fractional distillation

• crude oil is made over a long period of time
• crude oil is a fossil fuel, it’s formed by plants, animals and mainly plankton that died millions of years ago and were buried in mud. over millions of years with high temperature and pressure, the remains turn into crude oil which can be drilled up from the rocks where it’s found
• fossil fuels like coal, oil and gas are called non renewable fuels as they take so long to make that they are being used up much faster than they’re being formed
• fractional distillation can be used to separate hydrocarbon fractions
• crude oil is a mixture of lots of different hydrocarbons most of which are alkanes
• different compounds in crude oil are separated by fractional distillation
• step 1

  oil is heated until it’s turned to gas, gas enters fractionating column
• step 2

  the column has a temperature gradient (hot at bottom and cool as you go up)
• step 3

  the longer hydrocarbons have high boiling points, they condense back into liquids and drain out of the column early on at the bottom. the shorter hydrocarbons have lower boiling points, they condense and drain out near the top where it’s cooler
• step 4

  toy end up with the crude oil mixture separated out into different fractions, each fraction contains mixtures of hydrocarbons that all contain a similar number of carbon atoms so have similar boiling points
• Fractions

  • LPG
  • Petrol
  • Kerosene
  • Diesel oil
  • Heavy fuel oil
  • Bitumen