Fractionation

Fractionation is a set of processes used to separate a mixture into fractions that differ in one or more properties, such as boiling point, solubility, or density. The goal is to obtain components with greater purity or to study individual components.

In chemistry and chemical engineering, fractional distillation is common. A mixture is heated to vaporize components; vapors rise through a fractionating column containing internal surfaces that promote repeated condensation and vaporization, creating successive volatilities and enabling separation by boiling point. Other methods include fractional crystallization, which relies on different solubilities upon cooling, and solvent extraction, which partitions components between immiscible solvents.

In biology and biochemistry, cellular fractionation uses differential centrifugation or density-gradient centrifugation to separate subcellular structures such as nuclei, mitochondria, chloroplasts, lysosomes, and cytosol, enabling analysis of structure and function.

In other contexts, fractionation can refer to isotopic fractionation, where chemical or physical processes prefer one isotope over another, leading to variations in isotope ratios. It is also applied in the petroleum industry to separate crude oil into fractions like gases, naphtha, gasoline, kerosene, and fuel oils by successive distillation.

Limitations include overlap of properties among components and potential degradation during processing; selecting appropriate conditions and verification methods is essential for achieving meaningful separation.