Study on Pseudo-Equilibration of FCC Catalyst
Rei Hamada, Katsuhide Teshima
Catalysts Research Center, JGC Catalysts and Chemicals Ltd.
13-2 Kitaminato-machi, Wakamatsu-ku, Kitakyushu-shi, 808-0027 Japan
Abstract
When properties of FCC catalysts are evaluated in the laboratory, the aspect most focused on is
pseudo-equilibration of the catalyst. The objective of pseudo-equilibration is to obtain activity and
selectivity close to the equilibrium catalyst in an actual unit. Pseudo-equilibration can be classified
into the following main methods:
1. Mitchell method impregnating with metals (usually Ni and V) and high temperature steamtreating (simplified method).
2. CPS (Cyclic Propylene Steaming) method repeating oxidation and reduction of impregnated
metals.
3. CMD (Cyclic Metal Deposition) method depositing metals by repeating cracking reaction and
regeneration.
The Mitchell method is the simplest method for sample preparation however replication of equilibrium
catalyst is poor. It is thought that CMD is the method which most simulates the equilibrium situation
of an actual unit. However, the procedure is complicated and sample preparation requires a long time.
As speedy evaluation is necessary in catalyst research and development in addition to improved test
accuracy, in many cases, these pseudo-equilibration methods are chosen according to objectives.
This report describes several topics related to the pseudo-equilibration method, which is one of the
important points to check FCC catalyst performance and to investigate the metals effects of actual
equilibrium catalyst.
1. Introduction
The properties of equilibrium catalysts differ according to catalyst type, FCC process, feed oil and
operation conditions.
The main factors affecting FCC catalyst deactivation are as follows.
1) Regeneration conditions such as temperature and steam affected by zeolite collapse.
2) Deactivation due to poisonous metals deposition.
3) Deactivation due to carbon deposition from the residual carbon (CCR) in the feedstock or
carbon generated in the cracking reaction.
4) Deactivation due to basic nitrogen in the feedstock.
In general, the important factors for FCC catalyst's deactivation to make pseudo-equilibrated
catalysts in the laboratory are 1) and 2). As feedstock and operating conditions are different at each
refinery, the properties and activity characteristics vary according to the amount of metals on
catalyst, retention time in the system and regeneration conditions etc.
Accordingly, pseudo-equilibration of catalyst in the laboratory is very diverse depending on the
operation conditions and other factors for each refinery's FCCU.
In this report, we will introduce a more simplified method named "Effective Metal Control (EMC)"
method
as
an
additional
pseudo-equilibration
method
to
CPS
and
CMD
methods.
Pseudo-equilibrium catalyst obtained by the EMC method possesses more similar performance with
equilibrium catalyst than that of the Mitchell method.
2. Characteristics of Metals on Equilibrium Catalyst
2.1 Regenerator atmosphere and morphology of vanadium
As is well known, vanadium has a large effect on FCC catalyst activity. Vanadium reacts with
framework alumina of Y-type zeolite and ion-exchanged rare earth and collapses the zeolite
structure. The regenerator conditions in FCC unit are greatly related to the loss in catalyst activity.
The oxygen concentration within the flue gas differs according to the mode of operation but is
controlled to about 0~4%. In addition, the higher the oxygen concentration in the regenerator, the
more carbon is burned off. However, excess oxygen promotes the oxidation of vanadium on the
catalyst (V3+⇒V5+) and an increase in regenerator temperature. A low melting point vanadium
compound such as V2O5 accelerates the destruction of the zeolite crystal. A diagram of the
vanadium deposition mechanism is shown in Figure 1.
in Reactor
in Regenerator
O2
V in Oil
Catalyst
V3+, V4+
H2O
V4+, V5+
Mobilization of
V2O5 and H3VO4
Fig. 1 Schematic Illustration of Vanadium Deposition on Catalyst
Figure 2 shows the relationship between the amount of Carbon on Regenerated Catalyst (CRC)
obtained from one RFCC unit and MAT conversion. MAT conversion was measured after
calcination at 600oC, that is, carbon free condition of equilibrium catalysts. The higher the CRC, the
higher the MAT conversion that was obtained for carbon free catalysts. In this data, the metals level
(as V+Ni/4, ppm) of equilibrium catalyst does not change very much.
