Oxidative Dehydrogenation of Cyclonaphthenes over Molecular Sieves Ion-Exchanged with Cuprous and Cupric Ions lsao Mochida,' Yoshimasa ikeda, Hiroshi Fujitsu, and Kenjiro Takeshita Research Institute of Industrial Science, Kyushu University, Fukuoka, Japan 8 12
Catalytic activities of cuprous and cupric ion-exchanged Y-molecular sieves (Cu(I)-Y and Cu(II)-Y) for the oxidative dehydrogenation of cyclonaphthenes were studied by an ordinary flow reactor. In the highly selective formation of benzene from cyclohexane, over 90% yield resulted using Cu(l)-Y at 200 '(3. The reactions in oxygen were first order over Cu(II)-Y and half order over Cu(I)-Y, respectively. Oxidation of cyclopentane over both catalysts gave carbon dioxide. However, the catalytic activity of Cu(I)-Y was lost very quickly, although only a slight decrease of activity was observed in the case of cyclohexane. Based on these observations, the active species of the oxygen on the catalysts were concluded to be molecular and dissociative over Cu(II)-Y and Cu(I)-Y, respectively.
Introduction Catalytic activity of Cu(I1)-Y for the oxidative dehydrogenation of cyclohexane has been studied in previous papers (Mochida et al., 1971, 1975), where the high activity and considerable selectivity of benzene formation were reported. Recently, Kubo et al. (1972, 1973) found the catalytic conversion of cyclohexane into cyclohexene over ferrous ionexchanged molecular sieve to be of low yield, and they ascribed the source of activity to the dissociatively adsorbed oxygen which was revealed with Mossbauer spectroscopy (Delgas, 1970; Garten, 1973). In the present study, catalytic activities and reaction orders in oxygen over Cu(1)-Y in the oxidation of cyclohexanes and cyclopentanes are observed to discuss the reaction mechanism in comparison with that over Cu(I1)-Y. Because the dissociatively adsorbed oxygen over Cu(1)-Y can be expected to carry out the oxidative dehydrogenation of cyclohexane by high activity and selectivity and the oxidative dehydrogenation is more preferable than the dehydrogenation in the thermodynamics aspect if the high selectivity is performed, it may be of value to study the reactivity of the dissociative oxygen in this reaction. Examination of its reactivity may have a possibility to find new catalytic oxidation.
were obtained from Wako Junyaku Co. Neither olefinic nor aromatic impurity was detectable in them by gas chromatography. Apparatus and Procedure. The catalytic activity and kinetics were observed by an ordinary flow reactor with a fixed catalyst bed diluted with carborundum [Nakarai Co.] to enlarge the heat capacity of the catalyst bed. The total flow rate was 100 ml/min and the weight of catalyst and carborundum were around 200 mg and 2 g, respectively. The size of the bed was 16 mm in diameter and 15 mm in height. Cyclohexane was fed by the reaction gases which passed through the cyclohexane saturator kept at 0 "C. Other cyclonaphthenes were fed by a microfeeder. The concentrations of naphthenes were set around 1%.The thermowell was located in the middle of the catalyst bed packed in a glass tube of 18 mm diameter. The partial pressure of oxygen was changed from 0.05 to 0.5 atm under the fixed naphthene pressure. The reactant gas was balanced to 1atm by nitrogen. All products and reactants were analyzed by means of a gas chromatograph. The following columns were used: 2-m Molecular Sieve 13X at room temperature for Nz, 0 2 , and CO; 7-m VZ-7 at room temperature for CO,; 4.5-m TCP + 1-m PEG 1000 a t 65 "C for cyclonaphthenes, cycloolefins, and aromatics. The reaction rate, V (ml/g min), was obtainable from the following equation at the low conversion
