257
Ind. Eng. Chem. Process Des. Dev. 1980, 19, 257-263
catalyst from run NE4, after 7 h of operation, was used for run NE5. The spent oil from run NE11 was used for run NE15. Neither the half-order kinetics nor the rate constants were changed. There is no contradiction between our findings and previous papers which mentioned the deactivation of hydrodemetallation and hydrodesulfurization reactions by the deposition of coke and metals. The spent catalyst of run NE5 has less than 3.5% nickel and less than 3% carbon (not necessarily coke) deposited on the spent catalyst. The low metal and coke deposited on the catalyst is due to short operation hours and probably the absence of aromatic compounds in Nujol; it is not surprising that the rate of deactivation is not detectable. For run NE14, the portion of nickel in the spent catalyst that is xylene extractable amounts to 1.4 X wt 70 of dried catalyst. The amount of nickel by scanning electron X-ray microanalyzer is 1.75 w t 70of catalysts, which agrees well with the material balance calculation of 1.72 wt %. The spent catalyst analyzed by Galbraith (Knoxville, Tenn.) showed 1.71 wt % nickel by atomic absorption spectrophotometer, less than 2.51 % carbon, 0.87 % hydrogen, and 0.53% nitrogen. There should be little nickel porphyrin on the surface, since for Ni-Etio the weight ratio of Ni:C:H:N should be 1:6.54:0.55:0.95, while the catalyst showed a ratio of 1:1.46:0.51:0.31. (5) Comparison with Previous Work. Oleck and Sherry (1977) operated at an oil/catalyst ratio of 20, temperature of 398.9 " C , and pressure of 13888 kPa. Their second-order data can be converted to two parallel firstorder reactions with rate constants 26.9 and 3.84 g of oil/g of cat.-h. An extrapolation of our run NE11 gives a pseudo-first-order rate constant of 2933 g of oil/g of cat.-h, which is 100-800 tirnes greater than the values of Oleck and Sherry. This difference in activity can be due to a number of factors. Our system is clean, without sulfur and nitrogen compounds. Our nickel compounds are all porphyrins, without the more refractory asphaltene compounds. Our catalyst has not been presulfided. Our runs did not involve
a simultaneous presence of vanadium and nickel compounds. All these may contribute to the greater activity. Acknowledgment The authors are grateful to the National Science Foundation for support of the work under Grant No. ENG 75-16456. Literature Cited Albers, V. M., Knorr, H. V., J . Chem. Phys., 9, 497 (1941). Baker, E. W., Palmer, S. E., Chapter 11 of "The Porphyrins", Vol. I, D. Dolphin, Ed., Academic Press, New York, 1978. Bischoff, K. B., AIChE J., 11, 351 (1965). Chang, C. D., Silvestri, A. J., Ind. Eng. Chem. Process D e s . Dev., 15, 161 (1976). Chang, C. D., Silvestri, A. J., Ind. Eng. Chem. Process Des. Dev., 13, 315 (1974). Cukor, P. M., Prausnitz. J. M., J . Phys. Chem., 76, 598 (1972). Dorough, G. D., Huennekens, F. M., J . Am. Chem. SOC.,74, 3974 (1952). Edison, R. R., Siemssem, J. O., Masologites, G. P., OilGas J.. 20, 54 (1976). Fiero, G. W., Ann. Allergy, 23, 226 (1965). Fleischer, E. B., J . Am. Chem. SOC.,85, 146 (1963). Franks, A. J., Soap Perfum. Cosmet., 221 (Mar 1964); 319 (Apr 1964). Hambright, P., Howard University, private communication, 1978. Inoguchi, M., Kagaya, H., Daigo, K., Sakurada, S., Satomi, Y., Inaba, K..Tate, K., Nishiyama. R., Onishi, S., Nagai. T., Bull. Jpn. Pet. Inst., 13(2), 153 (197 1). Miller, J. R.. Dorough, G. D., J . Am. Chem. Soc., 74, 3977 (1952). Nelson, W. L., OilGas J . , 72 (Nov 15, 1976). Nelson, W. L., OilGas J . , 247 (Mar 2, 1977). Oleck, S. M., Sherry, H. S..Ind. Eng. Chem. Process Des. Dev., 16, 525 (1977). Peychai-Heiiing, G., Wilson, G. S., Anal. Chem., 43, 550 (1971). Prather. J. W., Ahangar, A. M., Pitts, W. S., Henley, J. P., Tarrer, A. R., Guin, J. A., Ind. Eng. Chem. Process Des. Dev., 16, 267 (1977). Riley, K. L., Am. Chem. SOC.Div. Pet. Chem. Prepr., 23(3), 1104 (1978). Satterfield, C. N., "Mass Transfer in Heteropeneous Catalysis". MIT Press, Cambridge Mass., 1970. Simnick, J. J., Lawson, C. C..Lin, H. M., Chao, K. C., AIChE J., 23, 469 (1977). Simnick, J. J., Liu, K. D., Lin, H. M., Chao, K. C.. Ind. Eng. Chem. Process Des. Dev.. 17. 