C9 - Crude oil and fuels

• Crude oil 


  A thick black liquid mixture made up of a large number of hydrocarbons
• Hydrocarbons


  Compounds that contain hydrogen and carbon only
• Properties of long chain hydrocarbons


  • Low flammability
  • High boiling point
  • High viscocity
• Properties of short chain hydrocarbons


  • High flammability
  • Low boiling point
  • Low viscocity
• Complete combustionnn produces carbon dioxide and water
• Incomplete combustion produces carbon monoxide and water
• One family of hydrocarbon molecules is called alkenes
• Alkenes oonly haave single bonds in them
• Methane


  One carbon, four hydrogens
• Ethane


  Two carbons, six hydrogens
• Propane


  Three carbons, eight hydrogens
• Butane


  Four carbons, ten hydrogens
• The molecular formula of an alkene can be worked out by C(n)H(2n+2)
• The different hydrocarbons in crude oil can be separated into fractions based on their boiling points through fractional distillation
• Fractional distillation takes place in a fractionating column, which is hottest at the bottom and cooler at the top
• The process of fractional distillation


  • Crude oil is vapourised
  • The hydrocarbon gases enter the fractionating column
  • The hydrocarbon gases rise up the column
  • As the gases rise, they cool down
  • When the different gases reach their different boiling points, they condense
  • The hyrdocarbon fractions are collected
• Short chain hydrocarbons have the lowest boiling points so are collected near the top of the column
• Long chain hydrocarbons have the highest boiling point so they are collected near the bottom of the column
• Cracking


  A process used to break long chain hydrocarbons up into shorter ones
• Cracking produces shorter alkenes and alkanes
• Catalytic cracking


  Vapourise hydrocarbons and pass them over a hot catalyst
• Steam cracking

  Mix the hydrocarbonss with steam at a very high temperature
• Alkenes


  A family of hydrocarbons that contain double bonds between carbon atoms
• Alkenes are used as fuels and to produce polymers
• To test for alkenes, mix with bromine water - if it turns colourless, then alkenes are present