Ind. Eng. Chem. Res. 1989,28, 1110-1112
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Paulik, F. E.; Roth, J. F. Catalysts for the Low Pressure CarbonyChem. Comlation of Methanol to Acetic Acid. J . Chem. SOC., mun. 1968, 1578-1582. Roth, J. F.; Craddock, J. H.; Hershman, A.; Paulik, F. E. Low Pressure Process for Acetic Acid via Carbonylation of Methanol.
Chem. Technol. 1971, 600-605. Smith, B. L.; Torrence, G. P.; Murphy, M. A.; Aguilo, A. The Rhodium Catalysed Methanol Carbonylation to Acetic Acid at Low Water Concentrations: The Effect of Iodide and Acetate on Catalyst Activity and Stability. J . Mol. Catal. 1987, 39, 115-136.
NCL Communication 4609.
Subodh B. Dake, Rengaswamy Jaganathan Raghunath V. Chaudhari* National Chemical Laboratory Pune 411008, India
Received for reuiew December 19, 1988 Accepted April 24, 1989
Mixed Ruthenium-Tin Boride Catalysts for Selective Hydrogenation of Fatty Acid Esters to Fatty Alcohols A new catalyst system, ruthenium-tin boride, was developed for the selective hydrogenation of fatty acid esters to fatty alcohols a t 270 "C and a pressure of 640 psi of H2. The yields of fatty alcohols from various long-chain fatty acid esters varied from 70% to 89%. The catalyst had an atomic ratio of ruthenium to tin of 1:l and could be unsupported or supported on y-A1203. The importance of the method of preparation using sodium borohydride as the reductant was also demonstrated. A tentative mechanism for the selective activation of the ester carbonyl by the new catalyst system was proposed, based on the surface characterization of the catalysts reported elsewhere. Hydrogenolysis of fatty acid esters to fatty alcohols is a high-pressure reaction. Fatty alcohols are important products that find extensive use for making surfactants of all kinds. Industrially, fatty alcohols are produced using copper chromite based catalysts. These catalysts operate at a high pressure of 4000 psi at temperatures of 250-300 "C. In the literature, only two other catalyst systems, palladium-rhenium and rhodium-tin, have been reported (Traverse et al., 1984; Snappe and Bourneville, 1982) as catalysts for the hydrogenolysis of esters in the pressure range 150-750 psi. In our laboratory, we recently undertook studies on the preparation and catalytic properties of metal boride catalysts. During our studies, it was found that mixed metal borides, ruthenium-tin boride, ruthenium-germanium boride, etc., exhibit the unique property of activating preferentially a specific functional group (e.g., C=O in the presence of C 4 ) . For instance, we have reported the high activity and selectivity shown by a new mixed metal boride system, ruthenium-tin boride, for hydrogenating unsaturated aldehydes to unsaturated alcohols (Narasimhan et al., 1988). It was found, to our pleasant surprise, that the same catalyst system, Ru-Sn-B, was highly effective in selectively activating the inert carbonyl of the fatty acid esters to form fatty alcohols in yields close to 90% at a H2 pressure of 640 psi or less (Narasimhan et al., 1987a,b). The present communication reports the above results and also brings out the importance of tin and boron in the active and selective catalysts.
to NaE3H4is 1:6) was added in drops to the aqueous slurry of impregnated y-alumina support. After the reduction was complete,the solids were washed free of Na+ ions with distilled water and then finally with absolute alcohol. The solids were then air dried before using them as catalysts. This catalyst is designated Ru-Sn-B/A1203. In the catalyst, the atomic ratio of ruthenium to tin was adjusted to be 1:1, with a ruthenium metal loading of 1%with respect to the support. Unsupported catalysts were also prepared in the same manner as described above. The mixed metal catalyst was also prepared by a conventional technique wherein the metal impregnated support was dried at 100 "C followed by calcination at 400 "C and reduction in H2 flow at 350 "C. This catalyst is designated Ru-Sn/A1203, while the corresponding monometallic catalyst is designated Ru/A1203. Methyl palmitate (99% pure, Acme Chemicals Limited, Bombay, India) and H2 of 99% purity (Indian Oxygen Limited, India) were used as reactants. The hydrogenation reaction was carried out in a 300-mLcapacity Parr autoclave (Model 4561, Moline, IL). The autoclave was charged with the substrate and the catalyst purged with H2 6 times and finally pressurized to 420 psi. At the end of 6 h, the reaction was stopped by gradually cooling the autoclave to room temperature. The products were analyzed by GC using a Carbowax 400M on Chromosorb column.
