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Objectives of Distillation

Distillation is the most common technique used to separate two or more substances into their component parts. This is achieved by using a solvent which is generally water. There are several methods of distillation and these are used depending on the components of the liquids that need to be separated. Distillation is widely used in industry and features in the production process of many items necessary for daily life.

  1. Simple Distillation

    • The objective of simple distillation is to purify an impure or contaminated liquid. The various components in the liquid to be distilled will have different boiling points. The impure liquid is boiled and some converts into vapor. The vapor is then cooled and becomes liquid again. This is called condensing. The condensed liquid is the liquid in its pure form. The impure parts of the liquid have a much higher boiling point, so do not vaporize. This process is widely used in the production of spirits, such as whiskey, vodka and perfumes.

    Fractional Distillation

    • If the objective is to separate two liquids that have similar boiling points, simple distillation will not work. The separation of these liquids has to be achieved by fractional distillation. This process involves repeated distillations and condensations. This process is usually carried out using a fractional column, which is a column containing glass beads or shelves that will give the maximum surface area on which the vapor from the boiling liquids can condense. This is the process used to separate gasoline, kerosene and other fuels from crude oil.

    Azeotropic distillation

    • The objective of azeotropic distillation is to separate a mixture where the components are liquids that cannot be separated by fractional distillation. This occurs when the liquids are of a fixed weight and temperature that will cause them to distill together. In azeotropic distillation a third component is added to the mixture to distort the weight temperature ratio in the liquids to be distilled. This method is used to separate absolute alcohol from rectified spirit.

    Vacuum

    • The objective of vacuum distillation is to separate liquids that cannot be distilled using the simple distillation method because they decompose before reaching boiling point. Using the principle that a liquid boils when its vapor pressure becomes equal to the atmospheric pressure, the outside pressure around the liquid to be distilled is reduced. This causes it to boil and therefore distill, at a lower pressure. Sugarcane juice becomes sugar using this method and it's an important process in freeze drying.

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