Selective membrane separation of CO2 using novel epichlorohydrin-amine-based crosslinked protic ionic liquids: Crosslinking mechanism and enhanced salting-out effect

Abstract

In this work, a simple and cost-effective method of using epichlorohydrin (ECH) was developed to prepare ECH-amine-based crosslinked protic ionic liquids (CPILs) that were further used as membrane materials for selective separation of CO2. FT-IR, NMR, ESI-MS and HRMS were applied to confirm the crosslinking mechanism of 3-(dimethylamino)-1-propylamine methoxyacetate ([DMAPAH][MOAc]) reacting with ECH, as well as the possible chemical structures of ECH-amine-based CPILs. Aqueous sols and gels of CPILs were introduced into porous PES membrane supports, and the as-prepared membranes were tested for their CO2 separation performance under humidified condition. It was found that the ideal selectivities of CO2/N2 and CO2/CH4 in these membranes were up to 318.4 and 138.4, respectively, while the CO2 permeability was 517.7 barrers (0.1 bar, 40 °C). Analysis showed that the high separation selectivity benefited primarily from the enhanced salting-out effect in these CPILs. The influences of ECH-to-[DMAPAH][MOAc] molar ratio, CO2 transmembrane pressure, water content as well as operating temperature on the separation performance were also systemically investigated. In particular, tuning the molar ratio of carboxylic acid to amine (MOAc-to-DMAPA molar ratio) was proposed and applied to optimize CO2 separation performance. This work offers a feasibile fabrication of ECH-amine-based CPIL membranes with both good mechanical property and CO2 separation performance.