Results and Discussion
Table I lists the data for the hydrogenation of methyl palmitate. The following points may be noted from the table. Experimental Section Ruthenium boride shows high activity (88.2% conversion) but very low selectivity (1.5%) for alcohol formation. The catalysts were prepared as follows: appropriate Most of the products are hexadecane, methyl myristate, quantities of aqueous solutions of RuC13.3H20 (Fluka, and a number of low molecular weight fragments. These Buchs, Switzerland) and stannous chloride (BDH, Bomproducts are obviously formed by indiscriminate hydrobay, India) were mixed in a beaker. A weighed amount of y-alumina (Harshaw-chemie, B.V, The Netherlands; genolytic cracking of the C-C bond of the starting ester surface area 200 m2/g) was impregnated with the mixed or the hydrogenolysis of the C-OH bond of the product aqueous solution by the conventional incipient wet techalcohol. However, when tin is introduced, the mixed metal nique. This paste was left to stand for 16 h. An aqueous boride system, Ru-Sn-B, exhibits dramatic improvement solution of sodium borohydride (molar ratio of Ru Sn in the selectivity for the alcohol formation. This is found 0888-5885/89/2628-1110$01.50/0 0 1989 American Chemical Society
+
Ind. Eng. Chem. Res., Vol. 28, No. 7, 1989 1111 Table I. Activity and Selectivity Data for Hydrogenolysis of Methyl Palmitate catalyst Ru-Sn-B Ru-Sn-B/A1203 Ru-B / A1203 Ru/A1203 Ru-Sn/A1,OS
conversion, % 98.9 86.4 88.2 50.9 30.0
temp of reaction H2 pressure methyl palmitate
cetyl alcohol, 70 89.7 72.0 1.3
27.7 17.2
270 "C 640 psi 5 mL
hexadecane, % 2.5 1.0 4.0 12.2 2.8
other products," % 6.5 13.4 46.9 11.1 10
amt of catalyst H2:ether (molar ratio) duration of reaction
selectivity for cetyl alcoholb 90.7 83.3 1.5 54.4 57.3 125 mg 12.5:l 6h
OOther products are mostly unidentified low molecular weight fragments. About 60-70% of these product is methyl myristate, as found by GC retention time. Selectivity for cetyl alcohol = % cetyl alcohol/ % conversion.
Table 11. Activity Data for Hydrogenolysis of Esters reactant
catalyst charge, % (wt/wt)
temp, "C
conversion, %
1. methyl IO-undecenoate
2.5
270
79.0
2. hexyl acetate
5
260
90.5
20
200
98
3. dimethyl succinate
product distribution I-undecanol other products" I-hexanol other productsa 1,4-butanediol tetrahydrofuran methyl y-hydroxybutyrate
71.2 7.8 70.5 20.0 76.0 8.9 11.2
Other products are mostly lower molecular weight fatty acid esters. Conditions: H2 pressure was 640 psi for reactants 1 and 2 and 1200 psi for the reactant 3.
