Mechanism of extracting poorly-caking components from Shenhua long-flame coal using [N4441][Cl]

The effects of different kinds of ionic liquids (ILs) on the caking property of Shenhua long-flame coal (SHLC) were studied. SHLC and its residue after [N₄₄₄₁][Cl] treatment under optimum conditions were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and pyrolysis-gas chromatography and mass-spectrometric analysis (Py-GC/MS). The results showed that the ILs used could extract the poorly-caking components from SHLC, and [N₄₄₄₁][Cl] with C₃H₆O as a solvent exhibited the best effect among the ILs and solvents used. [N₄₄₄₁][Cl] could destroy the H bonds in SHLC, and the structure of the cross-linked macromolecules of SHLC was loosed, leading to the release of the small molecules within the macromolecular framework of SHLC. Additionally, [N₄₄₄₁][Cl] could easily penetrate into the interior of the relaxed SHLC and break the weak covalent bonds (e.g., C‒O bonds) of the macromolecules of SHLC. As a result, aromatic hydrocarbons with 3‒5 rings and aliphatic side chains, which are the precursor of the poorly-caking components, were formed and were then extracted from SHLC by C₃H₆O. Consequently, [N₄₄₄₁][Cl] treatment could decrease the caking property, thermal ability, and macromolecular size of SHLC.