Synthesis And Structure Characterization Of NaA Zeolite Membrane On Porous α-Al₂O₃ Substrate From Fly Ash

Synthesis and characterization of NaA zeolite membranes on the porousα-Al₂O₃ substrate from fly ash by the secondary growth method were investigated in this paper. First of all,NaA zeolite powders were synthesized from fly ash by the two-step method.Emphasis was put on investigate the influential parameters such as alkali sources,synthesis temperature,concentration of alkali solution and synthesis time on the structure and crystal size of synthetic zeolites.The powders under different conditions were characterized by XRD,SEM and particle size measurement.The results showed the pure-form NaA zeolites with small crystal size(250nm) could be synthesized when following conditions were used:NaOH concentration,6.67mol/L; the synthesis time,3h;the synthesis temperature,90℃.NaA zeolite membranes were synthesized on theα-Al₂O₃ substrate by the secondary growth method using synthetic NaA zeolites as seeds.The effects of synthesis time,seeds concentration, synthesis times on the forming and performance of NaA zeolite membranes were discussed.The structures,appearance and performance of the membranes were characterized by XRD,SEM and gas permeability test.XRD patterns showed that NaA zeolite membranes were synthesized on the porous substrate.The SEM analysis revealed that a dense intergrown zeolite membrane about 20～22μm in thickness was formed on the substrate and the membrane and substrate were firmly combined together.Under the pressure of 0.1MPa,the ideal selectivity of H₂/N₂ was 3.96,higher than the Knudsen diffusion ratio of 3.74;and the ideal selectivity of H₂/Ar was 4.47, up to thel Knudsen diffusion ratio.It showed that the obtained NaA zeolite membrane possessed partial molecular sieving.