Introduction - Spent Hydroprocessing Catalysts - page 3

the hazardous nature, the procedures applied for handling of spent hydroprocessing catalysts
may differ from those used for the other types of catalysts. For example, particle size of spent
FCC catalysts is much smaller than that of spent hydroprocessing catalysts. Therefore, all
precautions have to be taken during the handling of the former catalysts.
The reasons for significant increase in the production of spent hydroprocessing catalysts in
recent years may be summarized as follows:
(1) A rapid growth in the distillates hydrotreating capacity to meet the increasing demand for
ultra-low sulfur transportation fuels.
(2) Reduced cycle times due to higher severity operations in diesel hydrotreating units to meet
stringent fuels specifications.
(3) A steady increase in the processing of heavier feedstocks having high sulfur, resins,
asphaltenes, and metal contents to distillate by hydrogen addition technology.
(4) Rapid deactivation and unavailability of reactivation process for residue hydroprocessing
catalysts.
Disposal of spent catalysts requires compliance with stringent environmental regulations.
Spent hydroprocessing catalysts have been classified as hazardous wastes by the
environmental protection agency (EPA) in the USA. The EPA added spent hydrotreating
catalyst (K171) and spent hydrorefining catalyst (K172) to its hazardous waste list in August
1998 [16] because of their self-heating behavior and toxic chemicals content. In regulatory
documents, these spent catalysts are referred to as K171 and K172 spent catalysts,
respectively. Spent hydrocracking catalyst was added to the list in 1999 [17,18] . Metals, such
as Co, Ni, and V, that are present in spent hydroprocessing catalysts from dual operations (e.g.,
simultaneous hydrotreating and hydrocracking) are included in the list of potentially
hazardous wastes published by the Environment Canada. These metals can be leached by
water after disposal and, as such, pollute the environment. Trace metals, such as As, Cr, Cd,
Hg, Se, and Pb, may also be present. Besides the formation of leachates, the spent
hydroprocessing catalysts, when in contact with water, can liberate toxic gases. The formation
of the highly toxic HCN gas from the coke deposited on hydroprocessing catalysts that
contains a substantial amount of nitrogen has been reported [19,20] . Spent catalysts also fall
under the controlling terms of the Basel Convention and Organization for Economic
Cooperation and Development (OECD) rules. According to these rules, spent catalysts cannot
be exported to third world countries. Furthermore, the producing works and/or generators have
a legal obligation to ensure that their spent catalysts are properly disposed of or safely
recycled. The USA pioneered the principle that waste remains forever the generator's
responsibility and this is being adopted throughout the rest of the developed world. It should
be noted that the 20 years liability in effect before has been replaced by unlimited liability.