Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978 231
-NORMAL AC*IVITY DECLINE +WATER-H13?3GEN R E A C T VAT @ N Ai i E 23TH H O U R
J
l
I
\
a
,
24
16
32
,
\
1 40
HOViiS
F i g u r e 8. Water-hydrogen reactivation (operating conditions: same as shown in Figure 1). T a b l e IV. R e a c t i v a t i o n Studies. X - r a y P o w d e r D i f f r a c t i o n M e a s u r e m e n t s of P a l l a d i u m C r y s t a l l i t e Size duration sintering
H,-H,O H,-H,O
reg. reg.
n o r m a l run ( n o t reg.) n o r m a l run (not r e g . )
catalyst
of regen-
run
eration
duration
av c r y s t a l l i t e size
2h 2h
__-
36 h 36 h 36 h
281 A 287 A 306 A
___
36 h
302 A
conditions, but no significant improvement in activity or activity maintenance resulted. It was then hypothesized that since the water reaction is slow a t these conditions, the simultaneous presence of hydrogen may be advantageous. As the area around P d crystallites is slowly attacked by the water, hydrogen might be catalyzed by the P d to cause hydrocracking of adsorbed species and thereby aid in removing coke in the neighborhood of the P d crystallites, In this manner a relatively small amount of coke removal would either restore activity or prevent further decline by inhibiting the sintering that seems to be facilitated in the presence of coke. The results of a typical run on the laboratory reactor are shown in Figure 8. Midway in the run the DNB feed was stopped, but hydrogen flow was continued and water was substituted for DNB over a 2-h period. Following this procedure, DNB feed was restored and the activity remained essentially constant thereafter for the remainder of the test ( ~ 2 h). 0 Average P d crystallite sizes were compared for waterhydrogen treated catalyst and untreated catalysts with the
same run times, DNB flow rates, and operating temperatures. The results shown in Table IV indicate an apparent reduced rate of sintering for the treated catalysts. It would seem, in view of the leveling off of activity after treatment and the observed decline in sintering, that the water-hydrogen treatment inhibits sintering by removing coke as previously suggested. Tests of recycle gas revealed a doubling of carbon oxide gases after water-hydrogen treatment from 1300 to 2600 ppm, confirming that reaction had indeed occurred. In the presence of Pd, the CO would ultimately be converted to C 0 2 as the gas was recycled.
Conclusions It is possible to combine fundamental knowledge reported in the literature on catalyst deactivation for simple systems with observations on complex industrial systems to yield useful hypotheses on multiple paths to deactivation. Such hypotheses, though not confirmed in fine detail, can be adequately related in a casual sense to observed behavior so that they prove useful tools in avoiding rapid deactivation and in developing procedures for reactivating or inhibiting deactivating phenomena. Although this study is for a specific industrial system, the approach and techniques used for monitoring pertinent changes in catalysts should prove useful for other systems. Literature Cited Amato, I., Columbo, R. L., Protti, A. M., J . Am. Ceram. SOC.,41, 407 (1963). Bailey, W. J., in "High Polymers", Vol. 24, Part 2, p 757, E. C. Leonard, Ed., Wlley-Interscience, New York, N.Y., 1971. Baily, W. E., Danko, J. C., Ferrari, H. M.,Columbo, R., Am. Ceram. SOC.Bull., 41, 768 (1962). Butt, J. B., Adv. Chem. Ser., No. 109, 259 (1972). Clay, R. D., Petersen, E. E., J . Catal., 16, 32 (1970). Gregg, S.J., "The Surface Chemistry of Solids",Chapter 3, Chapman and Hall, London, 1965. Harrison, D. P., Hall, J. W., Rase, H. F., Ind. f n g . Chem., 57 (2), 18 (1965). Hartley, F. R., "The Chemistry of Platinum and Palladium", Wiley, New York, N.Y., 1973. Hilyear, J. C., Stallings, P. S.,Pet. Refiner, 35 (12), 157 (1956). Klug, H. P., Alexander, L. E., "X-Ray Diffraction Procedures", 2nd od, Wiley, New York, N.Y., 1974. Lewis, F. A,, "The Palladium-Hydrogen System", Academic Press, New York, N.Y., 1967. Lynch, J. F., Clewley, J. D., Flanagan, T. B., Phil. Mag., 28 (6), 1415 (1973). Maxted, E. G., Adv. Catal., 3, 129 (1951). Oblad, A. G., Marschner, R. F., Heard, L., J. Am. Chem. Soc., 62, 2066 (1940). Pope, D., Smith, W. L., Eastlake, M. J., Moss, R. L., J. Catal., 22, 72 (1971). Sherwood, P. W., Ind. Eng. Chem., 55 (I), 37 (1963).
