Crude Oil

• What is crude oil?

  Mainly alkanes
• How does fractional distillation work?

  Crude oil - vaporised at 350°C

  This crude oil moves to a fractionating column and rises up through the tray

  As the crude oil vapour goes up the fractionated column - cooler

  Each fraction condenses at different temperatures and they're all drawn off at different levels
• What happens to the largest hydrocarbons?

  They don't vaporised at all and sink to the bottom to form residue as they have the largest boiling points
• Why does it get colder at the top of the fractionating column?

  Alkane molecules have different chain lengths and then different boiling points
• What happens to the hydrocarbons that have the lowest boiling points?

  They don't condense and are drawn off as gases at the top of the column
• Heavy fractions can be ...... to make smaller hydrocarbons

  Cracked
• Why do we crack heavier fractions?

  Due to high demand of lighter fractions - petrol

  Alkane - alkane + alkene
• Thermal cracking

  High temp (up to 1000°C)

  Produces a lot of alkenes

  Alkenes make polymers
• Catalytic cracking

  Zeolite catalyst

  Slight pressure

  High temp (450°)

  Mostly produces aromatic hydrocarbons and motor fuels
• What can alkanes be reformed into?

  Cycloalkanes ans aromatic hydrocarbons
• What is knocking?

  Alkanes explode on their own when the fuel/ air mixture in the engine is compressed

  Straight chain alkanes are most likely the hydrocarbons causing this
• Car - petrol etc

  Adding branched chains and cyclic hydrocarbons to petrol mixture makes knocking less likely to occur

  Combustion - more efficient
• How can we convert straight chain alkanes into branched chain alkanes and cyclic hydrocarbons?

  Reforming

  Using a catalyst (platinum stuck on aluminium oxide)