【作者】 彭勇；

【导师】 严玉山； 王正宝；

【作者基本信息】 浙江大学 ， 工业催化， 2013， 博士

【摘要】 沸石分子筛膜由于其优异的性能引起了人们的普遍关注,其中以MFI型分子筛膜的研究最为广泛和深入,在分离、催化等领域中具有重要潜在应用价值。但是,目前MFI分子筛膜一般需在小孔径(≤1.0μm)、表面无缺陷的载体上制备；b轴取向膜的制备需要在预先涂覆介孔中间层的载体上进行,涂晶过程复杂。本论文采用大孔性的多孔氧化铝管和多孔玻璃管为载体,设计了新型的晶种涂覆方法和新颖的合成方式,简便高效地制备了(b轴取向)MFI分子筛膜,并进行了分离性能的测试。(1)低成本大孔氧化铝管载体上MFI分子筛渗透汽化膜的制备及分离性能本论文构建了一种新型的溶剂润湿辅助擦涂涂晶法。采用低成本、表面存在大洞缺陷的大孔氧化铝管(平均孔径1～3μm)为载体,预先将该载体于溶剂中润湿,然后在其外表面擦涂MFI分子筛晶种粉末。对比并分析了水、正丁醇、乙醇、正丙醇等不同的润湿试剂对涂晶效果和膜分离性能的影响,结果表明,醇特别是正丁醇是一种非常有效的润湿试剂,可以在这种低成本的大孔氧化铝管载体上制备均匀无缺陷的MFI分子筛晶种层,再通过二次水热合成法制备了无缺陷的MFI分子筛膜。测试了其对60℃下质量分数为5%的乙醇/水混合溶液的渗透汽化分离性能,结果表明,175℃下合成仅4h的MFI分子筛膜,分离因子和通量分别高达62和1.82kg m-2h-1。该涂晶方法所合成的MFI分子筛膜重复性高,且可放大用于长载体(20cm)上膜的制备。探讨了二次水热条件对MFI分子筛膜的微观结构及其分离性能的影响。目前,人们对二次合成的条件与膜的微观结构,以及微观结构与膜的分离性能的关系并不十分清楚。本论文详细考察了二次合成过程中的重要参数如碱度、模板剂浓度等的影响,采用SEM-EDX.水接触角测试、气体透过、单组份渗透汽化等手段深入表征了MFI分子筛膜的结构性质,并测试了MFI分子筛膜的乙醇/水分离性能。结果表明,MFI分子筛膜焙烧后的致密性是影响其分离性能的关键因素。当合成液中TPA+/TEOS比为0.17时,二次合成得到的MFI分子筛膜层中会产生较多的孪晶,这些孪晶在焙烧过程中会导致膜缺陷的产生,降低了MFI分子筛膜的致密性。当TPA+/TEOS比降低至0.05以下时,MFI分子筛膜层中孪晶的数量大大减少,从而避免了焙烧过程中膜缺陷的产生,膜的致密性大大提高,其对乙醇／水的渗透汽化分离性能也进一步提高,在通量大于1.00kg m-2h-1时,MFI分子筛膜的分离因子高达80以上。(2)多孔玻璃表面b轴取向MFI分子筛膜的制备本论文直接在孔径为0.1μm的多孔玻璃载体上原位水热合成b轴取向MFI分子筛膜。将多孔玻璃完全浸没于合成液中,难以得到连续的膜层。部分浸入合成液时,在露出的多孔玻璃表面获得了b轴取向MFI分子筛膜,靠近液面的表面膜比较致密,越向上越稀少。据此,我们提出由于载体孔的毛细作用力将合成液吸引至露出部分的载体表面,形成一层合成液液膜,该液膜在合成过程中形成了取向膜。通过系统地调变合成液配方以及合成时间等相关参数,得到了适宜的合成条件,当合成配比为0.64TPAOH:1TEOS:165H2O时,部分浸入165℃下合成3h,可以在多孔玻璃表面形成大面积连续的b轴取向MFI分子筛膜。延长合成时间至6h,载体上的膜层连续致密,但是呈现随机取向。研究还发现在气泡处的多孔玻璃表面获得了非常致密的b轴取向膜。这对原位水热合成b轴MFI分子筛膜具有指导意义。构建了一种新颖的、简单有效的取向晶种层印刷转移技术,在多孔玻璃载体上二次水热合成连续致密的b轴取向MFI分子筛膜。预先在印刷载体(如保鲜膜)上采用手工自组装的方式涂覆一层b轴取向MFI晶种层,再将其包裹在多孔玻璃表面,取向晶种层即被印刷于载体上,二次生长时合成液从载体管内侧渗透到晶种层,晶种长大连生后即形成连续的b轴取向MFI分子筛膜。通过对比不同材质的保鲜膜的影响,发现聚甲基戊烯(PMP)保鲜膜是一种合适的印刷载体。在此基础上,进一步优化了二次水热合成的方式以及合成液配方等,结果表明,通过两步合成法,能够提高所合成的b轴取向MFI分子筛膜的致密程度,同时也大大增强了膜层和载体之间的相互结合力。采用该方法制备的b轴取向MFI分子筛膜对于对邻二甲苯／对二甲苯混合物表现出了一定的分离性能,该制膜方法值得进一步深入研究。更多还原

