Preparation Of Supported Polyacid Catalysts And Catalytic Synthesis Of Tributyl Citrate

Tributyl citrate（TBC）is a non-toxic plasticizer with high thermal stability.TBC is widely used in medical appliances,toys,printing inks and coatings,biodegradable polymers,cosmetics and other fields due to its good compatibility,high plasticization efficiency,low volatility,light resistance,water resistance and cold resistance.Polyoxometalates（POM）are a kinds of metal-oxygen clusters formed by the condensation of acid salts of V,Nb,Ta,Mo,W.They have the advantages of diverse composition and structure,high thermal stability and adjustable acidity.They have become the green catalysts for the synthesis of tributyl citrate.Although polyacid in catalytic synthesis of tributyl citrate system has a wide range of applications and great development prospects,but for the development of the system still need to solve two key scientific problems:1)synthesis of a series of polyacid catalysts for catalytic synthesis of tributyl citrate reaction,the catalytic activity of systematic study.In this paper,a series of phosphotungstic acid catalysts with different proton H⁺were prepared by ion exchange method and their catalytic activities were systematically investigated.2)A new carrier should be introduced into the catalytic synthesis of tributyl citrate,realize catalyst recovery and utilization.Therefore,in this paper,using surfactants and graphene as carriers,two-phase electrostatic embedding technology,electrostatic self-assembly method and organic modification method were used to prepare polyacid@surfactant phase transfer catalyst and polyacid@graphene composite catalyst to systematically investigate their catalytic activity.And the structure,composition and morphology of the catalysts were characterized by FT-IR,XRD,Raman,SEM and TGA.The catalysts were applied to the synthesis of tributyl citrate.The optimum process conditions for the catalytic synthesis of tributyl citrate and the reusability of the composite catalyst were investigated.And the specific research contents are as follows:A series of heteropoly acids containing different protons（H⁺）H₃PW₁₂O₄₀,K_0.61H_5.39P₂W₁₈O₆₂,K_0.5H_10.6Na_2.9[Na P₅W₃₀O₁₁₀]were successfully prepared by ion exchange method.Through the comparison of the catalytic activities of the three catalysts for the synthesis of tributyl citrate,the results showed that the catalytic activityorderofthethreecatalystswas K_0.5H_10.6Na_2.9[Na P₅W₃₀O₁₁₀]>K_0.61H_5.39P₂W₁₈O₆₂>H₃PW₁₂O₄₀;The factors affecting the catalytic synthesis of tributyl citrate were investigated by single factor and orthogonal experiments.The results showed that the optimum process conditions for the catalytic synthesis of tributyl citrate with heteropoly acid catalyst were alcohol acid molar ratio of 4:1,catalyst dosage of 0.3 g,reaction temperature of 150℃and reaction time of 7 h.The highest esterification rate of tributyl citrate was 91.47%.A series phase transfer composite catalysts PW₁₂@DODA,P₂W₁₈@DODA,P₅W₃₀@DODA,P₅W₃₀@DTAB,P₅W₃₀@TTAB,P₅W₃₀@CTAB,P₅W₃₀@OTAB were prepared by water/chloroform two-phase electrostatic embedding technology employing polyacid anions as inorganic core and cationic surfactants as shell layer.By comparing the catalytic activity of heteropoly acid@surfactant composite catalysts for the synthesis of tributyl citrate,the results showed that the orders of catalytic activity of the composite catalysts were:P₅W₃₀@DODA>P₂W₁₈@DODA>PW₁₂@DODA,P₅W₃₀@DODA>P₅W₃₀@OTAB>P₅W₃₀@CTAB>P₅W₃₀@TTAB>P₅W₃₀@DT AB;The factors affecting the catalytic synthesis of tributyl citrate were investigated by single factor and orthogonal experiments.The results showed that the optimum process conditions for the synthesis of tributyl citrate catalyzed by heteropoly acid composite catalysts were as follows:the molar ratio of alcohol to acid was 4:1,the amount of catalyst was 0.10 g,the reaction temperature was 150℃and the reaction time was 8 h,the esterification rate of tributyl citrate was up to 74.72%.And after repeated use for 5 times,the esterification rate could reach 63.89%.The supported polyacid catalyst P₅W₃₀/PEI/GO was prepared by electrostatic interaction and organic modification employing P₅W₃₀as catalyst,hyperbranched polyethyleneimine（PEI）as crosslinking agent and graphene oxide as carrier;The factors affecting the catalytic synthesis of tributyl citrate were investigated by single factor experiment and orthogonal experiment.The results showed that the optimum process conditions for the catalytic synthesis of tributyl citrate with supported polyacid catalyst were as follows:the molar ratio of alcohol to acid was 4:1,the amount of catalyst was 0.07 g,the reaction temperature was 160℃and the reaction time was 8 h,the esterification rate of tributyl citrate was 65.29%,and the esterification rate could still reach 59.89%after 5 times recyling.