New Catalysts from Spent Catalysts - Spent Hydroprocessing Catalysts - page 239

Figure 9.5: Effect of Mo content of the catalyst (catalyst A) on hydrodesulfurization (HDS)
activity [From ref. 522 . Reprinted with permission].
active phase. Thus, several studies showed that in the presence of V, this phase is gradually
converted to V-Mo-S phase which is much less active than the Ni-Mo-S phase [162] .
Apparently, the HDS and HDM activities of the reprocessed catalysts prepared from spent
catalyst A and B were similar in spite of a greater level of deactivation of the latter. In their
activity, these catalysts approached that of commercial NiMo/Al 2 O 3 catalysts. In fact,
reprocessed catalysts prepared from spent catalyst A were more active for both HDS and
HDM, as it is shown in Fig. 9.8 [522] . A high content of V in the catalysts prepared from
catalyst C was responsible for low HDS activity. However, negative effect of V on HDM
activity was less evident. In fact, even the catalysts prepared from the heavily deactivated
catalyst C may exhibit adequate activity in less severe applications.
It should be noted that the trends in Figs 9.5 and 9.6 [522] are in a general agreement with
those observed in the studies on preparation of hydroprocessing catalysts reported in the
literature [27] . Yet, the reprocessed catalysts were prepared from the material which differed
significantly from that used for preparation commercial catalysts. Thus, in the former case, the
material has undergone transformations of the fresh catalyst during commercial operation
lasting almost one year until its replacement was necessary because of the activity decline.
After removing from commercial reactor, the spent catalyst could be subjected to either
oxidative regeneration or rejuvenation providing that the level of the activity recovery was still
acceptable. Otherwise, other options for the spent catalyst, i.e., metal reclamation, disposal in
landfills, etc. had to be identified. However, even for a heavily deactivated catalyst, the activity
can be restored by reprocessing spent catalysts according to the method shown in Fig. 9.1 [9] .
Another attempt to reprocess spent hydroprocessing catalysts was made by Gardener and
Dennis [527] who prepared an active catalyst from spent catalyst that contained Co, Mo, and