A mordenite membrane was prepared on an α-Al2O3 tube by in situ hydrothermal synthesis. The crystallization was carried out at 443K for 2 to 4 days. Silica sol and sodium aluminate were used as the sources of silica and alumina, respectively, and tetraethylammonium bromide as the template. The molar composition of the parent solution was 11.4Na2O: 1.0Al2O3:40SiO2:2500H2O:1.5TEABr. SEM and XRD were used to characterize the powder product and the composite membrane. The synthesized mordenite membrane proved to be in a full coverage and an excellent intergrowth. The mordenite crystals were about 20 to 30μm and the thickness of the mordenite membrane was 30 to 40μm. Based on the SEM pictures of the membrane in the early stage of hydrothermal synthesis, a growth model for the mordenite membrane was assumed. At first a gel layer was formed on the surface of the alumina tube. Nucleation took place in the gel layer but not at the interface of the gel layer and bulk solution. The gel layer provided the nutrients for the growth of zeolite crystals. After the gel layer was consumed completely, the zeolite crystals or membrane were exposed to the bulk solution. The membrane separation test on the mordenite membrane showed that the permeances of pure H2 and N2 at 298K were 6.92 x 10-7 and 1.81 x 10-7mol/m2sPa, respectively. The ideal selectivity of H2/N2 was 3.82, which was higher than that of Knudsen mechanism. It suggested that the mordenite membrane had the ability of molecular sieving.

In situ Synthesis of Mordenite Membrane on Alumina Tube by Hydrothermal Method. Y.Zhang, Z.Xu, Q.Chen: Chinese Journal of Catalysis, 2001, 22[4], 402-4