Ind. Eng. Chem. Process Des. Dev. 1980, 19,263-267
Table 111. Comparison between VO-Etio, Ni-&io, and Ni-TPP Demetallatiori Runs VO-Etio Ni-Etio (a) activation energy for total metal removal, kcal/g-mol ( b ) activation energy for metalloporphyriri disappearance, kcal/g-mol ( c ) hydrogen pressure dependence for total metal removal ( d ) hydrogen pressure dependence for metalloporphyrin disappearance ( e ) half-order rate constant at 316 " C , 6995 kPa H,for total metal removal ( f ) half-order rate constant a t 316 ' C, 6995 kPa H,for metalloporphyrin disappearancea a
Units:
(ppm)l'*
1x71~ of
-
Ni-TPP
37.1
27.6
34.0
35.8
28.1
33.7
263
before nickel could be removed effectively. This is supported by Larson and Beuther (1966), who stated that a vanadium-containing molecule is more polar and surface active than a nickel-containing molecule in general. (d) Most of the vanadium and nickel on the catalyst cannot be in the form of metalloporphyrins. (e) The hydrodemetallation experiments with VO-Etio, Ni-Etio, and NiTPP were not influenced by diffusion effects. Acknowledgment
1.16
1.34
2.26
1.23
1.66
2.13
The authors are grateful to the National Science Foundation for support of the work under Grant No. ENG 75-16456. Literature Cited
202.2
403.4
249.5
205.7
440.9
450.3
oil/g of cat. h.
is consistent with prlevious literature (Oleck and Sherry, 1977; Chang and Silvestri, 1974, 1976; Riley, 1978; Oxenreiter et al., 1972; Larson and Beuther, 1966) which reported that vanadium has higher activity. Table I11 summarized the activaticln energy, hydrogen pressure dependence, and the calculated half-order rate constants at 316 "C and 6995 kPa hydrogen for VO-Etio, Ni-Etio, and Ni-TPP runs. VO-TPP was much more active than VOEtio, Ni-Etio, and Ni-TPP. (b) The rates of vanadium and nickel runs fit well with 0.5-order kinetics. However, the dependence of kinetic order on temperature and hydrogen pressure is less significant for vanadium runs. (c) Vanadium adsorbed on the catalyst more strongly than nickel. The concentration decline in the transient period was larger for vanadium than for nickel. In mixed vanadium and nickel runs, the vanadium had to be removed first
Audibert, F., Duhaut, P., paper presented at the 35th Mid-year Meeting of the American Petroleum Institutes Division of Refining, Houston, Texas, May 13-15, 1970. Baker, E. W., Palmer, S. E., Chapter 11 of "The Porphyrins", Voi. I, D. Dolphin, Ed., Academic Press, New York, 1978. Beuther, H., Schmid, B. K., "Proceedings, Sixth World Petroleum Congress", Sec. 111, Paper 20, PD7. Frankfurt/Main, 1963. Chang, C. D., Silvestri, A. J., Ind. Eng. Chem. Process Des. Dev., 13, 315 (1974). Chang, C. D., Silvestri, A. J. Ind. Eng. Chem. Process Des. Dev., 15, 161 (1976). Clark, D. S., Varney, W. R. "Physical Metallurgy tor Engineers", Van Nostrand, Princeton, N.J.. 1962. Hambright, P.,Howard University, Private Communication, 1978. Hung, C. W., Wei, J., Ind. Eng. Chem. Process Des. Dev.. preceding paper in this issue, 1980. Larson, 0. A., Beuther, H., Am. Chem. Soc. Div. Pet. Chem. Prepr., 6-95, 11966) Oleck,-S: M., Sherry, H. S.,Ind. Eng. Chem. Process. Des. Dev., 16, 525 (1977). Oxenreiter, M. F., Frye, C. G., Hoekstra, G. B.. Sroka, J. M., "Desulfurization of Khafji and Gach Saran Resids", paper presented at the Japanese Petroleum Institute, Nov 30, 1972. Riley, K L.. Am. Chem. Soc. Div. Pet. Chem. Prepr., 23-3, 1104 (1978). Saraceno, A. J.. Fanale, D. T.. Ccggeshall, N. D., Anal. Chem., 33, 500 (1961). Sato, M., Takayama, H., Kurita, S., Kwan, T., Nippon Kagaku Zasshi, 92(10). 834 (1971). Sato, M., Kwan, T., Shimizu, Y., Inoue, K., Koenuma, Y., Nishikata, H., Takenurna, Y., Aizawa, R., Kobayashi, S., Egi, K., Matsumota, K., PoNut. Contr. Jpn., 5(2), 121-131 (1970). Yen, T. F.. Chapter 1 of "The Role of Trace Metals in Petroleum", T. F. Yen, Ed., Ann Arbor Science, Ann Arbor, Mich., 1975. Yen, T. F., Energy Source, 4(3), 4 (1977).