Received f o r review J a n u a r y 3, 1978 Accepted May 30, 1978
Methanol Homologation Reaction Catalyzed by Cobalt Carbonyl Gerald S. Koermer" and William E. Sllnkard Celanese Chemical Company Technical Center, Corpus Christi, Texas 78408
The cobalt carbonyl catalyzed methanol homologation reaction was reinvestigated in a batch unit and, for the first time, in continuous unit experiments. Ethanol was the major product, but more than 20 other reaction products were also identified. The same range of products was observed in both batch and continuous unit experiments; however, selectivity to ethanol and potential precursors was markedly greater in the continuous experiments. The effects of temperature, CO/H, ratio, residence time, solvent, and cobalt concentration were studied.
Introduction Current forecasts emphasize the potential increased availability of synthesis gas derived from coal gasification (Wender, 1976). This has spurred renewed interest in the 0019-7890/78/1217-0231$01.00/0
catalytic formation of chemicals from synthesis gas (e.g., Pruett, 1976). A reaction of interest in this area is the cobalt carbonyl catalyzed reaction of methanol and synthesis gas (methanol 0 1978 American Chemical Society
232 Ind. Eng. Chern. Prod. Res. Dev., Vol. 17, No. 3, 1978
homologation) to give ethanol and other C2 and higher products. CH30H
+ CO + 2H2
HCo(C0)d
CH3CH20H
+ HzO
The active catalytic species is generally accepted as being cobalt hydridocarbonyl formed in situ from cobalt carbonyl and synthesis gas (Piacenti and Bianchi, 1977). This reaction was first reported in the late 1940's (Brooks, 1948; Wender et al., 1949), and was briefly studied by several research groups (Wender et al., 1951; Ziesecke, 1952; Burns, 1955). Since that time little work has been reported on the reaction (Albanesi, 1973). All published experiments concerning the methanol homologation reaction have used batch unit autoclaves and few reaction products were reported. We wish to report the results of our recent methanol homologation reaction experiments which include both continuous and batch unit operation, as well as the first extensive analysis of methanol homologation products. Experimental Section Batch reaction studies were carried out in a 400-mL 316 stainless steel rocking autoclave. In a typical experiment, 26.0 g of methanol and 1.35 g of dicobalt octacarbonyl were charged to the autoclave; the autoclave was purged of air and pressured to 3200 psig with a 50:50 blend of CO and hydrogen. The reaction mixture was heated to 190 "C over a period of about 2.5 h with rocking agitation and held at that temperature for about 4 h; then heating and agitation were stopped. During the reaction time at 190 OC, about 1000 psig of 5050 CO/H2 gas blend was added to maintain the pressure between 3900 and 4600 psig. Vent gas components (CO, C02,and CH4)were analyzed by a CEI 21-104 mass spectrometer calibrated with known samples. Liquid products were analyzed by gas chromatography (as detailed below) using two Varian 1200 GC's equipped with flame ionization detectors: (1) temperature, 129 "C isothermal; column, 20 f t X in. 20% Carbowax TPA terminated on 20 mesh Chromosorb W, acid washed; components analyzed, acetaldehyde, 1,l-dimethoxyethane, 1-methoxy-1-ethoxyethane, methyl formate, dimethyl ether, methyl ethyl ether, diethyl ether, methyl propyl ether, and 1,4-dioxane; (2) temperature, 1OG230 "C at 4"/min; column, 12 f t X 1/8 in. Chromosorb 101; components analyzed, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, methyl acetate, ethyl acetate, 1-methoxy-2-propanol, 2-methoxy-1-propanol, and 2-methyl-2-butanol. Identification of product peaks was confirmed on a Varian MAT I11 gas chromatograph-mass spectrometer. Water was determined by Karl Fischer analysis. Continuous unit studies for the methanol homologation reaction were conducted in a 1-L 316 stainless steel autoclave modified for both liquid (methanol plus dissolved catalyst) and sparged gas (CO plus H2) feeds (see schematic diagram, Figure 1). A vent gas take-off allowed for continuous vapor removal, while liquid was continuously removed through a standpipe. The rate of removal was sufficient to maintain a constant reactor liquid level. After leaving the reactor, the vent gas was passed through a chilled water condenser and knock-out pot with demister pad to minimize any carry-over of entrained liquid or condensable products. Any liquid carried over to the knockout pot was recycled to the reactor. The collected liquid product (including unreacted methanol) taken out through the standpipe was analyzed in the same manner as for the batch unit operation. Feed and vent gas compositions were determined continuously using on-line
L GO
@t T
KNOCK- OUT PO1
\I
+ Hp COMPRESSOR
METHANOL FEED
*m__
-
c
t
CATALYST
PUMP LIQUID TAKE.OFF
Figure 1. Schematic drawing continuous unit-methanol ogation.