204 (1978). Spry, J. C., Sawyer. W.'H., paper presented at 68th Annual AIChE Meeting, Nov 16-20, Los Angeles, Calif., 1975. Sugihara, J. M., Branthaver. J. F., Wu, G. Y., Weatherbee, C., Am. Chem. SOC. Div. Pet. Chem. Prepr., 15(2), C5 (1970). Whitiock, H. W., Jr., Hananer, R., Oester, M. Y., Bower, 9. K.. J . Am. Chem. Soc., 91, 7485 (1969). Yen, T. F., Chapter 1 of "The Role of Trace Metals in Petroleum", Yen, T. F., Ed., Ann Arbor Science, 1975.
Received for review April 20, 1979 Accepted November 29, 1979
The Kinetics of Porphyrin Hydrodemetallation. 2. Vanadyl Compounds Chi-Wen Hung and James Wel' Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02 139
The kinetics of hydrodemetallation (HDM) of vanadyl etioporphyrin (VO-Etio) have been studied in batch autoclave experiments, with white oil as solvent and Co03-Mo03/A120, as catalyst without presulfiding. The results showed that up to 90% vanadium removal the data can be described by fractional order kinetics. In comparison to nickel removal, vanadium removal has a larger activation energy and a smaller hydrogen pressure dependence. A few runs on mixed vanadyl and nickel etioporphyrins showed that while the presence of vanadyl compounds will suppress the nickel removal reaction, the reverse suppression is less significant. Finally, runs on free base etioporphyrin showed that free base porphyrins quickly disappear in the autoclave even before the injection of catalyst.
Introduction Both vanadium and nickel compounds are found in petroleum. With few exceptions, the concentration of vanadium is higher than that of nickel (Yen, 1975). In the previous literature, the kinetic order of hydrodemetallation for vanadium and nickel was found to be
the same (Oleck and Sherry, 1977; Chang and Silvestri, 1974, 1976; Riley, 1978). However, there are some differences in the demetallation behavior of vanadium and nickel compounds. (1)The rate constant for vanadium removal is always somewhat larger than that of nickel removal (Oleck and Sherry, 1977; Chang and Silvestri,
0196-4305/80/1119-0257$01.00/00 1980 American Chemical Society
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Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980 B
4
1
0
vo-
TPP
$
M W = 679.61 Car N 4 H 2 8 VO
9
Phenyl
VO
-
M W = 543.61 N4
-E!hyl -Methyl
H36 " O
Group Group
type)
N\ ,N
VO-Chlorir
I Etio
type)
Figure 2. Structure of vanadyl chlorin. Table I. Operating Conditions
Figure 1. Structure of VO-TPP and VO-Etio (I).
oil used
1974, 1976;Riley, 1978; Oxenreiter et al., 1972; Larson and Beuther, 1966; Beuther and Schmid, 1963). (2) The concentration profile of nickel deposited on the catalyst is often uniform, but the profile for vanadium has a "U" shape, with less deposited on the center and more on the edge (Sato et al., 1971; Audibert and Duhaut, 1970). (3) There is an axial gradient of the concentration profile of vanadium and nickel deposited on the catalyst along the trickle bed; the gradient is much steeper for vanadium than for nickel, so the ratio of Ni/V on catalyst increases from the entrance to the exit of the reactor (Sato et al., 1970). This paper, which is a continuation of a previous paper by Hung and Wei (1980), deals with the kinetics of hydrodemetallation of vanadyl etioporphyrin (I) and of a mixture of vanadyl etioporphyrin and nickel etioporphyrin.
