Desulfurization and demineralization of coal using H₂O₂ and imidazoles ionic liquids

In order to investigate the effect of H₂O₂-imidazoles ionic liquids systems on the desulfurization and demineralization of coal,five hydrophilic and two hydrophobic ionic liquids with same cation,i. e.BMIM Br,BMIM Cl,BMIM BF₄,BMIM HSO₄,BMIM H₂PO₄,BMIM PF₆ andBMIM NTf₂,were selected and respectively combined with 30% H₂O₂ to remove sulfurs and minerals from Ningdong SM coal,after which the ionic liquids were recycled and reused. The sulfur species of the coal samples before and after the treatment were determined by a wet-chemical method,and characterized by FT-IR,XRD,BET and TG analyses. The results showed that the use of ionic liquids could greatly improve the efficiency of H₂O₂ towards the desulfurization and demineralization of coal. Specifically,in comparison with the H₂O₂ system,the H₂O₂-BMIM PF₆ system showed an enhanced desulfurization rate by 18.76%,while the H₂O₂-BMIM NTf₂ system exhibited an improved demineralization rate by 27.50%. Overall,the hydrophobic ionic liquids had superior desulfurization and demineralization performances to their hydrophilic counterparts. FT-IR characterization results showed that the characteristic peak strength of sulfur-containing functional groups in the coal sample after treated with H₂O₂-ILs system was significantly lower than that of the coal sample treated with H₂O₂ alone,indicating that the content of sulfur in the coal was decreased in the presence of ionic liquids. The XRD results showed that the diffraction peak intensities of quartz and other minerals in the coal sample after treatment with H₂O₂-ILs system were significantly lower than that of the coal sample with treatment of H₂O₂ alone,indicating that the removal efficiency of ash in the coal was enhanced due to the presence of the ionic liquids. BET results showed that the specific surface area and average pore diameter of the samples treated with H₂O₂-ILs system were increased as compared to that of the samples treated with H₂O₂ alone,indicating that the structure of the coal would become loose. TG results showed that the samples processed by H₂O₂-ILs system had more volatile substances escaping during the pyrolysis than raw coal,and the calorific value was slightly reduced. More importantly,the ionic liquids only showed slightly decreased desulfurization and demineralization efficiency during the regeneration of 7 cycles,showing the good stability of ionic liquids.