Metal-organic frameworks (MOFs) as additives in mixed matrix membranes (MMMs) for gas separation have gained significant attention over the past decades. Many design parameters have been investigated for MOF based MMMs, but the spatial distribution of the MOF throughout MMMs lacks investigation. Therefore, magnetically aligned and enriched pathways of zeolitic imidazolate framework 8 (ZIF-8) in Matrimid MMMs were synthesized and investigated by means of their N2 and CO2 permeability. Magnetic ZIF-8 (m-ZIF-8) was synthesized by incorporating Fe3O4 in the ZIF-8 structure. The presence of Fe3O4 in m-ZIF-8 showed a decrease in surface area and N2 and CO2 uptake, with respect to pure ZIF-8. Alignment of m-ZIF-8 in Matrimid showed the presence of enriched pathways of m-ZIF-8 through the MMMs. At 10 wt.% m-ZIF-8 incorporation, no effect of alignment was observed for the N2 and CO2 permeability, which was ascribed anon-ideal tortuous alignment. However, alignment of 20 wt.% m-ZIF-8 in Matrimid showed to increase the CO2 diffusivity and permeability (19%) at 7 bar, while no loss in ideal selectivity was observed, with respect to homogeneously dispersed m-ZIF-8 membranes. Thus, the alignment of MOF particles throughout the matrix was shown to enhance the CO2 permeability at a certain weight content of MOF.
Keywords: CO2 based separations; alignment; mixed matrix membranes; zeolitic imidazolate frameworks.