Commercial reactions of alkenes

Background on Crude Oil

• Crude oil is a mixture of hydrocarbons of varying chain lengths.

  • Short hydrocarbons are more useful and in higher demand than longer chains.

  • Long chains can be broken down into shorter ones via cracking.

Cracking Process

• Cracking is a common process in the petrochemical industry.

  • Two main types of cracking: Catalytic Cracking and Thermal Cracking.

Catalytic Cracking

• Carried out at:

  • High temperature: around 500 degrees Celsius.

  • Slight pressure: usually at atmospheric pressure.

• Uses a zeolite catalyst, which is a large solid lattice made of:

  • Aluminum, silicon, and oxygen.

• Yields hydrocarbons with:

  • 5 to 10 carbons.

  • Predominantly branched isomers.

• Advantages:

  • Lower boiling points make branched isomers preferable as fuels.

  • Very common for producing petrol.

Thermal Cracking

• Carried out at:

  • Higher temperature: around 700 degrees Celsius.

  • Higher pressure than catalytic cracking.

• Yields:

  • A larger number of alkenes and shorter hydrocarbon chains (usually less than 5 carbons).

• Applications:

  • Excellent for polymerization due to presence of alkenes.

Combustion of Alkanes

• Alkanes serve as effective fuels, especially the shorter chains.

• Complete Combustion:

  • Occurs in the presence of plentiful oxygen.

  • Produces carbon dioxide (CO₂) and water (H₂O).

  • Example: Complete combustion of octane (C₈H₁₈):

    • Balanced equation:

      C₈H₁₈ + 12.5 O₂ → 8 CO₂ + 9 H₂O

• Incomplete Combustion:

  • Occurs when oxygen supply is limited.

  • Produces carbon monoxide (CO) and water.

  • Example: Incomplete combustion of hexane (C₆H₁₄):

    • Balanced equation:

      C₆H₁₄ + 6.5 O₂ → 6 CO + 7 H₂O

• Concerns:

  • Incomplete combustion is dangerous as it produces toxic carbon monoxide.

  • Carbon monoxide is a poisonous gas and reduces overall energy output during combustion.