What does crude oil consist of? What does fractional distillation do to crude oil?

1 Answer
Jan 31, 2016

Crude oil is raw material extracted from the ground, which consists of many different hydrocarbons. Fractional distillation is the process of separating these different hydrocarbons.


Crude Oil:

  • Crude oil is a mixture of hydrocarbons that exists as a liquid in natural underground reservoirs and remains a liquid when brought to the surface.

  • You will often hear oil referred to as petroleum. However, petroleum is a collective term that includes crude oil, condensate and gas.

  • The various forms of crude oil are extracted from the earth using a drilling process, and then further refined into fuels such as petrol, kerosene, diesel and many heavy waxes.

  • Petroleum plants can use the process known as cracking to reduce the size of very large hydrocarbon molecules in to more applicable molecules for every day life.

Fractional Distillation:

  • As the different components in crude oil have different boiling points, the substances in crude oil can be separated using fractional distillation.
  • The crude oil is evaporated and its vapours allowed to condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms.
  • Hydrocarbon molecules with a higher molecular weight have stronger dispersion forces which subsequently increases their boiling point. For example fuel oil.

  • Hydrocarbon molecules with a lower molecular weight have weaker dispersion forces which subsequently decreases their boiling point. For example refinery gases.