The significance of the interfacial interaction in mixed matrix membranes for enhanced propylene/propane separation performance and plasticization resistance

Abstract

Mixed matrix membranes (MMMs) are an attractive platform for challenging gas separations since they are the state-of-the-art scalable molecular sieve membranes. Here, the commercially attractive polysulfone (PSF) was grafted by poly(polyethylene glycol) methyl ether methacrylate (PEG) side chains to improve the interfacial interaction with zeolitic imidazolate framework-8 (ZIF-8) nanoparticles and the affinity towards C3H6 for enhanced C3H6/C3H8 separation performance. The PSFPEG graft copolymers monotonically increased the intersegmental distance of polymer chains with increasing the PEG contents based on the XRD results and the density functional theory calculations. Also, the cross-sectional SEM images of MMMs visualized that the interfacial adhesion between ZIF-8 and polymer was improved as the PEG content increased. Both DSC and FT-IR analyses revealed that such an enhanced interfacial adhesion was attributed to a combination of flexible nature of PEG side chains and various chemical interactions. More importantly, the PSFPEG73/ZIF-8 (65/35 vol/vol) MMM enhanced both C3H6 permeability and C3H6/C3H8 permselectivity compared to the PSF/ZIF-8 counterpart by 57% and 55%, respectively. Besides, the equimolar C3H6/C3H8 mixed gas permeation isotherm exhibited that the PSFPEG73/ZIF-8 (65/35 vol/vol) MMM enhanced the plasticization resistance against C3H6 compared to the PSF/ZIF-8 counterpart (e.g., C3H6-induced plasticization pressure of 5 vs. 3 atm), demonstrating the significance of the interfacial interaction.