Microstructure manipulation of MFI-type zeolite membranes on hollow fibers for ethanol-water separation

MFI-type zeolite membranes on hollow fibers are fabricated by a facile secondary growth method. The microstructure of the membranes is systematically manipulated by tuning the seed size, seed morphology and the structure-directing agent content. The as-synthesized MFI-type zeolite membranes are thoroughly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, water contact angle, pervaporation and gas permeation tests. High quality thin membranes (~3 μm) can be obtained on alumina hollow fibers by using appropriate seed size and morphology (e.g., 500 nm coffin-shaped crystals), and certain low TPA+ content (e.g., TPA+/Si=0.05), achieving a separation factor as high as 58 with a high flux of 9.8 kg m−2 h−1 for pervaporation of a 5 wt% ethanol aqueous solution at 60 °C. A linear decrease relationship between the total flux and the separation factor is obtained. The high pervaporation performance of the membranes can be ascribed to their dense membrane layer and low concentration polarization effect owing to their particular microstructures.