Rapid preparation of high hydrothermal stability Si-rich LTA membrane by hydroxyl radical strategy for separation of high-temperature and water-rich organics

Compared with conventional LTA membranes (Si/Al ratio = 1), Si-rich LTA membranes with higher Si/Al ratios are considered to exhibit better hydrothermal stability under high-temperature and water-rich conditions. In this work, high-performance Si-rich LTA membranes were successfully prepared on rough macropore alumina tubes via a hydroxyl radical route in a short synthesis time of merely 8 h. The membrane had the highest Si/Al ratio of 1.63 in the reported LTA membranes. The crystallization processes of Si-rich LTA membranes fabricated with and without hydroxyl radicals were investigated systematically. The role of hydroxyl radicals was detailly discussed by density-functional theory (DFT), SEM, XRD, EDX, EPR, and fluorescence characterizations. Results demonstrated that hydroxyl radicals first promoted the depolymerization of Si substances and then enhanced the Si–O–Si bond formation, thus resulting in an increasing crystallization rate and a higher framework Si/Al ratio of Si-rich LTA membrane. The fabricated Si-rich LTA membrane exhibited outstanding water selectivity with the water content in permeate of exceeding 99.96 wt% and excellent permeation flux of higher than 2.50 kg m −2  h −1 in the case of a 90 wt% EtOH/H 2 O mixture at 348 K. Additionally, the membrane displayed remarkable hydrothermal stability by vapor permeation (VP) test with equimolar of EtOH/H 2 O and MeOH/H 2 O mixtures at a high temperature of 423 K for 120 h, respectively. The Si-rich LTA membranes fabricated with hydroxyl radical showed excellent reproducibility, suggesting that these membranes had a broad promising prospect for separation dehydration of organic solvents even under high-temperature and high-water-content conditions.