How does fractional distillation of crude oil work?
Fractional distillation separates crude oil into fractions by their different boiling points, using a column that is hot at the bottom and cooler at the top.
GCSE Chemistry
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In more detail
Crude oil is heated so it evaporates, and the vapours rise up the fractionating column. The column has a temperature gradient — hot at the bottom, cool at the top. Hydrocarbons with high boiling points (long chains) condense low down where it is hot; hydrocarbons with low boiling points (short chains) rise higher and condense where it is cooler. Each fraction is a mixture of hydrocarbons with similar chain lengths and boiling points.
Key points for the exam
- Separation is by boiling point, which depends on molecule size.
- Short chains → low boiling point → collected near the top; long chains → high boiling point → collected near the bottom.
- The column has a temperature gradient (hot bottom, cool top).
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