Low temperature synthesis of NaA zeolite membranes: The effect of primary and secondary crystallizations

NaA zeolite membranes were prepared on porous α-alumina support tubes (inner side) by primary (in-situ) and secondary (ex-situ) crystallization processes at 65 °C for 6 h, 12 h and 24 h each. For secondary crystallization process, poly(ethyleneimine) (PEI) was used as a buffer layer for proper attachment of the NaA seed crystals (prepared at 65 °C/2 h) onto the alumina support surface. The membranes prepared by primary crystallization process showed thicknesses of about 10 μm, 20 μm and 30 μm for growth times of 6 h, 12 h and 24 h, respectively, while the membranes prepared by secondary crystallization process rendered the corresponding thicknesses of 25 μm, 35 μm and 70 μm, respectively. PEI coating rendered good quality of membrane for secondary crystallization process with lower growth time (6 h). The better quality of membrane which had interlocked dense structure with minimum defects was obtained for primary crystallization at 65 °C for 12 h growth time. Pervaporation study for ethanol/water mixture was performed with the prepared membranes.