Synthesis of thin defect-free hydroxy sodalite membranes: New candidate for activated water permeation

Successful and rapid synthesis of thin defect-free hydroxy sodalite (H-SOD) membranes on α-Al2O3 supports was carried out using direct hydrothermal synthesis. The membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetric analysis (TG/DTA), single gas permeation measurements, and water pervaporation experiments at different temperatures and pressures. The synthesis was carried out under rotation for only 3.5 h at 413 K. An inter-grown pure H-SOD membrane was made with a layer thickness of 2 μm. Gas permeation results showed that the membrane was impermeable to N2 and the He permeance was as low as 10−11 mol−1 m−2 Pa−1, which validates absence of defects. Pervaporation experiments showed reasonable water fluxes up to 2.25 kg m−2 h−1 at 473 K. Water permeance was found to increase exponentially with increasing temperatures and was not affected by changing the absolute feed pressure. Permeance at temperatures above 350 K was attributed to activated transport of water through H-SOD membranes.