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Microgel supported heteropoly acid the quaternary ammonium micro reactor building and the deep desulfurization

Author: YangJuXiang
Tutor: HuDaoDao
School: Shaanxi Normal University
Course: Materials Science
Keywords: Ultra-deep desulfurization Biphasic catalyst Polyoxometates Microreactor Composite microspheres Core/shell structure Microgel
CLC: TE624
Type: PhD thesis
Year: 2008
Downloads: 342
Quote: 2
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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)(O22(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.

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