Porous multi-site ionic liquid composites for superior selective and reversible adsorption of ammonia

Abstract

Ionic liquids (ILs) with low vapor pressure, tunable structures and good NH3 affinity provide an inspiring way to efficiently capture NH3. However, the high viscosity of most ILs limited mass transfer, which incumbers their industrial applications. Besides, how to simultaneously achieve high selectivity, capacity and reversibility of NH3 still face great challenge. Herein, four novel hydroxyl ammonium protic ILs (HAPILs), including methyldiethanolammonium trifluoromethanesulfonate ([MDEAH][CF3SO3]), triethanolammonium trifluoromethanesulfonate ([TEAH][CF3SO3]), dimethylethanolammonium trifluoromethanesulfonate ([DMEAH][CF3SO3]) and diethylethanolammonium trifluoromethanesulfonate ([DEEAH][CF3SO3]), with multiple hydrogen bonding donors that can interact with more over two NH3 molecules were designed and synthesized, and were further supported onto porous molecular sieves to overcome the above problem. Among the prepared porous HAPIL composites, 50 wt% [TEAH][CF3SO3]@MCM-41 showed the highest NH3/CO2 selectivity of 62 under 313 K and 0.1 MPa compared with the state-of-the-art values, along with high capacity of 114.3 mgNH3/g-adsorbent. The excellent NH3 adsorption performance was attributed to the synergistic interaction of mesoporous effect and multiple hydrogen bonding between NH3 and HAPILs. Furthermore, the porous HAPIL composites exhibited great recyclability after six cycles, revealing great potentials in industrial application of efficient and reversible NH3 separation.