【作者】 张明；

【导师】 杨恒权；

【作者基本信息】 山西大学 ， 材料化学， 2018， 博士

【摘要】 有机/水、有机/离子液等两相催化体系是一类重要的绿色化学合成平台,广泛用于实验室合成和工业化生产。然而,由于两相“不互溶”,两种液体总倾向减小其界面,导致催化剂与反应物接触效率低下。为了提高双相体系的反应效率,不得不加入相转移催化剂,为物质转移提供“运载工具”;或加入表面活性剂形成胶束、乳液,以增大反应的界面。这些额外添加物的引入给产品分离、纯化带来困难。工业上通常采用高速搅拌的方式来获得高的反应效率,但反应完毕后需要将两相进行分离用于回收产物和催化剂,不得不在间歇式反应釜中进行,严重制约了其规模化应用。尽管目前通过连续搅拌反应釜、负载液相技术以及微流控技术等可实现两相体系连续化,但这些方法在实现连续化过程中仍然需要附加或者依赖于特殊的设备或材料,对大规模的工业化连续应用仍然不适用。针对上述问题,本论文采用界面活性SiO₂稳定乳液,并将其填充于固定床反应器,构建了新型的基于乳滴的固定床连续流动体系。从实验和理论上对流动体系中油相的流动性、水滴的稳定性及乳滴对催化剂的限域能力进行系统地研究,证实该类乳滴具有极高的稳定性,能够像固体颗粒催化剂一样填充于固定床反应器内而不流失,水溶性催化剂如酶、酸、碱等被限域在乳滴内部实现“固载化”,而油相则能够从乳滴间空隙自由流动,流动过程中油相中反应物与乳滴中催化剂在相界面处接触并发生催化反应,生成的产物随着油相从反应体系流出。酶催化酯手性水解、酸催化醚化、杂多酸催化环氧化合物开环等反应证明了该方法的普适性。反应结果表明,在流动状态下该乳滴固载均相催化剂体系可将催化效率提高至目前间歇釜式反应的10倍以上,并且酶催化手性拆分反应连续运行2000h后催化效率没有明显降低。在此基础上,还揭示了催化反应效率与乳滴界面性质的内在关系。由于有机物在水中的溶解度低,上述基于水滴的固定床连续流动催化反应仅在界面上发生,对乳滴内部的催化剂利用率低。为了进一步提升酶以及均相催化剂的催化效率,本论文将乳滴固定床连续催化反应的概念拓展到有机/离子液（IL）体系,原因是离子液能溶解有机物,反应物分子能有效地扩散进入乳滴内部与催化剂接触并发生反应。按照上述思路制备了IL/O型Pickering乳液,再将其填充于固定床上,成功地实现了酶催化醇的手性动力拆分反应和CuI催化环加成反应。反应结果显示,该体系可进一步将酶的催化活性提高至间歇式反应的20倍以上,并且在固定床上连续运行4000h后,酶的活性仍保持了其初始活性的77%。通过理论模拟,揭示了酶比活性提高的原因在于乳滴微纳空间内存在浓度梯度,驱使反应物不断地从界面扩散到乳滴内,而产物不断地从乳滴内移除,从而消除了产物对酶的抑制效应,提高了反应效率。理论模型还预见了乳滴大小与反应效率的关联,并得到实验上支持。为了进一步证明乳滴固定床连续流动反应体系的优越性,构建了间歇式反应体系和乳滴固定床反应体系催化效率的数学模型,并从理论上对两种反应体系的催化效率进行比较,预测乳滴固定床连续流动体系能够使反应效率得到量级上的提升。以CuI催化环加成为模型反应,对乳滴固定床反应体系和间歇式反应体系催化效率之间的差异进行实验上的验证。实验结果与理论模拟较好的吻合,进一步有力地证明乳滴固定床反应体系能够显著提高两相体系的反应效率这一结论的可靠性。更多还原

