Fractional Distillation

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Fractional Distillation

1. Crude Oil is heated strongly to evaporate it

2. Hot vapours are led into the bottom of the fractionating column. The hottest at the bottom and becomes cooler towards the top.

3. The vapours cool down as they rise though it.

4. When the vapour reaches a part of the column that is cool enough they condense.

5. The liquid falls into a tray and is piped out

Long Chain Alkanes → Bottom of column, High Boiling point, High Viscosity, Low Volatility point, Low flammability.

Short Chain Alkanes → Top of Column, Low boiling point, Low Viscosity, High Volatility, High Flamability.

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Fractional Distillation

Distillation - Boiling Points

Viscosity - How runny it is.

Volatility - How esaily it evaporates.

Flammability - How easy it is to ignite.

Long Chain Alkanes make poor fuels.

- They are solid at room temperature, not very         

flammable and are difficult to ignite.

Short Chain Alkanes are good fuels.

- Gases at room temperature, ignite easily

- Bulky to store, stored under pressure as


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Fractional Distillation

The top of the column is cool (25 degrees celsius). Fractions taken from here have small molecules, low boiling points, are very volatile, flow easily and ignite easily. Crude oil enters at the bottom of the column and is heated to 350 degrees celsius. Fractions taken here have large molecules, high boiling points, are not very volatile, and don't flow or ignite easily. From top to bottom the fractions are: Refinery gases (bottled gas), gasoline (petrol), naptha (used for making chemicals), kerosene (aircraft fuel), diesel oil (fuel for cars, and lorries, etc), fuel oil (fuel for ships, power stations), residue (bitumen for roads and roofs). (

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