non stick” cooking utensils.

The production of PVC (polyvinyl chloride) which is used for:

Insulation around electrical cables.

Packaging.

Products traditionally produced from glass, rubber.
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Unit 4 Chemistry – The Production of Ethene
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
The production of polystyrene which is used for:

Tape and film reels, toys, packaging.

Audio cassette boxes.

Casings for TV's and radios.

Thermal insulation.
Ethene is also used in:

Production of fibres.

Production of co-polymers, such as ABS (a plastic made from polymer chains of three
monomers – styrene, acrylonitrile and butadiene).
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Unit 4 Chemistry – The Production of Ethene
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THE PRODUCTION OF ETHENE
Ethene is made from a variety of feedstocks, all of which mainly consist of saturated
hydrocarbons. Example of such feedstocks include:

Natural gas, which primarily consists of methane (about 90%) as well as small
quantities of ethane, propane and butane.

Petroleum (crude oil) which is a mixture of solution of hundreds of saturated
hydrocarbons and results from the decay of marine plants and animals.
Feedstocks are first refined and impurities are removed and then sent to a refinery for
“cracking” – a process which converts large saturated hydrocarbons into smaller saturated
and unsaturated products.

Impurities such as water and hydrogen sulfide are removed from natural gas.

Petroleum is separated into fractions using “fractional distillation”.
Petroleum, crude oil

Fractional Distillation
Naphtha or gas oil fractions or natural gas

Cracking (usually steam cracking)
Removal of Impurities
+ Cracking
Natural Gas
© The School For Excellence 2012
Ethene
Unit 4 Chemistry – The Production of Ethene
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PETROLEUM:
The crude oil component of petroleum is separated into various fractions containing
hydrocarbons of similar molecular weights, via a process known as fractionation.
This procedure is carried out in a fractionating tower.
The fractionating tower is divided into a series of horizontal trays that contain hundreds of
bubble caps; raised holes in the trays that contain loose fitting covers or caps. The bubble
caps ensure that the rising vapour percolates through the liquid that has already condensed
on each tray.
The sample is heated to approximately 350 o C to form a mixture of gaseous vapour and
liquid. The vapour moves up the fractionating tower, whereas the liquid settles at the bottom
of the tower and is removed.
The temperature in the fractionating tower changes from approximately 350 o C at the
bottom of the tower to 20 o C at the top of the tower. This temperature gradient is created
by the rising vapour that is cooling as the gas moves up the tower. This means that the
trays are arranged in such a manner, that each tray is at a lower temperature than the tray
below it.
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Unit 4 Chemistry – The Production of Ethene
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As the vapour moves up the tower:
Hydrocarbons whose boiling points are equal to or higher than that of the condensed
fraction will condense (become a liquid).
Hydrocarbons whose boiling points are lower than that of the condensed fraction will again
vaporise, and move up to the next tray.
Eventually, each tray will contain a mixture of hydrocarbons with similar boiling points.
As the boiling temperatures of compounds depends upon the strength of the intermolecular
forces, the smaller hydrocarbon molecules condense near the top of the tower, whereas the
heavier molecules condense near the bottom.
The desired fractions are then collected (usually naphtha C 6  C10 and gas oil C14  C 20 ),
and sent to the refinery for cracking.
Note:

The exact operating conditions and the fractions that are obtained depend upon the
nature of the raw materials and market demands.

The liquid remaining at the bottom of the tower is usually redistilled at low pressures so
as to separate its components.
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Unit 4 Chemistry – The Production of Ethene
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CRACKING
The distillation process is insufficient to meet consumer demands for the lighter hydrocarbon
fractions. Greater quantities of the lighter fractions are therefore produced via a process
referred to as cracking.
Cracking is the process that breaks large molecules into smaller molecules, and may be
achieved by two different methods; thermal cracking and catalytic cracking. The technique is
used not only to produce greater quantities of lighter fractions from crude oil, it is used to
produce unsaturated hydrocarbons for various chemical industries. Eg. ethene.
THERMAL CRACKING
Thermal Cracking involves the production of small molecules by subjecting large molecules
to high temperatures ( 750  900 o C ). The products of thermal cracking are mainly smaller
molecular weight alkanes, along with some unsaturated hydrocarbons such as ethene and
propene.
Ethene is primarily produced by a type of thermal cracking called steam cracking.
The raw materials or feed stocks for steam cracking include:

Ethane and/or propane from natural gas.