homol-
gas chromatographs as detailed below: (1) instrument, Beckman 620 D thermal conductivity GC; temperature, 64 "C; column 1, 6 ft X 1/8 in. Porapak T; column 2 , 9 ft X in. Supelco, Carbosieve (60-80 mesh); components analyzed, carbon monoxide, carbon dioxide, methane, and nitrogen; (2) instrument, Varian 1200 flame ionization detector GC; temperature, 100 "C; column, 20 f t X 1/8 in. 20% Carbowax TPA terminated on 20 mesh acid washed, dimethylchlorosilane treated Chromosorb W; components analyzed, dimethyl ether, methyl ethyl ether, diethyl ether, methyl propyl ether, acetaldehyde, 1,l-dimethoxyethane, 1-methoxy-1-ethoxyethane, methyl formate, methyl acetate, methanol, and ethanol. As in the case of the batch unit operation, identification of product peaks in the liquid product and in the vent gas were confirmed on a Varian MAT I11 gas chromatograph-mass spectrometer. Cobalt was fed to the reactor as methanol solutions of cobalt(I1) salts or dicobalt octacarbonyl. These compounds are readily converted to HCO(CO)~ in the presence of hydrogen and carbon monoxide (Emmett, 1957). When C O ~ ( C Owas ) ~ used, the unit feed solutions were prepared, filtered, and stored under a carbon monoxide atmosphere. Calculated selectivity values to any one particular product are molar selectivities based on a product accounted for basis. (molar selectivity to product i) = (moles of product i recovered) x 100% (total moles of all products recovered) For purposes of this calculation, water was neglected as a product. In some cases the selectivity of the catalyst is defined in terms of ethanol potential. This is defined as the sum of the selectivities to ethanol plus products easily hydrogenated to ethanol, including acetaldehyde and 1,l-dimethoxyethane, and twice the molar selectivity to 1-methoxy-1-ethoxyethane(contains 2 mol of recoverable ethanol). Discussion Batch Unit Studies. The cobalt carbonyl catalyzed reaction of methanol with synthesis gas produces ethanol as the major product as shown in Table I, experiment 1. This is consistent with the results of Wender et al. (1951). However, the reaction is not so selective to ethanol as previously reported. We have been able to measure and/or identify many more by-products from this reaction (20 or more different compounds) than the eight products identified in the original disclosure of this reaction. Consequently, on a molar basis, the selectivity to ethanol
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978 233
Table I. Methanol Homologation Experiments experiment no. mode pressure, psig temperature, C liquid reaction volume, mL gas flow, L/min (STP) CO/H, catalysta [catalyst] g/L of methanol liquid feed rate, mL/min solventb molar selectivities, %c acetaldehyde 1,l-dimethoxyethane ethanol 1-methoxy-1-ethoxyethane methyl acetate methyl formate ethyl formate 1-propanol 2-propanol 1-butanol 2-butanol 2-methyl-2-butanol 1-methoxy-2-propanol 2-methoxy-1-propanol dimethyl ether methyl ethyl ether diethyl ether methyl propyl ether methane carbon dioxide carbon monoxide conversion, % methanol conversion, % methanol accountability, %
1
2
3
batch 3900-4600 190 34
continuous 5000 190 400 2.3 0.91 Co(acac), 13 3.1 none
continuous 5000 190 400 2.7 1.1 Co(acac), 13 3.3 25%
1.o CO,(CO), 41
none 2 .o 5.2 37.5 17.4 2.8 3.1 2.3
1.1 2.7 11.3 1.o
10.9 2.7 17 30 108
2 .o 10.2 51.6 0.6 8.3 1.4 1.7 3.8 0.4 0.5 0.3 1.5 2.5 2.3 4.7 2.1 0.2 5.9
1.5 12.1 56.6 0.4 4.7 4.2 2.8 3.3 0.5 0.2 0.2 0.2 d,e d,e 2.7 2.6 0.2 0.2 8.2
41 31 96
26 25 96
Tr