Experimental Methods Materials. Cu(I1)-Y and Cu(I1)-Z (Z; zeolon) were prepared V = [ F / ( 1 r )W ] X by ion-exchange Y-molecular Sieve (Linde SK-40), Na(1)-Y, where X is the conversion, F is the total flow rate, W is the or zeolon, respectively, with an aqueous solution of cuweight of catalyst, and r is the ratio of oxygen plus nitrogen proammonium ion. The exchanged levels were ca. 10W0.This to cyclonaphthenes, respectively. The typical conversion treatment was followed by a thorough washing with deionized observed was 10%.The rate was determined 2 h after the rewater and drying at 100 "C and then calcined at 400 OC for 7 action started. Deactivation of the catalyst was not observed h in the atmosphere. The particle size of the catalyst was during the rate determination except for the case of cycloprepared to be between 28 and 60 mesh. Details were depentane over Cu(1)-Y. scribed in a previous paper (Mochida et al., 1971, 1975). Cu(1)-Y was prepared by ion-exchange of Na-Y with Cu(1) in Results liquid ammonia ,according to the method described by Oxidative Dehydrogenation over Cu(1)-Y. Arrhenius Kruerke and Belgium (1970). The exchanged level is ca. 30%. Cu(I1)-S was obtained by the calcination of the C u ( N 0 3 ) ~ - plots of Cu(1)-Y for the dehydrogenation of cyclohexane are shown in Figure 1.Its activity in Table I was almost equal to impregnated silica gel. Cyclohexane, cyclopentane (EP grade), that of Cu(I1)-Y at 280 "C; however, its activation energies of methylcyclohexane (EP), and methylcyclopentane (EP grade)
+
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Ind. Eng. Chern., Prod. Res. Dev., Vol. 15, No. 3, 1976
Table I. Initial Rates and Activation Energies for the Oxidation of Cyclohexane over Ion-Exchanged Zeolites Rate at 280 "C, ml/g min
Cu(I1)-Y Cu(1)-Y Cu(I1)-z c u (11)-s
0.49 0.35 0.00018 0.043
0.10 0.11
0.041 0.089
Reaction order
E,, Kcal/mol
29
27
21
18
14
38 20
21
83 76 0.44 33
1.0
0.5 0 0
0.5 0.5 0.5 0.5
Table 11. Reactivities of Cyclonaphthenes on Ion- Exchanged Zeolites
Reactant
Rate at 280 "C, ml/g min Product Cu(I)-Y Cu(II)-Y N a W Y Cu(II)-S
cyclopentane
COa
0.13
Cyclohexane
C6H6 c02
0.35 0.11
CO2
0.073
C7Hs
0.0016
Methylcyclopentane Methylcyclohexane
Con
0.16
0.44 (22)" 0.49 0.10 0.26 (23) b
0.16 (34)
0.19
0.065 0.29 0.28 0.028 0.13
0.094 (24) 0.043 0.089 0.077 (16) 0.0097 (25)
0.049 (20)
a Numbers in parentheses are activation energies (kcal/mol). Too small to be observed.
benzene and carbon dioxide formations were significantly smaller than those of Cu(I1). The selectivity of benzene formation is very high and reached up to 91%at 200 "C below 1oo/o conversion. Dependence of oxidation rates on the partial pressure of oxygen over Cu(1)-Y is shown in Figure 2. Both formations of benzene and carbon dioxide were a half order in oxygen. The formation of cyclohexene was not observed a t all by means of a hydrogen flame detector gas chromatograph even in the reaction of 1%conversion a t 200 "C under an oxygen pressure of 0.05 atm, although Kubo et al. (1972,1973) reported its formation in a low yield. Catalytic Activity of Cu(11)-Y, Cu(I1)-Z, and Cu(I1)-S. Catalytic activities and activation energies of Cu(I1)-Y, Cu(I1)-Z, and Cu(I1)-S are summarized in Table I. The extraordinarily small activity of Cu(I1)-Z should be noticed. Cupric ion on the molecular sieve is clearly different from the oxide on silica gel in the catalytic activity and selectivity of benzene formation. Furthermore, Cu(I1)-S produced cyclohexene at low conversion, although its yield was quite low. In contrast, cyclohexene was not found a t all over Cu(I1)-Y or Cu(I1)-Z under various conditions. Reaction orders of these copper catalysts in oxygen were summarized in Table I. Although the formation of carbon dioxide was always half order in oxygen regardless of the catalysts, the reaction orders of benzene formation were different from catalyst to catalyst. Thus, the function of copper ion on Cu(I1)-Y, Cu(1)-Y,and Cu(I1)-S for the activation of oxygen in the oxidation reaction is considered to be quite different. Oxidation Reactivities of Cyclonaphthene over Zeolite Catalyst. Reactivities of cyclonaphthenes were studied on Cu(I1)-Y,Cu(1)-Y,Na(1)-Y, and Cu(I1)-S. Their reactivities were summarized in Table 11, where the reaction rates at 280 OC after 2 h reaction are described. Except for cyclohexane, carbon dioxide was the almost exclusive product. Different reactivity patterns among cyclonaphthenes are observable on Cu(1)-Y and Cu(I1)-Y as shown in Table 11. Cyclopentanes are considerably less reactive than cyclohexanes on Cu(1)-Y,
1.8
1.7
1.9
,/,x163
Figure 1. Arrhenius plots of cyclohexane oxidation over Cu(1)-Y;0, benzene; 0 , carbon dioxide. Partial pressures of oxygen and cyclohexane were 0.5 and 0.01 atm, respectively.
