High performance membranes based on ionic liquid polymers for CO 2 separation from the flue gas

Abstract

Three vinyl functionalized imidazolium based room-temperature ionic liquids (RTILs): 1-vinyl-3-ethylimidazolium dicyanamide ([veim][dca]), 1-vinyl-3-butylimidazolium dicyanamide ([vbim][dca]) and 1-vinyl-3- heptylimidazolium dicyanamide ([vhim][dca]) were synthesized and UV-polymerized to form free standing membranes. The pure gas permeabilities of CO 2 and N 2 of these newly developed membranes acquired at 1 atm 35 °C increased with an increase in the number of N-alkyl group in the monomers but their ideal CO 2-N 2 selectivities decreased. The three vinyl functionalized monomers were blended with three free RTILs: 1-ethyl-3-methylimidazolium dicyanamide ([emim][dca]), 1-ethyl-3- methylimidazolium tetracyanoborate ([emim][B(CN) 4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF 4]) and subsequently subjected to UV-polymerization to form the poly(RTIL)-RTIL composite membranes. The incorporation of free RTILs not only significantly increases the CO 2 permeability but also greatly improves the CO 2-N 2 selectivity. The best separation performance is achieved for the poly([vbim][dca])-[emim][B(CN) 4] (1:2) and poly([vbim][dca])-[emim][dca] (1:2) composite membranes, which have CO 2 permeabilities of 340 and 273 barrers and CO 2-N 2 selectivities of 42 and 53, respectively, at 1 atm 35 °C. The mixed gas permeabilities of these two composite membranes are 297 and 253.5 barrers with corresponding CO 2-N 2 selectivities of 38.8 and 50.6, respectively, using a 50:50 CO 2-N 2 mixed gas at 2 atm 35 °C. These two composite membranes have separation performance very close to the 2008 "Robeson Upper Bound", suggesting their potential for industrial applications, especially for the post-combustion flue gas treatment. © 2012 The Royal Society of Chemistry.