Enhanced ethylene/ethane selectivity of PI membrane with functionalized zeolite addition

Mixed-matrix membranes (MMMs), consisting of fillers dispersed in a polymer matrix, have been extensively studied for gas separation. However, their application in ethylene/ethane (C₂H₄/C₂H₆) separation remains limited. This study examines the impact of incorporating highly selective zeolite fillers into a 6FDA-DAM-type polyimide on C₂H₄/C₂H₆ separation performance. We selected 4-methoxybenzene-functionalized MOR (f-MOR) as the filler due to its exceptional C₂H₄/C₂H₆ adsorptive selectivity. Adding 20 wt% f-MOR increased C₂H₄ permeability by 63% and enhanced C₂H₄/C₂H₆ ideal selectivity by 11%, reaching 22.7 Barrer and 5.2, respectively, compared to the neat polymer membrane (13.9 Barrer, ideal selectivity of 4.7). In contrast, incorporating 20 wt% neat MOR increased C₂H₄ permeability to 34.7 Barrer but reduced ideal selectivity to 3.1. The enhanced selectivity of MMMs is attributed to the increased solubility difference of ethylene by the addition of f-MOR, while diffusion selectivity is not improved by the filler. Under a binary mixed-feed gas, the MMM with 20 wt% f-MOR exhibited a drop in selectivity (2.5), indicating low-pressure plasticization-like behavior. While this is the first report to show the enhanced C₂ hydrocarbon gas separation performance with zeolite addition, these findings highlight the need for strategies that integrate adsorbent and membrane functionalities to achieve high-performance C₂H₄/C₂H₆ separation.