| The Si/Al of NaA zeolite membrane is1, due to its high hydrophilicity and small pore size that ranges between most organic solvents and water molecules, has become a potential candiditaes on dehydration of organic by pervaporation (vapor permeation). The limited amount of the natural fresh water resource emphasizes the importance of potable water supply, such as seawater desalination. Seawater desalination is most commonly conducted using multistage flash distillation and reverse osmosis. Since the former consumes more energy, the latter is rapidly coming to the forefront in the seawater desalination market. However, with RO, there is a need to pre-treat and pressurize raw seawater to approximately50bars and polymeric membranes have only short life spans, due to biofouling.The study of inorganic membrane became very important. So it is of importance to study dehydration of organic by pervaporation using NaA zeolite membranes.The paper firstly explored different seeding methods. The simple and effective seeding methods, seed pastes method and spraying seeding method, were expored. And then, the high quality of seed layer was obtained by varying-temperature hot dip-coating seeding method on the80cm cheap macroporous supports. After the successful synthesis of zeolite NaA membranes, the pervaporation performance of dehydrating90wt.%IP A/10wt.%H2O mixtures was investigated. At last, the pervaporation performance with NaCl in the feed at different temperature, different NaCl concentration in the feed and time was investigated. The main research results are briefly introduced as follows:1) Spraying seeding technology was developed to synthetize zeolite NaA membranes on the low-cost macroporous01-Al2O3supports. The supports were firstly modified by spraying the large (2μm) NaA crystals, and then the small (0.4μm) NaA seeds were sprayed on the pre-treated supports to obtain a thin and continuous seeds layer. At last, the zeolite NaA membrane was fabricated by the secondary growth method at353K. The as-synthesized NaA zeolite membrane was characterized by SEM, XRD and pervaporation measurement. The results showed that well inter-grown zeolite NaA membranes were formed. The total flux of the zeolite NaA membranes reached to2.71kg·m-2·h-1, and the separation factor was more than10000in dehydrating the90wt.%ethanol/10wt.%H2O solution at348K.2) A seeds paste seeding method was employed to prepare zeolite NaA membranes in this section. The pervaporation performance of zeolite NaA membranes synthesized from two hydrothermal synthesis solutions was investigated. Simultaneously, different large and small NaA seeds concentrations were added into the paste, and the PV performances of the resultant zeolite NaA membranes were tested. The as-synthesized NaA zeolite membranes showed good separation performances in dehydrating90wt.%EtOH/10wt.%H2O mixtures at348K. The flux and separation factor of zeolite NaA membranes were2.33kg-m-2-h-1and4327, respectively.3) Zeolite NaA membranes with high pervaporation performance were hydrothermally synthesized after the80cm cheap macroporous supports were modified by hot dip-coating seeding method. The synthesized zeolite NaA membranes showed good separation performances with the flux and separation factor was3.00kg-m-2·h-1and over10000, respectively, in dehydrating90wt.%isopropyl alcohol/10wt.%H2O mixtures at348K. Furthermore, the influences of various feed flows, temperatures and concentrations on the pervaporation performances of separating IPA/H2O mixtures were studied.4) The flux and the permeate water concentration of the as-prepared zeolite NaA membranes was about2.5kg·m-2h-1and99.2wt.%, respectively, in dehydrating the90wt.%EtOH/10wt.%H2O mixture at348K, However, the flux decreased to2.0kg·m-2-h-1while the permeate water concentration increased to99.9wt.%after the addition of1wt.%o NaCl into the feed mixture. With increasing the experiment time to30h, the flux decreased continuously to0.7kg·m-2-h-1but the permeate water concentration retained at99.95wt.%. The flux increased from1.4kg·m-2·h-1to2.0kg·m-2·h-1as the temperature increased from338K to348K, while the permeate water concentration showed no change. |
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