5.7 describe and explain how the industrial process of fractional distillation separates crude oil into fractions

NOTE: the process of fractional distillation is mentioned in point 1.7

One use of fractional distillation is separating crude oil into fractions (compounds). Heres how it happens...

- Heat the crude oil until almost all of it has turned into gas, these gases will enter the fractioning column as they evaporate. NOTE: the left over liquid is bitumen, it has a very high boiling temperature so is instead tapped off at the bottom of the column.
- NOTE: in the column there is a temperature gradient. Basically, it is really hot at the bottom and quite bit colder in the top (not actually cold though). This is useful as the substances that make up crude oil have different boiling temperatures, when the substance meets the part of the tube where it is cooler than their boiling temperature, they will condense and drain off down a tube. (NOTE: hydrocarbons with short carbon chains have a low boiling point, so they condense near the top of the fractioning column whilst hydrocarbons with long carbon chains have high boiling points, so they condense near the bottom of the fractioning column.
- This means you result with the different fractions of crude oil (each fraction contains a mixture of hydrocarbons with similar boiling points).