Kai Xu,Haiming Jin,Linfang Wang,Yi Liu,Chen Zhou,Jürgen Caro,Aisheng Huang
A seeding-free synthesis method is developed for preparation of oriented zeolite LTA membranes by using 1,4-phenylene diisocyanate (PDI) as a molecular linker. Before hydrothermal synthesis, –NCO groups are introduced with the functionalization of Al2O3 supports by PDI. A thin, well intergrown zeolite LTA membrane with a thickness of about 4.0 µm can be formed on the PDI-modified Al2O3 supports. The zeolite LTA membrane displays high pervaporation performances for dehydration of alcohols. At 90°C, the separation factor of the zeolite LTA membrane is 4480 for dehydration of 95 wt% ethanol/water mixtures, with a high water flux of 3.4 kg·m−2·h−1.
It is well known that zeolite LTA membranes have poor acid resistance although they have been considered the best hydrophilic zeolite membranes for the dehydration of organic aqueous mixtures. In the present work, we develop a simple and effective road to enhance the acidic stability of the zeolite LTA membrane through the depositing of a graphene oxide (GO) layer as an acid-resisting barrier on the surface of the zeolite LTA membrane. A relatively thin (about 5.5 μm) but dense and firm LTA@GO composite membrane is obtained by using dopamine as a covalent linker between the zeolite LTA and GO layers. The presence of the protective GO layer effectively inhibits the degradation of the zeolite LTA membrane by acetic acid, which greatly enhances its acid-resistant stability, leading to a high selectivity and stability for the dehydration of acetic acid. For the separation of 95 wt% acetic acid/water mixture at 333 K, the separation factor and flux of the LTA@GO composite membrane are about 400 and 1.5 kg m−2 h−1, respectively, and keep almost constant for 168 h.
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.
危险品化学品经营许可证（带存储）