Synthesis of a ZSM-5/NaA hybrid zeolite membrane using kaolin as a modification layer

Abstract

Considering the reliable characteristics and the suitable silica alumina content of kaolin, a new way of synthesizing a ZSM-5/NaA hybrid zeolite membrane on 170 mm length ceramic tubes by employing kaolin as a modification layer using a hydrothermal synthesis process was presented for the first time in this work. Kaolin was filtrated on the surface of the support (not only the ceramic tube, but also the NaA membrane layer) as a modification layer not only promoting the interface interlinkage among the support, NaA membrane and ZSM-5 membrane layer, but also promoting the growth of zeolite membranes. The SEM and XRD results showed that compact and homogeneous NaA and ZSM-5 zeolite layers were both formed with the thicknesses being 7.06 μm and 6.14 μm, respectively, after modification with kaolin. The permeation separation experiments demonstrated that the performance of the ZSM-5/NaA hybrid membrane was better than that of the monolayer zeolite membrane with permselectivities of H₂ over CO₂, N₂, CO and CH₄ of 5.40, 4.65, 4.70 and 3.93, respectively, which were higher than the corresponding Knudsen diffusion coefficients. Above all, modifying the support with kaolin and then synthesizing the ZSM-5/NaA hybrid membrane could strengthen the performance of the zeolite membrane effectively, which provided a new approach for the synthesis of high performance zeolite membranes in the field of membrane separation.