Table of Contents
IGCSE Coordinated Science: Fuels
Fuels
Recall coal, natural gas and petroleum as fossil fuels that produce carbon dioxide on combustion.
Fossil Fuels are:
- Petroleum
- Coal
- Natural Gas
The reason these are called fossils are because they are the remains of plants and animals that lived a few million years ago.
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- Petroleum: These are formed from the remains of dead organisms that fell to the ocean floor and were then buried by the thick sediment. The high pressure in which the dead organisms are buried eventually converts the dead organisms into petroleum, but this is a process that takes millions of years.
- Natural Gas: This is composed mainly of methane and is often found with petroleum. High temperatures and pressure causes the compounds to break down into gas.
- Coal: This is the remain of lush vegetation that grew in ancient swamps. Over the millions of years, high pressure and heat eventually converted the vegetation into coal.
Understand the essential principle of fractional distillation in terms of differing boiling points (ranges) of fractions related to molecular size and intermolecular attractive
forces.
- Petroleum is a mixture of hundreds and hundreds of different hydrocarbons.
- Putting all these mixtures together isn’t really productive.
- In order to solve this problem, we have to refine the petroleum in the process of Fractional Distillation.
We will go into more detail about this in a second. However, in this point we only need to acknowledge fractional distillation in terms of differing boiling points of fractions related to molecular size and attractive forces. The compounds with large molecules are likely to have a higher boiling point, so therefore condense faster and are collected on a lower position in the fractionating column.
Name methane as the main constituent of natural gas
Natural gas is composed mostly out of methane.
Describe petroleum as a mixture of hydrocarbons and its separation into useful fractions by fractional distillation
We already mentioned what fractional distillation is but now we’re going to go deeper in how a fractionating column works.
The image below shows an apparatus that can be used for fractional distillation.
Steps involved:
- When you heat the petroleum, the compounds start to evaporate as particles will more Kinetic Energy and therefore will more likely be able to break bonds. The compounds which are smaller and lighter evaporate first as it takes less energy to evaporate these.
- The hot vapour rises and the vapour then condenses in the cool test tube.
- when the thermometer reaches 100 degrees, the first test tube is then replaced with an empty one. The liquid in the first test tube is the first fraction from the distillation.
- Repeat, replacing the test tube at 150 degrees, 200 degrees, and 250 degrees.
However, industrially, the process is often done in a tower which has a very hot base, something like the one below.
Sorry I couldn’t get a more accurate diagram, but if you look in your textbook, you should be able to find one, or simply google it.
Here is what happens in the Fractionating Tower:
- Petroleum is pumped in at the base.
- The compounds start to evaporate.
- Those with the smallest molecules evaporate off first, and rise to the top of the tower.
