Effect of asphaltene dispersion on slurry-phase hydrocracking of heavy residual hydrocarbons

Abstract

Asphaltenes are the heaviest molecular substances that can be found in crude or refined residual oils. It is generally known that irreversible cokes are mainly derived from colloidal macrostructures comprising asphaltenes and resins during the thermal upgrading processes of heavy oils. The addition of artificial resin can significantly alter the colloidal states of the feedstock and affects the rate of coke formation during these processes. In the current study, the effect of the initial asphaltene stability on the hydrocracking performance was investigated by applying chemical compounds containing both polar and non-polar functional groups. Among those chemical compounds tested, polyisobutenyl succinimide (PIB-SI) allowed the most efficient coke reduction irrespective of the type or amount of dispersed catalyst and improved the overall yield of distillable liquid product. The structural changes in the asphaltene molecules during hydrocracking are further investigated in a quantitative analysis based on 1H and 13C NMR spectra associated with the molecular weight distributions for extracted asphaltenes. This analysis shows that considerably smaller molecules can be found in asphaltenes extracted from the liquid product of hydrocracking in the presence of PIB-SI. The results reveal that increasing the dispersion of asphaltenes can be a good strategy for reducing coke formation and improving the yield of the desired liquid products in the hydrocracking process.