High-performance silicalite-1 membranes on porous tubular silica supports for separation of ethanol/water mixtures

Production of bioethanol, a renewable energy source, is limited by the costly, energy-consuming concentration processes involved. Membrane separation techniques have emerged as promising alternatives to overcome these limitations. In this study, silicalite-1 zeolite membranes with high pervaporation (PV) performance were prepared on porous tubular silica supports by a secondary growth method. The effects of the deposited seed amount on the support and synthesis parameters, namely, the tetra- n -propylammonium concentration (TPA + /Si), alkalinity (OH − /Si), and crystallization time, were investigated. A dense zeolite layer was formed between the typical columnar crystal layer of silicalite-1 membranes and the silica support. The PV performance was mainly dependent on the thickness of the dense layer: as the thickness increased, the separation factor increased. The silicalite-1 membrane prepared using a synthesis solution with a molar composition of 1SiO 2 :0.05TPABr:0.08NaOH:75H 2 O at 433 K for 8 h exhibited the highest separation performance with a separation factor of 92 and a flux of 3.00 kg m −2 h −1 for 10 wt% ethanol/water mixtures at 323 K, which is the best result reported to date for tubular supports. Thus, silica supports proved to be suitable for the preparation of high-performance silicalite-1 membranes for ethanol/water mixture separation.