具有相转移催化功能磁性纳米粒子结构优化及应用

【作者】 崔新爱；

【导师】 胡道道；

【作者基本信息】 陕西师范大学 ， 高分子化学与物理， 2012， 博士

【摘要】 液-液两相催化反应因其环境友好性已得到迅速的发展。然而,解决两相反应体系底物接触以及催化剂回收等难题仍具有很大的挑战性。围绕这些问题,相继出现了许多新方法和新技术,如温控相转移催化剂、乳液相转移催化剂体系以及固载型催化剂等。为此本课题组也曾提出以水凝胶为模板负载相转移催化剂,制备类似胶束结构的、适用性更广的复合微反应器。研究结果表明,此类微反应器在两相催化反应中具有良好的催化效果,且对极性产物具有一定的萃取功能。与此相关的研究为两相催化反应开辟了新途径。然而,前期研究发现：较大的微反应器因不利于传质而影响催化反应效率。作为本课题组前期工作的继续,本研究拟制备适于过氧化氢催化氧化深度脱硫两相反应的易回收纳米尺寸微反应器,并对其催化反应性能进行系统研究,期望为有效提高微反应器催化反应效率开辟新途径。基于以上的研究目的与意义,本论文的工作主要从以下两个方面展开：一、磁性纳米粒子/水凝胶/相转移催化剂微反应器的构筑及性能研究利用反相乳液体系制备磁性纳米二氧化硅(Magnetic Silica Nanoparticles, MSN),以有机硅氧烷对其修饰,使MSN表面富含双键,通过过硫酸钾(KPS)引发丙烯酰胺(AM)和N,N’-亚甲基双丙烯酰胺(BA)交联聚合,在MSN表面包裹一层水凝胶PAM。以磁性纳米水凝胶Fe3O4/SiO2/PAM (MHN)为模板,利用浸渍法将硅氧烷季铵盐3-三甲氧基硅基丙基十八烷基N.N-二甲基氯化铵(18QAS)通过网络互穿以及氢键作用负载于MHN上,最后通过18QAS与双核过氧钨酸钾(W2)之间的离子交换作用制备得到磁性纳米微反应器MHN/18QAS-W2。利用X射线衍射仪、红外光谱仪、热重分析仪、透射电子显微镜、能谱仪、振动样品磁强计等多种表征仪器对微反应器各阶段的结构和组成进行了表征。以过氧化氢氧化十氢萘中的二苯并噻吩(DBT)为模型反应,对制备得到的微反应器MHN/18QAS-W2的催化氧化行为进行系统研究,探讨影响此微反应器催化效果的关键性因素。实验结果表明：所制备的MHN尺寸为纳米级,具有核-壳结构和超顺磁性。成功构筑的磁性微反应器MHN/18QAS-W2具有较好的催化脱硫性能和产物萃取功能,影响其催化效率的主要因素是DBT的初始浓度,且此微反应器具有超顺磁性,反应完成后可通过外磁场迅速分离。由于MHN与18QAS-W2之间弱的相互作用,导致重复使用的微反应器MHN/18QAS-W2稳定性较差。二、磁性纳米粒子／相转移催化剂微反应器的制备及性能研究1)磁性纳米粒子／磷钨酸十八烷基季铵盐相转移催化剂为了增强相转移催化剂与载体之间的相互作用力,以提高其稳定性,实施了以18QAS水解产物与二氧化硅表面Si-OH之间的缩合作用,将硅氧烷季铵盐以共价键形式固载于磁性纳米二氧化硅表面的策略。经18QAS与磷钨酸(PTA)之间的离子交换作用,获得两相反应微反应器MSN/18QAS-PTA。