Catalyst Deactivation - Spent Hydroprocessing Catalysts - page 60

Figure 4.7: Loss of surface area and pore volume in spent catalysts from atmospheric residue
desulfurization (ARDS) reactors [From ref. 12 . Reprinted with permission].
were used to estimate level of the surface area recovery on the oxidative regeneration [12] .For
catalysts taken from reactors 1 and 2, the recovery was rather low, suggesting a permanent
deactivation by metals. A significantly higher level of the surface area recovery was achieved
for the catalysts taken from reactors 3 and 4. For these catalysts, coke deposition was the
primary cause of catalyst deactivation.
Figure 4.8 identifies major factors causing the catalyst deactivation during hydroprocessing of
the asphaltenes and metals containing feeds in the three-stage ebullated-bed reactors process
[188] . The results were obtained using the heavy feed containing about 400 ppm of V+Ni. For
every stage, the last point on the curve was recorded after 110 days on stream. Therefore, for
the stage 3 catalyst, deactivation was caused mainly by coke deposition, whereas for stage 1
catalyst, the deposition of metals and restricted diffusion were the predominant modes of
deactivation with the contribution of the latter increasing with time on stream until it became
the main cause of the loss of activity. Furthermore, the relative contribution of these factors
depends on the properties of heavy feeds. Deactivation patterns observed in stage 3 may
Figure 4.8: Major factors causing catalyst deactivation versus metals on catalyst [From ref. 188 .
Reprinted with permission].