Introduction - Spent Hydroprocessing Catalysts - page 2

non-catalytic processes, will increase the volume of such distillates relative to that of the
conventional distillates. Then, even in the case of distillate feeds, a continuous increase in the
catalyst consumption and the generation of spent catalysts associated with it can be anticipated.
The catalysts used in the refining processes deactivate with time on stream [8-12] . When the
activity of catalyst declines below the acceptable level, it must be replaced with either fresh or
regenerated catalyst. However, there is a limit on the number of regeneration cycles. Moreover,
it is not always economically attractive to conduct regeneration of spent catalysts [7,13,14] .
Thus, after several cycles of regeneration and reuse, the catalyst activity recovery may
decrease below acceptable levels. Therefore, further regeneration may not be economically
attractive. Then, other options for the spent catalysts utilization have to be considered before
they are discarded as solid wastes [14,15] .
The market demand for hydroprocessing catalysts was estimated to increase with an annual
growth rate of 4.4% [6] . Currently, the market for fresh hydroprocessing catalysts approaches
120,000 tons per year. About half of this amount has been used for hydroprocessing of
distillates to produce clean fuels, whereas the other half has been used for residue upgrading
[7] . The demand for the hydrocracking catalysts, which is currently about 10,000 tons annually,
is also expected to grow at a rate of more than 5% per year. Consequently, the production of
spent catalysts will be steadily increasing. Therefore, the actual quantity of spent catalysts
discharged from different processing units depends largely on the amount of fresh catalysts
used and quality of feeds. This depends on the amount of the processed feed per weight unit of
catalyst and the amount of deposits formed during the operation. Therefore, the amount of
spent catalysts is generally greater than that of the fresh catalyst by the amount of deposits. For
example, spent catalysts from distillate upgrading units contain typically 10-20% coke and
7-15% sulfur together with some hydrocarbons carry-overs. Both organic and inorganic forms
of sulfur are present. In the case of residue hydroprocessing operations, metals, such as V and
Ni, are present in the feed deposit on the catalyst together with coke. If dispersed solids are
present in the feed, they deposit on the front of catalyst fixed bed. The spent catalysts
discarded from these units usually contain 7-20% V+Ni, 15-25% coke, 7-15% sulfur, and
5-10% residual oil together with active metals (Mo and Co or Ni) and Al 2 O 3 originally
present in the catalyst. However, the amount of deposit on catalyst may be decreased on the
refinery site by applying de-oiling and drying procedures before unloading spent catalyst from
reactor. According to the estimate made by Dufresne [7] , the total quantity of spent
hydroprocessing catalysts generated worldwide is in the range of 150,000 to 170,000 tons per
year. Therefore, with anticipated 5% annual increase in catalyst consumption, the generation
of spent hydroprocessing catalysts may exceed 200,000 tons annually within a few years.
Besides hydroprocessing, fluid catalytic cracking (FCC) and reforming units may be another
source of solid spent catalysts on refinery site. The feeds for these processes must be subjected
to hydroprocessing to minimize catalyst poisoning by nitrogen bases and metals. Because of