Destructive distillation
Destructive distillation is a chemical process. During destructive distallation decomposition of unprocessed material is caused by heating the material to a high temperature. The term usually applies to processing of organic material in an area with little or no oxygen  or other reagents, catalysts, or solvents. These would include things  such as steam or phenols. It is an use of pyrolysis. The process breaks up or 'cracks' large molecules. Coke, coal gas, gaseous carbon, coal tar, ammonia liquor, and coal oil are examples of things made by the destructive distillation of coal.