High-Efficiency Extraction and Modification on the Coal Liquefaction Residue Using Supercritical Fluid with Different Types of Solvents

摘要

This study aims to systematically illustrate the mechanism of supercritical fluid extraction (SFE) and modification on the coal liquefaction residue (CLR) and to identify the evolution and characteristics of the mesophase produced from the carbonization of SFE extracts. Results show that the extraction performance of SFE and the properties of the mesophase precursor were strongly dependent upon the selection of operating conditions and solvents. The SFE process using acetone and isopropanol presented excellent extraction performance, owning to the effect of solvent polarity on the degradation or supercritical reaction, achieving their respective CLR extraction yields of 45.85 and 30.12 wt %, while an extraction yield of 53.78 wt % was attained when using benzene, benefiting from its strong affinity to condensed aromatic hydrocarbons. More practically, quinoline-insoluble (QI) fraction decreased from 48.84 to 1.13 wt % after SFE processing, which significantly upgraded the quality of the mesophase precursor. To an extent, supercritical acetone exhibited strong reaction activity during extraction because its extract contained a higher amount of the hexane-soluble (HS) fraction, which could optimize the molecular weight distribution of the mesophase precursor. The well-developed bulk mesophase in the carbonized SFE extracts was remarkably improved in comparison to raw CLR. Presumably, the SFE extract was favorable to forming 100% mesophase, where dominated flow textures were observed.