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Hydrodemetallization in Resid Hydroprocessing
C.H. Bartholomew and J.B. Butt (Editors), Catalyst Deactiuation 1991 1991Elsevier Science Publishers B.V., Amsterdam
273
HYDRODEMETALLIZATIONIN RESlD HYDROPROCESSING Jesper Bartholdy and Peter N. Hannerup, Haldor T o p s ~ eA/S, Nym~lkevej55, DK-2800 Denmark SUMMARY The study of the Vanadium deposition profiles in spent catalyst particles from resid hydrcv processing confirms that HDM is a sequential reaction. Furthermore, it is shown that the distribution parameter for the deposited Vanadium Qv is constant through the reactor for each catalyst type and that Qv is proportional to the efficiency of the Vanadium removal reaction.
INTRODUCTION In many studies it has been shown that V and Ni deactivate resid hydroprocessing catalysts [7, 9, 11, 131. The deactivation is caused by poisoning/fouling of the active sites and by restriction of the access of reacting species to the catalyst pore system. Removal of Ni and V from residual oils is diffusionally limited [8], and therefore Ni and V are deposited in the catalyst pores in a characteristic deposition profile [7, 11, 131 which is either U- or M-shaped, i.e. the maximum metal deposition is either located at the catalyst pellet surface or inside the pellet. These phenomena have been investigated for both V and Ni using various V/Ni porphyrins as model compounds [l, 2, 3, 4, 51. It has been concluded that the removal of V and Ni porphyrins proceeds via a sequential reaction network, where the porphyrins are hydrogenated in the first step and deposited in a subsequent one. These studies have also indicated that the degree of complexity of reaction pattern depends on the types of porphyrins used. In these studies, no H2S was present. In a recent study [6] of demetallization of Ni and V porphyrins, the reaction path of HDV and HDNi reactions has been investigated in the presence of HzS. The aim of the present study is to test the applicability of these conclusions on HDM data obtained on real feedstocks at industrially relevant conditions. EXPERIMENTAL The experimental set-ups for conducting resid hydroprocessing experiments, product analyses and metal profile measurements on the spent catalysts have been described elsewhere 1111. The experiments were performed on 1 / 3 2 cylindrical catalyst particles with a catalyst bed diluted with 0.2-0.3 mm glass beads. In each experiment, more than one type of catalyst was used (HDM, HDM/HDS, HDS), forming a composite catalyst filling [12]. All experiments were performed on a Kuwait AR using similar process conditions. The properties of the feed and the process conditions are listed in Tables 1 and 2, respectively.
274
Table 1: Feed stock specifications. SG,
(60/60F)
Sulfur, w t %
0.9742
CCR, wt%
4.3 2465 10.4
Visc @122F, cSt
920
Nitrogen, p p m Pent. Ins , w t % Ni, p p m
Vr
PPm
Table 2: Process conditions.
3.4
H,/Oil,
N1/1
P r o d u c t Sulfur, wt%
0.45
20 63
After termination of the experiments, the catalysts were withdrawn from the reactor. Catalyst samples were obtained from various positions in the reactor. For each catalyst sample, the chemical composition and the distribution of metals inside the catalyst particle were determined.