(I Co(acac), is cobalt(I1) acetylacetonate. It is well known that cobalt salts react with carbon monoxide under high pressures t o give Co,(CO), which disproportionates to HCo(CO), in the presence of hydrogen (Emmett, 1957). Experiments using dicobalt octacarbonyl and Co(acac), gave essentially the same results. (See Experimental Section.) Solvent was 1,4-dioxane; % solvent by volume before mixing. Molar selectivity to product i = (moles of product i recovered)/(total Analysis obscured by solvent peak. e Based moles of all products recovered) X 100%. Water was excluded as a product. on batch studies with dioxane as a solvent where analysis of methoxypropanols was accomplished, the maximum contribution of methoxypropanol is estimated t o be n o more than 5 relative % of the total ethanol potential. For this experiment (no, 3 ) if this estimate of methoxypropanols were included, the individual product selectivities would be reduced by a maximum of 3.5% and total ethanol potential would drop from 71.0% t o 68.5%
is about 40% a t methanol conversions of 30-50% with substantial quantities of acetates, ethers, higher alcohols, methyl formate, methoxypropanols, methane, carbon dioxide, and other products also being produced. The activity of the catalyst is also low with an ethanol yield of about (50 g/L of catalyst solution)/h at 180-190 " C and 4-5000 psig. This ethanol production rate measurement, however, is not very precise since it is difficult to ascertain the contribution to product yield occurring during the heat-up and cool-down periods in batch unit operation. Attempts to improve the selectivity or activity of the cobalt catalyst by the addition of various ligands or cocatalysts were not successful. Ligands tested included phosphines, amines, nitriles, pyridines, and phenols with co-catalysts consisting primarily of other metal carbonyls (Fe, Cr, Mn, Re) or soluble metal complexes (Rh, Pt, Cu, V). Halide promoters were specifically excluded from this investigation due to their corrosive properties. Solvents were used with limited success. Many of the solvents tested either were reactive or suppressed the methanol homologation reaction. However, nonpolar, water miscible solvents, in particular 1,4-dioxane, did increase ethanol potential (molar selectivity to ethanol plus products easily hydrogenated to ethanol including acetaldehyde, 1,l-dimethoxyethane, and l-methoxy-l-ethoxyethane) by about 10 relative 70. The by-product
showing the greatest decrease in selectivity was methyl acetate, 78 relative % reduction. Nonpolar, water immiscible solvents, such as n-octane or benzene, also reduced methyl acetate yield but did not improve ethanol potential due to increased yields of methoxypropanols. Continuous Unit. Batch unit data for the methanol homologation reaction seemed unsatisfactory for several reasons. Long residence times inherent in the batch process due to long heating and cooling times could lead to many by-products. A buildup of by-products or water could change the reaction medium and alter the course of the reaction. Also, batch unit data have sometimes proven to be imprecise and unreliable; for example, different investigators have reported very different results (see Albanesi, 1973; Wender, 1976). Since the true potential of the methanol homologation reaction could best be determined at steady-state conditions, experiments were conducted in a continuous high-pressure unit as previously described. Table I, experiment 2, contains conditions and molar selectivity data for a typical continuous unit run at 5000 psig, 190 "C, without solvent. The same range of products observed in the batch studies is present; however, the relative amounts, as reflected by molar selectivities, have changed. Total ethanol potential has increased to about 65% from 45%. This represents a significant increase in