catalyst
Experimental Section Details about equipment, catalyst, solvent, gas, and procedure can be found in the previous paper. Only a brief summary is given here. (1) Equipment. A 1-L autoclave (Autoclave Engineers, Erie, Pa., Model AFP 1005) was used as the reactor. (2) Materials Used. (a) Catalyst. Commercially available Co0-Mo03/A1203 catalyst from American Cyanamid (Bound Brook, N.J.) was used. All the catalysts were crushed into 0.074-0.088 mm size and were not presulfided. They were preheated at 440 "C for 24 h to remove water from the catalyst. (b) Solvent. White oil (Nujol) from Plough Inc. (Memphis, Tenn.) was used as the solvent. ( c ) Gas. Hydrogen was ultrahigh purity with less than 3 ppm O2 and contained at least 99.999% Hz. Helium was of 99.995% purity. Both were purchased from Matheson Gas Products (Gloucester, Mass.). (a) Model Metal Compounds. Both vanadyl tetraphenylporphine (VO-TPP)and vanadyl etioporphyrin (I) (VO-Etio) were purchased from Man-Win Coordination Chemicals (Washington, D.C.). The molecular structures of VO-TPP and VO-Etio are shown in Figure 1. Unlike nickel porphyrins, the vanadyl porphyrins have an oxygen atom connected to the vanadium. This oxygen is perpendicular to the planar structure of the remainder of the molecule. Most vanadium atoms in petroleum occur with a valence of +4 (nickel is +2), which exist almost exclusively as vanadyl ions, V02+(Saracen0 et al. 1961; Yen, 1977). While VO-Etio is available in a pure form, VO-TPP is reported to contain some vanadyl chlorin. The structures of vanadyl chlorins are shown in Figure 2.
C TPP
$J
Group
'
'32
H
Chlcrin
oilicatalyst hydrogen pressure temperature model compound impeller speed
-
420 g (-25 g in loader and 395 g in reactor)" 0.89 to 1.8 g (dry), CoO-MoO,/Al,O, or alumina, 0.074-0.088 m m 340-700 cm3/g 4237-11820 kPa 300-350 " C VO-Etio o r VO-TPP" 500 rpm
" Free base etioporphyrins were used in runs E l and E2, tetraphenylporphine was used in run T1,nickel etioporphyrin in run NE19. (3) Procedure. (a) Dissolving the Vanadyl Porphyrins in Nujol. The method of dissolving vanadyl porphyrins is the same as that of dissolving nickel porphyrins, described in the preceding paper. While vanadyl etioporphyrin appears to have similar solubility in Nujol to nickel porphyrins, vanadyl tetraphenylporphine is less soluble. We were unable to dissolve more than 20 ppm of vanadyl tetraphenylporphine in Nujol. (b) Demetallation Experiment. The procedures are the same as in the nickel porphyrin runs. The operating conditions are listed in Table I. (4) Analysis. All the equipment used for analysis is essentially the same as before. However, the wavelengths for the adsorption peaks in the visible range for vanadyl porphyrins are for VO-Etio: 407,534, and 571.5 nm; for VO-TPP: 423,508,548, and 583 nm. Free base porphyrins peaks are for Etio: 400,498.5, 530.5, 569, and 623.5 nm; for TPP: 418,514,548,590, and 646 nm. The spectra for VO-Etio and VO-TPP are shown in Figure 3, and the spectra for Etio and TPP are shown in Figure 4. Compared with nickel porphyrins, it is clear that all the major peaks for vanadyl porphyrins have shifted to longer wavelength, and the ratio of 571.51534 peaks for VO-Etio is smaller than the ratio of 553/517 peaks for Ni-Etio. This is due to the additional coordination of vanadyl porphyrins with oxygen (=O) to yield a pentacoordinate complex (Baker and Palmer, 1978). The spent catalysts were analyzed by scanning electron X-ray microanalyzer, with the same procedures as for nickel runs. Results Nine experiments were carried out with VO-Etio, three with VO-TPP, six with mixed VO-Etio and Ni-Etio, two with free base Etio, one with free base TPP, and one with Ni-Etio in a glass liner for comparison. A summary of the operating conditions for each run is given in Table 11.
