• Alkanes?are hydrocarbons that can be produced by the?addition?reaction?of hydrogen to an alkene or by?cracking?of longer alkane chains

Crude oil

• Crude oil is a?mixture?of hydrocarbons containing?alkanes,?cycloalkanes?and?arenes?(compounds with a benzene ring)
• The crude oil is?extracted?from the earth in a?drilling?process?and transported to an?oil?refinery
• At the oil refinery the crude oil is separated into useful fuels by?fractional distillation
• This is a separating technique in which the wide range of different hydrocarbons are separated into fractions based on their boiling points
• However, the smaller hydrocarbon fractions (such as gasoline fractions) are in high demand compared to the larger ones
• Therefore, some of the?excess?heavier fractions are broken down into smaller,?more useful compounds
• These more useful compounds include?alkanes?and?alkenes?of?lower?relative formula mass (Mr)
• This process is called?cracking

The heavier fractions that are obtained in fractional distillation are further cracked into useful alkane and alkenes with lower Mr?values

Production of alkanes from cracking

• In?cracking?these large, less useful hydrocarbon molecules found in crude oil are broken down into smaller, more useful molecules
• The large hydrocarbon molecules are fed into a?steel?chamber?and?heated?to a high temperature and then passed over an?aluminium?oxide?(Al2O3) catalyst
  • The chamber does not contain any?oxygen?to prevent?combustion?of the hydrocarbon to water and carbon dioxide

   

• When a large hydrocarbon is cracked, a?smaller?alkane?and one (or more)?alkene?molecules are formed
  • E.g. octane and ethene from decane

   

Long hydrocarbons are cracked by heating them and using aluminium oxide catalyst into a smaller alkane and an alkene