Received for review April 20, 1979 Accepted November 29, 1979
Kinetics of the Gas-Phase Catalytic Isomerization of Xylenes Avelino Corma and Antonlo Cortis" Instituto de Cat6lisis y Petroleoquimica del C.S.I.C., Serrano, ff9, Madrid (6),Spain
The kinetics of the gas-phase isomerization of xylenes in the presence of hydrogen have been studied in a fixed-bed flow reactor under initial conditions. The study was carried out using a silica-alumina catalyst containing 4 wt % nickel, at 400 to 465 O C and a total pressure of up to 3.95 kg/cm2. The kinetic parameters thus obtained when used in our mathematical model reproduce the observed product distribution up to equilibrium conversion in an isotherimal reactor packed with powdered catalyst. By introducing an effectiveness factor into the model, it is also possible to fit data obtained under similar conditions using a pellet sized catalyst.
Int oductia The gas-phase catalytic isomerization of xylenes is a process of significant commercial interest. A great deal of work has been done on the development of suitable catalysts and reaction conditions to obtain maximum yields 0196-4305/80/1119-0263$01.00/0
and selectivities for the desired isomers. It is noteworthy that despite this, literature dealing with the detailed mechanism and kinetics of the reaction is scarce. In previous papers (Corti% and Corma, 1978; Corma e t al., 1979) it was shown that the interconversion of xylenes 0 1980 American
Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
264
Table I. Influence of Hydrogen Partial Pressure o n Xvlenes Isomerization at 430 "C
w>a g
0.250 0.250
0.150 0.150 0.050 0.050
F H . c.9
pressures, atm
mol/L H.C.
H,
product analysis, mol o/o
0-X
Feed: o-Xylene 0.20 0.73 96.7 0.150 0.20 3.73 96.3 Feed: m-Xylene 0.105 0.20 0.73 2.4 0.105 0.20 3.73 2.4 Feed: p-Xylene 0.074 0.20 0.73 0.0 0.074 0.20 3 . 7 3 0.0 0.150
rn-X
p-X
TOL
3.1 3.2
0.0 0.0
0.2 0.5
93.6 93.4
3.9 3.9
0.1 0.3
2.1 2.0
97.8 97.4
0.2 0.6
0
0 2
0.4
0 6
0.8
P,Iatm)
Figure 2. Initial rates of isomerization of p-xylene to m-xylene. 5
Average particle size of t h e catalyst = 0.105 mm.
-i LSSV
/
I -.I
*
n
_1-LpL-L 0
02
0.4
0 6
0 8 Pr !ot m i
Figure 3. Initial rates of isomerization of m-xylene to o-xylene, Po I o t r n )
Figure 1. Initial rates of isomerization of o-xylene to m-xylene.
over a silica-alumina catalyst containing 4 wt % nickel follows a mechanism ortho Q meta Q para which proceeds by intramolecular 1,2 shifts of the methyl groups. This probably occurs by the cyclization of an adsorbed Wheland type complex to a bicyclo[3.1.O]hexenyl species, migration of the three-membered ring to a neighboring side of the pentagon, and finally the regeneration of a protonated complex as precursor of a new xylene isomer. Hydrogenolysis is the major competing reaction, while disproportionation is present only to a minor extent. The present study is concerned with the kinetics of the isomerization of xylenes over a catalyst and in the presence of hydrogen and with the development of a mathematical model, which includes hydrogenolysis and is capable of reproducing product distribution data obtained in a fixed-bed isothermal reactor up to equilibrium conversions. Experimental Methods A detailed description of the high-pressure stainless steel reactor and of the methods of catalyst preparation and reaction products analysis has been published previously (Cortb and Corma, 1978). All kinetic data reported in the following sections were obtained under conditions of constant activity by using a suitable partial pressure of hydrogen and an appropriate hydrogen to hydrocarbon ratio to prevent catalyst deactivation (Corma and CortBs, 1976). Results Preliminary Experiments. Preliminary experiments were conducted in order to select the range of working conditions where diffusional limitations in the catalyst bed are avoided (Corma, 1976). The average particle size of the catalyst chosen as a result of the above work for the kinetic experiments was 0.105 mm. Additional runs, carried out a t a constant partial pressure of hydrocarbon (see Table I), indicated that the influence of hydrogen pressure on the isomerization rates of xylenes is negligible.