to be the case for supported as well as unsupported catalysts. While the unsupported catalyst Ru-Sn-B gives a conversion of 98.9% with a selectivity of 90.7% for cetyl alcohol, the corresponding figures of activity and selectivity for the supported catalyst are 86.4% and 83.370,respectively (see entries 1and 2 of Table I). Similar results were obtained with other substrates such as methyl 10-undecenoate, hexyl acetate, and dimethyl succinate (see Table 11). I t may be seen from Table I1 that in all the cases alcohol is the major product of the reaction. It is interesting to note that the ruthenium and ruthenium-tin catalysts prepared by conventional methods do not show such high activities and/or selectivities (see entries 4 and 5 of Table I). Thus, the method of reduction of the catalysts, using sodium borohydride and incorporating boron in the catalyst, appears to be important for the selective hydrogenation as well as catalytic activity. In order to understand the role of the new catalyst system for selective hydrogenation to alcohols, extensive characterization of the catalysts was carried out using XPS, TEM/EDX, and SIMS techniques. These results are reported elsewhere (Narasimhan et al., 1989). The important findings of the above surface studies were that (i) ruthenium is present in zero oxidation state while tin is predominantly present as SnC12 and partly as Sno and (ii) bimetallic interaction exists between Ruo and Sn2+via chlorine. Based on the above conclusions, a mechanism for the activation of the ester by the catalyst leading to alcohol formation is proposed. According to the mechanism, tin ions are responsible for activating or polarizing the otherwise inert C=O of the ester by virtue of its Lewis acidity. A Ruo site, adjacent to the Sn2+site, could then activate H2,and a hydrogen transfer across the C = O could result as shown below:
In the first step, after the hydrogen transfer takes place, the carbanion forms. This is very unstable and eliminates the OR group spontaneously,which is a good leaving group and forms the aldehyde. The hydrogenation of the aldehyde to the alcohol should be a facile catalytic process at the operating pressure at 640 psi. The role of boron probably lies in changing the electron charge density around ruthenium, thereby enhancing its intrinsic catalytic activity. Such a hypothesis was made earlier in the case of nickel boride catalysts from XPS measurements (Schreifels et al., 1980).
Conclusion In summary, we conclude that the new metal boride catalyst, ruthenium-tin boride, shows excellent activity and selectivity for fatty alcohol formation from fatty acid esters at low H2 pressures of 640 psi, by virtue of its ability to selectively activate the inert carbonyl of the ester.
Acknowledgment We thank IEL Limited for financial support. Registry No. Ru, 7440-18-8; Sn, 7440-31-5; B, 7440-42-8; cetyl alcohol, 36653-82-4; methyl palmitate, 112-39-0; methyl 10-undecenoate, 111-81-9;hexyl acetate, 142-92-7;dimethyl succinate, 106-65-0; 1-undecanol, 112-42-5; I-hexanol, 111-27-3; 1,4-butanediol, 110-63-4.
Literature Cited Narasimhan, C. S.; Deshpande, V. M.; Patterson, W. R. Studies on Ru-Sn Boride Catalysts. Part I. Characterisation. J. Catal. 1989, in press. Narasimhan, C. S.; Deshpande, V. M.; Ramnarayan, K. An Improved Process for the Preparation of Unsaturated Alchols from Carbonyl Compounds by Catalytic Hydrogenation. Patent Application 570/CAL/87, 1987a; Alchemie Research Centre, Thane, India. Narasimhan, C. S.; Deshpande, V. M.; Ramnarayan, K. An Improved Process for the Preparation of Fatty Alchols and Diols from Carbonyl Compounds by Catalytic Hydrogenation. Patent Application 571/CAL/87,1987b; Alchemie Research Centre, Thane, India.
Ind. Eng. Chem. Res. 1989,28, 1112-1113
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Narasimhan, C. S.; Deshpande, V. M.; Ramnarayan, K. Selective Hydrogenation of a$-unsaturated Aldehydes to Unsaturated Alchols Over Mixed Ruthenium-Tin Boride catalysts. J . Chem.
* To whom all correspondence should be addressed.
Soc., Chem. Commun. 1988, 2, 99.
Chakravarthula S. Narasimhan* Vinayak M. Deshpande, Krishnan Ramnarayan
Schreifels, J. A,; Maybury, P. C.; Swartz, W. E., Jr. X-Ray Photoelectron Spectroscopy of Nickel Boride Catalysts: Correlation of Surface States with Reaction Products in the Hydrogenation of Acetonitrile. J . Catal. 1980, 65, 195. Snappe, R.; Bourneville, J. P. Alcohol Production by Catalytic Hydrogenation of Organic Acid Esters. Ger. Offen DE 3217429,1982. Traverse, H.; Bourneville, J. P.; Martino, G. New Route to Rhodium Tin Bimetallic Catalysts Selective for the Hydrogenation of Esters into Alcohols. 8th International Conference on Catalysis; Pachema, T., Ed.; Verlag Chemie Weinheim Deerfield Beach: Bond, 1984; Vol. 111, p 89.