Naphtha or gas oil fractions obtained from the fractional distillation of crude oil.
METHOD
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Unit 4 Chemistry – The Production of Ethene
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STEP 1: THE CRACKING PROCESS
Steam and feed stocks enter a furnace at temperatures between 750 o C and 900 o C , and
travel through coiled metal tubes where cracking occurs.
Typical reactions that occur in the metal tubes include:
C2 H 6 ( g )  C 2 H 4 ( g )  H 2 ( g )
Ethane
H  138 kJ / mol
ethene
C3 H 8( g )  C2 H 4( g )  CH 4( g )
Propane
ethene
C10 H 22  C8 H18  CH 2CH 2
Decane
H  81 kJ / mol
H   kJ / mol
octane ethene
C13 H 28( g )  C11 H 24( g )  CH 2CH 2( g )
Gas oil
octane
H  93.5 kJ / mol
ethene
General Equation: Alkane  Alkene + Smaller Alkane
Reaction Conditions:
As the cracking process is endothermic, Le Chatelier’s Principle suggests that high
equilibrium yields of ethene will be favoured by higher temperatures and lower pressures
(less than 1 atm).
In practice, however, the gas is only allowed to remain in the furnace for less than one
second so as to prevent ethene from cracking into smaller molecules (over-cracking). Not
only does over-cracking result in decreased ethene yields, it results in the production of
carbon (coke), which reacts with water to produce carbon monoxide and hydrogen gas:
C( s )  H 2O( g )  CO( g )  H 2( g )
Note:

Typical yields of ethene from ethane feedstock are in the order of 50%.

As the size of the hydrocarbons in the feedstock increases, the products from the
cracking process become more diverse and the yield of ethene decreases.
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
Page 15
STEP 2: QUENCHING
The gas leaving the furnace is quickly cooled to below 100 o C in a quench tower to avoid
secondary reactions (further cracking).
STEP 3: DISTILLATION AND WASTE TREATMENT
The components of the cracking process are further cooled to below  100 o C by gradually
compressing and expanding it and the components are then separated by distillation.
H 2 and CO2 are removed, and any un-reacted ethane is recycled back into the feedstock.
STEP 4:
Residue fractions containing hydrocarbons are returned to the refinery.
DISADVANTAGES OF THERMAL CRACKING

It is difficult to control the quality of products produced. Over-cracking may occur,
resulting in the formation of lighter fractions than that required.

The process is expensive.
CATALYTIC CRACKING
Catalytic Cracking involves the production of smaller molecules by subjecting large
molecules to lower temperatures (  500 O C ) and an appropriate catalyst such as zeolite.
As lower temperatures are employed, it becomes easier to control the products produced in
the cracking process.
For example: C10 H 22  C8 H 18  CH 2 CH 2
decane
octane
ethylene (ethene)
Note: This equation only represents ONE of the possible outcomes of the cracking of
decane. Decane is able to crack at a number of different points, resulting in the
formation of many different molecules.
The products of cracking are then separated by fractional distillation.
DISADVANTAGES OF CATALYTIC CRACKING

The technique is expensive.
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
Page 16
WASTES AND MANAGEMENT

Organic compounds can react with nitrogen oxides in the atmosphere in the presence
of sunlight to form photochemical smog. Leaks of hydrocarbons are therefore
minimised preventing environmental contamination.

Unconverted feedstock is recycled back to the cracking furnace, so there is very little
wastage of hydrocarbons.

Undesirable products are treated in the following manner:

Ethyne ( C2 H 2 ) is converted to additional ethene by reacting it with hydrogen using
a transition metal catalyst, such as Pd or an Fe/Ni mixture.
C2 H 2 ( g )  H 2 ( g )  C 2 H 4 ( g )

Carbon dioxide and hydrogen sulfide (both which are weak acids) are removed by
treatment with dilute sodium hydroxide solution:
2 NaOH ( aq )  H 2 S( g )  Na2 S( aq )  2 H 2O( l )
2 NaOH ( aq )  CO2( g )  Na2CO3( aq )  H 2O( l )

Propene is extracted and used for making polypropene.

