Fractional distillation

• Crude oil - Crude oil is a mixture of hydrocarbons which is formed from the remains of dead animal and plants matter which fossilised millions of years ago extracted from deep under ground.
• Fractional Distillation - The process by which crude oil is separated into its constituent fractions or components based on their boiling points
• During the fractional distillation of crude oil:

  • heated crude oil enters a tall fractionating column, which is hot at the bottom and gets cooler towards the top
  • vapours from the oil rise through the column
  • vapours condense when they become cool enough
  • liquids are led out of the column at different heights
• Small hydrocarbon molecules have weak intermolecular forces, so they have low boiling points. They do not condense, but leave the column as gases. Long hydrocarbon molecules have stronger intermolecular forces, so they have high boiling points. They leave the column as hot liquid bitumen.
• Crude oil fractions

  The different, useful mixtures are called fractions. This is because they are only part of the original crude oil.
• Petrol (gasoline) – used to power cars and other vehicles. It has an octane rating between 91-95. Octane ratings indicate how well petrol will burn without causing engine damage.
• Kerosene/paraffin – used as fuel for lamps and heaters. Kerosene can be made more flammable by adding lighter substances such as benzene.
• Liquefied Petroleum Gas (LPG) – mainly propane and butane. Used as cooking gas and heating fuel.
• Diesel - Fuel for cars, lorries and buses
• Fuel oil - Fuel for ships and power stations
• Bitumen - Road and roof surfacing
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