Composite organic ionic plastic crystal membranes: The effect of ether-functionalized cations on light-gas separation performance

In light of increasing concerns about climate change, there is a growing need for innovative solutions to address CO 2 emissions. Addressing this urgency, this work presents a unique approach to CO 2 separation utilizing composite membranes of organic ionic plastic crystals (OIPCs) with ether-functionalized cations and poly (vinylidene fluoride- co -hexafluoropropylene) (PVDF-HFP). Here we report the gas separation performance of OIPC-based membranes of 3,3-dimethyloxazolidinium [C 1 moxa] + , 4-ethyl-4-methylmorpholinium [C 2 mmor] + and 4-isopropyl-4-methylmorpholinium [C i3 mmor] + cations paired with the bis(fluorosulfonyl)imide [FSI] - anion. These composites demonstrated very good gas separation properties, especially [C 1 moxa][FSI] which produced a permeability of 63 barrer for CO 2 and an overall selectivity (CO 2 /N 2 ) of 205, which is the highest amongst all the OIPCs reported so far. Additionally, a large change in separation performance was observed for the [C i3 mmor][FSI] membrane upon heating above the solid-solid phase transition (II - I) at 48 °C; the CO 2 permeability increased from 7 to 163 barrer and an approximately 3-fold increase in selectivity was observed. These findings advance the design of composite membranes based on OIPCs towards increased selectivity and sustained effectiveness in the separation of light gases. • CO 2 separation performance in organic ionic plastic crystals (OIPCs) based membranes was studied. • Ether-functionalized cation in OIPCs play a key role in high permeability/selectivity of CO 2 . • High CO 2 permeability is attributed to OIPCs' phase transition and free volume as well as high solubility of CO 2 in these membranes.