Cracking, isomerisation and reforming.
Once fractional distillation is complete there is still not enough product from the crude oil to meet the needs of industry. It is for this reason why certain fractions are cracked. Cracking is when an oil fraction is heated with a catalyst. The product of this is a low molecular mass alkane and an alkene. C-C bonds and C-H bonds are both broken randomly so other products like hydrogen may be given out. It is also possible for branched-chain isomers to be formed.
Here is an example:
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
(Decane)
H
|
→ CH3CH2CH=CH2 + H3C-C-CH2CH2CH3
(But-1-ene) |
CH3
(2-Methylpentane)
Cracking is happens in a catalytic cracker. In here the vaporised oil and catalyst act like a fluid and this mixture is called a fluidised bed.
Isomerisation is when the straight-chain isomers are heated and a platinum catalyst is present. It gives a branched chain that can then be separated by a molecular sieve. Straight-chained molecules fit through the pores but branched chain isomers are too big. The straight-chained molecules are recycled.
Reforming is turning alkanes to cycloalkanes and cycloalkanes to arenes. Bimetallic catalysts are used in reforming reactions. An example is using a cluster of platinum and rhenium atoms, as the catalyst, to remove hydrogen from methylcyclohexane to form methlybenzene. The metal clusters used are from between 1nm and 5nm thick and are deposited on an inert support.
Hydrocarbons and other organic compounds as fuels.
A fuel is anything that is used on a large scale to transfer energy to its surroundings. The fossil fuels, coal, oil and gas, account for 90% of the energy used in most industrialised countries. Hydroelectricity and nuclear power supply 9% with the other 1% of energy including solar power.
To be a good fuel it must make this reaction:
Fuel + Oxygen (or other oxidiser)
→ Oxidation Producs + Energy Transfer
Hydrocarbons are a good source of energy because they burn easily to give off energy, they are available in large quantities and they can be stored easily. However, they, when burned, give off harmful gases, as do all organic compounds apart from hydrogen, when burned.
The problem with organic compounds as fuels is that they are running out, as they are non-renewable. Once they have completely run out that will be the end of them and alternative energy sources will have to be used. It is estimated that most oil reserves will be used up within 100 years.
Another problem with organic fuels is that when they are burned they give off Carbon Dioxide. This is a main contributor to the Greenhouse Effect that’s causing an increase in the Earth’s temperature. Another gas, Carbon Monoxide, is also given off by burning organic compounds. If inhaled then the effects of this gas can be fatal, as it is a poisonous gas. Today the biggest emitters of Carbon Monoxide are cars. However cars are now fitted with catalytic converters that have oxidising and reduction catalysts in to help remove some of the harmful gases.
Alternative Fuel Sources
Today, there are more alternatives to Fossil Fuels being used. Biofuels are popular, as are nuclear fuels and the movements of wind and water. Also sunlight and geothermal energies can be used as can hydrogen and electricity produced in chemical cells.
Plants are grown to be used as fuels or to be converted into fuels. Waste products on landfill sites are decayed and biogas is given off.
Methanol is made cheaply and is used in racing cars because it burns cleanly. This could be possible alternative to petrol in cars. However, its fumes are more toxic than ethanol’s and it supplies much less energy per litre than petrol does.
Nuclear fission and fusion have the potential to produce a large amount of energy. However, they are expensive to use and radioactive waste products are harmful.
Moving wind and water through turbines is becoming increasingly popular in many countries. They are both renewable and make no pollution. However, both are expensive to set up and can be noisy and ugly on the landscape.
Solar panels take in solar heat to heat up water. Photovoltaic cells convert light energy to electrical energy. Both of these require sunlight that is not always plentiful, with there being none at night. But both are renewable and make no pollution or waste products.
Pumping water underground to hot rocks heats up the water so that it can be used to heat buildings and homes. This is geothermal energy and there is a lot of it. However, the hot rocks are not found just anywhere and it is expensive to set up.
Hydrogen is easily extracted from water and is proven to work in powering cars. However, it is difficult to store and dangerous as it is highly flammable.
Some batteries are already used to power delivery vehicles and there are plans to make different batteries to provide more power for the vehicles.