Pq
/otm/
Figure 4. Initial rates of isomerization of m-xylene to p-xylene.
Initial Isomerization Kinetics. The initial rates of isomerization of o-, p - and m-xylene, a t 400,430, and 465 "C vs. partial pressures of hydrocarbon are presented in Figures 1-4. Each rate was calculated in the usual manner, i.e., from the initial slope of the plot of X vs. W / F obtained at low conversions (less than 7% conversion per pass). Similarly, the initial rates for the isomerization of several binary and ternary mixtures of xylenes have been calculated, and the results are given in Table 11. Integral Isomerization Kinetics. Figures 5 and 6 present experimental results from integral reactors for the isomerization as well as the hydrogenolysis reactions of p - , m-, and o-xylenes a t 465 "C and 0.93 and 3.93 kg/cm2 total pressure over a 0.105-mm catalyst. In these figures solid lines represent predicted values and are compared with the experimental values. Results of the isomerization of rn-xylene over a 3-mm particle size catalyst are presented in Figure 7. Integral Hydrogenolysis Kinetics. For the hydrogenolysis of the three xylenes, the following kinetic rate equation was used rH = kHPHaPX (1)
Ind. Eng. Chern. Process Des. Dev., Vol. 19, No. 2, 1980
Table 11. Initial Rate of Isomerization of Binary and Ternary Mixtures of Xylene a t 400 "C (Partial Pressure of H 2 = 0.73 a t m ; H,/Hydrocarbon Ratio = 3.7 mol/mol) partial pressure of xylenes in mixtures, atm px X
10' 2.8 10.0 0.0 0.0 17.2 9.9 8.1 4.2
m, X 10' 17.1 10.0 17.5 10.2 0.0 0.0 4.0 3.7
ox
1LI
-
rm
0.38 -0.42 0.58 0.44 -1.54 -0.78 -0.60 -0.18
1.1 7.8 12.0
:
_I
i?l 6
2
"n
-0.71 0.20 -0.88 0.02 1.51 1.67 0.93 0.72
TOL
10
Figure 7. Isomerization of rn-xylene on a 3 X 2.5 mm catalyst at 465 "C, 0.93 atm, and H2/H.C. = 7.2 mol/mol. Isolated points correspond to experimental results and solid lines to values predicted by the kinetic model. Table 111. Pseudo Kinetic Rate Constants (k')for t h e Hvdroeenolvsis Reaction
465 465
role
,
12
1
20
,
28 W F
gcot-h
mole
22
r (mole)
0.33 0.20 0.21 -0.47 -0.13 -1.07 -0.38 -0.62
temp,
F
18
li
W g.cotxh
kH X
28 36 K , gcatxh
y
:: st 22 11
r13
0.0 0.0 2.5 9.8 2.8
1
1 1
X
1.02
L
;E
rate of formation of each isomer, mol/(g of cat. h )
-
265
P,,
PH,
0.22 0.58
0.73 3.37
lo2 X
pHa,
( g of cat. h ) / ( m o l a t m )
~ _ _ _ _ _ _ _ 0.27 0.73
0.31
-
calcd
0.22
-
0.95
5 and 6, up to 30% of isomerization conversion, were fitted using eq 2. The toluene produced by hydrogenolysis was calculated by subtracting from the total toluene formed, the amount of trimethylbenzenes formed by the disproportionation reactions. The values of the k'constants thus obtained are presented in Table 111.
