Solid-state facilitated transport of carbon monoxide through mixed matrix membranes

Carbon monoxide (CO), along with CO₂ and N₂, forms a significant byproduct gas from steel mills. Here, we report, for the first time to the best of our knowledge, solid-state facilitated transport of CO based on mixed matrix membrane (MMM) consisting of comb copolymer-silver salt-MgO nanosheet (MgO-NS) complexes as solid-state CO carriers for the separation of CO/N₂ and CO/CO₂ mixtures. In particular, the structure and composition of the comb copolymer are crucial to membrane operation, and the desired structure is achieved by synthesizing poly(ethylene glycol) behenyl ether methacrylate-poly(methacrylic acid) (PEGBEM-PMA) comb copolymer. Subsequently, we compare its gas separation performance with those of poly(ethylene glycol) behenyl ether methacrylate-poly(oxyethylene methacrylate) (PEGBEM-POEM) comb copolymer and the commercial PEBAX block copolymer. The use of MgO-NS as the metal oxide enhances the activity and stability of silver ions via electrostatic interactions. We find that the PEGBEM-PMA membrane with a 7:3 wt ratio of AgBF₄ and MgO-NS exhibits the highest CO separation performance with a CO permeance of 79 GPU (1 GPU = 10⁻⁶ cm³ (STP)/(s·cm²·cmHg)), CO/N₂ selectivity of 14.7, and CO/CO₂ selectivity of 12.0, which is the highest CO separation performance ever reported. The observed high CO/CO₂ selectivity is an anomalous behavior that results from increased CO solubility by silver ions stabilized by MgO-NS and decreased CO₂ permeance due to the presence of CO₂-phobic PMA chains.