Butadiene is extracted and is used to make synthetic rubber.

Hydrogen and methane are extracted and used as a fuel gas for furnaces.

The coke that builds up on the walls of the furnace is periodically removed and is
used as a fuel.

Waste hydrocarbons are burned (flared) using high-pressure steam to ensure that
smoke is not produced.

Thermal energy from the hot cracked gases is used in heat recovery boilers to
generate high-pressure steam. This drives compressors and pumps and heats
distillation columns.

Waste water from cooling and cleaning is treated to remove hydrocarbons, and may be
reused in production or used for watering gardens.

Noise from burners/compressors is minimised.
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
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
Desulfurisation
Desulfurisation involves the removal of sulfur containing compounds and is carried out
before fractions are sent to a refinery for cracking.
This process is carried out for the following reasons:

To reduce SO2 emissions when fuels are burned.

Sulfur acts as a catalytic poison, impeding or destroying the catalytic activity of
many catalysts that are used in the refinery.
The sulfur that is removed during the desulfurisation process is used as a raw material
for the production of chemicals such as sulfuric acid.
HEALTH AND SAFETY

Working with gases at pressures below 1 atmospheric is hazardous as a leak would
cause air to be drawn in, which may form an explosive mixture.

Ethene is an asphyxiant and at moderate to high concentrations can cause nausea and
headaches. Butadiene gas emissions are carefully monitored because high exposures
may cause damage to the nervous system, and other illnesses.

Ethene is a highly volatile and flammable gas posing a great threat to the environment
through explosions. Having industries that use the products of the refining process in
close proximity means that the explosive materials do not have to be transported
across large distances, reducing the threat of explosions and consequential damage to
the surrounding environment. In addition, extensive fire prevention and fire fighting
strategies are employed by the industry.

The biggest risk to workers in the petrochemical industry is usually considered to be
explosions and fire. Like other hydrocarbons, ethene can readily form explosive
mixtures with air. As a consequence,

