Friday, 8 April 2016

Chemicals from Oil

Next stop is chemistry, today you would have a guided tour about chemicals from oil.

How oil is formed?

Natural gas is formed alongside of oil and it is thought that oil was formed of millions of years from the break down of tiny dead creatures.

Dead organisms sank to the bottom of lakes or seas and become trapped in muddy sediments. As the sediments build up, the lower layers were under pressure. They returned to rock. If there were no oxygen in the sediments, heat and pressure turned the remains of the organisms into oil and natural gas.

Some rocks are porous-they have a network of tiny holes in them such as sandstone. Oil is liquid so it seeps into porous rocks. Gas also diffuses into these rocks.

Porous rocks may also contain water. Gas and oil do not mix with water. They are less dense than water which means they form layers above the water.

Sometimes the rock layers form so that oil and gas are trapped under the rock such as shale that is not porous. Large amounts of oil and gas may collect in a porous rock. The pressure on the oil may build up so much that when a hole is drilled through the rock cap, oil gushes out.

Fractional distillation of crude oil

Crude oil is a mixture of many thousands of different compounds with different properties. They are called hydrocarbons because they only contain the elements hydrogen and carbon.
To make crude oil useful, batches of similar compounds with similar properties needed to be sorted. These batches are called fractions and they are separated by fractional distillation.

The theory behind this technique is that some of the compounds in crude oil are easily vaporised, for example they are volatile due to their low boiling points. Others are less volatile and have higher boiling points.

In fractional distillation, the crude oil is heated to make it vaporise. The vapour is then cooled. Different fractions of the oil are collected at different temperatures.

As the hydrocarbon molecule chain increases its boiling point increases, it becomes more viscous, becomes more difficult to light, the flame becomes sootier and it develops a stronger smell.

BBC (2006) GCSE Bitesize: Alkanes. Available at: (Accessed: 8 April 2016).

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