ZIF-8 Gel/PIM-1 mixed matrix membranes for enhanced H2/CH4 separations

[Display omitted] •ZIF-8 gel was introduced as novel filler to fabricate MMMs.•The ZIF-8 gel was uniformly distributed within MMMs.•Continuous gas transport pathway constructed by interconnected ZIF-8 gel.•The separation performances surpass the upper bound of H2/CH4. Developing high-performance H2/CH4 separation membranes is of great potential for H2 production in the petroleum industry. Incorporating nanofillers into a polymer matrix to form mixed matrix membranes (MMMs) can elevate selectivity and permeability, but poor polymer-filler interfacial compatibility and filler aggregation are formidable problems. Targeting this, we propose a novel approach by incorporating a metal–organic framework (MOF) gel, ZIF-8 gel, as the versatile filler to a high free volume polymer PIM-1 and investigate the H2/CH4 separation capabilities of the MMMs. Benefiting from the gel network morphology of ZIF-8, they were dispersed evenly in the PIM-1 matrix. The interconnected gel network structure of ZIF-8 gel helped to construct continuous gas transport pathways in the polymer. As a result, the H2/CH4 separation performance was notably improved, demonstrating a substantial increase in H2 permeability by 78.9% (exceeding 6800 Barrer) and a 38.0% enhancement in H2/CH4 selectivity at a ZIF-8 gel loading of 31.0 wt%. These improvements surpassed the upper bound established in 2008. The Maxwell and Lewis-Nielsen models were developed to clarify gas transport mechanisms across membranes, and the experimental data of ZIF-8 gel/PIM-1 was well-matched with the calculated results of the Lewis-Nielsen models. Adopting MOF gel as fillers may pave a new approach to design high-performance MMMs with interconnected transport pathways.