Facile Defect Engineering of Zeolitic Imidazolate Frameworks towards Enhanced C3H6/C3H8 Separation Performance

Membrane-based olefin/paraffin separations can be an attractive alternative to the current energy-intensive cryogenic distillation for their high energy efficiency. This paper reports an amine modulator-induced defect engineering of zeolitic imidazolate framework-8 (AZIF8) nanoparticles (60 nm) for enhanced molecular sieving ability and good compatibility with various polymer matrices. It is revealed that an initial suppression of nuclei formation during synthesis enables amine modulators to deprotonate the neutral organic ligand as well as coordinate with Zn2+ ions. The resulting AZIF8s exhibit more rigid characteristics compared to the conventional ZIF-8 counterparts as demonstrated by its delayed gate opening pressure. Molecular dynamics simulations also suggest that AZIF8s exhibit a narrower pore size distribution with a smaller opening compared to the conventional ZIF-8 analogues, which makes them more suitable for size-discrimination between C3H6 and C3H8. Furthermore, the coordination of alkyl amines into frameworks allows excellent compatibility with various commercial polymer matrices. The highly concentrated 6FDA-DAM/AZIF8 (50/50 w/w) mixed matrix membrane (MMM) exhibits superior C3H6/C3H8 separation performance (C3H6 permeability of 79.38 Barrer and C3H6/C3H8 selectivity of 39.8 at single gas condition) to most existing MMMs. The structural engineering proposed herein can be applied to other metal-organic frameworks for optimizing their performance in molecular separations.

Automated summary

Membrane-based olefin/paraffin separations can offer a more energy-efficient alternative to cryogenic distillation, with the use of amine modulators inducing defect engineering in AZIF8 nanoparticles to enhance molecular sieving ability. The engineered AZIF8s demonstrate improved rigidity and pore size distribution, leading to better size-discrimination between C3H6 and C3H8. This approach also enables superior compatibility with various polymer matrices, as evidenced by the performance of the resulting mixed matrix membrane in C3H6/C3H8 separation.