| Kaolin resource in China with excellent quality is widely distributed and abundantly reserved. It is applied in plenty of areas, such as ceramics, paper, agriculture, rubber, plastic, refractory, cutting-edge technology for national defense and high-grade powder cosmetics and so on. Kaolin, one of aluminosilicates with high quality and low price, is suitable for raw materials of NaA zeolite and its membrane. NaA zeolite membranes have high hydrophilicity, the molar ratio Si/Al nearly equal to 1 and three-dimensional open-framework, and they exhibit outstanding potential on dehydration of the organic by pervaporation in recent years due to their uniform molecular-sized pores and rapid material transportation. They have the resistance to the harsh operation conditions compared to the organic membranes, and the operation cost in pervaporation is reduced greatly as a result of high flux, excellent stability and long working life. Hence, they show strong competitiveness and huge demand in industrial market.In this work, NaA zeolite is synthesized from kaolin using hydrothermal and microwave-assisted method; NaA zeolite membranes are synthesized by hot dip-coating on the outer surface of a-Al2O3 substrates using hydrothermal and microwave-assisted method from kaolin, and the as-synthesized membranes are applied in dehydration of ethanol by pervaporation. The main results achieved are as follows:(1) The effect of factors during hydrothermal synthesis of NaA zeolite from kaolin is investigated. The higher the molar ratio of Na2O/SiO2 and Na2O/H2O is, the more stable the crystallization state of NaA zeolite is; high molar ratio of Na2O/H2O promotes the dissolution of kaolin and the following nucleation. The as-synthesized NaA zeolite has a mean particle size of 4μm with the static water adsorption 28.02wt.% and the calcium ion exchange 316.55mgCaCO3/g dry basis.(2) The influence of factors during microwave-assisted synthesis of NaA zeolite from kaolin is investigated. Short reaction time under microwave radiation requires fully complete dissolution of kaolin, and the heating intensity of microwave is so great that NaA zeolite is prone to transform into other phases which are more stable under the experimental conditions. The as-synthesized NaA zeolite has a mean particle size of 2μm with the static water adsorption 28.26wt.% and the calcium ion exchange 341.40mgCaCO3/g dry basis. (3)The effect of factors during hydrothermal synthesis of NaA zeolite membrane from kaolin is investigated. When the composition of 5SiO2:Al2O3:50Na2O:1000H2O and crystallization time 4h at 80℃are used, the thickness of the as-synthesized NaA zeolite membrane is 6μm, and the flux, separation factor and PSI are 1.465kg·m-2·h-1, 5231 and 7664 respectively.(4) A bench test is conducted for the pervaporation of NaA zeolite membrane using Kaolin as Al source by hydrothermal method. After operation for 32.85h, the molar content of ethanol in feed enriches from 93.31% (97.27wt.%) to 99.04% (99.61wt.%), which exceeds the requirement (99.50wt.%) of the bench test. As the operation time prolongs, the fluxreduces from 0.726kg·m-2·h-1 to 0.064kg·m-2·h-1 , meanwhile, the separation factor increases from 13600 to 75700.(5) The influence of factors during microwave-assisted synthesis of NaA zeolite membrane from kaolin is investigated. The thickness of the as-synthesis NaA zeolite membrane at 90℃for 20min is 4μm, and the flux, separation factor and PSI are1.133kg·m-2·h-1,10359 and 11737 respectively. |
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