Energy & Fuels 1993, 7,430-431
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Communtcattons Intercalated Metal-Clay Catalysts in Direct Liquefaction of Bituminous Coal Levent Artok, Prakash B. Malla,? Sridhar Komameni,t and Harold H. Schobert* Fuel Science Program, Department of Materials Science, and Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 Received June 1, 1992. Revised Manuscript Received February 12, 1993
We report results of the first investigation of unique catalysts-montmorillonite with intercalated zerovalent metal clusters-in temperature-staged liquefaction. The liquefaction of Blind Canyon (Utah)bituminous coal in the presence of a copper-intercalated montmorillonite results in enhanced conversion to tetrahydrofuran-solubles relative to reaction without catalyst. It is particularly noteworthy that almost the whole of the increase in conversion is a result of increased yields of asingle product fraction, the asphaltenes. Clays were one of the first materials to be used for Clays have been catalysis of fuel processing displaced by other materials, notably zeolites, for many applications. Recently, interest in clays has revived, stimulated by development of pillared clays,in which large cations are used to separate, on a molecular scale, the silicate layer^.^ The structure of these catalysts allows entry of very large molecules typical of heavy petroleum fractions, molecules too large to penetrate the pores of zeolites.2 For the same reason, new clay Catalysts may have potential for treatment of large coal-derived molecules, e.g., preasphaltenes. Song et al. have shown the importance of pore size of supported catalysts on conversion of asphaltenes and preasphaltene~;~ an increase in pore size of supported Ni/Mo catalysts significantly increased conversion of preasphaltene~.~,~ Olson and coworkers have investigated a variety of interesting catalysts for hydrotreating coal-derived liquids, including acidexchanged montmoriUonite,8hydrotalcites?Jo and pillared montmorillonites.'l This group achieved 90 5% conversion of Wyodak subbituminous coal with an alumina/ ironpillared montmorillonite catalyst." Clays containing intercalated zerovalent metal clusters + Materials Research Laboratory. (1) Decroocq, D. Catalytic Cracking of Heavy Petroleum Fractions;
Editions Technip: Paris, 1984. (2) Gates, B. C. Catalytic Chemistry; Wiley: New York, 1992. (3) Satterfield, C. N. Heterogeneous Catalysis in Industrial Practice; McGraw-Hill: New York, 1991. (4) Quayle, W. H.; Pinnavaia, T. J. Znorg. Chem. 1979, 18, 2840. (6) Song, C.; Hanaoka, K.; Nihonmatau, T.; Nomura, M. Proc. Znt. Conf. Coal Sei. 1989, 226. (6)Song, C.; Nihonmatau, T.; Hanaoka, K.; Nomura, N. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1991,36,542. (7) Song, C.;Hanaoka, K.; Nomura, M. Prepr. Pap.-Am. Chem. SOC., Diu. Fuel Chem. 1992,37,215. (8)Olson, E. S.; Diehl, J. W.; Sharma, R. K. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1990, 35, 563. (9) Sharama, R. K.; Stanley, D. C.; Holm, P. L.; Olson, E. S. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1991,36,570. (10)Sharma, R. K.; Olson, E. S. Coal Sei. Technol. 1991,18, 377. (11) Olson, E. S.; Yagelowich, M. L.; Sharma, R. K. Prepr. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1992,37, 262.
apparently have not been examined as potential Catalysts for fuel processing. However, nickel- and cobalt-substituted mica montmorillonites have been investigated as isomerization and cracking catalysts.12 These catalysts are prepared by replacing aluminum in the clay by nickel (or cobalt) ions.12 The catalyst becomes active only after a portion of the nickel is reduced to the metallic Hydrogenation depends on the presence of metallic reactions of alkanes on these catalysts show a dependence on the amount of reduced ni~ke1.l~ Our choice of copper as the metallic component of the intercalated clay catalyst was a matter of convenience, since samples were already at hand and hence available for a preliminary study. Copper is used only rarely as a hydrogenation catalyst,I6in part because hydrogen is not as strongly adsorbed on copper as on some of the other metals, such as n i ~ k e l . Furthermore, ~ copper and its compounds have seldom been investigated as catalysts for direct liquefaction. Nevertheless, dispersed copper compounds were among the most effective catalysts for liquefaction of Morwell brown ~ 0 a l . I ~Conversion to methylene chloride-solubles was increased to 78%,compared to 57 % without added catalyst.'* Metallic copper is an excellent catalyst for enhancing hydrogen transfer from such hydrogen donors as formic acid.I9 The procedure for preparation of the copper-intercalated montmorillonite catalyst has been published elsewhere.20 Briefly, a natural sodium montmorillonite was ionexchanged with Cu2+ by leaching with excess 0.5 M CuCL2HzO for 24 h at room temperature. The Cu2+exchanged montmorillonite was then reacted with ethylene glycol at 195 OC (reflux conditions) for 6 h under Ar. This process produces 0.4-0.5 nm Cuo clusters which separate the silicate layers in analogous fashion to ceramic oxides (12)Swift, H. E.; Black, E. R. Ind. Eng. Chem. Prod. Res. Deu. 1974, 13,106. (13) van Santen, R. A,; Rbbschkger, K. H. W.; Emeis, C. A. In Solid
State Chemistry in Catalysis; Grasselli, R. K . , Brazdil, J. F., E&.; American Chemical Society: Washington, DC, 1985; Chapter 17. (14) Comradt, H. L.; Garwood, W. E. Ind. Eng.Chem. Prod. Res. Dev. 1964, 3, 308.
