Microwave-assisted hydrothermal synthesis of hydroxy-sodalite zeolite membrane

A high quality pure hydroxy-sodalite zeolite membrane was successfully synthesized on an α-Al2O3 support by a novel microwave-assisted hydrothermal synthesis (MAHS) method. Influence of synthesis conditions, such as synthesis time, synthesis procedure, etc., on the formation of hydroxy-sodalite zeolite membrane by MAHS method was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas permeation measurements. The synthesis of hydroxy-sodalite zeolite membrane by MAHS method only needed 45 min and synthesis was more than 8 times faster than by the conventional hydrothermal synthesis (CHS) method. A pure hydroxy-sodalite zeolite membrane was easily synthesized by MAHS method, while a zeolite membrane, which consisted of NaX zeolite, NaA zeolite and hydroxy-sodalite zeolite, was usually synthesized by CHS method. The effect of preparation procedures had a dramatic impact on the formation of hydroxy-sodalite zeolite membrane and a single-stage synthesis procedure produced a pure hydroxy-sodalite zeolite membrane. The pure hydroxy-sodalite zeolite membrane synthesized by MAHS method was found to be well inter-grown and the thickness of the membrane was 6–7 μm. Gas permeation results showed that the hydrogen/n-butane permselectivity of the hydroxy-sodalite zeolite membrane was larger than 1000.