Sustainable Thin-Film Composite Mixed-Matrix Membranes Based on Cellulose Acetate, Bimetallic ZIF-8-67, and Ionic Liquid for Enhanced Propene/Propane Separation

Efficiently separating propene and propane is paramount for the chemical industry but notoriously difficult due to their minimal size and volatility differences. Here, an efficient strategy to overcome this separation challenge was demonstrated through the design of bimetallic zeolitic imidazolate framework (ZIF)-based mixed-matrix membranes (MMMs). Thin-film composite (TFC) membranes were fabricated by integrating monometallic ZIF-8, ZIF-67, and a synergistic bimetallic ZIF-8-67 into a uniquely formulated ionic liquid–cellulose acetate (IL–CA) polymer matrix. Structural and morphological analyses confirmed the high crystallinity of the ZIF fillers and their seamless integration within the polymer. The resultant ZIF-8-67/IL-CA membrane exhibited notable separation performance, surpassing its monometallic counterparts by a threefold increase in both C3H6 permeance and C3H6/C3H8 ideal selectivity relative to the base membrane. Under industrially relevant mixed-gas testing, the membrane achieved a competitive separation factor of eight for propene over propane. These findings reveal that the strategic integration of bimetallic nodes in ZIFs can unlock synergistic properties unattainable with single-metal frameworks. This work presents a robust and scalable platform for developing next-generation membranes that defy conventional performance trade-offs, paving the way for efficient membrane-based olefin/paraffin separations.