Fractional distillation

• Crude oil is made over a long period of time
• Crude oil is a fossil fuel, it forms from the remains of plants and animals, mainly plankton, that died millions of years ago and was buried in mud

  Over millions of years, with high temperature and pressure, the remains turn to crude oil which is drilled from the rock
• Fossil fuels like coal, oil and gas are called non- renewable fuels (take so long to make that they're being used up much faster than they're being formed)
• Fractional distillation is used to separate hydrocarbon fractions
• Crude oil is a mixture of lots of different hydrocarbons, most of which are alkanes
• The different compounds in crude oil are separated by fractional distillation
• HOW IT WORKS

  1. The oil is heated until most of it turns to gas, the gas enters a fractionating column (liquid bit drained off)
  2. In the column theres a temperature gradient (hot at bottom and gets cooler as you go up)
  3. The longer hydrocarbons have high boiling points- they condense into liquids and drain out of the column early on, near the bottom
  4. The shorter hydrocarbons have lower boiling points, they condense and drain out much later on, near to the top where its cooler
  5. End up with crude oil mixtures separated out into different fractions
• Each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points