-
THN + greater than that of the first step ( D H N 3 H ? ) . The cis-DHN species was slightly more reactive than the trans. Isomerization of the cis and trans species occurred concurrently with dehydrogenation. Compared to rates of dehydrogenation the rate of trans isomerization was lower by about an order of magnitude while that of the cis isomerization was lower by a factor of about four. This suggests that if isomerization does play a role in the dehydrogenation mechanism, that it is not the ratedetermining step. These relative rates of dehydrogenation and isomerization may be quite different with other catalysts. For example, it has been shown that the product distribution of cis and trans isomers was quite different for the hydrogenation of naphthalene using different metal catalysts (Weitkamp, 1968). Selectivity for naphthalene was governed by equilibrium and was favored by high temperature, high conversion, and low pressure. The highest heat sink obtained thus far with decalin was 1688 Btu:lb: of which 838 B t u / l b was due to heat of reaction (10 a t m , 1022”F, LHSV = 30). This corresponded to a total heat sink of 1903 Rtu,’lb a t 1340°F. The adverse effect of pressure on selectivity for naphthalene at pressures greater than 10 atm would be expected to decrease heat sinks only slightly. For example, a t complete D H K conversion a decline in selectivity for naphthalene of 20‘; would lower the heat of reaction by only about 7‘ and the total heat sink by about 4;‘. The laboratory platinum-on-alumina catalyst was somewhat unstable a t 10 a t m pressure; a commercial platinum catalyst was even more unstable. Stability of both catalysts was improved by operating the reactor at higher pressures and a t high conversions. From more extended studies on the dehydrogenation of D H S and methylcyclohexane over a variety of catalysts. it appeared that
catalyst stability was strongly dependent upon the catalyst pore structure. This work will be presented in a forthcoming paper. Acknowledgment
Permission to publish by the Air Force and Shell Development Co. is gratefully acknowledged. We thank R. D. Hawthorn and L. E. Faith for assistance with chemical calculations and D. P. Anderson for his laboratory skills. Literature Cited
Allam, M . I., Vlugter, J. C., J . Inst. Petrol., 52, 385 (1966). Benson, S. W., “The Foundat,ion of Chemical Kinetics,” p 27. McGraw-Hill. New York, X. Y., 1960. Miyazawa, T., Pitzer, K. S., J . Amer. Chem. Soc., 80, 60 (1958). Ritchie, A. W., Nixon, A. C., Ind. Eng. Chem. Prod. Res. De&p., 5 , pp 59.~64(1966). Ritchie, A. W., Sixon. A. C., ibid., 7, 209 (1968). Ritchie, A. W-., Nixon, A. C., ibid., 9, 213 (1970). W’eitkamp. A. W., “Advance Catalysis,” 18, 1 (1968). Wheeler. A. W.. ibid.,111, 249~-329(1951). RECEIVED for review November 24, 1969 ACCEPTED December 31, 1970 Presented at the Division of Petroleum Chemistry, 154th Meeting, ACS. Chicago. Ill., September 1967. This work was done under the sponsorship of the Fuels, Lubricants, and Hazards Branch of the Air Force Aero-Propulsion Laboratory, Wright-Patterson Air Force Rase with H. R . Lander serving as project engineer. Tables I and Tables 111 through VI1 will appear following these pages in the microfilm edition of this volume of the ,Journal. Single copies may be obtained from the Reprint Department, ACS Publications, 1165 Sixteenth St., N. W., Washington, I). C. 20036. Refer to author. title of article, volume, and page number. Remit $3.00 for photocopy or $2.00 for microfiche.
