Environmental Engineering Reference
In-Depth Information
phthalic, malonic, succinic, and salicylic as well as acetylacetone, ethylenediamine,
o
-aminophenol, and slicylaldehyde. Among these agents, acids were much more efficient
leaching agents than non-acid compounds.
The leaching with organic agents has been significantly advanced by the researchers at KISR,
who established the following order of the leaching efficiency of the most efficient agents:
oxalic
>
malonic
>
acetic acid. In addition, combination of these acids with various oxidizing
agents such as H
2
O
2
, HNO
3
, Al(NO
3
)
3
, Fe(NO
3
)
3
, etc. were evaluated as well
[475,480-482]
.
The effect of oxidizing agent differed from acid to acid. For example, when added to oxalic
acid (0.66M), Al(NO
3
)
3
(1M) had a dramatic effect on leachability of V and Ni, whereas for
malonic and acetic acids the effect was much less pronounced
[483]
.
As the most efficient agent, the oxalic acid (0.66M) in the mixture with H
2
O
2
(0.66M) was
used for rejuvenation of the spent catalyst obtained from the first stage of the atmospheric
residue desulfurization (ARDS) process used for hydroprocessing of the Kuwait atmospheric
residue
[476,483]
. The composition and surface properties of the fresh and corresponding
spent catalysts are shown in
Table 7.1 [483]
. Leaching experiments were performed in the
continuous upflow reactor at 298 K using both decoked and the spent as received catalysts. The
results of the experiments are shown in
Table 7.2 [475]
. The selectivity for the V removal was
much higher for non-decoked catalyst. The trends in the recovery of surface area and pore
volume with the amount of V leached out are shown in
Fig. 7.2 [484]
. They indicate that these
parameters, surface area in particular, improve significantly before about 35% of V was
removed. As it is shown in
Fig. 7.3 [476]
, the HDS activity recovery followed the same trends
as that of the surface area. The HDS activity data of the rejuvenated catalysts were obtained in
the continuous fixed bed reactor system at 623 K and 4.0MPa. For the activity estimate, the
AGO containing about 2 wt.% of sulfur was used as the feed. After removing
∼
30 wt.% of V,
Table 7.1: Chemical composition and physical properties of the fresh and spent catalysts [From
ref.
483
. Reprinted with permission].
Property
Fresh catalyst
Spent catalyst
Surface area (m
2
/g)
240
52
Pore volume (mL/g)
0
.
48
0
.
12
Bulk density (kg/L)
0
.
73
1
.
18
Mo (wt.%)
8
.
80
5
.
40
Co (wt.%)
3
.
20
1
.
90
Ni (wt.%)
0
3
.
07
V (wt.%)
0
14
.
90
Fe (wt.%)
0
8
.
00
Carbon (wt.%)
0
15
.
60
Sulfur (wt.%)
0
5
.
30
