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

Using protic ionic liquids (PILs) to treat ammonia (NH 3 )-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 NH 3 , the understanding of variations in physical properties of PILs during NH 3 absorption is important for process design. In this work, the density and viscosity variations of PIL of 1-butylimidazolium bis(trifluoromethylsulfonyl)imide ([Bim][NTf 2 ]) with different NH 3 concentrations were measured. The results showed that the density of [Bim][NTf 2 ]-NH 3 system decreased linearly as NH 3 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][NTf 2 ] (the proton was replaced with deuterium) that the hydrogen bond interaction exists in NH 3 and the imidazole ring. Quantum chemistry calculations further indicated that properties variations of the PIL during NH 3 absorption come from the changes of ionic interaction between the cation and anion and hydrogen bonding between PIL and NH 3 .