利用透射电镜、能谱仪、X射线光电子能谱仪、红外光谱仪、振动样品磁强计、视频接触角测定仪对微反应器MSN/12QAS-PTA的结构、组成以及特殊性能进行表征。以过氧化氢氧化十氢萘中的二苯并噻吩为模型反应,探讨微反应器MSN/18QAS-PTA应用于两相反应的可行性,系统研究了各种因素对微反应器催化效果的影响规律。实验结果表明：微反应器MSN/18QAS-PTA为明显的核-壳结构,具有双亲性与超顺磁性。此微反应器在温和条件下可催化过氧化氢氧化DBT生成其对应的砜,催化性能优越,在最佳优化条件下,体系硫含量可从487～2800ppm降低到0.8ppm。纳米颗粒表面合适的催化剂固载量以及过氧化氢的使用量是决定MSN/18QAS-PTA颗粒催化性能高低的主要因素。此双亲性催化剂和产物可同时在外磁场作用下从体系中分离出来。与上一章使用磁性纳米水凝胶为模板制备的微反应器MHN/18QAS-PTA相比,MSN/18QAS-PTA在回收再利用方面具有明显的优势,其催化性能具有很好的稳定性,重复使用四次仍保持良好的催化效果。2)磁性纳米粒子/磷钨酸十二烷基季铵盐相转移催化剂为了探讨相转移催化剂本身烷基链长短对微反应器性能的影响,合成烷基链更短的3-三乙氧基硅基丙基N,N-二甲基十二烷基氯化铵(12-QAS),通过水解缩合反应将其固载于MSN表面,并以其作为季铵盐与PTA发生离子交换作用,制备得到相应的两相反应微反应器MSN/12QAS-PTA。利用核磁共振、红外光谱等手段对12QAS进行表征,利用透射电镜、红外光谱、热重、视频接触角、X射线光电子能谱、振动样品磁强计对复合微反应器的各阶段进行结构、组成及特殊性质表征。探讨微反应器MSN/12QAS-PTA应用于过氧化氢氧化十氢萘中的二苯并噻吩的各种影响因素。实验结果表明：MSN/12QAS-PTA为核-壳结构,具有超顺磁性且表面亲/疏水性可调。此催化剂的设计思路可行,它在催化氧化脱硫中有着良好表现,它集催化与萃取于一体,可将500～3000ppm浓度范围内DBT氧化脱除到5ppm以下。MSN/12QAS-PTA表面的催化剂固载量以及过氧化氢的使用量是决定其催化性能高低的主要因素。此催化剂具有稳定的催化性能,循环使用五次后,催化效率仍然很高。这一研究为制备具有不同亲/疏水性两相催化微反应器建立一种新方法,对拓展该方法的应用具有积极意义。综上所述：以磁性纳米水凝胶或磁性纳米二氧化硅为模板,在其表面负载杂多酸季铵盐,构筑应用于两相反应的微反应器是切实可行的。根据实验结果得知所制备的微反应器确实具有预想的各种性质与功能,三种微反应器不仅具有高的比表面积,良好的催化性能和一定的极性产物萃取功能,而且都具有超顺磁性,分离过程简单易行。复合微反应器各种功能的体现主要源于对其组成与结构的巧妙设计。在结构型两相催化微反应器的构筑与性能研究过程中,本论文不仅着力于提高相转移催化反应传质效率,而且关注催化剂和反应物在空间上的有效分布,以达到提高催化反应效率的目的。由该研究所得到的启示,对于新型纳米催化材料的制备具有重要意义,尤其是对于设计应用于物种分布极为复杂的液-液两相催化反应的固载型催化材料更具参考价值。更多还原

