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A fractionating column or fractional column is equipment used in the distillation of liquid mixtures to separate the mixture into its component parts, or fractions, based on their differences in volatility. Fractionating columns are used in small-scale laboratory distillations as well as large-scale industrial distillations.
Fractionation is widely employed in many branches of science and technology. Mixtures of liquids and gasses are separated by fractional distillation by difference in boiling point. Fractionation of components also takes place in column chromatography by a difference in affinity between stationary phase and the mobile phase.
To improve fractionation the apparatus is set up to return condensate to the column by the use of some sort of reflux splitter (reflux wire, gago, Magnetic swinging bucket, etc.) – a typical careful fractionation would employ a reflux ratio of around 4:1 (4 parts returned condensate to 1 part condensate take off).
The McCabe–Thiele method is a technique that is commonly employed in the field of chemical engineering to model the separation of two substances by a distillation column. [ 1 ] [ 2 ] [ 3 ] It uses the fact that the composition at each theoretical tray is completely determined by the mole fraction of one of the two components.
Industrial distillation [41] [49] is typically performed in large, vertical cylindrical columns known as distillation towers or distillation columns with diameters ranging from about 0.65 to 16 metres (2 ft 2 in to 52 ft 6 in) and heights ranging from about 6 to 90 metres (20 to 295 ft) or more.
The distillation column is fed with a mixture containing the mole fraction xf of the desired compound. The overhead mixture is a gas or an aerosol which contains the mole fraction xD of the desired compound and the bottom product contains a mixture with the fraction xB of the desired compound.
Diagram of a Batch Rectifier. The simplest and most frequently used batch distillation configuration is the batch rectifier, including the alembic and pot still.The batch rectifier consists of a pot (or reboiler), rectifying column, a condenser, some means of splitting off a portion of the condensed vapour (distillate) as reflux, and one or more receivers.
Distillation by column still is the traditional method for production of Armagnac, although distillation by pot still is allowed. The use of column stills for the distillation of Cognac is forbidden, although they may be used for other types of brandy , likewise malt Scotch Whiskies must be distilled in a pot still.