一维孔结构沸石的传质特性研究

发布时间：2018-07-28 16:07

【摘要】：近年来,丝光沸石和EU-1沸石因其独特的结构优势和优良的水热稳定性而在催化领域中应用广泛,如将丝光沸石应用于烷烃与芳烃异构化领域,将EU-1沸石用作二甲苯异构化反应催化剂等。这两种沸石分子筛在精细化工、石油化工等领域均具有潜在的巨大的应用价值。并且丝光沸石及EU-1沸石均为一维孔道结构的沸石,这种结构特色即使其具有一定的择形选择功能,又会衍生传质问题而限制它们的进一步应用。因此,多级孔丝光及EU-1沸石也相继被开发出来。对于一个催化反应,反应物以及产物分子的吸附与扩散在其中扮演着十分重要的角色。因此,对吸附质分子在沸石孔道内吸附与扩散性能的研究将有助于优化催化反应过程。一些热力学和动力学数据的计算和分析对于沸石分子筛催化剂的设计、制备以及更好的应用具有一定的指导意义。目前集中在丝光及EU-1沸石上的研究主要还是在制备及催化方面,对这种结构如此有特色的沸石,其吸附和扩散性能却几乎没有相关报道。为了探究这类具有一维孔道结构的沸石,其吸附与扩散机制的独特性,以及中孔的引入对这类沸石吸附与扩散性能的影响,本文选取了甲苯及均三甲苯为探针分子,探究了多级孔丝光及EU-1沸石上的吸附与扩散性能,以期能够为多级孔丝光及EU-1沸石的评价、应用以及制备奠定理论基础。本论文的研究内容及主要结论如下:1.甲苯及均三甲苯在多级孔丝光沸石中的吸附与扩散甲苯可以吸附进入丝光沸石的微孔孔道,但是脱附异常困难,需高温方可脱附出来。均三甲苯不能进入丝光沸石的微孔孔道,但可在多级孔丝光样品中进行吸附,说明中孔的引入有利于提高大分子的可接近性。甲苯与均三甲苯在微孔丝光沸石中的吸附主要表现为化学吸附的特征,而在多级孔丝光沸石中,为物理吸附。甲苯在丝光样品中的TPD实验证明了,丝光沸石中确实存在着作用力不同的两种吸附中心,一种吸附作用力相对较弱,另一种则作用力较强。双位Toth模型可以很好地描述甲苯在多级孔丝光沸石中的吸附行为,拟合参数表明中孔有利于促进吸附,且减弱了甲苯分子与吸附剂间相互作用力。吸附动力学实验结果说明中孔的存在为吸附质分子缩短了扩散路径,提高了分子的传质速率。2.甲苯及均三甲苯在多级孔EU-1沸石中的吸附与扩散甲苯在微孔EU-1沸石中的吸附等温线为I型等温线,而在对应多级孔EU-1沸石中为I型和IV型复合等温线。均三甲苯不能进入EU-1沸石的微孔孔道,但可以进入多级孔EU-1的中孔,说明中孔的引入有利于提高大分子的可接近性。当吸附质分子仅吸附在EU-1沸石表面时,为物理吸附,而进入沸石的微孔孔道中后,由于分子受到强烈的扩散限制,则会表现为化学吸附的特征。采用双位Toth模型对甲苯在多级孔EU-1沸石中的吸附等温线进行拟合,拟合效果较好。相关参数分析表明,中孔引入有利于提高吸附量,且对于EU-1-3样品,中孔的引入打开了侧袋结构,使甲苯在微孔区和中孔区的吸附量均显著增加。吸附动力学研究表明中孔的存在有利于提高分子在EU-1沸石中的传质过程。
[Abstract]:In recent years, mordenite and EU-1 zeolite have been widely used in the field of catalysis because of their unique structural advantages and excellent hydrothermal stability. For example, mordenite is used in the field of alkanes and aromatics isomerization, and EU-1 zeolite is used as a catalyst for the isomerization of xylene. These two kinds of boiling stone molecular sieves are in the fields of fine chemical, petrochemical and other fields. Both mercerite and EU-1 zeolite are one of the one-dimensional pore structure zeolite. This structure characteristic, even if it has a certain shape selection function, will also limit the further application of mass transfer. Therefore, multistage mercerized and EU-1 zeolite have been developed successively. The adsorption and diffusion of chemical reactions, reactant and product molecules play a very important role. Therefore, the study of adsorption and diffusion properties of adsorbate molecules in the pore of zeolite will help to optimize the catalytic reaction process. Some thermodynamic and kinetic data calculation and analysis are designed for zeolite catalysts. Preparation and better application have certain guiding significance. The research focused on mercerized and EU-1 zeolite is mainly in preparation and catalysis. The adsorption and diffusion properties of this kind of zeolite with such a characteristic structure are hardly reported. In order to explore the adsorption and diffusion of zeolite with one-dimensional pore structure, the adsorption and diffusion of zeolite have been investigated. The uniqueness of the mechanism and the influence of the introduction of mesopore on the adsorption and diffusion properties of this type of zeolite. In this paper, toluene and three toluene are selected as probe molecules to explore the adsorption and diffusion properties of multistage orifice mercerizing and EU-1 zeolite, in order to lay a theoretical foundation for the evaluation, application and preparation of multilevel oropes and EU-1 zeolites. The contents and main conclusions are as follows: 1. the adsorption and diffusion of toluene and three toluene in the multistage mordenite can be adsorbed into the micropore of mordenite, but the desorption is difficult and the high temperature can be removed. All three toluene can not enter the micropore of mordenite, but it can be used in the multistage pore mercerizing sample. The introduction of the mesopore is helpful to improve the accessibility of the macromolecules. The adsorption of toluene and three toluene in the microporous mordenite is mainly characterized by chemical adsorption, while in the multistage mordenite, it is a physical adsorption. The TPD experiment in the mercerized sample of toluene has proved that there is a real force in mordenite. Two different adsorption centers, one kind of adsorption force is relatively weak, the other is stronger. The two bit Toth model can well describe the adsorption behavior of toluene in multistage mordenite. The fitting parameters show that the pore is beneficial to promote adsorption and weaken the interaction force between toluene molecules and adsorbents. Adsorption kinetics experiment. The results show that the existence of mesopore shortens the diffusion path for adsorbate molecules, improves the mass transfer rate of.2. and three toluene in multistage pore EU-1 zeolite, and the adsorption isotherm of toluene in microporous EU-1 zeolite is I isotherm, while I and IV type compound isotherms in the corresponding multistage EU-1 zeolite are both three. Toluene can not enter the micropore of the EU-1 zeolite, but it can enter the mesopore of the multistage hole EU-1, indicating that the introduction of the mesopore is beneficial to the improvement of the accessibility of the macromolecules. When the adsorbate molecules adsorb only on the surface of the EU-1 zeolite, they are physically adsorbed and enter the pore channels of the zeolite. For the characteristics of chemical adsorption, the adsorption isotherm of toluene in the multilevel pore EU-1 zeolite was fitted by two bit Toth model. The fitting effect was good. The analysis of related parameters showed that the introduction of mesopore was beneficial to the increase of adsorption capacity, and the side bag structure was opened for the introduction of EU-1-3 samples and the mesopore was introduced, and the adsorption amount of toluene in the microporous and mesoporous areas was made. The adsorption kinetics showed that the existence of mesopores improved the mass transfer process of EU-1 in zeolites.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ424.25

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