Effects of molecular composition and carbonization reactivity of FCC decant oil and its derivatives on mesophase development

FCC decant oil is the primary feedstock to delayed coker to produce needle coke, a premium carbon precursor to synthetic graphite electrodes. A study was carried out to analyze the molecular composition of the coker feeds as compared to the parent decant oils. Laboratory carbonization experiments were carried out on the decant oil and coker feed samples as well as on the bottom and top fraction (gas oil) of the decant oils separated by vacuum distillation. Samples of hydrotreated gas oil were also carbonized under comparable conditions. Semi-coke and asphaltene yields from the carbonization experiments were determined to compare the carbonization reactivity of different samples. Significant differences were observed between the molecular composition of FCC decant oil and its derivatives in two different sample sets. Coker feeds had higher concentrations of aromatic compounds and possessed higher pyrenes/phenanthrenes ratios compared to the parent decant oils. Differences in the extent of mesophase development from decant oil, coker feed, gas oil, hydrotreated gas oil, and vacuum tower bottoms could be explained by differences in their molecular composition that is closely related to their carbonization reactivity. Slower conversion of asphaltenes into semi-coke favored a high degree of mesophase development. At high asphaltene levels during carbonization, effective deformation of viscous anisotropic domains during conversion to semi-coke also promoted mesophase development.