In the Name of God
(Applied Chemistry)
Inorganic Industrials Chemistry
Sulfur
and its Compounds
R. Pourata
Outlines
Sulfur
Introduction
Properties
Production
Uses
Sulfuric Acid
Introduction
Properties
Production
Production of Sulfur Dioxide
Production of Sulfur Trioxide
Absoption
Uses
2
1
Introduction
Sulfur is the fifteenth most common terrestrial element, and the ninth
most abundant element in the universe.
Sulfur has been known since ancient times. The Greeks called it
theion, the Romans sulphurium.
In Europe, sulfur gained great importance after the Chinese invention
of gunpowder was introduced in the early 1200s. The first commercial
sulfur was produced in Sicily early in the 1400s. With the advent of
industrialization toward the end of the 1700s, sulfur became more and
more important in the form of sulfuric acid and fertilizers.
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Properties
4
2
Properties
General
Name, symbol, number
sulfur, S, 16
Element category
Nonmetals
Group, period, block
16, 3, p
Appearance
Lemon yellow crystals.
Standard atomic weight
32.065(5) g·mol−1
Physical properties
Phase
Solid
Density (near r.t.)
(alpha) 2.07 g·cm−3
Density (near r.t.)
(beta) 1.96 g·cm−3
Density (near r.t.)
(gamma) 1.92 g·cm−3
Liquid density at m.p.
1.819 g·cm−3
Melting point
388.36 K
(115.21 °C, 239.38 °F)
Boiling point
717.8 K
(444.6 °C, 832.3 °F)
Critical point
1314 K, 20.7 MPa
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Properties
Elemental sulfur occurs in several different allotropic forms, which
differ in solubility, relative density, crystalline form, etc..
The crystalline rhombic α-form is the most common type of solid
sulfur. At room temperature, it is pale yellow; at low temperature it
becomes lighter in color, almost white at the temperature of liquid air.
It is stable up to 95.5 °C, at which it is transformed to β-sulfur.
The crystalline monoclinic b-form occurs as needle-like crystals, and
is stable up to the melting point, 119.3 °C. It is almost colorless and is
slowly converted to the α-form on cooling below 95.5 °C.
The γ-form is also crystalline monoclinic, but with a different lattice
from that of the b-form. It is light yellow, nacreous, and metastable.
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3
Properties
Crystals of rhombic sulfur
Crystals of monoclinic sulfur
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Properties
8
4
Properties
(a) the S8 molecule
(b) chains of sulfur atoms in
viscous liquid sulfur.
The chains may contain as many as
10,000 sulfur atoms.
9
Properties
Sulfur vapor dissociates at higher temperature, from S8 through the
intermediate species S6 and S4, to S2. At temperatures above ca. 2000
°C, the gas consists only of sulfur atoms.
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5
Properties
11
Production
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6
Production
Raw Materials for Sulfur Production
Elemental sulfur: Ores containing native sulfur are found exclusively
in the upper layers of the Earth's crust and are either of sedimentary or
volcanic origin.
Sulfide ores: Heating iron pyrites to ca. 1200°C in the yields sulfur
and liquid iron(II) sulfide. The largest proportion of copper, zinc,
lead, nickel, and cobalt is obtained from sulfide ores.
Coal: All coals contain sulfur; the amount depends on their type and
origin (2 – 4 wt % ).
Crude oil: mostly contains 0.1 – 2.8 wt % sulfur.
Natural gas: contains sulfur, mainly as hydrogen sulfide
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Production
Main sulfur sources and processing routes
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14
Production
Elemental sulfur is extracted from deep sedimentary deposits with
particular geological formations, such as salt domes (impermeable
layers of anhydrite on salt with sulfurcontaining limestone on top) e.g.
along the Mexican Gulf, in Canada or Iran, by pumping in
superheated water (ca. 165°C) at a pressure of ca. 25 bar and pumping
out the molten liquid sulfur (Frasch process). In this process three
coaxial tubes are placed in a bore hole sunk down into the anhydrite
layer of the dome.
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Production
Sulfur extraction by the Frasch process
A) Structure of a sulfur dome: a) Borehole; b) Impervious cap rock; c) Sulfur-bearing
limestone;d) Anhydrite;e) Rock salt; f) Pump region
B) Principle of the Frasch pump: a) Inner tube; b) Middle tube; c) Outer tube; d)
Sulfurbearing limestone; e) Anhydrite
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8
Production
Frasch method for recovering sulfur from underground deposits.
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Production
Melted sulfur obtained from underground deposits by the Frasch process.
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18
Production
Claus process
Hydrogen sulfide is present in natural gas, refinery gases, synthesis
gas and coking oven gases. It has to be removed before the gas can be
used or further processed. This is carried out by physical or chemical
scrubbing, the hydrogen sulfide being recovered in concentrated form
upon regeneration of the absorption liquids. Conversion of the
hydrogen sulfide into elemental sulfur is accomplished using the
Claus process, which is exothermic.
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Production
Claus process
A typical Claus plant consists of a combustion chamber, a waste heat
boiler and two reactors, which are filled with catalyst.
