Fractional Distillation and Uses of Fractions — AQA GCSE Chemistry
Crude oil is separated into useful fractions by fractional distillation.
The process
Crude oil is separated into fractions (groups of hydrocarbons with similar boiling points) by fractional distillation:
- The crude oil is heated until it evaporates.
- The vapours enter a fractionating column that is hot at the bottom and cooler at the top.
- As the vapours rise and cool, each fraction condenses at the height where the temperature equals its boiling point.
- Larger molecules (higher boiling points) condense lower down; smaller molecules condense higher up.
Each fraction contains hydrocarbons with a similar number of carbon atoms.
The fractions and their uses
| Fraction | Use |
|---|---|
| Refinery gases | bottled gas (heating, cooking) |
| Petrol (gasoline) | car fuel |
| Kerosene | aircraft fuel |
| Diesel oil | fuel for cars, trains, lorries |
| Fuel oil | ships and power stations |
| Bitumen | road surfaces and roofing |
Feedstock for the petrochemical industry
Many fractions are also used as feedstock to produce useful materials such as solvents, lubricants, polymers and detergents.
Exam tips
- Fractions separate by boiling point (smaller molecules condense higher up).
- Each fraction has hydrocarbons of similar chain length.
- Learn the fractions in order and their uses.
- Crude oil is the main source of fuels and petrochemical feedstock.