【Abstract】 Zeolite membranes, due to their unique properties, have been attracted a great deal of research interests worldwide. Among all of these membranes, the most intensively investigated is the MFI-type zeolite membrane. It has been targeted for potential applications in many research fields such as separation and catalysis. At present, however, MFI zeolite membranes are usually prepared on small pore (≤1.0μm) and defect-free supports. b-oriented MFI zeolite membranes should be prepared on supports with pre-coated mesoporous intermediate layer, and the seeding process is also complex. In this dissertation, macroporous alumina tubes and glass tubes are investigated as membrane supports. Novel seeding methods and synthesis strategies are proposed to facilely and effectively prepare (b-oriented) MFI zeolite membranes, and there separation performances are also investigated.(1) Preparation of zeolite MFI pervaporation membranes on low-cost macroporous alumina tube support and their separation performanceWe developed a novel seeding method of wetting assisted rub-coating technique. Low-cost, macroporous alumina tubes (average pore size:1～3μm) with many large "holes" are employed as membrane supports. With this new method, support outer surface is first wetted with a liquid agent followed by rubbing dry MFI seed crystals. Effects of many wetting agents such as H2O, n-butanol, ethanol, and n-propanol on the seed layer formation and membrane performance are investigated. Experimental results show that alcohol wetting liquid, especially n-butanol, is much more effective for preparation of a uniform and defect-free MFI seed layer on the defective alumina support. The zeolite MFI membranes synthesized at175℃for only4h on the well-seeded supports exhibit a high pervaporation performance with the ethanol/water separation factor of62and permeation flux of1.82kgm-2h-1for the5wt.%ethanol/water mixture separation at60℃. The reproducibility of MFI zeolite membranes synthesized by this novel seeding method is very high. The seeding method can be extended to prepare MFI zeolite membrane on the alumina support of20cm length. The effects of secondary hydrothermal growth conditions on the micro-structure and separation performance of as-synthesized MFI zeolite membranes are investigated. At present, the relationship between secondary growth condition and membrane micro-structure, and membrane micro-structure and separation performance are not very clear. We investigate several important parameters in secondary growth such as alkalinity, template concentration. SEM-EDX, water contact angle test, gas permeation, and single component pervaporation are used to characterize the membrane structure properties in detail. It is found that the dense degree of template-removed MFI zeolite membrane is the key factor influencing membrane pervaporation performance. When the TPA+/TEOS ratio of the synthesis solution is0.17, many twin crystals can be found in the synthesized membrane layer. These twin crystals results in the formation of cracks during calcination process. Then the membrane denseness is significantly reduced. When the TPA+/TEOS ratio is decreased to lower than0.05, twin crystals are suppressed and therefore the formation of defects during calcination is significantly eliminated. Thus the pervaporation performance of zeolite MFI membrane is further improved. The ethanol/water separation factor is higher than80when the flux is higher than1.00kg m-2h-1.(2) Preparation of b-oriented MFI zeolite membrane on porous glass supportHere b-oriented zeolite MFI membranes are prepared directly on porous glass support with pore size of～0.1μm by in situ hydrothermal synthesis method. It is difficult to obtain continuous MFI zeolite membrane if the porous glass is immersed in the synthesis solution completely. When the support is partly immersed in the synthesis solution,b-oriented zeolite MFI membrane is obtained on the un-immersed part of the support. The membrane obtained near the synthesis solution level is much denser, while the membrane obtained on the top of the un-immersed support is much looser. We therefore propose that the un-immersed support surface can be covered by the synthesis solution film through the capillary force that occurred in the support pores. Then the synthesis solution film is crystallized during the secondary synthesis process, thus the b-oriented membrane is obtained. The preparation parameters such as the synthesis solution composition and crystallization time are systematically investigated. Under the optimized synthesis condition (0.64TPAOH:1TEOS:165H2O,165℃,3h),b-oriented zeolite MFI membrane with high coverage is achieved on support surface. When the crystallization time is extended to6h, the support can be fully covered by zeolite MFI membrane, however, the membrane is randomly oriented. We also find that dense b-oriented zeolite MFI membrane with a cycle shape can be obtained on the support nearing the bubble place. These results can provide guidelines for the mechanism research of b-oriented zeolite MFI membrane formation by in situ hydrothermal synthesis.We developed a simple yet effective oriented (MFI crystal) seed printing-transfer technique to prepare continuous and dense b-oriented zeolite MFI membrane on porous glass support by secondary growth. With this technique, a monolayer b-oriented MFI seeds is prepared on the printing support (e.g., wrap film) by manual assembly. Then the outer surface of the porous glass is wrapped by this seeded wrap film, and therefore the oriented seed crystals are printed on the porous glass. During secondary growth, the synthesis solution permeated to the seed layer from the inner side of the support and then continuous b-oriented zeolite MFI membrane is obtained. Many kinds of wrap films such as PMP, PVDC, and PE are investigated as printing supports. Using these wrap films, the quality of seed layer and the dense degree of synthesized b-oriented zeolite MFI membrane are compared in detail. It is found that PMP wrap film is the most effective printing support. The secondary growth strategies and synthesis solution compositions are then optimized. We find that, by using two-step secondary growth method, the dense degree of b-oriented zeolite MFI membrane can be improved and the interaction between membrane layer and support is highly strengthened. The synthesized oriented MFI membrane exhibits certain separation performance for the p-/o-xylene mixture. This membrane manufacturing technique deserves further research.更多还原