【Abstract】 Biphasic catalytic systems,such as organic/water and ganic/ionic liquids are of an important class of green chemistry synthesis platforms that are extensively used in laboratory synthesis and in industrial fabrication.However,due to the"immiscibility"of two phases,the overall tendency of the two liquids is to reduce their interface,resulting in inefficient contact of the catalyst with the reactants.In order to improve the reaction efficiency of the biphasic reaction system,a phase transfer catalyst has to be added to provide a"carrier"for the transfer of substances,or a surfactant is added to form micelles or emulsions to increase the reaction interface.Unfortunately,the introduction of these additional additives presents some more difficulties for product separation and purification.In industry,biphasic reactions typically require external mechanical agitation to obtain high reaction efficiency.However,the separation of the two phases is also need to recover the product when the reaction is completed,which has to be implemented in batch reactors and seriously restricts their large-scale application.Nonetheless,the breakthroughs up to date in this context are only achieved in continuous stirred tank reacors,supported liquid technonlogy,and microfluidic technology.Dispite significant advances,these methods still rely on external or special equipment or meterials in achieving a continuous flow manner.In this regard,they are still not suitable for large-scale industrial applications.To overcome the problems,an interface-active SiO₂ nanoparticle was used to stabilize droplets and then filled them into a packed-bed reactor to construct a droplet-based continuous flow packed-bed system.Key fundamental principles underpinning this method such as the oil phase flow behavior,the stability of compartmentalized droplets and the confinement capability of these droplets toward catalysts are experimentally and theoretically investigated.Due to the high stability,such droplets can be packed in a column reactor like particulate catalysts in conventional packed-bed reactors.The catalysts such as enzyme,acid and base are thus“immobilized”in the column reactor,while the interstices among the droplets allow the oil phase and substrates dissolved in it to flow down.During passage through the column reactor the reactants contact the catalyst at droplet interfaces,where catalytic reactions occur.Case studies including an enzymatic chiral reactions,a sulfuric acid-catalyzed addition reaction and a heteropolyacidcatalyzed ring opening reaction demonstrate the generality and versatility of this method.Impressively,the droplet-based reaction system exhibit not only excellent durability even over a span as long as 2000 h,but also exhibit up to10-fold reaction efficiency in comparison to their batch counterparts.On the basis,the relationship between catalytic efficiency and properties of the droplets interface were also revealed.In above system,catalysis reactions occur only at the interfaces of water droplets in oil rather than within the droplets,and the catalysts inside droplets are not accessible to reactant molecules because organic reactants are mostly insoluble in water.Herein,to continuously process enzymatic or homogeneous catalysis reactions more efficiently,a new droplet-based continuous flow packed bed reaction system was eatablished by using organic/ionic liquid（IL）biphasic system.The reasion is that the ionic liquid can dissolve organic compounds and the reactant molecules can effectively diffuse into the droplet and contact with the catalyst,which allows reactions to take place within the droplets.Similarly,this system adoptes ionic liquid（IL）droplets in an immiscible oil as building blocks to fill into a column reactor.Case studies including enzymatic chiral reactions,CuI-catalyzed cycloaddition demonstrate its generality and versatility.Impressively,the IL droplet-based reaction system exhibit not only excellent durability even over a span as long as 4000 h,but also exhibit up to 20-fold reaction efficiency in comparison to their batch counterparts.Furthermore,it was found that 77%of the initial specific activity of enzyme was still maintained.Morover,the theoretical investigation reveales that there exists a concentration gradient within the droplet for both reactant and product,which resulted the diffusion of the reactants into the droplets and the constant removal of products from droplets,thus mitigating the product inhibition effect,and the catalysis efficiency is also significantly boosted.The theotetical model not only allows to predict the the relationship between reaction efficiency and droplet size,but also suppoted by the experimental results.To further verify the superiority of the continuous flow packed-bed reaction system,a mathematical model based on catalytic efficiency of the batch reaction and the droplet-based packed-bed reaction system was also established.Furthermore,the calculations reivels that the droplet-based packed bed system exhibit several order of magnitude enhancement in catalysis efficiency than their batch counterparts.For a given model reaction,for example,the CuI-catalyzed cycloaddition reaction is still researched here,not only suooprting the theoretical results,but also proving that the droplet-bed packed bed reaction system can significtly improve the catalytic efficiency.更多还原