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Chemistry: Year 10

This is a short section... and we all love Chem, right? ... Right?

Fractional Distillation

It might sound like a bit of a mouthful, but it's very important. It allows us to turn crude oil from a blob, into useful fractions like diesel.

What is crude oil? It's a fossile fuel, so like the others, is formed from dead plants and animals that didn't decay millions of years ago. Other time, with high temperature and pressure, they were changed into oil, which we can drill up (there's a large industry in the search for new oil).

Crude oil, though, is useless in its "crude" form. It's a mixture of different length hydrocarbon molecule (you know, a compound that only contains hydrogen and carbon). Therefore, these varying lengths need to be split up. That's where the fractionating column comes in...

A fractionating column works because large molecules have a higher boiling point than small molecules.

The first step is to heat all the crude oil, so everything evaporates.

Then the gas goes into the column. As the hot gas rises, the column gets cooler, and the large molecules start to condense.

Fractions can be collected at different sections of the column.

And that's pretty much all there is to it!

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Cracking

Hydrocarbons are molecules made from only hydrogen and carbon. The smaller ones are much more useful than the larger ones. This is because:

  • Smaller molecules are more volotile (they turn into gas easier).
  • Smaller molecules are less viscous (they're runny).
  • Smaller molecules have lower boiling points.
  • Smaller molecules are more flammable.

This means they can be used to produce energy easily. The fomula for this is:

Hydrocarbon + Oxygen -> Carbon Dioxide + Water (+ Energy)

With large molecules, this is much harder. However, there's a solution: Cracking.

Cracking is using heat and a catalyst to break a long hydrocarbon into a smaller more useful hydrocarbon and an unsaturated hydrocarbon. In other words, it's a thermal decomposition.

For example:

 

 

 

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All text copyright © 2006 to EJ Taylor. Page Template created by James Taylor. Site created: 10 April, 2006. Last revised: 2 August, 2015