Thin-film composite mixed-matrix membrane based on polymerizable ionic liquid comb copolymer for CO₂ separation

A thin-film composite (TFC) mixed matrix membrane (MMM) was prepared using an ionic liquid (IL) and zeolitic imidazolate framework-8 (ZIF-8) dispersed in a polymerizable ionic liquid (PIL) matrix for CO2 separation. A PIL comb copolymer, i.e., poly(1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide-co-poly(ethylene glycol) methyl ether methacrylate) (poly(AMIM-TFSI-co-POEM), PAP), was synthesized via free radical polymerization. The IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) served as an enhancing agent for CO2 solubility, while 60 nm-sized ZIF-8 nanoparticles acted as a size-sieving agent. Excellent miscibility and chemical interactions among the ternary systems were achieved because of the strong adhesive properties of PAP and its similar chemical structure. The crystalline and pore structures of ZIF-8 were fully maintained in the MMM, with no significant PAP/IL infiltration into the pores of ZIF-8. The 600-nm-thick TFCMMM with the PAP/IL/ZIF-8 ternary system exhibited excellent CO2 separation performance, with a CO2 permeance of 1017 GPU, CO2/N2 selectivity of 33, and CO2/CH4 selectivity of 13, satisfying the commercial criteria required for post-combustion CO2 capture.