Gas permeation properties of NaA zeolite membranes: Effect of silica source on hydrogel synthesis and layer thickness

NaA zeolite membranes were prepared on the inner surfaces of ceramic α-alumina tubes based on an aqueous phase synthesis in order to investigate the influence of different silica sources on NaA zeolite membrane synthesis and zeolite layer thickness with reference to the gas separation properties. SEM and XRD results indicated that zeolite prepared with sodium metasilicate as the silica source can be synthesized for a NaA zeolite membrane, leading to uniform zeolite layers and good thermal stability. The H2 permeance at 25 °C was 4.99 × 10−7 mol m−2 s−1 Pa−1, and the H2/Ar and H2/He permselectivities were 3.78 and 1.36, respectively. The morphologies and single gas permeation properties of the NaA zeolite membranes prepared through repeated aqueous phase synthesis treatments were also studied. When the zeolite layer thickness increased from 2.9 to 53 µm, the H2 permeance gradually decreased, while the permselectivities increased from 3.78 to 5.17. The gas permeance was mainly controlled by the Knudsen diffusion in our NaA zeolite membrane