New Catalysts from Spent Catalysts - Spent Hydroprocessing Catalysts - page 233

Table 9.2: Atomic ratios of catalysts [From ref. 522 . Reprinted with permission].

Catalyst Ni/Mo V/Mo

A 0 . 84 0 . 84

B 0 . 95 1 . 67

C 1 . 08 3 . 20

Poremaster - 60) was used for pore volume and pore size distribution estimates, while
Quantochrome unit was used for the determination of Brunauer-Emmett-Teller (BET) surface
area. The content of metals in the decoked catalysts was estimated from the analysis in
Table 9.1 assuming that most of the carbon was removed on decoking.

The results in Table 9.1 [522] were used to estimate the V/Mo and Ni/Mo ratios shown in
Table 9.2 . For catalysts prepared from the same spent catalyst, these ratios remain the same
in spite of the different amounts of spent catalysts added to boehmite. These ratios exceed that
in the fresh NiMo/Al 2 O 3 catalysts. For example, for the fresh NiMo/Al 2 O 3 , the Ni/Mo ratio
approaches 0.45. At this ratio, the amount of the Ni-Mo-S active phase formed on sulfiding is
optimized [53] . Therefore, a direct involvement of the deposited Ni in excess of the optimal
amount in hydroprocessing reactions seems to be plausible. It is, however, anticipated that in
the presence of a large amount of V, the Ni-Mo-S active phase can be modified.

The preparation of the catalyst extrudates was conducted in the laboratory kneading and
mixing machine Type LUK 2.5 AS manufactured by Werrner and Phleiderer Co, Germany.
In this case, 300 g of spent catalyst-boehmite mixture in the desired ratio was added to the

mixing chamber. During mixing and kneading, 185 mL of the diluted HNO 3 (2%) was added
in drops to the boehmite powder, as peptizing agent. At the end of mixing and kneading, the
product was extruded through the die (1.5 mm) to form catalyst extrudates. The extrudates
were dried at 110 ◦ C for 24 h, followed by several calcining steps, i.e., 370 ◦ C for 1 h, 450 ◦ C
for 2 h, and 500 ◦ C for 2 h. After calcination, the extrudates were cooled in a desiccator.

∼

The radial metal distributions in extrudates were determined using a JEOL scanning electron
microprobe X-ray analyzer. The distribution profiles of V for the extrudates prepared from
spent catalysts A and B together with the corresponding spent catalysts are shown in Fig. 9.2
[9,524] . It is evident that for both spent catalysts, the V concentration near the outer edge is
substantially higher than at the center of particle. The former is the main cause of catalyst
deactivation during operation. On the other hand, in reprocessed catalysts, the radial
distribution of V is rather even.

The effect of the spent catalyst content in reprocessed catalysts on the pore size and pore
volume distribution is shown in Table 9.3 [523] . These results were obtained for the mixture of