Oxidative Dehydrogenation of Cyclohexane, Cyclohexene, Tetralin, and Decalins on Activated Alumina Akira Uchida’, Tokuaki Nakazawa, Kengo Oh-uchi, and Sumio Matsuda Department of Petroleum Chemistry, Facult) of Engineering, Osaka Unicersit?, Yamadakamr, Suita, Japan A l t h o u g h naphthenic hydrocarbons have a thermodynamic tendency to form aromatic hydrocarbons under atmospheric pressure a t temperatures above 250” C, the possibility of the oxidative dehydrogenation (oxydehydrogenation) of these cycloalkanes is of interest a t present. Surprisingly, the oxydehydrogenation of cycloalkanes is little investigated, and only the data reported by Jouy and Balaceanu (1960a.b) and Robinson (1934) are known. Robinson (1954) dehydrogenated cycloalkanes noncatalytically in the presence of oxygen and obtained cycloalkenes. Jouy and Balaceanu (1960a,b) investigated the To whom correspondence should be addressed.
oxydehydrogenation of cyclohexane (CHA) and hydronaphthalenes on platinum. platinuni- alumina, palladiumalumina. chromia-alumina, or copper and nickel phosphates. and observed that oxygen accelerated the dehydrogenation of these hydrocarbons. The catalysts subjected to the oxydehydrogenation of cycloalkanes or cycloalkenes are limited to date, and only the oxydehydrogenation on typical dehydrogenation catalysts was investigated. The molybdena catalyst was effective for the oxydehydrogenation of olefins. However, the oxydehydrogenation of cycloalkanes on molybdena is not known, and even less is known about that on activated alumina. Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
153
By the oxidative dehydrogenation of cyclohexane on activated alumina (I), phosphomolybdic acid-bismuth oxide-alumina (II), a n d chromia-cerium oxide-potassium oxidealumina (Ill) a t 350" to 450"C, benzene, cyclohexene, carbon dioxide, a n d carbon monoxide were formed. Large selectivities of benzene and cyclohexene were obtained on catalysts I1 and Ill, respectively. Catalyst I was also effective and had the intermediate selectivities of benzene a n d cyclohexene between catalysts I I and Ill. The oxidative dehydrogenation of cyclohexane, cyclohexene, tetralin, and decalins on activated alumina were investigated a t 300" to 400" C. Although the occurrences of the oxidative dehydrogenations of these hydrocarbons were observed, cyclohexane and decalins oxidized more easily to carbon oxides than the corresponding unsaturated hydrocarbons. The consumption rates of oxygen were analyzed kinetically, and a reaction mechanism, which includes an adsorption step of a carbanion intermediate on active centers on alumina, was proposed.
The present study deals with the oxydehydrogenation of CHA on catalysts I, 11, and 111, and that of cyclohexene (CHE), tetralin ( T E T ) , and decalins (DECs) on catalyst
I. Experimental
All reagents used in this study were reagent grade. DECs (Murawaka Chem.) were used as received, and other starting hydrocarbons (U'ako Chemicals) were distilled over sodium wire before use. The physical properties of the starting hydrocarbons are: CHA, n$ 1.4263, d? 0.7780; CHE, n z 1.4465, d:" 0.9104; T E T , n$ 1.5414, d:' 0.9698; cis-DEC, n$ 1.4813, d:" 0.8953; trans-DEC, nsl.4693, d:O0.8708. Catalyst I (8-to 14-mesh) was used as received. The catalyst was analyzed by fusion with sodium hydrosulfate. The results showed: ignition loss, 16.4%;S O ? , 1.6%; Fe?Oi, 0.7%; A1101, 80.65. Catalyst I1 was prepared by adding 27 grams of catalyst I to a solution of 4.7 grams of phosphomolybdic acid in 15 ml of distilled water and a solution of 6.9 grams
Air
-
of bismuth nitrate in 10 ml of acetic acid, drying, and calcining in a stream of air a t 500" C for 4 hr. Catalyst 111 was prepared by adding 41.3 grams of catalyst I to a solution of 9.8 grams of chromium oxide. 1.0 gram of cerium nitrate, and 1.8 grams of potassium nitrate in 30 ml of distilled water, drying, and calcining in a stream of hydrogen a t 5000C for 5 hr. The apparatus used are shown in Figures 1 and 2. The predetermined amounts of air and nitrogen from cylinders and the starting hydrocarbons from an evaporator or a feeder are mixed and fed into the reactor. A quartz tube (50-cm long, 0.9-cm id), or a glass tube (50cm long, 1.2-cm id), in which another glass tube (30cm long, 0.8-cm id) is placed concentrically t o hold a thermocouple, is used as the reactor in the apparatus in Figures 1 or 2, respectively. A sheet of stainless steel mesh is inserted into the reactor and serves as the catalyst holder. The reactor is heated to 350" to 450°C in an electric furnace (71 cm long). The temperature of the reactor is controlled by means of a thermocouple and a temperature controller (Chino Works).
