Mixed gas diffusion and permeation of ternary and quaternary CO2/ CO/N2/O2 gas mixtures in Matrimid®, polyetherimide and poly(lactic acid) membranes for CO2/CO separation

The CO2/CO mixed-gas separation performance of a polyimide (Matrimid®), polyetherimide (PEI) and polylactic acid (PLA) membrane, were characterized in the presence of CO2- rich ternary (CO2/ CO/ O2) and quaternary (CO2/ CO/ O2/ N2) feed gas mixtures mimicking the products of CO2 reforming conversion reactions. The membrane-based separation of this mixture is poorly characterized and original data were obtained in a novel mass spectrometric apparatus that permits to monitor the instantaneous permeate composition, thus allowing to evaluate both mixed gas diffusion and permeability coefficients of all gases. CO2, CO, O2 and N2 permeability and diffusivity in single gas tests were measured between 298 and 353 K up to 1 atm feed pressure and relevant activation energies were evaluated. At 298 K Matrimid® exhibits CO permeability of 0.50 ± 0.03 Barrer and an ideal CO2/ CO selectivity of 16 ± 1. PEI and PLA exhibit similar ideal selectivity values but lower CO transport rates. In all examined polymer films the CO2/ CO selectivity has absorption-selective character that favours the permeation of CO2. The ideal CO2/ CO selectivity of all membrane samples decreases with temperature, reaching values of 10 ± 1 at 335 K in Matrimid®. The CO2/ CO selective performances of all examined membrane do not show markable variations exposing the membrane samples to CO2- rich gas mixtures as feed gas. The upper bound correlation among selectivity and permeability for the CO2/ CO gas couple is here for the first time proposed.