Destructive distillation
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Destructive distillation is the process of pyrolysis conducted in a distillation apparatus (retort) to allow the volatile products to be collected. The process led to the discovery of many chemical compounds before such compounds could be prepared synthetically. Destructive distillation is not a unit operation as true distillation, but a chemical reaction. It is a strongly reductive reaction, cracking macromolecules into smaller, more volatile, components.
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, terpenes 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 and coal tar
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