Air
0
6
n DP
4
'U
1
1
4
I (x2)
Evaporator 3. Thermocouple 4. Temperature controller 5 . Product receiver and Dry Ice traps
154
(x2 1
5
Figure 1. Flowsheet of apparatus A 1.
4
I I
6. Soap film flow meter
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
Figure 2. Flowsheet of apparatus 1, Evaporator 2. Feeder 3. Thermocuple 4. Temperature controller
(x4)
5
B
5 . Product receiver and Dry Ice traps 6. Soap film flow meter 7. CO?absorption bottle
The gas from the reactor exit is cooled, and the liquid product is collected in traps, which are cooled in ice and Dry Ice-acetone baths. The liquid product was analyzed by vapor phase chromatography (vpc) using Gas Chromatograph GC-1A (Shimazu Seisakusho). For the analysis of the products from CHA and C H E , a 3-meter long, 5-mm id tubing column containing 1 5 5 dioctylphthalate on Neopak 1A was used. Hydrogen flow was 80 ml per min and the column temperature was 100°C. Dioxane served as the internal standard, and the relative retention times were: CHA, 0.47; C H E , 0.6; benzene ( B E N ) , 0.7; dioxane, 1.0. On all of the gas chromatograms, the peaks which correspond to methylcyclopentane and cyclohexadiene were not detected. For the analysis of the products obtained by the reactions of T E T and DECs, a 3-m long column containing Silicone DC 550 on Celite was used. Hydrogen flow rate was 80 ml per min and the column temperature is 160°C. The internal standards are acetophenone for the analysis of the products from T E T and cyclohexanone for the products from DECs. The relative retention times were: T E T , 1.5; naphthalene ( N A P ) , 1.8; acetophenone, 1.0: B E N , 0.3; toluene (TOL), 0.5; xylene (XY), 0.7; c ~ s - D E C 1.8; , VCZLS-DEC, 2.2; T E T , 3.3; NAP, 4.0; cyclohexanone, 1.0. The concentrations of carbon dioxide ( C o r ) , carbon monoxide (CO), and oxygen in the gas from the outlet of the last trap (the exit gas) were measured by Hempel's method. As shown in Figure 2 , the exit gas was introduced into a saturated solution of barium hydroxide to catch C 0 2 as barium carbonate. Although acidic products in the exit gas might form precipitates, only a negligible amount of acidic product was extracted with ether when the precipitates were decomposed with hydrochloric acid and sulfuric acid. Thus, the yield of CO, was calculated directly from the weight of the precipitates and the results of the gas analysis by Hempel's method. For this report, a constant flow rate of the reaction gas mixture was maintained, and the amount of the catalyst placed in the reactor was varied to change the space velocity. Results and Discussion
Oxydehydrogenation of CHA on Catalysts I, 11, and 111. Although CHA was oxydehydrogenated on chromia by Jouy and Balaceanu (1960a,b), molybdena-the typical catalyst for the oxydehydrogenation of olefins-and activated alumina-used generally as catalyst carrierwere not subjected to the oxydehydrogenation of naphthenes. T o compare the catalytic activities of these three catalysts, the oxydehydrogenation of CHA was conducted on the catalysts a t 350" t o 550'C. Apparatus A was used in this section. The reaction gas, composed of 15% CHA and 85% air, was fed into the reactor a t gaseous hourly space velocities of 900 and 6100 to 6400 hr-'. Some experimental results, the conversion of CHA, and the one-pass yields of C H E , B E N , C 0 2 , and CO, are given in Table I. At reaction temperatures over 450" C, the conversion of CHA and one-pass yields of CO increase markedly. At the same time, decreases in one-pass yields of B E N and CO, are observed irrespective of the catalysts. This phenomenon might suggest that some side reaction, if any, which produces large amounts of CO, became significant a t temperatures above 450" C with these catalysts.
