Environmental Engineering Reference
In-Depth Information
Table 4.2: Properties of catalysts [From ref.
189
. Reprinted with permission].
Catalyst A
Catalyst D
Mo (wt.%)
8
.
1
8
.
0
Ni (wt.%)
2
.
3
2
.
0
Particle size (mm)
1
.
0
2
.
1
Surface area (m
2
/
g)
320
146
Average pore diameter (A)
126
233
Surface area (m
2
/g) in pore
size range (A)
0-0
32
4
60-00
80
9
100+
208
133
central axis of the two fixed-bed reactors, which were part of a commercial unit. In the first
reactor, baskets were placed at the top and middle of the bed, whereas in the second reactor in
the middle and bottom of the bed. The objective of the commercial run was to produce feed for
the subsequent fluid catalytic cracking (FCC)
[189,190]
. The system operated at the total
pressure of about 10MPa. To compensate for deactivation, the temperature between the
start-up and shutdown was increased from 603 to 628 K and from 646 to 658 K in the first and
second reactor, respectively. The evaluation of the catalyst was performed after 241 days on
stream. For catalyst A, the significant increase in the coke formation towards the end of the
second reactor should be noted compare with a little change for catalyst D. It is suggested that
in the former case, poisoning of the catalyst by N-bases was the main cause of the catalyst
deactivation. Catalyst A exhibited a greater metal storage capacity than catalyst D in spite of
the larger average pore diameter of the latter. Most likely, smaller particle size of catalyst A
than that of catalyst D ensured more efficient catalyst utilization. Moreover, the surface area
of the former catalyst, in the 60-100 A pore range, was nine times greater than that of the
catalyst D.
It is expected that the amount of coke deposited initially is governed by the content of
asphaltenes and resins in the feed. This is supported by the results in
Fig. 4.10 [191]
. In this
case, the feeds with different content of resins and asphaltenes were obtained by solvent
deasphalting of the two vacuum residues and one atmospheric residue derived from different
crudes each. A close examination of the scatter of data in
Fig. 4.10
indicates that the amount of
deposited coke was influenced by the origin of the asphaltenes and resins. To certain extent,
the observations made by Morales and Solari
[192]
complement the results in
Fig. 4.10
. These
authors used several heavy feeds and established the correlation between the content of
asphaltenes in the heavy feed and its HDS, HDM and Conradson carbon residue (CCR)
conversions. Thus, the conversions decreased with the increasing content of asphaltenes but
they leveled off when about 20 wt.% of asphaltenes in the feed was approached. However, it is
