Destructive distillation is the process of heating complex substances such as coal in a limited supply of air so that it breaks down to form simpler substances. In this process coal is heated to 10000C in the absence of air to obtain different useful components, such as coke, coal tar and coal gas.
Destructive Distillation of Coal
Finely powdered coal taken in a test tube is heated. As the coal breaks down coke, coal tar, ammonia and coal gas are produced. Coal tar collects at the bottom of the second test tube and coal gas escapes out through the side tube. The ammonia produced is absorbed in the water forming ammoniacal liquor (ammonium hydroxide). The black residue left in the 1st tube is called coke.
Coke is a fuel used in homes and factories. But it is largely used as a reducing agent in the extraction of metals from their ores. It is also used in making fuel gases like water gas which is a mixture of carbon monoxide and hydrogen.
Another by product namely coal tar which is a mixture of different carbon compounds can be used to make soap, fats, dyes plastics perfumes, drugs, pesticides, explosives etc.
The coal gas, also called as a town gas is a mixture of hydrogen, methane and carbon monoxide which are combustible making the coal gas an excellent fuel having high calorific values.