C9.2 - Fractional distillation of oil

• Fractional distillation can be used to separate hydrocarbon fractions. Cruse oil is a mixture of lots of different hydrocarbons, most of which are alkanes. Crude oil is separated into hydrocarbons with similar boiling points, called fraction. This process is called fractional distillation.
• Approximate number of carbons in the hydrocarbons in that fraction:

  
• Once collected, the fractions need more processing before they can be used
• 1. The oil is heated until most of it has turned into a gas. The gases then enter a fractionating column (and the liquid bit is drained off).
  2. In the column, there is a temperature gradient (it is hot at the bottom and gets cooler as you go up)
  3. The longer hydrocarbons have high boiling points. They condense back into liquids and drain out of the column early on, when they are near the bottom. The shorter hydrocarbons have lower boiling points. They condense and drain out much later on, near to the top of the column where it is cooler