Synthesis and characterization of (h0l) oriented high-silica zeolite beta membrane

Abstract

The (h0l) oriented high-silica zeolite beta membrane was prepared with improved method in fluoride media. Dealuminated zeolite beta nanocrystals used as seeds were preliminary deposited on support, and then the seeded supports were vertically placed in autoclaves for hydrothermal synthesis. After the secondary growth of seeded supports at 413 K for 2 days, zeolite membranes were characterized by X-ray diffraction and scanning electron microscopy to determine their morphology and preferred orientation. Zeolite beta membranes with a thickness of intergrown crystal layer around 2 mu m were prepared and the crystals with typical truncated square bipyramidal morphology were packed tightly with their pyramidal (h0l) face perpendicular to the plane of membrane. in addition, ICP-AES chemical analysis was utilized to confirm the composition of seeds and membrane, and the Si/Al molar ratio of zeolite beta membrane was around 5000. The (001) and randomly orientated zeolite beta membranes were also prepared by changing the composition of starting synthesis gel and pH value. A competitive growth model was proposed to explain the formation of oriented membranes. The (h0l) oriented high-silica zeolite beta membrane with few cracks exhibited higher pervaporation flux. (C) 2009 Elsevier Inc. All rights reserved.