Printable fluorinated poly(ionic liquid)-ionic liquid composite membranes for fluorinated gas separation

Abstract

Membrane technology offers a compelling approach for separating hydrofluorocarbon (HFC) refrigerant mixtures, primarily due to lower energy demands and lower capital investment compared to traditional separation techniques. Herein, we report the development of fluorinated poly(ionic liquid)-ionic liquid composite membranes, combining the advantageous properties of both polymers and ionic liquids (ILs), for HFC gas separation. Two vinyl imidazolium-based fluorinated ionic liquid (FIL) monomers were synthesized, along with two FILs containing complementary cations and anions, which were incorporated as “free” liquid. Free-standing, IL-containing membranes were prepared by photopolymerization of the FIL-based monomer and a crosslinker in the presence of free IL. As a complementary study, membranes were also prepared from a methacrylate-based non-fluorinated imidazolium IL monomer with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₆C₁im][Tf₂N]) as free IL. The extent of crosslinking and the relationship between membrane composition and thermal properties are reported. Pure-gas permeability of commonly used HFC gases, specifically HFC-32 (difluoromethane) and HFC-125 (pentafluoroethane), were evaluated. For all membranes, HFC-32 had higher permeability than HFC-125. Finally, we demonstrate the use of digital light processing (DLP) additive manufacturing to print the membranes, presenting a promising avenue for the rapid fabrication of bespoke membranes for difficult separations.