Continuous distillation is an ongoing separation process in which a liquid mixture of two or more miscible components is continuously fed into the process and physically separated into two or more products by preferentially boiling the morevolatile (i.e., lower boiling point) components out of the mixture.
Large-scale, continuous distillation is very commonly used in the chemical process industries where large quantities of liquids have to be distilled, as in petroleum refining, natural gas processing, petrochemical production, hydrocarbon solventsproduction, coal tar processing, the liquefaction of gases such as hydrogen,oxygen, nitrogen, and helium), and other low-temperature processing.
Industrial distillation is typically performed in large, vertical cylindrical columns commonly referred to as distillation columns, distillation towers or fractionators with diameters ranging from about 65 centimetres to 11 metres and heights ranging from about 6 metres to 60 metres or more.
To provide for the intimate mixing of the upward flowing vapor and downward flowing liquid in distillation columns, the columns usually contain a series of horizontal distillation trays or plates. The distillation trays or plates are typically separated by about 45 to 75 centimetres of vertical distance. However, some columns are designed to use beds of packing media rather than trays or plates.
Distillation is one of the fundamental unit operations of chemical engineering. If the feed contains more than two components, it is commonly referred to as multi-component distillationand, if it contains only two components, it is referred to as binary distillation.
If the distillation column feed contains a very great number of components (such as is the case in distilling petroleum crude oil), separation into pure components is impractical and such columns are therefore designed to yield fractions which are groups of components within a desired range of boiling points. Those fractions are probably the origin of the terms fractional distillation and fractionation.
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