Ethylene diffusion in crystals of zeolitic imidazole Framework-11 embedded in polymers to form mixed-matrix membranes

C-13 Pulsed field gradient (PFG) NMR was used to study the self-diffusion of ethylene in loosely packed beds of ZIF-11 crystals and ZIF-11 based mixed matrix membranes (MMMs) at different sorbate loadings and diffusion times. The ZIF-11 based MMMs were formed by embedding ZIF-11 crystals in one of the following three polymers: Torlon, Matrimid, and 6FDA-DAM. PFG NMR data allowed obtaining ethylene diffusivities inside ZIF-11 crystals in the crystal beds and MMMs under the same or similar conditions. It was observed that the intra-ZIF diffusivities in ZIF-11/Torlon MMM are smaller than the corresponding diffusivities in the ZIF-11 bed. The observed diffusivity reduction becomes less significant with increasing ethylene loading. At the same time, within uncertainty, no difference in the intra-ZIF diffusivities between ZIF-11 bed and MMMs were observed for ZIF-11/Matrimid and ZIF-11/6FDA-DAM MMMs. The intra-ZIF diffusivity reduction observed for ZIF-11/Torlon MMM is tentatively attributed to the reduced framework flexibility of ZIF-11 crystals once embedded in the Torlon to form the MMM. The absence of such diffusivity reduction in the other two studied MMMs is tentatively explained by the higher bulk modulus of Torlon compared to Matrimid and 6FDA-DAM.