Rejuvenation - Spent Hydroprocessing Catalysts - page 190

CHAPTER 7
Rejuvenation
It is again emphasized that the removal of both contaminant metals and coke with the aim to
recover activity of the catalyst is the principal objective of rejuvenation. This differs from
regeneration in which case only coke removal has been the objective. Most of the methods for
catalyst rejuvenation are based on selective leaching of contaminant metals from spent
catalysts. At the same time, all efforts are made to ensure that the leaching of active metals is
kept at a minimum. The non-leaching methods have been receiving attention, although to a
much lesser extent.
Figure 7.1 [462] describes the strategy for rejuvenation of spent catalysts developed by Kuwait
Institute for Scientific Research (KISR). It should be noted that it is there where the only of its
kind database on various aspects of spent hydroprocessing catalysts has been established with
primary focus on rejuvenation. It is noted that some steps shown in Fig. 7.1 are common for
regeneration, e.g., starting with de-oiling up to mechanical separation of particles. The
proposed strategy took into consideration three options described briefly as:
Option I, where spent catalyst is de-oiled by washing with kerosene in the first step.
Then the oil-free catalyst is mechanically separated into catalyst fines ( < 0.5mm
particles), as well as lightly, medium, and heavily fouled portions. The medium dense
and heavy portions are subjected to chemical treatment to remove metals by leaching.
Subsequently, the leached catalysts are mixed with the lightly fouled catalyst portion
and decoked by controlled burn-off to produce rejuvenated catalyst.
Option II
After de-oiling and separating the spent catalyst into three groups as in Option I, the
heavily fouled portion is sold to metal reclamation companies, while the medium
fouled portion is subjected to leaching. The leached catalyst and lightly fouled catalyst
are decoked to produce rejuvenated catalyst.
Option III
De-oiling and grouping is performed as in Options I and II. The heavy and medium
fouled portions are sold to metal reclaimer, whereas lightly fouled catalyst is decoked
under conditions approaching those employed during the oxidative regeneration.
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