Energy & Fuels 1987,1, 226-227
226
shown that it is possible to isolate a fraction from a coal extract that primarily contains sulfur compounds.
16587-46-5; dibenzothiophene, 132-65-0; 4-methyldibenzothiophene, 7372-88-5; 3-methyldibenzothiophene, 16587-52-3;
Acknowledgment. The authors are indebted to Joseph Malli, Jr., PETC, for operating the high-resolution mass spectrometer, and to Masaharu Nishioka and Milton Lee, Brigham Young University, for isolating the sulfur-enriched heterocycle fraction. Registry No. 3,5-Dimethylbenzo[b]thiophene,1964-45-0; 3,6-dimethylbenzo[b] thiophene, 16587-50-1;1,2,3,4,4a,4b-hexahydrodibenzothiophene, 69076-07-9;2-ethy1-5,l-dimethylbenzo[ b] thiophene, 18428-05-2;2-propyl-7-ethylbenzo[ blthiophene,
methyldibenzothiophene, 31317-19-8; 1,7-dimethyldibenzothiophene, 89816-53-5;phenaleno[6,7-bc]thiophene, 79965-99-4; benzo[b]naphtho[2,1-d]thiophene,239-35-0;phenanthro[4,3-b]thiophene, 195-686; 11-methylbenzo[b]naphtho[2,1-d]thiophene, 106651-52-9; lO-methylbenzo[b]naphth0[2,1-d]thiophene, 83821-58-3;11-methylbenzo[b]naphtho[1,2d]thiophene,8425884-4; 3-methylbenzo[b]naphtho[2,1-d]thiophene,4567-45-7; 2methyldibenzothiophene, 20928-02-3; 2,8-dimethyldibenzothiophene, 1207-15-4;3,7-dimethyldibenzothiophene,1136-85-2.
1-methyldibenzothiophene,31317-07-4; 3-ethyldibenzothiophene, 89816-98-8; 4,6-dimethyldibenzothiophene,1207-12-1; 2,6-di-
Communications ~~
Solvent Swelling of Liquefaction Residues Sir: Investigation of the chemistry of coal conversion under liquefaction conditions has been hampered by a lack of good methods for characterizing liquefaction residues. Solvent-swelling studies have now been made of residues prepared under low-severity liquefaction conditions. The results provide an indication of relative changes in crosslink densities of the macromolecular structure of residues made under different conditions. The application of solvent swelling to liquefaction residues is a simple extension of methods already developed's2 and used to derive information on the macromolecular structure of c0als~9~ and to investigate the chars produced by the rapid pyrolysis of coals.5 The preliminary experiments described below indicate solvent-swelling studies are able to yield important new information about the course of the disintegration of the macromolecular structure as liquefaction begins. Liquefaction conditions employed were rather mild. Thus, coal conversions were generally low, and the liquefaction residues are related more to the original coal structure than to a side product derived by condensation of reactive fragments. As in earlier investigations,6?'water was used as the liquefaction medium; thus, all organic products originate from the feed coal. Two series of experiments were conducted in a 0.5-L stirred autoclave using a range of applied hydrogen pressures estimated to be from 0 to 4400 psia a t temperature. Slurries of 50 g of -60 mesh coal in 100 g of water were held for 30 min a t liquefaction temperatures of either 350 or 380 "C. At the higher temperature, the amount of added water was progressively reduced to 50 g to accommodate the higher hydrogen pressures. The coal was from the Illinois No. 6 seam, River King mine. Anal. Found (maf): C, 73.7%; H, 5.6%; N, 1.5%; 0,14.8%; S, 4.5%. The ash content was 13.6% on a dry basis. The liquefaction
2*
t
2q2
HYDROGEN PRESSURE, psi
Figure 1. Residue swelling and coal conversion. Liquefaction temperature = 350 "C.
ooi l - - - -T2
(1)Green, T. K.; Kovac, J.; Larsen, J. W. Fuel 1984, 63, 935-938. (2)Matturro, M.G.;Liotta, R.; Isaacs, J. J. J. Org. Chem. 1985,50, 5560-5566. (3)Larsen, J. W.;Green, T. K.; Kovac, J. J. Org. Chem. 1985, 50, 4729-4735. (4) Green, T.; Kovac, J.; Brenner, D.; Larsen, J. Coal Structure; Meyers, R.A., Ed.; Academic: New York, 1982;pp 199-282. (5)Suuberg, E. M.; Lee, D.; Larsen, J. W. Fuel 1985,64, 1668-1671. (6)Blaustein, B. D.;Bockrath, B. C.; Davis, H. M.; Friedman, S.; Illig, E. G.; Makita, M. A. Prepr. Pup.-Am. Chem. Soc., Diu. Fuel Chem. 1985, 30(2),359-367. (7)Bockrath, B.C.;Finseth, D. H.; Illig, E. G. Fuel Process. Technol. 1986,12, 175-188.
-
k. coal
2.2 -
0
-
0
75
-
E E
0
ae
E
-
50
z 0 v) a w > z
-25; I
I C HYDROGEN.PRESSURE, pai
Figure 2. Residue swelling and coal conversion. Liquefaction temperature = 380 "C.
products were subjected to exhaustive Soxhlet extraction with tetrahydrofuran (THF). Conversion values are based on the dry weight of T H F insolubles. The yield of T H F extractables from the raw coal was 10 wt %. Conversion and swelling data are plotted in Figures 1 and 2 as a function of hydrogen partial pressure. The
This article not subject to U S . Copyright. Published 1987 by the American Chemical Society
Energy & Fuels 1987,1, 227-228
swelling ratios, Qhd, were obtained with T H F by measuring the volumes of swollen and unswollen residues in calibrated centrifuge tubes following the method outlined by Green, Kovac, and Larsen.’ The observed swelling ratios were corrected for mineral matter, assuming that mineral matter does not swell. The mineral matter in the residue was estimated on the basis of the measured ash content of the coal combined with the equation suggested by Given et al.s The plots in the figures show that both coal conversion and the swelling ratio of the residues increase with hydrogen pressure. In all cases, the swelling ratio of the feed coal was greater than that of the residues. These results can be rationalized in general terms with a mechanism for conversion based on the frequently used concept of competitive reactions. In this argument, one pathway leads to the formation of soluble fragments from the macromolecular structure through bond dissociation reactions. A competing pathway leads to the formation of additional cross-links in the macromolecular structure. Additional cross-links would render the residues less swellable in THF. The imposition of additional hydrogen pressure changes the balance between the net rates of reaction along the two pathways. Higher hydrogen pressures increase the net amount of dissociative reactions and decrease the net amount of condensation reactions. Two things become evident. The unconverted portion of coal cannot be considered as chemically unaltered, and molecular hydrogen must directly influence the relative net rates of reactions within the coal matrix. A catalyst was added to the system in two cases. These preliminary experiments indicate that catalysts may affect the reaction chemistry even a t very mild reaction temperatures. When ammonium molybdate was added to the slurry so that molybdenum was 0.12 w t 70 of the dmmf coal, the conversion of coal and the swelling ratio of the residue were both modestly increased (see Figure 1). When 1 wt % of tin dichloride was added, conversion was virtually unchanged, but the swelling ratio was markedly decreased (see Figure 2). These two examples indicate that solvent-swelling studies may provide a different measure of the efficiency of catalysts or the manner in which they are applied. The correlation between coal conversion and residue swelling was obtained for only one coal in these experiments mainly by changing only one variable, the hydrogen partial pressure. There is no reason to believe similar correlations between swelling ratio and conversion would be obtained if other process variables or different coals were studied. Indeed, one pyrolysis study revealed a correlation opposite to that found here. That is, as tar yields from a lignite went up because of increasing pyrolysis temperatures, swelling ratios of the remaining chars went down.5 The present results indicate that the application of the solvent-swelling technique to liquefaction residues is of value. In particular, it offers the opportunity to focus on the chemistry that happens inside the macromolecular matrix before it disintegrates. Work in progress is directed toward revealing the influence of variables other than hydrogen partial pressure. Acknowledgment. The authors are indebted to Dr. John Larsen for suggesting this approach and for valuable discussions. Walter Lipinski provided invaluable assistance in the laboratory during this work. (8) Given, P. H.; Cronauer, D. C.; Spackman, W.; Lovell, H. L.; Davis, A.; Biswas, B. Fuel 1975, 54, 40-49.
