Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 217-225
reaction (reaction 1) over Cu and for both the series reaction (reaction 1) and the direct oxidation (reaction 2) over Pt. Ismagilov et al. examined the selectivity for ethanol oxidation over Cu and Pt catalysts by varying the space velocity through their reactor. They found that, over Cu, acetaldehyde was produced almost exclusively at high space velocities (Le., low conversions of ethanol) whereas C02was produced almost exclusively at low space velocities (Le., high conversions of ethanol). With the Pt catalyst, Ismagilov et al. found the selectivity for acetaldehyde to be nearly constant (over ethanol conversions ranging from 0.3 to 0.6) while selectivity for C02 increased. They interpreted the selectivity data as indicating that ethanol oxidation proceeds almost exclusively by the series reaction mechanism (reaction 1) over Cu and by a combined series-direct reaction mechanism (reactions 1 and 2) over
217
Acknowledgment The catalysts used in this study were prepared by Dr. Michael D'Aniello, Jr., and Miss Kim Dang. We also wish to thank Mr. R. M. Sinkevitch for helpful suggestions regarding modifications to the reactor system. Registry No. Cu, 7440-50-8; Cr, 7440-47-3; Pt, 7440-06-4; Mn, 7439-96-5; ethanol, 64-17-5;acetaldehyde, 75-07-0; carbon monoxide, 630-08-0; carbon dioxide, 124-38-9.
Literature Cited Bailey, W. H.; Edwards, C. F. Proceedings of the Fourth International Symposium on Alcohol Fuels Technology, Guaruja, Sao Pauio, Brazil, Oct 1980, Paper 6-61. BechtoM, R.; Pullman, J. B. Society of Automotive Engineers, 1980; Paper No. 600260. Chui, G. K.; Anderson, R. D.; Baker, R. E.; Pinto, F. B. Proceedings of the Thlrd International Symposlum on Alcohol Fuel Technology, Asiiomar, CA, May 1979, Paper 11-18, Edwards, J.; Nicoiaidis, J.; Cutlip, M. 6.; Bennett, C. 0.J . Catal. 1977, 5 0 , 24. Ganguiy, N.; Janaklram, K.; Nag. N.; Bhattacharyya, S. J . Appl. Chem. Biotechno/. 1975, 25, 335. Goodrich, R. S. Chem. Eng. Prog. 1982, 78, 29. Ismagiiov, Z . R.; Dobrynkin, N. M.; Popovskii, V. V. React. Kinet. Catal. Lett. 1979, 10, 55. Iwasawa, Y.; Nakano, Y.; Ogasawara, S.J . Chem. Soc.. Faraday Trans 1 1978, 7 4 , 2968. Kiimisch, R. L. "Oxidation of CO and Hydrocarbons Over Supported Transition Metal Oxide Catalyst"; GM Research Publication GMR-842, 1968. Krylov, 0. V.; Fokina, E. A. Repr. Fourth Int. Congr. Catal. Moscow 1968, 3, 1166. Legendre, M.; Cornet, D. J . Catal. 1972, 25, 194. Pernicone, N.; Lazzerin, F.; Liberti, G.; Lanzavecchia, G. J . Catal. 1969, 14, 293. Santacesaria, E.; Morbideili, M. Chem. Eng. Sci. 1981, 3 6 , 909. Sexton, B. A. Surf. Sci. 1979, 88, 299. Sexton, B. A.; Renduiic, K. D.; Hughes, A. E. Surf. Sci. 1982, 121, 181. Srihari, V.; Viswanath, D. S.J . Catal. 1976, 4 3 , 43. Takezawa, N.; Hanamaki, C.; Kobayashi, H. J . Res. Inst. Catal. Hokkaido Univ. 1980, 28(3), 347. Thomas, C. L. "Catalytic Processes and Proven Catalysts"; Academic Press: New York, 1970. Wachs, I. E.; Madix, R. J. Appl. Surf. Sci. 1978, 1 , 303. Walker, J. F. "Formaldehyde"; Reinhold: New York, 1964.
Pt. Our proposed mechanisms are also consistent with recent studies of ethanol oxidation on Cu and Pt single crystals. Wachs and Madix (1978) found acetaldehyde to be the principal carbon-containing product in temperature-programmed reaction (TPR) of adsorbed ethanol with adsorbed atomic oxygen on Cu(ll0). In contrast, Sexton et al. (1982) found CO to be the only carbon-containing gaseous product from the TPR of ethanol with oxygen on a Pt(ll1) surface. Thus, the TPR studies confirm the existence of the first step of the consecutive reaction mechanism (reaction 1) on Cu and suggest that our proposed direct oxidation pathway (reaction 2) in the combined series-direct mechanism on Pt may involve the formation of carbon monoxide as a reaction intermediate. The reaction steps leading to the formation of acetaldehyde from the oxidation of ethanol on Pt have not been elucidated, however, and additional work is needed, both on single crystals and supported catalysts, to identify the reaction intermediates produced in the oxidation of ethanol and to identify the factors controlling selectivity for the production of carbon dioxide and acetaldehyde.
