carbon compounds as fuels

• what is crude oil?

  • a finite resource found in rocks
  • the remains of ancient biomass consisting mainly of plankton that was buried in mud
  • a mixture of a very large number of compounds - hydrocarbons.
• what are hydrocarbons?

  • molecules made up of hydrogen and carbon atoms only
• what are alkanes?

  • the formula for alkanes is CnH2n+2
  • the first four alkanes are methane, ethane, propane and butane
  • most of the hydrocarbons in crude oil and alkanes
• fractional distillation uses

  • hydrocarbons in crude oil can be separated into fractions, each of which containing molecules with a similar number of carbon atoms by fractional distillation.
  • the fractions can be processed to produce fuels and feedstock for the petrochemical industry such as kerosene, petrol, diesel, heavy fuel oil and liquefied petroleum.
  • useful materials like solvents, lubricants, polymer and detergents are made from fractional distillation.
• the vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds.
• how does fractional distillation work?

  • crude oil is a mixture of hydrocarbons and they are heated until they vaporise and then enter the column where it is hotter at the bottom and cooler at the top.
  • they all have different boiling points so separate out at different temperatures
  • long chain hydrocarbons have high boiling points so they condense at the bottom of the column, while short chain hydrocarbons have low boiling points so they rise and condense at the top.
• properties of hydrocarbons

  • the size of hydrocarbon molecules influence the boiling point, viscosity and flammability of the hydrocarbon.
• viscosity and hydrocarbons

  • increasing the length of the hydrocarbon increases the viscosity of the hydrocarbon.
  • decreasing the length of the hydrocarbon decreases the viscosity.
• boiling point and hydrocarbons

  • the longer the hydrocarbon, the higher the boiling point as more energy is needed to break up the molecules
  • the shorter then hydrocarbon, the lower the boiling point as less energy is needed to break up the molecules
• flammability and hydrocarbons

  • as the hydrocarbon length increases, flammability decreases
  • as hydrocarbon length decreases, flammability increases
• combustion of hydrocarbons?

  • during combustion, the carbon and hydrogen in the fuels are oxidised
  • the complete combustion of a hydrocarbon produces carbon dioxide and water
• what is cracking?

  • breaks long chain hydrocarbons into shorter chain hydrocarbon molecules by heating, passing over a catalyst (aluminium oxide) and splitting the molecules.
• products of cracking?

  • alkenes and alkanes are produced.
  • alkenes can be tested for using bromine water which turns from orange to colourless because they are more reactive.
  • there is a high demand for fuels with small molecules so some of the products of cracking are useful as fuels.
  • alkenes are used to produce polymers and are starting materials for production of other chemicals.