Azeotropic distillation

A separation process that adds an entrainer to alter vapor–liquid equilibrium, allowing components that form an azeotrope to be separated.

Azeotrope: A liquid mixture that boils at a constant composition because its vapor and liquid compositions are equal at equilibrium. The process targets the composition barrier created when the feed forms this mixture.
Raoult's law: An ideal-solution relation connecting a component’s liquid mole fraction and vapor pressure to its partial pressure. Deviations from this ideal behavior help produce the azeotropes the process addresses.
Ethanol dehydration: The removal of water from ethanol beyond the concentration attainable by ordinary distillation. Azeotropic methods have been used to break the ethanol–water separation limit.
Entrainer recovery: The recovery and reuse of an added process solvent or auxiliary component after separation. The process requires managing the entrainer so it does not contaminate products or accumulate.
Entrainer: A substance added to a mixture to alter its separation behavior without becoming a desired product component. Its interactions with the feed components create a new vapor–liquid equilibrium.
Activity coefficient: A factor that adjusts chemical potential calculations for nonideal interactions in a mixture. Entrainer selection depends on how it changes component activities in the liquid.
Benzene: An aromatic hydrocarbon historically used as an entrainer in ethanol dehydration. Its use illustrates how a third component can enable separation while creating safety concerns.
Azeotropic distillation column: A distillation column configured to separate a feed using an added entrainer. Column arrangement and recycle streams determine how the altered equilibrium is exploited.
Vapor–liquid equilibrium: The thermodynamic condition governing the compositions of coexisting vapor and liquid phases. The entrainer must change this equilibrium enough to make separation possible.
Nonideal solution: A solution whose thermodynamic behavior deviates from ideal-mixture predictions because of molecular interactions. Azeotropic formation and entrainer effects arise from nonideal mixture behavior.

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