Effect of active composite ionic liquids treatment on chemical structure and wettability of coal

•The contact angle of [Bmim][BF4]/[Emim][BF4] with the mixture ratio of 1:5 on the coal surface reached the min value of 34.483°.•[Bmim][BF4]/[Bmim][Cl] and [Bmim][BF4]/[Emim][BF4] composite solutions can not only increase the content of hydrophilic functional groups, but also decrease the content of hydrophobic functional groups.•CO was the primary functional group affecting contact angle. –OH and COC were the main functional groups affecting moisture content.•[Bmim][BF4]/[Bmim][Cl] with a compounding proportion of 1:5 had the best water retention performance. To investigate the effect of different ionic liquid composite solutions on the wettability and chemical structure of coal dust, 14 ionic liquid compound solutions with various composite ratios were selected to act on long flame coal. Through the contact angle measuring instrument, 14 ionic liquid compound solutions were optimized, and 4 ionic liquid compound solutions with the same anion/cation were selected. The wetting agent with good water retention performance in the 4 kinds of composite solutions was selected by the water retention experiment. FTIR was used to research the change of functional group content in the coal treated by the 4 kinds of composite solutions. The results displayed that the contact angle of [Bmim][BF4]/[Emim][BF4] solution with the mixture ratio of 1:5 on the coal surface reached the min value of 34.483°. The [Bmim][BF4]/[Bmim][Cl] solution with a compounding proportion of 1:5 had the best water retention performance. The hydrophilic and hydrophobic functional groups of long flame coal treated by ionic liquid composite solutions had changed significantly. The [Bmim][BF4]/[Emim][BF4] composite solutions with the compounding proportion of 2:4 and 1:5 and the [Bmim][BF4]/[Bmim][Cl] composite solutions with the compounding proportion of 2:4 and 1:5 can not only increase the content of hydrophilic functional groups OH⋯O, Si–O–Si, COC, CO, and CO, but also decrease the content of hydrophobic functional groups CH2 and 2H. By analyzing the relationship between coal wettability and functional groups, it was discovered that the hydrophilic functional group CO was the primary functional group affecting the contact angle, and –OH and COC were the primary functional groups affecting the moisture content of coal samples. In this essay, the novel composite wetting agent type was prepared by compounding ionic liquid solutions with the same anion/cation in pairs, which has certain guiding