10000
75
8000
V+Ni/4
70
6000
65
4000
Conversion
60
55
0.00
0.10
0.20
V+Ni/4 (ppm)
MAT Conversion (%)
80
2000
0.30
0.40
0
0.50
CRC (%)
Fig. 2
Correlation between CRC and MAT Conversion
Treatment : 600oC-2hr Calcined
MAT Conditions : DSVGO, 482oC, 3.0C/O
Accordingly, the higher the CRC, the greater the lack of oxygen in the regenerator and the
oxidation reaction of the vanadium to V5+ decreases. It is presumed that catalyst activity loss
from vanadium is inhibited.
Equilibrium catalyst in an actual unit is a mixture of catalysts that have had differing retention
times in FCCU. The migration of vanadium is also relatively easy and it moves between the
particles. Figure 3 shows the distribution of the metals concentration of equilibrium catalyst
obtained from an actual unit and divided into four by magnetic separation. The y-axis in the
graph shows the fraction with the weakest magnetism (LL) through to the strongest (HH). Data
show the proportion of metals concentration for each with the metal concentration of the
weakest fraction (LL) being the standard. In this graph, the stronger the magnetism (HH), the
longer the catalyst has remained in FCCU. Difference in nickel concentration between LL and
HH is larger than that of vanadium because of the weak diffusivity of nickel.
2.5
2
V
Metal Ratio
Ni
1.5
1
0.5
0
LL
L
Low
Fig. 3
H
HH
Magnetism
High
Metal Distribution of Eq-Catalyst
2.2 Behaviour of Nickel in Equilibrium Catalysts
Nickel has a high ability for dehydrogenation and it brings about a drop in gasoline yield by
increasing H2 and coke. Nickel is different to vanadium in that in the equilibrium catalyst. As is
well known, nickel mainly deposits on the outer layer of the catalyst particles. This is due to the
weak diffusivity of nickel. A diagram of nickel deposition and agglomeration mechanism is
shown in Figure 4.
Ni Particle
Ni in Oil
Catalyst
in Reactor
Ni Deposition on
External Surface
in Regenerator
Ni Agglomeration
Ni Compound
Fig. 4 Schematic Illustration of Nickel Agglomeration
Agglomeration of nickel weakens the dehydrogenation activity and has less effect on gasoline
yield and coke formation than highly dispersed nickel. Figure 5 shows the change in H2
formation in MAT versus the amount of metal deposited on equilibrium catalyst (Ni+V/4). The
amount of metal on equilibrium catalyst (Ni+V/4) in an actual unit rose from 2,700ppm to
5,500ppm (equilibrium catalyst of Ni-increase) and then dropped to 3,000ppm (equilibrium
catalyst of Ni-decrease).
From this graph, we can see that when the amount of metal (Ni+V/4) built up on catalyst rose
from 2700~4500ppm, the nickel particles were highly dispersed and the H2 yield in MAT was
high compared with Ni-decrease case. In addition, once the amount of metal was in the vicinity
of 4,500ppm, the H2 formation rate drops. In this refinery, the amount of antimony injected as
nickel passivator was kept constant at Sb / Ni≒0.27. Furthermore, the change in vanadium
during this period was only 350 ppm (as V/4) and it is thought that it has a relatively small effect
on H2 formation.
During the period of Ni-decrease, it is thought that relatively low H2 yield originates from nickel
aggregation and/or the formation of nickel compounds such as NiAl2O4.
