High-flux NaA zeolite pervaporation membranes dynamically synthesized on the alumina hollow fiber inner-surface in a continuous flow system

A continuous flow system that can make the process variable more stable was proposed to prepare NaA zeolite membranes on the inner-surface of alumina hollow fiber, in which the gel solution was recirculated and only preheated at the required section, thus avoiding the unnecessary depletion of the nutrients in the bulk. The influence of synthesis parameters including temperature, flow rate and time over the property of obtained membrane were investigated. The thickness and the morphology of the membranes were explored by SEM. Their separation performance for dehydration of ethanol/water mixture was tested in a pervaporation (PV) set-up with the feed flowing through the membranes' lumen-side, which varied significantly when the feed flowed at different rates. The reason was inquired by studying the PV behavior at different operating conditions. It was found that the boundary layer resisted the heat transfer, leading to the lower temperature of PV at membrane surface than that of the feed, therefore, the intrinsic PV performance of the membrane could hardly be obtained when the feed flew at low rate. The optimal performance of 19.7 kg/m(2) h for the permeation flux and more than 80,000 for the separation factor was tested at the flow rate of 148 mL/min with 90 wt% ethanol/water solution at 348 K, yielding an unprecedented PV performance to our knowledge. The results revealed the high reproducibility and uniformity of the membranes prepared by continuous flow system, as well as that the zeolite membranes located on ceramic hollow fiber inner-surface possessed a competitive advantage of PV performance especially of the permeation flux, which have not been realized by the previous studies and may generalize to the other zeolite or metal-organic frameworks (MOF) membranes.