Preparation and microstructural analysis of high-performance mordenite membranes in fluoride media

High-performance mordenite membranes were prepared in fluoride media on porous tubular mullite supports by a single hydrothermal synthesis. Mordenite membranes and powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), magic-angle spinning nuclear magnetic resonance (MAS NMR) and contact angle with water droplets. The microstructure (i.e. hydrophilicity and crystal morphology) and pervaporation (PV) performance were influenced by the fluoride source and synthesis temperature. The 19F MAS NMR evidence shows the fluorine anion is present in channels of the mordenite crystal as a counterion of cations. Eight mordenite membranes (M-3 serial) prepared using NH4F-modified gels exhibited high fluxes of 1.50 ± 0.25 kg m−2 h−1 together with high separation factors of 1380 ± 110 for a water/ethanol (10/90 wt.%) mixture at 75 °C. The membranes also displayed good water-selective for the water/i-propanol mixture. The high performance is attributed to the thin zeolite layer and good surface hydrophilicity of mordenite membranes prepared in fluoride media.

Left: surface SEM image of F-modified mordenite membrane (serial M-3); Right: 19F MAS NMR spectra of mordenite powder crystallized together with the membrane (serial M-3).Figure optionsDownload as PowerPoint slideHighlights
► Microstructural analysis of mordenite membranes prepared in fluoride media.
► Fluorine anion is located in channels of mordenite crystal as a counterion of cations.
► F-modified mordenite membrane shows the highest PV performance for water/ethanol and water/i-propanol mixtures.