234
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978
Table 11. Effect of Process Variables on Methanol Homologation Reduction-Continuous Unit OperationC experiment no. pressure, psig temperature, "C liquid reaction volume, mL gas flow, L/min (STP) CO/H, catalyst" [catalyst] g/L of methanol liquid feed rate, mL/min molar selectivities, %b acetaldehyde 1,l-dimethoxyethane ethanol 1-methoxy-1-ethoxyethane methyl acetate methyl formate ethyl acetate 1-propanol 2-propanol 1-butanol 2-butanol 2-methyl-2-butanol 1-methoxy-2-propanol 2-methoxy-1-propanol dimethyl ether methyl ethyl ether diethyl ether methyl propyl ether methane carbon dioxide carbon monoxide conversion, R methanol conversion, % methanol accountability, %
4
5
6
7
8
9
5000 180 450 2 .o 1 Co(acac), 13 3.3
5000 180 469 2 .o 1 Co(acac), 13 2.1
5000 180 470 2.0 0.93 Co(acac), 13 5.0
5000 180 47 0 1.5 0.65 Co(acac), 13 5.5
5000 180 450 2.1 0.85 Co(acac), 13 3.3
5000 180 400 2.0 2.3 Co(acac), 13 3.3
5.1 13.2 44.7 0.2 7.6 2.0 1.2 2.6 0.9 0.5 0.3 1.0 3.2 1.8 7.7 2.5 0.9
2.3 34.7 22.6
4.4
0.1 3.4
37 18 105
15 16 103
3.3 16.7 40.9 0.2 8.2 1.8 1.5 2.6 0.9 0.5 0.3 1.5 3.1 2.1 7.7 2.3 0.1
2.4 25.1 32.3
5.6
2.4 13.2 42.6 1.o 9.2 1.6 1.4 3.0 0.3 0.7 0.2 2.1 2.2 2.2 8.7 2.6 0.2 Tr 6.0
12.1 1.0 2.6 2.0 1.0 0.5 0.1 1.1 3.6 1.7 6.3 1.6 0.1 Tr 6.0
2.0 15.6 47.2 0.2 6.8 0.8 3.4 3.2 0.6 0.6 0.3 1.8 3.7 2.9 4.5 1.5 0.1 Tr 4.2
42 27 96
30 28 100
36 24 100
62 23 100
Tr
Tr
15.9 2.0 6.0 0.9 0.5 0.2 0.3 0.2 3.4 0.9 4.8 1.7
Tr
a Co(acac), is cobalt(I1) acetylacetonate. It is well known that cobalt salts react with carbon monoxide under high pressures to give Co,(CO), which disproportionates to HCo(CO), in the presence of hydrogen (Emmett, 1957). Experiments Molar selectivusing dicobalt octacarbonyl and Co(acac), gave essentially the same results. (See Experimental Section.) ity t o product i = (moles of product i recovered)/(total moles of all products recovered) X 100%. Water was excluded as a See Table I11 for process variables studied. product.
Table 111. Process Variable Effects--Summary parameter
comparative expts
change
temperature
2,4
190
residence time
5,6
3.7
high CO/H, ratio
8,9
0.85
low CO/H, ratio
6,7
0.93 --+ 0.65
cobalt concentrationb
180 "C
-f
+
1.6 h
-f
2.3
0.05 0.20 mol of Co/L of solution -f
results" Rate about halved in going from 1 9 0 t o 180 "C. Ethanol selectivity decreased by 21%. (AcH t DMOE) selectivity increased by 64%. Changes relative amounts of ethanol and DMOE. Short residence times favor DMOE. Little overall effect on selectivities. Ethanol selectivity decreased by 49%. 2 (AcH t DMOE) selectivity increased by 49%. Methyl acetate selectivity increased by 109%. Increased ethanol selectivity by 46%. .z (AcH + DMOE) selectivity decreased 36%. Decreased methyl acetate selectivity by 44%. Increasing Co concentration gives higher rate and methanol conversion. High Co concentrations result in solid deposition.
a AcH = acetaldehyde, DMOE = 1,l-dimethoxyethane; %changes reported are relative; for example, a variable change reCo,(CO), as catalyst sulting in a drop in ethanol selectivity from 50 t o 40% gives a 20% decrease in ethanol selectivity. source, methanol feed vessel with dissolved catalyst kept under CO atmosphere.
