Chemistry - 1.4 - Crude Oil and Fuels

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C1.4.1 - Fuels from Crude Oil

  • Crude oil - many different compounds with different boiling temperatures - burn under different conditions so have to be separated to be useful
  • Separation of liquids can be done by distillation - simple crude oil distillation produces liquids that boil within different temperature ranges - these liquids are called fractions
  • Most compounds in crude oil are hydrocarbons - many are alkanes (CnH2n+2) - alkanes ontain as many hydrogen atoms as possible so are called saturated hydrocarbons
  • Molecules are represented in different ways - molecule formula shows number of each atom in the molecule, displayed formula shows how atoms are bonded together
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C1.4.2 - Fractional Distillation

  • Crude oil - separated using fractional distillation - boiling point of a hydrocarbon depends on the chain length - larger molecule = higher boiling point
  • Crude oil is vapourised -> vapour is put into column (tower - hotter at bottom; cooler at top) -> vapours move up the column getting cooler as they go up (holes in column allow gases through) -> hydrocarbons condense to liquids when they reach their boiling point -> different liquids collect on trays at different points -> outlets to collect fractions
  • Smallest molecule = lowest boiling point - collected at top, fractions at the bottom contain long chain hydrocarbons with high boiling points
  • Low boiling point = low viscosity (runny liquids), flammable, burn with clean flames (little smoke) - useful fuels
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C1.4.3 - Burning Fuels

  • Pure hydrocarbons oxidise to CO2 and H2O when burnt completely - not always burnt completely and may contain other substances
  • Incomplete combustion - limited air supply -> CO is produced - carbon may be produced and some of the hydrocarbons may not burn -> produces colid paricles containing soot (carbon) and unburnt hydrocarbons - paticulates
  • Sulfur dioxide - fossil fuels containing sulfur compounds burn to produce sulfur dioxide - this causes acid rain
  • Nitrogen oxides - high temperatures produced when burning fossil fuels make O and N combine to form NO2 - also cause acid rain
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C1.4.4 - Cleaner Fuels

  • Burning fuels produces substances that affect the environment
  • Any fuel containg carbon burns to make CO2 - greenhouse gas believed to cause global warming, incomplete combustion = CO - poisonous gas, can prouce tiny solid particules that reflect sunlight and cause global dimming
  • SO2 and NO2 produced - dissolve in water and react with O2 in the air = acid rain
  • Removing substances from waste gases - sulfur dioxide removed from waste gases from power stations, catalytic converters in exhaust systems in cars remove CO and NO2, filters remove partculates, sulfur removed from fuels before sold so less SO2 is produced
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C1.4.5 - Alternative Fuels

  • Biofuels - made from plant or animal products, renewable, biodiesal can be made from vegetable oils extracted from plants
  • Adv of biodeisel - little CO2 level contribution - plants took it in when growing
  • Disadv of biodeisel - plants grown take up large areas
  • Ethanol made from dugar cane or sugar beet - biofuel - liquid so sored and distributed like other liquid fuels, can be mixed with petrol
  • Hydrogen as fuel - only produces water when burnt, gas -> large volume - difficult to store in needed quantities, can be produced from water by electrolysis but requires large amounts of energy
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