Dirty Oil

By Katherine Bourzac

Description text

Bitumen is a viscous mixture of long hydrocarbon chains--strings of as many as thousands of carbon atoms bonded to hydrogen atoms. These molecules must be "upgraded" to shorter molecules before they can be refined into petroleum products.

Purified bitumen is heated to break its long hydrocarbon chains into lighter molecules, such as naphtha, that can be refined. This process is called coking and takes place in large towers. The high-carbon by-product of the process, called coke, in turn fuels the coking furnaces. Distillation and a hydrogenation process are the final steps.