Efficiently trapping asphaltene-type materials from direct coal liquefaction residue using alkylsulfate-based ionic liquids

Alkylsulfate-based ionic liquids (ILs) were synthesized and used as solid–liquid separation solvents to extract asphaltene-type materials from direct coal liquefaction residue (DCLR). Among the ILs employed, tetraethylammonium ethylsulfate ([E4N][ESO4]) was proved to be a potential solvent for trapping asphaltene-type materials from DCLR due to the higher extraction yield and the lower H/C atomic ratio of the extract. N-methyl-2-pyrrolidone (NMP) was added to reduce the viscosity of [E4N][ESO4]. It also increased the extraction yield and decreased H/C atomic ratio of the asphaltene-type materials. The mechanism of extraction might be concluded that the interactions are formed between ILs or [E4N][ESO4]/NMP mixed solvents and asphaltene-type materials, which disturbs the interactions between DCLR and leads to the dissolution of asphaltene-type materials into solvents. The obtained asphaltene-type materials possessed low H/C atomic ratios, high aromaticities, no ashes and no quinoline insolubles, which meet the requirements of preparing carbon materials.