THEORY
The assumption is a sequential 1st order reaction network for HDM:
The significance of the individual steps has been investigated in model compound studies [2, 4, 61. The first step A - B consists of hydrogenation of the metal-bearing porphyrins forming mobile, hydrogenated metal porphyrins. The second step is a reaction between the hydrogenated porphyrim and HzS, forming deposits of metal sulfide on the catalyst surface. The rate constant of the two reactions, kl and k:! is assumed to be proportional to P H and ~ ptm, respectively. = 0 and that the It is further assumed that B is not present in the feed oil, i.e. C I ~ O reactions are taking place in spherical particles of porous material and are controlled by effective diffusion coefficients DA = DB = D. (The actual catalyst particles used in the experiments were short cylinders). By conventional techniques, the concentration gradients inside the particle can be found. The concentrations through the reactor then become (for explanation of symbols, see Symbol List):
275
where
It can be seen that the ratio CB/CAwill approach an equilibrium value CB/CA= p, when (kae - kl,) x V/F x y is large. This situation arrises when k2 >’ kl and the conversion is high. The overall reactor efficiency can be found by comparing diffusionally limited operation with diffusion Gee operation. Assuming that the above equilibrium ratio has been reached in both cases we find:
which for low F/V and small p will approach the limit:
In realistic situations the maximum metals concentration in the particles will be displaced from the particle surface in the top of the reactor (M-profile), but for
the maximum metals concentration will be found at the particle surface (U-profile). In this case we find for the distribution parameter:
When the equilibrium value
A
=
p has been reached:
RESULTS AND DISCUSSION In the previous section, we have developed a mathematical description of a two-step diffusionally limited reaction sequence. In the following we will discuss whether the p h e n c mena observed are in agreement with the theory.
276
SHAPE OF V DEPOSITION PROFILES Figure 1 shows measured Peak shifts (Peak shift is defined as the distance from the particle edge to the point of maximum Vanadium concentration, expressed as a fraction of the particle radius) for various catalysts vs. fractional distance from the top to the reactor. Qualitatively, the results are in full agreement with the theory that predicts: Large Peak shifts can only be found in the top of the reactor. Large pore catalysts (HDM) have larger Peak shifts than smaller pore catalysts (HDM/HDS and HDS).
1. 2.
It should be noted that Peak shifts of less than 0.04 are below the detection limit of the microprobe apparatus used in this study and could mean either M- or U-shaped profiles. 0.2
Y)
a
m
3
0c
0.1 I
c
t
d
2
A
3
0.c
0.1
:
"
0
e
0
0
0
0.2 0.3 0.4 0.5 0.6 0.7 0.8 Fractionaldistance from reactor top
0.9
Figure 1: Peak shift of Vanadium maximum, influence of catalyst type. (- HDM, A HDM/HDS, 17 HDS)
EFFFiCTS OF H2S PARTIAL PRESSURE ON OVERALL WACTOR PERFORMANCE. From the theoretical considerations it can be seen that the magnitudes of kl and kz influence the depth at which we can expect to find M-shaped Vanadium deposition profiles in the catalyst bed. The magnitude of the steady state B/A ratio, p, also depends on kl and k2 values. If it is assumed that kz is proportional to the partial pressure of HzS, the magnitude of k2 can be changed by changing the partial pressure of H2S. In order to investigate how the partial pressure of H2S affects the HDS and HDV activities as well as the deposition profiles of Vanadium inside the catalyst particle, two experiments were conducted on Kuwait AR. These experiments were identical except for the fact that the first was carried out with "normal" HZ/oil ratio and the second with a 17 times higher H2/oil ratio, leading to a 17 times lower H2S partial pressure, with no significant change in the Hz partial pressure. In the "low" H2S partial pressure experiment, the Peak shifts were far larger than those of the other experiment (Fig. 2). Figure 3 shows that H2S inhibits the HDS reaction as previously reported for lighter feedstocks [14]. Figure 4 shows that higher H2S pressure gives higher HDV activity. After correction (E = 20 kcal/mol) for the different temperatures of the experiments, the difference in activity is about 9%. This can be explained by the theory if kz is much larger than kl, because the overall reaction is then mainly controlled by kl.
Figure 2: Influence of H2S partial pressure on the Peak shift for Vanadium. ( Normal H2S partial pressure. A Low H2S partial pressure, Solid lines: Predicted from theory).
-
Fractional distance from reactor top
0
<
500
1500 2000 2500 3000 Run hours
1oM)
3500
00
Figure 3: Influence of H2S partial pressure on HDS activity. (- Normal H2S partial pressure, A Low H2S partial pressure).
0.4
O 0
'1 0
500
.