0.3
Hydrogen Make (%)
Ni increase
Ni decrease
0.25
Sb/Ni≒0.27 constant
0.2
0.15
0.1
0.05
2000
3000
4000
5000
6000
Ni + V/4 on Catalyst (ppm)
Fig. 5 Deposited Metal Impact on Eq-Cat for Hydrogen Make,
by MAT Reaction
Treatment : 600℃-2hr Calcined
MAT Conditions : DSVGO, Rx. Temp=482℃, 3.0C/O
3. Inter-particle Metal Migration
As described previously, vanadium on equilibrium catalyst diffuses and migrates between catalyst
particles depending on conditions such as temperature, steam and oxygen in the regenerator. Tests
were conducted such as those in Figure 6 to verify this migration between catalyst particles.
Eq-Cat or V & Ni
Impregnated-Cat
+75μm
+75μm
Steaming
or CPS
Treatment
Mixture
Fresh-Cat
Separation
of Particle
-45μm
-45μm
Fig. 6 Test Scheme of Vanadium and Nickel
Migration
Catalyst samples were divided into two parts, one was over 75 micron particles and another was
minus 45 micron particles by sieving. Then, metal impregnated catalyst or equilibrium catalyst
(+75μm) was mixed with fresh catalyst (-45μm) and steam or CPS treatment was performed. In
order to check the effect of catalyst particle size, we also investigated the case where equilibrium
catalyst was minus 45 microns and fresh catalyst was over 75 microns.
Table 1
Test
Donor
Migration rate of Vanadium and Nickel
Acceptor
Donor
Particle Size(μ) Particle Size(μ)
Treatment
V/Ni(ppm)
V Migration Ni Migration
Rate (%)
Rate (%)
1
+75μm E-1
-45μm F-1
7820/2790
100% Steaming
30
5
2
-45μm E-2
+75μm F-2
8990/5720
100% Steaming
29
4
3
-45μm E-2
+75μm F-2
8990/5720
CPS O2 = 1%
20
11
4
+75μm I-1
-45μm F-1
5020/4960
CPS O2 =21%
33
4
5
+75μm I-1
-45μm F-1
5020/4960
CPS O2 = 7%
31
8
6
+75μm I-1
-45μm F-1
5020/4960
CPS O2 = 1%
29
11
7
+75μm I-2
-45μm F-1
Ni=4980
CPS O2 =21%
―
5
8
+75μm I-2
-45μm F-1
Ni=4980
CPS O2= 1%
―
11
9
+75μm I-1
-45μm F-1
5020/4960
4
3
E-1, -2 : Eq-Cat.
I-1, -2 : Impregnation Cat.
Steaming : 790℃-13hr 100%Steam
*CPS
O2= 7%
F-1, -2 : Fresh Cat.
CPS : 790℃-30cycle (20hr) 67%Steam　* : no Steaming
The catalyst was sieved again after treatment and the concentration of each metal was analyzed.
Migration rate between catalyst particles was calculated from metal concentrations of fresh catalyst.
The effect of oxygen concentration in CPS treatment was also investigated. Results are shown in
Table 1. In the Table, "Donor" refers to an initially metal deposited catalyst and " Acceptor" refers to
fresh catalyst which is metal free.
1) When steam treatment (790oC) was performed on equilibrium catalysts, approximately
30% of vanadium migrated to the fresh catalyst independent of catalyst particle size
（+75μm⇒-45μm &
-45μm⇒+75μm）.
2) In the case of metal impregnated catalyst I-1, we changed the oxygen concentration in
regeneration. Test results show that the migration rate depends on oxygen concentration.
When the oxygen concentration decreased, the vanadium migration rate dropped
however, the nickel migration rate increased as shown in Figure 7.
It is thought that the
change of vanadium migration rate comes from V5+ concentration change. The reason for
change in nickel migration rate is not clear.
