Efficient extraction of direct coal liquefaction residue with the [bmim]Cl/NMP mixed solvent

Abstract

A novel solvent mainly consisting of ionic liquid 1-butyl-3-methylimidazolium chloride ([bmim]Cl) and N-methyl pyrrolidinone (NMP), was used to treat Direct Coal Liquefaction Residue (DCLR). The aim was to extract an important organic precursor compound from the DCLR as the raw material of carbon fibers. The performance of extraction and properties of the extract with the mixed solvent were analyzed and characterized by FT-IR, solid state 13C-NMR, DTA, micrograph and elemental analysis. The results showed that the mixed solvent was efficient to extract organic components from DCLR, but inert to inorganic substances. Adding NMP into [bmim]Cl not only accelerated the solid–liquid separation after the dissolution of DCLR, but also increased the extract yield. The possible synergistic mechanism was proposed based on the characteristic results. NMP in the mixture plays an important role to swell the fixed carbons contained in DCLR, and the ionic liquid [bmim]Cl contributes to destroying hydrogen bond forces in DCLR.