【作者】 郎林；

【导师】 张宝泉；

【作者基本信息】 天津大学 ， 工业催化， 2009， 博士

【摘要】 分子筛膜具有可调控的微孔结构、可调变的催化活性、优良的稳定性,被广泛应用于分离、催化、光电材料、化学传感器等诸多领域。MFI型分子筛具有三维孔道结构,孔径约为0.55 nm,适于分离许多重要的工业原料;且具有优良的择形催化性能,可以催化大多数C6以下烃类物质的部分氧化反应,因而MFI型分子筛膜是最具开发潜力的分子筛膜之一。由于MFI型分子筛具有各向异性的孔道结构,其不同取向分子筛膜内的纳米级孔道结构的差异较大,会严重影响分子筛膜的分子筛分效果和催化性能,因而近年来MFI型取向分子筛膜的制备与应用越来越受到人们的重视。本文以纯硅MFI型取向分子筛膜和含过渡金属杂原子的Fe-MFI型取向分子筛膜的制备为核心,重点研究了分子筛膜微观纳米结构的差异对其宏观分离性能和催化作用的影响。首先考察了多孔载体表面结构和化学性质对原位合成纯硅MFI型分子筛膜的影响,证实分子筛膜的取向和完备性主要受载体表面化学性质影响。采用壳聚糖进行表面化学改性可使载体表面富集功能基团,诱导分子筛晶体的定向生长,有利于b-轴取向分子筛膜的形成。实验中采用高分辨TEM和原位高压DSC技术,考察在壳聚糖薄膜上生长b-轴取向分子筛膜的过程,全面地阐释了纯硅MFI型分子筛膜的原位成膜机理。进而从成膜机理出发,开发出新型两步法二次合成工艺,该法可直接在大孔α-Al₂O₃载体上实现分子筛膜取向的调控。采用这种合成方法,在随机取向silicalite-1晶种层上,在150℃条件下可制备出硅铝比极高的h0h取向silicalite-1分子筛膜,在180°C条件下则合成出c-轴取向silicalite-1分子筛膜。实验中发现在合成液中引入Fe3+离子有利于分子筛膜的面内定向生长,分别在随机取向和b-轴取向的silicalite-1或Fe-ZSM-5晶种层上,制备出h0h取向和b-轴取向的Fe-silicalite-1或Fe-ZSM-5分子筛膜。采用新发明的低温煅烧脱除模板剂工艺可有效避免分子筛膜缺陷的形成,显著提高Fe-silicalite-1分子筛膜对乙醇/水混合液的渗透蒸发性能。与b-轴取向分子筛膜相比,h0h取向分子筛膜更有利于乙醇/水混合液的分离,该膜可突破乙醇/水共沸点的限制,在60℃下直接将5 wt.%的乙醇水溶液提纯至乙醇浓度至96.4 wt.%,其乙醇/水分离因子高达530。此外,本文还将h0h取向的Fe-ZSM-5分子筛膜应用于相接触式膜反应器,针对苯酚羟基化反应,考察了传统浆化床反应器和催化膜反应器在催化性能上的差异。实验证实了催化膜反应器可以充分利用分子筛孔道内的活性中心,这种接触方式和反应路径的改变可以极大提高反应的转化率和选择性。更多还原

【Abstract】 Zeolite membranes have advantages such as precisely defined pore structure,controllable catalysis-based characteristics and high stability, which could enable applications in gas or liquid separations, catalytic membrane reactors, photoelectric materials, and host for chemical sensors. MFI zeolite crystal （ZSM-5） has a two -dimensional system of intersecting channels with subnanometer pore size （0.55nm）. Because of its unique molecular sieving effect and selectively catalytic performances, MFI zeolite membrane can be used for separation of many industrially important compounds and catalysis of the partial oxidation of C1 to C6 hydrocarbons. Thus, MFI zeolite membranes are considered as one of the most potential zeolite membranes. Thanks to its anisotropic pore structure, the oriented nanometer-sized pore network of constituent microcrystals in a MFI zeolite membrane can significant- ly affect its molecular sieving effect, and permeation and catalytic performances, which are crucial for practical applications in various fields. In recent years, therefore, there has been growing interest in the preparation and applications of oriented MFI zeolite membranes.The core of this thesis is to prepare the oriented pure-silica MFI and the oriented transition metal hetero-atom Fe-MFI zeolite membranes. Much attention has been paid to the relation between the nanometer-sized zeolitic pore network in a MFI zeolite membrane and its permeation and catalytic performances. The effect of the microstructure and chemistry of the porous substrate surface on the growth of zeolite film was firstly invesitigated in detail, which confirmed that the orientation and microtructure of Si-MFI zeolite films onα-Al2O3 supported silica-zirconia layers were dominantly controlled by the chemical nature of the substrate surface. The abundance of organic functional groups could be successfully seeded onto the substrate surface by modification, where the functional groups served as the structure-directing matrix to induce the orientation and growth of the zeolite crystals with their b-axes perpendicular to the substrate surface.In the present study, we firstly fabricated a close-packed b-oriented monolayer Si-MFI film supported by a thin chitosan film, and provided the direct, specific high-resolution TEM and high-press DSC evidence to illustrate the true evolution of zeolite films during in-situ hydrothermal synthesis. This approach gives us a unique opportunity to explain the self-assembly mechanism of pure-silica MFI crystals on the surface of the chitosan film during in-situ crystallization.Based on the formation mechanism of zeolite membrane, a novel twice seeded growth synthesis procedure was proposed to fabricate oriented zeolite films onα-Al2O3 substrates directly. On the randomly oriented silicalite-1 seed layers, thin, continuous and h0h-oriented silicalite-1 membranes with an extremely high Si/Al ratio could be prepared at 150℃, and thick, dense and c-oriented silicalite-1 membranes could be obtained at 180℃. It was found that Fe³⁺ ions in the synthesis solution could be favourable to the intergrowth of MFI zeolite crystals along the in-plane direction. We have fabricated h0h-oriented and b-oriented Fe-silicalite-1 or Fe-ZSM-5 membranes on randomly oriented and b-oriented silicalite-1 or Fe-ZSM-5 seed layers, respectively.A unique low-temperature calcination technique was adopted in this thesis, which could quite efficient to restrain the formation of open grain boundaries and cracks during the template removal. This method can dramatically improve the pervaporation performance of Fe-silicalite-1 membranes for ethanol/water mixtures. Compared with the b-oriented membrane, the h0h-oriented Fe-silicalite-1 membrane was more suitable to the separation of ethanol/water mixtures. It could exceed the ethanol/water azeotropic point, directly concentrate the 5 wt.% ethanol/water fermentation broths to over 96 wt.% bio ethanol, and the ethanol/water separation factor could reach to as high as 530 at 60oC.In order to investigate the advantage of catalytic membrane reactions, the highly h0h-oriented Fe-ZSM-5 membranes were utilized in a modified interphase membrane reactor. The hydroxylation of phenol catalyzed by Fe-ZSM-5 using H2O2 as oxidant was investigated in the traditional slurry reactor and the interphase membrane reactor, respectively. Compared with the catalytic performance of Fe-ZSM-5 crystal grains loaded in the traditional slurry reactor, the use of the h0h-oriented Fe-ZSM-5 membrane in the interphase membrane reactor gives rise to a pretty high conversion for phenol and 100% selectivity for catechol and hydroquinone.更多还原