Destructive distillation

Destructive distillation is a chemical process in which decomposition of unprocessed material is achieved by heating it to a high temperature; the term generally applies to processing of organic material in the absence of air or in the presence of limited amounts of oxygen or other reagents, catalysts, or solvents, such as steam or phenols. It is an application 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 commercial products historically produced by the destructive distillation of coal.

Destructive distillation of any particular inorganic feedstock produces only a small range of products as a rule, but destructive distillation of many organic materials commonly produces very many compounds, often hundreds, although not all products of any particular process are of commercial importance. The distillate are generally lower molecular weight. Some fractions however polymerise or condense small molecules into larger molecules, including heat-stable tarry substances and chars. Cracking feedstocks into liquid and volatile compounds, and polymerising, or the forming of chars and solids, may both occur in the same process, and any class of the products might be of commercial interest.

Currently the major industrial application of destructive distillation is to coal.^[1][2]

Historically the process of destructive distillation and other forms of pyrolysis led to the discovery of many chemical compounds or elucidation of their structures before contemporary organic chemists had developed the processes to synthesise or specifically investigate the parent molecules. It was especially in the early days that investigation of the products of destructive distillation, like those of other destructive processes, played parts in enabling chemists to deduce the chemical nature of many natural materials.^[3] Well known examples include the deduction of the structures of pyranoses and furanoses.^[4]