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

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.