Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 481-486
droisomerization/MTBE/alkylationcan result in a 4.9 (R
+ M)/2 octane advantage over straight alkylation of FCC
butenes.
Literature Cited Albright, L. F. ACS Symp. Ser. 1077, No. 55, 128. Albrlght, L. F. Chem. Eng. July 4, 1088. 119. Albrlght, L. F.; Houle, H.; Sumutka, A. M.; Eckert, R. E. Ind. Eng. Chem. Process Des. Dev. 1972, 7 7 , 446. Anderson, J.; McAllister, S. H.: Derr. E. L.; Peterson, W. H. Ind. Em.Chem. 1048, 40, 2295. Bond, G. C.; Webb, G.; Wells, P. 8.; Winterbottom, J. M. J. Chem. Soc. 1085, 3218. Chase, J. D.; Gahrez, B. B. ”Processes for Gasoline Blending Ethers-TAME and MTBE-11,” Presented at Division of Petroleum Chemistry, 179th National Meeting of the American Chemical Society, Houston, Texas, March 1980. Cuplt, C. R.; Gwyn, J. E.; Jernigan, E. C. PeholChem. Eng. Dec 1961, 33; Jan 1082, 34. Ekazar, A. E.; Heck, R. M.; Wtt, M. P. “Hydrc-isomerization of C4 Hydrocarbons”, API 44th Midyear Meeting, May 1979, Proceedings-Reflnlng Department Vol. 58. 3-13.
401
Eleazar, A. E.; Heck, R. M.; McClung, R. G.; Olson, B. A. “Process Modlfications Can Improve MTBE Production”, Presented at the A.1.Ch.E. 88th National Meeting, June 1980. Haag, W.; Pines, H. J. Am. Chem Soc.1060, 82, 2488. Heck, R. M.; McClung, R. G.; Wkt, M. P.; Webb, 0. Hydrocarbon Process. 1980, 59(4) 185. Hofmann, J. E.; Schrbscheim, A. J. Am. Chem. Soc. 1082, 84, 957. Hutson, T.; Hayes, 0. E. ACS Symp. Ser. 1077, 55, 38. Hutson, T.; Logan, R. S., wrocarbon Process. 1075, 9, 107. Li, K. W.; Eckert, R. E.; Albrlght, L. F. Ind. fng. Chem. PIocess Des. Dev. 1070, 9, 441. Roebuck, A. K.; Evering, B. L. Ind. fng. Chem. Prod. Res. Dev. 1070, 9 , 76. Zimmerman, C. A.; Kelly, J. T.; Dean, J. C. Ind. Eng. Chem. prod. Res. Dev. 1082, 7 , 125.
Received for review February 4, 1980 Accepted April 6, 1981 Presented at the 179th National Meeting of the American Chemical Society, Houston, TX, Mar 23-28, 1980, Div. Petr. Chem.
Oxidation of Toluene by Cobalt(II1) Acetate in Acetic Acid Solution. Influence of Water Michael P. Crytko and Gunther K. Bub’ Lehrstuhl fur Technische Chemie, Ruhr-Universkat Bochum, 4630 Bochum, West Germany
The influence of water on the oxidation of toluene by cobalt(II1) acetate in acetic acid has been studied kinetically under aerobic and anaerobic conditions at 87 O C in the range 0.3 < [PhCHJ < 1.2 M, 0.05 < [Co], < 0.4 M, 0.03< [H,O] < 3 M, and 0 C Po, < 0.6 bar. Whereas no influence of water has been detected under anaerobic conditions, under aerobic conditions water enhances the oxidation at lower and inhibits at higher concentrations of water. A maximum rate of benzoic acid production was found at [H20] 1.3 M under the conditions investigated. Based on known findings, a reaction scheme describing the influence of water by waterlfree radical interaction is formulated of which the kinetic constants are determined experimentally.
