Poly(RTIL)-RTIL Composite Membrane for CO2 Separation From the Flue Gas

Poly(RTIL)-RTIL Composite Membrane for CO₂ Separation from Flue Gas

 

Pei Li¹, D. R. Paul², Tai-Shung Chung*¹

 

¹Department of Chemical and Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 117602

²Department of Chemical Engineering, The University of Texas at Austin, Austin, TX  78712-1062

^*Corresponding author, Email: chencts@nus.edu.sg Fax: (65) 6779 1936

An UV-polymerization method was developed to form the freestanding poly (room temperature ionic liquid) (poly(RTIL)) and poly(room temperature ionic liquid)-room temperature ionic liquid (poly(RTIL)-RTIL) composite membranes. Three vinyl-functionalized imidazolium based 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 freestanding membranes. The pure gas permeabilities of CO₂ and N₂ of these membranes acquired at 1 atm 35 °C increased with an increase in the number of N-alkyl group in the monomers but the ideal CO₂/N₂ selectivities decreased. The three vinyl functionalized RTILs 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-methyl-imidazolium 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/N₂ 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/N₂ 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 CO₂/N₂ selectivities of 38.8 and 50.6, respectively, using a 50:50 CO₂/N₂ 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. 

  Keywords

UV polymerization, poly(RTIL)-RTIL composite membranes, gas separation membrane, flue gas separation