Template-free Synthesis Of MFI Zeolite Membranes And Ethanol/Water Pervaporation

Silicalite-1 zeolite membranes as one kind of MFI zeolite membranes have shown wide foreground for ethanol/water pervaporation that requires high Si/Al ratio and high hydrophobic property. It is traditional to synthesize silicalite-1 membrane with template, which induces defects in dense membranes and Si/Al ratio debasement during the unavoidable high temperature calcination step. Besides, template reagent is expensive, and it will add costs of production. The aims of this work are to prepare dense silicalite-1 zeolite membranes onα-Al2O3 support by secondary growth method without template, to apply it in ethanol/water pervaporation of low ethanol concentration and to discuss the influences of membrane appearance on pervaporation.Three different sizes of seeds were prepared, dispersed by H-HPC solution and spinned onto supports for obtaining seed layers. The three kinds of seed layers grew into silicalite-1 zeolite membranes by four methods without template. The membranes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), ethanol/water pervaporation and CO2/N2 binary gases separation.It indicated that 800 nm seed layers did not grow into dense silicalite-1 zeolite membranes from"high alkalinity-high silicon concentration"solution or"high alkalinity-low silicon concentration"solution in secondary growth. There were influences on membrane appearances in case of big seeds and high alkalinity. Zeolite membranes from 200 nm seed layers had obvious defects after one time growth in"low alkalinity-low silicon concentration"solution for 8 or 16 hours, which became denser after twice growth in the same solution for 8 plus 8 hours with pervaporation effect. When growing in"low alkalinity-high silicon concentration"solution for a short time, 200 nm seed layers were not dense. Continuously growing until 24 hours, continued silicalite-1 membranes were formed and had effect in ethanol/water pervaporation. Randomly oriented zeolite membranes on 400 nm seed layers were prepared from template solution after a short time, then they were immerged into"low alkalinity-low silicon concentration"template-free solution for the second growth, which only grew further on the surface and had defects in the space. There were little changes between pervaporation flux, permeation and binary gases separation before and after the template-free synthesis. However, the hydrophobic property was reduced.