CO2 permeability, diffusivity and solubility in polyethylene glycol-grafted polyionic membranes and their CO2 selectivity relative to methane and nitrogen

Polyethylene glycol (PEG) is grafted onto ionic polymers poly[p-vinylbenzyltrimethylammonium tetrafluoroborate] (P[VBTMA][BF4]) and poly[2-(methylacryloyloxy)ethyl-trimethylammoniumtetrafluoroborate] (P[MATMA][BF4]). Membranes made of P[VBTMA][BF4]-g-PEG and P[MATMA][BF4]-g-PEG are found to be CO2 selective for CO2/CH4 and CO2/N2 separations, and less brittle than those made of pure P[VBTMA][BF4] and P[MATMA][BF4]. At the same permeability, the P[MATMA][BF4]-g-PEG membranes are demonstrated to have a higher CO2 selectivity than the previous polymeric membranes. The selectivity of both P[VBTMA][BF4]-g-PEG and P[MATMA][BF4]-g-PEG is primarily due to the solubility differences, not the diffusivity differences.