铝硅酸溶液中NaA型沸石分子筛膜合成规律的研究

对支撑体预处理、制膜液碱度、晶化温度和晶化时间对NaA型沸石分子筛膜性能的影响进行了综合研究,得出较优的条件是;支撑体采用去离子水浸泡,在90℃条件下晶化5小时,制膜液摩尔组成为Na2O:SiO2:Al2O3:H2O=8:1:0.2:200.SEM表明所合成的NaA型沸石分子筛在支撑体表面紧密排列形成膜层,膜厚约为3μm;NaA型沸石分子筛膜的氢气和氮气的渗透系数几乎不随平均压力变化而改变,其理想分离系数约为5,高于Knudsen扩散值,表明所合成的NaA型沸石分子筛膜具有一定的分子筛分效应.     

ZrO2 和Al2O3支撑的MFI 型沸石分子筛膜:支撑体材料对膜性能的影响

采用水热合成法，以纯SiO2为源物质，在介孔Y2O3掺杂的ZrO2(YZ)及大孔α-Al2O3支撑体上制备出高质量的MFI型沸石分子筛膜，通过H2／n-C4H10气体混合物的渗透分离和p-xylene的蒸发研究了不同支撑体上MFI型沸石分子筛膜分离性能，在较低温度范围，YZ支撑的MFI型沸石分子筛膜中n-C4H10的渗透率比Al2O3支撑的膜高很多，最大n-C4H10与H2的分离率达到500，Al2O3支撑的膜中py-xylene的蒸发流量随时间下降很快，而YZ支撑的膜中的蒸发流量则变化缓慢，用XRD对膜的晶体结构进行分析，通过多种温度下热处理不同支撑体上的膜样品研究了其热稳定性与支持体材料的关系，YZ支撑的MFI型沸石分子筛膜的MFI结构在1000摄氏度后仍能保持，而Al2O3支撑的膜950摄氏度时已完全转变为石英相，研究结果表明，YZ支撑的MFI型沸石分子筛膜比Al2O3支撑的膜表现出更好的厌不性，热稳定性以及抗阻塞性。     

NaA沸石膜的制备及在一氯甲烷脱水中的应用

以氢氧化钠、铝酸钠和硅溶胶为原料,利用热浸渍提拉法预涂晶种,在孔径为2～3μm的亲水性α-Al2O3载体和孔径为800nm的疏水性炭载体上制备NaA沸石膜。借助于X射线衍射和扫描电子显微镜对合成的沸石膜进行了表征,采用单组分气体渗透法对NaA沸石膜的气体渗透性能进行了检测。结果表明:当H2渗透通量相近时,在亲水性α-Al2O3载体上制备的NaA沸石膜对H2/n-C4H10的分离因数为27.6,远远高于在疏水性炭载体上制备的NaA沸石膜的分离因数。NaA沸石膜在α-Al2O3载体上的生长速率为1.0μm/h,比在炭载体上生长速率快1倍,说明亲水性α-Al2O3载体更适合作为制备致密的强亲水性NaA沸石膜的载体。将在α-Al2O3载体上制备的NaA沸石膜用于一氯甲烷脱水实验,当进料水含量为0.252%(质量分数)时,水/一氯甲烷的分离因数为7.5×104。     

NaA型分子筛膜的水热合成与表征

采用水热合成技术,选择摩尔比为Na2OSiO2Al2O3H2O=321200的合成液,在孔径为2μmα-氧化铝陶瓷管内上合成了NaA型分子筛膜,经XRD、SEM等表征结果表明,所合成的为NaA型沸石膜,其厚度大约为15um.硅源和铝源的不同,对形成NaA型分子筛膜的影响很大;气体渗透表明,碱度降低有利于成膜,使膜的性能提高;增加合成次数有利于减少膜的缺陷,提高膜的气体分离性能.NaA型分子筛膜对H2、N2的渗透是以粘性流和努森扩散共同起作用.在系统压力(0.02～0.10MPa)下,H2透过膜的渗透率在5.5×10-7mol·m-2·s-1·Pa-1左右,膜管对H2/N2的理想分离因数分别在3.36左右,略低于对应的努森扩散因数3.74.     

