Silicalite-1晶体形貌和尺寸的调控及MFI型分子筛膜的制备

发布时间：2018-05-01 07:37

本文选题：silicalite-1 + 形貌　；参考：《浙江大学》2015年硕士论文

【摘要】：MFI型分子筛由于其独特的交叉孔道结构、较高的机械强度和水热稳定性以及亲油疏水能力,在催化和分离等多种领域有着十分广泛的应用。其中,全硅型MFI分子筛(silicalite-1)由于其骨架结构中不含铝,具有疏水性,特别适用于有机物提纯等应用。众所周知,silicalite-1晶体的形貌和粒径对其性能有较大的影响,所以其形貌和性能的研究一直是分子筛领域的一大热点。但是,目前调控的范围大多集中在纳米级颗粒,鲜有文献报道关于微米级范围内晶体粒径的调节,而且大多数需要苛刻的合成条件与昂贵的有机模板剂(如多聚四丙基铵,TPAOH等)和原料(如正硅酸乙酯),合成过程复杂,这些问题限制了它们在工业生产中的实际应用。因此,根据特定的需要(如制备分子筛膜用晶种),利用价格低廉的原料并通过简单的合成过程实现对微米或亚微米silicalite-1晶体的调控具有十分重要的意义。本文基于在大孔氧化铝管上制备MFI型分子筛膜的晶种出发,实现silicalite-1粒径大小和形貌的调控,探讨不同晶种对于MFI分子筛膜结构和醇水分离性能的影响。主要研究内容和结果如下：1. Silicalite-1晶体形貌和粒径的调控在传统水热合成体系中,以廉价气相二氧化硅为硅源,TPABr为模板剂,采用电子显微镜(SEM)、X光衍射(XRD)和激光粒度仪(LLS)等技术对分子筛晶体的形貌和粒径进行表征,分别采用一步法和两步变温法实现分子筛形貌和粒径的调控。一步合成法：考察了合成液的水量、碱度、模板剂含量、晶化条件和搅拌方式对晶体粒径和形貌的影响。研究发现,增大合成液的水量可以使晶体由球形转变为棺形,提高碱度则可以促使晶体向球形转变,且随着碱度的增加,晶体粒径逐渐减小。增大模板剂的含量和缩短晶化时间均可以在不影响分子筛产率的情况下实现较小粒径silicalite-1晶体的制备。在晶化过程中转动式合成能够得到粒径较为均一的晶体,而搅拌式合成能得到粒径分布较广的晶体,粒径相对较小。两步变温合成法：研究低温预晶化和高温晶化的两步变温法制备silicalite-1晶体的规律。低温预晶化温度控制在40-80℃,时间3-81 h；控制高温晶化温度在130℃,时间3-120 h。研究发现,预晶化温度在50-60℃时晶体粒径较小,而在40℃和80℃时粒径较大。随着预晶化时间的延长,晶体的粒径逐渐减小,但超过24 h时,晶体粒径下降速率较为缓慢,且进一步延长预晶化时间,晶体的产率有所下降。当晶化时间为3h时,即可制备出较高产率(68.6%)的0.5μm左右的silicalite-1晶体,进一步延长晶化时间,晶体粒径基本不发生变化。在较优合成条件(在60℃预晶化24 h,130℃晶化3h)下可以制备出产率约为70%的0.5μm左右的silicalite-1晶体。与传统的一步法相比,两步变温法在同等条件下可制备出粒径远小于一步法的晶体；晶体的产率较一步法提高了约15%；大大缩短了制备分子筛所需的晶化时间,节约能源。2.不同晶种对MFI分子筛膜的结构和分离性能的影响以不同形貌、硅铝比、粒径分布及Na+含量的MFI型分子筛为晶种,在一定条件下在大孔氧化铝管表面合成MFI分子筛膜,并通过SEM观测膜层形貌,采用渗透汽化测试其对60℃下5 wt%乙醇/水混合溶液的分离性能。研究发现,不同形貌的晶种制备的分子筛膜有着不同的膜层结构,随着晶种形态由单晶(棺形)向多晶(带孪晶的棺形和球形)变化,所得膜层表面的孪晶也逐渐增加。同时,多晶形貌的晶种相对于单晶形貌更容易制备出致密的膜层。且当膜层均致密时,含孪晶的棺形晶种制备的膜层分离性能略高,在合成液中TPAOH/TEOS=0.005时,其分离因子高达114。比较了不同硅铝比的MFI晶种成膜的性能,发现少量Al的存在并不会影响分子筛膜的性能,甚至当TPAOH/TEOS=0.05时,以ZSM-5(140)为晶种制备膜层的分离因子可达103。同时,研究发现,球磨有助于增大晶种的粒径分布,球磨后晶种制备的膜层分离因子提高约10。晶种中Na+的含量对于其成膜性能有影响,Na+含量越高,所制备膜层分离乙醇/水的性能越低。
[Abstract]:MFI type molecular sieves are widely used in many fields, such as catalysis and separation because of their unique cross channel structure, high mechanical strength, hydrothermal stability and hydrophobicity and hydrophobicity. Among them, all silicon MFI molecular sieves (silicalite-1) are hydrophobic and are especially suitable for organic purification because of their skeleton structure without aluminum. It is well known that the morphology and particle size of silicalite-1 crystals have a great influence on their properties, so the study of their morphology and properties has been a hot spot in the field of molecular sieves. However, the scope of the current regulation is mostly concentrated in nanoscale particles. There are few reports about the regulation of crystal size in the micron range, and most of them have been reported. A number of demanding synthetic conditions and expensive organic templates, such as poly (four propyl ammonium, TPAOH, etc.) and raw materials (such as ethyl orthosilicate), are complex, which limit their practical applications in industrial production. The realization of the single synthesis process is very important for the regulation of the micrometer or submicron silicalite-1 crystal. Based on the preparation of the MFI type molecular sieve membrane on the macroporous alumina tube, the size and morphology of the silicalite-1 particle size and morphology are controlled. The effects of different crystal species on the structure of the MFI molecular sieve membrane and the separation performance of alcohol and water are discussed. The main contents and results are as follows: 1. Silicalite-1 crystal morphology and particle size are regulated in the traditional hydrothermal synthesis system, using cheap gas phase silica as the silicon source, TPABr as a template, using electron microscope (SEM), X light diffraction (XRD) and laser particle size analyzer (LLS) to characterize the morphology and particle size of the molecular sieve crystal. One step method and two step