Preparation Of Zeolite NaA Membrane

Pervaporation (PV) has attracted increasing attention as an effective and energy-efficient technique for the separation of azeotropic or close-boiling liquid mixtures. A dense zeolite NaA crystal layer is formed on the surface of a porous tubular support to obtain a hydrophilic zeolite NaA membrane. This kind of zeolite membranes has excellent water-permselective performance in PV toward water/organic liquid mixture. Zeolite NaA membranes have also excellent well thermal, mechanical and chemical stability. Many papers have been reported on the synthesis of zeolite NaA membranes in the recent years. In this work, a new method was developed to prepare zeolite NaA membranes by hydro thermal synthesis on the outer surface of porous tubular supports.Primary, the effects of material sources, gel compositions on synthesis of zeolite NaA powders were studied in order to get the preliminary synthesis conditions for preparation of zeolite NaA membranes. The results indicated that zeolite NaA powders with high crystallite were prepared with gel composition of 5SiO2:2.5Al2O3:7Na2O:400H2O aged for 0.5h at synthesis temperature of 100癈 for 3.5h.The porous a-AO3 and mullite tubes were used as supports for synthesis of zeolite NaA membranes. On base of the above synthesis conditions, zeolite NaA membranes were prepared, however most of them were leak since no dense crystal layer was formed on the surface of the supports. The gel compositions for synthesis of zeolite NaA membranes were further adjusted corresponding to the used material sources. On the other hand, the properties of the supports were very important factor, which strongly affected pervaporation performances of zeolite NaA membranes. Supports must be designed for preparing zeolite NaA membranes. According to the PV results, mullite support M75 prepared at present time was the most suitable for synthesis of good zeolite NaA membranes.Furthermore, the synthesis time was also important. From the pervaporationresults and SEM characterizations, good zeolite NaA membranes were prepared for synthesis time of 2.5 to 3.5h at 100Pervaporation experiments were carried out at 348K for alcohol/water mixture containing 10wt% water. Zeolite NaA membranes prepared in this work displayed an excellent pervaporation performance. For example, the water flux (Q) was 2.5 kg/m2h and water/ethanol separation factor (a) was over 10000. Compared with the best zeolite NaA membrane reported in the literature, the zeolite NaA membranes prepared in this work had the similar pervaporation performance.Zeolite NaA membranes with 20cm in length were also prepared in the same synthesis conditions. The preliminary results indicated the membrane had good PV performance. In order to prepared a larger size of zeolite NaA membranes, a lot of works will be carried out in the future.