Petroleum is a mixture of many alkanes. The alkanes are separated and purified at oil refineries. What process decribes what happens in an oil refinery?

Fractional distillation

Explanation:

The process of separating petroleum products into its fractions is called fractional distillation.

Fractional distillation is a method of separating a mixture of substances based on the differences in their boiling points.

Petroleum is a mixture of hydrocarbons separated in a large fractionation tower having many trays maintained at different temperatures.

As the vapor containing the petroleum mixture ascends the fractionation tower, the mixture is separated at each tray to yield the various fractions of petroleum.