temperature change method are used to control the morphology and particle size of molecular sieves. One step synthesis method: the effect of water quantity, alkalinity, template content, crystallization condition and stirring mode on the particle size and morphology of the synthetic liquid. With the increase of basicity, the particle size of crystal gradually decreases with the increase of alkalinity. Increasing the content of the template and shortening the crystallization time can achieve the preparation of the smaller size silicalite-1 crystal without affecting the molecular sieve yield. The crystal with a wide particle size distribution can be obtained with a relatively small particle size distribution. The two step temperature synthesis method: the study on the preparation of silicalite-1 crystals at low temperature precrystallization and high temperature crystallization by two step temperature variation method. The temperature precrystallization temperature is controlled at 40-80, 3-81 h, and the crystallization temperature is controlled at 130 and 3-120 h. at high temperature. The grain size of the crystal is smaller at 50-60 C, and the particle size is larger at 40 and 80. As the precrystallization time prolongs, the particle size of the crystal gradually decreases, but the grain diameter decreases more slowly than 24 h, and further prolongs the precrystallization time and the crystal yield decreases. When the crystallization time is 3h, the grain size can be prepared. The silicalite-1 crystal with high yield (68.6%) of about 0.5 m, further prolongs the crystallization time, and the crystal size does not change basically. Under the better synthesis condition (precrystallization 24 h at 60, 130 C 3H), the silicalite-1 crystal with about 0.5 mu m production rate can be prepared. Compared with the traditional one step method, the two step temperature method is equal. The crystal yield is far less than one step, the yield of crystal can be increased by about 15% compared with one step method; the crystallization time required for the preparation of molecular sieves is shortened, and the effects of different crystal species on the structure and separation performance of MFI molecular sieve membrane are reduced by different morphologies, silicon aluminum ratio, particle size distribution and Na+ content of MFI type molecules. The MFI molecular sieve membrane was synthesized on the surface of a large pore oxide tube under certain conditions, and the morphology of the membrane was observed by SEM. The separation performance of the mixed solution of 5 wt% ethanol / water at 60 C was measured by pervaporation. As the crystal (coffin) changes to polycrystalline (with twin coffin and spherical), the twin crystals on the surface of the membrane also increase gradually. At the same time, the crystal species of the polycrystalline morphology is more likely to produce a compact membrane than the single crystal morphology. And when the film is dense, the separation performance of the film with twin crystal coffin crystals is slightly higher, and when TPAOH/TEOS=0.005 is in the synthetic liquid. The separation factor is up to 114. to compare the properties of MFI seed formation with different Si / Al ratio. It is found that the presence of a small amount of Al does not affect the performance of the molecular sieve membrane. Even when TPAOH/TEOS=0.05, the separation factor of the film prepared by ZSM-5 (140) is up to 103.. The ball milling helps to increase the particle size distribution and after ball milling. The membrane separation factor prepared by the crystal seed increases the content of Na+ in about 10. crystals, and the higher the content of Na+, the lower the performance of the preparation of the membrane to separate ethanol / water.

【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.893

【参考文献】