Solid-state facilitated transport membrane for CO/N₂ separation based on PHMEP-co-PAA comb-like copolymer: Experimental and molecular simulation study

Carbon monoxide (CO) is an important raw material in chemical industries; however, its separation through solid-state polymer membranes has not been extensively investigated. Herein, a series of comb-like copolymers, i.e., poly(2-hydroxypropyl-2-(methacryloyloxy) ethyl phthalate-co-acrylic acid) (PHMEP-co-PAA), is synthesized and used as a matrix to incorporate AgBF₄ and ionic liquid ([bmim][BF₄]) for solid-state facilitated CO transport membrane. The carbonyl moeities of the copolymer phthalate and carboxyl groups effectively form a complex with the Ag ions. CO/N₂ separation performance is improved by introducing AgBF₄ together with [bmim][BF₄] into the copolymer matrix, which is supported by spectroscopic analysis and molecular dynamics simulations. Incorporating AgBF₄ significantly increases the interaction energy between the membrane and CO molecules, demonstrating that Ag salts act as facilitated CO transport carriers and increase CO solubility in the membrane. Results show that the ionic liquid prevents comb copolymer aggregation and improves CO/N₂ selectivity. The PHMEP-co-PAA copolymer monomeric ratio affects the CO/N₂ selectivity and carrier stability. Copolymers with high PHMEP content (70 wt%) show the highest CO/N₂ selectivity due to strong polymer-CO interaction energies. Performance optimization provided a CO/N₂ selectivity of 16.2, one of the highest values reported so far, with a CO permeance of 2.1 GPU. Simultaneous increase in CO permeance and CO/N₂ selectivity with carrier loading clearly indicates facilitated CO transport. The simulation analysis effectively interprets the experimental separation performance and can be used for designing CO separation membranes.