Spent Catalysts from Dewaxing Operations - Spent Hydroprocessing Catalysts - page 262

increase in H 2 pressure and temperature. Because of its potential benefit to operation, this
should be the focus of additional investigations.

10.2.3 Environment and Safety

The environmental and safety aspects of spent hydroprocessing catalysts used in the upstream
and downstream units of dewaxing units were discussed in details in Chapter 5 . After being
unloaded from reactor, spent dewaxing catalysts have to be handled according to the
procedures prescribed by environmental and health authorities, similarly as spent
hydroprocessing catalysts. The properties of spent catalysts from dewaxing may differ from
those of typical hydroprocessing catalysts. First of all, milder operating conditions and only
trace quantities of contaminants (sulfur, nitrogen, asphaltenes, and metals) in the feeds,
combined with a high HYD activity of dewaxing catalysts, ensure a low aromaticity of coke on
catalyst surface [587] . Most likely, such coke possesses a high concentration of sites, which
are very active for oxygen adsorption. Consequently, a pyrophoric nature of coke is much
greater that that of coke on spent conventional hydroprocessing catalysts. In addition, if
present, noble metals are generally in a reduced form and, as such, are active sites for oxygen
chemisorption as well. Some noble metals compounds form complexes with hydrogen [55] .
Such complexes may be present in the coke, unless the spent catalyst was subjected to a
special pretreatment. Then, if present, these complexes would react rapidly on the exposure to
air. Therefore, much more precautions have to be taken during handling, storage,
transportation, and disposal, particularly during the unloading of such catalysts from reactor,
compared with spent hydroprocessing catalysts. A total lack of information on the pyrophoric
nature of spent catalysts from dewaxing operations should be noted. In this regard, a database
of properties of spent dewaxing catalysts is desirable.

Similarly as for pyrophoric properties, there is little information on the behavior of spent
dewaxing catalysts during the contact with water alone and/or in combination with air and
water. The leachability of spent noble metals containing catalysts and their toxicity levels
while in a solution have not yet been determined. This may be attributed to a high value of
noble metals. Thus, rather than to dispose of, such spent catalysts are of a much greater
interest to both refining companies and metal reclaiming companies compared with spent
hydroprocessing catalysts.

10.2.4 Regeneration

First of all, the amount of coke on spent dewaxing catalysts may approach 5 wt.%, whereas

for some spent hydroprocessing catalysts, this amount may exceed 20 wt.%. As it was already
indicated, the coke on spent dewaxing catalysts is much more reactive (less refractory) than
that on the latter catalysts. These differences suggest that a desirable level of catalyst activity

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