Blended membranes with ionic liquids tailoring by hydroxyl group for efficient NH3 separation

Abstract

Ionic liquids (ILs)-based membranes are prospective for efficient NH3 separation due to their designability and high gas affinity. This work developed Pebax blended membranes with aprotic IL [EtOHmim][NTf2] and protic IL [EtOHim][NTf2] tailoring by hydroxyl group to improve NH3 separation performance and deeply investigate ILs structure-membrane property-separation performance relationship. The incorporation of ILs remarkably improves NH3 separation performance and leads to different gas transport properties of membranes confirmed by experiments and simulation calculations. The Pebax/EtOHmim-100 blended membrane exhibits exceptional NH3 permeability of 3729.3 barrer, which is 2.65 times higher than that of neat Pebax membrane. The increased FFV and moderate hydrogen bonding interaction simultaneously raise NH3 diffusivity and solubility, resulting in an evident increase of NH3 permeability. Although stronger hydrogen bonding interaction between [EtOHim][NTf2] and NH3 significantly improves NH3 solubility, it also blocks the NH3 fast diffusivity in the membrane, so the NH3 permeability of Pebax/EtOHmim blended membranes is lower than that of Pebax/EtOHmim blended membranes. Moreover, the solubility selectivity depended on interactions between ILs and gas molecules plays a dominant role in the enhancement of NH3 selectivity, thus the highest NH3/N2 selectivity of 1822.3 and NH3/H2 selectivity of 200.7 is obtained by Pebax/EtOHim-100 membrane owing to the stronger hydrogen bonding interaction between [EtOHim][NTf2] and NH3. This work not only demonstrate that the introduction of ILs is beneficial for improving NH3 separation performance of membranes but also emphasize the importance of moderate interaction between ILs and NH3 molecules for containing-NH3 separation.