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Energy & Fuels 1996, 10, 220-224
Structural Studies on Illinois No. 6 Coal through Quinoline Extraction† Satoru Murata, Eiji Kawakami, and Masakatsu Nomura* Department of Applied Chemistry, Faculty of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565, Japan Received May 30, 1995. Revised Manuscript Received October 11, 1995X
Extraction of two subbituminous and four bituminous coals with quinoline at 350 °C under 4.9 MPa of N2 pressure was conducted, this giving extract (quinoline-soluble materials) in 6590 wt % yield. Only the extract from Illinois No. 6 coal (85% yield) was found to be completely soluble in more conventional solvents such as pyridine and N,N-dimethylformamide (DMF). Therefore, the structural study was focused on the extract. Comparison of the structural features of the QS fraction with that of the original coal suggests that bond cleavage reaction occurs during the extraction, this seeming to be partly responsible for solubilization in quinoline. To examine the nature of the extract association, light scattering and size exclusion chromatographic experiments were conducted in DMF solution. The results indicate that molecular size of the QS is very large even in the polar solvent and this might consist of association of the smaller compounds with ca. 3000 molecular weight. These are discussed briefly.
Introduction Non-covalent bonding interactions among coal organic materials (COM) are thought to be one of the key factors to affect coal conversion technology.1,2 Larsen and Kovac had reported the importance of nonbonding interaction among the coal molecules and proposed the associated coal structure for the first time.3 Nishioka had investigated solvent-induced swelling of Illinois No. 6 coal and concluded that significant portions of the coal molecules are not a three-dimensional network but are physically associated.4 Iino et al. had also pointed out that some coal extracts have a strong tendency to associate on the basis of the data from measurement of molecular size distribution by size exclusion chromatography, in which they found that anthracene, 1,1,2,2tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane, and lithium bromide could cleave some nonbonding interactions between coal molecules.5 These studies seem to suggest the importance of non-bonding interactions among coal molecules. The purpose of the present work is to evaluate nonbonding interaction of coal molecules. We thought that effective solubilization was needed to accomplish this purpose. Several studies to solubilize coal in conventional solvents have been conducted extensively,1 for example, pyrolysis, hydropyrolysis, liquefaction, reductive alkylation, or depolymerization with superacids. Among these studies, we were interested in the treatment of coal with various solvents at around 350 °C reported by Larsen et al.6 and Ouchi et al.7 The † A part of this study was presented in the International Conference on Coal Science held at Oviedo, Spain, in September 1995. X Abstract published in Advance ACS Abstracts, November 15, 1995. (1) Gorbaty, M. L., Larsen, J. W., Wender, I., Eds. Coal Science; Academic Press: New York, 1982; Chapter 4. (2) Gorbaty, M. L. Fuel 1994, 73, 1819. (3) Kovac, J., Larsen, J. W. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1977, 22, 181. (4) Nishioka, M. Fuel 1993, 72, 1719. (5) Iino, M.; Takanohashi, T.; Obara, S.; Tsueta, H.; Sanokawa, Y. Fuel 1989, 68, 1588.
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treatment could make much amount of organic materials in coal soluble in conventional solvents without considerable change of chemical structure. Consequently, we employed this method for two subbituminous and four bituminous coals to obtain much amount of solvent soluble fraction and investigated its association nature using size exclusion chromatographic and light scattering methods by limiting the extract of Illinois No. 6 coal. Experimental Section Samples. Illinois No. 6 and Upper Freeport coals were purchased from Argonne National Laboratory. The other four coals, such as Wandoan (Australian subbituminous coal), Akabira (Japanese bituminous coal), Miike (Japanese bituminous coal), and Zao Zhuang coals (Chinese bituminous coal), are our samples stored in glass vessels under a nitrogen atmosphere. Coals were pulverized under 100 mesh and dried at 40 °C in vacuo prior to use. All solvents were distilled before use. Extraction of Coals with Quinoline. The autoclave including 2 g of pulverized and dried coal and 10 mL of quinoline was pressurized with nitrogen up to 4.9 MPa and then heated to 350 °C at a heating rate of 8 K/min. The autoclave was kept at this temperature for 1 h with shaking. After 1 h passed, the autoclave was cooled to room temperature, gaseous products being collected and analyzed by a Shimadzu GC-8AIT (silica gel column). Solid and liquid products were recovered by washing the inside of the autoclave with quinoline, being separated into quinoline-soluble (QS) and -insoluble (QI) fractions by centrifugation. After removal of quinoline by evaporation at 80 °C under 5 mmHg, the resulting solid materials were washed three times with a mixture of methanol-water (8:2, v/v) under ultrasonic irradiation in order to remove small amounts of quinoline remained. The results of the extraction of six coals are summarized in Table 1. The resulting QS and QI fractions were dried at 40 °C in vacuo; the extract was then submitted to analysis by NMR, size exclusion chromatography, pyrolysis GC/MS, and so on. (6) Larsen, J. W.; Yurum, Y.; Sams, T. L. Fuel 1983, 62, 476. (7) Ouchi, K.; Itoh, S.; Makabe, M.; Itoh, H. Fuel 1989, 68, 735.
© 1996 American Chemical Society
Structural Studies on Illinois No. 6 Coal
Energy & Fuels, Vol. 10, No. 1, 1996 221
Table 1. Extraction of Six Coals with Quinoline at 350 °C for 1 h yield (wt %, daf)
coal sample (location)
carbon contents (wt %, daf)
gas
QSa(PS)b
QIc
Illinois No. 6 (US) Wandoan (Australia) Akabira (Japan) Miike (Japan) Upper Freeport (US) Zao Zhuang (China)
77 78 83 83 86 87
1