40
Migration rate (%)
35
30
25
Vanadium
20
Nickel
15
10
5
0
0
5
10
15
20
25
% Oxygen at CPS Treatment
Fig. 7 Oxygen Inpact for V/Ni Migration between
Catalyst Particle
3) In order to eliminate the effect of co-existing vanadium on nickel migration, only nickel
was impregnated in Test 7 and Test 8. The result was that the nickel migration rate was
almost the same as that of the case of vanadium co-existing. Although the migration rate
of nickel is low compared with vanadium, inter-particle migration of nickel is promoted
under the low oxygen atmosphere.
4) In addition, in order to check the effect of steam on metals migration, we tested heat
treatment under the same conditions as CPS except with steam injection. In Test 9, steam
injection was stopped. The result was that both nickel and vanadium had a metal
migration rate of approximately 3%. This shows that the effect of steam on inter-particle
migration of metals is quite large.
4. Investigation into Pseudo-Equilibration of FCC Catalyst
4.1 Mitchell method and Effective Metal Control (EMC) method
Figure 8 shows the change of MAT H2 formation as metals (Ni+1/4V) function for 2 cases, one is
the lab. metal impregnated catalyst by Mitchell method and another is equilibrium catalyst obtained
from actual unit. In both cases, increase of H2 becomes slow in the high metal region.
MAT H2 Make
Mitchell Method
Metals
High
Fig. 8 Metals vs. MAT H2 Make
It is well known that Mitchell method produces more hydrogen than equilibrium catalyst. In our
newly proposed EMC method, metal free and metal impregnated sample are steam- deactivated and
then mixed with each other and metals level is adjusted to those of equilibrium catalyst. Details are
as follows. Vanadium and Nickel were impregnated according to the Mitchell method and several
types of impregnated catalyst were prepared and subjected to steam treatment as shown in Table 2.
These steam-deactivated samples were then mixed with each other and the metals level was adjusted
to that of equilibrium catalyst, that is Ni/V=2,010ppm/3,960ppm. Mitchell-1 is the
pseudo-equilibrium catalyst prepared by the Mitchell method. EMC-1 is the pseudo-equilibrium
catalyst prepared by mixing five types of catalyst sample with differing metal amounts. EMC-2~4
are the pseudo-equilibrium catalysts prepared by mixing two types of steam deactivated catalyst
sample with differing metal amounts.
In addition, pseudo-equilibrium catalyst named Mitchell-2 was prepared by steam treating after
mixing 50% of metal free catalyst and 50% of metal impregnated catalyst.
Table 2 Test Scheme of Mitchell and EMC Method
Mitchell-1
EMC-1
EMC-2
EMC-3
EMC-4
Mitchell-2
V (ppm)
Ni (ppm)
Blend Ratio (%)
0
0
0
20
33
50
67
50
2000
1000
0
20
0
0
0
0
4000
2000
100
20
0
0
0
0
6000
3000
0
20
67
0
0
0
8000
4000
0
20
0
50
0
50
12000
6000
0
0
0
0
33
0
Table 3 shows the test results of activity, surface area and the amount of nickel and vanadium on
catalyst samples.
Table 3
Evalution Results of Mitchell and EMC Method
ACE-R+ Conditions : 50%DSAR+50%DSVGO, Rx.Temp=520℃, 5.0C/O
Eq-Cat.
Mitchell-1
EMC-1
EMC-2
EMC-3
EMC-4
Mitchell-2
V (ppm)
3960
3990
3910
3960
3880
3890
3880
Ni (ppm)
2010
1900
1870
1900
1890
1890
1890
SA(m2/g)
156
127
126
120
125
141
117
Conv.(%)
78.4
72.6
74.7
74.5
76.9
78.2
72.5
H2 (%)
0.40
0.63
0.50
0.46
0.37
0.25
0.62
Coke (%)
6.5
7.0
6.4
6.3
6.1
5.5
7.3
(1)
Mitchell-1 has a lower activity (Conv.) and lower surface area than equilibrium catalyst, but
the H2, coke yield is high. In the Mitchell method, hydrogen and coke selectivity becomes
high because of the homogeneous distribution of metals.
