ZIF-8/PDMS mixed matrix membranes for propane/nitrogen mixture separation: Experimental result and permeation model validation

In this contribution, zeolitic imidazolate framework (ZIF-8)/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) were prepared for hydrocarbon recovery using propane/nitrogen mixture as a model feed gas pair. All MMMs obtained a homogeneous particle dispersion and intimate interface interaction, which were confirmed by high resolution scanning electric microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) mapping. Gas permeation test shows that ZIF-8/PDMS MMMs demonstrate an enhanced separation performance with improved separation selectivity (38% higher than that of pure PDMS membranes) and propane permeance over 100   GPU. However, it is worth noting that the enhanced selectivity and decreased permeance of MMMs contradict the prediction by Maxwell model, which suggests the existence of pore blockage and inhibited chain mobility at polymer-particle interface. The inhibited chain mobility is further confirmed by differential scanning calorimetry (DSC) analysis. Based on these observations, a new modified Maxwell model is proposed taking non-ideal interface morphology and particle agglomeration into consideration. Both the selectivity and gas permeance predicted by the proposed model are in good agreement with experimental data, which thereby extends the application scope of original Maxwell model.