Process Des. Dev., Vol. 19, No. 2, 1980
Ind. Eng. Chem.
t -
380
v 3 Et 0
II
571 5
420
460
503
12 -
620
O,/Aa
: 4
500
540
i n rn)
A'AVELEkGTH
0,
259
Vo T P P
r
08
0
>
2
3
-
5
T VE
,
6
3
-
32
420
460 500 540 580 WAVELENGT~ (nm)
8
Figure 5. Comparison of vanadium and nickel runs (runs VE8 and NE18) over alumina support. - - . 1c3
380
7
hr5
620
1
3
2 Ei
a
0
Rur
7
i E 5H
i ! - ' r i L l c -
FP
2
I.
3
su
Figure 3. Absorption spectra of VO-Etio (top) and VO-TPP (bottom). Samples were dissolved in Nujol first and then diluted by xylene; background, xylene.
I \
i i
4 c
4
530 5
c
i 330
420
46C
500
540
WAVELENGTH
580
620
660
nm)
i
i
380
420
460
500
WAVELENGTH
540
i rm
580
620
660
)
Figure 4. Absorption spectra of free base porphyrins: Etio (top) and T P P (bottom); all diluted by xylene.
(1) Experimental Results. (a) Vanadium (VO-Etio) Runs. Just as in previous nickel runs, the atomic absorption concentration was always higher than the visible spectrophotometer concentration during reaction. However, this difference for vanadium runs was not as large as in nickel runs. In the first 10 min after catalyst injection, there was also a transient period of rapid concentration decline of up to 10 ppm, which was larger than in nickel runs. When alumina replaced catalysts or helium replaced hydrogen, the oil/catalyst ratios for the two vanadium runs (VE8and VESH) were smaller than similar runs for nickel (NElGH, NT18H, and NE18), and the decline in concentration was 7.5 ppm/g of cat. for vanadium runs and only 1.4 ppm/g for nickel runs. This suggests that the adsorption of vanadyl porphyrins is stronger than the adsorption of nickel
d
~
;
l
i
3
.
:
5
6
-
e
s
fr-,
Figure 6. Comparison of vanadium and nickel runs (runs VESH, NElGH, and NT18H) under helium pressure.
porphyrins on either alumina or Co0-MnO,/A1,O3 catalyst. Figure 5 shows the comparison between Ni-Etio and the higher activity VO-Etio runs over alumina. Figure 6 shows the comparison between Ni-Etio, Ni-TPP, and VO-Etio runs under helium pressure. It is clear from the figures that the initial drop of the concentration was very large for vanadium runs and insignificant for nickel runs. (b) Mixed Vanadium and Nickel (VO-Etio and Ni-Etio) Runs. In the first 15 min after injection of catalyst, the decline of vanadium concentrations is 2.5 to 9 times greater than the decline of nickel concentrations, depending on the initial metal concentrations. This shows that vanadyl porphyrins have stronger affinity to the catalyst than nickel porphyrins. While the vanadium removal rate in the mixed run was the same as individual vanadium runs, the initial nickel removal rate was suppressed by the presence of vanadium compounds, until the concentration of vanadium in the bulk was less than 4 ppm. Figure 7 shows the half-order plot of run NVE5, where the fast reaction region for nickel had 60% of the reaction rate of the individual nickel run, and the slow reaction region for nickel had 16% of the rate of individual run. The reaction rate for vanadium had 93% of the rate of the individual vanadium run. By changing the ratio of initial concentration of VO-Etio to Ni-Etio from 1:l (Run NVE5) to 1:3 (Run NVE3), the suppression effect of vanadium on nickel was minimized. While the vanadium rate remained the same, the slow reaction region for nickel in run NVE3 had 52% of the rate of individual nickel run, and the fast reaction region had 85%. (See Figure 8.) Figure 9 shows the visible spectra of run NVE2 before and 1.6 h after the injection of catalyst, which clearly shows
260
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
Table 11. Operating Conditions for Each Run”
run no.
