Hydrocarbons as Fuels


Hydrocarbons are found naturally in the Earth as a mixture of different chain lengths, which can then be separated by using fractional distillation in a fractionating column. This separates the mixture into fractions dependent on their length.

The more volatile fractions (ones with lower boiling points) condense near the top where it’s cooler

Commercial Value of Products

Three main processes are used to increase the commercial value of products.

· Reforming
The forming of cycloalkanes from straight chain alkanes, which can then form into arenes.

Uses: Improves the combustion of petrol. It produces compounds with a ‘high octane number’ which prevents the pre-ignition of petrol in the engine.
Conditions: Platinum catalyst. High temperature and pressure.


· Isomerisation
The forming of branched chained alkanes from straight chained alkanes.

Uses: Improves the combustion of petrol, produces compounds with a ‘high octane number’. Conditions: Platinum catalyst. High temperature and pressure

· Cracking – Converts long-chain hydrocarbons into smaller molecules and produces an alkene (hydrocarbons that have a carbon-carbon double bond).


Conditions: High temperature and a catalyst of Aluminium Oxide

Cracking in the Lab
When performing cracking in the lab the hydrocarbon can be heated and passed over a hot catalyst of Al2O3 and the gas that forms collected. When collecting the gas, the first test-tube of gas is discarded because it will contain mostly air that has expanded under heating. It is also important to try and prevent ‘suck-back’ at the end of the experiment. This is when after heating the air cools and contracts, which could cause water to be sucked up the hot tube and into the test-tube.

Catalytic Converters
These are used in the exhausts of cars to remove the pollutants by redox reactions. Nitrous Oxides are converted to N2 and CO is converted to CO2. The catalyst used in catalytic converters is platinum.

 

Biofuels
As we all know the fossil fuels will eventually run out. Therefore scientists are now researching alternatives such as Biofuels. These are fuels that are produced from natural biological processes such as decay from plants or animal waste.

Bio-oil, for example, can be produced from the chippings of wood heated in the absence of air and Biogas can be produced from the anaerobic decay of waste at landfill sites.

Fermentation
Alcohol is another prominent biofuel, produced from fermentation and used as fuel. The reaction requires a yeast enzyme. An enzyme is a biological catalyst that performs best under optimum conditions such as a temperature greater than 30 degrees. Alcohols may become relied on more in the future, due to the fact that crude oil reserves will soon run out, however alcohols can be produced via fermentation of glucose from plants.

C6H12O6 2C2H5OH + 2CO2
Glucose Ethanol Carbon Dioxide

Advantages of fermentation: low tech, renewable sources, biological catalyst.
Disadvantages: batch process, impure product.