Table I. Oxydehydrogenation of CHA on Catalysts I, II, and Ill GHSV, Catolyst
X 10
hr
'
'
ConverT e r m , sion of "C CHA, %
One-poss yields
Conversion of
(Oh)
CHE
BEN
CO?
CO
01,
%"
0.9
350 450 550
24 41 88
0 2 3
11 18 7
6 6 4
2 2 14
92 100 99
6.1
350 460 550
36 40 89
2 5 3
5 13 3
4 6 3
3 4 19
64 97 91
0.9
350 450 550
50 64 92
2 1 trace
11 25 10
'i 8 9
3 1 8
93 100 96
6.4
350 450 550
34 49 88
2 2 3
17 21 5
5 6 3
trace 1 20
87 93 93
0.9
350 450 550
52 60 85
3 4 2
1 4 6
9 9 5
2 2
97 99 96
I
I1
11
I11 350 29 6 11 6 2 85 450 11 5 2 100 55 6 550 94 1 5 5 25 98 "Calculated with the following equation: conversion of 0, = [I - flow rate of 02 in exit gas (ml/sec)/flow rate of 0, in reaction gas (ml! sec) 1 x 100. 6.3
From the results in Table I , the following tendencies can be deduced: The selectivities of CHA to BEN can be arranged in decreasing order as: catalyst I1 > catalyst I > catalyst 111; and to C H E as: catalyst I11 > catalyst I > catalyst 11. Catalyst I11 is effective at comparatively lower temperature than other catalysts. Though much C H E is produced on catalyst I , the yield of BEN is less. Among all catalysts, the fact that catalyst I shows the intermediate activity between catalysts I1 and I11 is unexpected. Although CHA and C H E were dehydrogenated on catalyst I in the absence of oxygen by Germain et al. (1958), the oxydehydrogenation of naphthenes on catalyst I is not yet known. T o investigate the catalytic activity of catalyst I , the oxydehydrogenations of CHA, C H E , TET, and DECs are attempted. Oxydehydrogenation of CHA, CHE, TET, and DECs on Catalyst I. Apparatus B is used in this section. The hydrocarbon supplied from the feeder is mixed with air (and nitrogen if necessary) and is fed into the reactor a t the predetermined feed rate. The feed rate of air or the mixture of air and nitrogen is 5 ml per sec for the experiments with CHA, C H E , and DECs and 2.5 ml per sec for TET. The experimental results are shown in Table 11. The relationship between the percentage conversion of CHA or the one-pass yields of products and the reciprocals of the space velocity, V,F,,, reactants (hr), seems to correspond to that of the consecutive reactions whose intermediates are C H E and BEN, and whose final products are C o n and CO. The data of C H E also are not contrary to the consecutive reactions where the starting hydrocarbon is C H E . When C H E is mixed with nitrogen and is brought into contact with catalyst I at 350" C without added oxygen Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, N o . 2, 1971
155
Table II. Oxydehydrogenation of CHA, CHE, TET, and DECs on Catalyst I Consu 111pt io n rate of 0 ,
Run
