Ind. Eng. Chem. Res 1988,27, 2241-2246
2241
Acknowledgment
Literature Cited
This work was supported by the National Science Council of Taiwan ROC under Grant NSC76-0402-E03301.
Alvarez-Fuster, C.; Midoux, N.; Laurent, A.; Charpentier, J. C. Chem. Eng. Sci. 1980, 35, 1717. Astarita, G.; Bisio, A.; Savage, D. W. Gas Treating with Chemical Solvents; Wiley-Interscience: New York, 1983. Blanc, C.; Demarais, G. Znt. Chem. Eng. 1984, 24, 43. Blauwhoff, P. M. M.; Versteeg, G. F.; Van Swaaij, W. P. M. Chem. Eng. Sci. 1984, 39, 207. Chakraborty, A. K.; Astarita, G.; Bischoff, K. B. Chem. Eng. Sci. 1986, 41, 997. Charpentier, C. J. Adv. Chem. Eng. 1981, 11, 1. Danckwerts, P. V. Gas-Liquid Reactions;McGraw-Hill: New York, 1970. Danckwerts, P. V.; Shwma, M. M. Chem. Eng. 1966, 10, CE244. Goldstein, A. M.; Brown, E. C.; Heinzelmann, F. J.; Say, G. R. Energy Prog. 1986, 6, 67. Hikita, H.; Asai, S.; Katsu, Y.; Ikuno, S. AIChE J . 1979, 25, 793. Kim, C. J.; Savage, D. W. Chem. Eng. Sci. 1987,42, 1481. Laddha, S. S.; Diaz, J. M.; Danckwerts, P. V. Chem. Eng. Sci. 1981, 36, 228. Nijsing, R. A. T. 0.;Hendriksz, R. H.; Kramers, H. Chem. Eng. Sci. 1959, 10, 88. Sada, E.; Kumazama, H.; Butt, M. A. J . Chem. Eng. Data 1977,22, 277. Sada, E.; Kumazawa, H.; Butt, M. A. J . Chem. Eng. Data 1978,23,
Nomenclature AMP = 2-amino-2-methyl-1-propanol DEA = diethanolamine DGA = diglycolamine DIPA = di-2-propanolamine MDEA = methyldiethanolamine MEA = monoethanolamine TEA = triethanolamine CA* = dissolved gas concentration in equilibrium at the gas-liquid interface, kmol/m3 CB = amine concentration, kmol/m3 DA = diffusion coefficient of gas in liquid, m2/s DB = diffusion coefficient of reactant in liquid, mz/s d = wetted wall column diameter, m E = enhancement factor g = gravitational acceleration, m/sz Ha = Hatta number HA = Henry's law constant, (kPa.m3)/kmol h = wetted wall column height, m k,, = reaction rate constant, m3"/(kmol%) kc = gas-phase mass-transfer coefficient, kmol/ (m2.s.kPa) kL = liquid-phase mass-transfer coefficient, m/s L = liquid flow rate, m3/s NA= specific absorption rate, kmol/(m2-s) PA, pAi= C 0 2partial pressure; partial pressure at interface, kPa r = reaction rate, kmol/(m3-s) t , = contact time, s Greek Symbols = liquid viscosity, Paes
p p
= liquid density, kg/m3 Registry No. AMP, 124-68-5; N20, 10024-97-2; COz, 124-38-9.
161.
Sartori, G. US Patent 4 112 052, Sept 5, 1978. Sartori, G.; Leder, F. US Patent 4 112 050, Sept 5, 1978. Sartori, G.; Savage, D. W. US Patent 4094957, June 13, 1978. Sartori, G.; Savage, D. W. Znd. Eng. Chem. Fundam. 1983,22, 239. Savage, D. W.; Kim, C. J. AZChE J. 1985, 31, 296. Savage, D. W.; Sartori, G.; Astarita, G. Faraday Discuss. Chem. SOC. 1984, 77, 17.
