Useful Products from Crude Oil

Another name for crude oil is petroleum, and it is obtained from the earth’s crust. It is part of the group called fossil fuels. A fuel is an element or compound or mixture of compounds which can be burned to supply energy economically. A fossil fuel (Coal, Oil, Gas) are formed from organisms or living materials which have been kept underground over millions of years. They have been kept under high pressures and temperatures and bacteria action in the absence of air. This material has been covered by layers of sediment rock.

Oil and gas are less dense than water so they rise to the top of porous rock layer. They may then be trapped under a layer of non-porous rock.

Trapped oil or gas can be obtained by drilling through the non-porous rock.

Crude oil is a mixture of very large compounds.

We remember that a mixture consists of two or more elements or compounds not chemically combined together. The chemicals in the mixture are unchanged. This makes it possible to separate the mixture by physical methods. (N.B. Physical changes can be reversed, chemical changes are not easily reversible). Distillation is a useful process. This depends on the different boiling points.

Most of the compounds that include oil are hydrocarbons. I.e. there molecules are made up of hydrogen and carbon atoms only.

A fraction is a mixture of hydrocarbons with a narrow range with different boiling points. The many hydrocarbons which include oil are separated into fractions, each of which contains molecules with a similar number of carbon atoms, by evaporating the oil allowing it to condense at a number of different temperatures. This is known as fractional distillation. In industries a fractionating column is used (Hot at the bottom, cool at the top) so that there is a temperature gradient, and different heights correspond to different temperatures.

The hydrocarbon molecules in crude oil vary in size. The larger the molecules and the greater number of carbon atoms in a hydrocarbon, the stronger the inter particle force, thus making;

its boiling point higher,
it less volatile (evaporates less),
it flow less easily (more viscous),
it ignite less easily (less flammable).

This limits the use of hydrocarbons with large molecules as fuels.
Large hydrocarbon molecules can be broken down using high temperatures as a special catalyst to produce smaller, more useful molecules including alkines
This process is called cracking. Some of these smaller molecules are useful as fuels.
The alkene products can be used to make plastics - polymers such as poly(ethene) and PVC-poly(chloroethene).