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Energy & Fuels 2002, 16, 1006-1007
Relationship between Thermal Extraction Yield and Softening Temperature for Coals Takahiro Yoshida, Toshimasa Takanohashi,* Kinya Sakanishi, and Ikuo Saito Institute for Energy Utilization, National Institute of Advanced Industrial Science and Technology, 16-1 Onogawa, Tsukuba, Ibaraki-ken, 305-8569, Japan
Masaharu Fujita and Kiyoshi Mashimo College of Science and Technology, Nihon University, 1-8 Kanda-Surugadai, Chiyoda-ku, Tokyo, 101-8308, Japan Received October 9, 2001 Extraction with a carbon disulfide/N-methyl-2-pyrrolidinone (CS2/NMP) mixed solvent (1:1 by volume) at room temperature gives high extraction yields (40-65%) for several bituminous coals without significant chemical reaction.1,2 The high yields can be the result of solventinduced relaxation of noncovalently associated coal aggregates followed by the facile diffusion of the highly polar solvent into raw coal.1 While nonpolar solvents routinely give very low extraction yields,3 Miura et al. obtained a 70% yield by thermal extraction with tetralin at 350 °C using a flow-type extractor.4 We previously studied thermal extractions with tetralin, 1-methylnaphthalene, and nonpolar industrial solvent, light cycle oil (LCO), at 360 °C using a batch-type extractor under nitrogen.5 The extraction yields were 24-38% (daf) when filtration was performed at room temperature. Some portion of extract might have deposited during quenching to room temperature. In the present study, we extracted 14 bituminous coals with LCO at 360 °C using a flow-type extractor; both extraction and filtration were carried out at 360 °C. We found that higher extraction yields of more than 60% were obtained, and that the softening temperature of raw coal gave an excellent correlation with extraction yield. LCO, a nonpolar byproduct obtained from an upgrading process of vacuum gas oil, was used for all coals. It consists mainly of two- or three-aromatic ring compounds (measured by GC/MS); the elemental analysis (wt%) is C: 89.6%, H: 9.8%, N: 0.15%, and S: 0.5%. For comparison, extractions with the dimethylnaphthalene (DMN) at 360 °C, and the CS2/NMP mixed solvent at room temperature were also performed for five and 14 coals, respectively. The DMN is a mixture of isomers and contains a significant amount of impurities; the elemental analysis is C: 89.1, H: 7.5, N: 1.6, and S: 0.4 (wt%). Thermal extraction of the coals (76-86 wt% C (daf), particle size:
