Question

Describe the manufacture of $H_{2}S{O}_4$ by contact process?

Answer 1

The steps involved in the manufacture of sulphuric acid by contact process are as shown:

(1) Sulphur (or iron pyrites) are burnt in air to form sulphur dioxide.
$S+O_2\to S{O}_{2}4Fe{S}_2+11O_2\to 2F{e}_2{O}_3+8S{O}_2$

(2) Catalytic oxidation of sulphur dioxide to sulphur trioxide.
$2S{O}_2+O_2\stackrel{V_2{O}_5}{\to }2S{O}_3{\Delta }_r{H}^o=-196.6$kJ

The reaction is reversible and exothermic.

(3) Sulphur trioxide is dissolved in 98% sulphuric acid to form oleum (fuming sulphuric acid).

$S{O}_3+H_{2}S{O}_4\to H_2{S}_2{O}_7$

(4) Oleum is diluted with water to form sulphuric acid of desired concentration.
$H_2{S}_2{O}_7+H_{2}O\to 2H_{2}S{O}_4$

and

Manufacture of $H_{2}S{O}_4$ by contact process involves three steps:

1. Burning of sulphur in air to generate $S{O}_2$.

2. Conversion of $S{O}_2$ to $S{O}_3$ by oxidation with air in the presence of $V_2{O}_5$ as catalyst.

3. Absorption of $S{O}_3$ in $H_{2}S{O}_4$ to obtain oleum $H_2{S}_2{O}_7$. A flow diagram for the manufacture of $H_{2}S{O}_4$ is given below: