Hydrogel Load Meddab Heteropoly Acid Composite Microspheres Preparation And Its Catalytic Desulfurization

A microchemical reactor, or microreactor, is one of several chemical engineering unit process devices that are now being designed on the micrometer (as opposed to the meter) scale. The potential advantages of using a microreactor, rather than a conventional reactor, include better control of reaction conditions, improved safety, and portability. Better control of reaction conditions refers to the ability to precisely control the temperature of the reactor, a direct result of the reactor's extremely high surface to volume ratio. Improved safety results from the reactor's extremely small size. Based on these advantages, microreactor technology has become a very attractive area. Generially, micro -reactor based on micelle technology can be divided into reverse micellar microreactor, polymer microreactor, template microreactor, etc. This research mainly focuses on the preparation of poten -tial microreactors based on polymerizable surfactant-phosphotungstic acid complexes supported on microgel composite microspheres.The main advantage of this kind of structural heteropolyacid composite microspheres is of the microsphere with water-soluble core and phase transfer catalysts shell. So, this microsphere material can be used as microreactor for two-phase transfer catalysis. The microsphere can store water -soluble substance in the core and perform potential catalysis at the interface. Addtionally, the advantage of the composite microspheres includes two aspects. One is that the micrometer size of the composite microsphere makes its easy separation from the system. Another is that the surface of the composite microsphere has micro-nano scale catalysts to result in a good performance in catalysis. In order to meet these requirements, a polymerizable surfactant methacryloxyethyl dodcydi -methyl ammonium bromide (MEDDAB) was introduced in the microgel of poly acrylamide (PAM) by copolymerization and dipping methods, respectively. After that, the structural heteropolyacid composite microspheres were prepared by ionic exchange.This research includes the following parts:(1) The new type polymerizable surfactant MEDDAB was synthesed. MEDDAB was synthesised by reaction between dimethylamminoethylmethacrylate (DM) and n-dodecanebromide. The product was characterized by infrared spectrum (IR), ¹H-NMR and elemental analysis.P(AM-co-MEDDAB) microspheres were prepared by reverse suspension polymerization technique. P(AM-co-MEDDAB)/PWO will be obtained through ion-exchange between P(AM-co -MEDDAB) microspheres and heteropolyacid. Some factors affected component and morphology of the microspheres have been also investigated. The composite microspheres P(AM-co-MEDDAB) and P(AM-co-MEDDAB)/PWO prepared in different conditions were characterized by the SEM, FT-IR, TGA and EDX etc, respectively.The results demonstrated that P(AM-co-MEDDAB)/PWO microspheres in shape were of general microsphere with different surface morphology. The composite microspheres with micrometer size in entire and nanometer particles in surface were observed. For microspheres P(AM-co-MEDDAB), with addition of MEDDAB in the template microspheres, the surface morphology did not change, the size, however, was gradually diminished. The results indicated that amount of MEDDAB introduced in P(AM-co-MEDDAB) was limited due to appearance of de-emulsification. For composite microspheres P(AM-co-MEDDAB)/PWO, amount of MEDDAB would affect surface morphology. The surface wrinkles observed are attributed to the different shrinkage of polymeric chains in surface and inner of the microgel, and the different shrinkage derives from the different amount of deposite PWO in different area. In is not difficult to understand that the preparation of composite microspheres with controllable surface morphology and heteropolyacid amount is significant in enhancement of potential catalytic properties. So, this reaction is very useful in application of this composite material.(2) A new method for preparation of PAM/MEDDAB-PWO composite material was proposed. For this protocol, dipping method was employed to prepared the PAM/MEDDAB-PWO composite material. Firstly, PAM microspheres were prepared by reverse suspension polymerization technique, and then the PAM microspheres swelled by water were freezedly dryied. The resulting PAM microspheres were immersed by ethanol solution containing MEDDAB, and polymerization was finally initiated. By this method, the composite microspheres PAM/MEDDAB would be obtained. Secondly, the PAM/MEDDAB-PWO composite microspheres with potential catalysis were prepared by ionic exchange between PAM/MEDDAB and heteropolyacid. The morphology and loading amount of heteropolyacid of the composite microspheres were characterized by SEM, FT-IR, TGA and EDX, respectively.The effects of monomer's ratios, amount of BA, the concentration of HPW, stirring speed on the component and morphology of the composite microspheres were investigated. The results demonstrated that PAM/MEDDAB-PWO microspheres in shape were of microspheres with different surface morphology. The composite microspheres with micrometer size in entire and nanometer particles in surface were observed. The amount of MEDDAB significantly affected the surface morphology of PAM/MEDDAB. With the increase in MEDDAB, the porous structure on the PAM/MEDDAB microspheres become significant. Base on the PAM/MEDDAB microsphere, the composite microspheres PAM/MEDDAB-PWO with different patterns on the surface were obtained. The surface wrinkle of the composite microspheres became dense and fine with the increase of BA and heteropolyacid HPW concentration. Compared with the copolymerization to prepare the composite microspheres, this method is an efficient to obtain the composite microspheres with more MEDDAB. The composite microspheres with different morphology and ammount of HPW controlably prepare are very useful for enhancement of this composite material in application of catalysis.The formation of the wrinkly surface is attributed to the difference in shrinkage between inside and outside of PAM microgel frameworks due to deposition of MEDDAB-PWO on the surface, and the formation of MEDDAB-PWO small particles originates from the reaction between MEDDAB aggregation and the ionic exchange of HPW.(3) The catalytic performence of the composite microspheres PAM/MEDDAB-PWO was systematically investigated by using dibenzothiophene (DBT) oxidized by H₂O₂ as a model system. Based on the results, some key factors related to the catalytic performences of the composite microspheres were obtained.The results indicated that the composite microspheres used as microreactors have the excellent performence in ultra-deep desulfurization. Meanwhile, the microreactors were renewable. It also indicate that the increase both in reaction temperature and amount of the microreactors are beneficial to increase DBT conversion in the ultra-deep desulfurization. However, the appropriate amounts both for catalyst loaded on the microreactors and H₂O₂ used to immerse the microspheres 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. Amount of the extremely loaded catalyst is unfavorable for mass-transmittance, and amount of H₂O₂ excessively immersed the microspheres is unfavorable for dispersion of the microspheres. The catalysis in the optimum conditions is almost unchangeable after the microreactors used with 4 times.In summary, the composite microspheres with the hydrogel core and the shell composed of the composite microspheres have an excellent performence 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.