SULPHURIC ACID Sulphuric acid is manufactured commercially by the contact process. The raw materials used in this process are a 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) + O 2(g) SO 2(g) Heating sulphide ores like pyrite in an excess of air: 4FeS 2(s) + 11O 2(g) 2Fe 2 O 3 ( s ) + 8SO 2 (g) Decomposing calcium sulphate in the presence of coke 2CaSO 4 ( s ) + C (s) 2CaO (s) + CO 2 (g) + 2SO 2 (g)

2. Oxidation of sulphur dioxide to sulphur trioxide: Sulphur dioxide is mixed with excess air and passed through an electrostatic precipitator which removes dust and impurities. The purified sulphur dioxide combines with oxygen in the presence of a catalyst, vanadium oxide to form sulphur trioxide, the anhydride of sulphuric acid: 2SO 2 (g) + O 2 (g) 2SO 3 (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 an exceptable reaction rate. It is done close to atmospheric pressure. The reaction is further enhance by increasing the concentration of oxygen in the mixture which is supplied by the air

It must be noted that since the forward reaction is exothermic the temperature of the surrounding system increases thus the gases are cooled down by a cooling system which employs the use of a closed water circuit.

3.Hydration of sulphur trioxide to sulphuric acid:- The sulphur trioxide is first dissolved in concentrated sulphuric acid to form oleum: H 2 SO 4 (I) + SO 3 (g) H 2 S 2 O 7 (I) It is then diluted with water to produce concentrated sulphuric acid: H 2 S 2 O 7 (I) + H 2 O(I) 2H 2 SO 4 (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 also used in petroleum refining and metallurgy.

Some impacts of the sulphuric acid industry Sulphuric acid production is a net producer of energy The spent sulphuric acid is regenerated and recycled to prevent it from becoming a waste and a problem to the environment.

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