Preparation Of Heteropoly Acid Supported On Molecular Sieve SBA-15 And Study On Catalysis Synthesis Of Tributyl Citrate

Heteropoly acid is a type of catalytic material which possesses outstanding performance,it has the advantages of low temperature,high activity,high selectivity,environmental friendliness and so on. Mesoporous molecular sieve SBA-15 has normal,long-range order pore structure,higher hydrothermal stability and larger surface area,it is regarded as an excellent catalyst support.In this paper, molecular sieve SBA-15 was used as catalyst support,a series of supported heteropoly acid catalyst were prepared adopted hydro-thermal decentralization method,impregnation methodand,in-situ synthesis method and reaming in-situ synthesis method,which were characterized by XRD,FT-IR,NH₃-TPD,N₂ adsorption-desorption and chemical analysis etc.The supported heteropoly acid catalyst were used to catalyse the synthesis of tributyl citrate (TBC),the optimum reaction conditions and stability of catalysts were investigated, and good effects had been obtained.The results indicated that the supported heteropoly acid catalyst had larger surface area,high activity,long longevity,the problem that recycling difficulty lied in homogeneous phase catalytic reaction was solved. First of all, hydrothermal decentralization and impregnation method were used to prepare heteropoly acid catalyst (PW₁₂/ SBA-15).The graphics of XRD,FT-IR and pore diameter distribution indicated that heteropoly acid was decentralized on the surface of pore canal uniformly, and the Keggin structure of heteropoly acid was still kept. The optimum contidions of catalytic the synthesis of tributyl citrate (TBC) under PW₁₂/SBA-15 are following:mass ration of the catalyst used in the reactants is 1.1%,reaction temperature is 150°C,reaction time is 5～7h,the capacity of heteropoly acid is 20.3 %～27 %,mole ratio of alcohol to acid is 4:l⁵:l,esterification can reach 95%,the catalyst remains activity after used for 30h.Secondly, in-situ synthesis method was used to prepare heteropoly acid catalyst (PW₁₂-SBA-15).The catalyst prepared possessed characteristic X-peak of pure SBA-15,N₂ adsorption-desorption and NH₃-TPD showed that the pore diameter increased and strong acid hub exits on its surface, the result of FT-IR indicated that heteropoly acid still kept Keggin structure.The catalyst was used to catalyse the synthesis of tributyl citrate (TBC), esterification could reach 95 % under the optimum contidions. Catalyst kept favorable stability during its serives.Finally, reaming in-situ synthesis method was used to prepare heteropoly acid catalyst (PW₁₂-KSBA-15). XRD analysis showed that the crystal skeleton was formed and the characteristic diffraction peak was migrated to low angle; N₂ adsorption-desorption indicated that aperture largened and surface area decreased in certain extent,FT-IR analysis told us that the keggin structure of PW₁₂ kept still. The catalyst was used to catalyse the synthesis of tributyl citrate (TBC), esterification could reach 90% under the optimum contidions.The catalyst kept well activity after used for 30h.Phosphotungstic acid,silicotungstic acid and phosphomolybdic acid were mixed in certain proportion, the catalytic effect was good when it was supported by hydro-thermal decentralization and impregnation method, during the synthesis of tributyl citrate (TBC), esterification could reach 97.75%,94.92% respectively,the catalyst had favorable industrial prospect.