(2)
In the case of the newly proposed EMC method, EMC-3 shows the most similar hydrogen
and coke formation to those of equilibrium catalyst, that is, a blend of 50% of metal
impregnated catalyst and 50% of metal free catalyst.
(3)
Both Mitchell and EMC methods show lower surface area than equilibrium catalyst.
(4)
In Mitchell-2 where two catalysts of metal impregnated with different metals level were
pre-mixed and steamed. H2 and coke selectivity, surface area and activity of Mitchell-2 did
not simulate those of equilibrium catalyst. We could see that metal dispersion shows strongly
in the case of the Mitchell method.
4.2 Cyclic Propylene Steaming (CPS) Method
CPS-1 is a method where metals are impregnated by the Mitchell method and the actual unit’s
reaction/regeneration is imitated by repeating reduction and oxidation. In this procedure,
reduction used 5% propylene, oxidation used air and the reduction/oxidation was performed for
30 cycles (780degC for 20 hours). Catalysts in CPS-2 were steamed at 780degC in advance and
then impregnated with metals.
In Table 4, activity test results for CPS-treated samples were compared with equilibrium
catalyst.
(1) Surface area of CPS-treated sample was relatively close to that of equilibrium catalyst.
(2) H2 and coke yield of CPS-treated sample were lower than that of equilibrium catalyst
and it is thought that the metal activity is suppressed by the reduction treatment.
(3) In addition, the steam pretreatment of CPS-2 accelerates the drop in activity and coke.
(4) It is necessary to control the number of cycles and reduce the CPS treatment temperature
in order to approximate further the activity etc of equilibrium catalyst using CPS
treatment.
Table 4 Evalution Results of CPS Method
ACE-R+ Conditions : 50%DSAR+50%DSVGO, Rx.Temp=520℃,
5.0C/O
Eq-Cat.
CPS-1
CPS-2
Pretreatment
―
None
780℃-13hr Steam
V (ppm)
3960
3950
3950
Ni (ppm)
2010
1890
1920
SA(m2/g)
156
165
160
Conv.(%)
78.4
77.4
75.0
H2 (%)
0.40
0.30
0.27
Coke (%)
6.5
5.4
4.5
4.3 Cyclic Metal Deposition (CMD) Method
The CMD method simulates actual unit conditions more than all pseudo-equilibrations reported
in this paper. In the experiment on CMD, fresh catalyst was steam deactivated at 790degC for
13hrs. In CMD treatment, we tested the effect of oxygen concentration of regenerated gas to
control the metal activity. In addition we added a CMD-3 where pseudo-equilibrated catalyst
was replaced to fresh catalyst two (2) times in the cycle process (20% of total amount). This
addition of fresh catalyst was conducted at 15 and 45 cycles during total 46 cycles.
Table 5 shows the results of the CMD method compared with equilibrium catalyst.
Table 5 Evalution Results of CMD Method
ACE-R+ Conditions : 50%DSAR+50%DSVGO, Rx.Temp=520℃, 5.0C/O
Eq-Cat.
CMD-1
CMD-2
CMD-3
Fresh Cat. Addition
Yes
No
No
Yes
O2 Conc. (%) *
―
21
7
7
V (ppm)
3960
3980
3970
3940
Ni (ppm)
2010
2020
1840
1880
SA(m2/g)
156
160
171
170
Conv.(%)
78.4
75.2
78.8
78.4
H2 (%)
0.40
0.55
0.33
0.29
Coke (%)
6.5
6.4
6.0
5.5
* : Oxygen for Regeneration
(1)
Compared with equilibrium catalyst, CMD-1 shows a slightly low conversion but a slightly
high H2 yield.
