Dry distillation

Dry distillation is the heating of solid materials to produce gaseous products (which may condense into liquids or solids). The method may not involve pyrolysis or thermolysis. The products are condensed and collected. This method usually requires higher temperatures than classical distillation. The method has been used to obtain liquid fuels from coal and wood. It can also be used to break down mineral salts such as sulfates through thermolysis, in this case producing sulfur dioxide/sulfur trioxide gas which can be dissolved in water to obtain sulfuric acid. By this method sulfuric acid was first identified and artificially produced. When substances of vegetable origin, e.g. coal, oil shale, peat or wood, are heated in the absence of air (dry distillation), they decompose into gas, liquid products and coke/charcoal. The yield and chemical nature of the decomposition products depend on the nature of the raw material and the conditions under which the dry distillation is done. Decomposition within a temperature range of 450 to about 600°C is called carbonization or low-temperature degassing. At temperatures above 900°C, the process is called coking or high-temperature degassing. If coal is gasified to make coal gas or carbonized to make coke then Coal tar is among the by-products.

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