Environmental Engineering Reference
In-Depth Information
Table 9.1: Properties of spent catalysts [From ref.
522
. Reprinted with permission].
Catalyst
Composition (wt.%)
Surface area
(m
2
/g)
Pore volume
(mL/g)
Mo
Ni
V
C
121212
A
6
.
3
.
2
.
4
.
4
.
4
.
4
.
1
90
0
.
15
B
5
.
6
.
0
.
9
.
9
.
9
.
4
.
2
73
0
.
16
C
4
.
5
.
3
.
0
.
7
.
7
.
4
.
3
18
0
.
10
1: determined by analysis; 2: assuming most of carbon was removed on decoking.
9.1.1 Reprocessing
Among several options, re-utilization of the metal-fouled non-regenerable catalysts in a
reprocessed form in hydroprocessing operations has been explored
[9,522-524]
. In this
case, spent catalysts, either de-oiled or decoked, are crushed to 20-90
m particle size.
According to the observation made by Santhyia and Ting
[525]
, such level of crushing favors
the liberation of metals from the support matrix. Then, the active metals such as Ni and Mo as
well as V became more freely accessible for the interaction with boehmite used as a
reprocessing agent. The reprocessed mixture is then formed into the size and shape of particles
approaching those of commercial catalysts. Promising results on hydrodemetallization (HDM)
and HDS of an atmospheric residue confirmed that reprocessing is a viable option for
re-utilization of spent hydroprocessing catalysts. Apparently, there have been attempt to
reprocess a smaller-size spent-regenerated catalysts into alternatives sizes and shapes
[525]
.
For example, hollow cylinder offers an optimal combination of void space and activity for
grading applications. Top bed grading materials for bed topping were introduced in four
diameters ranging from 10 to 25 mm.
9.1.1.1 Procedure and Analysis
In this procedure, spent hydroprocessing catalysts from the atmospheric residue
desulfurization (ARDS) process were used. This process comprises four fixed-bed reactors in
the series (
Fig. 3.13
). Two catalysts used for reprocessing included catalysts A and B from the
fourth and third reactor, respectively, whereas the most deactivated catalyst C was from the
H-Oil reactor. The properties of these spent catalysts are shown in
Table 9.1 [522]
. These
reactors have been part of the processes operated by the Kuwait National Petroleum Company
(KNPC). The pretreatment of spent catalysts included either successive extraction in the
Soxhlet apparatus using naphtha and toluene or decoking. Catalyst decoking was performed in
a horizontal rotary furnace. The temperature was increased in steps to 370, 450 and 500
◦
Cin
theflowof5%O
2
in N
2
. Subsequently, the diluted O
2
was replaced by air, while temperature