(15) Heinerman, J. J. L.; Frericks, I. L. C.; Gaaf, J.; Pott, G. F. T.; Coolagem, J. G. F. J. Catal. 1983, 80, 145. (16) Hudlicky, M. Reductions in Organic Chemistry; Ellis Horwood: Chichester, UK, 1986. (17)Jackson, W. R.; Larkins, F. P. In The Science of VictorianBrown Coal; Durie, R. A., Ed.; Butterworth-Heinemann: Oxford, UK, 1991; Chapter 10. (18) Cassidy, P. J.; Jackson, W. R.; Larkins, F. P.; Sakurovs, R. J.; Sutton. J. F. Fuel 1986.65. 374. (19)'Davies,R. R.; Hodgson, H. H. J. Chem. SOC.1943, 281. (20) Malla, P. B.; Ravindranathan, P.; Komarneni, S.; Roy, R. Nature 1991, 351, 555.
o s a ~ - o ~ ~ ~ ~ ~ ~ ~ ~ ~ 0o 1993 ~ - oAmerican ~ ~ o ~Chemical o ~ . o Society o/o
Energy & Fuels, Vol. 7, No. 3, 1993 431
Communications Table I. Characteristics of Blind Canyon Coal ASTM rank class hvBb 4.73 moisture, % as-received 6.67 mineral matter, % dry basis ultimate analysis, % dmmf carbon hydrogen nitrogen sulfur (organic) oxygen (by diff)
81.72 6.22 1.56 0.40 10.10
in pillared clays.20 Liquefaction was performed in 25-mL microautoclave reactors. The coal was Blind Canyon bituminous coal from the Penn State/DOE Coal Sample Bank and Data Base; its behavior has been investigated extensively in collateral work in our l a b ~ r a t o r y . ~ lIts -~~ principal characteristics are shown in Table I. Phenanthrene was used as the vehicle; 5 g each of vehicle and coal were used. Catalyst weight was 1g. The initial hydrogen pressure was 7 MPa (at ambient conditions). Temperature-staged reactions were conducted in preheated fluidized sandbaths at 275 OC for 30 min, followed by 425 OC for 30 min. Product workup has been discussed in detail e l s e ~ h e r e . ~ lConversion -~~ is calculated from the weight of THF-insoluble residue; preasphaltenes are THF-soluble and toluene-insoluble;asphaltenes are toluene-soluble and hexane-insoluble, and oils are hexane-soluble. The results are shown in Table 11, together with data from collateralexperimentswithout catalyst,with a ferrous sulfate catalyst percursor, and with pyridine-swollen coal impregnated with bis(tricarbonylcyclopentadieny1m o l y b d e r ~ u m ) . ~The ~ , ~last ~ case is the highest conversion we have obtained in temperature-staged liquefaction of this coal. Clearlythe intercalated copper catalyst enhances conversion, relative to a noncatalytic reaction, but not to the same extent as the other examples. Virtually all of the increased conversion is a result of increased asphaltene (21)Artok, L.; Davis, A.; Mitchell, G. D.; Schobert, H. H. Fuel, in press. (22) Artok, L.; Davis, A.; Schobert, H. H. Fuel Process. Technol. 1992, 32, 87. (23) Artok,L.; Davis,A.; Mitchell, G. D.; Schobert, H. H. Energy Fuels 1993, 7,67.
Table 11. Temperature-Staged Liquefaction (275/426 "C) Results for Blind Canyon Bituminous Coal in Phenanthrene with Various Catalysts conversion preaephaltenes aephaltenes Oil8
gas
O/(P + A)b
no catalyst 48.0 12.3 8.5 21.9 5.3 1.05
Cu-clay 64.0 12.4 21.5 23.6 6.5 0.70
FeSOd 81.8 15.5 29.2 30.6 6.5 0.68
Py + CPMC' 91.6 7.9 35.4 42.1 5.2 0.97
Pyridine-swollen coal impregnated with bis(tricarbonylcyc1opentadienylmolybdenu), liquefied in 955 H2:HzS atmosphere. Ratio of oils to preasphaltenes + asphaltenes.
yield, with only very slight increases in oils and gases. This is not the case for the other catalysts. To ensure that the results were not simply a consequence of catalysis by the clay itself, control experiments were run under identical conditions but using montmorillonite which had not been loaded with copper. In this case, conversion was increased only by 4.9 percentage units, whereas in the intercalated copper catalyst enhanced conversionby 16.0percentageunits (Table 11). Thus there is some small effect of montmorillonite, but much of the enhanced conversion observed with the intercalated copper catalyst must be attributed to the copper. These results suggest the possibility of designing catalysts which favor high yields of a particular product fraction by using the intercalation technique to adjust the layer spacing in the clay (and hence selectively admit molecules of particular sizesto the interior of the catalyst). It may be possible to increase the effectiveness of the catalyst by using instead of copper other metals-such as nickel or iron-which are superior hydrogenation catalysts. We plan to investigate these issues in future work and will report the results in due course.
Acknowledgment. Two of the authors, S.K. and P.B.M., were supported by the U.S.Department of Energy under grant DE-FG02-85ER45204. It is a pleasure to thank Ms. Lili Huang for her kindness in performing the control experiments with the montmorillonite not loaded with copper.
