Chemistry - Fractional distillation of crude oil
Fractional distillation of crude oil
Crude oil is separated into fractions of similar molecular mass (and
boiling point) in a fractionating tower, represented in the diagram below.
Fractional distillation involves heating crude oil to temperatures in
excess of 400C, a temperature high enough to vaporise most of the
hydrocarbons present in the mixture. The hot vapours rise up the
fractionating column. The temperature gradually falls as they rise up the
column and different hydrocarbons will_ liquefy_ as the temperature drops
below their boiling temperatures.
Bubble caps in the column allow vapour to continue to rise up the column
through condensed liquid which collects on trays.
Depending on the temperature, certain hydrocarbons in the vapour stream
liquefy on each tray. The mixture of hydrocarbons that collects on a
particular tray is called a _fraction._ Each fraction contains a set of
hydrocarbons with a_ narrow range of boiling temperatures._
The higher boiling temperature fractions are collected near the bottom of
the fractionating column. The lower boiling temperature fractions rise to
the top of the fractionating column.
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