Hydrothermal synthesis of hydroxy sodalite zeolite membrane: Separation of H2/CH4

Abstract In this study, hydroxy sodalite (HS) zeolite was synthesized via hydrothermal method. As reported in the literature, the recommended molar composition of H2O/Al2O3 for HS zeolite synthesis is about 1000. However in our work, HS zeolite was synthesized using new molar compositions of H2O/Al2O3 for different synthesis times and their effects on morphology and crystallinity of the synthesized zeolites were investigated. Also, HS zeolite membranes were synthesized on seeded supports using synthesized powders and the effect of seed size was also investigated. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Gas permeation through the membranes was also measured. First of all, it was found that synthesis time has a significant effect on crystallinity and crystal size of the synthesized zeolite. Also, water molar ratio can control crystal size of the synthesized zeolite. It was found out that with increasing the seed size, H2 and CH4 permeations decrease, from 3224 to 279 (Barrer) and from 611 to 45 (Barrer), respectively, while the H2/CH4 selectivity increases from 5.28 to 6.20. Finally, to obtain HS zeolite with desirable particle size, crystallinity and morphology, optimum synthesis conditions were proposed.