ABSTRACT
In addition to hydrocracking reactions, a number of other reactions take place during the hydrocracking process (Table 6.1). In most hydrocracking processes, the feedstock is submitted to hydrotreating prior to hydrocracking, in the same or in different reactors. Hydrotreating is a pretreatment that partially hydrogenates unsaturated hydrocarbons and removes hetero atoms from the feedstock. Compounds containing these hetero atoms have a deleterious effect on the hydrocracking catalyst and must be removed. The initial reactions in the hydrocracking process are therefore hydrotreating reactions and occur at a relatively high rate over a hydrotreating catalyst. These reactions include hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodeoxygenation (HDO), olefin hydrogenation, and partial aromatics hydrogenation. A comparison of the rates of different hydrotreating reactions shows that the reaction rate decreases in the order HDS > HDN > olefin saturation> aromatic saturation.
