Regeneration - Spent Hydroprocessing Catalysts - page 155

As it follows from Fig. 6.22 [367,368] , the recovery of surface area may not be a good
indication of the recovery of catalyst activity even for spent catalysts used for upgrading light
feeds. It was reported that the acidity of regenerated catalysts measured by pyridine adsorption
correlated well with the activity [410] . At the same time, no correlation with surface area was
observed in spite of the complete surface area recovery. This may be attributed to the
agglomeration and/or sintering of active phase on the support during regeneration, while little
change was incurred by the latter [410] . Therefore, any additional treatment of regenerated
catalysts leading to an enhanced metal distribution would almost certainly improve catalyst
activity.

The regeneration of spent catalysts shown in Table 6.7 was used to illustrate the other extreme
of the catalysts deactivation due to both coke and metal deposits [411] . The spent catalysts
were obtained from the two different hydrodemetallization (HDM) operations using the
HYVAHL process [138,412,413] . In the fresh form, the macroporous catalyst consisted of
2.7 wt.% of NiO and 14.0 wt.% of MoO 3 and had surface area of 140m 2 /g. The results of
regeneration shown in Table 6.8 [411] were obtained for either fresh or regenerated catalysts
that were subsequently presulfided according to the established procedures. They clearly

Table 6.7: Analysis of toluene-extracted spent catalysts [From ref. 411 . Reprinted with permission].

Element (wt.%) Catalyst A Catalyst B

Carbon 15 . 0 13 . 6

Sulfur 5 . 9 13 . 5

Vanadium 3 . 3 10 . 1

Nickel 2 . 7 4 . 6

Iron 0 7 . 7

Table 6.8: Properties of fresh and regenerated catalysts [From ref. 411 . Reprinted with

permission].

Surface area (m 2 /g)

Catalyst Treatment Conversion (wt.%)

HDS HYD

Fresh None 140 46 . 7 27 . 5

SpentA None 17

Spent B None 11

Spent A 2% O 2 127 15 . 0 10 . 7

Spent B 2% O 2 60 15 . 7 12 . 9

Spent A Air 54 12 . 3 9 . 3

Spent B Air 17 6 . 4 5 . 9

HDS: hydrodesulfurization; HYD: hydrogenation.