微凝胶负载杂多酸季铵盐微反应器的构筑及在深度脱硫中的应用

【作者】 杨菊香；

【导师】 胡道道；

【作者基本信息】 陕西师范大学 ， 材料学， 2008， 博士

【摘要】 两相催化的研究受到人们的极大关注，但涉及两相催化反应的应用领域特别广泛，且反应体系间存在一定的差异性，因此，有目的的研究具有重大应用价值的两相催化反应不仅对于解决重大实际问题具有重要意义，而且具有重要的理论价值。当今国内外都以深度脱硫满足严格的燃料油尾气新排放标准及燃料电池的无硫化。基于目前两相催化过氧化氢氧化深度脱硫被公认为最具发展前景的方法之一，结合燃料油脱硫是一个典型的两相催化反应体系，本研究提出根据两相催化过氧化氢氧化深度脱硫的基本原理，通过将具有催化活性的双核过氧钨酸钾（K₂{W（=O）（O₂）₂（H₂O）}₂（μ-O），W2）与负载于高分子水凝胶微球表面的季铵盐（3-（三甲氧基硅基）-丙基-十八烷基二甲基氯化铵，AEM）发生离子交换作用，构筑具有核／壳结构特点的两相催化微反应器，旨在有效提高过氧化氢氧化效率的同时，解决产品难于纯化、催化剂难于回收和再利用问题。更重要的是，通过本研究实施为建立具有普遍适应性的两相催化微反应器的构筑方法及其应用奠定基础。依据上述目的，本研究主要包括以下几个方面：1以收缩态的聚（甲基丙烯酰胺-甲基丙烯酸）P（AM-MAA）微凝胶作为模板，利用浸渍法合成P（AM-MAA）／AEM复合微球。通过AEM和W2之间的离子交换作用制得具有核／壳结构特点的P（AM-MAA）／AEM／W2微反应器。（1）浸渍法合成P（AM-MAA）／AEM复合微球以反相微乳液聚合法得到收缩态的P（AM-MAA）微凝胶作为模板，利用限域原位沉积季铵盐型表面活性剂AEM于微球表面，通过AEM的水解缩合反应得到目标复合微球。通过改变AEM的引入方式和负载量，得到了组成不同的P（AM-MAA）／AEM复合微球。（2）离子交换法构筑P（AM-MAA）／AEM／W2复合微球利用P（AM-MAA）／AEM复合微球上AEM的季铵盐基团与W2阴离子之间的离子交换作用，制得目标复合微球。通过在不同搅拌速度条件下所得到不同粒径的微凝胶为模板，得到粒径不同的P（AM-MAA）／AEM／W2复合微球；通过改变AEM负载量和W2溶液的浓度，以及AEM和W2离子交换时间，得到表面负载催化剂量不同的复合微球。（3）利用红外光谱、热重分析、扫描电子显微镜及能谱仪等多种表征手段对P（AM-AA）／AEM复合微球和P（AM-MAA）／AEM／W2复合微球的表面形貌和组成进行了表征。研究结果表明：（1）AEM作为共表面活性剂参与反相微乳液聚合制备P（AM-MAA）高分子微凝胶将AEM引入到微凝胶上的方法，以及将AEM溶解于反相微乳液水相中使其在引发聚合反应时将AEM引入到微凝胶上的方法，均不能有效的提高AEM在微凝胶上的负载量。（2）以反相微乳液聚合法制备了P（AM-MAA）高分子微凝胶为模板，再通过浸渍法将AEM引入到P（AM-MAA）高分子微凝胶上，经AEM在高分子骨架上发生水解和缩聚反应，将AEM固定化于P（AM-MAA）微球上，然后通过离子交换作用得到P（AM-MAA）／AEM／W2复合微球。该方法是制备P（AM-MAA）／AEM／W2复合微球的有效方法。（3）所得P（AM-MAA）／AEM／W2复合微球具有核／壳型结构，核主要为P（AM-MAA），壳层主要为双核磷钨杂多酸季铵盐（AEM／W2）。此复合微球具有本研究预设微反应器的结构特点。模板微球粒径越小，负载AEM越多，为通过离子交换调节W2负载量创造了条件；在AEM负载量一定的条件下，并非W2浓度越大，越有利于负载W2量的提高；AEM负载量对于W2负载量有明显影响，较高的W2负载量取决于较高的AEM负载量；足够的离子交换时间对于提高W2的负载量也是必要的。2为增加模板微球负载催化剂的量，以比表面较大的孔结构微凝胶微球为模板，利用浸渍法合成P（AM-MAA）／AEM复合微球，再通过季铵盐基团与W2阴离子之间的离子交换作用制得具有特异微凸表面形貌的P（AM-MAA）／AEM／W2复合微球。（1）浸渍法合成P（AM-MAA）／AEM复合微球以溶胀态冷冻干燥处理后具有多孔道结构的P（AM-MAA）微球作为模板，利用浸渍法限域原位沉积AEM于微球表面，再置于氨水气氛中水解，通过调节AEM的负载量和AEM处理次数，得到表面形貌不同的P（AM-MAA）／AEM复合微球；通过改变在氨水气氛中放置时间和处理次数来控制复合微球表面形貌；通过改变孔结构高分子微球的交联度来调节复合微球的表面形貌。（2）离子交换法制备P（AM-MAA）／AEM／W2复合微球利用P（AM-MAA）／AEM复合微球上AEM季铵盐基团与W2阴离子之间的离子交换作用，制备目标复合微球。通过改变AEM负载量和W2溶液的浓度得到了表面形貌不同的P（AM-MAA）／AEM／W2复合微球。（3）利用红外光谱、热重分析、扫描电子显微镜、能谱仪及X-光电子能谱等多种表征手段对P（AM-MAA）／AEM复合微球和P（AM-MAA）／AEM／W2复合微球的表面形貌和组成进行了表征。研究结果表明：（1）以孔结构的高分子微球作为模板构筑的复合微球除具有以收缩态高分子微球为模板合成复合微球的特点之外，其最大的特点在于具有较高的催化剂负载量以及复合微球的表面形貌具有微凸结构。（2）通过改变BA的含量可以有效调节模板微球的孔结构；不同孔结构模板对AEM负载量及形貌产生显著影响；BA含量增加模板孔径减小，AEM担载量增加，在氨水气氛中水解缩合使P（AM-MAA）／AEM微球表面微凸结构特征愈加明显；当其他条件不变时，AEM担载量越少，模板微球表面微凸结构特征愈不明显，当AEM担载量增加到一定程度时这种微凸结构特征变化不大。（3）以给定AEM负载量P（AM-MAA）／AEM微球与W2进行离子交换时，用于离子交换的W2浓度对P（AM-MAA）／AEM／W2复合微球表面形貌产生明显影响；太高或太低的W2浓度均使复合微球微凸结构变得相对不明显，在合适的W2浓度下可获得较明显的微凸结构。同时实验表明：随P（AM-MAA）／AEM负载AEM量增加，离子交换后所得到的P（AM-MAA）／AEM／W2复合微球上钨和硅含量增加。（4）根据对复合微球形成过程的各种因素进行综合分析，提出孔结构P（AM-MAA）为模板负载AEM的复合微球经水解缩合形成表面微凸结构形貌的“迁移与固化交替作用-表面张力导向驱动”机理。3以过氧化氢催化氧化十氢萘中二苯并噻吩（DBT）为模型反应，对上述以收缩态和孔结构高分子水凝胶为模板所构筑的核／壳型复合微球为微反应器的催化氧化行为进行系统研究，以获得对此类两相催化微反应器应用具有普遍指导的关键因素。实验结果表明：（1）基于高分子微凝胶为核，以负载于其表面的杂多酸季铵盐为壳所构筑的两相催化微反应器均表现出良好的催化氧化脱硫性能。同时，这类微反应器具有反复使用特点。表明该研究达到了预设的研究目的。（2）无论何种方式所制备的微反应器，提高反应温度和减小微反应器的粒径均有利于提高脱硫效率。（3）微反应器负载催化剂量和反应中过氧化氢用量对脱硫效率的影响存在最佳量。随催化剂负载量增加，催化反应能力增强，并达到最大值。再进一步增加催化剂负载量，将由于催化剂壳层厚度增加不利于传质过程而导致催化反应效率减弱。