Fractional Distillation *updated*

The generally-accepted origin of crude oil is from plant life  predominantly from 100 to 600 million years ago. “Dead vegetarian dino dinner” is more correct than “dead dinos”. The molecular structure of the hydrocarbons and other compounds present in fossil fuels can be linked to the leaf waxes and other plant molecules of land and sea plants believed to exist at that time. Crude oil is a mixture of different hydrocarbons. It’s usually found with deposits of natural gas which is about 92% methane. (m/c question)

Notice that the smaller hydrocarbons are gaseous with low mp and bp’s and the longer chain ones are liquids, then waxes, and finally, solids.

The fractional distillation of crude oil is a key industrial process, as it produces compounds such as methane, bitumen and gasoline. Seventy per cent of organic chemicals are produced from crude oil and a massive 3000 million tonnes of crude oil products are used worldwide every year. Fractional distillation separates crude oil into more useful hydrocarbons. These hydrocarbons are separated by their boiling points, each of these sections are called fractions. Properties of fractions at the top:

  • Low boiling point
  • Burn with a clear flame
  • Light coloured
  • More runny
  • Burn readily
  • Are smaller molecules

Properties of fractions at the bottom:

  • Have a high melting point
  • Are darker in colour
  • Are thicker
  • Less likely to burn
  • Are larger molecules
  • These hydrocarbons have a high boiling point and have longer carbon chains.

One fraction may contain many different hydrocarbons, not just one. The fractions collect further up the fractionating column if they have lower boiling points. Uses of different fractions

§  Refinery gas –> fuel

§  Gasoline –> fuel in cars (petrol)

§  Naphtha –> chemical manufacture

§  Kerosene/Paraffin –> fuel for jet engines

§  Diesel or Gas oil –> fuel for diesel engines

§  Fuel oil –> fuel for ships and for home heating

§  Lubricating oil –> waxes and polishes

§  Residue (the rest) –> bitumen manufacture and surfacing roads

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