Bitumen is a mixture of organic liquids that are highly viscous, black, sticky and composed primarily of highly condensed chemical compound. Bitumen is the residual or by product obtained by fractional distillation of crude oil. It is the heaviest fraction and the one with the highest boiling point. Bitumen is referred to as 'asphalt' or 'asphalt cement'.

Most bitumens contain sulphur and several heavy metals such as nickel, vanadium, lead, chromium, mercury and also arsenic, selenium and other toxic elements. Bitumens can provide good preservation of plants and animal fossils.

Background

Most geologists believe that naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic once-living things. These organisms died and their remains were deposited in the mud on the bottom of the ocean or lake where they lived. Under the heat and pressure of burial deep in the earth, the remains were transformed into materials such as bitumen. Bitumens are found also in meteorites, archean rocks, copper, zinc mineralizations, and caves. It is possible that bitumens are primordial material formed during accretion of the earth and reworked by bacteria that consume hydrocarbons.

Distillation is the most common form of separation technology used in petroleum refineries, petrochemical and chemical plants and natural gas processing plants to separate crude oil into useful substances (or fractions) such as petroleum products, motor oils, LP gas, bitumen etc. In most cases, the distillation is operated at a continuous steady state. New feed is always being added to the distillation column and products are always being removed.

Industrial distillation is typically performed in large, vertical cylindrical columns known as "distillation or fractionation towers" or "distillation columns" The distillation towers have liquid outlets at intervals up the column which allow for the withdrawal of different fractions or products having different boiling points or boiling ranges. The "lightest" products (those with the lowest boiling point) exit from the top of the columns and the "heaviest" products (those with the highest boiling point) exit from the bottom of the column.