-
Introduction In the past the oxidation of toluene by cobalt(1II) acetate in acetic acid solution has been investigated by several authors (Morimoto and Ogata, 1967; Heiba et al., 1969; Sakota et al., 1969; Scott and Chester, 1972; Hendriks et al., 1978). The reaction sequences proposed by the authors have several common characteristics: the oxidation proceeds via a free radical sequence, the benzaldehyde formed as intermediate acts as cooxidant, and Co(II1) reacts with toluene yielding a radical cation by an electron transfer mechanism. The radical cation in a subsequent step loses a proton yielding a benzyl radical (Heiba et al., 1969). Though it was already recognized in earlier investigations that water which is formed during the oxidation has a marked effect on the absorption rate of oxygen and the reduction rate of cobalt(II1) acetate (see, e.g., Kamiya and Kashima, 1972),the role of water on benzoic acid formation has not been investigated to date: in most cases measurements were conducted with excess water to adjust a constant level during reaction (see, e.g., Hendriks et al., 1978) or its influence has been simply overlooked. I t is the intent of this study to give some first insights into the influence of water when oxidizing toluene by cobalt(II1) acetate in acetic acid under aerobic and anaerobic
* Chemische Werke Huls AG, Zentralbereich Forschung und Entwicklung FF 33, Lipper Weg, D 437 MARL, West Germany. 0196-4321/81/1220-0481$01.25/0
conditions to benzoic acid and to give a possible explanation of the effect of water on the oxidation. Experimental Section Materials. Toluene, acetic acid, chlorobenzene and cobalt(I1) acetate were used with AR quality as received. For preparation of cobalt(1II) acetate (Walker and Kopsch, 1932), air containing 5 % acetaldehyde was bubbled through a solution of 300 g of cobalt(I1) acetate in 3 L of acetic acid with 1% water at 80 “C. When 7040% conversion was reached the solution was evaporated a t 40 “C at a pressure of 2.7 X bar. The acetate obtained was dissolved in glacial acetic acid. The water content of all chemicals used was determined by Karl Fischer titration. Procedure. The oxidation was carried out at 87 “C in the reactor shown in Figure 1 (inner diameter 4 cm, length 25 cm). The whole reactor was made of glass, and the bearings consisted of Teflon. Since under the conditions used the reaction was so fast that oxygen depletion in the bulk of the liquid phase was observed, the six-blade stirrer together with four baffles as shown in Figure 1have been used, by which the oxygen concentration in the reaction mixture was maintained at 7590% of the saturation concentration. The liquid phase volume of 270 mL was stirred at a rate of 670 rpm. The oxygen-nitrogen mixture was blown in at the bottom of the reactor. The upper bearings were rinsed by a small N2stream. The exit gas stream of the reactor was cooled in such a way that with 0 1981 American Chemical Society
482
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981
f
1 \\
0
C
I
1
2
3
L
5
t ihl
Figure 2. Oxidation of 0.85 M toluene with pol = 5.7 X bar in the presence of 0.135 M cobalt(II1) acetate ([Co],, = 0.257 M and [H,O]O = 0.05 M) showing product formation from heating period: A, [Co(III)]; 0,[PhCHO]; V, [PhCH20Ac]; O , [PhCOOH]; 0 , 0.1[PhCHJ.
Figure 1. Reactor used for kinetic measurements: 1,stirring shaft; 2, PVC piston rod collar; 3, Nz inlet for rinsing; 4, Teflon bearings; 5, thermometers; 6, sampling cocks; 7, gas exit for reflux cooler.
the exception of toluene only negligible amounts of the reaction mixture were lost during an experimental run. Whereas the concentration of cobalt(II1) acetate during reaction was determined by iodometric titration, toluene, benzaldehyde, and benzyl acetate were analyzed by gasliquid chromatography using a Varian 2740 gas chromatograph with flame ionization detector and a 2 m, ' / e in. 5 % silicone OV 17 column and temperature programming (80-220 "C with 8 OC/min, helium flow 25 cm3/min). Benzoic acid, benzaldehyde, and benzyl acetate were analyzed by high-pressure liquid chromatography using a UV detector (Perkin-Elmer LC 15,254-nm mercury lamp) and a 30-cm y-Bondapak CI8column (inner diameter 3.9 mm, particle size 10 pm, 23 "C). The mobile phase flowing at a rate of 2.3 mL/min was a mixture of 17.3% acetonitrile, 8.28% methanol, 74.3% water, and 0.12% phosphoric acid. The oxygen-nitrogen mixture was adjusted by capillary flow meters. The initial toluene concentrations were varied between 0.3 and 1.2 M, the initial cobalt(I1) and cobalt(II1) acetate concentrations between 0.03 and 0.2 M, the initial water concentrations between 0.03 and 3 M and oxygen between 0 and 0.6 bar partial pressure in the gas. Chlorobenzene (0.36 M) was added to the solution as internal standard for GLC. The water concentrations of the reaction mixture during an experimental run were determined from a balance because Karl Fischer titration has been too time consuming. For investigating the effect of water and for determining the kinetic constants of the reaction scheme used, 40 concentration-time curves for toluene, cobalt(II1) acetate, benzaldehyde, benzyl acetate, and benzoic acid with varying initial conditions in the range given above have been measured. The kinetic constants have been determined by the maximum likelihood method with prescribed diagonal covariance using a third-order variable step predictor corrector method for numerical integration of the reaction rate equations according to the reaction scheme used; for finding the maximum the Gauss-Newton method
with modifications by Greenstadt-Eisenpress, Bard, and Carol1 was taken (Bard, 1974). Because of the loss of toluene during reaction the measured toluene concentrations were only used as actual values for integration but not for evaluating the maximum likelihood function (for further details see Czytko, 1979). Results Under anaerobic conditions toluene was converted by cobalt(II1) acetate into benzyl acetate as the main product; a subsequent formation of benzaldehyde and benzoic acid was observed. Benzyl alcohol, xylenes, benzylidene diacetate, and an unidentified benzyl dimer (not 1,2-diphenylethane) were formed as byproducts (all together
