Fractional Distillation of Crude Oil

Crude oil is a mixture of hydrocarbons
1. Crude oil is a mixture of many different compounds. Most of the compounds are hydrocarbon molecules
2. Hydrocarbons are basically fuels such as petrol and diesel. They are made of just carbon and hydrogen
3. There are no chemical bonds between the different parts of a mixture so the different hydrocarbon molecules in crude oil arent chemically bonded to one another
  1. This means that they all keep their original properties such as their condensing points. The properties of a mixture are just a mixture of the properties of the separate ions
4. The parts of a mixture can be separated out by physical methods e.g. crude oil can be split up into its separate fractions by fractional distillation. Each fraction contains molecules with a similar number of carbon atoms to each other
The fractionating column works continuously with heated crude oil piped in at the bottom. The vaporised oil rises up the column and the various fractions are constantly tapped off at the different levels where they condense
1. The longer the molecule the further down the fractionating column they are
Crude oil is mostly alkanes
1. All the fractions of crude oil are hydrocarbons called alkanes
  1. Alkanes are made up of chains of carbon atoms surrounded by hydrogen atoms
    1. Different alkanes have chains of different lengths
      1. The first four alkanes are methane, ethane, propane and butane
        Carbon atoms form four bonds and hydrogen atoms only form one bond.
Basic trends
1. The shorter the molecules the more runny the hydrocarbon is
2. The shorter the molecules the more volatile they are. That means they turn into a gas at a lower temperature. So they have a lower boiling point
3. The shorter the molecules the more flammable they are
The uses of hydrocarbons depend on their properties
1. The volatility helps decide what the fraction is used for. The refinery gas fraction has the shortest molecules so it has the lowest boiling point. This makes it ideal for using as bottles gas. Its stored under pressure as liquid in bottles.
2. The petrol fraction has longer molecules so it has a higher boiling point. Petrol is a liquid which is ideal for storing in the fuel tank of a car. It can flow to the engine where its easily vaporised to mix with the air before its ignited
3. The viscosity also helps decide how the hydrocarbons are used. The really gloopy viscous hydrocarbons are used for lubricating engine parts and for covering roads
Crude oil provides an important fuel for modern life
1. Crude oil fractions burn cleanly so they make good fuels. Most modern transport is fuelled by a crude oil fraction. Parts of crude oil are also burned in central heating systems in homes and in power stations to generate electricity
2. Massive industry
3. Alternatives are possible e.g. nuclear power
4. Things tend to be set up for using oil fractions
5. More reliable
May run out
1. New oil reserves are discovered from time to time and technology is constantly improving so its now possible to extract oil that was once too difficult or expensive to extract
2. Some people think we should immediatly stop using oil for things that have alternatives
3. It takes time to develop new alternatives that will satisfy all our energy needs
  1. renewable sources
Environmental Problems

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Fractional Distillation of Crude Oil

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	Created by sian.allison about 10 years ago