The main sources of fuels are

1) Natural gas

-Found together with crude oil trapped under pressure in vast deposits below the sea-bed

-About 95% in methane (CH₄) with small amounts of H₂, N₂, CO, CO₂, H₂S

-Carried in pipes and used in homes for cooking and heating or it can be liquefied and transported as liquefied natural gas (LNG) in large tanker.

2) Petroleum

-Petroleum is a black viscous liquid. A complex mixture of hydrocarbons with small amounts of sulfur-, nitrogen-, and oxygen- containing compounds present as impurities. In this form, petroleum is of little use because it has to be refined to make useful fuels and chemicals.

-In oil refining, the separation of petroleum into useful fractions is achieved by fractional distillation. This is because the hydrocarbons have different boiling points.

- Fractional distillation of petroleum

· In the fractional column, both condensation and vaporization occurs.

· As vapour rises up the column, the vapours condense and are collected in the trays.

· More hot vapours enter the column and causes the liquid in the tray to further vapourise and rise up the volumn.

· Repeated cycles of condensation and vaporization will push the vapours of the volatile liquids higher up the column.

· Results in the separation of the mixture of vapours so that different fractions are collected at different heights of the column.

- Some fractions obtained by fractional distillation are more useful than others, therefore chemists have developed ways to convert the large hydrocarbon molecules in the heavy fractions to small lighter molecules, through cracking, the long-chain hydrocarbons in the heavier fractions are smaller molecules in the petrol, kerosene or diesel fraction.

Cracking is the process of breaking down larger hydrocarbon molecules into smaller molecules.

Ø Conditions for catalytic cracking

Ø Catalyst e.g. finely powdered aluminium oxide and silicon (IV) oxide

Ø High temperature

Ø High pressure