Definition | Distillation | Futura Sciences

Distillation is a process for separating two substances miscible forming a homogeneous mixture. It consists of heating the liquid relying on the difference of volatility ingredients. AT atmospheric pressure, water boils for example at 100 ° C and ethanol at 78.5 ° C. It is therefore sufficient to heat the mixture above the boiling point of ethanol while remaining below 100 ° C. and to collect the vapor at the top. This is then cooled by passing through a coil to give the distillate.

Fractional distillation

When liquids have sufficiently distant boiling temperatures, simple distillation is sufficient. Otherwise, a fractional distillation will have to be carried out. The latter is carried out using a distillation column (or Vigreux column) comprising different levels of hollow points which condense the vapors as they rise. With a sufficient number of steps, an almost pure distillate of the most volatile liquid is obtained. A separation complete is not always possible to obtain. In the case of the water-ethanol mixture for example, a proportion of 95% ethanol is obtained for 5% water.

History of distillation

The first stills used for distillation were found in Mesopotamia, dating from around 3,500 years. First used for make perfumes and decoctions, they were then used to produce brandies by distillation of fermented fruit. Distillation was also commonly used by alchemists in the Middle Ages. The stills and retorts have today been largely replaced but are still appreciated by some alcohols fine and liqueurs like cognac or scotch whiskey, as well as for essential oils in perfumery.

Uses of distillation

Distillation is a process widely used in industry, to separate or purify products.

  • Oil refinery : the oil crude is injected into a large distillation tower about 60 meters high where it is heated to 400 ° C. The hydrocarbons the lightest (gas and petrol) are thus collected at the top of the tower, the heaviest (oils, bitumens, fuel oil…) remaining at the bottom. Medium hydrocarbons undergo a second so-called vacuum distillation phase, making it easier to recover heavy residues whose boiling point is lowered.

  • Chemistry: fractionation towers are used to separate or purify gases (oxygen, nitrogen liquid, argon, helium…). The distillation of chlorosilane also makes it possible to obtain silicon high quality for the semiconductors.

  • Desalination of sea water.

  • Perfumery and pharmacy: distillation is used to extract the compounds aromatic plants, or to obtain water of high chemical and microbial purity for the manufacture of medicines.

  • Food industry: distillation is mainly used for the production of spirits, but is also used on the contrary to eliminate alcohol to obtain non-alcoholic beer for example. Distillation is also used to decaffeinate coffee.

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