dry distillation, decomposition or destruction of organic substances by means of heat and an absence of air (produces products such as coke, charcoal, oils and gases)
Destructive distillation is the process of
pyrolysis conducted in a distillation apparatus to allow the volatile products to be collected. The process led to the discovery of many chemical compounds before such species could be prepared synthetically.A historically significant example of destructive distillation is
tar making. Pinewood slices, which are rich in
terpenes, are heated in an airless container causing the material to decompose. The by-products are
turpentine and
charcoal. This process is still used in Scandinavia for tar-making. Coal tar
pitch volatiles (CTPV) are the result of destructive distillation of
bituminous coal. These CTPVs often contain
polynuclear aromatic hydrocarbons (PNA's), which sublime readily and are
carcinogenic. Other examples of substances that are commonly destructively distilled to extract chemicals and other materials include:
Wood to give
methanol, and
guaiacol.
Coking' refers to the transformation of coal or heavy oil into coke, typically at temperatures near 1,000 °C.
Coal (lower grades) to give
Coal gas
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