9.1 Manufacture of Sulphuric Acid

The manufacture of sulphuric acid is called Contact Process.

The raw materials required in contact process are sulphur, air and water.

The contact process involves THREE stages of chemical reactions as below:

Stage I : Production sulphur dioxide, SO₂

Sulfur is burnt in dry air in the furnace to produce sulphur dioxide.

S + O₂ → SO₂

Stage II : Conversion of SO₂ to SO₃

Pure SO₂ reacts with oxygen in catalytic converter to produce sulphur trioxide at a temperature between 450°C to 550°C.

2SO₂ + O₂ → 2SO₃

This stage requires catalyst vanadium(V) oxide.

Stage III : Production of sulphuric acid

In the absorber, sulphur trioxide is dissolved in concentrated sulphuric acid to produce oleum, H₂S₂O₇.

H₂SO₄ + SO₃ → H₂S₂O₇

Oleum is the diluted in water to produce two molecule of sulphuric acid.

H₂S₂O₇ + H₂O → 2H₂SO₄

SO₃ gas is not directly dissolved in water to produce H₂SO₄ because the reaction releases large amount of heat and is able to vaporize sulphuric acid and produces acid mist.

Among the uses of sulphuric acids are:

i. to manufacture fertilizers

ii. to manufacture detergent

iii. to manufacture paint pigment

iv. to remove metal oxide from metal surface

v. to manufacture pesticide

vi. as the electrolyte in lead-acid accumulators

The burning of products manufactured from sulphuric acid will produce SO₂. The SO₂ dissolved in atmospheric water vapour to produce acid and subsequently causes the acid rain.

SO₂ + H₂O → H₂SO₃