Since both high temperature and low temperature stages are involved in ethene
production, special attention is also given to the prevention of burning and freezing
injuries.
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
Page 18
MIXED QUESTIONS
QUESTION 1
If you had to transport ethene in a cylinder, which safety sticker would you place on the
cylinder?
A
B
C
D
Non-flammable liquid
Non-flammable gas
Flammable liquid
Flammable gas
QUESTION 2
The major source of unsaturated hydrocarbons for industrial use is:
A
B
C
D
Distillation of natural petroleum
Catalytic cracking of natural petroleum
Hydrolysis of starch
Combustion of natural gas
QUESTION 3
In the petroleum refining industry, crude oil is subjected to fractional distillation. In this
process:
A
B
C
D
Various mixtures of chemicals, each boiling within a selected temperature range are
separated
High molar mass molecules are vaporised at low temperatures and high pressures
Each of the individual chemicals in crude oil are separated
The fractionating column is kept at constant temperature throughout so that
equilibrium can be attained
QUESTION 4
Fractional distillation is a process by which crude oil is separated into different fractions.
Each fraction contains molecules which:
A
B
C
D
Are from one homologous series
Are vastly different in molar mass
Differ greatly in boiling temperature
Are relatively insoluble in each other
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Unit 4 Chemistry – The Production of Ethene
Page 19
The following information relates to Questions 5, 6 and 7.
Below is a diagram of a gas processing tower used for the fractional distillation of natural
gas. The natural gas can be sourced from various locations and consists mainly of methane,
ethane, propane and butane.
QUESTION 5
The identities of W, X, Y and Z respectively are:
A
B
C
D
Methane, ethane, propane, butane
Ethane, methane, propane, butane
Ethane, propane, butane, methane
Butane, propane, ethane, methane
QUESTION 6
Which of W, X, Y and Z is removed at the lowest temperature?
A
B
C
D
W
X
Y
Z
QUESTION 7
Process A immediately follows the fractional distillation. This process is most likely to be:
A
B
C
D
Reduction
Hydration
Chlorination
Cracking
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Unit 4 Chemistry – The Production of Ethene
Page 20
QUESTION 8
What property determines how hydrocarbons are separated in the fractionating tower?
Solution
QUESTION 9
Sulfur compounds are often present in crude oil. If a sample of crude oil containing 1%
sulphur was burnt in air, which of the following compounds would be produced in the
smallest amount in the flame?
A
B
C
D
SO3
SO2
H 2O
CO2
QUESTION 10
The cracking of petroleum fractions involves:
A
B
C
D
Breaking of long chain hydrocarbons into shorter ones.
Joining of short chain hydrocarbons to form longer ones.
Polymerisation of alkenes.
Conversion of linear hydrocarbons to cyclic structures.
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
Page 21
QUESTION 11
Unsaturated hydrocarbons such as ethylene (ethene) are produced in industry by cracking
of crude oil fractions. The process of cracking involves:
A
B
C
D
The separation of the components of crude oil according to their boiling temperatures.
Reducing the pressure in order to separate hydrocarbons of high molecular mass.
Heating crude oil in the presence of pure oxygen to ensure complete reaction of the
oil’s components.
Breaking long chained hydrocarbons into shorter ones by heating crude oil in the
absence of air.
QUESTION 12
Which one of the following is most likely to have been produced by a ‘cracking’ process?
A
B
C
D
Paraffin wax
Lubricating oil
Diesel fuel
Petrol
QUESTION 13
Which one of the following reactions is an example of a ‘cracking’ reaction of a
hydrocarbon?
A
B
C
D
CH 3  CH 2  CH 3  CH 2  CH 2  CH 4
CH 2  CH 2  H 2  CH 3  CH 3
CH 4  2O2  CO2  2 H 2 O
CH 2  CH 2  H 2 O  CH 3  CH 2  OH
QUESTION 14
When the gas propane is cracked, several different products can be obtained. Write the
formulas for four likely products of this process.
Solution
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Unit 4 Chemistry – The Production of Ethene
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QUESTION 15
The products of thermal cracking include an alkane and an alkene. Explain why alkenes are
produced during the process.
Solution
QUESTION 16
Why is the cracking of ethene produced using catalysts rather than high temperatures?
Solution
QUESTION 17
Discuss the conditions that are required to maximise the yield of ethene, during thermal
cracking.
C2H6(g)
ethane
 C2H4(g) + H2(g)
H = +138 kJ/mol
ethene
C3H8(g)  C2H4(g) + CH4(g)
propane
ethene
H = +81 kJ/mol
Solution
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
Page 23
QUESTION 18
Use Le Chatelier’s principle to describe the theoretical conditions that should be used to
maximise the yield of ethene from cracking reactions. Are these the conditions actually
used? If not, why not?
Solution
QUESTION 19
Catalytic cracking of alkanes is carried out by passing the hydrocarbon vapour over a heated
catalyst in the absence of air. Which of the following is not a possible product of the catalytic
cracking of hexane?
A
B
C
D
Propene
Methane
Hydrogen
Carbon dioxide
QUESTION 20
What is the purpose of using a catalyst in catalytic cracking processes?
Solution
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
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QUESTION 21
Why is the gas that leaves the furnace cooled to below 100 o C ?
Solution
QUESTION 22
(a)
What is the physical property used in fractional distillation?
(b)
What is the difference between thermal and catalytic cracking?
(c)
State 3 properties of ethene.
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Unit 4 Chemistry – The Production of Ethene
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QUESTION 23
Ethene is obtained in large quantities by the catalytic cracking of naphtha.
(a)
(i)
Write an equation for the production of ethene from the cracking of butane. Use
this equation to explain why the products of cracking reactions will also consist of
saturated and unsaturated hydrocarbon.
(ii) How does the use of a catalyst reduce the costs of producing ethene from
