纳米沸石及其在有机微球模板上的组装制备大孔沸石

发布时间：2018-08-24 13:52

【摘要】：在可预见的未来,化石能源将仍然是人类能源供应的主要组成部分,伴随着目前原油的过度开采和使用,未来原油供应中,原油重质化和劣质化的趋势不可避免,因此,优化目前的石油炼化工艺成为目前亟待解决的技术问题。沸石类催化剂以其高的比表面积、均匀的微孔结构、可调控的酸性能以及良好的稳定性成为石油化工领域中最重要的催化材料,被广泛的应用于催化裂化、烷基化和异构化。然而,其狭窄的微孔孔道导致了物质在孔道内的扩散限制,因此,缩短微孔内的扩散路径和增大沸石催化材料的外表面积成为目前沸石材料的主要研究方向。解决上述沸石材料所存在的缺陷主要有两种方法:一种是通过减小沸石晶粒的尺寸,制备具有纳米尺寸的沸石分子筛,得到高的外比表面积和短的微孔长度；另一种是通过在沸石结构中引入多级孔结构,即在微孔沸石的基础上引入介孔或大孔,增加活性位的可接近性。这两种解决方法同样存在一定的局限性:纳米沸石颗粒过小回收困难,而多级孔沸石则大多受制于其高昂的制备成本。本论文致力于以廉价的有机微球为模板,通过纳米自主装的方法,将纳米沸石组装于有机模板之上,得到纳米堆积的大孔沸石。该方法结合了纳米沸石和多级孔沸石的优点,具有高的外壁表面和短的扩散路径,同时避免了纳米沸石分离困难以及介孔沸石制备成本高昂的缺点,均匀的大孔对原油具有选择性的分离作用,在重油的催化裂化中存在极大的应用潜力。论文具体的研究内容分为:纳米沸石的制备、有机微球模板的制备及在大孔材料中的应用、纳米沸石在有机微球模板上的组装三个部分。在纳米沸石的制备的章节中,通过不同方法分别制备出纳米Y和方钠石,详细探讨了水相中纳米Y沸石的制备和干凝胶法Y沸石的制备。首先纳米Y沸石的制备是在水热合成体系中采用无模板法进行制备,文中详细考察了碱度、阳离子浓度和凝胶硅铝比等因素对纳米Y沸石的形成、形貌及骨架硅铝比的影响。利用XRD、SEM、TEM、NH_3-TPD、FT-IR、氮吸附-脱附、NMR等表征手段对纳米Y沸石的结构及形貌进行了详细的表征,结果表明:这种制备纳米沸石的方法具有很宽的相区间,凝胶配比经大幅度的调节后仍能得到具有高的外比表面积的纳米Y沸石；从纳米Y沸石的形貌上看,根据凝胶中各物质比例的不同,纳米沸石具有小晶粒、片状、紧密团聚的球状、疏松堆积的不规则块状等多种形貌,其大小和团聚状态均可根据变量进行调节；从孔结构看,所有的样品均保持了良好的微孔结构且外表面都得到了很大的提升,外表面积最高达到186m~2/g,总孔容达到0.81cm~3/g；而从纳米Y沸石结构的骨架硅铝比来看,根据碱度和凝胶硅铝比的改变,沸石骨架的硅铝比、酸性能和结构的稳定性可在一定的范围内进行改变。本论文中首次采用干凝胶法在低于100℃的温度下制备出Y沸石,采用骨架红外、热重、固体核磁等手段对干凝胶和晶化后的样品进行分析,结果表明:干凝胶中已经具备Y沸石的部分初级结构单元,而这些初级结构单元中的硅铝比明显低于晶化后样品的骨架硅铝比,证明富铝的体系有利于Y沸石的晶核的形成,而晶化过程中则使得较多的硅进入到骨架中。在干凝胶法制备方钠石的过程中首次将干凝胶法制备沸石的温度降低至70℃。在有机微球的模板的制备中,分别采用乳液聚合法和无皂乳液聚合法制备出聚苯乙烯(PS)和聚甲基丙烯酸甲酯(PMMA)微球,通过改变引发剂用量、单体用量、乳化剂用量等反应条件对模板的粒径在200~430nm内进行连续调节。为制得小于200nm的模板,分别采用稀乳液体系、阻断聚合反应和更换乳化剂等方法使模板在30~200nm内连续可调。以有机微球为大孔模板,成功制备出三维有序大孔氧化硅、Al_2O_3/γ-Al_2O_3以及空性球材料,以有机微球为模板制得的不同的大孔材料均保持了规则的球状大孔结构和良好的热稳定性。以纳米沸石和大孔模板为基础制备大孔沸石,对PS模板的表面性质及改性进行了探索,详细讨论了模板与沸石结合的可行性方案,并以实验进行验证,结果表明:通过对凝胶进行改性处理,首次证明晶化后有机微球模板可以进入到沸石的晶体内部,而离心处理可以进一步增大模板的空间限制作用有利于制备大孔沸石。分别将本文中纳米沸石的制备方法应用于大孔沸石的制备,结果表明:(1)沸石合成中由于凝胶的溶解与再生长的过程以及有机相与无机相的不兼容性是阻碍模板进入沸石结构的主要影响因素；(2)疏松的堆积状及规则的晶体形貌使得大孔结构很难呈现规则的球状；(3)通过干凝胶法和适当的改性条件及离心处理,可以制得具有均一孔径大孔(~300nm)的沸石结构。
[Abstract]:In the foreseeable future, fossil energy will still be the main part of human energy supply. With the over-exploitation and use of crude oil, the trend of heavy and inferior crude oil will be inevitable in future crude oil supply. Therefore, optimizing the current petroleum refining process has become an urgent technical problem. Because of its high specific surface area, uniform microporous structure, controllable acidity and good stability, the catalyst has become the most important catalytic material in the petrochemical field. It is widely used in catalytic cracking, alkylation and isomerization. However, its narrow micropore leads to the diffusion restriction in the pore, so the micropore is shortened. Nowadays, the main research directions of zeolite materials are the diffusion path and the increase of the external surface area of zeolite catalytic materials. There are two main methods to solve the defects of zeolite materials: one is to prepare nano-sized zeolite molecular sieves by reducing the size of zeolite grains, and obtain high external specific surface area and short micropore length. The other is to increase the accessibility of active sites by introducing mesoporous or macroporous zeolites into the zeolite structure, which has some limitations: it is difficult to recover nano-zeolite particles when they are too small, while the cost of preparation is limited. In this paper, we focus on the preparation of macroporous nano-zeolites by self-assembly of nano-zeolites onto organic templates using cheap organic microspheres as templates. Difficulty and high cost of preparation of mesoporous zeolite, homogeneous macropore has selective separation of crude oil, and has great potential for application in heavy oil catalytic cracking. In the chapter of preparation of nano-zeolite, nano-Y and sodalite were prepared by different methods. The preparation of nano-Y zeolite in aqueous phase