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The Synthesis And Application Of Heteropolyphosphatotungstate Phase-transfer Catalyst

Posted on:2008-09-02Degree:MasterType:Thesis
Country:ChinaCandidate:Z XiaoFull Text:PDF
GTID:2121360215479810Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Olefin oxides are important synthesis intermediates in chemical industry, which are widely used in the synthesises of polymers, fine chemicals, medicines, and agriculture pesticides. Currently, except ethylene oxide that is obtained by the direct oxidation of ethylene by oxygen, other olefin oxides are generally produced from the chlorohydrin process. However, the traditional chlorohydrin process generated large amount of waste water and stoichiometric amount of by-product, such as CaCl2. In the current work, a new phase-transfer catalyst heteropolyphosphato- tungstate was prepared from sodium tungstate, phosphoric acid, and cetylpyridinium chloride. In catalytic reaction, ethyl alcohol and chloroform mixture was employed as solvent. The influences of catalyst preparation conditions on catalytic performance were investigated. The catalyst preparation conditions and the catalyst testing conditions were optimized. Our investigation shows that it is possible to rule out the influences of metal ion impurities on olefin conversion and olefin oxide selectivity by washing of the catalysts. The application of ethyl alcohol and chloroform mixture solvent made it possible to fully dissolve the catalysts and resolve the product-catalyst isolation problem.Catalyst stability and circulation property were investigated by employing propylene chloride as a substrate. The FTIR measurement of both the fresh catalyst and the used catalyst shows that the catalyst is stable in reaction cycles. There is almost no structure and catalytic property change after several cycles of reaction.The epoxidation of cyclohexene was conducted over the same catalysts at similar reaction conditions. In the epoxidation of cyclohexene, cyclohexene oxide was obtained as the major product and 1,2-cyclohexanediol was formed as the major by-product, which came from the hydrolysis reaction of cyclohexene oxide. The hydrolysis of cyclohexene oxide was found catalyzed by acid sites. Hence, reducing the acidity of the reaction system should inhibite the hydrolysis reaction of cyclohexene oxide. It was found that K2HPO4 was an efficient reagent to reduce the acidity of the reaction system and higher cyclohexene oxide was obtained when K2HPO4 was added into the reaction mixture. With chloroform as solvent, the optimizal reaction conditions were found to be: cyclohexene:H2O2:catalyst =1:0.7:0.003 in molar ratio, reaction temperature 50~60℃, reaction time 90 min. At these reaction conditions, cyclohexene oxide selectivity of 98% and cyclohexene oxide yield of 66.5% were obtained.
Keywords/Search Tags:heteropolyphosphatotungstate, phase-transfer catalyst, cyclohexene, cyclohexene oxide, epoxidation, hydrogen peroxide
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