Efficient Absorption Of Ammonia With Hydroxyl-Functionalized Ionic Liquids

Ammonia ?NH₃? emitted from ammonia synthesis process is a kind of waste chemical resource and a major environmental pollutant. The traditional water scrubbing method suffers from high energy consumption. Ionic liquids ?ILs? are one of the most promising alternatives for NH₃ capture because of their unique properties, including high thermal stability, negligible vapor pressure and tunable chemical properties. In this work, hydroxyl groups were introduced into imidazolium ionic liquid to improve the absorption performance. The major work and main results are as follows:A series of hydroxyl-functionalized imidazolium ILs ?[EtOHmim]X, X=[NTf2], [PF6], [BF4], [DCN], [SCN] and [NO3]? were designed and prepared. Their physical properties including density, viscosity and thermal decomposition temperature were measured. The introducing of hydroxyl group results into the slight increase of viscosity and good thermal stability.The ammonia solubilities under different temperatures and pressures were systematically investigated with the vapor-liquid equilibrium. The effects of hydroxyl cation, anionic structures, pressure and temperature on absorption performance were sufficiently studied. Compared with conventional IL [Emim]X, a higher absorption capacity was achieved byintroducing the hydroxyl group on the imidazolium cation. Anions also play a role on NH₃ absorption. Among these ILs, [EtOHmim][NTf2] has the highest NH₃ solubility. The absorption cyclic experiments suggest these ILs can be regenerated. Furthermore, the thermodynamic properties, such as the Gibbs free energy, standard enthalpy and standard entropy were also calculated from the Henry's constant.In addition, the absorption mechanism was detailedly investigated by spectral analysis and quantum chemistry calculations. The mechanism results showed the fascinating absorption performance of the task-specific ILs was attributed to the stronger hydrogen bonding interaction between NH₃ and the H atom of hydroxyl group. Considering the excellent Absorption performance, high thermal stability, and super reversibility, this type of IL provides great improvement over conventional IL and shows their enormous potentials in NH₃ recovery.