(Cross-Linked Poly(Ionic Liquid)–Ionic Liquid–Zeolite) Mixed-Matrix Membranes for CO₂/CH₄ Gas Separations Based on Curable Ionic Liquid Prepolymers

Abstract

A three-component (cross-linked poly­(ionic liquid) (PIL)–ionic liquid (IL)–zeolite), mixed-matrix membrane (MMM) platform based on curable IL prepolymers of controlled length has been developed for separating CO2 from CH4. Solutions of these curable prepolymers demonstrate increased resistance to support penetration compared to comparable solutions of analogous cross-linkable IL monomers. By adjusting the curable IL prepolymer chain length, it is possible to manipulate polymer susceptibility to support penetration, polymer solution gelation time, and gas separation performance in MMMs based on these materials. When a 50 wt % solution of the curable IL prepolymer with a degree of polymerization (x) of 87 was cast on an ultrafiltration support membrane, only 3.7 wt % of the polymer penetrated into the support. As the degree of polymerization of the curable IL prepolymer increases, the CO2/CH4 gas separation performance of the resulting MMM performance also improves. For example, an MMM synthesized using 64 wt % curable IL prepolymer (x = 87), 16 wt % [EMIM]­[Tf2N] as the IL, and 20 wt % SAPO-34 zeolite exhibited a CO2/CH4 selectivity of (42 ± 5) and a CO2 permeability of (47 ± 1) barrers. This CO2/CH4 separation performance is comparable to the previous generation of MMMs based on curable small-molecule IL monomers with the same IL and zeolite. However, this new MMM system also exhibits faster curing gelation times and the ability to be solution-cast onto a porous support for formation of thin-film composite membranes without significant selective layer soak-in.

Recent progress in the development of ionic liquid‐based mixed matrix membrane for CO 2 separation: A review

“…They also observed that the CO 2 permeability was enhanced as the IL loading was increased in the MMM since more IL has plasticized the polymer matrix. Development of IL‐MMM comprising of polymerized IL was also reported by other researchers where the same blending method was adapted in their works 194‐196 . Besides polymerized IL, IL was also incorporated into MMM containing other polymers such as PES and PI.…”

A Review on Ionic Liquid Gas Separation Membranes

“…The monomer unit homogeneity provides further differentiation between a single group of homopolymer cationic/anionic PILs and polyampholytes, representing the other group of co-polymers [ 129 ]. In addition, co-polymers encompass PILs that are built from both IL-like monomers and neutral monomers [ 125 , 137 , 138 , 139 , 140 ]. PILs diversity is further enriched by the way of their monomer assembly, or more precisely, by their architecture ( Figure 4 ).…”

“…PILs diversity is further enriched by the way of their monomer assembly, or more precisely, by their architecture ( Figure 4 ). The major architecture types of PILs are linear (a) [ 141 , 142 , 143 ], branched and/or hyperbranched (b) [ 132 ], and cross-linked (c) [ 140 ], where the branched are further subdivided into dendrimer (d) [ 144 ], star (e) [ 145 , 146 ], and cyclic (f) [ 147 ]. This variability in charge carrying group configurations and polymer architecture not only highlights the creativity of synthetic chemists, but also underscores the versatility of PILs with inexhaustible possibilities for their performance fine-tuning.…”

Green solvents for membrane manufacture: Recent trends and perspectives

“…Furthermore, ILs have been long used as immobilized solvents within the porous support for supported ILs membranes for gas separation. Recently, the Noble's and Gin's groups [45] reported mixed matrix membranes (MMMs) for CO 2 /CH 4 separation, prepared from poly(ionic liquid)/IL/zeolite. Dispersed solutions of a curable IL prepolymer and zeolite in [EMIM]Tf 2 N were cast on a UF support membrane and then photo-crosslinked to form the membrane.…”