naphtha?
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Unit 4 Chemistry – The Production of Ethene
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QUESTION 24
Explain the differences between fractional distillation and thermal cracking, and the products
that are produced in each process.
Solution
QUESTION 25
What are the potential waste products of this industrial process? What risks are posed to
human beings or the environment by these waste products?
Solution
© The School For Excellence 2012
Unit 4 Chemistry – The Production of Ethene
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QUESTION 26
When crude oil is fractionally distilled, six fractions are obtained, as shown in the following
table.
Fraction
Size Range of Molecules
Boiling Point Range ( o C )
Gas
C1 - C5
-160 to 30
Gasoline
C5 - C12
30 to 200
Kerosene, Fuel oil
C12 - C18
180 to 400
Lubricants
C16 and up
350 and up
Paraffins
C20 and up
>350
Asphalt
C36 and up
>350
(a)
What is the general trend in boiling points as the number of carbon atoms increases?
Explain the observed trend in terms of bonding.
(b)
What process can be used to convert some of the heavier fractions to lighter
fractions?
(c)
As the world reserve of liquid hydrocarbons are depleted, how could gaseous
hydrocarbons be used as a replacement for gasoline?
Solution
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Unit 4 Chemistry – The Production of Ethene
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QUESTION 27
A simplified flow chart involving ethene is shown below.
(a)
Describe the composition of crude oil.
(b)
Name processes X and Y.
(c)
Describe the composition of mixture Z.
(d)
Name another raw material from which ethene can be manufactured.
(e)
Identify substances A, B and C and write equations for the reactions that produce
them.
(f)
What type of reaction is involved in the production of substances A and B?
Solution
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Unit 4 Chemistry – The Production of Ethene
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QUESTION 28
The crude oil component of petroleum is separated into various fractions via a process
known as fractionation. This procedure is carried out in a fractionating tower, as illustrated
below.
(a)
Crude oil consists of a large number of different compounds. Explain how fractional
distillation is used to produce useful compounds from crude oil.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
3 marks
The distillation process is insufficient to meet consumer demands for the lighter hydrocarbon
fractions. Greater quantities of the lighter fractions are therefore produced via a process
referred to as cracking.
(b)
Give an equation for the production of ethene from hexane from a cracking process.
_____________________________________________________________________
1 mark
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Unit 4 Chemistry – The Production of Ethene
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The production of ethene from larger hydrocarbons are endothermic processes.
(c)
(i)
State the conditions of temperature and pressure which would result in the
greatest yield of ethene in cracking processes.
__________________________________________________________________
__________________________________________________________________
1 mark
(ii) State one reason why cracking of ethene is often employed using catalysts rather
than at higher temperatures?
__________________________________________________________________
__________________________________________________________________
1 mark
(iii) State two properties of ethene.
__________________________________________________________________
__________________________________________________________________
1 mark
Total 7 marks
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Unit 4 Chemistry – The Production of Ethene
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QUESTION 29
A diagram representing a fractionating tower is illustrated below.
(a)
(i)
Briefly explain the function of the horizontal trays and bubble caps inside the
fractionating column.
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
2 marks
(ii) The order in which the molecules below are distilled is best represented by:
(a)
(b)
(c)
(d)
A
C
E
F
C30 H 32
C30 H 32
C2 H 6
C2 H 6
C2 H 6
C10 H 22
C5 H 12
C30 H 32
C5 H 12
C5 H 12
C10 H 22
C10 H 22
C10 H 22
C2 H 6
C30 H 32
C5 H 12
Circle the correct answer (a, b c or d).
1 mark
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Unit 4 Chemistry – The Production of Ethene
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(iii) What property determines the level at which each hydrocarbon is collected?
Explain your answer.
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
1 mark
(b)
A hydrocarbon isolated from one of the fractions was found to contain 85.71% by
mass of carbon.
(i)
Find the empirical formula of the hydrocarbon.
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
2 marks
(ii) To which homologous series does this hydrocarbon belong to?
__________________________________________________________________
__________________________________________________________________
1 mark
(iii) Given that the molar mass of the compound is 98, state the molecular formula of
this compound.
__________________________________________________________________
__________________________________________________________________
1 mark
(iv) Draw the structural formulae of two isomers of this hydrocarbon.
2 marks
Total 10 Marks
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Unit 4 Chemistry – The Production of Ethene
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QUESTION 30
(a)
Calculate the atom economy of ethylene oxide, created in the following reaction:
(b)
Would this method of production of ethylene oxide be considered as a “Green”
process? Give a reason for your answer.
(c)
Recently, a method of synthesising ethylene oxide from ethene and oxygen using a
silver catalyst was developed. What’s the atom economy of this alternative reaction?
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Unit 4 Chemistry – The Production of Ethene
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