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
55 56 57 58 59 60 61 62 63 64 65 66 67 68 69
156
Hydrocarbon"
CHA
CHE
TET
cis-DEC
Temp, CC
325 350 400 325 350 400 325 350 400 325 350 400 325 350 400 400 400 400 400 400 400 400 400 400 325 350 400 325 350 400 325 350 400 325 350 400 325 350 400 350 350 350 350 350 350 350 350 350 300 350 400 300 350 400 300 350 400 300 350 400 350 350 350 350 350 350 300 350 400
GHSV, x 10 hr
'
5.28 5.28 5.28 2.68 2.68 2.68 2.01 2.01 2.01 1.34 1.34 1.34 No cat. No cat. No cat. 2.01 2.01 2.01 2.01 2.01 2.01 2.01 2.01 2.01 5.26 5.26 5.26 2.66 2.66 2.66 2.00 2.00 2.00 1.33 1.33 1.33 No cat. No cat. No cat. 2.66 2.66 2.66 2.66 2.66 2.66 2.66 2.66 2.66 1.52 1.52 1.52 0.76 0.76 0.76 0.38 0.38 0.38 No cat. No cat. No cat. 0.76 0.76 0.76 0.76 0.76 0.76 4.99 4.99 4.99
Mol ratiob HC/O,
10.41 18.8 10.41 18.8 10.41 18.8 10.41 18.8 10.41 18.8 10.4118.8 10.4118.8 10.4118.8 10.41 18.8 10.4118.8 10.4118.8 10.4118.8 10.4118.8 10.41 18.8 10.41 18.8 10.4/15.0 10.4/11.3 10.417.5 10.413.8 10.410 2.5118.8 3.8118.8 5.31183 7.9118.8 10.0118.9 lO.Ojl8.9 10.0118.9 10.0118.9 10.0118.9 10.0118.9 10.0118.9 10.0118.9 10.0118.9 10.0/18.9 10.0118.9 10.01 18.9 10.0118.9 10.01 18.9 lO.O/l8.9 10.0114.2 10.0/9.5 10.0/4.7 10.010 7.2118.9 4.5118.9 2.2/ 18.9 1.3/18.9 1.0118.9 20.9/16.6 20.9116.6 20.9116.6 20.9116.6 20.9116.6 20.9116.6 20.9/ 16.6 20.9/16.6 20.91 16.6 20.9/ 16.6 20.91 16.6 20.9116.6 20.9/10.0 20.916.7 20.910 2.1116.6 5.4116.6 10.7116.6 4.9120.0 4.9120.0 4.9/20.0
Conversion of HC, Yo
22 28 35 26 29 41 28 33 51 32 35 53
conversion
One-pass yield, % CHE
3 5 7 5 8 11 5 8 10 4 4 6
BEN
TOL
XY
DEC'
TET
of 0.
NAP
COJ CO
1 3 4 2 4 8 3 5 7 4 5 7
1
1
2 2 2 3 4 3 4 5 3 4 6
3 3 2 4 6 3 5 7 4 5 8
YO
24 41 48 43 56 66 52 66 75 64 72 81
0 0 0
(9-mol)
(liter catalyst) (hr)'
102 183 215 96 127 145 88 111 127 72 81 91 0 0 0 61 43 21 5
49 42 25 13
9 7 4 2
5 4 2 1
4 2 2 1
5 2 2 1
45 42 30 15
27 45 48 52 11 37 40 16 40 52 28 51 60 39 63 68
4 5 7 9
3 4 7 9 2 8 12 4 18 25 9 24 35 17 30 36
2 4 4 7 1 2 4 1 3 5 2 4 5 4 6 7
3 5 5 7 1 3 5 2 5 7 3 6 8 6 9 10
19 27 35 51 23 43 54 43 59 70 53 68 77 66 77 84 0 0 0 59 58 58
0 0 101 65 33
24 21 16 7 37 31 24 22 21 26 31 35 39 43 45 42 46 54
Ind. Eng. Chem'. Prod. Res. Develop., Vol. 10, No. 2, 1971
0
10 8 4
3 2 1
4 2 1
23 21 19 15 15
3 3 3 3 2 0 1 1 0 1 1 1 1 1
5 42 4 27 4 14 4 7 4 5 0 26 1 4 2 1 75 0 38 62 1 89 1 1 62 84 1 1 98
95 61 31 16 11 30 48 84 21 35 50 17 24 28
0 0
0
8 9 11 13 16 20 27 32 41
10 7
39 34 35 41 54 39 54 67
32 46 60 87 100 189 24 1 97 133 157 89 115 129 74 86 95
2 4 8
1 3 7
1 1 5
11 14 23 1 5 4 3 3 8 5 4 3 1 1 5
0 0
0 0
1
1 1 1
1 1
5
6 6
7 5
7
0 60 61
0 0 19 13
62 62 62 2 7 73
