fractionering

Fractionering, or fractionation, is the process of separating a mixture into fractions that differ in composition, usually based on differences in physical properties such as boiling point, solubility, or molecular weight. In practice, the most common form is distillation, especially fractional distillation, which uses a fractionating column to create many theoretical plates and achieve separation of components with relatively close boiling points.

Besides distillation, other methods for fractioning include crystallization, solvent extraction, membrane separation, adsorption, and centrifugal methods. The choice of method depends on the nature of the mixture and the desired purity of the fractions.

In industry, fractionering plays a central role. In petroleum refining, crude oil is separated into fractions such as naphtha, gasoline, kerosene, diesel, gas oil, and heavy residues, each with different uses. In the food and oleochemical industries, fats and oils can be fractionated into olein and stearin fractions to tailor texture and melting behavior. In chemistry and bioprocessing, fractionation can purify products, separate polymers by molecular weight, or isolate components based on polarity. Isotopic fractionation refers to small systematic changes in isotopic composition during physical or chemical processes and is used in geochemistry and environmental science.

Key concepts include relative volatility, azeotropes, reflux, and column design for distillation. Limitations of fractionering include energy requirements, equipment costs, and the existence of azeotropes that complicate separation.