Question

Describe the manufacturing of H₂SO₄ by the contact process.

Write chemical reactions in the manufacture of sulfuric acid by contact process.

How is sulphuric acid manufactured by contact process?

Give a brief account of the manufacture of sulphuric acid by contact process.

Answer 1

Sulphuric acid is manufactured by the contact process, which involves the following three steps.

1) Roasting in air: Sulphur or sulphide ore (iron pyrites) on burning or roasting in air produces sulphur dioxide.

i) \[\ce{\underset{Sulphur}{S_{(s)}} + O2_{(g)} ->[\Delta] \underset{Sulphur dioxide}{SO2_{(g)}}}\]

ii) \[\ce{\underset{Iron sulphide}{4FeS2_{(s)}} + 11O2_{(g)} ->[\Delta]  2Fe2O3_{(s)} +\underset{Sulphur dioxide}{8SO2_{(g)}}}\]

2) Catalytic oxidation of sulphur dioxide:

i) Sulphur dioxide is oxidised catalytically with oxygen to sulphur trioxide in the presence of V₂O₅ catalyst.

\[\ce{\underset{Sulphur dioxide}{2SO2_{(g)}} + O2_{(g)} ->[V2O5] \underset{Sulphur trioxide}{2SO3{(g)}}}\]

ii) The reaction is exothermic and reversible, and the forward reaction leads to a decrease in volume. Therefore, low temperature (720 K) and high pressure (2 bar) are favourable conditions for maximum yield of SO₃.

3) Absorption, followed by dilution of sulphur trioxide gas:

i) Sulphur trioxide gas (from the catalytic converter) is absorbed in concentrated H₂SO₄ to produce oleum.

\[\ce{\underset{Sulphur trioxide}{SO3} + H2SO4 -> \underset{Oleum}{H2S2O7}}\]

ii) Dilution of oleum with water gives sulphuric acid of desired concentration.

\[\ce{\underset{Oleum}{H2S2O7} + H2O -> \underset{Sulphuric acid}{2H2SO4}}\]

iii) The sulphuric acid obtained by the contact process is 96-98% pure.