33 35 33 275 298 327
Table II. Oxydehydrogenation of CHA, CHE, TET, and DECs on Catalyst I (Continued)
Run
Hydrocarbon"
70 cis-DEC 71 contd. 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 trans-DEC 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111
Temp, "C
GHSV, X 10,' hr
300 350 400 300 350 400 300 350 400 350 350 350 350 350 350 350 350 350 300 350 400 300 350 400 300 350 400 300 350 400 300 350 400 350 350 350 350 350 350 350 350 350
2.53 2.53 2.53 1.58 1.58 1.58 No cat. KOcat. No cat. 2.53 2.53 2.53 2.53 2.53 2.53 2.53 2.53 '2.53 5.07 5.07 5.07 2.57 2.57 2.57 1.93 1.93 1.93 1.28 1.28 1.28 No cat. No cat. No cat. 2.57 2.57 2.57 2.57 2.57 2.57 2.57 2.57 2.57
Mol ratio" HC/O:
Conversion of H C , % CHE
4.9/20.0 48 4.9120.0 66 4.9120.0 90 4.9120.0 51 4.9/20.0 83 4.9120.0 94 4.9;20.0 4.9/20.0 4.9/20.0 4.9115.0 60 4.9:lO.O 52 4.915.0 45 4.910 4.4;ZO.O 64 2.9i20.0 61 2.2/20.0 50 0.5/20.0 41 0.08;20.0 :16 6.6#19.6 33 6.f319.6 53 6.6i19.6 64 6.6:19.6 48 6.6119.6 60 6.6,'19.6 69 6.6:19.6 59 6.6;19.6 68 6.6119.6 74 6.6119.6 64 6.6,'19.6 73 6.6119.6 81 6.6119.6 6.6119.6 6.6119.6 6.015.7 59 6.6111.8 53 6.617.9 42 6.613.9 29 6.610 trace 5.3119.6 56 4.2i19.6 53 2.2119.6 49 1.0119.6 42
One-pass yield, BEN
3
8 10 8 8 9
4 2 1
TOL
XY
2 6 6 5 4 6
3
3
4 1 1
2 3 7 1 3 5 trace 1
4 1 4 2 1
NAP COI
TET
CO
7 6 4 6 7 4 1 1 1 1 5 8 5 13 14 6 9 4 9 1 2 4 7 5 1 1 1 6 5 8 7 12 19 6 10
4 3 4
8 4 1 trace trace 1 3 6 2 5 7 3 5 4 2 3 4
6 3 4 9 9 2 2 4 5 6 1 1 3 4 5 trace trace 2 2 trace trace 1 1 1 trace 8 2 2 1 7 3 3 5 3 5 4 3 1 1 11 4 3 1 1 0 5 6 1 1 0 9 2 1 1 2 4 5 2 11 6 5 1 1 0 7 4 1 1 3 5 5 1 1 1 5 4 1 8 7 9
3 2 1 trace
3 1 7 4 2 1 5 4 1 trace 4 trace trace 4
4 3 2
3 1 7 5 3 1 7 5 1 trace 5 trace 4 3
1
Oh@
4 86 92 79 90 96 0 0 0 5 5 31
167 193 207 111 126 135 0 0 0 126 61 17
1 8 8 46 30 50 8 8 66 77 86 74 83 93 79 89 7 0 0 0 6 9 68 66
183 153 130 103 69 222 256 303 148 172 194 126 140 157 89 100 109 0 0 0 136 93 61 30
2 2 46 29
162 140 103 66
Conversion of O?
Yo
DEC'
Consumption rate of O,, (9-mol)/ (liter catalyst) (hr)'
2 1 1
4 4
4 3
7 7 4
8 6 5
5
8
2 2 1 5 6 3 5 7 3 5 7 3 6 9
2 2
4 4
7 6
4 1 1
1 1 1
2 4 3 5 7 4 6 8 5 7
3 4 2 3 4 2 3 5 2 3
4 3 3 3
7 5 1
1
5 4 2
4 4
4 2
3 3 1 1
2 1
3 2 5 4
2 5
7 6 3 2
'Starting hydrocarbon. 'Mole ratio of starting hydrocarbon t o O? in reaction gas. ' Trans-DEC when HC is cis-DEC, and cisDEC when HC is trans-DEC. dCalculated by: conversion of 02 (%) = 11 - flow rate of O1 in exit gas (ml/sec)/flow rate of O? in reaction gas (ml/sec)] x 100. 'Calculated by: consumption rate of 0, (g-mol)/(liters catalyst)(hr) = [feed rate of O2 (g-mol/ h r ) ] x [conversion of 0, (%)]/100 x [volume of catalyst (liters)].