1000
0
1 5 w 2000 25W Run hours
3000 3500
1
X I
Figure 4: Influence of H2S partial pressure on HDV Activity. (- Normal H2S partial pressure, A Low H2S partial pressure).
Based on the very reasonable assumption that equilibrium values of CB/CAwere reached in both cases, the difference in performance is solely due to different levels of B in the product. With kz being proportional to H2S partial pressure the relative magnitudes of kl and k2 can be estimated. At the "normal" H2S partial pressure (similar to that of industrial reactors) it is found that k2 = 85 x kl. When the partial pressure of H2S is Lowered by a factor of 17 (low H2S partial pressure), it is found that k2 = 5 x kl. The solid lines in Figure 2 represent the calculated Peak shift versus reactor length for the two cases assuming the A + B + C reaction path.
278
Qv VALUES VERSUS CATALYST EFFICIENCY It has been shown above, that kz > > kl, when the partial pressure of H2S is "normal". In this situation, the importance of the sequential scheme is limited to the top of the reactor, and the HDV reaction for the entire plug flow reactor can therefore be approximated by an irreversible first order reaction with a rate constant for HDV equal to ki, (eq 5 ) . As a consequence of the above, we will expect to find that:
1) 2)
Qv is unaffected by the reactor position for the same catalyst. Qv is equal to the efficiency of Vanadium removal, ~ 1 .
Furthermore, it can be shown that Qv can be predicted on the basis of the Thiele theory for irreversible first order reaction. Figure 5 shows the Qv value obtained on different types of catalyst. The samples have been withdrawn from various positions in the reactor. For a given catalyst type, Qv is constant and independent of position in reactor.
A A
0:1 012 0:3 0:4 015 016 0:7 018 019
Figure 5: Influence of catalyst type and reactor position an Qv.(- HDM, A HDM/HDS,o HDS)
Fractinal distance from reactor top
Three runs with different compoOur tests have shown that Qv is proportional to site fillings have been carried out. The activity of the individual type of catalysts has then been calculated and correlated with Qv determined for each catalyst (Fig. 6).
Figure 6: Influence of Qv on catalyst activity.
279
The Qv value is found to vary mainly with the type of catalyst and pore size. This variation can be predicted by the Thiele theory.
CONCLUSION It has been shown that the suggested sequential reaction scheme, A + B C, fully explains the phenomena observed for Vanadium removal from Kuwait AR at industrially relevant conditions. However, it has also been shown that the A B reaction controls the Vanadium removal in most of the reactor, and this implies that, in practical terms, the overall HDV reaction can be considered as a simple first order reaction with Qv values a5 effectiveness factors. The quality of the data does not allow us to evaluate if one of the more complicated reaction schemes suggested by Wei and Massoth gives a better representation of our data. --1
+
ACKNOWLEDGEMENTS Special thanks to our colleague Dr. B. Donnis for embarking on this work in 1978 by proposing the A B C reaction scheme as an explanation of M-shaped metal deposition profiles. +
+
SYMBOL LIST A: B: C: CA, CB:
Metal porphyrin present in the feed. Intermediate hydrogenated metal porphyrin. Metal sulfide deposited on the catalyst. Concentration of A and B in the bulk phase outside the catalyst particles,
kle, b e :
PPm. Concentration of A and B in the feed oil, ppm. Effective diffusivity, cm2/s. Bulk diffusivity, cmy/s. 1 - radial position of V max. par t 1 cle r ad I us Feed flow, cm3/s. Intrinsic rate constant for the A + B and B + C reaction, s-1. Observed rate constant, kl, = k l x q and kze = kz x 72, s-1.
m. n:
Thiele module m
c,w, Cno: D:
Do: Peak shift: F: ki,
P:
Qv:
ka:
=
ki
kz-kl
Distribution parameter for V, Avera e V-concentration i n ellet Qv = Max. $-concentration i n pelyet
280
R: rp:
rs: V: Y: t: 917
92:
Vr: T:
Particle radius, cm. Pore radius, A. Radius of diffusing species, A. Catalyst volume, cm3. Reactor length parameter. Catalyst porosity. Efficiency for A 4 B and B + C reaction. Reactor efficiency for V-removal. Tortuosity.
