Calcined coke goes overwhelmingly into aluminium smelting, where it is blended with coal tar pitch and baked into the carbon anodes consumed in the reduction cell — roughly four hundred kilograms per tonne of aluminium produced. Needle coke, a premium anisotropic grade, is graphitised into electrodes for electric arc furnace steelmaking and is increasingly used as precursor for synthetic graphite battery anode material. Fuel-grade coke is burned in cement kilns and power boilers, and smaller volumes serve as steel recarburiser and as the reductant in titanium dioxide production.

Green coke is the material as it leaves the delayed coker, still containing eight to fifteen per cent volatile matter and typically a substantial amount of moisture from the cutting operation. Calcined coke has been heated to between 1200 and 1400 °C in a rotary kiln or rotary hearth, which drives off the volatiles, shrinks and densifies the particles, and increases the ordering of the carbon structure. Real density rises to around 2.06 g/cm³ and electrical conductivity improves substantially. They are separate commercial products with separate CAS numbers — 64741-79-3 for green and 64743-05-1 for calcined — and a specification or shipping document should always state which.

Impurities, inherited from the crude that produced the residue. Anode grade requires low sulphur — generally three per cent or below, with individual smelters setting their own limit — and low vanadium, nickel, sodium, calcium, silicon and iron. Fuel grade is everything that does not meet those limits, and it can run to seven per cent sulphur or more. The physical form matters too: sponge coke has the porous structure anodes need, while shot coke, formed when the coker runs on very heavy or aromatic feed, is hard and spherical and goes to fuel regardless of chemistry. The price gap between the two markets is large, which is why refiners work hard on feed selection.

Because each one causes a distinct problem in the smelter. Vanadium is not removed in the reduction cell and reports directly into the aluminium, degrading its electrical conductivity, which matters enormously for conductor-grade metal. Sodium catalyses the oxidation of anode carbon by air in the hot cell, increasing net carbon consumption and shortening anode life. Calcium and silicon affect anode density and reactivity to carbon dioxide. Nickel behaves similarly to vanadium as a metal contaminant. A smelter will reject a cargo that meets its sulphur limit but exceeds any one of these, which is why a certificate showing sulphur alone is not sufficient for anode-grade trade.

Needle coke is made from highly aromatic feedstock — decant oil from a fluid catalytic cracker, or coal tar pitch — coked under carefully controlled conditions so that the carbon layers align into long, parallel, needle-like domains. That anisotropy is what allows it to be graphitised into an electrode with very low coefficient of thermal expansion, which is essential because an arc furnace electrode is subjected to violent thermal cycling and will crack if it expands unevenly. Coefficient of thermal expansion is the governing specification rather than sulphur or ash. Needle coke commands a very large premium over ordinary calcined coke, and demand from lithium-ion synthetic graphite anode production now competes directly with the electrode market for it.

Every cargo includes a Certificate of Analysis stating whether the material is green or calcined and covering total sulphur, volatile matter, moisture, ash, the full metals panel including vanadium, nickel, sodium, calcium, silicon and iron, real and bulk density for calcined material, Hardgrove grindability index, and calorific value for fuel grade; a Safety Data Sheet for the specific grade; written confirmation of the applicable CAS number; an origin certificate; and destination-market documentation including emissions-related declarations where required.