(run 43), CHA and B E N are obtained. This is in accord with the results reported by Germain et al. (1958) except that methylcyclopentane is not formed. Thus, the reaction diagram for the oxydehydrogenation of CHA or C H E can be shown by the following consecutive reactions which partly include an equilibrium reaction:
coz, c Similar relationships are observed when T E T is oxydehydrogenated. This seems not to belong to the consecutive reactions, but to parallel reactions where NAP is one of the final products. The formation of BEN, TOL, and X Y is not observed, and, moreover, the yields of CO? or CO are negligible. On the other hand, when DECs are oxydehydrogenated, the formation of B E N , TOL, XY,
CO?, and CO from DECs and the isomerization of cisDEC or trans-DEC are observed. The one-pass yields of the reaction products from cis-DEC are larger than those from trans-DEC, and the reverse is true in the recovery of the starting hydrocarbons. These phenomena suggest that TET is comparatively stable, and cis-DEC is more reactive than the trans-isomer under the present conditions. Thus, the reaction diagram for the oxydehydrogenation of T E T and DECs is shown by the following scheme,
NAP Ind. Eng. Chem. Prod.
Res. Develop., Vol. 10, No. 2, 1971
157
Table Ill. Consumption Rate of Oxygen, r
CHA CHE TET cis-DEC tranr-DEC
m
11
2 1 1 2 1
1
=
the concentration of oxygen in the reaction gas, Co,; the rates are proportional to Co- in the cases of C H E , T E T , and trans-DEC. and t o C& in the cases of CHA and cis-DEC. However, for the concentration of the starting hydrocarbons in the reaction gas, C H C , not all of the reaction rates are dependent on CHC. Although the rates are proportional t o CH(?in the cases of CHA and CHE, and to CH&'in the cases of DECs, the situation is different in the case of TET as the rate is virtually independent of CTE.I.when C.ri.:r is larger than 3 x 10.' g-mol per liter of reaction gas. This might suggest the strong adsorption of T E T on the catalyst surfaces. From the data in Table 11, the saturated hydrocarbons obviously yield less B E X or N A P and more CO? and CO than the corresponding unsaturated hydrocarbons. Also, the saturated hydrocarbons have larger rate constants and lower activation energies than the corresponding unsaturated hydrocarbons. The lower activation energy of cis-DEC than t h a t of trans-DEC is expected, for two geminal protons in cisD E C can easily contact the catalyst surfaces simultaneously.
kCECl,
I 0 1 1
where the routes from TET to X Y , CO?. and CO and those from S A P t o XY. CO?, and CO are neglected for the reason just described. Consumption Rate of Oxygen. The consumption rate of oxygen. r. can be estimated by the following equation:
r = X i (ViFo ) = kCt! Chc
(1)
where I ' =
x = V =
Fo
=
k =
co
=
CHC
=
consumption rate of oxygen, (g-mol) '(liters catalyst) [hr) percentage conversion of oxygen. c volume of catalyst. liters feed rate of oxygen, g-mol 'hr rate constant concentration of oxygen in the reaction gas, g-mol/l. reaction gas concentration of the starting hydrocarbon in the reaction gas, g-mol liter reaction gas
Mechanism
For the dehydrogenation of CHA and C H E on activated alumina in the absence of oxygen, Germain et al. (1958) suggested two possible reaction mechanisms. One was based on the observation of Hindin and Weller (1956, 1957) and was related t o the Lewis or Bronstedt active centers on activated alumina, while the other was based on the semiconductivity of alumina recognized by Hartmann (1936). On the other hand, for the cracking of cetane on activated alumina, Greensfelder et al. (1949) suggested the coexistence of two types of active centers.
