Study on Extraction Asphaltenes from Direct Coal Liquefaction Residue with Ionic Liquids

Abstract

Direct coal liquefaction residue (DCLR) contains about 25% asphaltenes which are proved to be important precursors for preparing high value-added carbon materials. In this work, ionic liquids (ILs) were used as potential solvents to extract asphaltenes from DCLR, and a series of dialkylphosphate ILs, i.e., imidazolium-based, pyridinium-based, and ammonium-based, were synthesized and used to extract asphaltenes from DCLR. The influences of extractive time, extractive temperature, and mass ratio of ILs to DCLR on extraction efficiency of asphaltenes were investigated and the optimized conditions were determined. In order to understand the mechanism of extraction asphaltenes with ILs, the extracts were characterized by elemental analysis, FT-IR, 13CNMR, and so on. The results show that it is feasible to extract asphaltenes from DCLR with dialkylphosphate ILs. The structure and size of anion and cation of ILs probably are the main factors that influence the extraction yield and the physicochemical characteristics of extracted asphaltenes, such as atomic ratio of H/C, the structure and aromatic cluster size, and so on.