Study Of Synthesis Of Zeolite NaA Membranes And Pervaporation Of Ethanol/Water

Zeolite NaA membranes, with small pore size(4.lA) and strong hydrophilicity, have been found a potential application in the separation of small size gases by molecular sieving and dehydration of liquid mixtures by pervaporation. Zeolite NaA composite membranes are synthesized by in-situ hydrothermal synthesis on the outside of rough a -Al₂O₃ tube(pore size 2 5 μ m). Synthesis conditions and support modification are studied in this work in order to prepare good membranes. XRD, SEM and single gas permeation are used to characterize the as-synthesized membranes. The membranes are tested for the removal of water from ethanol/water mixtures by pervaporationThrough orthogonal experiments the effects of factors on the synthesis of zeolite NaA are studied.The influence of Synthesis temperature, synthesis time, synthesis stages, seeds dispersion and seeding method on the forming and performance of zeolite NaA membranes are discussed. On the same batch supports zeolite NaA membranes are synthesized with gel and clear solution respectively. Permeance of H2 across the membrane synthesized under optimism condition is 9.3x10-7 mols-1m-2Pa-1 ideal permselectivity of H2/N2 and H2/C3H8 is 4.1 and 6.7,respectively. It indicates that the NaA membrane has molecular property. SEM results shows that the zeolite NaA crystal continuously grown on the support with a layer 10-15 μ m.Using PP wax as masking agents zeolite NaA membranes are synthesized on the supports without pores. To certain extent masking can decrease the deepth of zeolite NaA in the support pores. The average permeance of H2 across the membranes can increase from 1.57 X 10-6mol.Pa^-1.m^-2.s^-1 to 9.24 X 10^-6 mol.Pa^-1.m^-2.s^-1 with masking technique.And the permselectivity of H2/N2 increase from 3.36 to 4.94 . Masking also can increase the replication of membrane synthesis.The 250mm membrane is tested for the removal of water from ethanol/water mixtures by pervaporation. When the feed ethanol concentration is 90wt. %, the flux and selectivity is 0.71Kg/(m-2h) and 850 at 50 ℃,showing good pervaporation property than PVA membranes. But the selectivity is not so good as the results in some literatures using zeolite NaA for pervaporation. The reasons may due to the density of the zeolite layer and the sealing of the membrane.