I n runs 16 t o 20, 40 to 43, 61 to 63, 79 to 82, and 103 to 107, Co is varied, while the reaction temperature, CHC, V, and the feed rate of the total gas are kept constant. I n runs 21 t o 24, 44 to 48, 64 t o 66, 83 t o 87, and 108 t o 111, CH( is varied. while the reaction temperature, C O , V, and the feed rate of the total gas are kept constant. By means of Equation 1, r is calculated and by plotting log r against log Co or log C H C , the following pairs of rn and n are determined (Table 111). When the conversions of oxygen, X , are plotted against the reciprocals of the space velocities, V F o ,the initial consumption rate of oxygen can be determined as the slope a t the origin. From the initial consumption rate of oxygen and Co or C H C , the rate constant, k , can be calculated. The activation energies and the frequency factors. calculated by the method of least squares, are shown in Table IV. Though the details of the reaction mechanisms of these oxydehydrogenation are not clear, the differences in the rate equations seem to indicate the existence of several mechanisms. All of the rate equations are dependent on
nf
-
-AI-
I
0-AI-
CH 0 -AI-
I
I
I
-
11202
YH
-AI
I
I
\+
-Al-O-Al-0-AI-
)
..-
'
-0 -AI-
I
I
0-
OH
I I
0 -AI--
I I
Modification of Germain mechanism
Table IV. Rate Constants, Activation Energies, and Frequency Factors for the Consumption Rate of Oxygen Rate constant, k n
300' C
CHA
1.1 x 10" 3.2 x 10"'
CHE
TET ck-DEC trans-DEC
325" C
2.0 x 10' 2.0 x 10" 4.3 x lo9
350" C
2.0 x 6.7 x 3.4 x 2.9 x 6.5 x
10"
10;" 10' 10" 10"
400" C
2.7 x 1.1 x 7.6 x 5.0 x 8.8 x
10" 10" 10' 10" 10'
Activation energy, E, kcal/mol
9 12 10 4 5
Frequency factor, An
2.0 x 1.1 x 1.3 x 5.7 x 5.1 x
loL6 10'" 10" 10''' 10"
"Units of the rate constants and the frequency factors are as follows: CHA, (liters reaction gas)' /(liters catalyst)(hr)(g-mol)~ ; CHE, (liters reaction gas) / (g-mol)(liters catalyst) (hr); TET, (liters reaction gas)! (liters catalyst) (hr); cis-DEC, (liters reaction gas)"/ (g-mol)(liters catalyst) (hr); trans-DEC, (liters reaction gas)"/ (g-mol)"(liters catalyst) (hr).
158
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
One took part in the carbonium ion reaction, and the other was related to the radical-like species. As is easily understood from Table 111, the mechanisms for the present oxydehydrogenations are not the same for all the starting hydrocarbons. Therefore, it seems impossible to formulate the mechanisms for each hydrocarbon without more detailed experimental results. However, because the catalyst I contains small amounts of SiO? and Fe?Oi as its impurities, it can be taken as a bifunctional catalyst with both types of active centers and any mechanism in which a bifunctional catalyst took part in some radical reaction can be postulated. If we are compelled t o neglect the effect of FeiOi because of its low concentration in catalyst I , the modification of Germain’s mechanism seems instructive, in some cases, to explain the catalytic action of activated alumina in the presence of oxygen, in which the attack of a carbanion to an acidic center is postulated (see opposite page).
literature Cited
Germain, J. E., Bassery, L., Blanchard, M., Bull. Soc. Chim. Fr., 35, 958 (1958). Greensfelder, B. S., Voge, H . H., Good, G. Ind. Eng. Chem., 41, 2573 (1949). Hartmann, W., 2 . Phys., 102, 709 (1936). Hindin, S. G., Weller, S. W., J . Phys. Chem., 60, 1501, 1506 (1956). Hindin, S. G., W-eller, S. W., Aduan. Catal., 9, 70 (1957). Jouy, M., Balaceanu, J. C., French Patent 1,230,447 (September 16, 1960a). Jouy, M., Balaceanu, J. C., Proc. Int. Congr. Catal., 2nd, (Paris), 1, 645 (1960b). Robinson, I. M., U. S. Patent 2,692,292 (October 19, 1954).
d.,
RECEIVED for review August 31, 1970 ACCEPTED February 16, 1971
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
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