Regeneration - Spent Hydroprocessing Catalysts - page 171

6.3.6 Regeneration by Attrition/Abrasion

The objective of this method is the removal of either the “skin” of inorganic solids or this part
of metals, which deposited predominantly on or near the external surface of catalyst particles.
For V and Ni, the sulfides formed via the non-catalytic reaction of porphyrins with H 2 S could
be easily removed from spent catalysts by the attrition. Under dry conditions, such an attrition
test could be conducted in a fluidized bed reactor. The spent catalyst has to be kept in a motion
when the attrition test is conducted under wet conditions.

The method used by Gray et al. [243] involved rolling the mixture of the metal deposited
catalyst particles with the particles of

-Al 2 O 3 in water. After drying, catalyst was separated

from the -Al 2 O 3 by sieving. Some removal of the “skin” metals (e.g., Fe and Ca) was

observed, but it was less efficient than the extraction with the diluted HCl. The experiments
could also be conducted under dry conditions. Nevertheless, this method can only remove
metals from the external surface of catalyst. The removal of metals from pores would require a
prolonged attrition, which could affect the size and mechanical properties of catalyst particles.
It is believed that the attrition/abrasion methods for regeneration of hydroprocessing catalysts
have limited practical applications. Apparently, such method may be more suitable for
removing metals from the spent FCC catalysts.

6.3.7 Resulfidation of Regenerated Catalysts

On the industrial scale, regeneration of spent hydroprocessing catalysts has been dominated by
the oxidative method employing air and/or diluted air. Thus, even industrial reactivation,
which has been receiving much attention in recent years, is always preceded by oxidative
regeneration. Rather than to transport the regenerated catalyst to refinery in its oxidic state,
regenerating companies have been performing off-site presulfiding as an additional service to
refiners. Because of the environmental and economic benefits, which result from the off-site
presulfiding, many refineries have been taking advantage of this service. Handling of toxic
compounds associated with on site regeneration is avoided in the case that refiners opt for
off-site regeneration. In addition, faster reactor start extends production time of the overall
operation.

In one off-site presulfiding method, the oxidic catalyst is first impregnated with a sulphur
containing compound dissolved in an organic solution and dried in an inert atmosphere.
Under these conditions, sulfur reacts with metal oxides incompletely. The catalyst is then
subjected to H 2 activation at a higher temperature and pressure for complete sulfidation
[440-442] . Thioglycolic acid was used as sulfiding agent in the study published by Frizi
et al. [443] . This agent ensured an efficient sulfidation in addition to complexation. The
latter was confirmed by a high level of active metals dispersion. The impregnation of
regenerated catalyst with diethyleneglycolbutylether enhanced activity of the catalyst after