High performance membranes based on ionic liquid polymers for CO2 separation from the flue gas

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 CO2 and N-2 of these newly developed membranes acquired at 1 atm 35 degrees C increased with an increase in the number of N-alkyl group in the monomers but their ideal CO2-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][BF4]) and subsequently subjected to UV-polymerization to form the poly (RTIL)-RTIL composite membranes. The incorporation of free RTILs not only significantly increases the CO2 permeability but also greatly improves the CO2-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 CO2 permeabilities of 340 and 273 barrers and CO2-N-2 selectivities of 42 and 53, respectively, at 1 atm 35 degrees C. The mixed gas permeabilities of these two composite membranes are 297 and 253.5 barrers with corresponding CO2-N-2 selectivities of 38.8 and 50.6, respectively, using a 50 : 50 CO2-N-2 mixed gas at 2 atm 35 degrees 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.