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Distillation has long been used as the separation process in the chemical and petroleum industries because of its reliability, simplicity, and low-capital cost. It is employed to separate benzene from toluene, methanol or ethanol from water, acetone from acetic acid, and many multicomponent mixtures. Fractionation of crude oil and the production of deuterium also rely on distillation.

Today, with 40,000 distillation towers in operation, distillation makes about 95% of all current industrial separation processes; however, distillation systems also have relatively high energy consumption. Significant effort, therefore, has been made to reduce the energy consumption and to improve the efficiency in distillation systems. This includes incorporating new analytical sensors and reliable hardware into the system to achieve advanced process control, using heat rejected from a condenser of one column to reboil other columns, and coupling other advanced process such as adsorption and crystallization with distillation to form energy-saving hybrid operation systems.

Pang-Jen Kung


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Activity coefficient

—The ratio of the partial pressure of a component in the gas phase to the product of its mole fraction in the liquid phase and its vapor pressure as a pure liquid which is an important factor encountered in many vapor-liquid separation processes.

Bubble point

—For a saturated liquid, because any rise in temperature will form bubbles of vapor, the liquid is said at its bubble point.

Dew point

—The point at which air or a gas begins to condense to a liquid.

Differential distillation

—During distillation, only a very small portion of the liquid is flashed each time and the vapor formed on boiling the liquid is removed at once from the system.


—The product withdrawn continuously at the top of the distillation column.


—Part of the condensate from the condenser is returned to the top tray of the distillation column as reflux to provide liquid flow above the feed point for increasing separation efficiency.

Additional topics

Science EncyclopediaScience & Philosophy: Direct Variation to DysplasiaDistillation - General Principles, Applications