Alkylmethylimidazolium tricyanomethanide based supported ion gel membranes for CO2 separation

Abstract

Supported ion gel membranes (SIGMs) with good mechanical stability for CO2 separation were prepared using triblock copolymers in an ionic liquid (IL). Ion gels were obtained by the addition of a small amount of poly(styrene-block-ethylene oxide-block-styrene) (SEOS) copolymer in the 1-alkyl-3-methylimidazolium tricyanomethanide family ([RMIm][TCM], with alkyl group R = ethyl (E), butyl (B) and hexyl (H)), and their properties were investigated. Mechanically stable SIGMs were prepared by self-assembly of [RMIm][TCM]/SEOS solution on the surface of the porous support, and their CO2 separation performances were measured. The ideal CO2/CH4 separation factors were 9.7, 12.3 and 11.2 for the SIGMs containing [EMIm][TCM], [BMIm][TCM] and [HMIm][TCM], respectively. Morphological structure and complex formation, as determined by wide-angle X-ray diffraction analysis and theoretical calculations, respectively, were conducted to study the permselectivity. The SIGM of [BMIm][TCM] shows a higher selectivity than that of [EMIm][TCM], since the interaction with CO2 of [EMIm][TCM] is stronger than that of [BMIm][TCM] or [HMIm][TCM] and the large intermolecular distance of [EMIm][TCM] leads to the non-selective structure for CO2 transport.