Alkanes

• Fractions (and their increasing boiling points) in a fractioning column:

  TOP : Refinery Gas

  • Petrol - 40 °C
  • Naptha - 100 °C
  • Kerosine - 190 °C
  • Diesel - 250 °C
  • Oil - 330 °C
  • Bitumine
• Fractional column
 


  • Column with a temperature gradient (hottest at bottom)
  • Seperates fractions from petroleum ( because molecules have different boiling points
  • Increasing hydrocarbon chain length increases boiling point
  • Shorter chains fraction at the top of the column
• Fraction


  Hydrocarbons with similar boiling points.
• Boiling point of Petrol.

  40 degrees
• Boiling point of Naptha

  110 degrees
• Boiling point of Kerosene

  180 degrees
• Boiling point of diesel oil

  250 degrees
• Boiling point of fuel oil

  300 degrees
• Boiling point of lubricating oils.

  340 degrees.
• Why do bigger alkanes have higher boiling points.

  There are greater van-der-walls forces in the bigger alkane so more energy is required to break them.
• Thermal Cracking Conditions

  High Temperatures: 1000°

  High Pressure 7000kPa
• What does thermal cracking mostly produce

  Alkenes: Ethene for polymers and ethanol

  Hydrogen: Used in harbour process
• Catalytic cracking conditions

  High Temperature; 750°

  Zeolite Catalyst,
• What does Catalytic Cracking produce

  Branched Alkanes, Cycloalkanes and Aromatic compounds.
• Which cracking method is cheaper and why?

  Catalytic Cracking: lower temperature and pressure used so energy is saved.
• Products of complete combustion

  CO2 and H2O
• Why are Alkanes used as fuels

  Readily burnt in presence of oxygen. Combustion is highly exothermic, thus giving off energy
• Products of incomplete combustion

  CO, or C ( spots )