Molecular insight into the effect of ion structure and interface behavior on the ammonia absorption by ionic liquids

Abstract

Abstract Molecular dynamics simulations were performed to elucidate the roles of ion structure and interface behavior in absorption of gases (NH 3 , N 2 , H 2 ) by ILs (protic IL [Bim][Tf 2 N] and conventional IL [Bmim][Tf 2 N]). The results indicated that NH 3 compete with [Tf 2 N] − to interact with N3‐H site of [Bim] + cation, forming a strong N3H∙∙∙N(NH 3 ) hydrogen bond with the energy of −79 kJ/mol, which is twice as much as the energy of the hydrogen bond between C2H of [Bmim] + and NH 3 (−33.2 kJ/mol). Moreover, there is a dramatic increase in the number density of cations near the IL‐gas interface, resulting in the NH 3 molecules permeate into the bulk rapidly and effectively and achieving the high selective absorption of NH 3 to H 2 and N 2 . Considering the inevitable trace water in the raw gases, the influence of water was studied and it was shown that trace water can enhance the absorption of NH 3 by [Bim][Tf 2 N].