the presence of excess oxygen only nearly equal amounts of CO and CO?. Thus, the enhanced COz production under reducing conditions cannot be explained by an enhanced consecutive reaction of acrolein. Instead, it is suggested that under these conditions a parallel pathway for complete combustion directly from propylene becomes important. I n conclusion, it may be stated that the primary catalytic reaction of propylene oxidation over bismuth molybdate is the formation of acrolein. The side products formed result from a subsequent oxidation of the acrolein or its surface species precursor. The selectivity for acrolein is also complicated by the reactor design and the propylene : oxygen ratio: a large postcatalytic volume increases significantly the occurrence of homogeneous reactions; and a deficiency of oxygen enhances the parallel pathway from propylene for complete combustion to COz. These factors need t o be carefully considered in obtaining the maximum selectivity for acrolein formation over bismuth molybdate catalysts. Literature Cited
Adams, C. R., Voge, H. H., Morgan, C. Z., Armstrong, W. E., J . Catal., 3, 379 (1964). Batist, Ph. A., Kapteijns, C. J., Lippens, B. C., Schuit, G. C. A,, ibid., 7, 33 (1967). Callahan, J. L., Grasselli, R . K., Milberger, E. C., Strecker, H. A., Ind. Eng. Chem. Prod. Res. Develop., 9, 134 (1970).
Dalin, M. A., Lobkina, V. V., Abaev, G. N., Serebryakov, B. R., Plaksunova. S. L., Dokl. Akad. Nauk SSSR, 145, 1058 (1962). Dietz, W. A., J . Gas Chromatogr., 5, 68 (1967). Gelbshtein, A. I., Bakshi, Yu. M., Stroeva, S. S., Kulkova, N. V., Lapidus, V. L., Sadovskii, A. S.,Kinet. Katal., 6, 1025 (1965). Gorshkov, A. P., Gagarin, S.G., Kolchin, I. K., Margolis, L. Ya., Neftekhimiya, 10, 59 (1970). Gorshkov, A. P., Kolchin, I. K., Gribov. A. M., Margolis, L. Ya., Kinet. Katal., 9, 1086 (1968). Hall, W. K., MacIver, D. S., Weber, H. P., Ind. Eng. Chem., 52, 421 (1960). Keulks, G. W., J . Catal., 19, 232 (1970). Kusuhara, S.,Reu. Phys. Chem. (Japan), 31, 34 (1961). McCain, C. C., Godin, G. W., Nature, 202, 692 (1964). Peacock, J. M., Parker, A. J., Ashmore, P. G., Hockey, J. A., J . Catal., 15, 398 (1969). Sachtler, W. M. H., Catal. Reo., 4, 27 (1970). Sampson, R. J., Shooter, D., in “Oxidation and Combustion Reviews,” C. F. H. Tipper, Ed., Vol. 1, Elsevier, Amsterdam, The Netherlands, 1965, pp 223,256. Voge, H. H., Adams, C. R., Aduan. Catal. Relat. Subj., 17,151 (1967). RECEIVED for review July 23, 1970 ACCEPTED January 28, 1971 Partial financial assistance for this work was provided by a National Science Foundation-Departmental Science Development Program Grant. Presented at the Division of Physical Chemistry, 159th Meeting, ACS, Toronto, Canada, May 1970.
Hydroformylation of 1 -Pentene and 1-Hexene in Presence of Phosphine-Modified Ca ta Iys t s Wolfgang Rupilius, John J. McCoy, and Milton Orchin’ Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221
I t is now well-known that the addition of trialkylphosphines to the conventional hydroformylation catalyst can lead to as much as 88 to 90% of straight alcohol (Slaugh and Mullineaux, 1966, 1968; Tucci, 1968) compared to the 60 to 70% in the absence of phosphines. I t is also well-established that the presence of phosphines retards the rate of hydroformylation. The early claim (Tucci, 1968) that the hydroformylation of terminal olefins in the presence of n-BusP leads to high proportions of straight-chain isomers independent of temperature (150” to 180”C ) , catalyst concentration, or carbon monoxide partial pressure now appears to be valid only when large concentrations of the bisphosphine complex, C O ? ( C O ) ~ -
‘ To whom correspondence should be addressed. 142
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
( P R J ? , are present, or, when excess butyl phosphine is present with small concentrations of cobalt. I n fact, the controlling conditions determining the selectivity to straight-chain isomer are probably the positions of the equilibria (Bianchi et al., 1969; Piacenti et al., 1970; Szabo et al., 1968)
C O ~ ( C O ) ~ ( P R+~CO )Z 2 C O ~ ( C O ) ~+ PR PR, ~ (1) HCo(C0)3PR, + CO 2 HCo(C0)d + PR, (2) In the presence of an excess of P R I , the active catalyst under most conditions is H C O ( C O ) ~ P R +This catalyst is responsible for high selectivity to straight-chain product. Under conditions where H C O ( C O )may ~ be present, considerably more branched-chain product is formed. This work shows that the relative amounts of the different catalysts
The effect on product distribution of phosphine-modified cobalt carbonyl catalysts in the hydroformylotion reaction at low cobalt concentrations was investigated. By use of preformed CO~(CO)G(PBU~)? as a catalyst, the selectivity of straight-chain product i s particularly sensitive to catalyst concentration at low concentrations of catalyst. At theie low concentrations, the addition of excess phosphine leads to very high ratios of straight-to-branched-chain product. The effect of carbon monoxide pressure, temperature, and volume of solvent can all be rationalized on the basis of the equilibrium The predominance concentration of the two active catalysts: HCo(CO)jPBu3 and HCO(CO)~. of the former leads to slower relative rates but high yields of straight-chain product; the presence of even relatively small amounts of HCo(C0)4 leads to increased rates but larger proportions of branched-chain product.
