Microgel Supported Heteropoly Acid Quaternary Ammonium Compound Microspheres And Its Desulfurization

With the growingly strong consciousness of environmental protection among people, the issue of desulfurization of fuel oils has become one of the most focuses recently, especially, catalystic oxidative desulfurization using H2O2 as green oxidant has drawn more concern among some scientists. Quaternary ammonium heteropolyphosphatotungstate, as one kind of the phase transfer catalysts, has good catalysis activity in two phase catalysis reaction of micelle. However, it is difficult to recycle catalyst and separate product. Immobilized phase transfer catalysts are easy to be separated, but along with lower mass transfer efficiency. For it, this research proposes a new methodology to build up smaller microreactors, on the premise of easy sedimentation, which is composed of smaller size hydrogel as template and quaternary ammonium heteropolyphosphatotungstate loaded on the surface of hydrogel in terms of micelle structural characteristic, and the composite microspheres as microreactors prepared above were applied to the ultra deep desulfurization of simulated fuel oil. In order to achieve the goal mentioned above, the research in this dissertation mainly includes three aspects, which are as follows:(1) Preparation and characterization of smaller size microgel. Acrylamide(AM) and methacrylic acid(MAA) copolymer hydrogel microspheres P(AM-MAA) with the size of-30μm were synthesized via inverse emulsion polymerization technology. In addition, several factors impacting morphology of P(AM-MAA) hydrogel has been explored. The morphologies and compositions of the hydrogel have been characterized by Scanning Electron Microscope(SEM), Energy Disperse Spectrum(EDS), FT-IR Spectrometer, et. al, respectively. The results indicated that the hydrogel washed with acetone are perfectly spherical, nearly monodisperse and their average diameters are about 30μm and their surfaces are smooth and compact, and their size can be controlled by adjusting some factors. Among these factors discussed in this experiment, mixing speed is the main factor affecting the size of microspheres, which is about 100μm at 380 rpm and 30μm at 900 rpm. The water-swollen P(AM-MAA) microgels treated by freeze-drying technology exhibit porous structures. The size of cavities can be adjusted by amount of crosslinker(BA) in the preparation process of microspheres.(2) Preparation and characterization of composite microspheres with core/shell structure. Selecting P(AM-MAA) microgels of 30μm and porous microgel by freezing dried as template,respectively, P(AM-MAA) microgels loaded quaternary ammonium 3-(trimethoxysilyl)-propyldimethyloctadecylammonium chloride(QAS), (P(AM-MAA)/QAS) with two different structures were obtained by impregnating method, and then QAS was immobilized onto P(AM-MAA) microgels via hydrolysis and condensation reaction. Eventually, P(AM-MAA)/QAS-W2 composite microspheres with two different structures were synthesized by ionic exchange between K2{W(=O)(O2)2(H2O)}2(μ-O)(W2) and quaternary ammonium groups of QAS immobilized on the P(AM-MAA) microgels. The morphologies and compositions of P(AM-MAA)/QAS and P(AM-MAA)/QAS-W2 composite microspheres can be analyzed by FT-IR, SEM, EDS, TGA, Contact Angle Meter, et. al, respectively. The results indicated that P(AM-MAA)/QAS and P(AM-MAA)/QAS-W2 composite microspheres prepared by method above have core/shell strucrure, and these prepared by porous microgel by freezing dried as template have convex structure, two kinds of composite microspheres with different amount of QAS and W2 can be obtained by regulating QAS dipping amount or/and concentration of W2 water solution.(3) Catalysis performances of composite microspheres. Simulated oil system can be constracted by dibenzothiophene(DBT) dissolved in a certain volume of decalin, selecting hydrogen peroxide(30wt%H2O2) as oxidant, P(AM-MAA)/QAS-W2 microreactor as catalyst materials, and then swollen by H2O2, the sulfur content was monitored by GC-Flame Ionization Detector(FID) before and after the catalysis reaction. The morphologies and compositions of P(AM-MAA)/QAS-W2 microreactors before and after desulfunzation can be analyzed by FT-IR, SEM, EDS, TG-DSC, et. al, respectively. The catalytic performances of the composite microspheres were systematically investigated by discussing some key factors related to the catalytic performances of the composite microspheres such as reaction temperature, recycle times, concentration of DBT and the size of microreactors were obtained. The results indicated that P(AM-MAA)/QAS-W2 composite microspheres used as microreacrors have excellent catalysis performance and high efficiency in ultra-deep desulfurization. Whatsmore, the microreactors are liable to be seperated, renewable and reused, which are not only related to morphologies and compositions of composite microspheres, but also strongly dependent on better mass transfer for smaller size composite microspheres. In addition, P(AM-MAA)/QAS-W2 composite microspheres can extract oxidative product DBT-sulfone well. Other things being equal, smaller size microreactors have better catalysis activity and efficiency in desulfurization process than bigger ones. This phenomenon is mainly attributed to more favorable mass transfer of smaller ones. Relatively speaking, swollen microreactors have lower desulfurization efficiency, which may be caused by worse mass transfer of interface. Simultaneously, phase transfer catalyst is prone to shell from surface of microreactors because of worse mechanical intensity.