Green synthesis of high-performance CHA zeolite membranes in pure K⁺ clear solution

CHA zeolite membranes possess a unique microporous structure and excellent hydrothermal stability, making them ideal materials for efficient dehydration of organic solvents. In this study, CHA zeolite membranes with SiO₂/Al₂O₃ ratios of 3.6-5.4 were successfully synthesized on α-Al₂O₃ supports using a high water-to-silica ratio (H₂O/SiO₂ = 230) system, using K⁺ as the structure-directing agent. The effects of the seed crystals' SiO₂/Al₂O₃ ratio and concentration, as well as the hydrothermal temperature, on the membrane microstructure and performance were systematically investigated. Particular emphasis was placed on elucidating the regulatory mechanism of seed properties and synthesis conditions on membrane growth. Low SiO₂/Al₂O₃ ratio seeds promoted the formation of prismatic crystals with sizes of 2-4 µm, whereas high ratios tended to generate impurity phases, which worsened with increasing concentration. Ultimately, under optimal conditions of a seed SiO₂/Al₂O₃ ratio of 4.84, seed concentration of 3 wt%, and synthesis temperature of 150 °C, the resulting CHA membrane exhibited outstanding pervaporation performance. For a 90 wt% ethanol/water solution (75 °C), the separation factor was as high as 5800, with a flux of 10.6 kg m^-2 h^-1. For a 40 wt% acetic acid/water solution, the permeate water content remained above 98.95%, with a flux of 4.8 kg m^-2 h^-1.