Regeneration - Spent Hydroprocessing Catalysts - page 121

recovery. The crushing strength and particle size distribution of the laboratory-regenerated
catalysts should conform to minimum specification requirements as well. The conditions of
the laboratory tests must be optimized to ensure reliability of the results. Otherwise, a situation
may be encountered in which laboratory tests indicate regenerability of the catalyst contrary to
the industrial regeneration results.
Because of the complexity involved, the refiner may request either catalyst supplier or catalyst
regenerating company to perform laboratory testing of spent catalysts prior to final decision is
made. The TCM approach discussed earlier is another potential option available to refiner.
Otherwise, testing on a pilot plant scale may provide more reliable information. According to
Smart [364] , such testing may comprise four parts, e.g.:
(1) Measurement of activity, kinetic rate constants, and activation energy.
(2) Measurement of catalyst response to the change in H 2 pressure, space velocity, and
temperature.
(3) Estimate of relative catalyst stability and lifetime using an accelerating aging test.
(4) Evaluation of the regenerability of catalysts and of the other factors governing
regeneration.
Of course, all these testing phases are usually complemented by determination of the chemical
and physical properties of catalysts.
It was indicated in Chapter 5 that the structure and composition of the deposits on spent
catalysts surface depend on the origin of feed, type of catalyst, and operating conditions.
A spent catalyst used for the hydroprocessing of atmospheric distillate feeds can be readily
regenerated because the content of contaminant metals in the deposit is negligible. Thus,
several regeneration-utilization cycles can be achieved with such catalysts. In this case, the
recrystallization of active phase and/or the loss of active metals due to diffusion to the support
may not be avoided. During the prolonged exposure to operating conditions, sometimes lasting
several years, this could be the main cause of deactivation during hydroprocessing of the
atmospheric distillates. Most likely, this would be the cause of a permanent deactivation.
Apparently, the spent catalysts from hydroprocessing of vacuum gas oil (VGO) and heavy gas
oil (HGO) can also be regenerated, although they were exposed to more severe conditions than
those applied during hydroprocessing of atmospheric distillates. More severe conditions would
result in an enhanced catalyst deactivation due to sintering. Therefore, the number of
regeneration-utilization cycles is expected to be lower than that for the spent catalysts from the
upgrading of atmospheric distillates. Temperature and H 2 pressure are among the most
important parameters influencing the regenerability of spent catalysts [366] . In fact, the