Supercritical fluid extraction of coal under pyrolysis conditions

Abstract Supercritical fluid extraction of Wandoan coal was carried out under pyrolysis conditions using hexane, benzene, toluene and a toluene-tetralin mixture. The residues and extracts obtained were analysed using solid state 13 C nuclear magnetic resonance (n.m.r.) spectroscopy, gas chromatography (g.c.), gas chromatography-mass spectrometry (g.c.-m.s.) and gel permeation chromatography (g.p.c.), respectively, to clarify the relation among the extraction yield, the solvent power of the supercritical fluid, and the reactions taking place during extraction. The decrease in conversion, defined by 100—residue yield, at higher extraction temperatures above 653 K, was mainly due to the aromatization of coal. The aromatization was suppressed by addition of tetralin to the extraction solvent, which resulted in an increase in conversion. The extract yield was increased, without increasing the gas yield, through the enhancement of solvent power by increasing the extraction pressure or selecting the solvent. The extraction solvents used were found to be partly condensed to dimers during the extraction. The condensation of toluene was inhibited by addition of tetralin, but another dimer between tetralin and toluene was formed instead. Conversion was increased and dimer formation suppressed by impregnating tetralin into the coal in advance.