Uses & Cracking of Crude Oil

• Crude oil has various uses important in modern life
• Oil provides the fuel for most modern trasnport - cars, tains, planes...Diesel oil, kerosene, heavy fuel oil and LPG all come from crude oil
• The petrochemical industry uses some of the hydrocarbons from crude oil as a feedstock to make new compounds for use in things like polymers, solvents, lubricants, and detergents
• All the products you get from crude oil are examples of organic compounds (compounds containing carbon atoms)
• The reason you get such a variety of products is because carbon atoms can bond together to form different groups called homologous series
• Homologous series contain similar compounds with many properties in common. Alkanes and alkenes are examples of different homologous series
• Cracking means splitting up long-chain hydrocarbons
• Short-chain hydrocarbons are flammable so make good fuels and are in high demand. However, long-chain hydrocarbons form thick viscous liquids like tar which aren't that useful
• A lot of the longer alkane molecules produced from fractional distillation are turned into smaller, more useful ones by a process called cracking
• As well as alkanes, cracking also produces another type of hydrocarbon called alkenes. Alkenes are used as a starting material when making lots of other compounds and can be used to make polymers
• Some of the products of cracking are useful fuels, e.g petrol for cars and paraffin for jet fuel
• There are different methods of cracking
• Cracking is a thermal decomposition reaction - breaking molecules down by heating them
• 1. The 1st step is to heat long-chain hydrocarbons to vaporise them (turn them into a gas)
• 2. Then the vapour is passed over a hot powdered aluminium oxide catalyst
• 3. The long-chain molecules split apart on the surface of the specks of catalyst - this is catalytic cracking
• 4. You can also crack hydrocarbons if you vaporise them, mix them with steam and then heat them to a very high temperature. This is known as steam cracking
• You need to be able to balance chemical equations for cracking, e.g:

  (long-chain) -> (short-chain) + alkene

  hexane: C6H14 -> butane:C4H10 + ethene: C2H4

  
• Make sure that when writing equations for cracking, there are the same number of carbon and hydrogen atoms on both sides of the equation