LIST OF REFERENCES
"1
(21
P1
[41
P1
[(71
171 181
PI
[ 101
[ I 11 [I21 1131 [141
Ware, R.A. and Wei, J., J. Catal., 93, 122-134, 1985. Ware, R.A. and Wei, J., J. Catal., 93, 100-121, 1985. Agrawal, R. and Wei, J., Ind. Eng. Chem. Process Des. Dev., 23,515-522, 1984. Agrawal, R. and Wei, J., Ind. Eng. Chem. Process Des. Dev., 23, 505-514, 1984. Wei, J. and Wei, R., Chem. Eng. Commun., 13, 251-260, 1982. Chen, H.J. and Massoth, F.E., Ind. Eng. Chem. Res., 27, 9, 1629-1039, 1988. Tamrn, P.W., Harnsberger, H.F. and Bridge. A.G., Ind. Eng. Chern. Process Des. Dev., 20, 262-273, 198 1. Bridge, A.C. and Green, D.C., 5th Chem. and Tech. International Congress, Bombay, India, Symposium 5, Paper 8, 1980. Ahn, B.J., Smith, J.M., AIChE J., 30, 739, 1984. Spry, J.C. and Sawyer, W.H., Paper 16-20, AIChE 68th Annual Meeting, Los Angeles Calif., Nov. 1975. Nielsen, A., Cooper, B.H. and Jacobsen, A.C., Preprints, Division of Petroleum Chemistry, ACS, 26, 440-455, 1981. Jacobsen, A.C. et al., AIChE Spring National Meeting, Houston, Texas, 1983. Hannerup, P.N. and Jacobsen, A.C., Preprints, Division of Petroleum Chemistry, ACS, 28, 576-599, 1083. Metcalfe, T.F., Preprint 20B, AIChE 64th National Meeting, March 1969.
273
HYDRODEMETALLIZATIONIN RESlD HYDROPROCESSING Jesper Bartholdy and Peter N. Hannerup, Haldor T o p s ~ eA/S, Nym~lkevej55, DK-2800 Denmark SUMMARY The study of the Vanadium deposition profiles in spent catalyst particles from resid hydrcv processing confirms that HDM is a sequential reaction. Furthermore, it is shown that the distribution parameter for the deposited Vanadium Qv is constant through the reactor for each catalyst type and that Qv is proportional to the efficiency of the Vanadium removal reaction.
INTRODUCTION In many studies it has been shown that V and Ni deactivate resid hydroprocessing catalysts [7, 9, 11, 131. The deactivation is caused by poisoning/fouling of the active sites and by restriction of the access of reacting species to the catalyst pore system. Removal of Ni and V from residual oils is diffusionally limited [8], and therefore Ni and V are deposited in the catalyst pores in a characteristic deposition profile [7, 11, 131 which is either U- or M-shaped, i.e. the maximum metal deposition is either located at the catalyst pellet surface or inside the pellet. These phenomena have been investigated for both V and Ni using various V/Ni porphyrins as model compounds [l, 2, 3, 4, 51. It has been concluded that the removal of V and Ni porphyrins proceeds via a sequential reaction network, where the porphyrins are hydrogenated in the first step and deposited in a subsequent one. These studies have also indicated that the degree of complexity of reaction pattern depends on the types of porphyrins used. In these studies, no H2S was present. In a recent study [6] of demetallization of Ni and V porphyrins, the reaction path of HDV and HDNi reactions has been investigated in the presence of HzS. The aim of the present study is to test the applicability of these conclusions on HDM data obtained on real feedstocks at industrially relevant conditions. EXPERIMENTAL The experimental set-ups for conducting resid hydroprocessing experiments, product analyses and metal profile measurements on the spent catalysts have been described elsewhere 1111. The experiments were performed on 1 / 3 2 cylindrical catalyst particles with a catalyst bed diluted with 0.2-0.3 mm glass beads. In each experiment, more than one type of catalyst was used (HDM, HDM/HDS, HDS), forming a composite catalyst filling [12]. All experiments were performed on a Kuwait AR using similar process conditions. The properties of the feed and the process conditions are listed in Tables 1 and 2, respectively.
