(673b) Microscopic Gas Diffusion inside ZIF-11 Crystals Dispersed in Different Polymers to Form Mixed Matrix Membranes

Authors: 
Baniani, A. - Presenter, University of Florida
Forman, E. M., University of Florida
Fan, L., University of Florida
Ziegler, K. J., University of Florida
Zhou, E., Georgia Institute of Technology
Zhang, F., Georgia Institute of Technology
Lively, R., Georgia Institute of Technology
Vasenkov, S., University of Florida
Mixed matrix membranes (MMMs) consisting of zeolitic imidazolate framework (ZIF) filler particles embedded in a polymer matrix have shown great potential for gas separations. These membranes were introduced to combine the gas-separation properties of the filler particle with the ease and scalability of fabrication of pure polymeric films. ZIFs represent a subgroup of metal organic frameworks (MOFs), which exhibit great chemical and thermal stability and functionality.

1H and 13C pulsed field gradient (PFG) NMR was used to study diffusion of ethane and ethylene inside a loosely packed ZIF-11 bed and various ZIF-11-based MMMs at equivalent loading pressures. Diffusion measurements were performed by utilizing a high magnetic field (17.6 T) to obtain sufficiently high signal-to-noise ratios for gas diffusion data and high magnetic field gradients (up to 25 T/m) to enable measurements of diffusivities for the length scales of displacements smaller than the mean size of the ZIF-11 crystals. It was observed that depending on the polymer type, the confinement of the ZIF-11 crystals in the polymer can lead to a reduction in the intra-ZIF diffusivities of the studied gases. This effect was investigated as a function of temperature as well as gas loading inside MMMs. It was tentatively explained by a reduction in the framework flexibility of ZIF-11 crystals due to the crystal confinement in a polymer.