There are at least four basic types of petroleum coke, namely, needle coke, honeycomb coke, sponge coke and shot coke. Different types of petroleum coke have different micro-structures due to differences in operating variables and nature of feed-stock. Significant differences are also to be observed in the properties of the different types of coke, particularly ash and volatile matter contents.
Needle coke, also called acicular coke, is a highly crystalline petroleum coke used in the production of electrodes for the steel and aluminium industries and is particularly valuable because the electrodes must be replaced regularly.
Needle coke is produced exclusively from either FCC decant oil or coal tar pitch.
Honeycomb coke is an intermediate coke, with ellipsoidal pores that are uniformly distributed. Compared to needle coke, honeycomb coke has a lower coefficient of thermal expansion and a lower electrical conductivity.