Ind. Eng. Chem. Prod. Res. Dev. 1985,2 4 , 340-342
34
Soum, A,; Fontanieile, M. Makromol. Chem. 1981, 16'2, 1743. Tait, P. J. T. Dev. Polym. 1979, 2. 81. Truong, V. T.; Williams, D. R. G.; Allen, P. E. M. f u r . Polym. J. 1985, in press. Wallis, R. C. University of Adelaide, South Australia, unDubiished data, 1981. Wiles, D. M.; Bywater, S . Polymer 1962, 3 , 175. Wittman, J. C.; Kovacs. A. J. J. Polym. Sci., Polym. Symp. 1969, 16, 4443. Yermakov. Yu.; Zakharov, V. Adv. Catal. 1975, 2 4 . 173. Yuki, H.; Hatada, K. Adv. Polym. S d . 1979, 3 1 . 1.
Zambelii. A.; Allegra, G. Macromolecules 1980, 13, 42.
Receiued for reuiew September 17, 1984 Accepted January 28, 1985 The work described was
by the
Research
Grants Scheme. It was presented in part at the 14th Australian Polymer Symposium, Ballarat, Victoria, February 1984.
COMMUNICATIONS Selective Synthesis of Acrylonitrile from Acetonitrile and Methanol over Basic Metal Oxide Catalysts Catalytic synthesis of acrylonitrile from acetonitrile and methanol was achieved by using basic metal oxide catalysts based on magnesium oxide. At elevated temperature (>350 "C), acrylonitrile was yielded selectively (>go%) with minor amounts of propionitrile and methacrylonitrile. The ratedetermining step of the reaction is the abstraction of the proton from the methyl group of acetonitrile by the surface basic site on the oxide catalyst, followed by C=C bond formation with methanol adsorbed on the oxide surface.
Introduction
Acrylonitrile is one of the most important chemicals in the chemical industry. The current industrial synthetic method is a partial oxidation process, called the SOH10 process, where propylene is oxidized by molecular oxygen in the presence of NH, over multicomponent bismuth molybdenum oxide catalyst (Callahan et al., 1970; Grasselli et al., 1982). In recent years, acrylonitrile synthesis from C1 chemicals such as CO, CH,OH, and CH4 has increased in interest. For example, acrylonitrile can be synthesized oxidatively from CH4and acetonitrile, which is synthesized from CO, Hz and NH, catalytically (Monsanto process) (Khcheyan et al., 1979, 1980: Olive and Olive, 1979). We have developed another general method for synthesizing acrylonitrile selectively from acetonitrile and methanol using binary metal oxide having surface basic properties as a catalyst. In this method, the C-H bond of the methyl group of reactant must be activated by inductive electron withdrawal by the unsaturated substituent such as carbonyl, cyano, or phenyl groups, converting the methyl into vinyl group by the addition of methanol. It is thus widely applicable for synthesizing a,@-unsaturatedcompounds. In this communication, we report the catalytic synthesis of acrylonitrile from acetonitrile by using methanol over various metal ion contained magnesium oxide catalysts and the role of the surface metal ion is discussed. Experimental Section Catalyst Preparation. All chemicals used were of regent grade quality and were commercially available. Various metal ion contained magnesium oxide catalysts, M-MgO [M = Cr(III),Fe(III),Al(III), Cu(II), Ni(II)],were prepared by impregnating magnesium oxide (Soekawa Rika, 99.92%) with the corresponding nitrate solution. The metal ion conntent (wt%) was based on the concentration of metal ion in the preparation solution. All the catalysts were heated in a nitrogen stream for 2 h at 600 0196-432118511224-0340$01.50/0
0
!
2
3
0
5
Time on stream ( h )
Figure 1. Acetonitrile conversion and selectivity to acrylonitrile in the reaction of acetonitrile and methanol over Cr-MgO (3.1 wt % ) catalyst at 350 "C.