（4）随着过氧化氢用量的增加，催化反应效率增加；当达到最大值后，再增加过氧化氢用量，催化效率将因微反应器过量浸渍而不利于其在疏水性介质中分散而导致催化效率降低。（5）整体而言，微反应器催化氧化循环使用四次后，微反应器负载催化剂的活性和表面形貌基本保持不变。但需指出的是：这两种不同方式构筑的微反应器在催化反应性能上还存在较大的差异。与以收缩态高分子微球构筑的微反应器相比，尽管以孔结构高分子微凝胶为模板所构筑的特异表面形貌的微反应器负载催化剂的量显著提高，但是催化活性稍有降低。这一现象与微反应器因壳层较厚而导致核内氧化剂向壳层的传质过程受阻有关。综上所述：以具有水溶胀行为的高分子微凝胶为核，以负载于其表面的杂多酸季铵盐为壳所构筑的微反应器在两相催化脱硫中的应用是切实可行的。该研究不仅在结构型材料制备方面具有明显的创新性，而且在两相催化反应方面也表现出较其他方法较强的优势。不同于已报道的其他两相催化反应方法，在无须加入其他辅助成分和保证高效催化反应效率的条件下，借助这种微反应器可使催化反应实施过程简单易行，微反应器易于分离和重复使用。同时，依据本研究所提出的构筑两相催化微反应器的基本设想，这类微反应器构筑方法具有普遍的适用性；另外，因高分子水凝胶具有结构较强的可修饰性，可以实现这类微反应器的多功能化，从而使这类微反应器在两相催化反应的应用中具有更广泛的发展前景。更多还原

【Abstract】 Recently, the study of biphasic catalysis has attracted wide interest. Although different biphasic catalyses were widely studied, it is still important to construct general method for biphasic catalysis due to extensive application and certain differences existing among the systems of biphasic catalysis reaction. Based on ultra-deep desulfurization of fuel oil by H₂O₂ oxidation being a typical biphasic catalysis, and internationally extensive request in ultra-deep desulfurization because of environmental protection purposes, and wide focus on using H₂O₂ as oxidant in ultra-deep desulfurization of fuel oil, a new protocol was proposed to construct a structural microreactor used in ultra-deep desulfurization of fuel oil by H₂O₂ oxidation. The aim for construction of the structural microreactor is to overcome some defects in biphasic catalysis based on emulsion droplets. The structural microreactor can surmount the difficulties in the process of separation and recovery of the catalysts of the emulsion-based biphasic catalysis. To achieve the goal, the novel composite microspheres, P（AM-MAA）/AEM/W2, were synthesized by the following process. Firstly, P（AM-MAA） microgels as template were prepared. P（AM-MAA） microgels loaded quaternary ammonium 3-（trimethoxysilyl）-propyldimethyloctadecylammomum chloride （AEM） were obtained by impregnating method, and AEM then was immobilized onto P（AM-MAA） microgels by hydrolysis and condensation reaction. Finally, P（AM-MAA）/AEM/W2 composite microspheres were synthesized by ion exchange between K₂{W（=O）（O₂）₂（H₂O）}₂（μ-O）（W₂） and quaternary ammonium groups of AEM loaded on the P（AM-MAA） microgel. The structure of P（AM-MAA）/AEM/W2 composite microspheres with hydrogel core and catalyst shell not only meets the emulsion-based biphasic catalysis, but makes the water phase and the catalyst unify. To verify its efficiency in biphasic catalysis, the resulting composite microspheres as microreactors were used in the ultra-deep desulfurization of fuel oil were studied.According to the objects above mentioned, the main contents of this research include three aspects as follows:1. P（AM-MAA）/AEM/W2 composite microspheres were prepared using the shrunk P（AM-MAA） microspheres as the template.