Say, G. R.; Heinzelmann, F. J.; Iyengar, J. N.; Savage, D. W.; Bisio, A.; Sartori, G. Chem. Eng. Prog. 1984, 72. Sharma, M. M. Trans. Faraday SOC.1965, 61, 681. Versteeg, G. F.; Blauwhoff, P. M. M.: Van Swaaii. W. P. M. Chem. Eng.Sci. 1987, 42, 1103: Zioudas, A. P.; Dadach, Z. Chem. Eng. Sci. 1986, 41, 405.
Received for review January 21, 1988 Revised manuscript received May 16, 1988 Accepted June 3, 1988
Action of Activated Coke as a Catalyst: Oxydehydrogenation of Ethylbenzene to Styrene Luis E. Cadus,* Luis A. Arrua, Osvaldo F. Gorriz, and Juan B. Rivarola Znstituto de Znuestigaciones en Tecnologia Quimica, INTEQUI, Casilla de Correo 290, 5700 San Luis, Argentina
Oxidative dehydrogenation of ethylbenzene to styrene has been carried out in an isothermal integral reactor on several samples of alumina having different superficial acidities. Variations in the acidity were achieved by doping of the alumipa with sodium and were measured by temperature-programmed desorption (TPD)of ammonia. An active catalytic coke was formed on the alumina during reaction. In order t o determine the degree of condensation, crystallinity, and characteristics of the functional groups responsible for the catalytic activity of the active coke, analyses were conducted by oxidation at programmed temperature (TPO), X-ray transmission, and electronic paramagnetic resonance (EPR). Changes in the C/H/O ratio of the coke, estimated by quantitative organic analysis, produce changes in the catalytic activity and in the styrene yield. The evidence of the presence of oxygenated species in the coke and the participation of this oxygen in oxidative dehydrogenation suggested a redox-type reaction mechanism. The first works reported on catalytic activity of carbonaceous species dealt with the catalytic possibilities of pyropolymers in dehydrogenation (Manassen and Khalif, 1969; Gallard et al., 1963; Gallard-Nechtschein et al., 1963; Dawars et al., 1963) and oxydehydrogenation (Manassen and Wallach, 1965). Further on, dehydrogenation of pa-
raffins, olefins, and alkyl-substituted aromatics (Roth and Schaefer, 1966, 1969; Berger and Roth, 1968 was thoroughly studied. In these reports, the catalytic carbonaceous species did not contain oxygen and were obtained from pyrolysis of a variety of hydrocarbons on the surface of activated alumina. Afterwards, research was performed
0888-5885/88/2627-2241$01.50/00 1988 American Chemical Society
2242 Ind. Eng. Chem. Res., Vol. 27, No. 12, 1988
on oxygenated carbonaceous species (Iwasawa et al., 1972, 1973), using pyrolyzed polynaphthoquinone for dehydrogenation of formic acid, alcohols, cyclohexane, ammonia, and ethylbenzene. In ethylbenzene dehydrogenation (Iwasawa et al., 19731, no hydrogen was detected at the system outlet, but a considerable loss of activity was evident as on-stream time progressed. The activity was recovered by regeneration with oxygen. This would suggest an oxydehydrogenation reaction with the participation of the coke oxygen to yield water as a byproduct, with the subsequent deactivation that is reverted by reoxidation with air. Several attempts have been made a t obtaining styrene by a process that might advantageously replace the traditional direct dehydrogenation of ethylbenzene. Oxydehydrogenation has been the most often studied alternative. Several types of catalysts have been reported, most of them being metallic oxides and metallic phosphates (Alkhazov et al., 1972, 1978; Rennard, 1973; Cortes and Seoane, 1974; Tagawa et al., 1982). With regard to the formation of carbonaceous deposits and their catalytic activity in oxydehydrogenation, the information is more scarce than for the direct dehydrogenation reaction. Alkhazov and Lisovskii (1976) considered, in principle, that the formation of styrene by oxydehydrogenation was achieved simultaneously on both the coke and the alumina. This approach was then questioned by Fiedorow et al. (1978), who held that the alumina only provides the coke forming centers, the coke providing the active centers for oxydehydrogenation. Similar conclusions were drawn by Lisovskii et al. (1978), using a pulse reactor. They did not detect production of either styrene or carbon dioxide after injecting the first pulses or ethylbenzene. But they did detect such products in the subsequent pulses after the appearance of coke centers on the alumina surface. The presence of oxygen in the carbonaceous deposit and its influence on the latter’s activity were studied by Alkhazov et al. (19771, who used SO2 as the oxidation agent instead of air and obtained a coke having a different composition, with scarce activity in ethylbenzene oxydehydrogenation. More recently (Fiedorow et al., 1981), alumina acidity has been evaluated by means of test reactions, comparing the information obtained from these tests with coke catalytic activity for oxydehydrogenation of ethylbenzene to styrene. Finally, in Emig and Hofmann (1983),the chemical nature and catalytic activity of a coke formed in zirconium phosphate have been studied. Superficial acidity did not show any effect on the nature of the active carbonaceous species. This paper is the result of having investigated the effect of superficial acidity on the final texture of the catalyst, on the degree of condensation of the carbonaceous species formed, and on their catalytic properties. The study included the influence of the type of hydrocarbon used to form the carbonaceous species on the latter’s catalytic properties. Finally, a possible reaction mechanism has been put forward.