-0.5
-1.0 LOG
02(ATM)
Figure 2. Reaction rate of cyclohexane oxidation vs. partial pressure of oxygen over Cu(1)-Y at 200 " C : 0, benzene; 0 , carbon dioxide. Partial pressure of cyclohexane was 0.01 atm.
whereas nearly equal reactivities were observed on Cu(I1)-Y. The catalytic activities of Cu(1)-Y for cyclopentanes were found to decrease very quickly with the progress of the reaction, whereas only a small activity decrease was observable on Cu(I1)-Y for both cyclopentane and cyclohexane. The competitive reactions of cyclohexane and cyclopentane over Cu(1)-Y and Cu(I1)-Y were studied to observe the effect of retardation due to cyclopentane on the active site of benzene formation from cyclohexane. The activity of Cu(1)-Y for benzene formation from cyclohexane was lost almost completely in the presence of cyclopentane, although the single oxidation of cyclohexane lost only a small portion of activity as shown in Figure 3. Cyclopentane introduced in the reaction occupied the active site of Cu(I1)-Y competing with cyclohexane, although the loss of activity is very small. The decrease in the rate of benzene formation from cyclohexane can be shown by the plots of VBo/VB vs. Pp/PH in Figure 4, where VB" and v g are the rates of benzene formation in the absence or presence of cyclopentane, respectively, and Pp and PHare partial pressures of cyclopentane and cyclohexane, respectively. The linear relation shown in Figure 4 will be discussed in connection with the reaction mechanism. Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 3, 1976
161
-f 0.5 Q -i 0.4 -.-
v
0.10
%¶
I
--ar
C 0
0.3 0.2
2
L
Y
1
OF 0
b C
a
'
1/48
C
0.05
Id.
-
10
3
2
1
0
u
a
r" 0"
0.1
Er
0 2 00
0
Figure 4. Competitive oxidation of cyclohexane and cyclopentane over Cu(II)-Ya t 280 O C : partial pressure of oxygen 0.5 atm; catalyst, 200 mg. V B O and VB are rates of benzene formation in the absence and presence of cyclopentane, respectively. Pp and PH are partial pressures of cyclopentane and cyclohexane, respectively.
Roaction T i r n c ( ~ 1 ~ )
Figure 3. Competitive oxidation of cyclohexane and cyclopentane over Cu(1)-Yat 280 O C (partial pressure of oxygen was 0.5 atm): 0,
benzene; 0 , carbon dioxide in the competitive reaction. Partial pressure of cyclohexane and cyclopentane was 0.060 and 0.086 atm, respectively; catalyst, 150 mg; 0,benzene formation by the single oxidation of cyclohexane (CeH12 0.01 atm).