init concn of total Va or Ni, PPm
catalyst
VE 1 VE2 VE3 VE4 VE5 VE6 VE7 VE8 VE9H VT 1 VT2 VT3 NVEl
CoO-MoO,/Al, 0 , coO - M ~o j ~ io; CoO-MoO,/Al,O, CO0-MOO ,/Ala0 , CO0-MOO ,/Ala0 , CO 0-MOO ,/A120, Co 0-MOO JA12 0 , alumina CO0-Mo 0 /Ala0 , CO0-MOO,/ A1,O , CoO-MoO,/Al, 0, Co 0-MOO ,/Al, 0, COO-Mo 0,/Ala0 ,
NVE2
CoO-MoO,/Al, 0,
NVE3
CoO-MoO,/Al,O,
NVE4
CO0-MOO /Al, 0 ,
NVE5
COO-MoO,/Al, 0
NVE6
CoO-MoO,/Al,O,
El E2 (5)“ T1 (5)a NE19 (5)”
CO0-Mo O,/ Al, 0, Co 0-MOO ,/A1,0, Co 0-Mo 0 ,/ Al,O Co 0-Mo 0,/Ala0,
V: Ni: V: Ni: V: Ni: V: Ni: V: Ni: V: Ni:
40.5 31.9 29.4 27.6 31.5 19.3 20.0 28.5 22.5 14.7 11.0 15.5 19.5 15.5 18.4 16.3 8.7 25.2 19.6 19.9 30.9 26.9 30.8 14.1 451 (6)” 451 (6)“ 366 (6)’ 29.3
cat. quantity, g
oil quantity, g
temp, “ C
0.89 1.71 0.89 1.30 0.90 1.11 1.08 1.31 1.17 0.84 1.18 0.91 0.91
426.4 420.0 422.5 424.4 423.6 425.0 419.6 425.6 426.3 427.5 427.2 414 427.1
315.5 299.1 348.8 315.7 315.1 315.8 332.5 344.3 343.7 332.2 317.1 316.5 316.1
6995 6995 6995 4237 11820 9152 6995 6995 6995 6995 699 5 6995 699 5
11.6 3.0 13.6 6.4 6.25 2.9 7.0 7.0 0.65 0.95 2.2 9.2
0.89
424.7
342.8
6995
3.85
0.89
422.7
343.4
6995
3.1
1.79
424.0
315.7
6395
8.5
0.91
439.3
343.4
6995
6
0.91
436.7
343.4
6995
5.25
0.88 0.88 0.89 0.43
432.4 -- 2293 73
316.2 315.8 313.7 340.7
6995 6995 6995 6995
7.5 8.7 4.1 2.8
-183
pressure, duration of kPa reaction, h 10.0
a (1)In the run number such as “VESH”, “V” represents vanadium, “ N ” represents nickel, “E” for Etio, “T” for TPP; the digits “9” represent run number, “H” for those runs under helium pressure, nothing for runs under hydrogen pressure. (2) The catalyst was fresh and the size was 0.074-0.088 m m in diameter. ( 3 ) For catalytic runs, time zero was the time catalyst was injected. (4) Initial concentration was the concentration of sample collected at reaction temperature before catalyst was injected. (5) Runs E2, T1, and NE19 were made in a glass liner t o avoid contact with stainless steel wall. (6) For runs E l , E2, and T1, the initial concentrations are the concentrations of free base porphyrins.
Olotol V o n o d i u m
FCzPPM
0
2
3
ME ‘ h r s )
Figure 8. Half-order plot for mixed VO-Etio and Ni-Etio run (run NVES). 0
1
2
3
4
5
6
TIME ( h r s )
Figure 7. Half-order plot for mixed VO-Etio and Ni-Etio run (run NVE5).
that the ratio of VO-Etio peaks (407 and 571.5 nm) to Ni-Etio peaks (391 and 553 nm) decreased during the reaction. (c) Free Base Porphyrin Runs. Run E l followed the procedures of previous metalloporphyrin runs. Even before injection of catalyst, all the etioporphyrins disappeared. Both the atomic absorption spectrophotometer
and the visible spectrophotometer showed the formation of 12 ppm of Ni-Etio. After injection of catalyst, this newly formed Ni-Etio also demetallized, but with slower rates than previous typical Ni-Etio runs. Possibly some compounds formed from the free base porphyrins suppressed the demetallation reaction of Ni-Etio. It is likely that the nickel came from the 316 stainless steel wall, normally containing about 10-14% nickel (Clark and Varney, 1962). Run E2 placed the metal dissolving oil in a glass liner to minimize the contact of solution with the stainless steel wall; the reactor was also heated in maximum speed to shorten the period of heating. By doing this, no nickel was
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
Run b E 3
5 Toto
, I
v o n ~ d # ~ n
b r O - E r
261
0
,
i
4
i
3
T C=PPM
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2
1
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1
T '-IC
I
I
2
3
I
i hri)
Figure 10. Half-order plot for VO-Etio run (run VE3). '^.