Experimental Section Four samples of alumina, each having a different superficial acidity, were prepared by doping a commercial alumina with variable amounts of sodium. Pines and Haag (1960) noticed that amounts as small as 0.2-2.0% sodium were sufficient to nullify the strong acidic sites present in alumina. The alumina used in our experiments was ALCOA F110, precalcined at 773 K for 3 h in the presence of air and then dipped into an aqueous solution of NaOAc for 1 day at room temperature. The content of NaOAc in the aqueous solution was varied in each case. The re-
sultant A1203was dried at 393 K for 1 day and calcined at 773 K for 3 h in the presence of air. The pure and doped aluminas were labeled 118A, 100A, 97A, and 79A, respectively, as a function of its acidities. The investigation of the BET surface as well as pore volume distribution has been performed by N2 low-temperature adsorption measurements. The acidity of the catalyst has been investigated by TPD of NH, in the DTG equipment. The carbon deposit of the A1203was determined by removing the catalyst from the reactor, burning off the carbon, and quantitatively determining the amounts of CO/C02. The catalytic activities of the four aluminas for oxydehydrogenation of ethylbenzene to styrene were measured in an isothermal integral reactor (length of the catalyst packing, 30 mm; diameter, 24 mm; particle diameter, 1 mm), operated at atmospheric pressure. Conversion of ethylbenzene was calculated on the basis of ethylbenzene feed. The standardized reaction conditions were 10.0 g of catalyst, 718 K, residence time of 10 (g.s)/cm3, and an ethylbenzene-to-oxygenfeed ratio of 1:l (Arriia, 1985). The liquid products were collected by traps cooled with ice and dry ice and were analyzed by gas chromatography with a 1.5-m PEG column and a 1-m DOP column at 383 K. To prevent possible condensation, all connecting gas lines and the sample valves were wrapped with heating tape. The gaseous products were analyzed instead by gas chromatography with a 1-m Porapak Q column and a 1.8-m activated carbon column at room temperature. ESR measurements of the coke catalysts were obtained at room temperature at a Klystron frequency of 9.7 GHz and a magnetic field modulation of 100 kHz. An ultramarine sample with spin concentration of 1 X 1015was used as a standard for estimating the concentration of unpaired electrons in a catalyst sample. To clarify the chemical nature of the coke, a quantitative organic C/H/O analysis was carried out for the coke (depending on the on-stream time and on the acidity of the alumina on which it was formed). In order to establish the degree of condensation of the coke as well as its crystallinity, a TPO and X-ray diffraction analyses were conducted.
