Determination and optimization of factors affecting CO₂/CH₄ separation performance in poly(ionic liquid)-ionic liquid-zeolite mixed-matrix membranes

Zeolite particles, cross-linked poly(room-temperature ionic liquid)s (poly(RTIL)s), and room-temperature ionic liquids (RTILs) are combined to form mixed-matrix-membranes (MMMs) that exhibit a CO₂/CH₄ selectivity of 90±10 and a CO₂ permeability of 260±20 barrers. This ideal (i.e., single-gas) separation performance is among the best reported in the literature, comparable to that of thermally rearranged polymers. The MMMs reported herein are physically robust and easily processed into membranes via conventional solvent-casting techniques. The elucidation and optimization of factors responsible for generating high-performance MMMs for CO₂/CH₄ separations were found to include: zeolite particle type, zeolite particle loading, poly(RTIL) structure, amount of cross-linking, and zeolite dispersion method in the RTIL. Optimization of these factors produced enhanced CO₂/CH₄ separation that significantly exceeds the 2008 Robeson upper bound, while the MMMs remain mechanically robust and easy to process.