oil & cracking

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  • Oil and cracking
    • Fractional distillation of crude oil
      • Crude oil is a mixture of hydrocarbons formed from the remains of simple marine organisms over millions of years.
      • Fractional distillation separates a mixture into a number of different parts
      • A fraction of crude oil is a mixture of chemicals in the crude oil that have similar boiling points.
      • As you go up the fractionating column, the hydrocarbons have:smaller chain lengthslower boiling pointsmore volatility (easy to evaporate)higher flammability (they ignite more easily and burn more cleanly)lighter colour (the bottom fraction is black, the middle fractions range from brown to yellow and the fraction at the top is colourless)
    • Other fossil fuels
      • Crude oil is not the only fossil fuel.
      • Natural gas mainly consists of methane. It is used in domestic boilers, cookers and Bunsen burners, as well as in some power stations.
      • Coal was formed from the remains of ancient forests. It can be burned in power stations.
        • coal is mainly carbon but it may also contain sulfur compounds,
        • his gas is a cause of acid rain.
      • fossil fuels contain carbon, the burning of any fossil fuel will contribute to global warming due to the production of carbon dioxide.
    • Global importance of crude oil
      • Economic importance
        • The price of crude oil is controlled by oil companies, which means they have a great deal of influence on the global economy, and poorer countries can easily lose control of their own economy.
        • Countries that produce oil for other countries hold a great deal of political power as they can essentially ‘cut off’ other countries from the crude oil supply over any political disagreements.
        • War or a political crisis in an oil-producing country can restrict crude oil supplies, which can have a major impact on the global economy.
      • Environmental issues
        • Burning fossil fuels releases carbon dioxide into the atmosphere. This is widely accepted as a major contributor to global warming.
        • Oil spillages can have a disastrous effect on the local environment, killing off thousands of animals such as fish and sea birds, and require a great deal of effort to clean up.
        • Oil refineries and oil-fired power stations take up a lot of land and so destroy potential wildlife habitats and spoil the countryside. However, this problem is the same for any industrial site and so is not just a problem for the oil industry.
    • Cracking
      • Fuels made from oil mixtures containing large hydrocarbon molecules are not efficient as they do not flow easily and are difficult to ignite.
      • Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules.
      • Fractions containing large hydrocarbon molecules are heated to vaporise  them.
        • They are then:              -heated to 600-700°C      -passed over a catalyst of silica or alumina
        • These processes break covalent bonds in the molecules, causing thermal decomposition reactions. Cracking produces smaller alkanes and alkenes.
      • Cracking of decaneThere is a greater demand for smaller hydrocarbons than larger ones.
        • decane ? octane + etheneC10H22 ? C8H18 + C2H4


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