Preparation And Characterization Of Zeolite NaA Membrane @ Microporous Ceramics

The NaA zeolite is a typical zeolite with a three-dimensional pore system with a pore size of 0.41 nm.There is a strong electric field and polarity inside the crystal cavity,and it has a strong affinity for water.The molecular sieve membrane formed by zeolite can remove moisture in organic matter through pervaporation,and has a wide application prospect in the field of dehydration of organic substances such as alcohol/water system.However,in the preparation and performance of NaA zeolite membranes,there are problems such as long synthesis cycle,low film formation efficiency and easy formation of membrane defects.Therefore,the exploration of the rapid synthesis method of molecular sieve membranes and the improvement of film formation quality have become the focus of research.In this paper,the porousα-Al₂O₃ ceramic supports were prepared by solid-state particle sintering method.NaA-type zeolite molecular sieve membranes were synthesized by seed induction-hydrothermal method.The preparation methods of the support and the support pretreatment were studied.Influence;The tubular submicron microporousα-Al₂O₃ ceramic was used as the support,and the seed zeolite film was synthesized by the seed induction-ring focusing single mode microwave method.The rapid synthesis routes and methods of the molecular sieve membrane were discussed.Alumina powder(D₅₀=5.2μm)was used as aggregate,TiO₂ was a sintering aid,and microporous alumina ceramic supports（φ40 mm×4 mm）were prepared by dry pressing and solid particle sintering.The amount of pore-forming agent（carboxymethyl cellulose）,binder（kaolin）,and the firing schedule were studied.When the amount of methyl cellulose added was 4%and the amount of kaolin was 6%,microporous alumina ceramics with a pore size of 1.5μm,a porosity of 33%,and a bending strength of 31.4MPa were prepared at 1300℃.The hydrothermal method and the ring-focusing single-mode microwave method were used to synthesize seed crystals with different particle sizes to modify the supports with different pore sizes.The seed synthetic liquid was prepared at a molar ratio of n（Na₂O）:n（SiO₂）:n（Al₂O₃）:n（H₂O）=3:2:1:150,and was synthesized by hydrothermal method at 98℃for 2h.The seed crystals with a particle size of 1.4～1.6μm were seeded at a temperature of 120℃,150 W,and 8 min using a single-mode microwave method.Methyl cellulose was used as a dispersant to prepare molecular sieve seed solution.The seed crystals were loaded on the surface of the ceramic support by pulling and dipping,and then the zeolite membrane was hydrothermally reacted to study the effect of seed dispersion on molecular sieve film formation.The impact of performance.The results showed that a 0.7 wt.%solution of methyl cellulose disperses 1 wt.%of seed crystals,and can be evenly coated on the support,effectively modifying the defects such as macropores of the support.On this basis,the molecular sieve membrane was smooth,continuous and dense,with a permeation flux of 2.1 kg·m^-2·h^-1 and a separation factor of3950,showing good separation performance.Single-channel submicron alumina ceramic tubes were used as supports,and a dense continuous NaA zeolite membrane was synthesized by the ring-focus single mode microwave method.Based on the single-mode microwave technology of AFC（Auto Focus Coupling）ring-focusing auto-coupling,the stable microwave energy output ensures the quantitative and reproducibility of the reaction,while the high microwave energy field density greatly shortens the synthesis time.A silica sol was used as a silicon source and the molar ratio was n（Na₂O）:n（SiO₂）:n（Al₂O₃）:n（H₂O）=3:2:1:150 to prepare a molecular sieve membrane synthesis liquid,which was aged for 24 hours in a microwave.With a radiation power of 150W and a radiation temperature of 120℃,a dense and continuous NaA molecular sieve membrane can be synthesized in only 12 minutes（conventional hydrothermal method takes 4 h）,and the membrane thickness is only 4μm.After the alcohol/water pervaporation separation test,the permeation flux was 2.3kg·m^-2·h^-1,and the separation factor was up to 3970.