Chemistry of carbonaceous mesophase development and petroleum coke texture

Delayed coking of petroleum distillation residua or FCC decant oil produces petroleum coke that can be classified as needle coke, sponge coke, or shot coke, depending, to a large extent, on the nature of an intermediate phase, called carbonaceous mesophase. Carbonaceous mesophase is produced by the growth and orientation of large polyaromatic compounds during low-temperature carbonization. The extent of this two-dimensional pre-graphitic order determines whether the resulting coke is graphitizable by further heat treatment (e.g., needle coke from FCC decant oil), or not (e.g., shot coke from some vacuum distillation residua). An intermediate coke texture can also be produced (e.g., sponge coke) from some vacuum distillation residua. Physical and chemical properties of these petroleum cokes and their derivatives depend strongly on the extent of mesophase development that effect their optical texture. This presentation reviews the correlations between the molecular composition of the coker feedstocks and mesophase development.