4
3
.IL7
490 530 570 \+ALELLNGTH nm 1
610
found before injection of catalyst. The first sample collected 18 min after injection of the catalyst showed no evidence of either free base porphyrins by the visible spectrophotometer, nor nickel by the atomic absorption spectrophotometer. However, the visible spectrophotometer picked up Ni-Etio peaks which should be equivalent to 19 ppm of Ni-Etio: these "Ni-Etio" peaks were believed to be in reality Co-Etio peaks, which are very similar in the visible range (Hambright, 1978). The same oil sample was analyzed by Galbraith (Knoxville, Tenn.), and found to contain 15 ppm of' cobalt. These Co-Etio peaks eventually disappeared from solution as the reactions went on. Run T1 with tetraphenylporphine in a glass liner gave results similar to those of run E2. In order to eliminate the wall effect on the typical nickel and vanadium runs, Run NE19 with Ni-Etio in a glass liner was made and the result showed that both the activity and the kinetics were similar to previous runs at the same conditions (NE3 and NE14). Furthermore, no cobalt was found in the oil for either vanadium or nickel runs, and no nickel was found in the oil for vanadium runs. (2) Kinetic Order. The kinetics of VO-Etio runs followed fractional order kinetics a t up to 90% conversion. Figure 10 shows the half-order plot of run VE3. The correlation coefficients of half-order kinetic order for all the seven NO-Etio runs were above 0.9970 and the scatter of data was random, ,so no attempt was made to find the best fit kinetic order as the function of temperature or pressure. The temperature and pressure dependence of kinetics is expressed in terms of the half-order rate constants. The Arrhenius plot at 6995 kPa is shown in Figure 11. VO-Etio demetallation has an activation energy of 37.1 kcal/g-mol for total vanadium removal and 35.8 kcal/g-mol for VOEtio disappearance. It can also be seen from Figure 11that the difference between the two rate constants is very small. Total vanadium removal rate constants should not be greater than the VO-Etio disappearance constants for some of the runs (VE3 and VE7) and may be due to experimental errors.
\\\ E . 3 7 1 4 2 coliq-mole
Figure 9. Absorption spectra of mixed VO-Etio and Ni-Etio run (run NVEZ): top, fresh sample; bottom, sample collected 1.6 h after injection of catalyst. All were diluted by xylene.
71
-t
lr h
,
,
'6
165 IT
O K
nlC0C
17
175
E
165 1
7
75
1 'K x C-7
Figure 11. Effect of temperature on half-order rate constants for VO-Etio runs: left, total vanadium removal; right, VO-Etio disappearance rate; k = ( p p m ) ' k m 3 of oil/g of cat. h; P = 6995 kPa.
Figure 12. Pressure dependence of half-order rate constants: k = (ppm)'"%m3 of oil/g of cat. h; P in kPa, T , 316 "C.
The pressure dependence for half-order rate constants for VO-Etio runs at 316 OC is given in Figure 12. The result shows that the order of dependence is about 1.2, which is smaller than the 1.5 power for Ni-Etio. No demetallation reaction was detected under helium pressure (See Figure 6). The results on VO-TPP runs are not satisfactory. (a) We were unable to prepare sufficiently high solution concentrations of VO-TPP for use. Starting from such low initial concentrations the sensitivities of analytical equipment are insufficient to obtain accurate kinetic data. (b) Three runs of VO-TPP a t low initial concentration
262
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
410
450
490
530
WAVELENGTH
Figure 13. Scanning electron X-ray microanalyzer indication of vanadium distribution: right, run VE3, w t % of vanadium an catalyst is 1.41% (280x1; left, run VTI, w t % of vanadium on catalyst is 0.60% (ZOOX).
