Synthesis And Properties Of Permeantion And Separation Of FER-type Zeolite Membrane

FER-type zeolite membrane has an orthorhombic framework containing one-dimensional channels of10-membered rings (0.42×0.54nm) and one-dimensional channels of eight-member rings (0.35×0.48nm). FER-type zeolite membrane with unique channel systems has high performance in separation of mixture, such as benzene/p-xylene, butane isomers and xylene isomers. So it is of significance to conduct synthesis and application studies of FER-type membrane to obtain excellent quality membrane. In this dissertation, combined with the growth characteristic of FER-type zeolite, the compact FER-type zeolite membranes are prepared on macroporous α-Al2O3supports by different methods with cheap raw materials. The single-gas permeation performance and separation properties of FER-type zeolite membrane are investigated in detail.When macroporous α-Al2O3support was modified by γ-Al2O3membrane, the FER-type zeolite membrane is prepared on the support surface by in situ hydrothermal synthesis. The effects of synthesis parameters for preparation of γ-Al2O3membrane such as HCl concentration, content and heating rate in calcination process are investigated. As a result, with adding18ml HC1(0.11mol/L) in the sol, the thin and continuous γ-Al2O3membrane was prepared on the support with two times synthesis. The heating rate is2.5℃/min. The FER-type zeolite membrane is calcined in air at600℃for6h to remove the template. At room temperature, under the pressure difference of0.06-0.14MPa, the H2permeance is (2.81～4.79)×10-7mol·m-2·s-1·Pa-1, and H2/N2and H2/SF6ideal separation factors of FER-type zeolite membrane are3.23～3.83and82.6～96.2, respectively.Using pyridine as template, the polycrystalline FER-type zeolite membrane is prepared successfully on macroporous α-Al2O3support by vacuum-assisted secondary growth. The effects of synthesis parameters such as template, alkalinity, dilution, synthesis temperature, crystallization time and raw materials are investigated in detail. As a result, parent gel with excellent molar composition of1Al2O3:60SiO2:6Na2O:1835H2O:64C5H5N is gained to synthesize FER-type zeolite membrane. The synthesis temperature is175℃and the crystallization time is24h. Under this optimization synthesis conditions, the FER-type zeolite membranes are prepared by vacuum-assisted secondary growth. At30℃, the three-stage synthesized FER-type zeolite membranes have the best properties with the single-gas permeances of10-7～10-9mol·m-2·s-1·Pa-1. The H2/N2ideal separation factor through three-stage synthesized FER-type zeolite membranes is3.95-4.07. The separation properties of FER-type zeolite membranes are evaluated by benzene/p-xylene pervaporation test. When the concentration of benzene in feed mixture is0.5mol%, the flux of benzene is3.63g·m-2·h-1and the separation factor (benzene/p-xylene) is as high as689. When the molar fraction of benzene in the feed mixture is57mol%, the fluxe of benzene is28.58g·m-2·h-1and the separation factor is98.FER-type zeolite membrane is prepared successfully on macroporous α-Al2O3support by rubbing seeds and solution-filling method. The small seeds with the size of0.5～2μm are prepared by rubbing method. By dip coating method, the FER-type zeolite seed layer is coated on the outer surface of the support with deep-seated pores filled with glycerol solution. The concentration of seed suspension is1wt.%and the coating time is1min once time. After crystallization, the compact FER-type zeolite membrane is prepared on this seed layer with thickness of about12～13μm. At room temperature, the H2permeance is (3.67～3.98)×10-7mol·m-2·s-1·Pa-1. The H2/N2and H2/SF6ideal separation factors of FER-type zeolite membranes are3.83-4.03and119-126, respectively. In pervaporation test of benzene/p-xylene mixture, when the concentration of benzene in feed mixture is0.5mol%, the flux of benzene is5.26g·m-2·h-1and the separation factor is680. When the concentration of benzene in the feed mixture is57mol%, the fluxe of benzene is44.39g·m-2·h-1and the separation factor is94.FER-type zeolite membrane is used to separate MeOH/DMC and MeOH/MeOAc mixtures in the pervaporation operation. The effects of feed concentration, temperature and vacuum of permeation side are investigated. The results indicate that the preferential permeation component is determined by feed concentration of the mixture. The MeOH and ester fluxes and the ester/MeOH separation factor increase, and the MeOH/ester separation factor decreases with increasing temperature or vacuum of permeation side. At40℃and0.098MPa, in the pervaporation separation of MeOH/DMC azeotrope, the fluxe of MeOH is25.92g·m-2·h-1, and the MeOH/DMC separation factor is20.38. At30℃and0.098MPa, in the pervaporation separation of MeOH/MeOAc azeotrope, the fluxe of MeOH is30.49g·m-2·h-1, and the MeOH/MeOAc separation factor is6.95.