Synthesis Of Zeolite 4A Membrane And Application To Separation Of Water-Ethanol Mixture

Nowadays, the petroleum resource is getting short day by day. A country will expand their economy hard if it relies on the petroleum excessively. The anhydrous ethanol can be mixed with gasoline at certain ratio to prepare ethanol gasoline used for fuel of car, which can reduce the dependence on petroleum in the world. Zeolite 4A membrane attracts more and more investigators' attention because it has an attractive application foreground in this area.The preparation of zeolite 4A membrane and application to separation of water/ethanol mixture was studied in this paper. The preparation of zeolite 4A membrane can be as follows. First, crystal seeds were prepared. Second, the supporter was prepared and pretreated before use. Third, the synthesis solution was prepared. Last, the zeolite 4A membrane was synthesized.The crystal seeds used for zeolite 4A membrane preparation were synthesized by hydrothermal method. The crystallinity of the seeds was high and the transformation of NaA zeolite into other type of zeolite was not found.The pretreating of the supporter was so important that it could affect the generation and the type of the zeolite membrane. In our experiments, the supporter was pretreated with the surface polishing, ultrasonic washing and coating with crystal seeds.The sodium silicate, aluminium hydroxide, sodium hydroxide and the deionized water were used as the starting material in the preparation of the zeolite 4 A membrane. The concentration of synthesis solution was expressed by the molar ratio of water and sodium oxide. The four different concentration of synthesis solution respectively wereH2O/Na2O=(1)60, (2)80, (3)100, (4)120 Then the synthesis solution had a composing of SiO2: A12O3: Na2O = 1:1:3.6The hydrothermal method, airtight microwave method and barometric microwave method were used in the preparation of zeolite 4A membrane.The synthesis solution concentration, reaction time and the coating method changed with the synthesis method.The synthesis solution's concentration of different synthesis method was optimized. For hydrothermal synthesis, the molar ratio of water/sodium oxide was between 80 and 120. For microwave synthesis, the separation factor reached the maximum when the molar ratio of water/sodium oxide was 100.The synthesis of 4A zeolite membrane needed 12h by hydrothermal method, while only needed 10min by microwave heating. The synthesis time was seventy times shorter by microwave heating than by hydrothermal method.For hydrothermal synthesis, the separation factor reached to the max when using the coating method B. For airtight microwave synthesis, the coating of C was superior. For barometric microwave synthesis, the D was the best. So, different coating method should be used in different method.The synthesized membranes were characterized with XRD and SEM. From the XRD patterns and SEM images it was showed that the crystallinity of the zeolite 4A membrane prepared by above-mentioned three methods were high and the zeolite crystals were uniform in size. Also the experiment indicated that the formation of a NaA zeolite membrane was drastically promoted by microwave heating.Membrane was used in the pervaporation of the 95%(wt) ethanol water solution. The separation factor of the membrane synthesized for the mixture of ethanol and water could reach 63.84, which was much larger than that of the sole supporter. For 95%(wt) ethanol water, the percent of water could reach 79%(wt) after the pervaporation and the ethanol percent reduced to 21%(wt). It was proved that the membrane synthesized could selectively separate water from the solution of ethanol and water.The pervaporation performance of microwave-synthesized membrane was superior to that of the hydrothermal synthesized membrane. The separation factor and the pervaporation quantity of the membrane synthesized by microwave method were larger than that of the membrane synthesized by hydrothermal method. Reproductiveprobability and the perfection of the as-synthesized membrane were preceded to hydrothermal s...