ABSTRACT
The catalysts used in the hydrocracking process gradually deactivate, due primarily to coke deposition and, in the case of hydrotreating catalysts, contamination with nickel, vanadium, iron, copper, silica, and arsenic. Cycle length may vary from 1 to 5 years. Catalyst regeneration and, in the case of noble metal catalysts, rejuvenation restores most of the catalyst activity (see Chapter 8). However, after two or three cycles the catalyst can no longer be used due to irreversible loss of catalytic and/or mechanical properties. The spent catalyst is removed from the unit and replaced with a load of fresh or regenerated catalyst.
