How does fractional distillation separate crude oil components?

Fractional distillation separates crude oil components based on their different boiling points.

Crude oil is a complex mixture of hydrocarbons, each with its own unique boiling point. Fractional distillation exploits this property to separate the components. The process begins by heating the crude oil to about 350 degrees Celsius, turning it into a vapour. This vapour is then fed into a distillation column, also known as a fractionating column.

The fractionating column is a tall, cylindrical 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 temperature gradually decreases. When the temperature drops below the boiling point of a particular component, that component condenses back into a liquid and is collected on one of the trays. This is known as a 'fraction'.

The fractions collected lower down the column, where the temperature is higher, contain hydrocarbons with lower boiling points. These are typically gases such as methane, ethane, propane and butane. Further up the column, where the temperature is lower, the fractions contain hydrocarbons with higher boiling points. These are typically liquids such as petrol (gasoline), kerosene, diesel and lubricating oil. At the very top of the column, where the temperature is lowest, the fractions contain hydrocarbons with the highest boiling points. These are typically solids such as bitumen, used for road surfacing and roofing.

The key to fractional distillation is the temperature gradient within the column. This gradient allows each component to condense at its own unique position within the column, effectively separating the crude oil into its constituent parts. The process is continuous, with fresh crude oil being added and the separated fractions being removed continuously.

In summary, fractional distillation separates crude oil components by heating the oil, turning it into a vapour, and then allowing it to condense at different temperatures within a fractionating column. The result is a range of fractions, each containing a different type of hydrocarbon.