Regeneration - Spent Hydroprocessing Catalysts - page 180

Figure 6.37: Length distribution of spent catalyst (feed) and its short fraction [From ref. 465 .
Reprinted with permission].
and heavy fractions. The properties of these fractions and relative HDS activity after their
regeneration are shown in Table 6.12 [465] . It is evident that only about 28 wt.% of the spent
catalyst could be regenerated to an acceptable level of catalyst activity. Therefore, the yield of
the regenerable catalyst may be a factor to be considered when justifying regeneration after the
length-density grading. Otherwise, all catalyst may be considered non-regenerable.
As it was indicated, screening is the simplest way of the size grading. In the case of one
refinery, screening of regenerated catalyst was routinely performed after receiving the catalyst
from regenerator [466] . Thus, an undesirable pressure drop development forced
discontinuation of the operation unless regenerated catalyst was screened to remove fines.