What is petroleum coke, the carbon-rich solid left after refining heavy oil residues?

Petroleum coke is the carbon-rich solid left after refining heavy oil residues.

It is produced mainly in a coker, a refinery unit that uses severe heat to break large hydrocarbon molecules into lighter products while leaving behind a solid carbon-rich material. The resulting coke can be sold for industrial fuel or, when its quality is suitable, for uses such as aluminum-anode production.

Petroleum coke is not the same as coal, although both are carbon-based solid fuels. Its sulfur and metal content depends on the crude oil and the refinery process. Higher-sulfur grades generally require pollution controls when burned.

The material is also distinct from naturally occurring coal and from oil shale, which is a sedimentary rock containing kerogen. Refiners value coking because it converts otherwise difficult heavy residues into lighter liquids while creating a marketable solid by-product.