this deals with the contact process for making sulfuric acid

1. H2SO4
Presenter: G. Delapenha

2. SPECIFIC OBJECTIVES

3. MANUFACTURE OF SULPHURIC ACID
The process can be divided into
THREE(3) stages:
1. Preparation and purification of
sulphur dioxide
2. Catalytic oxidation of
sulphur dioxide to sulphur
trioxide (using vanadium
pentoxide(V2O5) catalyst)
3. Conversion of sulphur trioxide
to sulphuric acid

4. Manufacture of Sulphuric acid –the Contact process

5. • . . . or by heating sulphide ores
like pyrite in an excess of air:
STAGE1: MAKING THE SULPHUR DIOXIDE
• This can either be made by burning
sulphur in an excess of air:
Purification of air and SO2 (using an
electrostatic precipitator) is necessary to
avoid catalyst poisoning.
The gas is then washed with water and
dried by sulphuric acid.
To conserve energy, the mixture is heated
by exhaust gases from the catalytic
converter by heat exchangers.

6. Stage 2: Catalytic oxidation: the Contact Process
• Catalyst V2O5 (vanadium pentoxide)
• High Temperature 450oC
• Medium Pressure 1-2 atmospheres
***These are compromise conditions***
Sulphur dioxide and oxygen then react in the manner as follows:
2 SO2(g) + O2(g) ⇌ 2 SO3(g) ΔH = −197 kJ mol−1
To increase the reaction rate, the following conditions are used to ensure
a 96% conversion.

8. • Note that directly dissolving SO3
in water is impractical due to the
highly exothermic nature of the
reaction.
• Acidic vapour or mists are formed
instead of a liquid.
STAGE3: CONVERSION OF SULPHUR TRIOXIDE TO SULPHURIC ACID
• Hot sulfur trioxide passes through
the heat exchanger and is
dissolved in concentrated H2SO4
in the absorption tower to form
oleum:
H2SO4(l) + SO3(g) → H2S2O7(l)

9. Step 4: Dilution of Oleum
H2O (l) + H2S2O7(l) 2H2SO4(l)
• the oleum is diluted to give the desired concentration of sulphuric acid
• The average percentage yield of this reaction is around 30%.

10. Factors: Catalyst V2O5
***These are compromise conditions***
The catalyst
works best as
the
temperature
increases
Provides an
alternative
path with a
lower Ea
Speeds up
time taken to
achieve
equilibrium
Several
catalyst beds
used to
achieve high
yield

11. Factors:Temperature 450oC
***These are compromise conditions***
• The yield of SO3 increases as T is decreased
However
•Catalyst does not work if T is too low
• Rate of attainment of equilibrium is slow if T is too low

12. • ***These are compromise conditions***
Factors: Pressure 1-2 atmospheres
• The yield of SO3 increases as P is increased
• High pressure is costly £££

13. USES OF
SULFURIC ACID

15. It might well be said that the industrial progress of a nation is directly proportional
to the amount of sulphuric acid that it consumes.
Microfined sulphur, and
derivatives of sulphur are
sprayed on plants and trees to
destroy the
Fungus Insects
bacteria
etc. that
attack them
Sulphuric acid is by far,
the most important
chemical produced from
sulphur.
Sulphuric acid - a basic
reagent in most
chemical preparations
and in many industrial
processes.

16. In explosive industry
Sulphur is an important constituent of explosives, like gunpowder,
fireworks and firecrackers.
Other important
compounds of
sulphur produced
are:
Sulphur dioxide :
Used in bleaching
straw, wool, etc.
Calcium
bisulphite : Used
for bleaching
wood pulp
Phosphorus
trisulphide : Used
in safety matches
Carbon disulphide
: Used as an
industrial solvent
etc.

17. In the vulcanization of rubber
• Raw rubber is soft, but many commercial
applications of rubber require it to be hard and
resistant to wear and tear caused through friction.
• For e.g., the rubber of automobile and aeroplane
tyres is very hard.
• Vulcanization is the process where raw rubber is
boiled with sulphur to make it hard. It is named
after Vulcan, the Roman god of "fire".

18. Question:
Describe briefly what you observe when the following are
treated with concentrated sulphuric acid.
• sugar (a carbohydrate)
• blue copper sulphate crystals

19. Practice Questions

21. END