Effect of side chain functional groups of ionic liquids on improving wettability of coal: Simulation and experimental discussion

Abstract

It is wise to investigate the influence of ionic liquids (ILs) on reducing hydrophobicity and dust pollution of coal from the perspective of side chain groups. In this study, two ILs ([Emim][Cl] and [HOEmim][Cl]), were selected and applied to bituminous coal. The density functional theory results showed that [HOEmim][Cl] containing the –OH group had an energy gap of 5.2895 eV, which was lower than the 5.3873 eV of [Emim][Cl] containing only the -CH3 group. A higher chemical activity of [HOEmim][Cl] was demonstrated due to the presence of the –OH group. A molecular dynamics-based contact angle system was constructed to investigate the wetting properties of coal samples treated with different ILs at the molecular level. The simulation results indicated that, compared to untreated coal, [HOEmim][Cl] exhibited a greater ability than [Emim][Cl] to improve the wetting properties of coal. Contact angle experiments demonstrated that treatment with [Emim][Cl] and [HOEmim][Cl] resulted in a decrease in contact angle by 22.67° and 25.04°, respectively, compared to deionized water, providing validation for the accuracy of molecular simulations. Lastly, the structural changes of coal samples induced by different ILs were observed by FITR, which explained the differences in wetting effects.