'
Figure 5. Integral isomerization data obtained at 465 "C, 0.93 atm, and H,/H.C. = 3.3 mol/mol: A, for p-xylene, B, for o-xylene. Isolated points correspond to experimental results and solid lines to values predicted by the kinetic model. L
21-
c
Discussion of Results In previous studies two different possibilities for the mechanism of isomerization of xylenes have been proposed. On the one hand, some authors (Lanewala and Bolton, 1969) have suggested that the isomerization takes place by transalkylation, i.e., by intermolecular displacement reactions of the SN2 type. This mechanism would be consistent with a triangular reaction scheme for the isomerization of xylenes proposed by several authors (Ameniya e t al., 1961; Izumi and Shiba, 1964). ortho
rneta L
M (=cat? F
TS
I
12
20
28
*
F
~
9cot.h note
,
Figure 6. Integral isomerization data for rn-xylene at 465 "C: A, 0.93 atm, H,/H.C. = 3.2 mol/mol; B, 3.93 atm, H,/H.C. = 5.8 mol/mol. Isolated points, correspond to experimental results and solid to values predicted by the kinetic model.
Here k H is the hydrogenolysis constant, P H is the partial pressure of hydrogen, a is the order of the reaction with respect to hydrogen, and Px is the partial pressure of the corresponding xylene isomer. In all our experiments the partial pressure of hydrogen is a t least 3.3 times higher than the partial pressure of xylenes. If we now oinly take the data up to 30% total isomerization conversion, the comsumption of hydrogen for hydrogenolysis to toluene is always less than 2% of the original values, so that the partial pressure of hydrogen remains practically constant, and eq 1 can be further simplified to
r = k'Px (2) In order to calculate the value for k ', experimental yields of toluene a t the experimental conditions shown in Figures
para
On the other hand, others have postulated the following consecutive reaction mechanism ortho s meta s para which can proceed by intramolecular 1,2 shifts of methyl groups (Brown and Junk, 1955; Pollitzer and Donaldson, 1970). As indicated in the Introduction, we believe we have provided enough evidence (CortBs and Corma, 1978) that the isomerization reaction over our silica-alumina catalyst proceeds through this second set of consecutive and reversible reactions by intramolecular 1,2 shifts of the methyl groups, so that 0- and p-xylene cannot be directly interconverted into each other, but through the meta isomer. Following the above reaction schemes, three different kinetic models (Hougen and Watson, 1959) have been considered. In two of these models the surface reaction is rate controlling: one involving a single adsorption site which would be consistent with the consecutive intramolecular mechanism, and the other with two adjacent chemisorbed species participating in the reaction. In the third case, the adsorption of the reactant xylene is con-
266
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
Table IV. Kinetic Parameters and Statistical Parameter Values for t h e Best Fits to the Langmuir-Hinshelwood Kinetic Model temp of reaction, "C 400 430 465 400 430 465 400 430 465 400 430 465
isom. reaction meta para -+
meta para
+
+
ortho
ortho
meta
--t
meta
kinetic parameters
hiKi X l o 2 , (g h ) / ( m o l a t m ) 3.97 i 0.20 7.44 t 0.36 17.59 t 2.08 2.84 i- 0.23 4.88 5 0.30 12.12 i 1.33 9.39 * 0.95 19.82 i- 1.04 34.78 i 2.90 6.85 f 0.17 9.98 I0.22 21.30 i 0.67
sidered as the rate limiting step. Mechanism I. Single site surface reaction controlling
1 + CKiPi
(3)
i=l
Mechanism 11. Reaction of two molecules adsorbed in two adjacent sites controlling
kiK;Pi2
ri =
(1 + k K i P J 2
(4)
i=l
Mechanism 111. Adsorption of the reactant controlling (5) i=l
At initial conditions, eq 3, 4, and 5 reduce to the following form kiKiPi ri, = (6) 1 KiPi
+
kiK;P? "irr
=
(1
+
rill*= kipi
(7) (8)
Equations 6, 7, and 8 were linearized and the initial rates a t the various partial pressures were compared with the three models by linear regression. Fisher's and Exner's statistical tests were applied in order to find the most probable model. In this way, the kinetic model corresponding to Mechanism I was found to give the best fit and the kinetic parameters obtained from this model are presented in Table IV. The activation energies for the isomerization of para to meta, ortho to meta, meta to para, and meta to ortho-xylene are: 20.0, 17.4, 22.8, and 22.3 kcal/mol, respectively. If we compare our values of 22.8 and 22.3 kcal/mol with the values of 25.6 and 25.4 kcal/mol reported by Hanson and Engel (1967) for the isomerization of m- to p - and o-xylenes on a silica alumina catalyst using N2 as a carrier, one can see that the activation energies are nearly the same for both silica-alumina and silica-alumina-nickel catalysts. Consequently, as far as the isomerization reaction is concerned, the active sites in both catalysts are the same. From this we conclude that the role of the hydrogenating function (Ni) in the bifunctional catalysts used in the xylene isomerization is not in the isomerization process