(10-15 ppm) showed that the observed rates were at least seven times faster than that of VO-Etio at identical conditions. Diffusion limitation would occur, so we would not obtain intrinsic (diffusion free) kinetic data. (3) Catalyst Effect. When alumina was used alone for VO-Etio, some demetallation reaction also occured. (See Figure 5.) However, the rate constant was only 8% of a typical CoO-MoO3/AI2O, run at identical conditions. Discussion ( 1 ) Diffusion Effect. VO-Etio runs showed no diffusion effects in the operating range. However, VO-TPP runs showed some diffusion limitation. (a) For VO-TPP runs, the initial concentration was too low for accurate kinetic data. However, run VT3 took only of the time for Ni-TPP to reach complete conversion at identical operating conditions. (b) A scanning electron X-ray microanalyzer was used to find the concentration profile of vanadium deposited on the spent catalyst. The concentration of vanadium was represented by the brightness of the spots. In Figure 13, the photo on the right shows the concentration profile of vanadium for VO-Etio run VE3, and the left shows the concentration profile of vanadium for VO-TPP run VT1. While the concentration profile for the VO-Etio run is quite uniform, there is a slight concentration gradient for the VO-TPP run. (2) Intermediates and Products. As in the nickel runs, there is evidence of the existence of intermediates for vanadyl runs. (a) The concentration difference between total vanadium and vanadyl porphyrins increased to a maximum and then decreased during reaction. (h) The color of the sample collected changed from red to reddish violet for VO-Etio runs and from reddish brown to green and finally to light yellow for VO-TPP runs during catalytic reaction. The absorption spectra of the samples collected during reaction showed the presence of a new peak at 631 nm for VO-Etio runs and a new peak at 632 nm with a minor shoulder at 592 nm for VO-TPP runs. The spectra are shown in Figure 14 for runs VE3 and VT1. Corresponding to the 616-nm peak in Ni-TPP or Ni-Etio runs, the 631-nm peak for VO-Etio runs and the 632-nm peak for VO-TPP runs possibly belong to vanadyl chlorin. The structures ofboth Etio and TPP type vanadyl chlorin are given in Figure 2. Free base porphyrins were not found for the samples collected during vanadyl porphyrin runs. A few runs on free base porphyrins (runs E l , E2, and TI) showed that the free base porphyrins are very unstable in the presence of metal sources (either nickel from the stainless steel wall or cobalt from the CoO-MoO3/AI2O3catalyst). Neither nickel porphyrins nor cobalt porphyrins were found in the vanadyl porphyrins runs. The free base porphyrin rings
I
I
,
I
410
450
490
530
610
650
,
,
I
590
610
650
590
("rn)
{nm) Figure 14. Absorption spectra of VO-Etio and VO-TPP m during reaction: top, run VE3 collected at 0.6 h reaction time; diluted by xylene and with xylene as background; bottom, run VT1 collected at 0.2 h reaction time; without dilution, with Nujol as background. WAVELENGTH
would either form cobalt porphyrins or crack rapidly to other organic species. In runs E l , E2, and T1, less than 25% of free base porphyrins formed metalloporphyrins (either Co or Ni), and more than 75% just disappeared. (3) Vanadium Deposition on Spent Catalyst. The kinetics and activity of VO-Etio runs are close to that of Ni-Etio or Ni-TPP runs. The rate of deactivation is not significant in the vanadyl porphyrin runs. The deposition of vanadium, carbon, nitrogen, and hydrogen on the spent catalyst were similar to that of nickel runs. For run VE3, the xylene extractable portion of vanadium was 1.4 X 10" wt % of dried catalyst. The amount of vanadium was 1.35 wt % by scanning electron X-ray microanalyzer and was 1.22 w t % at Galhraith (Knoxville,Tenn.); all of these are close to the theoretical mass balance calculation of 1.39 wt %. The results from Galbraith also showed 2.78% carbon, 0.94% hydrogen, and 0.48% nitrogen. For VOEtio, the weight ratio of V C H N are 1:7.540.631.1. As the catalyst analysis ratios were 1:2:0.68:0.35 instead, no more than 1/3 of all the vanadium deposited on the catalyst can be VO-Etio. In run VE8, the amount of xylene extractable vanadium was 0.27 wt % of dried catalyst. This is similar to the 0.33 w t % of vanadium lost in the transient period. In run VESH, the amount of vanadium that was xylene extractable was 0.31 wt % of dried catalyst. This is again similar to the 0.34 w t % of vanadium lost in the transient period. The observations from these runs suggest that the concentration decline in the transient period was due to reversible adsorption of metalloporphyrins on catalysts. (4) Comparison between Vanadium and Nickel Runs. As we have no kinetic data for VO-TPP runs, only the VO-Etio runs are used to compare with nickel runs. (a) In the Ni-Etio and VO-Etio runs, the reaction rates for VO-Etio were slower than Ni-Etio at 316 O C and 6995 Wa. However, VO-Etio has a higher activation energy and higher activity than Ni-Etio at higher temperatures. This
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 et al., 1979) it was shown that the interconversion of xylenes 0 1980 American
Chemical Society
