Fractional distillation

Fractional distillation separates a mixture by repeated vaporization and condensation, enriching components according to their different volatilities and boiling points.

Vapor–liquid equilibrium: The condition in which vapor and liquid phases coexist with compositions set by temperature, pressure, and mixture composition. Each condensation and re-vaporization step approaches a new vapor–liquid equilibrium.
Boiling point: The temperature at which a liquid’s vapor pressure equals the surrounding pressure. Differences in boiling points often indicate which component distills first.
Petroleum refining: The processing of crude oil into fuels and chemical feedstocks through physical separation and chemical conversion. Atmospheric and vacuum fractionation divide crude oil into boiling-range cuts.
Simple distillation: A distillation method using one principal vaporization-condensation step to separate a volatile liquid from less volatile material. It lacks the repeated equilibration that gives fractional distillation sharper separation.
Distillation column: An apparatus that separates components by contacting rising vapor with descending liquid over multiple stages. Fractional distillation is commonly implemented in this industrial column form.
Theoretical plate: An idealized stage in a separation column that brings rising vapor and descending liquid to equilibrium. A column’s effective number of stages measures how many repeated equilibrations it provides.
Vapor pressure: The pressure exerted by a vapor in equilibrium with its liquid or solid. A component’s vapor pressure helps determine its abundance in the rising vapor.
Fractional distillation of crude oil: The separation of crude oil into fractions according to their boiling ranges in a refinery column. It is a large-scale, familiar example of staged vaporization and condensation.
Steam distillation: A method that co-distills water and an immiscible volatile compound to lower the temperature needed for separation. It separates certain heat-sensitive compounds by a different vapor-pressure strategy.
Batch distillation: A distillation operation in which a fixed charge is processed over time rather than continuously fed and withdrawn. It applies fractional separation to discrete batches instead of a steady industrial stream.

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