Mechanism of supercritical fluid extraction of coal

This paper describes the mechanism of supercritical toluene (or toluene-tetralin mixture) extraction of coal. The effects of solvent power and solvent residence time in the cell on conversion and liquid yield were examined by using a two-stage extraction method: extraction at various conditions followed by high-solvent power extraction. The effect of tetralin addition on supercritical toluene extraction was also investigated by this method. Furthermore, in situ ESR measurement was conducted to evaluate the variation of radical concentration during supercritical fluid extraction. From these detailed analyses the effects of the solvent power of supercritical fluid on the reactions during extraction, namely on decomposition and polymerization of the primary products from coal decomposition, and on stabilization of the radicals through hydrogen transfer reaction were evaluated.