Kit atm-' 1 . 1 5 I0.38 1.10 i 0.37 1.66 t 1.00 1 . 4 5 t 0.68 1 . 0 3 k 0.50 1.61 t 0.92 1.45 i 0.84 1 . 1 5 t 0.42 1.11 ? 0.67 0.80 r 0.20 0.38 I 0.32 0.03 t 0.22
statistical parameters correl coeff 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99
Exner 0.07 0.07 0.17 0.12 0.09 0.16 0.14 0.08 0.12 0.06 0.03 0.04
F90%
1607 1658 244 519 877 284 333 1216 495 2200 7319 3515
itself, but involves control of the deactivation of the catalyst by removing the carbonaceous materials deposited on the silica-alumina surface. This conclusion agrees with the work of Pitts et al. (1955), who showed that xylene isomerizations probably do not require naphthenes (or partially hydrogenated aromatics) as intermediates. The influence of temperature on adsorption constants for the three xylenes is very small as is seen from the values of Ki a t the three temperatures shown in Table IV. This is in good agreement with the values of 4 kcal/mol reported by Okada et al. (1971) for the heat of adsorption of oxylene over a silica-alumina catalyst exchanged with nickel. From the values of t,he k'parameters presented in Table 11, and taking into account the total pressure as well as the partial pressure of hydrogen, the order of the reaction with respect to the hydrogen can be calculated to be 0.95 for the case of a m-xylene. Therefore, the resulting kinetic equation for the hydrogenolysis of xylenes on a nickel supported silica-alumina catalyst can be taken as rH = kHPHPX. This kinetic equation is in agreement with the results of Setinek et al. (19681, who found that the rate of hydrogenolysis of xylenes using a nickel on alumina catalyst is proportional to the partial pressure of hydrogen and to the partial pressure of xylene. Mat hematical Model. Using the differential rate expressions for the isomerization as well as for the hydrogenolysis of the three xylenes and the following reaction network para
we write
=m e t a -kl
k2
k- I
k- 2
ortro
Ind. Eng. Chem. Process Des. Dev. 1980, 19, 267-271
In order to checlk the validity of this model, several binary and ternary mixtures of xylenes have been reacted (Table 11) and initial experimental rates of isomerization were compared using Exner's statistical test, with the theoretical values predicted by the complete network model, using the kinetic parameters presented in Table IV. The \k statistical parameter has been found to be 0.09 and thus it may be concluded that the model agrees well with the observed initial rates of isomerization. Using the kinetic parameters from Tables 111and IV, and taking into account the total pressure, the complete model has also been integrated and used a t various initial conditions by using an Adams-Meoulton-Shell predictor-corrector method. From Figures 5 and 6 it is possible to see that the mathematical model agrees with the experimental results up to equilibrium conversion. At our experimental conditions, the amount of trimethylbenzenes was always less than 3% and for this reason the disproportionation reactions are not considered in the kinetic network model. However, if experiments have to be carried out a t lower temperatures or a t higher total pressures and lower hydrogen/hydrocarban ratios, the rate equations corresponding to the disproportionation reactions will have to be introduced into the model. Effectiveness Fiactor. The industrial process of catalytic isomerization of xylenes is carried out using a fixed-bed catalytic reactor; consequently a fine powdered catalyst cannot be used. The data presented above were obtained using such a powdered catalyst in order to avoid diffusion limitations. When our model is applied under conditions where the catalyst is working under diffusion limited conditions, this new factor may be taken into consideration by the introduction of an effectiveness factor in the kinetic rate equation (Satterfield, 1963). In our case, the effectiveness factor has been determined by calculating the ratio between the initial rate of the m-xylene isomerization reaction using a 3 X 2.5 mm pelletized catalyst and the initial rate of m-xylene isomerization using a 0.105 mm size catalyst. The resulting effectiveness factor was found to be 0.40. This value was taken to be applicable also to the isomerization of p - and o-xylene. The value 0.40 was therefore introduced into the mathematical model which was then integrated for the initial conditions presented in Figure 7 . In this figure the solid lines represent theoretical values and the circles represent experimental results for the isomerization cf m-xylene to p - and o-xylene and