274
Table 1: Feed stock specifications. SG,
(60/60F)
Sulfur, w t %
0.9742
CCR, wt%
4.3 2465 10.4
Visc @122F, cSt
920
Nitrogen, p p m Pent. Ins , w t % Ni, p p m
Vr
PPm
Table 2: Process conditions.
3.4
H,/Oil,
N1/1
P r o d u c t Sulfur, wt%
0.45
20 63
After termination of the experiments, the catalysts were withdrawn from the reactor. Catalyst samples were obtained from various positions in the reactor. For each catalyst sample, the chemical composition and the distribution of metals inside the catalyst particle were determined.
THEORY
The assumption is a sequential 1st order reaction network for HDM:
The significance of the individual steps has been investigated in model compound studies [2, 4, 61. The first step A - B consists of hydrogenation of the metal-bearing porphyrins forming mobile, hydrogenated metal porphyrins. The second step is a reaction between the hydrogenated porphyrim and HzS, forming deposits of metal sulfide on the catalyst surface. The rate constant of the two reactions, kl and k:! is assumed to be proportional to P H and ~ ptm, respectively. = 0 and that the It is further assumed that B is not present in the feed oil, i.e. C I ~ O reactions are taking place in spherical particles of porous material and are controlled by effective diffusion coefficients DA = DB = D. (The actual catalyst particles used in the experiments were short cylinders). By conventional techniques, the concentration gradients inside the particle can be found. The concentrations through the reactor then become (for explanation of symbols, see Symbol List):
275
where
It can be seen that the ratio CB/CAwill approach an equilibrium value CB/CA= p, when (kae - kl,) x V/F x y is large. This situation arrises when k2 >’ kl and the conversion is high. The overall reactor efficiency can be found by comparing diffusionally limited operation with diffusion Gee operation. Assuming that the above equilibrium ratio has been reached in both cases we find:
which for low F/V and small p will approach the limit:
In realistic situations the maximum metals concentration in the particles will be displaced from the particle surface in the top of the reactor (M-profile), but for
the maximum metals concentration will be found at the particle surface (U-profile). In this case we find for the distribution parameter:
When the equilibrium value
A
=
p has been reached:
RESULTS AND DISCUSSION In the previous section, we have developed a mathematical description of a two-step diffusionally limited reaction sequence. In the following we will discuss whether the p h e n c mena observed are in agreement with the theory.
276
SHAPE OF V DEPOSITION PROFILES Figure 1 shows measured Peak shifts (Peak shift is defined as the distance from the particle edge to the point of maximum Vanadium concentration, expressed as a fraction of the particle radius) for various catalysts vs. fractional distance from the top to the reactor. Qualitatively, the results are in full agreement with the theory that predicts: Large Peak shifts can only be found in the top of the reactor. Large pore catalysts (HDM) have larger Peak shifts than smaller pore catalysts (HDM/HDS and HDS).
1. 2.
