Download Uses of Sulfuric Acid

G H PATEL COLLEGE OF
ENGINEERING &
TECHNOLOGY
• Subject: Chemical Process industries
(2130505)
• Topic: Sulfur & sulfuric acid
• Branch: Chemical (2015-16)
• Sem: III
Prepared by…
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•
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140110105051-Jay Sadrani
140110105052-Mayur Sangadiya
140110105053 – Pavitra Sarang
140110105054 – Shubham Sardhara
140110105055 – Dhairya Shah
The frasch Process
Recovering sulfur from underground
deposits
• The Frasch process is a method to extract sulfur
from underground deposits. It is the only
economic method of recovering sulfur from
elemental deposits.
• Most of the world's sulfur was obtained this way
until the late 20th century, when sulfur recovered
from petroleum and gas sources (recovered sulfur)
became more commonplace (see Claus process).
• In the Frasch process, superheated water is
pumped into the sulfur deposit; the sulfur melts
and is extracted. The Frasch process is able to
produce high purity sulfur
Overview of frasch process
1
• In the Frasch process, three concentric tubes are
introduced into the sulfur deposit. Superheated water
(165 °C, 2.5-3 MPa) is injected into the deposit via
the outermost tube. Sulfur (m.p. 115 °C) melts and
flows into the middle tube. Water pressure alone is
unable to force the sulfur into the surface due to the
molten sulfur's greater density, so hot air is introduced
via the innermost tube to froth the sulfur, making it
less dense, and pushing it to the surface.
2
• The sulfur obtained can be very pure (99.7
- 99.8%). In this form, it is light yellow in
color. If contaminated by organic
compounds, it can be dark-colored; further
purification is not economic, and usually
unnecessary. Using this method, the United
States produced 3.89 million tons of sulfur
in 1989, and Mexico produced 1.02 million
tons of sulfur in 1991.
The Contact Process
The manufacture of sulfuric
Acid
Production of Sulfuric Acid
Sulfuric acid is made in several stages from SO2,
obtained from the oxidation of sulphur or collection of
SO2 from the smelting of sulfide ores such as copper,
zinc or lead. This second collection of SO2 is very
attractive as it is utilising the by-products of other
processes and reduces emissions and waste.
SO2(g)  SO3(g)  H2SO4(aq)
In the following slides we will break down this
process into three main steps.
1.
Furnace or Burner (Only necessary if raw sulfur is used)
Air is cleaned by electrostatic precipitation, dried then heated
to approx. 600oC.
Pure (liquid) sulphur is sprayed under pressure into the furnace,
reacting with the oxygen in the air. The product is sulphur
dioxide
S(l) + O2(g) SO2(g)
Alternative sources of sulphur dioxide are also used,
either extracted from natural gas (some deposits
contain a lot of hydrogen sulphide) or from the roasting
of sulphide ores in the extraction of metals like zinc or
lead. If so this stage can be skipped.
2.
The converter
The converter contains trays or layers of porous pellets of a
catalyst, vanadium (V) oxide (V2O5). The sulphur dioxide reacts with
more air to form sulphur trioxide. This reaction is reversible and
reaches an equilibrium. It is also an exothermic reaction and the
temperature will rise to over 600oC. The mixture is continuously
cooled to 400oC between each tray.
2SO2(g) + O2(g)  2SO3(g)
As the temperature rises the equilibrium shifts to the left (not
forming SO3). To counter this the gases are allowed to cool
slightly before they pass over the next layer of catalyst, by
carefully controlling the process almost all sulphur dioxide is
converted to sulphur trioxide
Yields and reaction rate
2SO2(g) + O2(g)  2SO3(g)
For the above reaction in the converter, the yield will increase as:
•The temperature _______________
•The pressure ____________
•And is excess reactant are added
But we have a compromise to make with reaction rates:
High reactions rates favour? ________
Thus conditions that are used as a compromise are:
Moderate temperatures
Moderate pressures (1 atm) – too expensive for high pressure!
And use of a catalyst
3.
The absorption tower
Sulphur trioxide will dissolve in water to form our final goal of
sulfuric acid. However it is violently exothermic and usually
results in a mist of sulfuric acid droplets that are very difficult
to control.
In practice the sulphur trioxide dissolves almost completely and
is bubbled through concentrated sulfuric acid (that contains
relatively little water) to form 98% sulfuric acid, known as
Oleum (H2S2O7)
a) SO3(g) + H2SO4(l)  H2S2O7(l)
b) H2S2O7(l) + H2O(l)  H2SO4(l)
Waste products
Most of the “waste” heat is recovered and used to heat
water, in this way much of the energy can be reused.
Because of this many sulfuric acid plants are co-located
with other industrial processes.
Great care needs to be taken with the waste gases that are
formed. There will be small amounts of sulphur dioxide,
sulphur trioxide, sulfuric acid and possibly particle sulphur,
all of which must be removed to prevent environmental
damage. There is a double absorption method that can be
used to prevent SO2 emissions. After a first round of
processing through the converter, any SO2 that was not
converted into SO3, can be collected and passed back
through. SO2 that is released into the atmosphere can
cause acid rain and respiratory irritants.
Overview of the Contact Process
Dry air
1
sulfuric acid
SO2
Sulphur
3
2
SO3
4
Waste gases
The Contact Process
Uses of Sulfuric Acid
The amount of sulfuric acid produced by a company is
often an indicator of a countries industrial activity.
Annual worldwide production is 170 million tonnes!
Transport and storage of sulfuric acid is hazardous, so
most of the acid produced is used by alternate
manufactures close to the production site.
Sulfuric acid is highly corrosive and burns skin and eyes.
For a large spill, the acid is treated with a natural hard
substances such as clay or sand, then slowly diluted with
water and finally neutralised with a base.
The main use of sulfuric acid in Australia is for
fertiliser.
Uses
Other uses include paper, dyes, drugs and the acid is a
main component of car batteries.
We utilise sulfuric made in Australia in a reaction with
rock phosphate to make superphosphate (other
fertilisers are ammonium nitrate and ammonium sulfate).
This is a wonderful fertiliser for plant growth, as farm
land often lacks phosphate required for crops. The
finely powered rock phosphate is imported cheaply from
north Africa and the reaction to make superphosphate
takes a couple of weeks! WOW!
Sulfuric acid is also used as a strong acid, dehydrating
agent and as an oxidant.
Let’s look at these uses a bit closer:
Uses
Sulfuric acid is diprotic. In a reaction with water, the
first proton will be donated to from the hydronium ion
and HSO4-. This reaction is virtually complete. The
second reaction to form sulfate (SO4-) has a smaller Ka.
Before a sheet of iron is galvanised, we use sulfuric acid
removes the iron(III) oxide layer.
WE ALWAYS ADD ACID TO WATER – AND VERY
SLOWLY. THE REACTION IS VERY EXOTHERMIC
AND EXCESSIVE HEAT IS GENERATED.
If we were to add water to acid, the small
amount of water boils instantly and cause
the acid to splatter everywhere!
Uses
Dehydrating agent – sulfuric acid dehydrates sugar into water
and carbon, and also will dehydrate copper sulphate as shown
below.
In the chemical industry , sulfuric acid is used to dry certain
gas mixtures (such as N2 and CO2) for analysis. Ammonia gas is
not able to be dehydrated by sulfuric acid as it is a base, and
if mixed together it will react with the acid instead!
Sulfuric acid is also an oxidant, especially when hot!
Depending on the temperature and strength of the reactant,
sulfur dioxide, sulfur and hydrogen sulfide gas can be
produced by reaction with zinc and sulfuric acid. (see p.340)