267
toluene over a 3 X 2.5 mm particle size silica alumina nickel catalyst. From these results it is possible t o see that the model also reproduces well experimental results obtained under diffusion limitation conditions. Conclusions The kinetics of the isomerization of m-, p - , and o-xylenes over a bifunctional silica-alumina Ni catalyst have been studied. Using the experimental results a mechanism where the controlling step is the reaction of one molecule adsorbed in one active site has been found to give the best statistical fit of the data. The kinetic rate constants as well as the adsorption constant and activation energies have been calculated for each of the isomerization reactions using this model. We conclude from these energies that the hydrogenating function (Ni) in our catalyst is only involved in extending the life of the catalyst but not in the isomerization reaction. Furthermore, a model which describes the overall process up to high levels of conversion of mixtures of xylene isomers has been developed. Finally, an effectiveness factor accounting for diffusion limitations in larger catalyst particles has been calculated and introduced in the model. In this way we can calculate from our model values for the case where a 3-mm pelletized catalyst was used, for which size the reaction is controlled by diffusion. The diffusion case is also well represented by our model using such an effectiveness factor. Literature Cited Ameniya, T., Tsumetoni, E., Nakamura, E., Nakazawa, T., Bull. Jpn. Pet. Inst., 3, 14 (1961). Brown, H. C., Junk, H., J . Am. Chem. SOC.,77, 5579 (1955). Corma. A., CortBs, A,, "V Iberoamerican Symposio of Catalysis", Lisboa, Vol. 11, p 309, July 1976. Corma, A., Cor&, A,, Nebot, I., Tomis, F., J . Catal., 57, 444 (1979). Corma. A. Ph.D. Thesis, University of Madrid, Spain, Dec 1976. Cortgs, A., Corma, A., J . Catal.. 51, 338 (1978). Exner, O.,Collect. Czech. Chem. Commun., 31, 3222 (1966). Hanson, K. L.. Engel, A. J. AIChE J., 13, 260 (1967). Hougerh 0.A., Watson, K. M., "Chemical Process Principles", Part 111, Seventh Printing, Chapter XIX, Wiley, New York. April 1959. Izumi, A., Shiba, T., J. Chem. SOC.Jpn., Ind. Chem. Sect., 64,559 (1964). Lanewaia, M. A,, Bolton, A. P. J . Org. Chem., 34, 3107 (1969). Okada, M.. Ohsato, K.. Asami, Y., Bull. Jpn. Pet. Inst., 13, (1971). Pins, P. M.,Connor, J. E., Leum, L. N., I n d . Eng. Chem., 47, 4 (1955). Pollitzer, E. L., Donaldson, G. R., Am. Chem. SOC. Div. Pet. Chem. Prepr. 15(3), 842-852 (1970). Satterfield, C. N., "The Role of Diffusion in Catalysis", p 65, Addison-Wesley Reading. Mass., 1963. Setinek, K., Pecev, N., Bazant, V., Collect. Czech. Chem. Commun., 33(5), 1451 (1968).
Received for reuieu: April 23, 1979 Accepted December 20, 1979
Measurements in a Commercial Catalytic Cracking Unit H. J. A. Schuurmans Koninklijke/Shell-Laboratorlum, Amsterdam, The Netherlands
An extensive series of tests has been carried out in a modern catalytic cracking unit. Especially the performance of the tall riser reactor was of interest. Useful correlations of riser cracking conversion and yield have been established. At the same time, indications have been found for possible further improvements. A better insight into the operation of the countercurrent baffled catalyst stripper has been obtained. Finally, measurements in the regenerator have yielded an entrainment correlation which seems to be generally applicable for a fluid bed of cracking catalyst.
Introduction A large number of measurements and tests have been carried out in a modern catalytic cracking unit (Figure 1). 0196-4305/80/1119-0267$01.00/0
This unit has a number of features not generally encountered in older plants: a long straight riser reactor, a baffled appendix-type countercurrent stripper, a non-swaged re@ 1980 American Chemical Society
