C9 - Crude Oil and Fuels

• Crude oil


  A finite resource found in porous rocks,

  it is formed from the remains of ancient biomass

  consisting mainly of plankton that was buried in mud

  over millions of years , under high temperature and under high pressure
• Crude oil composition


  A mixture of a large amount of hydrocarbons (molecules made up of hydrogen and carbon atoms only)
• Alkanes


  Alkanes are saturated compounds that contain only hydrogen and carbon atoms with single covalent bonds, therefore they consist of the maximum possible amount of hydrogen atoms . Alkanes are the most common hydrocarbons in crude oil, with the general formula CnH2n+2
• First four alkanes


  • Methane
  • Ethane
  • Propane
  • Butane
• Fractional distillation of crude oil


  Separates the Crude Oil - which is a complex mixture of various chain lengths hydrocarbons into fractions, each containing molecules of similar hydrocarbon chain lengths.
• Crude oil fractions


  Processed to produce fuels and feedstock for the petrochemical industry. Fractions are groups of hydrocarbons with similar boiling points and chains lengths
• Fuels produced from crude oil


  • Petrol
  • Diesel oil
  • Kerosene
  • Heavy fuel oil
  • Liquefied petroleum gases
• Materials produced by the petrochemical industry


  • Solvents
  • Lubricants
  • Polymers
  • Detergents
• The vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds
• Properties of hydrocarbons


  • Depend on the size of their molecules, including boiling point, viscosity and flammability
  • These properties influence how hydrocarbons are used as fuels
• Boiling point, viscosity and flammability change with increasing and decreasing molecular size
• Combustion of hydrocarbon fuels


  1. Releases energy

  2. Involves the oxidation of carbon and hydrogen atoms

  3. Complete combustion produces carbon dioxide and water

  4. Incomplete combustion produces carbon monoxide and water vapour
• Properties of hydrocarbons


  • Long chain: high viscosity, high boiling point, low flammability, low volatility
  • Short chain: low viscosity, low boiling point, high flammability, high volatility
• Cracking of hydrocarbons


  1. Breaks down long chain hydrocarbons to produce smaller, more useful hydrocarbons as fuels

  2. Can be done by catalytic cracking or steam cracking - both involve heat
• Products of cracking


  Alkanes and alkenes
• Alkenes


  More reactive than alkanes, react with bromine water (used as a test for alkenes)
• Bromine water is decolourised when it reacts with an alkene, changing from orange to colourless
• Alkenes


  Alkenes are unsaturated hydrocarbons which contain at least one double bond

  Hydrocarbons with the functional group C=C
• Alkenes burn in air

  With smoky flames due to incomplete combustion
• Hydrocarbon fuels


  • Short chain: more valuable as they have higher flammability/are easier to ignite
  • Long chain: less valuable as they have lower flammability/are more difficult to ignite
• Describe the process of Fractional Distillation.


  Long chain hydrocarbons are vaporised.
• What is steam cracking?

  
  

  In steam cracking, the long chain hydrocarbon is turned into a gas / vaporised , then mixed with steam. At very high temperatures, over 850 °C, and under pressure, the long chain hydrocarbon will split into shorter chain hydrocarbons and lots of small alkenes. The alkenes are separated from the alkanes by fractional distillation.
• What are alkenes used for?


  Alkanes are useful as fuels

  Alkenes are used to make chemicals such as plastic,

  which is a polymer.
• What is catalytic cracking?

  Catalytic cracking involves an aluminium oxide catalyst.

  The long chain hydrocarbon is turned into a gas,

  which then passes over a hot, powdered aluminium oxide catalyst

  at a temperature of about 550°C
• What is a catalyst?

  
  

  A catalyst is a substance that speeds up a chemical reaction, or lowers the temperature or pressure needed to start one, without itself being consumed during the reaction.
• Alkenes


  Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond in its molecular structure. Alkenes have two hydrogen atoms less than the corresponding Alkanes. The general molecular formula is CnH2n
• What is a homologous series?

  A homologous series is a family of hydrocarbons with similar chemical properties who share the same general formula.
• Hydrocarbons

  Organic compounds that contain only hydrogen and carbon atoms.
• Fractional Distillation - Process.

  Evaporation

  • Crude oil is heated to a high temperature until it evaporates.
  • The hydrocarbon gases are fed into a fractionating column at the bottom and rises upwards.
  • Condensation
  • The temperature is highest at the bottom of the column. Long-chain hydrocarbons condense at the bottom and are collected as liquids.
  • Short-chain hydrocarbons have lower boiling points. They pass up the column and condense at lower temperatures nearer the top.

  
  

  • Collection
  • The fractions are collected. They are then processed to create end products: