Energy & Fuels 1990, 4 , 231-236
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Activity and Characterization of Coprocessing Catalysts Produced from an Iron Pentacarbonyl Precursor D. E. Herrick, J. W. Tierney, and I. Wender* Department of Chemical and Petroleum Engineering, 1249 Benedum Engineering Hall, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
G. P. Huffman and F. E. Huggins Consortium for Fossil Fuel Liquefaction Science, University of Kentucky, Lexington, Kentucky 40506 Received December 15, 1989. Revised Manuscript Received March 1, 1990
It is generally believed that highly dispersed catalysts are very effective in the conversion of coal to liquids but the effects of dispersion and composition have not been adequately investigated. We chose to study the use of iron pentacarbonyl, Fe(CO),, to produce a highly dispersed catalyst in situ in the coprocessing of Illinois No. 6 coal and Maya ATB residuum. The activity of the catalyst produced from this precursor has been investigated, and its particle size and composition were measured by use of X-ray diffraction, Mossbauer spectroscopy, computer-controlled scanning electron microscopy (CCSEM), and transmission electron microscopy (TEM). Use of 0.5 wt % Fe added as Fe(CO)5resulted in an increase in coal conversion to methylene chloride solubles from 39% to 82%. The Fe(CO), precursor decomposed in the reactor to produce a mixture of highly dispersed pyrrhotite (Fel&3), Fe3C, and other iron compounds. However, with time at reaction conditions, 95% of the iron was converted to Fel=$. The pyrrhotite particles formed in the initial stages of reaction had a mean crystallite size of 12 nm when measured by use of X-ray diffraction line broadening; the small particle sizes were confirmed by TEM, CCSEM, and Mossbauer studies.
Introduction Coprocessing is the liquefaction of coal in a heavy oil that is not derived from coal. This heavy oil may be a heavy petroleum crude or residuum, oil derived from tar sands, etc. Conventional direct liquefaction processes must recycle about two-thirds of the coal-derived product, but coprocessing can operate largely or completely in a "once through" mode, eliminating the cost and complication of the large recycle.' In addition, metallic impurities in the oil deposit on the coal residue or pitch.2 In most direct coal liquefaction processes, the use of catalysts results in more desirable products under less severe processing conditions. The same is true for coprocessing, which may require even more effective catalysts because the petroleum-derived slurrying oils used in coprocessing are often poor hydrogen donors. In direct coal liquefaction, supported metal catalysts (e.g., CoMo/A1203) may suffer from poor contact with the feed. Unsupported dispersed catalysts can offer good contact between the coal and the catalyst. Addition of low surface area solids requires high catalyst concentrations. Particulate pyrite addition has been studied and found effective in concentrations of several weight p e r ~ e n t . ~ One method of increasing dispersion (catalyst surface area per mass) is to introduce the catalyst as a soluble precursor. Such precursors are distributed throughout the coal-oil mixture by dissolving in the oil, and they decompose upon heating or other treatment to form very small catalyst particles within the coal-oil mixture. It is believed that the high dispersion allows catalyst concentrations of (1) Speight, J. G.; Moschopedis, S. E. Fuel Process. Technol. 1986,13, 215-232. (2)Miller, T. J.; Panvelker, S. V.; Wender, I.; Shah, Y. T.; Huffman, G. P.Fuel Process. Technol. 1989,23, 23-38. (3)Garg, D.; Givens, E. Ind. Eng. Chem. Process Des. Deo. 1982,21, 113-117.
less than 1.0 wt % to be ~ s e d . ~Examples ,~ of these catalyst precursors are carboxylic salts of iron or molybdenum: water-soluble ammonium molybdate? molybdenum naphthenate.6 nickel acetate,' and carbonyl compounds of iron, molybdenum, and other metals.8 One study, using only X-ray diffraction line broadening to measure catalyst dispersion, reported nickel crystallite sizes as low as 15-30 nm for a nickel acetate precursor used in the liquefaction of low-rank coals.' Several studies have reported the use of Fe(C0)5and other iron carbonyls in direct liquefaction in solvents such as tetralin and l-methylnaphthalene,g-'z These studies showed that the Fe(CO)! precursor produced a catalyst active for hydroliquefaction of coal using Fe a t 2.0 wt 9'0 of the feed coal. The precursor was converted to a less active iron oxide (Fe304)in the absence of added sulfur, but when sulfur was added in the form of elemental sulfur or organic sulfur compounds, the more active iron pyrrhotite (Fel+S) was formed.'O Increases in coal conversion were found with both bituminous and subbituminous coa1s.l' Montano and otherslZJ3have suggested that the (4)Anderson. R. R.:Bockrath. B. C. Fuel 1984.63.329-333. (5)Ruether, J. A.; Mima, J. A:; Kornosky, R. M.;Ha, B. C. Energy Fuels 1987,1, 198-202. (6)Curtis, C. W.; Tsai, K. J.; Guin, J. A. Ind. Eng. Chem. Res. 1987, 26, 12-18. (7)Takemura, Y.; Okada, K. Fuel 1988,67,1548-1553. (8)Yamada, 0.; Suzuki, T.; Then, J. H.; Ando, T.; Watanabe, Y. Fuel Process. Technol. 1985, 11, 297-311. (9)Suzuki, T.; Yamada, 0.;Fujita, K.; Takegami, Y.; Watanabe, Y. Chem. Lett. 1982, 1467-1468. (10)Suzuki, T.; Yamada, 0.; Takehaski, Y.; Watanabe, Y. Fuel Process. Technol. 1985,10,33-43. (11)Watanabe, Y.; Yamada, 0.; Fujita, K.; Takegami, Y.; Suzuki, T. Fuel 1984,63,752-755. (12)Montano, P. A.; Stenberg, V. I.; Sweeny, P. J.Phys. Chem. 1986, 90,156-159. (13)Owaga, T.; Stenberg, V. I.; Montano, P. A. Fuel 1984, 63, 1660-1662.
0 1990 American Chemical Society
Herrick et al.
232 Energy & Fuels, Vol. 4 , No. 3, 1990 Table I. Ultimate and Proximate Analyses of Illinois No.6 Coal (wt %P carbon 74.0 organic sulfur 0.96 hydrogen 5.65 moisture 3.80 nitrogen 1.58 volatile matter 40.5 sulfur 3.07 fixed carbon (diff) 48.7 ash 10.8 pyritic Fe 1.05 oxygen (diff) 4.90
100,
"Ultimate analysis is on a dry basis. Analyses performed by BCR National Laboratory.
catalytic activity of Fel-$3 is a result of iron-deficient sites in the structure of this nonstoichiometric sulfide and that H2Sis necessary to maintain a surface with such sites. The use of other soluble precursors such as cyclopentadienyliron dicarbonyl dimer, (C5H5)2Fe2(C0)4, yielded increased coal conversions of the same order of magnitude as Fe(Co)5.sHowever, particle sizes of liquefaction catalysts produced from the decomposition of Fe(CO)5 have not been reported in the literature, but work in fields other than coal liquefaction has shown that iron particles less than 10 nm in diameter can be deposited on carbon or zeolite supports by thermal decomposition of Fe(C0)b14p15
Experimental Section Illinois No. 6 (Burning Star) hvB bituminous coal ground to -200 mesh (