Received f o r review August 9, Revised m a n u s c r i p t received November 22, Accepted November 22,
1982 1982 1982
Catalytic Amination of Aliphatic Alcohols in the Gas and Liquid Phases: Kinetics and Reaction Pathway Alfons Balker,' Walter Caprer, and Wllllam L. Holstein Swiss Federal Instltute of Technology (ETH), Department of Industrial and Engineering Chemistry, 8092 Zurich, Switzerland
The kinetics of the copper-catalyzed amination of long-chain aliphatic alcohols (octanol and decanol) by monomethylamine and dimethylamine have been investigated in both the gas and liquid phases at temperatures between 440 and 540 K. The Individual reactions leadlng to the production of stable intermediates and products are identified. The rate of dehydrogenation of the alcohol determines the overall rate of alcohol conversion to all products. The rate is first order in alcohol in both the gas and liquid phases and inhibited by alcohol, water, and the reactant amine in the gas phase only. The selectivity is determined primarily by the rate of hydrogenation of an adsorbed intermediate and the rate of disproportionation of reactant and product amines. The selectivity of the amination reaction to the desired tertlary amine increases with increasing hydrogen pressure, and first increases and then
decreases with increasing conversion of alcohol.
Introduction The catalytic amination of higher aliphatic alcohols represents an economical way for the synthesis of aliphatic amines. In spite of the industrial importance of this synthesis, to our knowledge, studies on its kinetics and 0196-432118311222-0217$01.50/0
reaction pathway have only been reported for the amination of octanol with ammonia on a molten iron catalyst (Kliger et al., 1975a,b). A variety of different catalyst types for the amination of alcohols has been suggested in the patent literature. As a result of the testing of numerous 0 1983 American Chemical Society
218
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 2, 1983 Table I. Properties of Catalysts Employed
c uI
7-alumina (A) 66% CuO 24% A1,0, 9%H,O 23
c uI 7-alumina (B) 11%CuO 77% A1,0, 12%H,O 19
c uI silica' (C) 22% CuO 74% SiO, 4%H,O 34
properties chemical composition before reduction, wt % mean copper particle size,b nm 106 84 BET surface area, 78 mZ/g specific pore volume, 0.556 0.480 0.529 g/cm3 a Manufacturer BASF. Determined by X-ray diffraction line broadening after reduction.
=.Heated
line
N2 I-$ Amine
Figure 1. Apparatus for liquid phase experiments: 1, flow meters; 2, column packed with KOH pellets; 3, column packed with sodium; 4,Deoxo purifier; 5, column packed with Drierite; 6, compressor; 7 , preheater; 8, stirred autoclave; 9, condenser; 10, gas meter.
catalysts for the amination of dodecanol with dimethylamine, supported copper catalysts were found to exhibit the highest selectivity to dimethyldodecylamine (Baiker and Richarz, 1977a; 1978a). The high selectivity of copper was attributed to its inability to break carbon-carbon bonds under amination conditions (Baiker and Richarz, 197713). The present study is centered on the investigation of the kinetics and reaction pathway of the copper-catalyzed amination of higher aliphatic alcohols. The objective was to gain a better understanding of the factors controlling the rate and selectivity of the amination. The reactions studied were the amination of 1-octanol and 1-decanolby dimethylamine ROH NMzH = NMzR + HzO
+
and monomethylamine ROH + NMHz = NMRH
+ HzO
where R = C8HI7for octanol, R = CloHzlfor decanol, and M 5 CH,. Experimental Section Apparatus. Experiments in the gas phase were performed with a continuous fixed bed reactor described previously (Baiker, 1981). The experimental apparatus for the liquid phase experiments (Figure 1) consisted of a stirred autoclave (600 mL), a metering system for hydrogen, nitrogen, and the reactant amine, and a membrane compressor (SERA, TYP 1000/320/16). The reactor temperature was controlled by a recirculating oil bath. Materials. The preparation and reduction procedure of the Cul ?-alumina catalysts has been previously described (Baiker and Richarz, 1978b). The commercial Culsilica (BASF) catalyst was reduced similarly with a final temperature of 520 K. Some physical properties of the catalysts used are summarized in Table I. The catalysts were characterized by BET nitrogen adsorption, mercury porosimetry, X-ray diffraction, and chemical analysis. X-ray diffraction patterns of the catalyst samples were obtained with a Norelco (Philips) X-ray diffractometer using Cu Kcu radiation. Corrections to the
observed line breadth for instrumental broadening were made using the curves given by Rau (1963). The following reactant purities were quoted by the manufacturers: 1-octanol and 1-decanol >99% ; monomethylamine and dimethylamine >97 % (impurities primarily other methylamines). Hydrogen (99.99%) was purified by passage through a Deoxo catalytic hydrogen purifier (Engelhardt) and Drierite. Nitrogen (99.99%) was purified by passage through a column packed with Ascarite, a hot copper-filled furnace, and Drierite. The a,a-dideuterated octanol employed for the isotope studies was synthesized by reduction of ethyl caprylate with L A D 4 according to a procedure reported by Nystrom and Brown (1947). Mass spectrometric analysis of the alcohol synthesized indicated that the octanol-dzcontent exceeded 96%. Analysis. Identification and quantitative analysis of the products has been described in earlier reports (Baiker and Richarz, 1977a; Baiker, 1981). Procedure. Experiments in the liquid phase were performed by semi-batch operation using the apparatus shown in Figure 1. A batch of 164 g of alcohol and 4.1 g of catalyst was charged into the autoclave. A continuous flow of hydrogen, nitrogen, and methylamine was fed to the reactor during the reaction. The total pressure was 630 kPa. The liquid, dissolved gas, and catalyst particles (diameter