The hydrogen sulfide-containing gas together with a stoichiometric
quantity of, for example, oxygen enriched gas and heating gas is
passed into the combustion chamber, in which ca. 60 to 70% of the
hydrogen sulfide is converted into sulfur.
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10
Production
Claus process
The process gas from the combustion chamber is cooled in the waste
heat boiler to the temperature required for the first reactor of ca.
300°C. In this reactor, filled with a cobalt-molybdenum catalyst (on
an aluminum oxide support), the conversion of up to 80 to 85% of the
hydrogen sulfide is carried out.
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Production
Claus process
After condensing out the sulfur formed at temperatures below 170 ºC,
the temperature of the reaction gases is increased to the reaction
temperature of the second reactor (ca. 220 ºC), which contains a
highly active aluminum oxide catalyst with a large surface area (200
to 300 m2/g) in which the residual hydrogen sulfide and sulfur dioxide
react with one another.
1) H2S + 3/2 O2 → SO2 + H2O
2) 2H2S + O2 → S2 + 2H2O
3) 2H2S + SO2 → 3/8 S8 + 2H2O
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11
Production
The Claus process
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Uses
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12
Uses
More than 85% of the total world production of elemental sulfur is
currently converted to sulfuric acid. More than 50% is used for the
production of fertilizers (together with pesticides, insecticides, and
fungicides, agriculture consumes more than half of the sulfur
produced).
The remaining 35% of the sulfur converted into sulfuric acid goes into
the production of detergents, pharmaceuticals, petroleum catalysts,
synthetic resins, titanium pigments, acetates, and explosives; other
uses of sulfuric acid are as a pickling agent in steel production, and
leaching of nonferrous ores.
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Uses
An important nonacid application of sulfur is in the manufacture of
carbon disulfide, which can be synthesized either directly from the
elements or by the reaction of sulfur with methane, with hydrogen
sulfide as byproduct.
Sulfur is used as a vulcanizing agent for rubber. Other users of
elemental sulfur are the pharmaceutical, cosmetics, photographic,
soap, and dye industries.
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13
Sulfuric Acid
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Introduction
The discovery of sulfuric acid is credited to the 8th century Arabian
chemist and alchemist, Jabir ibn Hayyan (Geber). The acid was later
studied by 9th century Persian physician and alchemist Ibn Zakariya
al-Razi (Rhazes), who obtained the substance by dry distillation of
minerals including iron(II) sulfate heptahydrate, FeSO4.7H2O, and
copper(II) sulfate pentahydrate, CuSO4.5H2O. When heated, these
compounds decompose to iron(II) oxide and copper(II) oxide,
respectively, giving off water and sulfur trioxide, which combine to
produce a dilute solution of sulfuric acid. This method was
popularized in Europe through translations of Arabic and Persian
treatises, as well as books by European alchemists, such as the 13thcentury German Albertus Magnus.
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14
Properties
29
Properties
Pure sulfuric acid, H2SO4, Mr 98.08, is a colorless, slightly viscous
liquid, mp 10.4 °C and bp 279.6 °C. It can be mixed with water in any
ratio. Aqueous sulfuric acid solutions are defined by their H2SO4
content in weight-percent terms. Sulfuric acid will dissolve any
quantity of SO3, forming oleum ("fuming sulfuric acid").
H2SO4 (aq) + H2O(l ) → H3O+(aq) + HSO4-(aq)
HSO4-(aq) + H2O(l) → H3O+(aq) + SO4-2(aq)
Ka1 = Large
Ka2 = 1.2 x 10-2
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15
Properties
Sulfuric acid
IUPAC name
Sulfuric acid
Other names
Oil of vitriol
Properties
Molecular formula
H2SO4
Molar mass
98.078 g/mol
Appearance
clear, colorless,
odorless liquid
Density
1.84 g cm−3, liquid
Melting point
10 °C, 283 K, 50 °F
Boiling point
290 °C, 563 K, 554 °F
Solubility in water
fully miscible
(exothermic)
Viscosity
26.7 cP at 20°C
Hazards
EU classification
Corrosive (C)
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Properties
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16
Production
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Production
Sulfuric Acid Manufacture
Production of sulfur dioxide
Oxidizing sulfur dioxide to sulfur trioxide
Reacting the sulfur trioxide with water (H2SO4 97-98% )
S+O2→
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17
Production
Raw Materials for Sulfur Dioxide Production
Sulfur dioxide is manufactured industrially from the following raw materials:
 Elemental sulfur
 Pyrite
 Sulfide ores of nonferrous metals
 Waste sulfuric acid and sulfates
 Gypsum and anhydrite
 Hydrogen sulfide- containing waste gases
 Flue gases from the combustion of sulfureous fossil fuels
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Production
Production from Elemental Sulfur
Combustion of sulfur to sulfur dioxide is exothermic and is carried out
industrially in a combustion chamber with spray burners for liquid
sulfur and dry air as oxidizing agent. Liquid sulfur at 140 to 150 ºC
(liquid sulfur exhibiting a viscosity minimum at this temperature) is
sprayed through jets in finely divided droplets into the combustion
chamber.
