Hydrocracking of polynuclear aromatic hydrocarbons. Development of rate laws through inhibition studies

The relationship between molecular structure and reactivity during hydrocracking of model polynuclear aromatic hydrocarbons was examined through detailed kinetic studies. Naphthalene and phenanthrene were reacted over a presulfided NiW/USY zeolite catalyst in an 1-L batch autoclave at P-H2 = 68.1 atm and T = 350 degrees C, in a cyclohexane solvent. Pure-component experiments were combined with experiments where hydrocarbons and ammonia were added as inhibitors to aid quantitative network analysis. In all, 21 rate, 18 equilibrium, and 36 adsorption parameters were estimated through fitting of the kinetics data to a dual-site Langmuir-Hinshelwood-Hougen-Watson rate law. Adsorption parameters on both metal and acid sites increased with the number of aromatic rings and the number of saturated carbons; however, the quantitative values were higher for the acid sites. Rate parameters showed that, for a given total number of aromatic rings, hydrogenations at terminal aromatic rings were favored over hydrogenations at internal rings. Isomerizations and ring openings were favored at positions a to an aromatic ring or a tertiary carbon. Equilibrium concentration ratios for all hydrogenation and ring-opening reactions were larger than unity; equilibrium ratios for all isomerizations were less than unity, indicating significant reverse reactions. The hydrocracking networks were organized into the reaction families of hydrogenation, isomerization, ring opening, and dealkylation. The reactivity trends within each reaction family may be used for the development of quantitative structure/reactivity relationships.