Extraction of Asphaltenes from Direct Coal Liquefaction Residue by Dialkylphosphate Ionic Liquids

Asphaltenes in direct coal liquefaction residue (DCLR) are important precursors for the preparation of carbon materials. Some traditional polar hydrocarbon solvents show the ability to extract asphaltenes from DCLR, but these solvents are volatile, toxic, and difficult to recycle. Dialkylphosphate ionic liquids (ILs) have been demonstrated to have the ability to extract asphaltenes fractions from DCLR environmentally friendly. In order to understand the relationship between the extractive performance and the structure of cations and anions of ILs, a series of N,N-dialkylimidazolium dialkylphosphate ILs were synthesized and used to extract asphaltenes from DCLR. The extracts were characterized by Elemental Analysis, FT-IR, 13C-NMR, etc. The results show that it is feasible to extract asphaltenes from DCLR by N,N-dialkylimidazolium dialkylphosphate ILs. The alkyl chain length of cations and anions of the ILs is one factor that influences the extraction yield and the physicochemical characteristics of the extracted asphaltenes, such as the atomic ratio of H/C, true density, aromaticity, and so on. The alkyl chain length of ILs might be modified successfully for controlling the physicochemical characteristics of the extracts from DCLR.