selectivity over batch unit operation (44 relative % increase). Major unwanted side products from the continuous runs are methyl acetate, dimethyl ether, methane, and methoxypropanols. Little or no COz is formed. Variables studied included temperature, methanol feed rate (residence time), CO/H2 ratio, solvent, and cobalt concentration. All experiments were done at 5000 psig. Effects of variable changes are compiled in Table I1 and summarized in Table 111. In general a variable change such as temperature will often affect the relative amounts of ethanol, acetaldehyde and 1,l-dimethoxyethane pro-
duced; however, the sum of these three products remains essentially constant. Increasing the cobalt concentration (0.05 to 0.20 mol of Co/L of methanol) increases the reaction rate and conversion but also results in a tendency for solid deposition on the reactor surface. Because of this loss of catalyst, the effect of increased cobalt concentration could not be quantified. Batch studies had suggested that 1,4-dioxane might be a good solvent for the reaction. Using batch conditions, dioxane was inert and its use resulted in a decrease in
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17,
unwanted by-products. Experiment 3, Table I, is a typical continuous unit run with 1,6dioxane as solvent (25% dioxane by volume before mixing). The liquid feed consisted of methanol, dioxane, and cobalt catalyst. Selectivity to ethanol potential was marginally improved. The rate of reaction declined approximately linearly with dilution at least in the 25-50% solvent range. For example, a 50% dilution of methanol with dioxane reduces the reaction rate by about one-half. Even without solvent the methanol homologation reaction is slow. Space time yields of ethanol potential a t conditions similar to experiment 2 in Table I are only (70-75 g of ethanol/L of catalyst solution)/h. This low rate represents a major obstacle to commercial exploitation of this reaction. No ligands or catalysts were found that significantly improved the reaction rate. Halogen promoters were not employed; however, other investigations (Berty and Markol, 1956; Mizoroki and Nakoyama, 1964; Riley and Bell, 1966; Slaugh, 1977) indicate their effect is not substantial. Previous researchers (Ziesecke, 1952; Sternberg and Wender, 1959; Albanesi, 1973) have suggested that acetaldehyde (which is then hydrogenated to ethanol) is the initial product from the methanol homologation reaction. Our results are consistent with this hypothesis. As mentioned previously, both batch and continuous unit experiments show a nearly constant sum relationship of ethanol and acetaldehyde selectivities. This interrelationship of ethanol and acetaldehyde selectivities, as well as the effect of residence time, CO/H2 ratio, and temperature is certainly consistent with a reaction pathway including acetaldehyde as a key intermediate product. Most of the numerous by-products produced can be explained on the basis of further reactions of initial products with either synthesis gas, methanol, or each other. Cobalt hydridocarbonyl facilitates these reactions by acting as either an acid or synthesis gas catalyst. At high methanol conversions the formation of by-products is particularly evident. Proposed mechanisms for formation of ethanol and other products are summarized in Scheme I. Acetate or formate by-products could be produced by an alternate mechanism to the formation of acetaldehyde (Piacenti and Bianchi, 1977) as illustrated in Scheme I. Methane most likely results from the hydrogenation of CO, catalyzed perhaps by traces of cobalt metal-a known methanation catalyst. The presence of methoxypropanols in the reaction product, however, is quite unexpected. It is possible that they result from a common 1,2-propanediol intermediate, although this diol was not detected in our analysis of the liquid product. H CH,CHO
+ HCo(CO),
I +
CH,CCo(CO),
--.)
I
Scheme I. Proposed Mechanisms for the Production of Ethanol and Other Products in the Cobalt Carbonyl Catalyzed Methanol Homologation Reaction a. Ethanol via Acetaldehyde Intermediate (Ziesecke, 1952; Sternberg and Wender, 1959) Co,(CO), + H, 2 2HCo(CO), HCo(CO), 2 HCo(CO), + CO (formation of the catalyst) CH,OH
+ HCo(CO),
CH,Co(CO),
CH,Co(CO), t H,O
CH,COCo(CO),
-+
+ H,
CH,COCo(CO), HCo(CO),
-+
-+
(methyl migration)
CH,CHO
I
CH,CCOCo( CO), I
OH
HZ
CH,CHCHO
+
-
(acetaldehyde produced)
CH,CHO t H, CH,CH,OH
HCdCO),
(reduction t o ethanol)
b. By-products via Activation of CO
ROH + HCo(CO), t 2H, RCH,OH t HCo(CO), t H,O (higher alcohols) -+
+ ROH
CH,COCo(CO), HCo(CO), HCo(CO),
;?
