(152g) Self-Diffusion of Pure and Mixed Gases in Mixed Matrix Membranes with Different MOF Loadings By Pulsed Field Gradient NMR

Mixed matrix membranes (MMMs) consisting of metal organic frameworks (MOFs) dispersed in polymers has shown promising gas separation performance. Such membranes have been widely considered for gas separations since they combine the ease of fabrication of pure polymeric membranes with the superior gas separation properties of the MOF fillers. MMMs formed with a MOF of the type UiO-66-NH₂, an amine derivative of the non-functionalized UiO-66, have shown promising separation performance for mixtures of light gases, including CO₂. Detailed understanding of gas diffusion in MMMs formed with this MOF is needed for optimizing performance of such MMMs in gas separations. The current work focuses on quantification of microscopic gas diffusion in UiO-66-NH₂ based MMMs as a function of increasing MOF loading.

¹³C pulsed field gradient (PFG) NMR measurements were performed to study diffusion of pure and mixed CO₂ and CH₄ inside UiO-66-NH₂ based MMMs with different MOF loadings between around 30 and 66 weight percent. The measurements were carried out at 253 K and 308 K using a high magnetic field (14 T) PFG NMR spectrometer with high magnetic field gradients up to 17 T/m. The PFG NMR measurements were conducted for a broad range of displacements larger than the average MOF crystal size, i.e. under the condition of a fast exchange between the UiO-66-NH₂ crystals and the surrounding polymer phase. The dependence of the measured data on the MOF loading will be presented and discussed in detail.