Effect of lighter constituents on the solubility of heavy constituents of coals

Zao Zhuang, Shin-Yubari and Upper Freeport bituminous coals were extracted with a carbon disulfide/N-methyl-2-pyrrolidinone (CS2/ NMP) mixed solvent a t room temperature. Extracts were further fractionated with acetone to give acetone-soluble (AS) and acetone-insoluble (AI) fractions; the AI fraction was further extracted with pyridine to give pyridine-soluble (PS) and pyri dine insoluble (PI) fractions. Despite the fact that they were part of the whole solute in the original extract, the PI fractions from all coals were only partially soluble in the mixed solvent. Combination of the AS and PS, which are lighter fractions than the PI, from the parent coal with the resp ective PI fraction greatly enhanced the solubility of PI in the mixed solve nt. In addition, the solubility in mixed solvent of the PI fraction from Za o Zhuang coal was increased by addition of AS and PS fractions from Miike, Shin-Yubari, and Illinois No. 6 coals; the amount of enhanced solubility in comparison with the solubility of PI alone depended on the coal fraction u sed, i.e. AS and PS. In general, the enhancement caused by PS fractions was greater than that by AS fractions. The mechanism of solubility enhancement of the heavy constituent (PI fraction) by the addition of lighter constitu ents (AS and/or PS) is discussed, from the viewpoint of differences in the chemical structures of the constituents, i.e. AS, PS and PI fractions. (C) 2000 Elsevier Science Ltd. All rights reserved.