(2)
CMD-2 shows high activity and low H2 and coke yields compared with CMD-1. Carbon
level of spent catalyst and regenerated catalyst in CMD-2 was approximately 1.2% and
0.6%, respectively. Oxygen within the flue gas was approximately 0.3%. Accordingly, it is
thought that CMD-1 had a higher proportion of V2O5 due to the excess oxygen and activity
becoming lower and H2 yield was higher due to vanadium being diffused. This result backs
up the CRC effect mentioned in Figure 2.
(3)
CMD-3 has even lower H2, coke yield than CMD-2. Regarding H2 and coke, CMD-3 does
not resemble the equilibrium catalyst but we think this is one way to make
pseudo-equilibrium catalyst.
4.4 Comparison of activity and yields of pseudo-equilibrated catalyst
In the equilibration methods tested in this experiment, we compared the performance of
pseudo-equilibrium catalyst with properties relatively close to those of equilibrium catalyst in
Table 6. In addition, Table 7 shows the comparison between the EMC method and an
equilibrium catalyst with a different metals level.
Table 6 Comparison of Pseudo-Equilibrated Catalyst
ACE-R+ Conditions : 50%DSAR+50%DSVGO, Rx.Temp=520℃, 3.75～6.0C/O
(same
conversion at 75%)
Eq-Cat
Mitchell-1
EMC-3
CPS-1
CMD-2
V (ppm)
3960
3990
3880
3990
3970
Ni (ppm)
2010
1900
1890
1900
1840
Cat/Oil
Base
2.8
0.7
0.2
-0.3
H2
Base
0.23
-0.03
-0.10
-0.07
C1+C2
Base
0.4
-0.1
-0.1
-0.2
LPG
Base
-0.9
-0.4
-0.1
0.1
Gasoline
Base
-2.3
0.5
1.0
0.9
LCO
Base
-1.3
-0.2
0.1
-0.2
HCO
Base
1.3
0.2
-0.1
0.2
Coke
Base
2.6
0.0
-0.7
-0.7
Table 7 Comparison of Eq-Cat and EMC Method
ACE-R+ Conditions : 50%DSAR+50%DSVGO, Rx.Temp=520℃, 3.75～6.0C/O
(same
conversion at 74%)
(same conversion at 73%)
Eq-Cat
EMC
Eq-Cat
EMC
V (ppm)
5210
5200
6920
7000
Ni (ppm)
2590
2600
4340
4300
Cat/Oil
Base
0.4
Base
-0.4
H2
Base
-0.02
Base
-0.02
C1+C2
Base
-0.2
Base
-0.1
LPG
Base
-0.3
Base
0.5
Gasoline
Base
0.3
Base
-0.8
LCO
Base
0.2
Base
0.1
HCO
Base
-0.2
Base
-0.1
Coke
Base
0.2
Base
0.4
(1)
In the preparation of a pseudo-equilibrium catalyst sample, the EMC method is as simple
as the Mitchell method compared with CPS and CMD and the performance of EMC
sample is close to that of equilibrium catalyst.
(2)
Catalyst samples prepared by CPS and CMD methods also show similar performance to
an actual unit’s equilibrium catalyst. However it is necessary to study the conditions
further in order to come close to equilibrium catalyst for each FCC unit.
5. Conclusion
(1) Steam largely accelerates the inter-particle migration of vanadium. The nickel migration
ability is small but the effect of steam is still the same for nickel.
(2) With pseudo-equilibration of catalyst, the oxygen concentration of steam atmosphere has
an effect on the diffusivity of metal. In particular, inter-particle migration of nickel is
promoted in a low oxygen atmosphere.
(3) The proposed EMC method is one of the simplest methods for preparing
pseudo-equilibrium catalyst in laboratory.
(4) In this report, we described the effect of several factors on metals deactivation for
pseudo-equilibrium catalyst preparation. As the one of the simplest methods, the EMC
method simulates the performance of equilibrium catalyst. Hereafter, we will examine the
correlation of laboratory screening tests using the EMC method and actual unit’s
performance in case of FCC fresh catalyst change.