Crude oil, hydrocarbons and alkanes
Crude oil is a finite resource. Petrol and other fuels are produced from it using fractional distillation. Cracking is used to convert long alkanes into shorter, more useful hydrocarbons.
Separating crude oil
Fran Scott explains fractional distillation - the separation of crude oil into fractions
Fractional distillation is used to separate crude oil into simpler, more useful mixtures. This method can be used because different hydrocarbons have different boiling points.
Fractional distillation
During the fractional distillation of crude oil:
- heated crude oil enters a tall fractionating column, which is hot at the bottom and gets cooler towards the top
- vapours from the oil rise through the column
- vapours condense when they become cool enough
- liquids are led out of the column at different heights
Small hydrocarbon molecules have weak intermolecular forces, so they have low boiling points. They do not condense, but leave the column as gases. Long hydrocarbon molecules have stronger intermolecular forces, so they have high boiling points. They leave the column as hot liquid bitumen.
Crude oil fractions
The different, useful mixtures are called fractions. This is because they are only part of the original crude oil.