Hydroprocessing of Petroleum - Spent Hydroprocessing Catalysts - page 31

Figure 3.4: Effect of feed origin on hydrodesulfurization (HDS) activity (CoMo/Al 2 O 3 )
[From ref. 90 . Reprinted with permission].
It is again emphasized that an optimal pore size and volume distribution are critical for
hydroprocessing of the high metal content feeds, particularly those derived from heavy crudes.
This results from the large molecular diameter of the V- and Ni-containing porphyrin
molecules, i.e., for microporous catalysts, the diameter may exceed that of pores. For small
pore diameters, most of the metals will deposit on the external surface of the catalyst particles
and the diffusion into the catalyst interior becomes the rate-limiting factor. It is therefore
expected that the tolerance of catalyst to metals will increase with the increasing pore diameter
as it is shown in Fig. 3.5 [78] . At the same time, the catalyst activity will decrease. At a certain
Figure 3.5: Effect of pore radius on metal tolerance and hydrodesulfurization (HDS) activity
[From ref. 78 . Reprinted with permission].