Fractional Distillation: Separating Crude Oil by Boiling Point

0:00How do refineries turn crude oil into useful fuels?

0:05Crude oil is a mixture of hydrocarbons, compounds of only carbon and hydrogen, with chains of many lengths.

0:13Refineries separate them by boiling point, using fractional distillation in a tall fractionating column.

0:20A furnace boils most of the crude oil, and the hot vapour enters near the bottom of the column.

0:26The column is hottest at the bottom and coolest at the top.

0:31The vapour rises through holes in the trays, shelves across the column, and cools.

0:37Below its boiling point, a hydrocarbon condenses to a liquid on a tray.

0:42Each liquid is piped out as a fraction: hydrocarbons with similar boiling points.

0:48Refinery gases, the smallest molecules with about one to four carbons, boil lowest and leave from the top.

0:56Longer chains condense on the middle trays: gasoline, kerosene and diesel.

1:03Near the bottom, heavy fuel oil condenses, and bitumen, with the longest chains, stays liquid and drains out.

1:11Why do longer chains boil higher? Hydrocarbon molecules attract each other by weak dispersion forces.

1:20Longer chains have more electrons and more contact, so these forces are stronger.

1:26So more energy is needed to pull them apart: a higher boiling point.

1:31The fractions become fuels for transport and heating, and petrochemicals, chemicals made from oil, such as plastics.

1:40Fractional distillation separates crude oil into fractions by boiling point.