Coking
Definition and meaning of Coking in chemistry.
Coking is the process of heating coal or heavy petroleum residues to high temperatures in the absence of air, driving off volatile components and leaving behind a hard, porous, carbon-rich solid called coke.
In more detail
Because no oxygen is present, the feedstock does not burn; instead it undergoes pyrolysis (destructive distillation), in which large organic molecules crack and condense, releasing volatile products while the remaining material fuses into coke. Coal coking is carried out in sealed coke ovens at roughly 1000-1100°C, yielding metallurgical coke plus byproducts such as coal gas, coal tar, and ammonia liquor. Metallurgical coke serves as both fuel and reducing agent in blast furnace ironmaking, since its carbon reduces iron oxides to molten iron. A related process, petroleum (delayed) coking, thermally cracks heavy refinery residues at lower temperatures to recover additional light fuels.
Key facts
| Process type | Pyrolysis / destructive distillation (no air) |
|---|---|
| Typical temperature | ~1000-1100°C (coal coking); ~450-550°C (petroleum delayed coking) |
| Main product | Coke (85-98% carbon by mass) |
| Field | General Chemistry |
Heating bituminous coking coal to about 1,000°C for 15-18 hours in an oxygen-free coke oven produces gray, porous metallurgical coke, along with recoverable byproducts including coal tar and coke oven gas.
Frequently asked questions
What is the difference between coking coal and coke?
Coking coal is the raw bituminous coal with the right caking properties; coke is the solid, carbon-rich product left after that coal is heated in the absence of air.
Is coking the same as combustion?
No. Combustion is oxidation that requires oxygen and releases heat as a flame, whereas coking is pyrolysis carried out without oxygen, so the material thermally decomposes rather than burns.