Study On Process Optimization And Kinetics Of The Synthesis Of Isobutyl Gallate Under Microwave Radiation

Isobutyl gallate is one of the most important derivatives of gallic acid,and it has been widely used in the fields of chemical engineering and food industry for its advantages such as good oxidation resistance.Microwave is a new type of heating source emerging in recent years.It has been widely used in various basic researches due to its characteristics of rapid heating,uniform heating,high efficiency,energy saving and selective heating.The application of microwave radiation technology to the esterification reaction has many advantages such as easy operation,excellent product quality and ease of post-processing.The traditional method for preparing Isobutyl gallate is to use sulfuric acid as a catalyst,but there will be a series of problems such as increase of side reactions,corrosion of equipment,environmental pollution,difficulty in post-processing and so on.In recent years,p-toluenesulfonic acid has been widely used in the synthesis of gallic acid alkyl esters.P-toluenesulfonic acid is a kind of non-oxidizing organic strong acid and has a superior catalytic effect on the esterification reaction.However,p-toluenesulfonic acid is so easily soluble in the reaction system that it is difficult to post-processing and to be recycled.In view of this,activated carbon was selected as the carrier and p-toluenesulfonic acid as the active ingredient.A new type of catalyst p-toluenesulfonic acid supported on activated carbon was successfully prepared by impregnation method and was first used to catalyze the synthesis of Gallic acid alkyl esters.The catalytic effect of catalyst loading on the synthesis of Isobutyl gallate and the reusability of the catalyst were studied.The results show that the yield of Isobutyl gallate is at a relatively high level and the catalyst has excellent reusability when the loading of the catalyst is 28.57%.In this paper,p-toluenesulfonic acid supported on activated carbon was selected as the catalyst to optimize the process conditions for the synthesis of Isobutyl gallate under two different heating conditions.Under normal heating conditions,the optimum synthesis conditions obtained by single-factor experiments and response surface methodology were as follows:catalyst amount 6.24%,material molar ratio 1:11.80,reaction temperature 125.26 °C,reaction time 111.80 min,the yield of Isobutyl gallate is up to 86.75%.Under microwave radiation heating,the optimum synthesis conditions obtained by single factor experiment and response surface method were as follows:catalyst amount 5.04%,material molar ratio 1:11.73,reaction temperature 125.42 °C,reaction time 40.55 min,the yield of Isobutyl gallate is up to 92.34%.The results of validation experiment under optimal process conditions are close to the predicted value,which indicating that the experimental results are quite reliable.Compared to conventional heating methods,microwave radiation heating requires shorter reaction time and smaller amount of catalyst to reach higher esterification yield.By contrasting the data of esterification yield,the catalytic effect of p-toluenesulfonic acid supported on activated carbon is significantly better than that of p-toluenesulfonic acid,which also proves the homemade supported catalyst has high activity.By analyzing the kinetics of the synthesis reaction of Isobutyl gallate,we can know from the intrinsic kinetic equation of the reaction,the activation energy E is 49.344 kJ/mol under normal heating conditions,and the pre-exponential factor A is 0.636 X 105 mol.L-1.min-1;And the activation energy E under the microwave radiation heating conditions is 16.275 kJ/mol,the pre-exponential factor A is 10.074 mol.L-1.min-1.It was found that the activation energy of the reaction under the conventional heating conditions was about 3.032 times that of under the microwave radiation heating conditions.That is,microwave irradiation makes the activation energy of the reaction lower significantly.And this is the reason why the esterification reaction can reach the chemical reaction balance faster under the microwave radiation heating conditions.