Results and Discussion The catalytically active carbonaceous species is produced under the operating conditions set up for the above-mentioned test reaction. In what follows, this carbonaceous material will be called coke. The alumina, which when fresh is white, turns rapidly into black, thus evidencing the formation of active coke. The increase in the level of the carbonaceous deposit is accompanied by a similar increase in styrene selectivity and a decrease in the BET surface. It is important to remark that the carbonaceous deposit reaches its maximum value after a 10-h on-stream period and then becomes stable at between 9 and 11 wt % coke, depending on the alumina superficial acidity. Styrene selectivity reaches its maximum level at the same time. Whereas in the works reported for dehydrogenation there is a decrease in the catalytic activity as on-stream time progresses, in this work ethylbenzene conversion does not decrease with on-stream time after having reached the highest level but remains constant for more than 400 h of operation. Figure 1shows conversion, selectivity, and coke weight percent in relation to on-stream time for sample 118A. Even though similar coke accumulation results have been reported on alumina (Berger and Roth, 1968), they referred to the direct dehydrogenation reaction, where coke formation was achieved in the absence of oxygen. In the reports mentioned above on oxidative dehydrogenation on metallic oxids and phosphates, no carbonaceous deposits
Ind. Eng. Chem. Res., Vol. 27, No. 12, 1988 2243 XI SI
Air(
0
10
A
20
30
LO time on s t r e a m l h l
Figure 1. Conversion, selectivity, and coke content of 118A as a function of time on stream.
D 118A
l00A
I 0080
0
97A
+
79A
1 0120
0 100 m E q 01 NU1
Figure 2. Conversion, selectivity, and carbon content as a function of the acid surface potential for 50 h on stream.
were observed on the catalysts. This would suggest that the mentioned catalysts caused total combustion of the nondesorbed species to COz,thus preventing the formation of coke. This assumption is based on the results obtained by utilization of steam as diluent, which causes an increase in selectivity because it facilitates desorption of styrene (Murakami et al., 1981). On the other hand, it is highly significant that a similar behavior to the one shown in Figure 1should have been reported (Roth et al., 1969) for direct dehydrogenation of paraffins by a Mo catalyst on alumina. It might be assumed that the coke formed on the Mo-A1203 is responsible for the catalytic activity. Figure 2 shows that the higher the alumina acidity and the lower the sodium content, the higher the percentage of coke deposited and the total conversion of ethylbenzene, which goes from 47.3% on the least acid alumina to 68.5% on the most acid one. On the other hand, styrene selectivity shows a slight variation in the range of acidity studied. It goes from 51.3% for the least acid alumina to 53% for the most acid one. This would indicate that both coke deposition and conversion directly depend on the total acidity of the fresh alumina, which is determined by the cumulative value of the NH3 desorbed in the TPD experiments whose results are shown in Figure 3. The
Temperature, OC
Figure 3. NH3 desorption curves obtained from a TPD, for the different catalysts used.
amounts desorbed at 250 "C or at lower temperatures are similar for all the samples.
Nature and Characterization of the Coke Figure 4 shows a thermogram obtained by TPO of the coke deposited on the most acid alumina (118A). It indicates a considerable degree of condensation of the carbonaceous species, in view of the high temperature a t which the maximum in AT/ W is achieved. Because the reaction proceeds at a temperature lower than that maximum in AT/ W, there is coke accumulation until dynamic equilibrium is reached. In order to determine the chemical nature of the coke deposited on the alumina, an elementary C / H / O quantitative organic analysis was conducted. Its results together with those of total acidity and coke percentage are listed in Table I for the various catalysts with a 30-h on-stream time. The values in Table I suggest that the alumina acidity has a considerable effect on the degree of condensation of
2244 Ind. Eng. Chem. Res., Vol. 27, No. 12, 1988 Table 1. Chemical Composition of Coke Deposits composition, wt % H 0
catalyst
mequiv of NH3/g
coke content, wt %
C
!18A 100.4 97A 79.4
0.118 0.100 0.097 0.079
12.7 11.4 11.0 9.9
61.5 64.1 63.7 65.8
-
1
m
6.5 7.6 10.6 11.4
C / H ratio
32.0 28.3 26.6 25.1
0.80 0.76 0.50 0.48
C/O ratio wt % O/wt % coke 2.57 3.27 3.20 3.49
2.5 2.5 2.4 2.5
Pl
k %
2
'
2
10
3:
70
50 t,me
0"
93 s t r e o m imsn
Figure 5. Sty/Etb ratio in the reactor exit versus time on stream for (1) coke from ethylbenzene and (2) coke from n-hexane.