沸石分子筛膜的应用与研究进展

介绍了NaA沸石分子筛膜的合成方法以及NaA沸石分子筛膜在液体分离、气体分离、催化反应,光学及光催化反应等高新技术领域的应用,提出了沸石分子筛膜面临的问题与挑战。     

清液体系中高性能T型沸石分子筛膜的合成

由摩尔组成为SiO2:Al2O3:Na2O:K2O:H2O=1:0.015:0.25:0.08:25的澄清溶液,在预涂晶种的管状莫来石支撑体上水热合成T型沸石分子筛膜.在高于100℃清液体系中合成出了高性能T型沸石分子筛膜.用X射线衍射(X-ray diffraction,XRD)仪和扫描电子显微镜(scanning electron microscope,SEM)对150℃下合成35 h的分子筛膜进行了表征.XRD谱表明:T型沸石分子筛成功地生长在预涂晶种的支撑体上.支撑体的外表面覆盖着20 μm厚有取向的晶体层.从SEM照片判断,起到分离作用的是生长致密的中间层,而不是表层.在150℃下制备的膜,对水/乙醇、水/异丙醇混合物具有高渗透汽化分离性能.优异的渗透汽化性能归因于在涂有晶种的多孔支撑体上生长了一层高结晶度且缺陷较少的T型沸石分子筛晶体层.     

在粗孔αAl2O3载体上合成NaA沸石膜

采用稀释的水玻璃作为分散介质配成0.5(ω)的NaA沸石悬浮液,对粗孔α-Al2O3(孔径3～5μm)载体管修饰并预涂晶种,进一步采取原位水热晶化法在((Al2O3载体管外表面制备NaA沸石膜. 重复合成5次后,在载体表面形成一层致密、连续的沸石晶体层. 由XRD确定该晶体为A型沸石,由SEM可观察到膜厚约15-20μm,膜表面上的沸石晶体大小约为3-5μm,晶体之间紧密孪生在一起,看不出晶间空隙. 制备的NaA沸石膜的H2渗透率为3.05×10-6 mol/(m2(s(Pa), 对H2/N2和H2/C3H8的理想分离因数分别为6.9和15.6,超过对应的努森扩散值3.74和4.69,说明所制备的NaA沸石膜具有分子筛分性能.     

PEA-NaA /α-Al2OPEA-NaA /α-Al2O3复合支撑分子筛膜的微波水热合成

采用微波水热合成法在聚醚酰亚胺(PEI)-NaA分子筛/α-Al2O3复合载体表面合成了具有高选择性的致密NaA型分子筛膜,重点考察了微波辐射时间对成膜的影响。采用X射线衍射图谱(XRD)和扫描电子显微镜(SEM)对NaA型分子筛膜进行了表征。XRD结果表明,复合载体表面生成的膜中只有NaA分子筛的晶相;SEM结果表明,复合载体基膜表面覆盖了一层致密连续的NaA型分子筛膜。合成的NaA型分子筛膜在不同质量分数乙醇中的渗透汽化性能结果表明,渗透通量随乙醇质量分数增大而减小,分离因子则反之,当乙醇质量分数为95%时,渗透通量仅0.05 kg/(m2.h),而分离因子高达13 000。     

NaA分子筛膜的制备及其用于醇水分离的研究进展

综述了NaA分子筛膜的制备方法及NaA分子筛膜在醇水分离应用中的最新研究进展和发展趋势.主要介绍了水热合成法、晶种法和微波加热法.总结了NaA分子筛膜制备过程的影响因素,包括支撑体及合成条件对分子筛膜醇水分离性能的影响.介绍了一些国外NaA分子筛膜工业应用情况.最后提出了我国NaA分子筛膜醇水分离方面工业应用的前景和需要进一步解决的问题.     

