Synthesis of LTA zeolite membranes from metal alkoxides and examination of the pervaporation performance

Abstract

In the dehydration of ethanol, membrane separation using LTA zeolites is commonly employed in place of distillation due to its lower energy consumption. In the membrane separation process, a thin zeolite membrane is preferred to reduce the permeation resistance of water in the membrane. From the aspect of reducing the resistance, the authors successfully prepared LTA zeolite membranes from metal alkoxides. The influence of the crystal growth conditions on the separation performance was investigated by the pervaporation of an ethanol-water mixture. As a result, the thickness of the LTA zeolite membrane could be decreased to less than 3 μm by optimizing the aging time of the secondary growth solution and secondary growth time. For 90 wt% ethanol solution at 343 K, the permeation flux and separation factor of the membrane were 6.3 kg m −2 h −1 and >10,000, respectively. In this paper, the SEM observation and XRD analysis were examined to understand the structure of zeolite membrane. As a result, the change in crystallographic orientation caused by the aging was proposed as key factor of permeability of the membrane. • LTA zeolite membrane was prepared by hydrothermal treatment of seed crystals with hydrolyzed metal alkoxide. • Influence of aging of secondary growth solution of the membrane on its pervaporation performance was examined. • Water permeability of the membrane decreased as the aging proceeded. • X-ray diffraction analysis of the membrane surface revealed that orientation of the crystallites in the LTA layer changed to less (200) plane being parallel to the surface of the membrane. • Decrease of (200) oriented plane by the aging may be responsible for the reduction of water permeability of the membrane.