• • The many Hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of Carbon atoms, by fractional distillation.

  • The fractions can be processed to produce fuels and feedstock for the petrochemical industry.

  • Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil.

  • Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergents.

  • The vast array of natural and synthetic Carbon compounds occur due to the ability of Carbon atoms to form families of similar compounds.

  • Students should be able to explain how fractional distillation works in terms of evaporation and condensation.

• Knowledge of the names of other specific fractions or fuels is not required.

  • Some properties of Hydrocarbons depend on the size of their molecules, including boiling point, viscosity and flammability.

  • These properties influence how Hydrocarbons are used as fuels. Students should be able to recall how boiling point, viscosity and flammability change with increasing molecular size.

There are hundreds of different Alkanes mixed together in Crude Oil.

It would be time-consuming and expensive to separate all the different Alkanes into pure substances.

So, we separate this complicated mixture into a simpler mixture of similar Alkanes - we call these simple mixtures fractions.

A fraction may contain dozens of different Alkanes but they will all be of similar size and so will behave in very similar ways (boil at similar temperatures, flow and burn equally well, etc)

The fractions are separated by boiling point through a process called Fractional Distillation.

The first process involves heating the crude oil to high temperature.

Hot crude oil is pumped in at the bottom.

The most volatile fractions (ones with lowest boiling points) burn best and flow most easily (low viscosity) - these are nearly all used as fuels.

Although longer molecules have more energy when burned, they are harder to light.

LPG burns easily and cleanly (no smoke) - so is useful for heating and cooking.

Petrol burns quite easily and quite cleanly but is easier to store because it is a liquid - so is useful as fuel for cars.

Kerosene and Diesel are harder to burn and burn less cleanly but are still liquid - so they are useful as fuel for jet engines and trucks respectively.

Heavy fuel oil is even harder to burn and burns even less cleanly but is still liquid - so it is re useful as fuel for huge ships, or to heat a large building like a hospital

Longer fractions are sometimes used for other purposes - lubricating oil is a fraction that doesn't burn well but is vital to keep engine parts moving well.

Bitumen is solid at room temperature and very hard to burn - it mostly gets used to make road surfaces.

Naphtha is just a touch too long to burn in a petrol engine - but a lot of it is used to make other substances.

It's molecules are usually shortened by Cracking to make more petrol, and this produces other substances that can be used to make polymers (plastics) etc.

It is a chemical feedstock.

All sorts of familiar substances contain molecules made from feedstocks separated from oil - paints, medicines, washing powder etc