Crude Oil is a mixture of hydrocarbons.
4:08 describe how the industrial process of fractional distillation separates crude oil into fractions
- Crude oil is separated by fractional distillation.
- Crude oil is heated and the oil evaporates.
- It then goes into the tower. As the vapours rise up the tower the temperature falls.
- Different sized fractions condense at different heights because they have different boiling points.
- Smaller molecules condense high up the tower. Larger molecules condense low down in the tower.
- The fractions are collected.
4:09 know the names and uses of the main fractions obtained from crude oil: refinery gases, gasoline, kerosene, diesel, fuel oil and bitumen
Crude oil is separated into fractions by the process of fractional distillation.
The boiling point increases as the number of carbon atoms (chain length) increases.
The viscosity increases as the number of carbon atoms (chain length) increases.
The viscosity of a fluid describes how easily it flows. Water has a low viscosity, it flows very easily. Crude oil has a higher viscosity than water, it does not flow very easily.
4:12 know the possible products of complete and incomplete combustion of hydrocarbons with oxygen in the air
Complete Combustion happens when there is enough oxygen available, producing carbon dioxide (CO2) and water (H2O)
Incomplete Combustion happens when there is not enough oxygen available, with possible products being carbon monoxide (CO), carbon (C, soot), carbon dioxide (CO2) and water (H2O)
4:13 understand why carbon monoxide is poisonous, in terms of its effect on the capacity of blood to transport oxygen references to haemoglobin are not required
Carbon monoxide may be produced from the incomplete combustion of fuels:
Carbon monoxide is poisonous because it reduces the capacity of the blood to carry oxygen.
4:14 know that, in car engines, the temperature reached is high enough to allow nitrogen and oxygen from air to react, forming oxides of nitrogen
When fuels are burned in vehicle engines, high temperatures are reached.
At these high temperatures nitrogen and oxygen from the air react to produce nitrogen oxides:
4:17 describe how long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking (using silica or alumina as the catalyst and a temperature in the range of 600–700⁰C)
Cracking involves the thermal decomposition of long-chain alkanes into shorter-chain alkanes and alkenes:
Catalyst: aluminium oxide, Al2O3
4:18 explain why cracking is necessary, in terms of the balance between supply and demand for different fractions
Cracking converts long chain hydrocarbons into short chain hydrocarbons.
Long-chain alkanes are broken down into alkanes and alkenes of shorter length.
Crude oil contains a surplus long chains.
Shorter chain hydrocarbons are in greater demand, e.g. petrol.
Cracking also produces alkenes which are used in making polymers and ethanol.