Synthesis, characterization and single gas permeation properties of NaA zeolite membrane

High quality NaA zeolite membrane was synthesized on an α-Al ₂O₃ support with the aid of nucleation seeds from a gel synthesis mixture. The influence of synthesis conditions, such as synthesis times, synthesis stages and nucleation seeds, on the formation and permeation properties of the NaA zeolite membranes was investigated. Nucleation seeds played a critical role on the formation of a continuous NaA zeolite membrane on the support surface. The quality of the NaA zeolite membranes were improved by employing the multi-stage synthesis method. The best NaA zeolite membrane was obtained after a three-stage synthesis with the synthesis time of 24 h and with the aid of nucleation seeds. Single gas permeation properties of the NaA zeolite membranes were studied. The permeance of H₂, O₂, N ₂ and n-C₄H₁₀ decreased as the molecular kinetic diameter of the gases increased. At 298 K and under pressure difference of 0.10 MPa, the permselectivity of H₂/N₂, H ₂/n-C₄H₁₀ and O₂/N₂ were 20.1, 106 and 2.61, respectively, which were much higher than those of the corresponding Knudsen diffusion ratios of 3.74, 5.39 and 0.96. With increasing temperature, the gas permeance increased and the permselectivity of H ₂/N₂, H₂/n-C₄H₁₀ and O₂/N₂ slightly decreased. All these properties indicated that the gases mainly permeated through the channels of NaA zeolite and the gas permeation was predominantly controlled by the molecular sieving effect of NaA zeolite membrane. However, the permeation of n-C₄H₁₀ indicated that the NaA zeolite membranes had certain defects with diameters larger than the pore size of NaA zeolite.