Interface engineering in MOF/crosslinked polyimide mixed matrix membranes for enhanced propylene/propane separation performance and plasticization resistance

The energy required for propylene/propane (C3H6/C3H8) separation is enormous: ∼0.3% of global energy consumption. Membrane separation is gaining much attention as an alternative or supplement for the conventional distillation processes, although the separation abilities and stabilities of current polymer membranes remain insufficient to meet industrial requirements. Herein, we propose a novel strategy to integrate the diamino crosslinking of polyimide (6FDA-DAM) membranes and the fabrication of their mixed matrix membranes (MMMs) to engineer the interfacial compatibility between filler and matrix. Crosslinking conditions for the 6FDA-DAM matrix are optimized for C3H6/C3H8 separation, and their MMMs were fabricated by incorporating UiO-66 (U) or UiO-66-NH2 (UN) fillers. After crosslinking the MMM precursors, detailed characterization results of the filler-matrix interfaces, which include morphological, spectroscopical, thermal, and mechanical analyses, indicate that the UN-incorporated MMMs display enhanced interfacial compatibility compared with their counterpart (i.e., the U-incorporated ones). Ultimately, the UN-incorporated MMMs showed significantly enhanced C3H6/C3H8 separation performances by surpassing both pure-gas and mixed-gas upper bounds. Besides, the MMM exhibited excellent plasticization resistance against the high feed pressure (5 bar) with high C3H6/C3H8 mixed-gas selectivity (23.7) and modest C3H6 permeability (6.3 Barrer), demonstrating its potential for use in industrial applications.