Lecture 9 – Sulphuric acid & the Contact Process

Sulphuric Acid:

Sulphuric acid is an extremely important industrial product. Many industries depend on using sulphuric acid.

Industrial manufacture of Sulphuric Acid:

Sulphuric Acid is industrially manufactured in a 7 step process, listed below:

1. Sulphur from the earth’s crust is burned in the presence of Oxygen to form Sulphur dioxide.
   
2. Sulphur dioxide is purified by passing through electrostatic dust precipitators to remove arsenic impurities. Arsenic impurities decrease the efficiency of Vanadium(V) oxide catalyst.
3. Sulphur dioxide and Oxygen are washed with water and dried before reaction.
4. Sulphur dioxide is reacted with more Oxygen to form Sulphur trioxide. This is a reversible reaction and therefore, the gaseous mixture is reacted at a temperature of 450°C and 2 to 3atm pressure, in a chamber of heated Vanadium(V) oxide mesh as a catalyst. This is the most critical step of the process and this manufacture of Sulphur trioxide is also known as the Contact’s Process.
   
5. The conditions for this process are strictly monitored and maintained to ensure a maximum yield of Sulphur trioxide.
6. Sulphur trioxide obtained by Contact’s process is dissolved in Sulphuric acid to form a dense liquid called, Oleum.
   
7. This oleum is diluted with distilled water to form Sulphuric acid.

Uses of Sulphur dioxide:

1. As a bleaching agent 
2. In the manufacture of wood pulp for paper
3. As an antibacterial for food preservatives

Uses of Sulphuric acid:

1. Detergents
2. Fertilizers
3. Battery acid