PEA-NaA /α-Al2OPEA-NaA /α-Al2O3复合支撑分子筛膜的微波水热合成

采用微波水热合成法在聚醚酰亚胺(PEA)-NaA分子筛/α-Al2O3复合载体表面合成了具有高选择性的致密NaA 型分子筛膜,重点考察了微波辐射时间对成膜的影响。采用X射线衍射图谱（XRD）和扫描电子显微镜（SEM）对NaA型分子筛膜进行了表征。XRD 结果表明,复合载体表面生成的膜中只有NaA 分子筛的晶相;SEM 结果表明,复合载体基膜表面覆盖了一层致密连续的NaA型分子筛膜。合成NaA型分子筛膜的渗透汽化性能和不同乙醇水溶液浓度对渗透汽化性能的影响的结果表明,渗透通量随乙醇溶液的浓度增大而减小,分离因子则反之,当乙醇溶液浓度为95%时,渗透通量仅0.05 kg/ (m2?h),而分离因子高达13000。     

NaA/MCM-41微介复合分子筛的合成与表征

按n(SiO2)∶n(Na2O)∶n(Al2O3)∶n(H2O)=1∶1.5∶0.5∶100加料,在90℃下水热晶化3 h合成NaA微孔分子筛,再按n(SiO2)∶n(NaOH)∶n(CTAB)∶n(H2O)=1∶0.3∶0.3∶90依次添加到NaA微孔分子筛中,于110℃下水热晶化24 h合成NaA/MCM-41微介复合分子筛,并采用XRD、SEM(EDS)和TEM等方法对其进行了表征。吸附阳离子红X-5GN模拟染料废水结果表明,在50 mLρ(阳离子红X-5GN)=20 mg/L的水溶液中,NaA/MCM-41微介复合分子筛的投加量为0.6 g/L、pH=6、振荡时间为60 min时,脱色率可达到96.4%,比NaA分子筛和MCM-41介孔分子筛独自吸附脱色效果要好。     

含甲基纤维素的NaA沸石膜的制备和表征

NaA沸石膜具有规则的孔道结构,利于分子传输,在有机物脱水领域有一定的应用。为使沸石膜生长更连续均匀,提高渗透汽化性能,本文以甲基纤维素作为空间限制剂加入合成液,探究碱度、晶化温度以及晶化时间对膜的影响,按最优条件制备合成液,并依据质量比m(MC)∶m(H₂O)=1∶100添加甲基纤维素,制备NaA沸石膜。表征方法采用XRD、SEM和渗透汽化3种方式,结果表明添加甲基纤维素的沸石膜表面结构完整,生长致密且性能优良,在75℃下对0.6mol/L的NaCl水溶液做渗透汽化测试时,通量达8.33kg/(m²·h),盐离子截留率为99.95%。在0.6mol/L的NaCl的水溶液中测试72h,结果表明添加甲基纤维素的NaA沸石膜时间依存性更好,通量保持在8.30kg/(m²·h)左右,离子截留率稳定在99.90%。渗透汽化分离ω(C₂H₆O)=90%乙醇的水溶液,随着温度从60℃升高到75℃,沸石膜的通量由1.55kg/(m²·h)升高到2.56kg/(m²·h),渗透侧水含量保持在99.90%左右。     

Synthesis of NaA and NaX Zeolite Membranes by Fumed Silica Via Clear Solution Gel

NaA zeolite membranes have been used for dehydration of organic solvents in laboratory and commercial scales. There are many synthesis methods and conditions for manufacturing the membranes. The use of lactescent and clear gel solutions are two of the most important choices for high quality hydrothermal synthesis of NaA zeolite membrane in gas separation or dehydration of organic solvents. In this article, effect of hydrothermal synthesis time was investigated using the clear gel solution (Al₂O₃:5SiO₂:50Na₂O:1000H₂O). Phase transformation from NaA to NaX was recognized as the most possible event when the clear gel solution was used. XRD spectra, SEM images, and GC analyses were used for evaluation of zeolite crystal phase, the membrane layer quality, and the contents of organic substances (ethanol or 2-propanol) in feed and permeate streams in pervaporation tests, respectively. From synthesis of zeolite membrane at different times, it was revealed that for achieving the pure NaA zeolite phase the synthesis time should not exceed 3 h at 100°C.     

