Distillation

 Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating of solid materials to produce gaseous products (which may condense into liquids or solids); this may involve chemical changes such as destructive distillation or cracking. Distillation may result in essentially complete separation (resulting in nearly pure components), or it may be partial separation that inceases the concentration of selected components; in either case, the process exploits differences in the relative volatility of the mixture's components. In industrial applications, distillation is a unit operation of practically universal importance, but is a physical separation process, not a chemical reaction. An instillation used for distillation, especially of distilled beverages, is a distillery.

Distillation includes the following applications:

• The distillation of fermented products produces distilled beverages with a high alcohol content, or separates other fermentation products of commercial value.
• Distillation is an effective and traditional method of desalination.
• In the petroleum industry, oil stabilization is a form of partial distillation that reduces the vapor pressure of crude oil, thereby making it safe for storage and transport as well as reducing the atmospheric emissions of volatile hydrocarbons. In midstream operations of oil refineries, fractional distillation is a major class of operation for transforming crude oil into fuels and chemical feed stocks.
• Cryogenic distillation leads to the separation of air into its components -  notably oxygen, nitrogen, and argon - for industrial use.
• In the chemical industry, large amounts of crude liquid products of chemical synthesis are distilled to separate them, either from other products, from impurities, or from unreacted starting materials.

The application of distillation can roughly be divided into four groups: laboratory scale, industrial distillation, distillation of herbs for perfumery and medicinals (herbal distillate), and food processing. The latter two are distinctively different from the former two in that distillation is not used as a true purification method but more to transfer all volatiles from the source materials to the distillates in the processing of beverages and herbs.

The main difference between laboratory scale distillation and industrial distillation are that laboratory scale distillation is often performed on a batch basis, whereas industrial distillation often occurs continuously. In batch distillation, the composition of the source material, the vapors of distilling compounds, and the distillate change during the distillation. Moreover, a still is charged (supplied) with a batch of feed mixture, which is then separated into its component fractions, which are collected sequentially from most volatile to less volatile, with the bottoms - remaining least or non-volatile fraction - removed at the end. The still can then be recharged and the process is repeated.

In continuous distillation, the source materials, vapors, and distillate are kept at a constant composition by carefully replenishing the source material and removing fractions from both vapor and liquid in the system. This results in a more detailed control of the separation process.

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