支撑体材料对NaA型沸石分子筛膜形成的影响

采用水热合成法制备NaA型沸石分子筛膜,实验比较了α-AI2O3、ZrO2及TiO2三种支撑体对NaA型沸石分子筛膜形成的影响。XRD测定所合成的沸石分子筛膜是NaA型。SEM和渗透实验结果表明,沸石分子筛膜的性能与支撑体有关,TiO2优于ZrO2和α-AI2O3。TiO2支撑体上合成沸石分子筛膜的H2、N2渗透系数大小基本与膜两侧平均压力无关,理想分离系数约为8,高于Kundsen扩散分离因子3．74,表现有一定的分子筛分效应。     

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.     

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.     

NaA型分子筛膜合成及应用进展

介绍了NaA型分子筛膜在合成及应用方面的研究进展,重点介绍了NaA型分子筛膜在渗透汽化分离方面的实际应用,展望了NaA型分子筛膜的应用前景。     

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.     

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。     

高性能Na A沸石膜的放大制备及表征

采用二次生长水热合成法,在廉价的大孔α-Al2O3载体上(长度为800 mm,外径为12 mm,平均孔尺寸为2～5μm)成功制备高分离性能NaA沸石膜。通过XRD和SEM等表征方法对制备的NaA沸石膜的分子筛晶体与表面形貌进行表征,并对其渗透汽化性能进行测试,在操作温度为75℃、真空度为500～700 Pa的条件下,对乙醇含量为90%(wt)的乙醇/水体系进行分离,渗透通量大于2.0 kg·m-2·h-1且分离系数在8 000以上。表征和测试结果表明,制备的NaA沸石膜表面晶体结晶度高、连续致密且重复性高。     

Preparation of NaA Membrane and Application on Dehydration of Chloromethane

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.     

在粗孔a–Al2O3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3.05′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。     

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.     

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.     

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.     

Ultrasonic treatment of polyacrylic acid sodium/NaA zeolite hybrid membranes for the pervaporation dehydration of ethanol

Ultrasonics was used to improve the dispersion of NaA zeolite in polyacrylic acid sodium (PAAS) membranes. The effect of ultrasonication time on the dispersion of NaA zeolite in the membranes, the membrane structure, and performance were investigated. The casting solution and resulting membranes were characterized by viscosity measurement, polarizing optical microscopy (POM), scanning electron microscopy, and X‐ray diffraction (XRD). With increasing ultrasonication time, the viscosity of the casting solution decreased as the chain entanglements decreased. The POM and XRD results showed that crystallization occurred in the PAAS membrane after ultrasonic processing. A more homogeneous morphology was obtained due to improvement in the dispersion of zeolite under ultrasonic treatment for 0.5–1.0 h. As a result, the separation performance was enhanced. The water/ethanol separation factor increased from 176.2 to 577.8. However, the relative separation factor decreased when the ultrasonic time exceeded 2.5 h, due to the appearance of a lamellar structure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3979–3984, 2013     

T型分子筛膜的制备及其对含酸乙腈-水的分离性能

石化医药行业会产生大量乙腈废液,通过无机分子筛膜分离技术进行回收可以创造可观的经济价值。然而,乙腈废液水含量较高,并且具有一定的酸性,目前应用比较广泛的NaA型分子筛膜不能在该体系下长期使用。使用自制的平均粒径为600 nm的T型分子筛作为晶种,采用真空涂敷法将晶种负载在α-Al₂O₃载体管表面,在150 ℃下水热晶化16 h制备出T型分子筛膜,并对其做膜性能评价实验。结果表明,自制的T型分子筛膜在进料流量为3.5 L/h、温度为100 ℃条件下对含有1%（质量分数）乙酸和10%水（质量分数）的乙腈混合溶液进行膜分离脱水实验,渗透通量为2.51 kg/（m ²·h）;在120 h长时间运行过程中,分离系数保持在2 250以上,T型分子筛膜性能基本保持不变。     

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。     

Maxwell-Stefan理论模拟NaA沸石膜分离一氯甲烷中微量水的渗透特性

通过热浸渍晶种法制备了高质量的NaA沸石膜,并将其应用于蒸汽渗透脱除一氯甲烷中的微量水. 实验结果表明,NaA膜对该体系显示了优异的分离性能,水对一氯甲烷的分离系数高达74831,产品中的水含量从0.2582%(w)降低到0.005%(w). 将基于Maxwell-Stenfan理论和Langmuir理想吸附理论推导的吸附-扩散模型用于模拟水渗透流速与渗透侧真空度和进料温度的关系,预测趋势与实验值吻合很好,且拟合得到的参数与文献报道较接近,表明水蒸汽在NaA沸石膜中的传递为表面扩散机制,水蒸汽的吸附对渗透速率的贡献很大. 水蒸汽的吸附热为-34.15 kJ/mol.     

Recent advances in acid-resistant zeolite T membranes for dehydration of organics

Zeolite membranes offer outstanding potentials in separation of many molecular mixtures due to their molecular sieving selectivity and the high thermal and mechanical stability that allow them to operate at harsh conditions.Development of durable and high separation performance membranes with lower fabrication and operation cost are highly demanded for industrial applications. Zeolite T membrane possesses good acid-resistance with excellent hydrophilic properties as compared to NaA zeolite membrane and can be extended to industrial organic dehydrations under an acidic environment. In the present review the research advances in development of zeolite T membranes for the dehydration of organic mixtures in acidic conditions are summarized. Especially the low temperature synthesis, and epitaxial growth of the zeolite membrane with high performance are well addressed, besides emphasis is particularly placed on ensemble synthesis of hollow fiber zeolite T membrane module and its future prospects for industrial separations.