Structure,stability and permeation properties of NaA zeolite membranes for H2O/H2 and CH3OH/H2 separations

NaA zeolite membranes were synthesised in the secondary growth hydrothermal method based on the seeding of the inner surface of a ceramic α-alumina tube. The impacts of crystallisation time and zeolite precursor concentration (in H₂O) were investigated. The structure and stability of the prepared NaA zeolite membranes were also investigated with operating temperatures, times and pressures. The results indicate that the optimal synthesis gel molar composition was 3Na₂O: 2SiO₂: Al₂O₃: 200H₂O. This led to cubic-shaped NaA zeolite which showed good stability. The optimal NaA zeolite membrane had H₂O and CH₃OH fluxes of 2.77 and 0.19 kg/m²h, with H₂O/H₂ and CH₃OH/H₂ separation factors of ∞ and 0.09 at a temperature of 30 °C. The NaA zeolite membrane had high thermal stability, but poor separation performance at high temperature (240 °C). The results suggested that the H₂ permeation flux is significantly influenced by preferential adsorption of vapour in the NaA zeolite membrane.     

Effect of cellulose buffer layer on synthesis and gas permeation properties of NaA zeolite membrane

NaA zeolite membrane coating was successfully synthesized on a porous alumina substrate by hydrothermal treatment. The effects of synthesis parameters like, seeding type (ex situ, in situ), time, temperature, sol concentration, coating stages, application of intermediate layer, etc. on membrane characteristics were investigated. A continuous membrane was formed on a seeded substrate. Surface seeding (ex situ crystallization) not only accelerates the zeolite crystallization process on the support surface, but can also enhance the formation of homogeneous NaA zeolite layer. The NaA zeolite membrane with a synthesis time of 4 h shows the best microstructure and the quality of membrane was improved by employing the multi-stage coating. But the main problem associated with membrane synthesis was crack formation, and it can be reduced by applying intermediate layer, between support surface and seed layer. A thin cellulose layer was applied to the support surface before applying seed crystals. The performance of the membranes was evaluated by gas permeation measurement. The permeance of O₂, N₂ decreased as kinetic diameter of gases increased. The permselectivity of O₂/N₂ was 1.9–2.34. This value showed the molecular sieving effect of NaA zeolite membrane.     

Enhancement of NaA zeolite membrane properties through organic cation addition

Thin NaA zeolite membranes, with uniform and small crystals, were prepared on the tubular -Al₂O₃ support by adding a small amount of tetramethylammonium hydroxide (TMAOH) in the clear synthesis solution. The as-synthesized NaA zeolite membranes were characterized by XRD and SEM. The permeation properties of the membranes were evaluated by pervaporation and gas permeation. The effects of TMAOH amount on membrane formation and permeation properties were investigated. By addition of suitable amount of TMAOH in the clear synthesis solution, the crystals size of NaA zeolite could be remarkably reduced from about 10 μm to 3–4 μm, and the membrane thickness correspondingly reduced from about 16 μm to 5 μm. The thinner membrane prepared by adding TMAOH in the clear synthesis solution, with uniform and small crystal, displayed higher perm-selective properties than that without adding TMAOH. For the as-synthesized NaA zeolite membrane prepared with adding suitable amount of TMAOH (x = 1), the separation factor (water/isopropanol) was 4700 and the flux was 1.67 kg/(m² h), which were higher than that without adding TMAOH of 339 and 1.08 kg/(m² h), respectively. The ideal separation factor of H₂/N₂ was 6.60, higher than that without adding TMAOH of 3.41.     

