Sn-Beta分子筛的快速合成及催化糖转化制备乳酸酯研究

发布时间：2018-05-30 21:17

本文选题：Si-Beta分子筛 + Sn-Beta分子筛　；参考：《郑州大学》2017年硕士论文

【摘要】：随着煤、石油等不可再生资源的日益消耗,和人们对使用化石资源带来的环境污染问题的关注,开发利用清洁、廉价的可再生资源受到国内外学者的极大关注。植物生物质是由植物通过光合作用利用太阳光、水和二氧化碳产生的,是一种来源丰富、廉价、零碳排放的可再生资源。糖类是植物生物质的主要组分,利用糖类制备液体燃料和化学品,是一条重要的可再生资源利用途径。乳酸及其酯是一种可从糖类制备的重要平台化合物,广泛应用在食品、医药、化妆品、化工等行业中。为了克服现有发酵法制备乳酸及其酯的不足,近年来,研究者们开发了化学催化转化法从糖类制备乳酸及其酯。以廉价、丰富的葡萄糖或蔗糖为原料,通过催化转化法制备乳酸酯,是一个包含多步反应的复杂过程。为了提高乳酸酯的收率,多种催化剂被用来催化这一反应。在所研究的固体催化剂中,含氟体系水热合成的Sn-Beta分子筛被认为是催化糖转化制备乳酸酯的性能最好的催化剂。但是,水热合成Sn-Beta分子筛比较困难,凝胶中Sn物种的存在极大地抑制分子筛的成核和生长,因此,需要较长的晶化时间(通常十几至二十几天),这极大地限制了Sn-Beta分子筛的应用。本论文在文献调研和课题组已有的工作基础上,建立了一种快速合成Sn-Beta分子筛的方法,用于高效催化葡萄糖转化制备乳酸酯。该法首先合成出纯Si-Beta分子筛,然后通过研磨、焙烧将Sn前体与Si-Beta分子筛作用,将Sn引入分子筛骨架,得到Sn-Beta分子筛。该法大大缩短了Sn-Beta分子筛的制备周期。研究表明,Sn能否成功引入骨架与Si-Beta分子筛的结晶度密切相关。Si-Beta分子筛的结晶度较低时,有较多内部硅羟基缺陷位,有利于Sn引入骨架;相反,不利于Sn引入骨架。对于高结晶度的Si-Beta分子筛,我们通过碱处理脱硅产生了内部硅羟基缺陷位,然后与Sn前体反应,成功制备了Sn-Beta分子筛。通过XRD、SEM、N2物理吸附、UV-vis漫反射光谱、吡啶吸附FT-IR、氘代乙腈吸附FT-IR等方法表征了制备的Sn-Beta分子筛的物理化学性质。将从不同结晶度的Si-Beta制备的Sn-Beta分子筛用于催化葡萄糖转化为乳酸甲酯反应中,在160 oC反应10 h,乳酸甲酯收率最高达到48%,高于直接水热合成的Sn-Beta-F分子筛(35%)和脱铝-补Sn两步法制备的Sn-Beta-P分子筛(22%)。最后,考察了制备的Sn-Beta分子筛的循环使用性,发现该法制备的Sn-Beta分子筛循环使用过程中,乳酸甲酯收率逐渐提高,使用6次后,乳酸甲酯收率由37%升高到52%。通过表征使用后的催化剂,发现造成这种现象的原因可能是分子筛表面的非骨架Sn物种在反应过程中流失,使骨架Sn活性位更易被接触。
[Abstract]:With the increasing consumption of non-renewable resources, such as coal and petroleum, and people's concern about the environmental pollution caused by the use of fossil resources, the exploitation and utilization of clean and cheap renewable resources have attracted great attention from domestic and foreign scholars. Plant biomass is produced by plants using sunlight, water and carbon dioxide through photosynthesis. It is a renewable resource with abundant, cheap and zero carbon emissions. Carbohydrates are the main components of plant biomass. The preparation of liquid fuels and chemicals from sugars is an important way to utilize renewable resources. Lactic acid and its esters are important platform compounds which can be prepared from sugar. They are widely used in food, medicine, cosmetics, chemical industry and so on. In order to overcome the shortcomings of the existing fermentation methods for the preparation of lactic acid and its esters, in recent years, researchers have developed a chemical catalytic conversion method for the preparation of lactic acid and its esters from carbohydrates. The preparation of lactate from cheap and abundant glucose or sucrose by catalytic conversion is a complex process involving multi-step reactions. In order to improve the yield of lactate, a variety of catalysts are used to catalyze this reaction. Among the solid catalysts studied, the hydrothermal synthesis of Sn-Beta molecular sieve with fluorine system is considered to be the best catalyst for the conversion of sugar to lactate. However, hydrothermal synthesis of Sn-Beta molecular sieve is difficult. The existence of Sn species in gel greatly inhibits the nucleation and growth of molecular sieve. It takes a long time to crystallize (usually more than 10 to 20 days), which greatly limits the application of Sn-Beta molecular sieves. On the basis of literature investigation and research work, a rapid synthesis method of Sn-Beta molecular sieve was established, which was used to catalyze the conversion of glucose to lactate. In this method, pure Si-Beta molecular sieve was synthesized, then Sn precursor was calcined to react with Si-Beta molecular sieve, and Sn was introduced into molecular sieve skeleton to obtain Sn-Beta molecular sieve. The preparation period of Sn-Beta molecular sieve was greatly shortened by this method. The results show that the successful introduction of the framework is closely related to the crystallinity of the Si-Beta molecular sieve. When the crystallinity of the Si-Beta molecular sieve is low, there are more defects in the internal silica hydroxyl group, which is favorable to the introduction of the framework to Sn, whereas it is not conducive to the introduction of the skeleton to the Sn molecular sieve. For the Si-Beta molecular sieve with high crystallinity, Sn-Beta molecular sieve was successfully prepared by alkali desilication to produce the internal silica hydroxyl defect site, and then reacted with Sn precursor. The physicochemical properties of the prepared Sn-Beta molecular sieve were characterized by UV-vis diffuse reflectance spectroscopy (UV-vis), adsorption of pyridine with FT-IRand deuterated acetonitrile (FT-IR). The Sn-Beta molecular sieve prepared from Si-Beta with different crystallinity was used to catalyze the conversion of glucose to methyl lactate. At 160oC for 10 h, the highest yield of methyl lactate was 48, which was higher than that of Sn-Beta-F molecular sieve 35 prepared by direct hydrothermal synthesis and Sn-Beta-P molecular sieve prepared by de-aluminization and Sn supplementation. Finally, the reusability of the prepared Sn-Beta molecular sieve was investigated. It was found that the yield of methyl lactate increased gradually during the recycling of the Sn-Beta molecular sieve prepared by this method. After six times of use, the yield of methyl lactate increased from 37% to 52%. By characterizing the catalyst, it is found that the reason for this phenomenon may be the loss of non-skeleton Sn species on the surface of molecular sieve during the reaction, which makes the active sites of skeleton Sn more accessible.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ225.24

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