On the effects of water exposure of as-synthesized LTA membranes on their structural properties and dehydration performances

Abstract

LTA (Linde Type A) type zeolites have been manufactured in a form of a continuous membrane and widely used for pervaporation-based dehydration of organic solvents. Despite the extremely high dehydration performances, the effects of parameters related to seed layer formation and, more importantly, water exposure of the resulting LTA membrane on the final membrane properties and, concomitant dehydration performances have not been investigated intensively. In this study, we examined how the immersion of as-synthesized LTA membranes in water (considering duration of water immersion) affected the membrane properties and dehydration performances. In addition, we focused on how to handle a LTA seed suspension (dependent on duration of precipitation) for forming proper seed layers on a-alumina tubes. We found that optimal preparation methods were necessary for securing a proper seed suspension and forming a seed layer that allowed for manufacturing high performance LTA membranes. In particular, when the disc-supported and tube-supported LTA membranes were immersed in water for similar to 12 h, they could show high dehydration performances with the H2O/CH3OH separation factors of similar to 860 +/- 260 and similar to 910 +/- 420, respectively, at 50 degrees C. However, after a critical time (similar to 100-200 h), the corresponding dehydration performance was dramatically decreased, apparently due to the dissolution of LTA zeolites. Along with regular structural investigation with scanning electron microscopy and X-ray diffraction analyses, fluorescence confocal optical microscopy clearly revealed that the immersion of the LTA membranes in water resulted in forming almost defect-free membranes, but after some time, damaging the corresponding membrane structure. Nevertheless, the LTA membrane that did not contain non-zeolitic defects could preserve its aforementioned high dehydration performance with respect to a water-containing feed (similar to 10 wt% H2O) up to similar to 102 h.