103
200
300
LOC
500
600
Temperature T
Figure 4. Thermogram by thermal programmed oxidation (TPO) of 118A coke performed on DTA equipment at a 20 "C/min heating rate.
the coke, shown by the C/H ratio. The degree of condensation and the oxygen content increase as the total acidity of the alumina increases. Thus, the mild acidic sites yield a coke having a lower degree of condensation and more hydrogen than the strong acidic sites, which tend to form a highly condensed coke that is richer in oxygen. This agrees with the results obtained by X-ray diffraction that show an increasing degree of crystallinity as the acidity of the alumina on which the coke was formed increases. According to what has been mentioned, the variation of activity can be explained in relation to the alumina acidity. This is shown in Figure 2. In order to determine whether the oxygen in the coke has any part in the oxidative dehydrogenation reaction of ethylbenzene to styrene through a redox mechanism or such a reaction takes place with O2 adsorbed from the gaseous phase, experiments were carried out feeding ethylbenzene in the absence of oxygen. Equivalent amounts of two cokes obtained by oxidation of ethylbenzene (118A) and of n-hexane on the most acid alumina and also on the fresh alumina without coke were tested. In all cases, the surfaces were previously cleaned with a N2stream at 470 "C for 12 h. The results shown in Figure 5 indicate the styrene/ethylbenzene ratio at the reaction outlet in relation to on-stream time. Both cokes initially yield considerable amounts of styrene which rapidly decrease as the coke is reduced. Coke 118A obtained from ethylbenzene oxidation shows a much higher activity. On the other hand, no styrene formation was detected when using fresh alumina. This study was supplemented by ESR on the fresh carrier and on the coke identified as 118A. Determinations
O LO
lime on s l r e ~ mI h l
Figure 6. Coke content and spin concentrations of 118A as a function of time on stream.
were made at various ethylbenzene oxidative dehydrogenation reaction times and at two different oxidation states of the coke. Whereas the fresh alumina did not show any ESR, the cokes in all cases showed a stable signal corresponding to the presence of a free radical with a gyromagnetic factor g = 2.0033. The results summarized in Figure 6 show a very low relative concentration of spins after the first 3 h on stream, followed by an abrupt increase by the 10th hour and a very milk increase from this point. This would account for the stability of the conversion curve after 15 h of run, in spite of the fact that the magnitude of the carbonaceous deposit continued to increase until approximately 30 h of operation had elapsed. On the other hand, a sample partially reduced by ethylbenzene/N2 in the absence of oxygen was analyzed. It corresponds to 15 min of operation in curve 1 of Figure 5, which shows a considerable decrease in the spin concentration ( Z /m = 0.9 spin/mg) in relation to the sample of time t = 0. With regard to the free radicals present in the coke, Collins et al. (1959) have suggested that electronegative groups, particularly quinone-type oxygen, have an important part in coke stabilization. This can be observed
Ind. Eng. Chem. Res,, Vol. 27, No. 12, 1988 2245
02
,
Coke
pore diameter I A )
HC=CH2
Figure 7. Reaction mechanism proposed for the oxydehydrogenation of ethylbenzene. Table 11. Properties of Catalysts Used in This Study catalyst specific surface, m2/g pore vol, mL/g 118A (fresh) 192.5 0.194 118A (7 h) 0.177 134.6 0.172 118A (10 h) 131.2 0.165 118A (30 h) 125.8 86.7 0.122 118A (50 h) 90.1 lOOA (50 h) 0.146 0.138 97A (50 h) 103.0
by ESR measurements. Thus, the ESR results and those shown in Figure 5 suggest the existence of a redox process during ethylbenzene oxidative dehydrogenation with participation of oxygen linked to the coke structure. This is shown in Figure 7. Texture analysis of the various catalysts characterized by their BET surface and pore volume distribution can be seen in Figure 8. Figure Sa shows the change in pore structure with the increase of coke on the alumina. As the on-stream time increases, there are few changes in the maximum of the radius of the small pores and the number of large pores decreases. After a relatively long on-stream time, only the 10-20-A-diameter pores prevail. The BET surfaces corresponding to the various on-stream times are listed in Table 11. Figure 8b shows pore volume distribution for the various samples, after 50 h of operation. The results shown indicate that, regardless of the alumina surface acidity, an identical pore volume distribution is obtained after the coke has been formed, the maximum diameter being 16 A. This suggest that the superficial acidity only affects the amount of coke deposited on the alumina and its degree of condensation.
