Energy & Fuels 1998, 12, 913-917
913
Effect of Heavy Solvent-Soluble Constituents on Coal Fluidity Toshimasa Takanohashi,* Takahiro Yoshida, and Masashi Iino Institute for Chemical Reaction Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Kenji Katoh Process Technology Research Laboratories, Nippon Steel Corp., 20-1 Shintomi, Futtsu, Chiba 293-0011, Japan
Kiyoshi Fukada Materials and Processing Research Center, NKK., 1 Kokan-cho, Fukuyama, Hiroshima 721-8510, Japan Received December 31, 1997. Revised Manuscript Received May 27, 1998
K-Prima, Witbank, Warkworth, Goonyella, Luscar, and Pittston-MV coal samples were heated to temperatures between 200 and 550 °C at a rate of 3 °C/min in an autoclave under nitrogen and then cooled rapidly to room temperature. Heat-treated coals were extracted with a carbon disulfide-N-methyl-2-pyrrolidinone mixed solvent at room temperature; the extracts were fractionated further with pyridine and chloroform. Raw coals contained a significant fraction of solvent-soluble constituents (20-45 wt %). For high-caking coals, the amount of heavy solventsoluble constituent, i.e., the pyridine-insoluble and the mixed solvent-soluble fraction, greatly increased at the fluidity stage. There is a good linear relation between the maximum extraction yield and the Gieseler fluidity of the coals. This result suggests that heavy constituents are an important factor for the occurrence of fluidity in coals.
Introduction Advanced coke-making techniques are being studied to enhance efficiency and to develop methods to use lowquality coals that are hard to soften during heating. Fluidity is the result of physical and chemical changes that occur in coals during heating, but the precise nature of these changes and their effect on fluidity are not understood. It is well known that there are relations between the amount of low-molecular-weight substances in coal, expressed as the solvent extraction yield, and Gieseler fluidity. Two theories have been proposed to explain fluidity behavior. One is that chloroform solubles, γ component, that exist originally in raw coals disperse coal particles (the γ component theory1-4). The other is that low-molecular-weight constituents (metaplasts) generated by cleavage of covalent bonds during pyrolysis disperse coal particles (the metaplast theory5-13). * Corresponding author. Present address: National Institute for Resources and Environment, Tsukuba 305-8569, Japan. (1) Wheeler, R. V.; Clark, A. H. J. Chem. Soc. 1913, 103, 1704. (2) Wheeler, R. V.; Cockram, C. J. Chem. Soc. 1931, 117, 854. (3) Shinmura, T. J. Fuel Soc. Jpn. 1929, 8, 379. (4) Shinmura, T. Rep. Fuel Inst. 1932, 14, 1. (5) Nadaziakiewitz, N. Fuel 1958, 37, 361. (6) van Krevelen, D. W.; van Heerden, C.; Huntjens, F. J. Fuel 1951, 30, 253. (7) van Krevelen, D. W.; Huntjens, F. J.; Dormans, H. N. M. Fuel 1956, 35, 462.
Recently Neavel14 and Yokono15 proposed that high fluidity results when low-molecular-weight components such as γ component and metaplast donate hydrogens to coal fragments generated during pyrolysis (the hydrogen-donating model). In agreement with this model, it has been reported that the addition of some radical stabilizers enhanced the fluidity of coals.16-18 In contrast, Sakurovs and Lynch found19 that coal fluidity can be enhanced by the addition of fused aromatic-rich additives and proposed a model in which the additives solvate the molecular structure of coals. Iino et al. found20,21 that extraction at room temperature of some bituminous coals with a carbon disulfideN-methyl-2-pyrrolidinone mixed solvent (CS2-NMP, 1:1 (8) Chermin, H. A. G.; van Krevelen, D. W. Fuel 1957, 36, 85. (9) Dormans, H. N. M.; van Krevelen, D. W. Fuel 1960, 39, 273. (10) Dryden, I. G. C.; Pankhurst, K. S. Fuel 1955, 34, 363. (11) Dryden, I. G. C.; Joy, W. K. Fuel 1961, 40, 473. (12) Hertog, W. D; Berkowitz, N. Fuel 1958, 37, 358. (13) Sarkar, S.; Krishmen, S. G. Fuel 1963, 42, 303. (14) Neavel, R. C. Coal Science; Gorbaty, M. L., et al., Ed.; Academic Press: New York, 1982; p 1. (15) Yokono, T. Report of the Section of Coking Property of Coals; The Iron and Steel Institute of Japan: Tokyo, 1985; p 83. (16) Clemens, A. H.; Matheson T. W. Fuel 1987, 66, 1009. (17) Clemens, A. H.; Matheson T. W.; Sakurovs, R.; Lynch, L. J. Fuel 1989, 68, 1162. (18) Clemens, A. H.; Matheson, T. W. Fuel 1995, 74, 57. (19) Sakurovs, R.; Lynch, L. J. Fuel 1993, 72, 743. (20) Iino, M.; Takanohashi, T.; Ohsuga, H.; Toda, K. Fuel 1988, 67, 1639. (21) Takanohashi, T.; Iino, M. Energy Fuels 1990, 4, 452.