Alchemie Research Centre Belapur Road Thane 400601, India Received for review September 22, 1988 Accepted April 18, 1989
CORRESPONDENCE Comments on "Solvent Extraction and Recovery of Ethanol from Aqueous Solutions" Sir: Egan et al. (1988) believe they have found a new low-cost method for recovering and concentrating ethanol from aqueous solutions: They say that the method allows them to obtain 95 vol 70 aqueous ethanol using 20-40% less energy than that required by traditional distillation. However, we-want to point out that it is not feasible to obtain ethanol concentrations of 95 vol % (or even greater than 85 vol %) using this method. The difficulty which is not considered by the authors lies in the modification of the volatilities of ethanol and water when a solvent like 2-ethyl-1-hexanol is present in the mixture. In an ethanol-water binary mixture at atmospheric pressure, the volatility of ethanol is much greater than that of water when the concentration of ethanol is less than 85 vol '3%. In the 85-95 vol 70range, the volatility of ethanol is still greater but both volatilities are closer when the concentration of ethanol is increased, and both of them are equal for 97 vol '70: the azeotropic point. However, the presence of a solvent like 2-ethyl-1-hexanol causes a reduction of the relative volatility of ethanol to water (let us consider, for example, that the main characteristic of the extractive distillation is this change of relative volatility when a solvent is added). The result is a water volatility similar to or even greater than the ethanol volatility in many ternary mixtures which contain a high concentration of 2-ethyl-1-hexanol. In this way, the water is stripped from the solvent as easily as ethanol, and it is not possible to obtain concentrated solutions of ethanol (greater than 85 vol % ) since the water/ethanol ratio in the extract which feeds the stripping column is not small enough because the selectivity of the solvent in the extraction is low. This effect can be seen in Table IV of their communication. For example, let us consider the product obtained with the best batch test (no. 4) containing 600 kg/m3 of ethanol, which shows only 77% recovery. Since the volatility of 2-ethyl-1-hexanol is extremely low, the product obtained can be considered to contain basically water and ethanol with a concentration of 76 vol '70. This concentration is much less than the 95 vol % sought by the authors. On the other hand, in a paper previously published in this journal (Ruiz et al., 1987), a complete study of the
Table I. Distribution Coefficients ( K J Calculated by UNIQUAC for Different Liquid-Phase Mole Fractions (xi) and Temperatures ( T ) in Water (W)-Ethanol (E)-2-Ethsl-l-hexanol (EH)Mixtures P, kPa T,"C XW XE XEH Kw K E K E H 100 100 100 100 100
50 75 100 75 75
0.22 0.22 0.22 0.17 0.30
0.28 0.28 0.28 0.09 0.35
0.50 0.50 0.50 0.74 0.35
0.6 1.4 3.6 1.7 1.0
0.4 1.0 2.4 1.0 0.9
0.003 0.003 0.048 0.011 0.014
liquid-liquid equilibrium of the ternary system waterethanol-2-ethyl-1-hexanolwas presented. In this work, a set of UNIQUAC parameters to describe the liquidliquid and vapor-liquid equilibria of the system was calculated. With these parameters, it is possible to estimate the distribution factor Ki= yi/xi (xi and yi represent the mole fractions of component i in the liquid and in the vapor in equilibrium) when the composition of the liquid, the temperature, and the pressure are set. The greater Ki is, the greater the concentration of i is in the vapor, and therefore there is more volatility of that component. For example, in Table I, the K:s obtained using different conditions are shown. The liquid compositions are some of those in extracts with 2-ethyl-1-hexanol that were published previously (Ruiz et al., 1987). For example, in Table I, it can be seen that the K's of 2-ethyl-1-hexanol are very small and the ICs of water and ethanol are similar. By use of the Ki's obtained with the UNIQUAC parameters, the conceptual process flow sheet presented by the authors and particularly the stripping column were analyzed. Several calculations were performed for different compositions of feed (organic phases of the equilibrium data (Ruiz et al., 1987)), feed temperatures (between 25 and 100 "C), flow rates, temperatures of the argon gas (50-100 "C), and pressures in the top and bottom plates (between 0.1 and 10 bar). The problem was solved on the design condition that the ethanol mole fraction in the stream of exhausted solvent be less than 0.2 mol % in order to allow the solvent to be recycled to the extraction column. The Edminster group method approximation (Henley and Seader, 1981) was applied. The K's were calculated by the UNIQUAC equation. For example, the
0888-5885/89/ 2628- 1112$01.50/0 0 1989 American Chemical Society
