Cracking is the process of converting alkanes into alkenes and shorter alkanes. We crack alkanes because the shorter chain alkanes are more valuable (they are used as fuel).

Thermal cracking

  • Thermal cracking uses harsh conditions like high temperature and high pressure.
  • It breaks the alkanes into a high percentage of alkenes and comparatively few alkanes.
  • Thermal cracking is done at about 1,000 degrees Celcius and 70 atm pressure.

Catalytic cracking

  • Using a catalyst allows you to lower the temperatures and pressures needed for the reaction. This reduces costs and makes the reaction faster.
  • Catalytic cracking is done at 450 degrees Celcius and only just above atmospheric pressure.
  • The catalyst we use is called a zeolite. This is an ionic compound containing aluminium, silicon, and oxygen.
  • You tend to get molecules containing benzene rings and short hydrocarbons.

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