S0887-0624(97)00239-9 CCC: $15.00 © 1998 American Chemical Society Published on Web 07/11/1998
914 Energy & Fuels, Vol. 12, No. 5, 1998
Takanohashi et al. Table 1. Analyses of Coal Samples
ultimate analysis (wt %, daf) Luscar Goonyella Pittston-MV Warkworth Witbank K-Prima
C
H
N
S
Oa
88.3 88.1 85.7 84.7 82.7 81.2
4.6 5.1 5.5 5.9 4.5 5.9
1.5 1.9 1.7 1.8 2.2 1.3
0.3 0.6 1.0 0.6 0.6 0.4
5.3 4.4 6.1 7.0 10.0 11.2
proximate analysis (wt %, db) VM
ash
23.5 23.4 34.3 34.2 32.9 43.4
9.5 9.8 6.9 13.8 8.0 3.8
a By difference. b Softening temperature. c Maximum fluidity temperature. fluidity). f Total dilatation. g Crucial swelling number.
caking property
FC
STb
MFTc
RTd
log MFe
TDf
CSNg
67.0 66.8 58.4 52.0 59.1 52.8
420 397 389 391 412 390
464 456 430 433 432 414
490 498 488 460 446 452
2.30 2.99 4.37 2.47 0.95 0.60
33 120 163 21 0 0
7.0 7.5 7.0 6.0 2.0 2.0
d
Resolidification temperature. e log(Gieseler maximum
Figure 2. Fractionation procedure for heat-treated coal.
Figure 1. Procedure for the heat treatment of coal.
v/v) gave high extraction yields (40-80 wt % (daf)). They found that significant amounts of solvent-soluble constituents originally existed in several raw coals. The CS2-NMP extraction yield of heat-treated coals increased greatly at the fluidity stage and then decreased toward resolidification stage, which suggested that solvent-soluble constituents were related to fluidity behavior.22 In the present study, the CS2-NMP extracts obtained from coals heated to various temperatures were further fractionated using pyridine and chloroform. Characterization of the extract fractions was carried out, especially the behavior at the fluidity stage of pyridineinsoluble constituents that are obtained only with the mixed solvent. Experimental Section
of 3 °C/min and then rapidly quenched in ice water. Samples cooled to room temperature within a few minutes. Solvent Fractionation. Approximately 2 g of heat-treated coals was extracted with the CS2-NMP mixed solvent (1:1 v/v) at room temperature. The extraction method is described in detail elsewhere;20,21 a schematic of the procedure is shown in Figure 2. After evaporation of solvent, the extract (the mixed solvent-soluble fraction, MS) was washed with an acetonewater (2:8 v/v) solution under ultrasonic irradiation to remove solvent,20 and the residue (the mixed solvent-insoluble fraction, MI) was washed with acetone in the same way. Redissolution on the MS extracts showed that a few percent became insoluble in the mixed solvent, probably because of association and/or polymerization. The extract and residue were dried in vacuo at 80 °C for 12 h. The extraction yield was determined from the weight of the residue as
extraction yield [1 - (residue(g)/coal(g))] × 100 (1) (wt %, daf) ) [1 - (ash(wt %, db))/100] The mixed solvent extract was further fractionated with pyridine and chloroform into pyridine-insoluble (PIMS), chloroform-insoluble and pyridine-soluble (CIPS), and chloroformsoluble (CS) fractions. Fractions were dried in vacuo at 80 °C for 12 h, and then weighed. Molecular Weight Distribution. Size exclusion chromatography was performed on a porous silica gel column with a refractive index detector; the CS2-NMP mixed solvent was used as an eluent.23 Molecular weight distribution of the extracts was determined using a calibration curve prepared with polystyrene standard samples.
Coal Samples. Two low-caking coals (K-Prima and Witbank), one middle-caking coal (Warkworth), and three highcaking coals (Goonyella, Luscar, and Pittston-MV) were used. Samples were ground to
