Environmental Engineering Reference
In-Depth Information
It has been observed that the efficiency of petroleum refining improves with the increasing size
of refinery. These trends are favorable for an efficient utilization of by-products, such as
refinery gases and residues. Moreover, large quantities of spent catalysts, which may be
generated in a large size refinery, could make the integration of spent catalyst recycling (e.g.,
regeneration, rejuvenation, and reprocessing) with refining operation economically attractive.
Thus, rather than to deal with complex regulatory issues concerning packaging, transportation,
disposal, etc. spent catalysts handling will be limited to refinery site. At present time, there is
no information suggesting an interest in such a venue, although very close cooperation
between some refineries and certified companies has been noted. However, a potential
integration of catalyst recycling with petroleum refineries in the future cannot be ruled out.
Until now, recycling of spent hydroprocessing catalysts has been dominated by oxidative
regeneration. At the same time, rejuvenation has been making little contribution in spite of
significant advances in developing a commercial process have been made. Thus, the database
required for the design and construction of a commercial rejuvenation plant has been
established. It is believed that time for introducing the first commercial rejuvenation plant is
approaching. In this regard, organic acids alone or in the mixture with various oxidation agents
appear to be the best alternative. Apparently, the potential of reprocessing spent catalysts has
not yet been fully realized, although very encouraging results have been obtained. It is
anticipated that both rejuvenation and reprocessing will be contributing to the overall recycling
of spent hydroprocessing catalysts.
It has been indicated that for extra heavy feeds (200-300 ppm of V+Ni) and particularly ultra
heavy feeds ( > 300 ppm of V+Ni), carbon rejection route (e.g., coking) may be the best option
for primary upgrading. In this case, the composition of primary liquids may differ from that of
the liquids derived either from conventional crudes or produced during catalytic upgrading,
such as hydroprocessing. Because of more severe conditions employed, aromatic and
heteroaromatic compounds in coking liquids are more refractory, requiring more catalyst and
hydrogen, compared with a similar boiling point liquids obtained under less severe conditions.
Numerous attempts have been made to find new outlets for spent catalysts with the aim to
avoid disposal in landfills as the least attractive option. Various degrees of success have been
indicated in the studies on incorporation of spent catalysts in a wide range of materials.
Growing concerns about the fate of spent hydroprocessing catalysts prompted research
activities in metal reclamation. The published results show that the efficiency of metal
recovery using different methods is similar. In this regard, it is not easy to identify a method of
choice. However, it is essential that other relevant factors are also taken into consideration. For
example, it is necessary that all waste by-products of metal reclamation, i.e., liquid streams
containing strong acids and bases, toxic gases, etc. are neutralized before their disposal. In a
wide range of organic and inorganic agents, water-soluble organic agents offer the efficiency
of metal recovery, which is comparable or better than that using other methods. At the same
 
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