-+
CH,COOR t
(acetates)
HCOCo(CO),
HCOCo(CO), t ROH HCo( CO),
--f
HCOOR
+
(formates) or
ROH t Co,(CO), ROCo(CO),
-+
-+
ROCo(CO),
+ HCo(CO),
ROCOCo(CO),
ROCOCO(CO)~+ H, -+ HCOOR t HCo( CO), (formates) c. By-products, Acid Catalyzed H+
ROH t R'OH 3 ROR' t H,O
(ethers)
H
H,C=CHOR -% CH,CH(OR), CH,CH,OR (ethers) -+
+
CH,CHO
ROH
CH,CH(OH)OR
+
H+ ;?
CH,CH(OH)OR H+
R'OH
CH,CH(OR')OR
(acetals)
hydridocobalt carbonyl, although, again, we did not observe the intermediate product, in this case, 2-methoxy-lpropanal. Wilson (1951) has reported such a reaction between 1,l-dimethoxyethane and synthesis gas using a cobalt catalyst with the identified products including 2-methoxy-1-propanal and 2-methoxy-1-propanol but not 1-methoxy-2-propanol. CH,CH(OCH,)OH
-
-H,O
+ HCo(CO),
CH,CHCo(CO),
OH H
No. 3, 1978 235
OCH,
+ HCo( CO),
I CH,CHCH,OH i ~ + HZ
CH,OH
CH,CH(OCH,)CH,OH t CH,CH(OH)CH,OCH,
Another possibility, of course, is that the methoxypropanols arise by different reaction pathways. For example the 2-methoxy-1-propanol could result from the interaction of the acetaldehyde hemiacetal or acetal with
HZ
CH,CHCOCo( CO), -* CH,CHCHO 1
OCH,
I
-+
I
+ HCo(CO),
OCH, CH,CHCH,OH I
HZ
co
+ HCo(CO),
OCH,
The mechanism for the methanol homologation reaction is still mainly speculation with much work needed in the area to even ascertain the route to ethanol, the major product. Derivation of the kinetics and mechanism for each of the products from this reaction would, indeed, be a challenging undertaking.
236
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 3, 1978
Conclusions Cobalt hydridocarbonyl is a rather unspecific catalyst for the reaction of methanol and synthesis gas (methanol homologation). We have identified more than 20 products from this reaction, which is considerably more than have been previously acknowledged in the literature. Therefore many yields and selectivities reported previously for this reaction may be misleading. Continuous unit operation represents a more reliable way of evaluating the potential of the methanol homologation reaction. We have found by comparing similar batch and continuous unit experiments that continuous operation increases selectivity to ethanol potential from 45 to about 65%. This represents a significant increase in potential ethanol yield from this reaction. The possible commercial exploitation of this process is hampered by high reaction pressure, lack of reaction specificity, and the overall low reaction rate. Future work should be directed toward overcoming these obstacles. Acknowledgment The authors wish to acknowledge the technical assis-
tance of Messrs. L. A. Miller, R. W. Jarrett, and R. Cuevas in analytical methods and for GC-mass spectral analyses and Mr. C. H. Floyd for help in carrying out the experimental work. Literature Cited Albanesi, G., Chim. Ind. (Milan),55, 319 (1973). Berty, J., Markol, L., Chem. Tech. (Berlin), 8,260 (1956). Brooks, R. E. (to DuPont), US. Patent 2457204 (Dec 28, 1948). Burns, G. R., J. Am. Chem. SOC.,77, 6615 (1955). Emmett, P. H.,in "Catalysis", Vol. V, p 73, Reinhold, New York, N.Y., 1957. Mizoroki, T., Nakayama, M., Bull. Chem. SOC.Jpn., 37, 236 (1964). Piacenti, F., Bianchi, M., "Organic Synthesis via Metal Carbonyls", VoI. 2, pp 1-42, I. Wender and P. Pino, Ed., Wiley, New York, N.Y., 1977. Pruett, R. L. (to Union Carbide), US. Patent 3 833 634 (Sept 3, 1976). Riley, A. D., Bell, W. 0. (to Commercial Solvents), US. Patent 3 248432 (Apr 26, 1966). Slaugh, L. H. (to Shell), Belgian Patent 842430 (Feb 11, 1977). Sternberg, H., Wender, I., Proc. Int. Conf. Coord. Chem., Chem. Soc. Spec. Publ., No. 13, 35 (1959). Wender, I., Friedel, R. A., Orchin, M., Science, 113, 206 (1951). Wender, I., Levine, R., Orchin, M., J. Am. Chem. SOC.,71, 4160 (1949). Wender, I., Catal. Rev. - Sci. Eng., 14, 97 (1976). Wilson, J. (to DuPont), US. Patent 2555950 (June 5, 1951). Ziesecke, K. H., Brennst. Chem., 33, 385 (1952).