present under reaction conditions can be reasonably deduced from the product distribution. Results and Discussion
Effect of Excess Phosphine and Catalyst Concentration. Most studies dealing with the effect of phosphine concentrations were conducted with concentrations of cobalt of about 1 mol % or higher, and, in most cases, with PBui as the phosphine. Under these conditions, appreciable quantities of alcohol are produced. However, the authors' results show that a t lower-e.g., 0.2 mol %-cobalt concentrations, and in the presence of PPh3, the products are almost exclusively aldehydes even when relatively large quantities of this phosphine are present. The presence of phosphines slows the rate of hydroformylation; even with a small concentration of cobalt there is a concentration effect of the phosphine. Thus, with CO:H? (1:l) a t 170°C (1840 psi) and 0.2 mol cc Co2(CO),,the relative rates of hydroformylation with the indicated molar ratios (in parentheses) of PPh3/Co are: l ( 0 ) ; 0.95(1); 0.52(2); 0.40(3); 0.12(5); 0.06(15). The detailed analyses of products from one of these reactions are given in Table I. The PPh3/Co ratio of five gives only 72OC straight-chain product. Apparently, triphenylphosphine modification of the conventional system is relatively ineffective in increasing the selectivity to straight-chain isomer. The much more basic tri-n-butylphosphine is much more effective in this regard. Similar conclusions were reached by Slaugh and Mullineaux (1968) and Tucci (1968). A series of experiments conducted with a constant concentration of 1-pentene at 170°C in which the quantity of preformed C O , ( C O ) ~ ( P B Uwas ~ ) ~varied a t a constant BuaP/Co mole ratio shows (Figure 1) that it is possible to increase the relative amount of straight-chain product by increasing the concentration of Co?(CO)6(PBu3)?. This figure also shows (upper curve) that a t catalyst concentrations (0.5 gram per 70 ml solvent) less than those which are optimal for producing straight-chain product, the addition of excess PBu? gives the maximum amount (90%) of straight alcohol. Essentially the same type of behavior was noted with 1-hexene as substrate. Under the conditions leading to high selectivity to straight-chain product, the active catalyst is completely in the form of HCo(C0)3PBu3. I n the presence of cobalt carbonyl only, but under otherwise similar conditions, 59.3% straightchain alcohol is formed. If one takes into account the fact that at 170°C, the rate of hydroformylation with Coe(CO)s[and hence only HCo(CO)?as the active catalyst] is a t least 25 times as fast (Kniese et al., 1969) as with C O ~ ( C O ) G ( P B U[under ~)~ conditions where the active
Table I. Hydroformylation of 1 -Pentene
100 mmol with C O ~ ( C O(0.2 ) ~ mol "c) and P P h l ( P ' C o C 0 = pHs = 940 psig at reaction temp = 17O'C; solvent : benzene, 70 cc
= 5);p
Hydrocorbonsc
Hydroformylation products'
Conversion'
Pentane
1-Pentene
2-Pentene
10% 20 30 50
Tc T T 2.6 8.1
88.4 85.1 75.1 51.5 28.3
11.6 14.9 24.9 45.9 63.6
70
Aldehydes
100 100
99.8 96.4 94.8
Yo Straight
70.9 71.6 71.7 70.3
72.1
%
Alcohols
Straight
T 0.2 3.6 5.2
73.1 67.5
"Percent of total hydrocarbon. 'Percent of total aldehyde and alcohol present; a small (1°C)amount of formate esters was formed near the completion of the reaction. Based on converted pentenes. T = trace. '
t Figure 1 . Hydroformylation of 1 -pentene. Effect of catalyst concentration on selectivity 0.1 mole I-pentene; 70 ml benzene; 1400 psi CO-HI ( 1 '1); temp, 170" C, conversion of 1-pentene over 90%
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 2, 1971
143
t
1 1
-1
9
1t 70
tI
0.15 g
1
30 ml Benzene
I
1 I
120
Figure 2. Hydroformylation of 1 -pentene. Effect of solvent volume on selectivity 0.1 mole 1-pentene; 1400 psi CO-H? (1:l); temp, 170” C; conversion of 1-pentene over 90%
catalyst is H C O ( C O ) ~ ( P B 1,U ~one ) can approximate the position of equilibrium in Equation 2. Thus, when about 70L straight-chain alcohol is produced in the presence of preformed C O ~ ( C O ) ~ ( P BitU may ~ ) ~ ,be estimated that more than 90‘; of the active catalyst is present as HCo(C0) P B u , and that the balance is present as HCo(CO),. Effect of Solvent Volume. If, under a standard set of conditions. the distribution of products is analyzed as a function of the quantity of solvent, it is found (Figure 2) that as the volume of solvent is reduced while keeping the molar ratio of catalyst : olefin constant, the selectivity to straight-chain alcohol is increased. These experiments were desirable as it is difficult to ascertain from Figure 1 whether the increase in Co:CO or the increase in Co: olefin was responsible for the increase in straight-chain product. In the presence of smaller amounts of solvent, the concentration of the phosphine complex relative t o the concentration of dissolved carbon monoxide is increased. The conversion of HCo(CO), to the phosphine complex (Equation 2) leads t o the observed increase in straight-chain product. Effect of Carbon Monoxide Partial Pressure. Under conditions that are standard except that the partial pressure of carbon monoxide is varied, one might reasonably expect that the higher the carbon monoxide pressure, the higher the concentration of H C O ( C O )relative ~ to HCo(C0)