【Abstract】 Liquid-liquid biphase catalytic reaction systems have been developed rapidly. In order to solve the problems related to mass transfer and catalyst recovery in biphase reaction system, many researchers conducted a thorough and meticulous research, such as the development and utilization of thermoregulated phase-transfer catalysts, phase transfer catalyst emulsion system and the immobilized catalyst. Recently, we had reported a novel methodology for creating the broader applicability of catalyst with hydrogel core and amphiphilic phase transfer catalyst shell structure similar to W/O emulsion droplet. The results indicated that the prepared catalysts not only were valuable for deep oxidation desulfurization but also can extract the polar product from system. And the related researches open up new ways for two phase catalysis. However, it was found that the size of composite microreactor is too large to influence the mass transfer. As the continuous part of previous work, we anticipated to explore the preparation of small-size and easy-separated biphase catalytic microreactor for H2O2catalyzed oxidative desulfurization. We constructed three new biphase catalytic microreactors and examined their catalytic properties and expected to open new way for effectively improvement of catalyst performance.Based on the purpose above, two aspects are concluded in the thesis as follow:1. The preparation and performance study of magnetic nanoparticle/hydrogel/phase transfer catalyst microreactorThe magnetic silica nanoparticles (MSN) were prepared via the emulsion system. The obtained MSN surface can be modified with silane coupling agent, led to the formation of terminal C=C bonds on the surface of each MSN core. Finally, in the presence of MPS-modified magnetic silica polymerization of acrylamide (AM, the monomer) and N,N-methylene bis-acrylamide (BA, the cross-linker) was initiated by using potassium persulfate (KPS) as an initiator, resulting in the formation of the magnetic hydrogel nanoparticles MSN/PAM (MHN). Then MHN was impregnated in ethanol solution containing3-(trimethoxysilyl)propyl-N,N-dimethyloctadecyl ammonium chloride (18QAS), followed by ion-exchange between18QAS loaded on the surface of MHN and K2{W(=O)(O2)2(H2O)}2(μ-O)(W2), microreactor MHN/18QAS-W2were obtained. The morphology and components of the composite material were characterized by TEM, EDX, XPS, FT-IR, TGA-DSC and VSM, respectively. Empolyed the oxidation of dibenzothiophene with hydrogen peroxide as the model reaction, the catalytic performances of the microreactor MHN/18QAS-W2and the effects of several factors on desulfurization reactivity were systematically investigated, so that some key factors on the catalytic performances were obtained.The results showed that the microreactor has core-shell structure with nanoscale dimensions. MHN/18QAS-W2not only has high catalytic activity in the oxidation of dibenzothiophene but also can extract the polar product from system. The DBT initial concentration is the key factor related to the catalytic performance. MHN/18QAS-W2can be quickly separated by the external magnetic field due to its superparamagnetic property. However, because of the weak interaction between MHN and18QAS-W2, the reused microreactor MHN/18QAS-W2was less stable.2. The preparation and performance study of magnetic nanoparticle phase transfer catalyst microreactora)MSN/18QAS-PTAIn order to enhance the interaction forces between the phase transfer catalyst and the carrier to prevent catalyst leak, we directly immobilized the phase transfer catalyst on the surface of MSN by the covalently bound. Magnetic silica/18QAS nanospheres were prepared by the condensation between Si-OH groups on surface of MSN and derived from hydrolyzed18QAS in solution. MSN/18QAS-PTA was constructed by ion-exchange between18QAS loaded on the surface of magnetic silica/18QAS and PTA. TEM, EDX, XPS, FT-IR, TGA-DSC, video contact angle analyzer and VSM were used to characterize the structure, composition and special performances of the microreactor MSN/18QAS-PTA. We took the oxidative desulfurization of fuel oil with hydrogen peroxide as an example to verify the feasibility of using the resulting composite microreactor to aqueous/organic biphasic catalysis. The effects of several factors on desulfurization reactivity were systematically investigated.The results showed that the composite nanospheres have core/shell structure with the properties of amphiphilicity and superparamagnetism. The composite nanospheres have high catalytic activity in the oxidation of dibenzothiophene to corresponding sulfones by hydrogen peroxide under mild reaction conditions. The sulfur level could be lowered from487ppm to less than0.8ppm under optimal conditions. The suitable amount of catalysts immobilized on the nanoparticles and hydrogen peroxide used as reactant are necessary for the high efficiency of desulfurization. Additionally, the amphiphilic catalyst and the oxidized product could be simultaneously separated from medium by external magnetism. Compared with the use of magnetic nano-hydrogels (MHN) as a template to construct microreactor in the previous chapter, MSN/18QAS-PTA has a distinct advantage in the recovery and reuse. The recovered composite material could be recycled for four times with almost constant activity,b) MSN/12QAS-PTAIn order to explore the influence of alkyl chain length in the phase transfer catalyst on the microreactor effects, we synthetize3-triethoxysilylpropyl-N,N-dimethyl-dodecylammonium chloride (12QAS) with shorter alkyl chain and immobilized12QAS on the surface of the MSN via hydrolysis and condensation reactions. Then after ion-exchange between12QAS and PTA, the biphase reaction microreactor MSN/12QAS-PTA was prepared.1H NMR,13C NMR and FT-IR were used to character12QAS, then TEM, EDX, XPS, FT-IR, TGA-DSC, video contact angle analyzer and VSM were used to characterize the structure, composition and special performances of the microreactor MSN/12QAS-PTA. The effects of several factors on desulfurization reactivity were systematically investigated.The results showed that the composite nanospheres have core/shell structure with the properties of superparamagnetism and the surface hydrophilic/hydrophobic adjustability. This conception of catalyst design is feasible. The microreactor MSN/12QAS-PTA has a good performance in the catalytic oxidation. The DBT level could be lowered from500-3000ppm to less than5ppm under optimal conditions. The amount of phase transfer catalyst loaded on the surface of MSN/12QAS-PTA and the usage amount of hydrogen peroxide is the critical factors to determine MSN/12QAS-PTA catalytic performance. Additionally, the microreactor can extract the oxidized product and exhibit a stable catalytic performance. Its catalytic efficiency is still high after recycling for five times.In summary, it is feasible to employ MHN or MSN as the template to construct immobilized phase transfer catalyst (the complexes of heteropoly acid quaternary ammonium salt) microreactor. According to the experimental results, the microspheres reactor does have the expected nature and function. Three microreactors mentioned above not only have high specific surface area, good catalytic activity and a certain degree of the product extraction, but also have superparamagnetic property which makes separation process simple. The performances mentioned above are attributed to the specific structure and components of the prepared nanoparticles.Based on the preparation and performance study of biphase catalytic microreactor, this paper not only focused on the improvement of the phase transfer catalyst reaction mass transfer efficiency, but also on the design of effective distribution of the catalyst and reactants in space, in order to achieve the purpose of improving catalytic reaction efficiency. The construction rote of such microreactors may be significant to design multifunctional catalytic materials used in the water/organic diphase systems.更多还原