Double-salt ionic liquid derived facilitated transport membranes for ethylene/ethane separation

Abstract Ethylene/ethane separation is one of the key industrial gas separations which challenges the world because of their similar physical properties. Membrane separation technology holds great promise to replace or combine the currently energy-intensive cryogenic distillation to achieve effective ethylene purification. In this study, a series of double-salt ionic liquid derived facilitated transport membranes (DSIL-FTMs) were designed for the first time aiming at the highly effective ethylene/ethane separation, which were configured by incorporating ethylene transport carrier and double-salt ionic liquids (DSILs) into a robust Nylon support. DSILs are the liquid ionic compositions composing of more than one cation or anion, which offer an opportunity to enhance the design flexibility and structural regulation of the corresponding FTMs. The DSIL-FTMs exhibit good ethylene/ethane separation performance as well as high thermal stability and long-term durability, where the ethylene permeability is about 250 Barrer and ethylene/ethane selectivity reaches up to 67. The spectroscopic characterizations and structure-performance relationship investigation reveal that the excellent separation performances are attributed to the favorable rearrangement of cations and anions in the DSIL-FTMs, where the newly formed ion arrangement and cation-anion interactions of DSIL-FTMs favor the building of the compact membrane structure and obtainment of high carrier activity. This study opens a novel avenue to manipulate the physical-chemical properties of separation membrane by structural diversity of DSILs, and promotes the sustainable prosperity of FTMs for energy-intensive gas molecule separations.