"C before the reaction in order to decompose the metal nitrate and to desorb water and COz. The catalyst was used in the form of pellets. Reaction Apparatus and Conditions. The reaction at atmospheric pressure was carried out in a conventional flow system equipped with a quartz reactor and a tubular furnace. The reactant mixture (acetonitrile/methanol = 1/10) was introduced into the flow line by a syringe pump and evaporated in a preheater tube. Nitrogen was used as the diluent and the flow rate was maintained at 70 mL/min. Quantitative analysis of the products was carried out by using gas chromatography [Adsorb P-1 (3 m, 170 "C, He carrier) for reactant and acrylonitrile, and Molecular Sieve 13X (0.5 m, 25 "C, Ar carrier) for HZ,CHI, and CO]. Results and Discussion Figure 1 shows the plot of acetonitrile conversion and selectivity to acrylonitrile as a function of time in the reaction of acetonitrile with methanol over Cr-MgO (3.1 w t % ) catalyst at 350 "C. An initial decrease in the con0 1985 American Chemical
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 24.
No. 2, 1985 341
Table I. Conversion and Selectivity Data for Catalytic Synthesis of Acrylonitrile over Various Metal Ion Contained Catalysts' cat. selectivity, % run M-MgO wt% cat. wt, g react. temp, "C acetonitrile conv, % AN PN 1 0 1 350 0.1 tr tr 350 2.5 tr tr 3.1 1 2 A1 73.2 11.6 3.1 1 350 11.2 3 Fe 350 6.2 95.0 5.0 0.48 1 4 Cr 350 8.8 94.9 5.1 1.5 1 5 Cr 350 3.1 96.5 3.5 3.1 0.24 6 Cr 350 6.2 95.1 4.9 3.1 0.54 7 Cr 350 9.6 94.2 5.4 3.1 1 8 Cr 350 10.7 89.9 10.1 3.1 2 9 Cr 375 13.0 90.1 8.7 3.1 1 10 Cr 400 20.2 89.9 8.6 3.1 1 11 Cr 450 24.5 53.6 11.3 3.1 1 12b Cr 95.5 4.5 5.6 1 350 5.7 13 Cr 350 3.3 95.2 4.8 11.0 1 14 Cr 350 5.5 2.8 33.5 3.1 1 15 Ni 350 2.2 91.0 9.0 3.1 1 16 cu
MAN
tr -
-
tr tr 1.2 1.5 1.6 tr
-
Reactant mixture: methanol 16%, acetonitrile 1.6%, remainder nitrogen. * Steady-state activity was not obtained
version of acetonitrile and a slight increase of selectivity were observed, but stable activity was obtained within a few hours. Similar activity and selectivity changes as a function of time were observed on the other catalysts and at different reaction conditions. Results at steady state are summarized in Table I. The conversion of acetonitrile proceeds over binary oxide catalysts at elevated temperature (>350 OC) and yields acrylonitrile (AN) selectively (>go%) with minor amounts of propionitrile (PN) and methacrylonitrile (MAN). M-MgO
CHSCN
+ CHSOH 3CH,=CHCN
(1)
Especially, it was found that AN was synthesized quite selectively by using magnesium oxide containing chromium (111) ion as catalyst (runs 4-14). Excess methanol was recovered after the reaction but small amounts of CHI and CO which might be formed by the methanol decompositionwere found on every reaction, especially, the reaction over the catalyst loaded with iron. Hydrogen formation was confirmed by gas chromatography and mass spectrometric analysis. Three main points emerge from Table I. First, significant synergism in catalytic activity and selectivity was observed on the binary M-MgO, depending on the kind of additive element. Although magnesium oxide did not show any effective catalysis (run l), the addition of chromium to magnesium oxide has a quite profound effect on the course of reaction; overall catalytic activity based on acetonitrile conversion increased by a fador of 100 and the highest selectivity and stability for the formation of AN is attained (run 8). Replacement of chromium by iron results in a similar effect on the catalytic activity, while the selectivity to AN is slightly low (run 3). Less active catalysts are obtained in the replacement by nickel or copper because of remarkable decay of activity in a short reaction time (runs 15,16). Characteristically, magnesium oxide containing nickel is not effectie for the formation of AN. Probably, AN oligomerized over nickel to form high molecular weight compounds, so that the material balance could not be attained. The addition of aluminum did not result in appreciable effects on activity and selectivity (run 2). Consequently, chromium ion was found to be an essential constituent for high yielding AN. Secondly, excess addition of chromium results in a decrease in activity, while selectivity is not affected at all