It should be noted that Peak shifts of less than 0.04 are below the detection limit of the microprobe apparatus used in this study and could mean either M- or U-shaped profiles. 0.2
Y)
a
m
3
0c
0.1 I
c
t
d
2
A
3
0.c
0.1
:
"
0
e
0
0
0
0.2 0.3 0.4 0.5 0.6 0.7 0.8 Fractionaldistance from reactor top
0.9
Figure 1: Peak shift of Vanadium maximum, influence of catalyst type. (- HDM, A HDM/HDS, 17 HDS)
EFFFiCTS OF H2S PARTIAL PRESSURE ON OVERALL WACTOR PERFORMANCE. From the theoretical considerations it can be seen that the magnitudes of kl and kz influence the depth at which we can expect to find M-shaped Vanadium deposition profiles in the catalyst bed. The magnitude of the steady state B/A ratio, p, also depends on kl and k2 values. If it is assumed that kz is proportional to the partial pressure of HzS, the magnitude of k2 can be changed by changing the partial pressure of H2S. In order to investigate how the partial pressure of H2S affects the HDS and HDV activities as well as the deposition profiles of Vanadium inside the catalyst particle, two experiments were conducted on Kuwait AR. These experiments were identical except for the fact that the first was carried out with "normal" HZ/oil ratio and the second with a 17 times higher H2/oil ratio, leading to a 17 times lower H2S partial pressure, with no significant change in the Hz partial pressure. In the "low" H2S partial pressure experiment, the Peak shifts were far larger than those of the other experiment (Fig. 2). Figure 3 shows that H2S inhibits the HDS reaction as previously reported for lighter feedstocks [14]. Figure 4 shows that higher H2S pressure gives higher HDV activity. After correction (E = 20 kcal/mol) for the different temperatures of the experiments, the difference in activity is about 9%. This can be explained by the theory if kz is much larger than kl, because the overall reaction is then mainly controlled by kl.
Figure 2: Influence of H2S partial pressure on the Peak shift for Vanadium. ( Normal H2S partial pressure. A Low H2S partial pressure, Solid lines: Predicted from theory).
-
Fractional distance from reactor top
0
<
500
1500 2000 2500 3000 Run hours
1oM)
3500
00
Figure 3: Influence of H2S partial pressure on HDS activity. (- Normal H2S partial pressure, A Low H2S partial pressure).
0.4
O 0
'1 0
500
.
1000
0
1 5 w 2000 25W Run hours
3000 3500
1
X I
Figure 4: Influence of H2S partial pressure on HDV Activity. (- Normal H2S partial pressure, A Low H2S partial pressure).
Based on the very reasonable assumption that equilibrium values of CB/CAwere reached in both cases, the difference in performance is solely due to different levels of B in the product. With kz being proportional to H2S partial pressure the relative magnitudes of kl and k2 can be estimated. At the "normal" H2S partial pressure (similar to that of industrial reactors) it is found that k2 = 85 x kl. When the partial pressure of H2S is Lowered by a factor of 17 (low H2S partial pressure), it is found that k2 = 5 x kl. The solid lines in Figure 2 represent the calculated Peak shift versus reactor length for the two cases assuming the A + B + C reaction path.
278
Qv VALUES VERSUS CATALYST EFFICIENCY It has been shown above, that kz > > kl, when the partial pressure of H2S is "normal". In this situation, the importance of the sequential scheme is limited to the top of the reactor, and the HDV reaction for the entire plug flow reactor can therefore be approximated by an irreversible first order reaction with a rate constant for HDV equal to ki, (eq 5 ) . As a consequence of the above, we will expect to find that:
1) 2)
Qv is unaffected by the reactor position for the same catalyst. Qv is equal to the efficiency of Vanadium removal, ~ 1 .
Furthermore, it can be shown that Qv can be predicted on the basis of the Thiele theory for irreversible first order reaction. Figure 5 shows the Qv value obtained on different types of catalyst. The samples have been withdrawn from various positions in the reactor. For a given catalyst type, Qv is constant and independent of position in reactor.
A A
0:1 012 0:3 0:4 015 016 0:7 018 019
Figure 5: Influence of catalyst type and reactor position an Qv.(- HDM, A HDM/HDS,o HDS)
Fractinal distance from reactor top
Three runs with different compoOur tests have shown that Qv is proportional to site fillings have been carried out. The activity of the individual type of catalysts has then been calculated and correlated with Qv determined for each catalyst (Fig. 6).
