| Heteropoly acids are a class of inorganic polymers with a definite structure, simple components and unique properities of strong acidity and redox. Heteropoly acid has wide application in industrial production as an acid catalyst, redox catalyst or novel bifunctional catalyst. Up until now, however, enhance the catalyst recycling and repeated use is still a problem to be solved. Considering that ionic polymers containing IL units are potentially capable of acting the bifunctions of IL and polymer, such as high thermal stability, easily shaping and variety of available structures, we think it rational to design and prepare a HPA-based polymeric hybrid catalyst by combining functionalized IL polymer with HPA, and the ionic polymers can solve the difficult problem of catalyst recovery and reuse.In this study, a series of HPA-based polymeric hybrid catalyst were prepared by combining functionalized PEG, polyvinyl imidazoles ILs or polyvinyl pyridine ILs with phosphotungstic acid. The catalytic activities were tested for the esterification of adipic acid with n-butanol. The influence of organic cations on the catalytic performance was investigated in detail. In addition, the structure and composition of catalysts were characterized by FT-IR, XRD, TG and ICP etc.A family of heteropolyanion-based PEG-paired dicationic alkyl imidazolium ionic liquids, which contain PEG with different molecular weight and alkyl group with different carbon number, are prepared by coupled PEG-paired dicationic alkyl imidazolium cations with heteropolyanions, and characterized by XRD, FT-IR, TG, NMR and elemental analysis. The result indicated that a new type of organic HPW salt was prepared by the combination of PEG-based dicationic alkly imidazolium organic cations witn keggin anion via ionic bonds, and heteropoly anion was highly dispersed on polymer cations surface. The catalyst showed a temperature-controlled phase transfer catalysis behavior during the reaction.The influence of PEG molecular weight and alkyl groups, function of proton in the heteropolyanion on the catalytic activity was investigated in detail. The [C8IM-PEG800-C8IM]0.5H2PW12O40 catalyst existed the highest activity.The optimum reaction conditions for the catalytic esterification are reaction temperature 388 K, mole ratio of n-butyl alcohol to adipic acid 4.5 : 1, mass ratio of catalyst to adipic acid is 5%, mass fraction of toluene(as water removal agent) in the reaction medium is 30%. Under these conditions, the conversion of adipic acid can reached up to 98.3%. This catalyst can keep a higher activity after a six-run recycle and remained original structure.Heteropolyanion-based polyvinyl imidazoles hybrid catalysts are prepared by coupling poly(founctionalized imidazolium) organic cations with Keggin-structred heteropolyanions via ionic bonds and characterized by XRD, FT-IR, TG and elemental analysis. The results indicated that the heteropolyanions were highly dispersed on the polymer cations surface and the Keggin-structure of heteropolyanions in the hybrid catalysts was remained. The SO3H- or COOH-functionalized hybrid catalysts showed higher catalytic activity. The Poly(VMPS)-HPW catalyst exhibits high catalytic activity, good structure stability and reusability. The adipic acid conversion dropped less than 7.0% after five times of reaction cycle.Heteropolyanion-based polyvinyl pyridine hybrid catalyst is prepared by coupling poly(SO3H-functionalized IL) with Keggin-structure heteropolyanion via ionic bond, and the Keggin-structure of heteropolyanions in the hybrid catalysts was remained.The optimum reaction conditions for the catalytic esterification are reaction temperature 388 K, mole ratio of n-butyl alcohol to adipic acid 3.3 : 1, mass ratio of catalyst to adipic acid is 2%, mass fraction of toluene in the reaction medium is 21%. Under these conditions, the adipic acid conversion could reach up to 95.0%. The hybrid catalyst is easy to recycle, exhibits good reusability and structure stability. |
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