Extraction and Swelling of Low-Rank Coals with Various Solvents at Room Temperature

Low-rank coals were extracted with various solvents under ultrasonication at room temperature. In the case of single solvent extraction, N-methyl-2-pyrrolidinone (NMP) gave the highest extraction yield for Loy Yang coal, 14.3 wt % (daf). Among the mixed solvents used in this study, NMP−methanol (8:2) and NMP−water (3:1) mixed solvents gave the high yields, 15.3 and 15.1 wt % (daf), respectively. The NMP−carbon disulfide mixed solvent was not effective, although it gave very high extraction yields for bituminous coals. FT-IR measurements for Loy Yang coal, its extract, and residue showed that they have similar chemical structures. In polar solvents, Loy Yang coal swelled more highly than subbituminous coals, and the highest swelling ratio was also obtained in NMP, indicating high affinity between Loy Yang coal and NMP. The mixture of Loy Yang coal with NMP forms a gel structure at the composition of about 83 wt % NMP and 17 wt % coal.