Environmental Engineering Reference
In-Depth Information
Figure 7.19: Electron microprobe analysis (
: spent catalyst;
: treated catalyst). A. Vanadium.
B. Nickel [From ref.
500
. Reprinted with permission].
removal of V and Ni was significantly greater than that of Mo and Al. Prior to leaching,
catalysts were de-oiled but not decoked. After removing contaminant metals, catalysts were
decoked by oxidative burn-off. A good selectivity for the removal contaminant metals could
not be achieved for decoked catalysts because decoking increased the removal of Mo relative
to that of V and Ni.
7.2.2 Basic Solutions
The decoking spent catalyst prior to leaching using basic solutions appears to be a
requirement. Tentative reactions occurring during leaching in basic solution are:
2NaOH
+
MoO
3
=
Na
2
MoO
4
+
H
2
O
2NaOH
+
V
2
O
3
=
2NaVO
2
+
H
2
O
2NaOH
+
Al
2
O
3
=
2NaAlO
2
+
H
2
O
With respect to catalyst rejuvenation, the reaction of NaOH with V
2
O
3
is of primary
importance. The rate of this reaction relative to the reactions involving MoO
3
and Al
2
O
3
can
Table 7.10: Physical properties of trilobe catalysts [From ref.
500
. Reprinted with permission].
Catalyst
Density (kg/L)
Pore volume
(mL/g)
Mean pore
diameter
(MPD) (A)
Surface area,
(m
2
/g)
Fresh
1
.
26
0
.
50
70
243
Spent
1
.
67
0
.
12
60
85
Rejuvenated
1
.
46
0
.
40
110
178
