SULPHURIC ACID
Sulphuric acid is manufactured commercially by thecontact process. The raw materials used in this process area source of sulphur dioxide, air, water and a catalyst.
The Contact Process
The main stages in this process are:-
1.Production of sulphur dioxide
2.Oxidation of sulphur dioxide to sulphur trioxide
3.Hydration of sulphur trioxide to sulphuric acid
1.Production of sulphur dioxide:-
This can be produced by;
Burning sulphur in an excess of air:
S(s) + O2(g) SO2(g)
Heating sulphide ores like pyrite in an excess of air:
4FeS2(s) + 11O2(g) 2Fe2O3(s) + 8SO2 (g)
Decomposing calcium sulphate in the presence of coke
2CaSO4 (s) + C(s) 2CaO(s) + CO2 (g) + 2SO2 (g)
2.Oxidation of sulphur dioxide tosulphur trioxide:
Sulphur dioxide is mixed with excess air and passedthrough an electrostatic precipitator which removes dustand impurities. The purified sulphur dioxide combineswith oxygen in the presence of a catalyst, vanadium oxideto form sulphur trioxide, the anhydride of sulphuric acid:
2SO2 (g) + O2 (g) 2SO3 (g) H= -196 kJ/mol
A Temperature of about 450 C is used with the catalyst,producing a fairly high yield of sulphur trioxide at anexceptable reaction rate. It is done close to atmosphericpressure.
The reaction is further enhance by increasing theconcentration of oxygen in the mixture which is suppliedby the air
It must be noted that since the forward reaction isexothermic the temperature of the surrounding systemincreases thus the gases are cooled down by a coolingsystem which employs the use of a closed water circuit.
3.Hydration of sulphur trioxide tosulphuric acid:-
The sulphur trioxide is first dissolved in concentratedsulphuric acid to form oleum:
H2SO4(I) + SO3 (g) H2S2O7(I)
It is then diluted with water to produce concentratedsulphuric acid:
H2S2O7(I) + H2O(I) 2H2SO4(I)
Uses of compounds of sulphur:-
Sulphur dioxide:
- in the manufacture of sulphuric acid (contact process)
- bleaching wool, straw and paper
- antioxidant in food preservation
- as a preservative in alcoholic drinks and dried fruits
Sulphuric acid: used in the manufacture of fertilizers,detergents, car batteries, paints and pigments. It is alsoused in petroleum refining and metallurgy.
Some impacts of the sulphuric acidindustry
Sulphuric acid production is a net producer of energy
The spent sulphuric acid is regenerated and recycledto prevent it from becoming a waste and a problem tothe environment.
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