Environmental Engineering Reference
In-Depth Information
Table 4.3: Properties of spent catalyst particles from ebullated-bed reactor [From ref.
12
.
Reprinted with permission].
Property fouled
Spent mix
Lightly fouled
Heavily
Vanadium (wt.%)
10
.
6
4
.
4
13
.
8
Nickel (wt.%)
4
.
0
3
.
5
5
.
2
Carbon (wt.%)
16
.
2
15
.
8
16
.
3
Surface area (m
2
/g)
68
122
55
Bulk density (kg/L)
1
.
09
0
.
97
1
.
21
Side crushing strength (lb/mm)
1
.
8
2
.
1
1
.
2
Pore volume (mL/g)
0
.
17
0
.
21
0
.
11
Particle length distribution (wt.%)
<
1.5 mm
25
.
2
14
.
4
40
.
0
1.5-0.0
42
.
3
23
.
5
37
.
0
3.0-0.0
32
.
5
61
.
3
23
.
0
>
6.0
0
0
.
8
0
Because of the continuous motion of particles in ebullated-bed reactors, the depletion of
catalyst material due to the particles attrition and/or disintegration is much more evident than
in the fixed-bed reactors. Moreover, with the aim to enhance the active phase utilization, the
typical diameter of the catalyst particles is 1mm inside diameter (ID) or less. Without
adequate mechanical strength, breaking of such particles could not be avoided. A vigorous
mixing in ebullated-bed suggests that the fresh particles added periodically may be well mixed
with the spent catalyst particles, which may need to be withdrawn. Then, a part of the particles
are withdrawn with the spent catalyst without being completely utilized. Little information on
these phenomena has been available until the work of Al-Dalama and Stanislaus
[12]
appeared
in the scientific literature. The results from this study are shown in
Table 4.3
. On the basis of
these results, it was estimated that the lightly fouled catalyst accounted for about 30 wt.% of
the mixture. The catalysts were separated from the mixture by jigging technique using a
mineral jig. Of particular importance is the length distribution of particles, which for fresh
catalyst, was dominated by 3.0-6.0mm particles. For the heavily fouled catalyst, more than
70% of these particles were broken to less than 3.0mm length. There was a significant
difference in surface area, pore volume and side crushing strength between the lightly and
heavily fouled catalysts as well. It was established that fine particles could be carried out from
the reactor together with the liquid streams. This represents a loss of activity per unit of the
catalyst loaded. The lightly fouled particles withdrawn prematurely represent another source
of the activity loss because of their incomplete utilization. These phenomena are physical
and/or mechanical and in their nature differ from those occurring during catalyst deactivation.
However, because the ultimate results are the loss of catalyst activity, they deserve attention
during the catalyst design as well as during the operation.
