Studies on the physical properties variations of protic ionic liquid during NH3 absorption

Using protic ionic liquids (PILs) to treat ammonia (NH3)-containing exhausted gases is a potential method to mitigate the air pollution and realize the ammonia recovery in industries. In order to design a new process to absorb and recover NH3, the understanding of variations in physical properties of PILs during NH3 absorption is important for process design. In this work, the density and viscosity variations of PIL of 1 -butylimidazolium bis(trifluoromethylsulfonyl)imide ([Bim][NTf2]) with different NH3 concentrations were measured. The results showed that the density of [Bim][NTf2]-NH3 system decreased linearly as NH3 concentrations increased, while the viscosity exhibited a turning trend, i.e., the viscosity first increased about 15 % and then decreased sharply to a lower value. It is confirmed by the NMR spectra of d-[Bim][NTf2] (the proton was replaced with deuterium) that the hydrogen bond interaction exists in NH3 and the imidazole ring. Quantum chemistry calculations further indicated that properties variations of the PIL during NH3 absorption come from the changes of ionic interaction between the cation and anion and hydrogen bonding between PIL and NH3. (C) 2019 Elsevier B.V. All rights reserved