Alkanes

Alkanes

Fractional Distillation of Crude Oil
1. Process
  1. Crude oil is vaporised at 350 degrees Celcius.
  2. Passed into the bottom of the fractionating column where it rises up.
  3. Large hydrocarbons do not vaporise and run to the bottom to form a "gooey" residue.
  4. As the vapor rises, it cools and forms a temperature gradient.
  5. Boiling points increase as molecules increase so they condense at different temperatures and are drawn off at different levels in the column.
  6. The smallest hydrocarbons do not condense and are drawn off as gas at the top of the column.
2. Petroleum is a fancy word for crude oil - the stuff in the ground. It is a mixture mostly made up of alkanes.
Modification of Alkanes by Cracking
1. Cracking is breaking long-chain hydrocarbons in to smaller ones. It involves breaking C-C bonds.
2. Types of Cracking
  1. Thermal Cracking
    1. Takes place at high temperatures (1000 C) and high pressures (70 atm).
    2. Produces lots of alkenes.
  2. Catalytic Cracking
    1. Uses a zeolite catalyst (hydrated aluminosilicate).
    2. Slight pressure used and a high temperature (500 C).
    3. Mostly produces aromatic hydrocarbons and the alkanes used in motor fuels.
    4. The catalyst cuts cost due to reducing pressure and temperature requirements and speeds up the reaction saving time and money.
Combustion of Alkanes
1. Alkanes are used as fuels because they release a large amount of energy when burnt.
2. Same as normal combustion - you get complete and incomplete.
3. Pollution Produced by Combustion
  1. Nitrogen Oxides - toxic and poisonous molecules with the general formula NOx.
  2. Not all hydrocarbons are burnt which react with nitrogen oxides in the presence of oxygen for form ground-level ozone (a component of smog)
  3. Carbon Monoxide
  4. Sulfur Dioxide is formed if the hydrocarbon contains sulfur. This dissolves in moisture and forms sulfuric acid which causes acid rain. Nitrogen Dioxide also does this.
  5. Catalytic converters remove these gaseous pollutants.
4. General Equation: Hydrocarbon + Oxygen -> Carbon Dioxide + Water
Chlorination of Alkanes
What are they?
1. Saturated hydrocarbons.

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	Erstellt von Josh Bullock vor etwa 9 Jahre