Distillation

Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixture and the condensation of the vapors in a still.

Distillation can operate over a wide range of pressures from 0.14 bar (e.g., ethylbenzene/styrene) to nearly 21 bar (e.g.,propylene/propane) and is capable of separating feeds with high volumetric flowrates and various components that cover a range of relative volatilities from only 1.17 (o-xylene/m-xylene) to 81.2 (water/ethylene glycol).^[2] Distillation provides a convenient and time-tested solution to separate a diversity of chemicals in a continuous manner with high purity. However, distillation has an enormous environmental footprint, resulting in the consumption of approximately 25% of all industrial energy use.^[3] The key issue is that distillation operates based on phase changes, and this separation mechanism requires vast energy inputs.

Dry distillation (thermolysis and pyrolysis) is the heating of solid materials to produce gases that condense either into fluid products or into solid products. The term dry distillation includes the separation processes of destructive distillation and of chemical cracking, breaking down large hydrocarbon molecules into smaller hydrocarbon molecules. Moreover, a partial distillation results in partial separations of the mixture's components, which process yields nearly-pure components; partial distillation also realizes partial separations of the mixture to increase the concentrations of selected components. In either method, the separation process of distillation exploits the differences in the relative volatility of the component substances of the heated mixture.

In the industrial applications of classical distillation, the term distillation is used as a unit of operation that identifies and denotes a process of physical separation, not a chemical reaction; thus an industrial installation that produces distilled beverages, is a distillery of alcohol. These are some applications of the chemical separation process that is distillation:

• Distilling fermented products to yield alcoholic beverages with a high content by volume of ethyl alcohol.
• Desalination to produce potable water and for medico-industrial applications.
• Crude oil stabilisation, a partial distillation to reduce the vapor pressure of crude oil, which thus is safe to store and to transport, and thereby reduces the volume of atmospheric emissions of volatile hydrocarbons.
• Fractional distillation used in the midstream operations of an oil refinery for producing fuels and chemical raw materials for livestock feed.^[4][5][6]
• Cryogenic Air separation into the component gases — oxygen, nitrogen, and argon — for use as industrial gases.
• Chemical synthesis to separate impurities and unreacted materials.