1-Butyl-3-methylimidazolium chloride involved in sequential extraction of lignite to separate group components and its effect on functional groups of residues

BACKGROUND In view of the low economic benefit for direct utilization of lignite, the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) has been used to extract Inner Mongolia lignite (IML) in order to efficiently separate lignite, develop the technology for clean and value-added utilization of lignite, and alleviate the enormous pressure of ecological environment pollution. Subsequently, sequential extraction of IML by [Bmim]Cl/ N -methyl-2-pyrrolidone (NMP), acetonitrile and ether was employed to separate group components in lignite. RESULTS Functional group results show that hydrogen bonds of IML including OH  ether, COOH dimers and SH  N, and weak covalent bonds such as C al  O, C al  N, C al  S and S  S, can be cleaved by [Bmim]Cl. Extraction experiments using mixed solvents of [Bmim]Cl and NMP or water indicate that the synergistic effect of NMP and [Bmim]Cl plays a vital role in increasing lignite extraction yield, but for water an opposite effect is observed. Importantly, the group components extracted by [Bmim]Cl/NMP and consecutively by acetonitrile and ether show a clear difference in composition according to gas chromatography–mass spectrometry. Specifically, polycyclic aromatic hydrocarbons and long-chain alkanes are present in the acetonitrile phase, with relative content of 8% and 88%, respectively, while most of esters, aliphatic acids and phenols are dissolved in ether with proportions of 35.24%, 35.53% and 16.57%, respectively. CONCLUSION This work demonstrates that sequential extraction of lignite by [Bmim]Cl/NMP, acetonitrile and ether may provide new insights for the separation of group components and clean utilization of lignite in industry. © 2023 Society of Chemical Industry (SCI).