Scale-up of NaA zeolite membranes onα-Al2O3 hollow fibers by a secondary growth method with vacuum seeding

NaA zeolite membranes were prepared by secondary growth method on the outer surface ofα-Al2O3 hollow fiber supports. Vacuum seeding method was used for planting zeolite seeds on the support surfaces. Hydrother-mal crystallization was then carried out in a synthesis solution with molar ratio of Al2O3:SiO2:Na2O:H2O=1:2:2:120 at 100 °C for 4 h. Effects of seeding conditions on preparation of hollow fiber NaA zeolite membranes were extensively investigated. Moreover, hollow fiber membrane modules with packing membrane areas of ca. 0.1 and 0.2 m2 were fabricated to separate ethanol/water mixture. It is found that the thickness of seed layer is obviously affected by seed suspension concentration, coating time and vacuum degree. Close-packing seed layer is required to obtain high-quality membranes. The optimized seeding conditions (seed suspension mass concentration of 0.5%–0.7%, coating time of 5 s and vacuum degree of 10 kPa) lead to dense NaA zeolite layer with a thickness of 6–8μm. Typically, an as-synthesized hollow fiber NaA zeolite membrane exhibits good pervaporation performance with a permeation flux of 7.02 kg·m?2·h?1 and separation factor N 10000 for sepa-ration of 90%(by mass) ethanol/water mixture at 75 °C. High reproducibility has been achieved for batch-scale production of hollow fiber NaA zeolite membranes by the hydrothermal synthesis approach.     

The effect of intermediate layer on synthesis and gas permeation properties of NaA zeolite membrane

NaA zeolite membrane coating was successfully synthesized on an alumina porous disc by hydrothermal treatment. The effects of synthesis parameters, such as seeding condition (in situ, ex situ), synthesis time, synthesis stages, application of intermediate layer, etc., on membrane characteristics were investigated. Surface seeding accelerates the zeolite crystallization process on the support surface, and also enhances the formation of homogeneous NaA zeolite layer. But the main problem associated with membrane coating synthesis is crack formation. Formation of crack was reduced by applying intermediate layer, between the support surface and seed layer. A thin Boehmite layer was applied to the support surface before applying seed crystals to enhance the adherence between zeolite seed layer and boehmite layer by hydrogen bonding and also to increase the mechanical strength of the membrane layer. The quality of the membrane layer can be improved by employing the multi-stage coating methods. The permeance of O₂, N₂ decreased as kinetic diameter of gases increased, which shows the molecular sieving effect of the NaA membrane. The permselectivity of O₂/N₂ was 1.9–2.0. This value of permselectivity ratio is higher than Knudsen diffusion ratio 0.94; it was also confirmed the molecular sieving properties of synthesized NaA zeolite membrane.     

在粗孔a-Al_2O_3载体上合成NaA沸石膜

采用稀释的水玻璃作为分散介质配成0.5%(w)的NaA沸石悬浮液,对粗孔a-Al2O3(孔径3~5 mm)载体管修饰并预涂晶种,进一步采取原位水热晶化法在a-Al2O3载体管外表面制备NaA沸石膜. 重复合成5次后,在载体表面形成一层致密、连续的沸石晶体层. 由XRD确定该晶体为A型沸石,由SEM可观察到膜厚约15~20 mm,膜表面上的沸石晶体大小约为3~5 mm,晶体之间紧密孪生在一起,看不出晶间空隙. 制备的NaA沸石膜的H2渗透率为3.0510-6 mol/(m2sPa), 对H2/N2和H2/C3H8的理想分离因数分别为6.9和15.6,超过对应的努森扩散值3.74和4.69,说明所制备的NaA沸石膜具有分子筛分性能.