5.7       describe  and explain how the  industrial process  of  fractional distillation separates  crude  oil  into fractions

1)   The oil is heated until it turns to vapour.

2)   The vapour is passed into the bottom of a tall column with outlets at various heights.  The column is hot at the bottom and cool at the top.

3)   The vapours rise up the column and cool.  They condense to liquids when they reach a low enough temperature.

4)   The lightest fractions rise to the top because they have the lowest boiling points.

5)   The heaviest fractions remain towards the bottom (where the column is warmest).

6)   The fractions are condensed at the outlets, except for the refinery gases, which leave the top of the column as gases.