Optimized Preparation And Pervaporation Performance Of T Zeolite Membrane

Organic solvent dehydration is an essential separation process in many fields such as petroleum,medicine,and chemical industry.Traditional separation rectification technologies possess some disadvantages such as high energy consumption and complicated operation.In contrast,pervaporation organic solvent dehydration technology through zeolite membranes has the advantages of low energy consumption and simple operation.NaA zeolite membranes with low Si/Al ratio have excellent hydrophilicity,but the aluminum atoms in the molecule will be removed in acidic medium and destroy its skeleton structure;Silicalite-1 zeolite membranes with high Si/Al ratio have better acid resistance,but their hydrophilicity is poor.Benefiting from its good hydrophilicity and certain acid resistance,T-type zeolite membrane with moderate silicon-aluminum ratio?Si/Al=3⁴?is a great zeolite membrane for pervaporation dehydration to obtain high-purity organic solvents.In this paper,2?m T zeolite large seeds and 0.4?m T zeolite small seeds were firstly prepared,and then T-type zeolite membranes rapidly grew on low-cost macroporous alumina ceramic supports with its pore size of 3⁴?m in a short time by an induced crystallization?secondary growth?method in clear solutions.A“two-step coating+two-step crystallization”method is used to prepare a&b oriented T-type zeolite membranes under the original coating conditions and synthetic system,and its PV performance is greatly improved compared with the randomly oriented zeolite membrane.Main contents are as follows:?1?Using the molar ratio of SiO₂:Al₂O₃:Na₂O:K₂O:H₂O:TMAOH=18.2:1:4.2:1.5:212.7:x to prepare the large zeolite seeds.We obtained T zeolite crystals of different sizes?1²?m?through investigating the impacts of crystallization time,template content?x=0.82¹.82?and the material addition order of the products,and the 2?m crystals were used as a large seeds;using the same composition ratio as above to prepare small seeds,the crystallization and aging time,template content?x=1.82².82?and seed induction were investigated in detail.The obtained 0.4?m crystals were as small seeds.?2?The raw materials dissolve faster and more uniformly in the high alkalinity clear liquid system,so a clear liquid with high alkalinity was used as the synthesis system?the composition alkalinity ratio is n?Na₂O+K₂O?/n?SiO₂?=7?)in this paper.Uniform and continuous seed layers were prepared with 3 wt.%large seed solution and 0.8 wt.%small seed solution.Then the seed layers were crystallized for 5 h at 150°C in a synthetic solution of n?H₂O?/n?SiO₂?=30 to synthesize a dense T-type zeolite membrane.The obtained T-type zeolite membranes were used to separate alcohol/water mixed solution containing 90 wt.%isopropanol at 75°C,the permeation flux was 3.34 kg·m^-2·h^-11 and the separation coefficient was 2536.?3?The morphology and growth direction of the membrane crystals are the key factors determining the thickness and performance of the membrane.Therefore,the preparation of oriented zeolite membrane is a better method to improve the pervaporation performance of zeolite membranes.In this work,the a&b oriented T-type zeolite membranes were prepared by the“two-step coating+two-step crystallization”method under the same crystal coating conditions and the ratio of the synthetic solution of the previous work.The effects of crystallization temperature and crystallization time during the two-step crystallization process were investigated in detail during the synthesis.a&b-oriented T-type zeolite membranes were successfully prepared by controlling seed-induced nucleation and epitaxial growth.The results show that the pervaporation performance of a&b oriented T-type zeolite membranes prepared by this method has greatly improved with flux up to 3.84 kg·m^-2·h^-11 and separation coefficient>10000 through separating alcohol/water mixed solution containing 90 wt.%isopropanol under 75°C.