Mixed-matrix membranes with soluble porous organic molecular cage for highly efficient C₃H₆/C₃H₈ separation

Gas mixture separation of C₃H₆/C₃H₈ has great importance in industry with increasing demand for value-added polypropylene. However, realization of a cost- and energy-efficient separation procedure and its practicability is still a challenge. This work reports a group of mixed-matrix membranes (MMM) by incorporating porous organic molecular cages (POMC) within polymer. Unlike traditional solid filler, POMC filler (CC3) can be dissolved in solvent and mixed with polymer in molecular lever. The uniform distribution of CC3 particles and/or even single CC3 cage in polymer form an attractive hierarchical transport channel, which allows binary mixture permeation test (1/1, v/v) on MMM-20 wt% (0.3 MPa and 20 °C) have very fast C₃H₆ permeability (390 Barrer) and good C₃H₆/C₃H₈ separation factor (12.1). Gas transportation mechanism was evaluated and unveiled by positron annihilation lifetime spectroscopy and molecular dynamic simulation. More importantly, the MMM-20 wt% demonstrates stable C₃H₆/C₃H₈ separation during long term test, which is far beyond the Robeson upper bound, indicating high potential for feasible usage.