The Lifshitz-van der Waals acid-base theory assisted fabrication of MFI-containing mixed matrix membranes for gas separations

A zeolite-containing mixed matrix membrane (MMM) is an attractive option to overcome the performance limits of polymeric membranes for large-scale gas separations. The poor interfacial adhesion between zeolites and polymers, however, should be addressed to realize the excellent separation performance of zeolites on large industrial scale. Herein, the interfacial void-free MMMs with incorporation of intact MFI type zeolite particles were successfully prepared by applying the Lifshitz-van der Waals acid-base theory for the selection of the appropriate polymer matrix. Our simple, but systematic approach was based on the adhesion force between MFI particles and a surrounding polymer matrix. The relatively high Lewis basicity of cellulose acetate (CA) leads to highest adhesion force with MFI particles among the tested polymer matrices, suppressing interfacial void formation. In addition, a careful analysis revealed that any residual surfactants on the surface of MFI particles are detrimental to fabricate interfacial void-free MMMs. Single gas (i.e. N₂ and NF₃) transport in the CA/MFI MMMs were characterized by changing the concentration of MFI particles up to 30 wt%. N₂ permeability of CA/MFI MMMs was improved by as much as 304% compared to that of bare CA membranes with maintaining N₂/NF₃ permselectivity. Furthermore, gas transports in CA/MFI MMMs by varying the size of MFI particles from 0.2 through 0.6 up to 1.5 μm were analyzed by using the Lewis-Nielsen model. Our systematic theory-based guidance can be utilized to offer the appropriate polymer candidates for the zeolite-containing MMMs for high performance gas separations.