Fractional distillation of crude oil

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- Crude oil is made up of hydrocarbons and is a fossil fuel (like coal and natural gas)

- These are separated by fractional distillation: a tower is heated and the fractions with the lowest boiling points are collected at the top (where itʼs coolest) and the fractions with the highest boiling points are immediately tapped off at the bottom in liquid form

- Incomplete combustion (combustion when there is not enough oxygen) can lead to carbon monoxide being formed. 

- Carbon monoxide is lethal as it bonds irreversibly with the haemoglobin which carry oxygen around the body, and so reduce your bodyʼs oxygen carrying capabilities

- In car engines, nitrogen is combusted to form nitrogen oxide

- Fractional distillation produces less short-chain molecules than required and more long-chain ones.

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The tower

1. Crude oil is pumped in at the base.

2. Compounds boil off one by one.

3. The smallest molecules boil off first and rise to the top of the tower.

4. Others rise part of the way (depending on boiling points)

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Fraction 1- Gas

Number of carbon atoms: C1 to C4

Use: Separated into fuels methane, ethane, propane and butane

For heating and cooking

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Fraction 2- Petrol (Gasoline)

Number of carbon atoms: C5 to C6

Use: Fuel for cars

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Fraction 3- Naphtha

Number of carbon atoms: C6 to C10

Use: Starting point

Feedstock for chemicals and plastics

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Fraction 4- Paraffin (Kerosene)

Number of carbon atoms: C10 to C15

Use: Fuel for aircraft (Jet fuel)

Oil stoves and lamps

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Fraction 5- Diesel

Number of carbon atoms: C15 to C20

Use: Fuel for diesel engines

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Fraction 6- Fuel oil

Number of carbon atoms: C20 to C30

Use: Fuel for power stations and ships

Heating systems (Industrial heater)

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Fraction 7- Lubricating Fraction

Number of carbon atoms: C30 to C50

Use: Oil for car engines

Oil for machinery

Waxes and polishes

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Fraction 8- Bitumen

Number of carbon atoms: < C50

Use: Road surfaces and roofs

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Catalytic Cracking


Alkane is a long-chain hydrocarbon, and these molecules are passed over a catalyst (silica or aluminium oxide) and heated to about 600°C. They then start to break down into a short- chained alkane, and at least one alkene.

Eg. Cracking of Decane (C10H22) to produce octane (C8H18) and ethene (C2H4).

 C10H22(g) --> C8H18(g) + C2H4(g)

INCOMPLETE COMBUSTION can create carbon monoxide, which reduces the bloods ability to carry oxygen.

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