Question

Explain in detail the manufacture of sulphuric acid by contact process.

Answer 1

Most of the sulfuric acid manufactured is produced using the Contact Process.

1. Solid sulfur, S(s), is burned in air to form sulfur dioxide gas, SO₂

$S\left(s\right)+O_2\left(g\right)\to S{O}_2\left(g\right)$

The gases are mixed with more air then cleaned by electrostatic precipitation to remove any particulate matter

3. The mixture of sulfur dioxide and air is heated to ${450}^0$ and subjected to a pressure of 101.3 - 202.6 kPa (1 -2 atmospheres) in the presence of a vanadium catalyst ($V_2{O}_5$) to produce sulfur trioxide, $S{O}_3$(g), with a yield of 98%.

$2S{O}_2+O_2\to 2S{O}_3$

Any unreacted gases from the above reaction are recycled back into the above reaction

4. Sulfur trioxide, $S{O}_3$(g) is dissolved in 98% (18M) sulfuric acid, $H_{2}S{O}_4$, to produce disulfuric acid or pyrosulfuric acid, also known as fuming sulfuric acid or oleum, $H_2{S}_2{O}_7$.

$S{O}_3\left(g\right)+H_{2}S{O}_4\to H_2{S}_2{O}_7$

This is done because when water is added directly to sulfur trioxide to produce sulfuric acid

$S{O}_3\left(g\right)+H_{2}O\left(l\right)\to H_{2}S{O}_4\left(l\right)$

the reaction is slow and tends to form a mist in which the particles refuse to coalesce.

5. Water is added to the disulfuric acid, $H_2{S}_2{O}_7$, to produce sulfuric acid, $H_{2}S{O}_4$

$H_2{S}_2{O}_7\left(l\right)+H_{2}O\left(l\right)\to H_{2}S{O}_4\left(l\right)$