Conclusions The results obtained suggest that the true catalyst participating in the oxidative dehydrogenation of ethylbenzene to styrene is the coke formed on the alumina, the latter being only a promotor of the carbonaceous species. The coke stability observed by ESR measurements and the oxygen content of the coke suggest the existence of a species having electronegative groups, perhaps quinoidtype oxygen. Thus, the reaction might occur by means of a redox-type mechanism. Depending on the acidity of the alumina used, the catalytic coke obtained has different concentrations of active centers partially measured by the C/O ratio. The conversion increase in the same direction in which the superficial acidity increases can be explained because the amount of oxygen in the coke increases. The fact that the weight percent oxygenlweight percent coke
Figure 8. Change in texture with time on stream and degree of doping: (a) (X) fresh, ( 0 )7 h, (0) 50 h; (b) (0) 118A, (X) 100A, and ( 0 )97A, after 50 h of operation.
ratio remains constant regardless of the alumina superficial acidity may explain that the selectivity remains approximately constant. The presence of an aromatic to yield this oxygen-rich coke is important in its quality but not exclusive, because a paraffin also yields a catalytic oxygenated coke. Regardless of the alumina superficial acidity, after the coke has been formed, there is only distribution of pore volume in the range of superficial acidity studied. Coke formation involves two phases: first, there is a rapid increase in the percentage of coke deposited up to the 10th hour, accompanied by low COXproduction, and then there is a slight increase followed by a steady-state phase in which there is more CO, produced. It might be assumed that in the steady-state phase there are a certain number of pores that are not reached by ethylbenzene (molecular dimension 7 A) because of the coke formation, but the oxygen (1.2 A) might reach the pores and continue oxidating the coke to COX. Thus, a cycle of coke regeneration would start which would explain its stability throughout the on-stream time. This agrees with what Emig and Hofmann (1983) have proposed in their work with ZrP as coke producer.
Acknowledgment The authors are grateful for the financial aid received from the National Council for Scientific and Technical Research of Argentina (CONICET) and from Universidad Nacional de San Luis (UNSL), San Luis, Argentina. Registry No. Sty, 100-42-5; Etb, 100-41-4; NaOAc, 127-09-3; 1344-28-1.
A1203,
Literature Cited Alkhazov, T. G.; Lisovskii, A. E. "Importance of Condensation Products in Oxidative Ethylbenzene Dehydrogenation over an Aluminum Oxide Catalyst". Kinet. Katal. 1976, 17, 434-9. Alkhazov, T. G.; Lisovskii, A. E.; Talybova, Z. A. "Oxidative Dehydrogenation of Ethylbenzene to Styrene Using Sulfur Dioxide". Neftekhimiya 1977, 17, 687-9. Alkhazov, T. G.; Lisovskii, E. A.; Ismailov, Yu. A.; Kozharov, A. I. "Oxidative Dehydrogenation of Ethylbenzene on Activated Carbons. I. General Characteristic of the Process". Kinet. Katal. 1978, 19, 611-4. Alkhazov, T. G.; Lisovskii, A. E.; Safarov, M. G.; Dadasheva, A. M. "The Nature of the Process of Oxidative Dehydrogenation of Ethylbenzene on Aluminum Oxide". Kinet. Katal. 1972,13,509. Arrba, L. A. "Oxidative Dehydrogenation of Ethylbenzene to Styrene over Phosphorus-Oxygen-Nickel Catalysts". Doctoral Dissertation, Universidad Nacional de San Luis, San Luis, Argentina, 1985. Berger, P. A.; Roth, J. F. "Electron Spin Resonance Studies of Carbon Dispersed on Alumina". J. Phys. Chem. 1968, 72, 3186.