Received for review January 16, 1978 Accepted May 30, 1978
Methylene Chloride from Chloroform by Hydrochlorination Dwain A. Dodson and Howard F. Rase' Department of Chemical Engineering, The University of Texas at Austin, Austin Texas 78772
Three catalysts (Pd-on-charcoal, Pt/A1203,and Pt-Re/A1203 reforming catalyst) were compared on the basis of activity, activity maintenance, and selectivity in the hydrodechlorination of chloroform to yield methylene chloride. The palladium catalyst deactivated rapidly because of coke formation and sintering of the palladium. Both R/AI2O3 and Pt-Re/AI2O3gave promising life, but Pt/A1203was more active at the conditions studied. Decline in activity was primarily caused by a coke deposit consisting of a chlorinated polymeric hydrocarbon. The deposit was successfully removed by regeneration using oxygen.
Many commercial chlorination processes involve photochemical or thermal reactions which produce a variety of products in proportions that are not always ideal in terms of current demands. This is particularly true in the case of chlorinated methanes. Existing processes combined with the practice of treating waste streams of chlorinated high molecular weight hydrocarbons by thermal degradation tend toward overproduction of carbon tetrachloride and chloroform. At the same time, interest and demand for methylene chloride has increased significantly. Unlike chloroform and carbon tetrachloride, methylene chloride (CH,Cl,) is nontoxic to test animals in levels up to 3500 ppm (Chem. Eng. News, 1977). Methylene chloride is valuable as a solvent, flame suppressant, vapor-pressure depressant, and a substitute for the controversial and more expensive chlorofluorocarbons in aerosol products. There is incentive to develop viable processes for converting carbon tetrachloride and chloroform to methylene chloride. One possible procedure is catalytic hydrodechlorination of these higher chlorinated compounds. This study was planned as a preliminary screening of likely candidate catalysts with the purpose of attaining some insights on performance, deactivation characteristics, and directions for future work. Three commercial catalysts were selected for study: palladium-on-granular carbon, platinum-on0019-7890/78/1217-0236$01.00/0
alumina, and platinum-rhenium-on-alumina. Each of these is an important hydrogenation-dehydrogenation and hydrogenolysis catalyst. The latter two are dual-function catalysts with both hydrogenation-dehydrogenation and acid-catalyst functions, and they are used primarily in catalytic reforming of petroleum naphthas to aromatics. Previous Work Various transition metals have been claimed in the patent literature as catalyts for hydrodehalogenation. These include Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, and Au (Mullin and Wymore, 1968; Ward, 1974). The metals Cu, Ag, Fe, Co, Ni, Pd, and Pt have been studied individually as deposits on silica in the dehalogenation of haloethanes and halopropanes. A pulse reactor was used under conditions in which the metals were halogenated by the haloalkanes (Mochida et al., 1972). Deactivation was very rapid. Weiss and Krieger (1966) conducted a detailed study of the chemistry and mechanism of vapor phase hydrodechlorination of dichloroethylenes using a 0.5 % Pt-onalumina reforming catalyst. Above 370 "C extensive pore diffusion and bulk mass-transfer resistances were encountered, and subsequent studies on carbon tetrachloride utilized an alumina support upon which Pt had been
0 1978 American Chemical
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