Figure 6: Influence of Qv on catalyst activity.
279
The Qv value is found to vary mainly with the type of catalyst and pore size. This variation can be predicted by the Thiele theory.
CONCLUSION It has been shown that the suggested sequential reaction scheme, A + B C, fully explains the phenomena observed for Vanadium removal from Kuwait AR at industrially relevant conditions. However, it has also been shown that the A B reaction controls the Vanadium removal in most of the reactor, and this implies that, in practical terms, the overall HDV reaction can be considered as a simple first order reaction with Qv values a5 effectiveness factors. The quality of the data does not allow us to evaluate if one of the more complicated reaction schemes suggested by Wei and Massoth gives a better representation of our data. --1
+
ACKNOWLEDGEMENTS Special thanks to our colleague Dr. B. Donnis for embarking on this work in 1978 by proposing the A B C reaction scheme as an explanation of M-shaped metal deposition profiles. +
+
SYMBOL LIST A: B: C: CA, CB:
Metal porphyrin present in the feed. Intermediate hydrogenated metal porphyrin. Metal sulfide deposited on the catalyst. Concentration of A and B in the bulk phase outside the catalyst particles,
kle, b e :
PPm. Concentration of A and B in the feed oil, ppm. Effective diffusivity, cm2/s. Bulk diffusivity, cmy/s. 1 - radial position of V max. par t 1 cle r ad I us Feed flow, cm3/s. Intrinsic rate constant for the A + B and B + C reaction, s-1. Observed rate constant, kl, = k l x q and kze = kz x 72, s-1.
m. n:
Thiele module m
c,w, Cno: D:
Do: Peak shift: F: ki,
P:
Qv:
ka:
=
ki
kz-kl
Distribution parameter for V, Avera e V-concentration i n ellet Qv = Max. $-concentration i n pelyet
280
R: rp:
rs: V: Y: t: 917
92:
Vr: T:
Particle radius, cm. Pore radius, A. Radius of diffusing species, A. Catalyst volume, cm3. Reactor length parameter. Catalyst porosity. Efficiency for A 4 B and B + C reaction. Reactor efficiency for V-removal. Tortuosity.
LIST OF REFERENCES
"1
(21
P1
[41
P1
[(71
171 181
PI
[ 101
[ I 11 [I21 1131 [141
Ware, R.A. and Wei, J., J. Catal., 93, 122-134, 1985. Ware, R.A. and Wei, J., J. Catal., 93, 100-121, 1985. Agrawal, R. and Wei, J., Ind. Eng. Chem. Process Des. Dev., 23,515-522, 1984. Agrawal, R. and Wei, J., Ind. Eng. Chem. Process Des. Dev., 23, 505-514, 1984. Wei, J. and Wei, R., Chem. Eng. Commun., 13, 251-260, 1982. Chen, H.J. and Massoth, F.E., Ind. Eng. Chem. Res., 27, 9, 1629-1039, 1988. Tamrn, P.W., Harnsberger, H.F. and Bridge. A.G., Ind. Eng. Chern. Process Des. Dev., 20, 262-273, 198 1. Bridge, A.C. and Green, D.C., 5th Chem. and Tech. International Congress, Bombay, India, Symposium 5, Paper 8, 1980. Ahn, B.J., Smith, J.M., AIChE J., 30, 739, 1984. Spry, J.C. and Sawyer, W.H., Paper 16-20, AIChE 68th Annual Meeting, Los Angeles Calif., Nov. 1975. Nielsen, A., Cooper, B.H. and Jacobsen, A.C., Preprints, Division of Petroleum Chemistry, ACS, 26, 440-455, 1981. Jacobsen, A.C. et al., AIChE Spring National Meeting, Houston, Texas, 1983. Hannerup, P.N. and Jacobsen, A.C., Preprints, Division of Petroleum Chemistry, ACS, 28, 576-599, 1083. Metcalfe, T.F., Preprint 20B, AIChE 64th National Meeting, March 1969.