S + O2 (g) →SO2 (g) ΔH = – 297 kJ/mol
liquid S is burnt with air, hot combustion gases are cooled and steam
produced.
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18
Production
Production by Pyrite Roasting
Pyrite contains ca. 30–50 % sulfur, 26–46 % iron and up to 2.7%
copper, 3% zinc, 1.4% lead, up to 10% arsenic, and a number of other
metals in small quantities
Sulfur dioxide is also produced by roasting sulfidic ores. Pyrites is
converted into sulfur dioxide and iron(III) oxide at least 800 ºC
according to the following equation:
2 FeS2 + 5.5 O2 → Fe2O3 + 4SO2 ∆H = -1660 kJ/mol
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Production
Metal sulfates can be cracked to sulfur dioxide. In this process
calcium sulfate (naturally occurring gypsum or anhydrite or gypsum
from the manufacture of phosphoric acid) is reacted with coal in the
presence of clay and sand in a rotary tube furnace a temperatures
between 700 and 1200°C.
CaSO4 + 2C → CaS + 2CO2
CaS + 3CaSO4 → 4CaO + 4SO2
_______________________
4CaSO4 + 2C → 4CaO + 4SO2 + 2CO2
The calcium oxide is heated with sand and clay at 1200 to 1400°C in a
second section of the rotary tube furnace forming Portland cement.
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19
Production
Metal sulfates are also cracked to sulfur dioxide in the recycling of socalled thin acid arising from the production of titanium dioxide by the
sulfate process.
FeSO4 . H2O
→ 2Fe2O3 + 4SO2 + O2 + 4H2O
→ CO2
_______________________
C + O2
4FeSO4 . H2O + C → 2Fe2O3 + 4SO2 + CO2 + 4H2O
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Production
Sulfur dioxide can also be obtained from waste sulfuric acid by
cracking. Impure sulfuric acid accrues in many processes, particularly
in organic chemistry, the petrochemical industry and the metal
industry. The safest way of avoiding waste problems and possible
environmental burdens is thermal cracking with the formation of
sulfur dioxide:
2 H2SO4 (Impure sulfuric acid) → 2 SO2 + O2 + 2 H2O
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20
Production
Production from hydrogen sulfide- containing waste gases
2H2S(g) + 3O2(g) → 2SO2(g) + 2H2O(g)
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Production
Conversion of Sulfur Dioxide to Sulfuric Acid
The oxidation of sulfur dioxide to sulfur trioxide and its subsequent
conversion to sulfuric acid is currently almost exclusively carried out
using the contact process, in particular the double contact process.
The lead chamber process is no longer important.
The contact process is based on the equilibrium between sulfur
dioxide and its oxidation product sulfur trioxide:
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21
Production
SO3-formation favored by:
Lowest temperature possible (lower limit determined by the
operating temperature of the catalyst used)
Lowering of the SO3-concentration
Increased pressure
Divanadium(V) oxide lowest operating temperature 420 to 440°C
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Production
Conversion of Sulfur Dioxide to Sulfuric Acid
Oxidation of sulfur dioxide to sulfur trioxide generally proceeds on
classical grid-type catalyst trays. In a contact chamber there are four
to five sieve trays, on which the catalyst is spread. Sulfur dioxidecontaining gas, whose concentration has been adjusted to 10% with
dried air, at 450°C before passing through the first tray, passes from
the top to the bottom of the chamber through the catalyst trays.
During passage through the first tray the gas is heated to 620°C.
Before entering the second tray it must be cooled down to 450°C.
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22
Production
Four-bed brick-lined converter
a) Inlet (bed 1); b) Catalyst bed grate; c)
Compartment separator; d) Outlet (bed 2); e)
Inlet (bed 3); f) Outlet (bed 4); g) Outlet (bed
1); h) Inlet (bed 2); i) Brick supporting
column; j) Outlet (bed 3); k) Inlet (bed 4); l)
Catalyst grate; m) Brick columns
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Production
Oxidation is carried out on catalyst trays.
After passage through the trays, the gas
has to be cooled again to ca. 45OºC.
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23
Production
Absorption
Sulfur trioxide formed by the catalytic oxidation of sulfur dioxide is
absorbed in sulfuric acid of at least 98 % concentration, in which it
reacts with existing or added water to form more sulfuric acid
H2SO4 + SO3 → H2S2O7
H2S2O7 + H2O → 2 H2SO4
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Uses
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24
Uses
The major use of sulfuric acid is in the production of fertilizers, e.g.,
superphosphate of lime and ammonium sulfate. It is widely used in
the manufacture of chemicals, e.g., in making hydrochloric acid, nitric
acid, sulfate salts, synthetic detergents, dyes and pigments, explosives,
and drugs. It is used in petroleum refining to wash impurities out of
gasoline and other refinery products. Sulfuric acid is used in
processing metals, e.g., in pickling (cleaning) iron and steel before
plating them with tin or zinc. It serves as the electrolyte in the leadacid storage battery commonly used in motor vehicles.
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The End
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