Occurrence and extraction
Crude oil ,natural gas and biogas are the main sources of alkanes:
(i)Natural gas is found on top of crude oil deposits and consists mainly of methane.
(ii)Biogas is formed from the decay of waste organic products like animal dung and cellulose.
When the decay takes place in absence of oxygen , 60-75% by volume of the gaseous mixture of methane gas is produced.
(iii)Crude oil is a mixture of many flammable hydrocarbons/substances.
Using fractional distillation, each hydrocarbon fraction can be separated from the other.
The hydrocarbon with lower /smaller number of carbon atoms in the chain have lower boiling point and thus collected first.
As the carbon chain increase, the boiling point, viscosity (ease of flow) and colour intensity increase as flammability decrease.
Hydrocarbons in crude oil are not pure.
They thus have no sharp fixed boiling point.
|
Carbon atoms in a molecule |
Common name of fraction |
Uses of fraction |
|
1-4 |
Gas |
L.P.G gas for domestic use |
|
5-12 |
Petrol |
Fuel for petrol engines |
|
9-16 |
Kerosene/Paraffin |
Jet fuel and domestic lighting/cooking |
|
15-18 |
Light diesel |
Heavy diesel engine fuel |
|
18-25 |
Diesel oil |
Light diesel engine fuel |
|
20-70 |
Lubricating oil |
Lubricating oil to reduce friction. |
|
Over 70 |
Bitumen/Asphalt |
Tarmacking roads |