2246
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Collins, R. L.; Bell, M. D.; Kraus, G. “Unpaired Electrons in Carbon Blacks”. J . Appl. Phys. 1959, 1(1),30, 56-62. Cortes, A.; Seoane, J. L. ”Oxidative Dehydrogenation of Ethylbenzene over Nickel-Tungsten Mixed Oxides”. J . Catal. 1974,34, 7. Dawars, F.; Gallard, J.; Teyssie, Ph.; Traynard, Ph. “Catalytic Activity of Polymers having Electron Spin Resonance Properties”. J. Polym. Sci. 1963, 4, 1385-1400. Emig, G.; Hofmann, T. “Action of Zirconium Phosphate as a Catalyst for the Oxydehydrogenation of Ethylbenzene to Styrene”. J . Catal. 1983, 84,-15. Fiedorow. R.: Kania. W.: Nowinska. K.: SoDa. M.: Woiciechowska, M. “Activity of Alumina Promoted ‘by inorganic kcids in the Process of Oxidative Dehydrogenation of Ethylbenzene”. Bull. Acad. Pol. Sci., Ser. Sci. Chim. 1978, 26, 641-9. Fiedorow, R.; Przystajko, W.; Sopa, M.; Dalla Lana, J. G. ”The Nature and Catalytic Influence of Coke Formed on Alumina: Oxidative Dehydrogenation of Ethylbenzene”. J . Catal. 1981,68,33. Gallard, J.; Laederich, T.; Salle, R.; Traynard, Ph. “Polymers having a Conjugated Structure. I. Conjugated Polymers as Catalysts”. Bull. SOC. Chim. Fr. 1963, 2204-9. Gallard-Nechtschein, J.; Pecher-Reboul, A.; Traynard, Ph. “Heterogeneous Catalysis on Organic Conjugated Polymers. 11. Electron Spin Resonance and Structural Factor”. J. Catal. 1969, 13, 261-70. Iwasawa, Y.; Nobe, H.; Ogasawara, S. ”Reaction Mechanism for Styrene Synthesis over Polynaphthoquinone”. J . Catal. 1973,31, 444. Iwasawa, Y.; Soma, M.; Onishi, T.; Tamaru, K. “Catalytic activities of Polynaphthoquinone, Containing Metal Halides. Dehydrogenation of Formic Acid, Cyclohexene, Ammonia, and Alcohols, and Isomerization of Butene”. J. Chem. SOC.,Faraday Trans. 1 1972, 68, 1617-25. Lisovskii, A. E.; Kozharov, A. I.; Feizullaeva, Sh.; Alkhazov, T. G. “Effect of the Genesis of Aluminum Oxide on its Catalytic Ac-
tivity during Oxidative Dehydrogenation of Ethylbenzene”. Kinet. Katal. 1978, 19, 605-10. Manassen, J.; Khalif, S.H., ”Organic Polymers: Correlation between Their Structure and Catalytic Activity in Heterogeneous Systems. 11. Oxidative Dehydrogenation: A Comparison between the Catalytic Activity of an Organic Polymer and that of Some Molybdate Catalysts”. J . Catal. 1969, 13, 290-298. Manassen, J.; Wallach, J. “Organic Polymers. Correlation between Their Structure and Catalytic Activity in Heterogeneous System. I. Pyrolyzed Polyacrylonitrile and Poly(cyanoacety1ene)”. J . Am. Chem. SOC.1965,87, 2671-7. Murakami, Y.; Iwayama, K.; Uchida, H.; Hattori, T.; Tagawa, T. ”Study of the Oxidative Dehydrogenation of Ethylbenzene. I. Catalytic Behavior of Sn02-P205”. J . Catal. 1981, 71, 257. Pines, H.; Haag, W. 0. “A1203Catalyst and Support. 1. Alumina and Its Intrinsic Acidity and Catalytic Activity”. J . Am. Chem. SOC. 1960,82, 2471-83. Rennard, R. J.; Innes, R. A.; Swift, H. E. “Oxidation over Magnesium Chromium Ferrite and Zinc Chromium Ferrite Catalysts”. J . Catal. 1973, 30, 128-38. Roth, J. F.; Schaefer, A. R. Belgian Patent 682 863, 1966. Roth, J. F.; Schaefer, A. R. US Patent 3446865, 1969. Roth, J. F.; Abell, J. B.; Fannin, L. W.; Schaefer, A. R. “Catalytic Dehydrogenation of Higher Normal Paraffins to Linear Olefins”. Symposium on refining petroleum for chemicals, presented before the division of petroleum chemistry, and the division of industrial and engineering chemistry, American Chemical Society, New York City Meeting, 1969, paper D 146. Tagawa, T.; Hattori, T.; Murakami, Y. “Study of Oxidative Dehydrogenation of Ethylbenzene. 11. Catalytic Activity and Acid and Base Properties of Na-Si02-Al,0,”. J . Catal. 1982, 75, 56. Received for review December 29, 1987 Accepted July 1, 1988
Liquid-Phase Oxidation of Cyclohexanone to Dibasic Acids with Immobilized Cobalt Catalyst Hung-Chung Shent and Hung-Shan Weng* Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan 70101, R.O.C.
