Strong Hints of Antiplasticization by Multivariate ZIF-8-67 in PIM-EA(Me2)-TB-Based Mixed-Matrix Membranes for Propene/Propane Separation

Abstract

The isolation of pure olefins and paraffins from their mixtures is a complex and energy-demanding process due to their nearly identical physical characteristics, which pose significant challenges for their separation. Membrane-based methods provide a more sustainable and energy-efficient solution, offering high selectivity and lower operational costs than conventional, energy-intensive methods such as cryogenic distillation. The present study explores the dispersion of the aqueous-media synthesized zeolitic imidazolate frameworks (ZIF-8, ZIF-67, and ZIF-8-67) into a Tröger’s base polymer of intrinsic microporosity (PIM-EA(Me2)-TB) to form mixed matrix membranes (MMMs), which are investigated for the efficient separation of C3H6/C3H8, as well as other light gases. At 20 wt % ZIF loading, the MMMs demonstrate a significant performance enhancement when compared to the neat membrane. The incorporation of ZIFs increases the ideal selectivity for propene/propane separation, with ZIF-67 achieving the highest value (17). Notably, the ZIF-8-67-based MMM shows a comparable C3H6/C3H8 selectivity to that of the ZIF-67-based MMMs, but with the smallest reduction in propene permeability, from about 4000 to 2000 Barrer, among all formulations. The ZIF/PIM-EA(Me2)-TB MMMs, particularly the bimetallic-containing one, showed a promising propene/propane selective performance and surpassed the 2020 C3H6/C3H8 upper bound by hitting 15. These findings suggest that ZIF/PIM-EA(Me2)-TB MMMs provide an effective approach for challenging gas separations and offer a promising solution for industrial applications in gas purification and separation processes. A good fit of the C3H6 and C3H8 permeation data with the modified Maxwell model suggests matrix rigidification, which translates into antiplasticization for these highly soluble gases.