Crude oil and fuels

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Crude oil mainly contains a mixture (2 or more elements or compounds that are not chemicaly combined, so they can be separated physically, the properties of the substances don't change) hydrocarbons. All of the different hydrocarbons have different boiling temperatures and burn under different conditions so the crude oil must be separated in order to make useful fuels from it. To separate crude oil we distill it ( fractional distillation). This process works as the larger a hydrocarbon is the higher the boiling point, this means that different hydrocarbons condense at different temperatures. During fractional distillation, the crude oil is vapourised and then fed into the fractionating column, where smaller hydrocarbons condense at the top ( where it is cooler) and larger molecules condense at the bottom ( where it is hotter). This happens as inside the column there are many trays with holes in them, to allow the gases though, this means gases can rise upwards, and cool down and condense when the temperature of their boiling point has been reached, the liquids are then fed off. Fractions that are small have low boiling temperatures, low viscosity (runny), very flamable and ignite easily and they burn with clean flames ( producing little smoke) which makes them useful as fuels.

Liquids that boil within different temperature ranges are called fractions

Most of the compounds in crude oil are hydrocarbons…


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