Abstract:
In order to investigate the effect of H
2O
2-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 BF
4,BMIM HSO
4,BMIM H
2PO
4,BMIM PF
6 andBMIM NTf
2,were selected and respectively combined with 30% H
2O
2 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 H
2O
2 towards the desulfurization and demineralization of coal. Specifically,in comparison with the H
2O
2 system,the H
2O
2-BMIM PF
6 system showed an enhanced desulfurization rate by 18.76%,while the H
2O
2-BMIM NTf
2 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 H
2O
2-ILs system was significantly lower than that of the coal sample treated with H
2O
2 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 H
2O
2-ILs system were significantly lower than that of the coal sample with treatment of H
2O
2 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 H
2O
2-ILs system were increased as compared to that of the samples treated with H
2O
2 alone,indicating that the structure of the coal would become loose. TG results showed that the samples processed by H
2O
2-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.