(730c) Surface-Modified Uio-66-NH2 Mixed Matrix Membranes for Xylene Isomer Separation

Mixed matrix membranes (MMMs) have been shown to greatly improve gas separation performance over purely polymeric membranes. However, their potential for organic solvent separations remains less explored, particularly in organic solvent reverse osmosis (OSRO) applications. Here, we fabricate MMMs based on the metal-organic framework (MOF) UiO-66-NH₂ and the polyimide Matrimid® and investigate their ability to separate para and ortho-xylene in both vapor permeation and hydraulic modes of permeation. In addition, we present a new approach to overcome interfacial defects for the UiO-66-NH₂/Matrimid® system. Pyromellitic diimide is used to homogenize the interface between filler and polymer and improved polymer-MOF adhesion is observed as a result. This improvement is tentatively attributed to charge-transfer complexes between the diimide, MOF ligand, and polyimide. Adhesion and stability was further improved through diamine crosslinking. The effects of the diimide compatibilizer on the interface are examined through FTIR and DSC measurements. MMM performance is measured on custom-built Wicke-Kallenbach and OSRO cross-flow cell systems. Pure component diffusion coefficients are estimated from isotherm measurements and the solution-diffusion model. The xylene isomer separation performance is shown to be significantly enhanced over Matrimid® and unmodified MMMs. At 10 weight percent MOF loading, surface modified MMMs show para-xylene permeability of 350 Barrer and a selectivity of 5.8 from a 50/50 feed mixture at unit activity compared to 3.2 Barrer and 1.05 for native Matrimid®.