Molecular thermodynamic and dynamic insights into gas dehydration with imidazolium–based ionic liquids

[Display omitted] •Structural effects on ILs suitability as gas dehydration agents were revealed;•Dehydration performances of various ILs were evaluated by free energy calculations;•The interaction mechanism of IL-H2O at the molecular level was deeply unraveled;•The relationship of dehydration performance and interactions was explored. Structural effects on various imidazolium–based ionic liquids (ILs) (i.e., [C][A], [C] = [EMIM]+, [BMIM]+, and [OMIM]+; [A] = [BF4]–, [PF6]–, and [Tf2N]–) suitability as drying agents for gas dehydration processes are explored from thermodynamic and dynamic insights by quantum chemistry (QC) calculations and molecular dynamics (MD) simulations. It is found that [EMIM][BF4] is regarded as the most promising drying agent because it exhibits the lowest Henry’s law constant and highest diffusion coefficient of H2O among all ILs. The microscopic mechanism at molecular level is revealed based on QC calculations and MD simulations, and the results demonstrate that the IL (i.e., [EMIM][BF4]) simultaneously with the smallest cation and anion size corresponds to both the strongest hydrogen bond (HB) interaction of H2O–anion and the strongest HB together with van der Waals interactions of H2O–cation. This work provides a valuable guidance from viewpoint of thermodynamics and dynamics for developing and screening novel ILs for gas dehydration.