ICSE Class 8 Answered

Refining of Petroleum (By Fractional Distillation)

The process by which different pure substances are obtained from a crude substance is called refining. Refining of petroleum is carried out in the oil refineries.

• Crude petroleum is heated to about 400^oC and introduced into a tall cylindrical column, called the fractionating column, fitted with horizontal trays.
• Each tray is provided with a number of holes and an overflow pipe with a bubble cap.
• As the vapours of crude oil move in the fractionating column, they start condensing in the order of their boiling point.
• The order of the boiling point of a compound can be determined by the presence of the number of carbon atoms in them. The boiling point increases with the increase in the number of carbon atoms.
• Lighter fractions, with 1 to 10 carbon atoms, have low boiling points and are collected at the top of the fractionating column at different heights, while heavier fractions, with more than 30 carbon atoms, have high boiling points, condense first, and are collected at the base of the fractionating column.
• The fractions with similar boiling points are collected together.
• This process is continued until crude petroleum is separated into its constituent fractions.

Fractions obtained by the refining of petroleum