Transformation of a compound into one or more other substances by heat alone, i.e., without oxidation. It is thus similar to destructive distillation. Though the term implies decomposition into smaller fragments, pyrolytic change may also involve isomerization and formation of higher molecular weight compounds. Hydrocarbons are subject to pyrolysis, e.g., formation of carbon black and hydrogen from methane at 1300C and decomposition of gaseous alkanes at 500–600C. The latter is the basis of thermal cracking (pyrolysis gasoline). One application of pyrolysis is conversion of acetone into ketenes by decomposition at about 700C; the reaction is CH3COCH3 → H2C═C═O + CH4. Pyrolysis of natural gas or methane at about 2000C and 100 mm Hg pressure produces a unique form of graphite. Synthetic crude oil can be made by pyrolysis of coal, followed by hydrogenation of the resulting tar. Large-scale pyrolysis of cellulosic wastes is being conducted for production of synthetic fuel oils and other products; the method is said to require only 30 minutes at about 537C (flash pyrolysis).See Destructive Distillation.
