Environmental Engineering Reference
In-Depth Information
Table 7.9: Mass balance for rejuvenated spent catalyst process (6000 tons/year) [From ref.
462
.
Reprinted with permission].
Option
Products
By-products
Fines
De-oiled
catalyst
Rejuvenated
catalyst
Residual
oil
Leached
metals
Combustibles
I
519
0
3264
810
318
1089
II
519
2184
1820
810
60
607
III
519
3171
1125
810
0
375
The estimated economic indicators for all three options revealed that it is much more attractive
to construct rejuvenation plant on and/or near refinery site than a stand-alone independent
plant. The integration of rejuvenation process with petroleum refinery ensures that the latter
needs not to pay third party to dispose of spent catalyst and to risk potential future liabilities.
Among three options considered, the Option II was the most profitable.
7.2 Inorganic Agents
The solutions of strong acids (e.g., HCl and H
2
SO
4
) alone and/or their mixtures with metal
ions (e.g., HCl
FeCl
3
) as well as and bases (NaOH, ammonia, etc.) have been used for
rejuvenation of the spent catalysts as well. Corrosive nature of these solutions suggests that
special precautions have to be taken to ensure safety of the operation and environment,
although many years experience with similar methods gained in hydrometallurgy can be
applied during rejuvenation as well.
+
In a summary of general observations one may say that during the rejuvenation of spent
catalysts using inorganic agents, a high selectivity for contaminant metals (V, Ni, and Fe) may
require a delicate control of pH
[493]
. At high pH of basic solutions an unwanted removal of
Mo/W simultaneously with V may occur. In acidic solution, Ni is removed preferentially, but
removal of Mo/W cannot be avoided unless the pH is carefully controlled. It is also anticipated
that the adverse effects of inorganic solutions on mechanical properties of catalyst particles
after rejuvenation may be more evident that those during rejuvenation using organic acids
solutions. It is therefore believed that rejuvenation using inorganic agents has some limitations
caused by complexity of leaching conditions. Nevertheless, some studies in literature indicate
interests in this route of catalyst reactivation.
7.2.1 Acidic Agents
The removal of metals in both oxidic and sulfided form from spent catalysts
using inorganic acids involves the dissolution based on the general