Liquid-phase oxidation of cyclohexanone to dibasic acids has been studied in a batch autoclave reactor using glacial acetic acid as the solvent and Co-type resin as the catalyst a t 83-118 “C and 5-15 atm. The length of induction period increased with increasing the concentration of cyclohexanone (C ) and decreased with increasing the oxygen partial pressure, reaction temperature, and amount of catalyst (w). In the rapid reaction phase, the initial rate can be expressed as ro = wkKCPo,’/2/(l + K C ) . Water is detrimental to the catalyst due t o promotion of the elution of cobalt ion, which results in deactivation. Adding acetic anhydride can reduce the amount of cobalt ion eluted and also promote the reaction rate. The catalyst can be reused several times without losing its catalytic ability significantly. The fractional yield of dibasic acids (including adipic acid, glutaric acid, and succinic acid) ranged from 0.70 to 0.87, depending on the reaction conditions. Two-step oxidation of cyclohexane is a commercial process for making adipic acid. Cyclohexanone and cyclohexanol are the intermediates. The oxidants used are air and nitric acid, respectively (Reis, 1965; Danly and Campbell, 1978). Because nitric acid induces the corrosion problem and its consumption is large, many works use air or oxygen as the oxidant in the second step of oxidation or one-step oxidation of cyclohexane (Reis, 1965, 1971; Tanaka, 1974; Rao and Raghunathan, 1984,1986). Acetic acid is usually used as the solvent, and salts of cobalt, copper, and mangnese are employed as the catalysts. The main products are dibasic acids which include adipic, glutaric, and succinic acids. The reaction is a liquid-phase homogeneous system. The fractional yields of adipic acid Present address: Refining & Manufacturing Research Center, Chinese Petroleum Corporation, Chia-Yi, Taiwan 60036, R.O.C.
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greater than 0.70 have rarely been reported except at relative low conversion and low reactant concentration. Heterogeneous catalysts are also capable of catalyzing the liquid-phase organic compounds oxidation. For example, transition-metal oxides are used for the oxidation of cyclohexene, phenol, p-xylene, acetic acid, cumene, etc. (Mukherjee and Graydon, 1967; Neuberg et al., 1972,1974, 1975; Varma and Graydon, 1973; Sadana and Katzer, 1974a,b;Srivastava and Srivastava, 1975; Levec and Smith, 1976; Hronec and Hrabe, 1986); cation-exchanged zeolites are used for the oxidation of butene and cyclopentene (Van Sickle and Prest, 1970); and cobalt-exchanged resins are used for the oxidation of acetaldehyde, benzoaldehyde, alkyl aromatics, etc. (Chou and Lee, 1985; Waller, 1986; Kuo, 1987). None of the investigation of the heterogeneously catalyzed oxidation of cyclohexane or cyclohexanone to dibasic acids has been reported in the literature. 0 1988 American Chemical Society
