Alkanes

• Alkanes are saturated hydrocarbons
• Crude oil can be separated by fractional distillation
• Crude oil is vaporised at about 350 °C
• Vaporised crude oil goes into the bottom of the fractionating column and rises up through the trays
• The largest hydrocarbons with high boiling points do not vaporise
• As the crude oil vapour moves up the column, it cools down, creating a temperature gradient
• Boiling points of alkanes increase with larger molecules, causing each fraction to condense at different temperatures
• Different fractions are drawn off at various levels in the column
• Hydrocarbons with the lowest boiling points do not condense and are drawn off as gases at the top of the column
• Crude oil fractions

  • gases
  • petrol
  • naphtha
  • kerosine
  • gas oil (diesel)
  • mineral oil
  • bitumen
• Cracking is the breakdown of large hydrocarbons into smaller, more useful alkanes and alkenes - involves the breaking of C-C bonds
• thermal cracking takes place at a high temperature (up to 1000 degrees celsius) and high pressure (up to 70 atm)
• thermal cracking produces lots of alkenes
• catalytic cracking uses a zeolite catalyst at a slight pressure and high temperature (around 500 degrees Celsius)
• catalytic cracking mostly produces aromatic hydrocarbons and alkanes
• Nitrogen oxides are toxic
• nitrogen monoxide is produced when the high temperature and pressure in car engines causes the nitrogen and oxygen in the air to react
• Unburnt hydrocarbons from engines react with nitrogen oxides in the presence of sunlight to form ground level ozone (O3) which is a major component of smog
• gaseous pollutants from internal combustion engines can be removed using catalytic converters
• Combustion of hydrocarbons containing sulphur leads to sulphur dioxide that causes air pollution