Theoretical calculation and experimental investigation on ionic liquid [C16mim]Cl affecting wettability of low-rank coal

Low-rank coal (LRC) is difficult to directly utilize. It is necessary to carry out clean separation before industrial. A great amount of oxidized functional groups on the surface, results in poor hydrophobicity of LRC. Ionic liquids (ILs) are evolving important materials for designing new clean technologies. The adsorption characteristic of 1-hexadecyl-3-methylimidazolium chloride on coal surface was studied by adsorption isotherms, thermodynamics, zeta potential, and molecular dynamics simulation to effectively enhance the hydrophobicity of low-rank coal. The results show that the adsorption of ionic liquid on low-rank coal surface is an endothermic spontaneous physical adsorption, the saturated adsorption increases with the rise of temperature, and the electrostatic attraction and intermolecular forces play the leading role in the process of ionic liquid adsorption. The analysis indicates that the positively charged imidazole group forms an effective coverage of the O = C-O group on the coal surface due to the adsorption of the ionic liquid, resulting in a decrease in the content of O = C-O group and an increase the surface potential of the coal; probably, the hydrophobic alkyl chain of ionic liquid also increases the C-C/C-H bonds. Moreover, the hydrophobicity is significantly improved after the adsorption of ionic liquid, making the water droplets more difficult to wet on the coal surface. Moreover, molecular simulation studies show that the imidazole group of the ionic liquid is first adsorbed on the coal surface due to electrostatic attraction, and finally, the ionic liquid is approximately laid on the coal surface due to the intermolecular force.

Automated summary

By studying the adsorption characteristics of ionic liquids on the surface of low-rank coal, it was found that the adsorption of ionic liquids effectively enhances the hydrophobicity of the coal, reduces the content of oxidized functional groups, increases the surface potential, and makes water droplets more difficult to wet the coal surface.