How are alkanes separated in the petroleum refining process?

Alkanes in petroleum are separated using a process called fractional distillation.

Fractional distillation is a technique used in the petroleum refining process to separate a mixture of alkanes. This process is based on the principle that different components in a mixture will boil at different temperatures. The petroleum mixture is heated until it vaporises, and then it is fed into a fractionating column.

The fractionating column is a tall tower filled with trays or plates. It is hotter at the bottom and cooler at the top. As the vapour rises through the column, the components with higher boiling points condense on the lower trays, while those with lower boiling points continue to rise and condense on the higher trays. This results in the separation of the mixture into different fractions, each containing alkanes with a similar number of carbon atoms.

The separated fractions are then collected at different levels of the column. The fractions with lower boiling points, such as methane, ethane, propane and butane, are collected at the top of the column. These are typically used for heating and cooking. The fractions with higher boiling points, such as kerosene and diesel oil, are collected lower down. These are used as fuels in jet engines and vehicles. The heaviest fractions, such as bitumen, are collected at the bottom and are used for road surfacing and roofing.

In summary, the separation of alkanes in the petroleum refining process is achieved through fractional distillation, where the petroleum mixture is heated and the vapours are separated in a fractionating column based on their different boiling points.