Preparation And Performance Of Zeolite NaA Membranes By A Continuous Flow Synthesis Method

Zeolite NaA membranes have been utilized in dehydration of organic aqueous solution industrially. The traditional way of membrane preparation is static crystallization in autoclave. It’s a way of batch operation which is not suitable for the industrial production of membranes. What’s more, it’s not advantageous for renewing the synthesis solution while preparing membranes on the inner-side of capillaries and multichannel tubes. A continuous process is desirable for the reasons:it is energy efficient; requires smaller equipment and fewer synthesis solutions at the same production rate; provides an outlook for the scale-up and continuous production. So in this paper, we utilize the continuous flow synthesis method to prepare zeolite NaA membranes on the inner-side of hollow fiber supports.(1) The static crystallization method was used for the preparation of Zeolite NaA seeds which were small and pure. The effect of basicity, time and temperature on the particle size and particle size distribution was investigated. The results were:the NaA zeolite crystals with cubic morphology and mean particle size of around150nm were produced at100℃for16h after19h aging with the molar composition of4.72(TMA)2O:0.057Na2O:Al2O3:4.2SiO2:297H2O; the NaA zeolite crystals with ellipsoidal morphology and mean particle size of around100nm were produced at80℃for10h after72h aging with the molar composition of4.72(TMA)2O:0.285Na2O:Al2O3:4.2SiO2:297H2O.(2) The membranes were prepared by the continuous flow synthesis method on the inner-side of the ceramic hollow fiber. Three kinds of synthesis solution recipes were studied. The effect of temperature, time, seed film, flow rate, the addition of PDDA (Poly (diallyldimethylammonium chloride)), the recirculation and the length of the feed pipe on the quality of the membranes were investigated. With the molar composition of48Na2O:1Al2O3:5SiO2:4500H2O, the optimal conditions were:seed suspension concentration of0.5wt.%, temperature of90℃, time of14h, flow rate of0.033mL/min. The as-synthesized membranes were continuous and well intergrown. With the molar composition of56Na2O:1Al2O3:5SiO2:2500H2O, the optimal conditions were:the addition of PDDA in the seed suspension, temperature of90℃, time of12h, flow rate of0.033mL/min, with recirculaion of the synthesis solution. The as-synthesized membranes showed great ability to dehydrate ethanol/water mixtures (90:10, w/w) by pervaporation with selectivities and fluxes, respectively, up to1039.47and0.44kg m-2h-1at70℃. And the H2/CO2selectivity of the single gas permeation test was10.97. With the molar composition of48Na2O:1Al2O3:5SiO2:4500H2O, the optimal conditions were:aging time of4h, temperature of80℃,time of5h, flow rate of0.033mL/min.(3) The seed films were self assembled by AP-TMS covalent linker in a flow system on the support of PES hollow fiber. Zeolite NaA membranes were prepared by second growth with the seed films. The parameters of hydroxylation of the supports, the seed films and the flow rate were investigated. The results were:hydroxylation of the supports was beneficial to the quality of the membranes; at the coupling flow rate of0.033mL/min and the membrane preparation flow rate of0.013mL/min the as-synthesized membranes were impermeable to N2gas.