（1） P（AM-MAA）/AEM composite microspheres were prepared by following method. Firstly, the shrunk P（AM-MAA） microspheres were impregnated in ethanol solution containing AEM, the resulting microspheres then were hydrolyzed to immobilize AEM onto surface of P（AM-MAA） microspheres.In this part, the P（AM-MAA）/AEM composite microspheres with different composition and surface structure were obtained by changing the way of AEM introduced and the content of AEM loaded.（2） P（AM-MAA）/AEM/W2 composite microspheres were constructed by ion-exchange between AEM loaded on the surface of P（AM-MAA）/AEM and W2. P（AM-MAA）/AEM/W2 composite microspheres with different size were synthesized by using different size of P（AM-MAA）/AEM as template; the P（AM-MAA）/AEM/W2 microreactor with different content of W2 were prepared by using P（AM-MAA）/AEM composite microspheres loaded different amount of AEM, and changing the concentration of W2 and the time of ion exchange.（3） The morphologies and compositions of the P（AM-MAA）/AEM and P（AM-MAA）/AEM/W2 were characterized by scanning electron microscopy （SEM）, thermogravimetric analysis （TGA）, Fouier transform infrared spectroscopy （FT-IR）, respectively.The results indicate that the P（AM-MAA）/AEM and P（AM-MAA）/AEM/W2 composite microspheres are of core/shell structure. For the above composite microspheres, the P（AM-MAA） hydrogels are dominantly present in the core. For P（AM-MAA）/AEM and P（AM-MAA）/AEM/W2 composite microspheres, the shells are dominantly composed of AEM for the former and the complex of polyoxometate with AEM for the latter. The P（AM-MAA）/AEM/W2 composite microspheres with the specific composition in the core/shell structure have potential catalytic function for biphasic catalytic reaction.2. P（AM-MAA）/AEM/W2 composite microspheres were prepared using the swollen P（AM-MAA） microspheres as the template.（1） P（AM-MAA）/AEM composite microspheres were prepared by following method. Firstly, the water-swollen P（AM-MAA） microspheres were treated by the freeze-drying to obtain porous microspheres. The porous microspheres were impregnated in ethanol solution containing AEM, the resulting microspheres were then placed in the NH₃·H₂O atmosphere to immobilize AEM onto the surface of P（AM-MAA） microspheres by hydrolysis and condensation.In this part, the P（AM-MAA）/AEM composite microspheres with different composition and surface structure were obtained by changing the way of AEM introduced and the content of AEM loaded.（2） P（AM-MAA）/AEM/W2 composite microspheres were constructed by ion-exchange between AEM loaded on the surface of P（AM-MAA）/AEM and W2.In this part, the P（AM-MAA）/AEM/W2 microreactor with different W2 content were prepared by using P（AM-MAA）/AEM composite microspheres loaded different AEM content, and changing the concentration of W2 and the time of ion exchange.