Preparation And Pervaporation Performance Of NaY Zeolite Membrane

Hydrophilic NaY zeolite has higher framework Si/Al ratios of 1.5?2 than NaA zeolite and owns a three-dimensional and 12-ring pore structure with a pore size of 0.74 nm. NaY zeolite membrane is applied widely in gas separation, organics separation and catalysis. The large pore size and good hydrophilicity make NaY membrane a great candidate for dehydrating of organic aqueous solution.The paper is focused on the synthesis of high performance NaY zeolite membranes on coarse macroporous ?-Al2O3 tubes by the two stage varying temperature hot dip-coating method (VTHD). The pervaporation performances in separating alcohols/water mixtures of the as-synthesized NaY zeolite membranes were tested, and the ion seperation properties were explored for the first time.(1) NaY zeolites with different crystal sizes of 1.3 ?m and 0.58 ?m were synthesized from water-clear precursor suspensions with mole ratios of 12.8 SiO2:Al2O3:20Na2O:975 H2O and 12.8 SiO2:Al2O3:16 Na2O:780 H2O, separately. The influences of synthesis conditions, such as crystallization time, alkali content, silicon source and aluminum source on the NaY zeolite were investigated. When synthesized at 100? for 6 h, Na2O/SiO2=1.093 or 1.250, silica sol as silicon source and aluminum sulfate as aluminum source, the crystallinity of the NaY zeolite was high and the crystal is well shaped.(2) NaY zeolite membranes were synthesized from a water-clear precursor suspension (12.8 SiO2:Al2O3:16 Na2O:780 H2O) on coarse macroporous ?-Al2O3 tubes by the two stage varying temperature hot dip-coating method (VTHD). The influences of synthesis conditions, such as aging temperature, crystallization time, crystallization temperature and concentration of seeds on the NaY zeolite membrane were studied. When aged at 25? for 12 h, crystallized at 100? for 8 h with a seeds concentration of 0.20 wt.%, the as-synthesized NaY membranes exhibited excellent pervaporation performances with a total flux up to 5.89 kg?m-2?h-1and a separation factor of 627, which were the best performance for the literature reported so far. The as-synthesized membranes were as thin as 3 ?m by the SEM characterization.(3) Properties of NaY zeolite membranes prepared under optimal conditions for the separation of different kinds of alcohols/water mixtures were tested at 75? by PV technology. The fluxes were 2.40 kg-m-2?h-1,4.21 kg?m-2?h-1, and 4.39 kg?m-2-h-1with separation factors of 50,560, and ? for ethanol/water, isopropanol(IPA)/water and normal butanol(NBA)/water mixtures, respectively. The results indicated that the as-synthesized NaY zeolite membranes had good hydrophilicity. The pervaporation performance of the NaY membranes enhanced with the increasing of feed temperature.(4) The Sr2+ ion rejection properties of the as-synthesized NaY zeolite membranes were also investigated for the valuation of potential application in the remove of radioactive nuclide such as Sr2+ or Cs+ from the industrial wastewater. At 75?, the fluxes were over 10 kg?m-2?h-1 and the ion rejections were over 99.9% of PV tests conducted with the Sr2+ concentrations of were 50 mg/L,100 mg/L, and 150 mg/L. Detected by inductively coupled plasma spectrum instrument (ICP), the concentration of Sr2+ in the permeate side was below 0.025 mg/L. The result indicated that NaY zeolite membrane is a promising candidate in application of radioactive ion rejections.