Discussion In a previous paper (Mochida et al., 1975), the oxidation mechanism of cyclohexane over Cu(I1)-Y was discussed from kinetic and adsorption data. The oxygen adsorption step is concluded to be rate determining for benzene formation. The possibility that adsorbed oxygen of molecular form may be an active species was also discussed because no cyclohexene was found even at low conversions under low oxygen pressures, whereas it was found on Na(1)-Y. Based on these conclusions, the oxidation of cyclonaphthenes can be described in Scheme I, where the molecular oxygen is considered to be a reactive species for the dehydrogenation. Scheme I. Reactions over Cu(I1)-Y
co,
The biggest difference in these reactions is that cyclohexadiene is led to stable benzene, whereas unstable cyclopentadiene should be converted to carbon dioxide very quickly. Thus, the total reactivities of both reactants are nearly equal on Cu(I1)-Y as shown in Table 11. The results on the competitive reaction may be explained by the proposed reaction mechanism. The retardation implies that the adsorbed oxygen which may form benzene from cyclohexane also interacts with cyclopentane. The slope of Figure 4 is considered the ratio of the amount of oxygen consumed by cyclohexane vs. cyclopentane. The reactivities of cyclohexane and cyclopentane are nearly equal, so that the value of the ratio implies the presence of the preequilibrium of naphthene adsorption in the oxidation reaction as Morooka and Ozaki (Morooka, Ozaki, 1967) assumed in the oxidation of olefins over nickel oxide, although the equilibrium constant does not appear in the kinetic equation of single oxidation because the step of oxygen adsorption is rate-determining. The value of the slope indicates that the adsorption of cyclo182
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 3, 1976
pentane on Cu(I1)-Y is four times stronger than that of cyclohexane. The dissociatively adsorbed oxygen may work for the formation of cyclohexene via oxidative dehydrogenation of cyclohexane as postulated over Fe(I1)-Y (Kubo et al., 1972, 1973). A half-order of benzene formation in oxygen over, Cu(1)-Y revealed in the present study is consistent with reactive species of the dissociative oxygen. The fact that there is no formation of cyclohexene in spite of the dissociative oxygen may be explained by the strong adsorption of cyclohexene on cuprous ion (Cotton and Wilkinson, 1972),which leads to a further oxidation of cyclohexene into benzene without desorption of cyclohexene. Such a process can described in Scheme 11. Scheme 11. Reactions over Cu(1)-Y
O-O-~-~ \
(7
0
co, 0
--t
adsorbed polymer
+
cokes
In the case of cyclopentane, cyclopentene once formed similarly to the case of cyclohexene may polymerize into carboneous compounds which retard the catalytic activity because cyclopentene adsorbed strongly cannot be converted into such a product of easy desorption as benzene on Cu(1)-Y. Thus, the assumed reaction mechanisms can explain the results of this study. Mordenite has been reported to have stronger adsorption ability for the alkane than the alkene (Eberly, 1971). Thus selective formation of cyclohexene is expected; however, it was very inactive, perhaps because of narrow pores. The small reactivity of methylcyclohexane over zeolite catalysts may also be related to the pore structure of the active site. The metal ions supported on the molecular sieve have been revealed to have significant catalytic activity subject to their electronic structure. Thus, Cu(1)-Y and Cu(I1)-Yhave a different manner of affinity against oxygen and behave differently in the catalytic reaction. The high activity and selectivity of Cu(1)-Yfor the oxidative dehydrogenation of cyclohexane into benzene may indicate a possibility for the commercial utilization of Cu(1)-Y as the catalyst. The unique nature of cuprous ion over the solid surface for the intimate affinity to olefins as well as oxygen may promise novel selective oxidation of olefins. This subject is now under investigation.
Literature Cited Cotton, F. A,, Wilkinson, G., "Advanced Inorganic Chemistry", 3d ed, p 911, Interscience, New York, N.Y.. 1972. Eberly, P. E., Jr., lnd. Eng. Chem., Prod. Res. Dev., 10, 413 (1971). Delgas, W. N., Garten, R. L., Boudart, M., J. Catal., 16, 90 (1970). Garten, R. L., Gallard N. J., Boudart, M., lnd. Eng. Chem., Fundam., 12, 299 (1973). Kruerke, U. K., Belgium, E., US. Patent, 3 497 462 (1970). Kubo, T., Tominaga, H., Kunugi, T., J. Chem. SOC.Jon.. 196 (1972).
Kubo, T., Tominaga, H., Hino, T., Kunugi, T., J. Chem. SOC. Jpn., 2257 1197.11 ~._._,. Mochida, I., Jitsumatsu, T., Kato, A,, Seiyama, T., Bull. Chem. SOC.Jpn., 44, 2595 (1971). Mochida, I., Jitsumatsu, T., Kato, A., Seiyama, T., J. Cafal., 36, 361 (1975). Morooka, T.. Ozaki, A., J. Am. Chem. SOC.,89, 5124 (1967).
Received for review May 19,1975 Accepted May 3,1976
Reduction of Mesityl Oxide Jaime Wisniak,' Mordechay Herskowltz, Drora Roffe, and Saul Smllovitz Department of Chemical Engineering, Ben Gurion University of the Negev, Beer-Sheva, lsrael
Mesityl oxide has been hydrogenated in the liquid phase to methyl isobutyl ketone and methyl isobutyl carbinol with palladium, ruthenium, and Raney nickel catalysts under conditions of chemical control. Under all conditions the reaction was highly selective, with the olefin bond being first hydrogenated. Energies of activation were calculated for the different catalysts. The rate-controlling step involved the surface reaction between chemisorbed hydrogen and adsorbed or unadsorbed reactant, depending on the temperature level.
