Regeneration - Spent Hydroprocessing Catalysts - page 167

reactions:

C + N 2 O = CO + N 2

C + NO = CO + 0.5N 2

C + 2NO = CO 2 + N 2

Because of very weak N O bonds in N 2 O, the generation of very active O* radical and its
participation in carbon removing reactions cannot be ruled out, e.g.:

O *

N 2 O = N 2 +

O * C + = CO

So far, N 2 O was the only nitrogen oxide tested for regeneration of spent hydroprocessing
catalysts [428,429] . In this case, a more complete carbon removal with N 2 O compared with
pure O 2 , was achieved, although the initial rate of carbon oxidation in the presence of the latter
was greater. It is believed that comparing N 2 O with diluted air makes more sense than with
pure O 2 because of the safety and other reasons discussed above. There is little information on
the use of other nitrogen oxides in spite of their suitability predicted by thermodynamics. In
this regard, a parallel may be drawn between regeneration of spent catalysts and ability of
various carbons to reduce nitrogen oxides to N 2 . The availability of nitrogen oxides in
desirable concentrations and quantities may be an obstacle for their utilization during
industrial regenerations.

6.3.3 Reactivation

The postoxidative regeneration treatment of spent catalysts with various organic agents having
chelating capabilities has been also successfully applied to regenerated catalysts. Such
treatment resulted in the significant enhancement of the active metals redispersion, similarly as
it was observed for calcined catalysts during catalyst preparation.

Generally, a partial sintering of active metals during regeneration cannot be completely
prevented. The impregnation of regenerated catalysts with various chelating agents resulted in
a significant enhancement of the active metals redispersion on subsequent resulfiding. On a
commercial scale, this method was introduced by Albermarble in 2003 as reactivation
(REACT) technology [329,430] . This technology enables the activity of the spent regenerated
STAR catalyst marketed by Albermarble to be recovered to more than 90% of the fresh
catalyst activity. This was attributed to redistribution of metals and reconfiguration of the type
II active phase to approach that in the original catalyst. Details of this process were given in
patent applications submitted by Ginestra et al. [431] and Eijsbouts et al. [432] . The latter list