(runs 4,5,8,13,14). The formation of saturated compound PN and consecutive C-C bond formation to produce MAN are more appreciable both in higher contact time and in higher reaction temperature, Le., at the conditions for high yields of AN (runs 6-12). These results clearly indicated that PN formed from AN by hydrogenationwith molecular hydrogen formed by the reaction or by the hydrogen transfer from methanol. Finally, magnesium oxide did not show any activity for the reaction of acetonitrile and methanol, while it was active to some extent for the catalytic synthesis of methyl vinyl ketone from acetone and methanol (Ueda et al., 1984). The rate of acetone conversion over magnesium oxide was about 100 times that of acetonitrile conversion. This is due to the lower acidity of methyl hydrogen in acetonitrile than in acetone. This result indicates that the rate-determining step is the abstraction of hydrogen at the methyl group by the surface basic site of oxide catalyst. On the basis of the above results, the mechanism for the present reaction and the role of chromium (111)ion on the magnesium oxide surface were considered briefly as follows. By analogy with the alkylation of toluene to give styrene and/or ethylbenzene over the solid bases (Itoh et al., 1980), this reaction may proceed via a formaldehyde intermediate formed from methanol by dehydrogenation, followed by the condensation of formaldehyde with cyanomethylene anion which formed on surface basic site from acetonitrile. However, since formaldehyde was scarcely detected in the product mixture, it seems reasonable to assume that methanol does not convert to formaldehyde and desorb in the form of formaldehyde from the catalyst, but methanol participates in the reaction at the partially dehydrogenated state on the catalyst surface. From the comparison of activity between MgO and Cr-MgO, it is easily assumed that the proton abstraction ability of surface basic sites of oxide catalyst is enhanced by the addition of chromium to MgO. At this stage, we believe that since chromium (111)ion shows stronger Lewis acidity than magnesium ion, the cyanomethylene anion formed by deprotonation of acetonitrile at basic sites is more stabilized by adsorbing on Cr(II1) ion sites than on Mg(I1) ion sites, so that the fission of the C-H bond of methyl groups is more feasible. Registry No. Cr (111), 16065-83-1; Fe (III), 20074-52-6; Cu (II), 15158-11-9; Ni (II), 14701-22-5; CH,=CHCN, 107-13-1; CHSCN, 75-05-8; CHSOH, 67-56-1; MgO, 1309-48-4; PN, 107-12-0; MAN, 126-98-7; nitrogen, 7727-37-9.
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Literature Cited Callahan, J. L.; Grasselll, R. K.; Milberger, E. C.; Strecker, H. A. I n d . Eng. chem. ~ o d~. e s mv. . 1070, 9 , 134. &amelll, R. K.; Burington, J. D.: Brazdll, J. F. Faraday Discuss. Chem. SOC. 1982, 72, 203. Itoh, I.; Miyamto, A.; Mwkaml, Y. J . Cab/. 1980, 64, 284. Khcbyan, Kh. E.: Revenko, 0. M.; Shatalova, A. N.: Gel'perlna, E. G.; Klebanova, F. D.; Arlnskaya, L. I . NefldrMmiya lO70, 77, 586. Khcheyan, Kh. E.: Shatabva, A. N.; Revenko, 0. M.;Arinskaya, L. I. Neftekhlmiya 1980, 2 O V876. Olive, G.: Olive, S. U.S. Patent 4 179462, 1979.
Ueda, W.; Yokoyama, T.; Moro-oka, Y.; Ikawa, T. J . Chem. Soc., Chem. Commun. 1984, 39.
Research Laboratory of Resources Utilization Tokyo Institute of Technology Nugatsutu-cho 4259 Midori-ku, Yokohama 227, Japan
Wataru Ueda* Toshio Yokoyama Yoshihiko Moro-Oka Tsuneo Ikawa
Received for review September 10, 1984 Accepted January 25, 1985