Introduction The catalytic hydrogenation of a&unsaturated ketones and aldehydes constitutes an interesting kinetic problem of selectivity and activity. Theoretically these compounds may be converted to saturated aldehydes or ketones, unsaturated alcohols, or hydrocarbons, but in fact reduction proceeds entirely through the saturated carbonyl. Few systematic kinetic studies have been published on the subject, particularly regarding the influence of catalyst nature and mechanism of the reaction. This work was undertaken to provide kinetic data on the liquid-phase hydrogenation of a,P-unsaturated ketones, and mesityl oxide (MO) was elected for this purpose. Mesityl oxide is commercially prepared by dehydration of diacetone alcohol and has long been known to exhibit two isomeric forms: 4-methyl-3-penten-2-one (conjugated MO) and 4-methyl-4-penten-2-one (iso-MO), the equilibrium mixture containing 91% of the conjugated form (Stross et al., 1947). Hydrogenation of MO produces methyl isobutyl ketone (MIBK) and methyl isobutyl carbinol (MIBC). The reduction scheme of MO may be illustrated as follows: H
O
OH
I
(CHJ,C=CHCCH,
Mo
\
r
(CH,),C=CHCHCH,
(CH,),CHCH,CHCH f
a$-Unsaturated ketones are reduced to saturated ketones and saturated alcohols under mild conditions by most platinum metal group catalysts. Raeva et al. (1970) hydrogenated MO in the presence of Pd, Ni, and Cu catalysts on active A 1 2 0 3 a t 130-250 OC, and found that P d was the most active one. Macho (1971) studied the kinetics of the vapor-phase hydrogenation of MO to MIBK over a Pd/A1203 catalyst at 40-210 OC and concluded that the catalyst was highly selective for the reduction of double bonds in the presence of ketonic groups. A decrease in the selectivity above 140 "C was caused
by the hydrogenolysis of MO to 2-methylpentane. Breitner and coworkers (1959) hydrogenated MO over different platinum metal group catalysts and found that the reaction was extremely selective and stopped after the saturation of the double bond. Even when the initial mixture consisted of three parts of MIBK and one part of MO the olefin was first completely reduced and subsequently the carbonyl bond. I t was assumed that the much stronger adsorption of MIBK by the catalyst prevented reduction of the carbonyl group. Kinetics of the vapor phase hydrogenation of MO has also been studied by Hashimoto et a1.(1969). The process was carried out in the low pressure range (0-1 atm) and 140-200 "C. It was found that the reverse reaction of the reduction of MO to MIBK was negligible, whereas in the reduction of MIBK to MIBC the reverse reaction was significant. They proposed that the kinetic mechanism involved a surface-reaction controlling step between atomically adsorbed hydrogen and adsorbed MO, and calculated the constants of the rate equation a t various reaction temperatures. Another widely used hydrogenation catalyst is Raney nickel. Weizmann (1946) and Heykoop and Van Dijk (1965) studied the hydrogenation of MO over Raney nickel. Weizmann worked a t mild conditions (room temperature and 2 atm hydrogen pressure) and hydrogenated 98 g of MO in the presence of 1 g of Raney Ni in 2 h to MIBK. Heykoop used pretreated Raney Ni and treated Mo with NaOH and a solution of H202. At 80-100 OC and 10-13 atm the products were 91.5-92.5% MIBK, 1.0-1.5% MIBC, 0.5-1.0% MO, and 6% other components. Reduction of an unsaturated ketone to an unsaturated alcohol is a much more difficult problem. Freidlin et al. (1958) were able to reduce selectively the olefinic double bond in MO using a Zn-Cu catalyst a t 75-175 "C. The selectivity was caused by the Zn component, and its lower isomerization ability in comparison with pure Zn catalyst was caused by the Cu component. This behavior is similar to the reduction of unsaturated aldehydes; in the absence of Zn the selective conversion of the aldehyde group is lost. Selective reduction of the aldehyde function in an a$-unsaturated aldehyde seems to be possible because of the proximity of the functional Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 3, 1976
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