0887-0624/87/2501-0227$01.50/0
227
Registry No. SnC12,7772-99-8;Mo, 7439-98-7. B. C. Bockrath,* E. G. Illig, W. D. Wassell-Bridger Pittsburgh Energy Technology Center US.Department of Energy Pittsburgh, Pennsylvania 15236 Received November 3, 1986 Revised Manuscript Received December 19, 1986
Evaluation of Nondonor Polyaromatic Solvents for Dissolution of Coal Sir: A number of authors’B have reported on the ability of nondonor polyaromatic solvents to dissolve bituminous coal. The conjugated-double-bond structure of polynuclear aromatic compounds2 is analogous to the chemical structure of coal molecules. Coal dissolution by these solvents is generally associated with major hydrogen-transfer reactions between coal and the solvent at high temperature. These hydrogen-transfer reactions are called “hydrogen~huttling”.4*~ Polyaromatic nondonor solvents are capable of redistributing hydrogen among different coal species under the mechanism of hydrogen shuttling. Little attempt has been made to correlate the ability of dissolution of PAC in terms of their chemical and physical properties. Marzec et aL6reported that coal extraction by solvent is, in principle, a substitution reaction; substances in the pores of the coal are replaced by solvent molecules participating in electron-donor and -acceptor interactions. I t has been known that iodine forms charge-transfer complexes with condensed polynuclear aromatic hydrocarbons.‘,8 The ability of PAC with iodine to form 1,-PAC complexes is expected to be useful in evaluating the electron donor ability of PAC. The purpose of this study is to elucidate the relation between the capability of PAC to dissolve coal and the ability for them to form I,-PAC complexes. Each PAC1, of guaranteed grade was supplied from Wako Chemical Co., Ltd., and used without further purification. The formation of I,-PAC complex was performed by following an iodine doping technique. Iodine and PAC (1:20 mole ratio) were dissolved in benzene. The benzene solution was placed in an ultrasonic bath for 10 min and stirred further for 1h at room temperature. The benzene was then evaporated, and the I,-PAC complexes were thus obtained. The ESR absorptions of the complexes were observed at room temperature with a Varian E-109 ESR spectrometer. All samples showed absorption and, consequently, the existence of unpaired electrons. The radical concentrations of the samples were obtained from the integral areas of absorption lines by comparison with that of standard coal as a reference calibrated with DPPH. The radical concentrations of I,-PAC complexes (1) Davis, G. 0.; Derbyshire, F. J.,Price, R. J. Inst. Fuel 1977,50, 121. (2) Polynuclear aromatic compounds: PAC.
(3) Ratto, J. J.; Heredy, L. A.; Showronski, R. P. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1979, 24, 155. (4) Neavel, R. C. Fuel 1976, 55, 237. (5) Whitehurst, D. D. EPRI Annual Report AF-480, July 1977; Chapter I, p 58. (6)Marzec, A.; Juzwa, M.; Betlej, K.; Sobkowiak, M. Fuel Process. Technol. 1979, 2, 35. (7) Uchida, T.;Akamatsu, A. Bull. Chem. SOC.Jpn. 1962, 35, 981. (8) Singer, L. S.; Kommandeur, J. J . Chem. Phys. 1961, 34, 133.
0 1987 American Chemical Society
