C9

• Crude oil is v. important to society and economy; formed from remains of ancient biomass that died millions of years ago. Raw crude oil is thick black liquid made with lots of compounds mixed together; most of compounds are hydrocarbons of various sizes; hydrocarbons are molecules made of only carbon and hydrogen.
• Hydrocarbons used as fuels bc. when react with oxygen they release a lot of energy - this is called combustion; complete combustion is where only products are CO2 and water.
• Whether a hydrocarbon is a useful fuel depends on its

  • flammability - how easily it burns
  • boiling point - temp at which it boils
  • viscosity - how thick it is
• long chain = low flammability, high BP, high viscosity (very thick)
• short chain = high flammability, low BP, low viscosity (very runny)
• Alkanes:

  • contain single bonds
  • first four are methane, ethane, propane, butane
  • formula foe them is Cn + H2n+2
• Alkenes:

  • contain double bonds between carbon atoms
  • used as fuels and to produce polymers and other materials
  • more reactive than alkanes
  • when mixed with bromine water, the Br water turns from orange to colourless - can be used to tell difference between alkanes and alkenes
• Fractional distillation:

  useful products produced include solvents, lubricants, polymers and detergents

  • different hydrocarbons are separated in fractionating column based on their BPs
  • all molecules with similar number of carbon atoms collect at same fraction
• Process of fractional distillation:

  • crude oil is vaporised
  • hydrocarbon gases enter column
  • hydrocarbon gases rise up column
  • higher up in column, cooler it gets
  • when different hydrocarbons reach their BP in column they condense
  • hydrocarbon fraction is collected
• Fractionating column working from top to bottom;

  • refinery/petroleum gas used as fuels ~ 50ºC
  • gasoline/petrol used for car fuel
  • kerosene used for aircraft fuel
  • diesel oil/gas oil used for boiler fuel and diesel engines
  • residue/tar used for making roads and flat roofs ~ 350ºC
• Cracking:

  • longer hydrocarbons are less useful so broken down into shorter ones
  • there’s a higher demand for shorter chain hydrocarbons
  • cracking produces shorter alkanes and alkenes
• catalytic cracking - vaporise hydrocarbons then pass them over hot catalyst
• steam cracking - mix hydrocarbons with steam at very high temp