Fractional distillation of crude oil
Fractional distillation separates a mixture into a number of different parts, called fractions.
A tall fractionating column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high The temperature at which a substance rapidly changes from a liquid to a gas. Condensation is a change of state in which gas becomes liquid by cooling. at the bottom and substances with lower boiling points condense on the way to the top.
Crude oil is a mixture of A compound that contains hydrogen and carbon only.. The crude oil is The process in which a liquid changes state and turns into a gas. and its vapours condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon A collection of two or more atoms held together by chemical bonds. with a similar number of carbon All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons. and a similar range of boiling points.
Oil fractions
The diagram below summarises the main fractions from crude oil and their uses, and the trends in properties. Note that the gases leave at the top of the column, the liquids condense in the middle and the solids stay at the bottom.
As you go up the fractionating column, the hydrocarbons have:
- lower boiling points
- lower viscosity (they flow more easily)
- higher flammability (they Set on fire. more easily).
Other fossil fuels
Crude oil is not the only Natural, finite fuel formed from the remains of living organisms, eg oil, coal and natural gas..
Natural gas mainly consists of methane. It is used in domestic boilers, cookers and Bunsen burners, as well as in some power stations.
Coal was formed from the remains of ancient forests. It can be burned in power stations. Coal is mainly carbon but it may also contain sulfur compounds, which produce sulfur dioxide when the coal is burned. This gas is a cause of Rain that contains dissolved acidic gases such as nitrogen oxides and sulfur dioxide.. Also, as all fossil fuels contain carbon, the burning of any fossil fuel will contribute to The rise in the average temperature of the Earth's surface. due to the production of carbon dioxide.