and the preparation of Y zeolite by dry gel method were discussed in detail. The effects of alkalinity, cationic concentration and silica-alumina ratio on the formation, morphology and framework of nano-Y zeolite were investigated in detail. The structure and morphology of nano-Y zeolite were characterized by XRD, SEM, TEM, NH_3-TPD, FT-IR, nitrogen adsorption-desorption and NMR. Nano-Y zeolite with high specific surface area can be obtained by adjusting the proportion of gel in a wide range of phases. According to the morphology of nano-Y zeolite, nano-Y zeolite has many morphologies, such as small grains, flakes, compact agglomeration spheres, loose accumulation of irregular blocks and so on. Size and agglomeration state can be adjusted according to the variables; from the pore structure, all samples have maintained good microporous structure and the external surface has been greatly improved, the maximum external surface area reached 186 m~2/g, the total pore volume reached 0.81 cm~3/g; from the framework of nano-Y zeolite structure, according to the basicity and the ratio of silica to aluminium gel. In this paper, Y zeolite was prepared by dry gel method at temperatures below 100 C for the first time. The samples were analyzed by skeleton infrared spectroscopy, thermogravimetry, solid state nuclear magnetic resonance and so on. The results showed that: dry gel. Some primary structural units of zeolite Y have been found, and the Si/Al ratios in these primary structural units are obviously lower than those of the crystallized samples, which proves that the Al-rich system is beneficial to the nucleation of zeolite Y, while the crystallization process makes more silicon into the framework. The temperature of zeolite prepared by dry gel method was reduced to 70 degrees. The polystyrene (PS) and polymethyl methacrylate (PMMA) microspheres were prepared by emulsion polymerization and soap free emulsion polymerization in the preparation of organic microspheres. The particle size of polystyrene (PS) and polymethyl methacrylate (PMMA) microspheres were changed by changing the amount of initiator, the amount of monomer and the amount of emulsifier. Continuous adjustment was carried out in 200~430nm. In order to make the template smaller than 200nm, dilute emulsion system, blocking polymerization and replacing emulsifier were used to make the template continuously tunable in 30~200nm. With organic microsphere as macroporous template, three dimensional ordered macroporous silicon oxide, Al_2O_3/ -Al_2O_3 -Al_2O_3 and hollow sphere material were successfully prepared, and organic microspheres were prepared. Macroporous zeolites were prepared on the basis of nano-zeolite and macroporous templates. The surface properties and modification of PS templates were explored. The feasibility of combining template with zeolite was discussed in detail. The results were verified by experiments. The results show that the template of the crystallized organic microspheres can enter the crystal of zeolite for the first time by modifying the gel, and the centrifugal treatment can further increase the spatial restriction of the template, which is beneficial to the preparation of macroporous zeolite. The dissolution and regeneration of gel and the incompatibility of organic and inorganic phases are the main factors that hinder the template from entering the zeolite structure in the synthesis of zeolite; (2) the loose accumulation and regular crystal morphology make it difficult for the macroporous structure to appear regular spherical; (3) through the dry gel method and appropriate modification conditions and The zeolite structure with uniform pore size (~300nm) can be prepared by centrifugation.
【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】：TQ426

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