Petroleum is an important fossil fuel.
Petro means rock and oleum mean oil. So petroleum is also called rock oil.
It is a thick viscous liquid of brown or greenish-black colour.
It is produced by the decay of living organisms buried in the earth crust million years ago.
Petroleum in unrefined form is called crude oil.
Crude oil is a mixture of hydrocarbons with different chain lengths.
Refining of Petroleum:
Suspended solids, sulphur impurities and gases are first removed from crude oil and it is then subjected to fractional distillation. Various fractions of hydrocarbons are obtained at different boiling ranges.
What is Fractional distillation?
It is the process by which oil refineries separates unprocessed oil (crude oil) into different useful hydrocarbon products on the basis of boiling points.
Basic Principle of Fractional Distillation:
The basic principle of fractional distillation is that different liquids boil & evaporate at different temperatures.
So the hydrocarbons with a low boiling point will evaporate first & convert into vapours.
Small chain hydrocarbon molecules are collected at the top of the fractional distillation column.
Small chain hydrocarbon molecules =Less intermolecular forces =Less energy is required to break=Low boiling point
long-chain hydrocarbon molecules are collected at the bottom of the fractional distillation column.
long-chain hydrocarbon molecules=more intermolecular forces=more energy is required to break=high boiling point
Fractions of Hydrocarbons:
Various fractions of hydrocarbons are obtained at different boiling ranges.