| Zeolite membranes have uniform, molecular-sized pores, and they are thus well suited for separating liquid-phase mixtures by pervaporation. At present, zeolite membranes have been used in pervaporation mostly to dehydrate alcohols with simple structures, while the de-hydration of alcohols with complicated structures and the separation of multicomponent orga-nic mixtures are presently the lease developed application of pervaporation.2,2,2-trifluoroeth-yl alcohol (TFEA) is main reaction reagent for the synthesis of2,2,2-trifluoroethyl methacryl-ate (3FMA) by esterification process, the removal of water which is produced as a byproduct of the esterification process can shift the equilibrium towards the products, and thus increase the conversion. Likely, the1,3-propanediol molecule is fermented from glycerol(1,2,3-propa-nediol,C3H8O3) or glucose (C6H12O6), and thus, selective separation methods would be valua-ble for recovery of1,3-propanediol from glycerol and glucose.FAU-type zeolite, including NaX(with Si/Al ratio of1-1.5) and NaY(with Si/Al ratio over1.5) type, bears a three-dimensional pore structure and12-member rings with a pore dia-meter of0.74nm. The large pore size and preferential adsorption make FAU-type zeolite me-mbranes capable in the separation of organic mixtures. At present, secondary growth method is the most important method for syntheis of FAU zeolite membrane, however, there still exi-sts some defects to synthesis of FAU zeolite membrane by this method, such as complicate operation, high cost, and few practical types etc., which make it unfavorable for the mass pro-duction of FAU-zeolite membranes. According to the mentioned questions, this thesis comp-rises the following studies:First, NaX zeolite membranes were prepared on porous α-Al2O3tubes by a two-stage in situ meothod.The first stage synthesis was performed in gel solution at20～50℃for24-168h and subsequently at90℃for4-12h. The second stage synthesis was performed in gel at90℃for4-12h. In situ aging played an important role at the first stage as it suppressed CHA, ANA phase, and promoted the formation of a continuous zeolite layer. The second stage synthesis was performed in a diluted solution (H2O/SiO2=500), where the zeolite layer synthesized is more uniform and compact than that synthesized in a solution (H2O/SiO2=400). Particularly, image of sample aged for48h at50℃and subsequently synthesized for4h twice consists of highly intergrown zeolite X crystals with size of2μm, moreover, the membrane surface is very even. At room temperature and the pressure difference of100kPa, the N2and CO2perm-eances are6.5×10-7mol/m2·s·Pa and4.8×10-7mol/m2·s·Pa respectively, and the ideal separate- on factor for N2/CO2is1.4, showing a better separation ability than membranes synthesized by secondary growth method.Second, NaY zeolite membranes were synthesized on porous α-Al2O3tubes by a two-stage in situ method. The first stage was performed in liquid phase structure-directing agent solution at room temperature for2h and subsequently at90℃for7～8h. The second stage was performed in different synthesis solution at100℃for6～12h. It is found that crystal size of membrane in the first stage synthesis can be controlled by adjusting the alkalinity of directing agent, aging time and temperature, and amount added. When aging time of directing agent was prolonged from24h to120h, crystal size decreased from2μm to500nm, accordingly, H2/N2and H2/C3H8ideal separation factor increase by12%and27%, indicating a good sep-aration ability for membrane with a small crystal size.The NaY membrane synthesized in gel for12h shows a good integrity, and consists of highly intergrown zeolite Y crystals. Moreover, no evident inter-crystalline traps and pin pores were observed on the membrane surface. At room temperature and the pressure difference of100kPa, the H2、N2and C3H8permeances are36.7×10-8mol/m2·s·Pa,5.8×10-8mol/m2·s·Pa and5.0×10-8mol/m2·s·Pa respectively, show-ing a better permeability than membranes synthesized in a sol for12h.In this thesis, continuous and dense NaX zeolite membranes prepared were used to sepa-rate water from an aqueous feed solution containing2.2.2-trifluoroethyl alcohol. When the operation temperature is between25℃～65℃, and mole fraction of water is between0.05～0.4, pervaporation process through NaX zeolite membrane can separate efficiently water/2.2.2-tri-fluoroethyl alcohol (TFEA) solution. After pervaporation process was carried out for a long term more than5days, the water flux through the NaX zeolite membrane was stabilized at0.8～1.0kg/m2h, with the separation factor of2900～3100for a given feed solution composed of0.05mole fraction of wa ter at25℃Composite NaY membrane prepared was used to separa-te1,3-propanediol from glycerol and glucose in aqueous solutions.The total flux for quatern-ary solution was significantly higher than those reported for Silicalite-1, ZSM-5and ZSM-11membrane, close to that reported for NaX membrane. However, the1,3-propanediol/glycerol separation factor is similar to those reported. The effect of crystal size in the NaY membrane was studied for the first time on permeation flux and separation factor. At25℃. the total flux for quaternary solution and all the components fluxes increase with crystal size range0.5～1.5μm, while1,3-propanediol/glycerol separation factor decreases with crystal size increased. When pervaporation process was carried out by NaX membrane with a small crystal size of0.5μm,1,3-propanediol/glycerol separation factor is64. which is increased by3%for NaX membrane with a larger crystal size of1.5μm. indicating a better separation ability for zeolite with a small crystals. |
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