Study On Synthesis Of Benzyl Acetate With Heteropoly Acid As Catalysts

As a kind of polynuclear inorganic macromolecule compound containing oxo bridge, heteropoly acids are the oxygenic polyatomic acid that coordinated with center atom and coordinating atom. The heteropoly acids have such unique cage structures that are similar with liquid phase. So catalysis can carry from not only the teeth outwards but also in the body and heteropoly acids have good catalyzed activity and selectivity. As catalyst, heterpoly acids have high prices and good solution power in acid alcohol and water. There are some problems about heteropoly acids such as recovery processing and so on. In addition, catalyst performance can't give out for small surface area. Therefore we put heterpoly acids loading on some carriers to increase surface area. This made for heterogeneous catalysis and heterpoly acid have widely appliance.A series of heteropoly acids with the Keggin structure such as 12-phosphotungstic acid are used as the active component. In addition, a series of supported heteropoly acids have also been prepared with activated carbon,diatomite and silica as their carriers by different methods.The catalysts were characterized by Hammeet,IR,XRD and BET. It showed that the supported catalysts still had the Keggin structure of PW₁₂, the surface area increased significantly, the acid strength was similar to PW₁₂, and active components in the various carriers dispersed well.The heteropoly acid catalysts were used in the esterification. The catalytic activity of different heteropoly acids and supported heteropoly acids were investigated by measurement of acid contents. Then the catalysts of high activity and selectivity were selected to be used in the preparation of benzyl acetate. Benzyl acetate was synthesized by benzyl alcohol with acetic acid as raw material. The molar ratio of acetic acid to benzyl alcohol,the content of the catalysts,the reaction time and the content of water carrier were studied in the experiment. Then the best reaction condition was determined.It was proved that 12-tungstophosphoric acid , PW₁₂/ diatomite and PW₁₂/ SiO₂ were good catalysts of esterification, the yield of each catalyst was 91.6%,87.8% and 88.9% accordingly .The activated carbon supported catalyst had lower activity. The supported catalysts had no corrosion and could be reused. High activity and selectivity was attained. We can foresee a bright future for the application of heteropoly acid catalyst to chemical industry.