（3） The morphologies and compositions of P（AM-MAA）/AEM and P（AM-MAA）/AEM/W2 composite microspheres were characterized by scanning electron microscopy （SEM）, thermogravimetric analysis （TGA）, Fouier transform infrared spectroscopy （FT-IR） and X-ray photoelectron spectrometer （XPS）, respectively.The research results indicate that the structural features for P（AM-MAA）/AEM and P（AM-MAA）/AEM/W2 composite microspheres originally prepared from P（AM-MAA） porous microspheres are similar to that of ones originally prepared from the shrunk P（AM-MAA） microgels. However, the most peculiarity of P（AM-MAA）/AEM and P（AM-MAA）/AEM/W2 composite microspheres prepared by using P（AM-MAA） porous microspheres are obviously increased in the loaded amount of AEM and W2, and have the special surface morphology. From the point of view of preparation materials, this method provides an approach for increasing in the loaded amount and surface area. In this part, the formation mechanism on the special micro-convex surface morphology of P（AM-MAA）/AEM composite microspheres was also proposed.3. The catalytic performances of the composite microspheres were systematically investigated by using dibenzothiophene （DBT） oxidized by H₂O₂ in decalin as a model system so that some key factors related to the catalytic performances of the composite microspheres were obtained.The results indicate that the composite microspheres used as microreactors have excellent performances in ultra-deep desulfurization. Meanwhile, the microreactors are renewable. From above results, the microreactors constructed meet the purpose proposed.The results also indicate that the increase in reaction temperature and the decrease in size of the microreactors are beneficial to increase DBT conversion in the ultra-deep desulfurization. However, the appropriate amounts in catalyst loaded on the microreactors and H₂O₂ used to infiltrate the microreactors for the ultra-deep desulfurization are very important. Namely, for given amount of the microreactors, there are optimum amounts in the loaded catalyst and H₂O₂ because too high amount of the loaded catalyst is unfavorable for mass-transmittance, and too high amount of H₂O₂ is unfavorable for dispersion of the microreactors.The results also indicate that the catalytic activity of the microreactors prepared in optimum conditions is almost unchangeable after the microreactors used with 4 times. It needs to point out that there is the difference in the catalytic performances between the two microreactors. Compared with the microreactors prepared by using the shrunk, P（AM-MAA） microgels as template, although the amount of catalyst loaded on the microreactors prepared by using the porous P（AM-MAA） microgels is remarkably increased, the catalytic efficiency of the microreactor is slightly decreased. This phenomenon is mainly attributed to the unfavorable mass-transmittance in this case.In summary, the composite microspheres with the hydrogel core and the shell composed of complex between AEM and W2 have an excellent performance in ultra-deep desulfurization based on biphasic catalysis. The protocol proposed here is not only creative in preparation of structural composite microspheres but superior in biphasic catalyses. Compared with other methods of biphasic catalysis, the method used here makes operational process and separation of catalyst easy. Additionally, this method is generally suitable for construction of microreactor, and easy to realize diversification in functional microreactor.更多还原