Study On Process Optimization And Kinetics Of N-butyl Gallate Under Microwave Radiation

N-butyl gallate?BG?is one of the important derivatives of gallic acid alkyl series.It can scavenge oxygen free radicals in the body,and has a good application prospect in medicine.It can also be used as food additives or antibacterial agents,as well as additives for new sensitive materials.Microwave is a short electromagnetic wave with a wavelength range of 0.1mm¹m.It has the characteristics of penetration,reflection and absorption.As a new heating source,microwave has the characteristics of fast heating,uniform,high efficiency,energy saving and selective heating.In recent years,as an efficient heating method,it is widely used in basic research.For the synthesis of alkyl gallate series material,mainly by homogeneous catalysts such as sulfuric acid,p-toluene sulfonic acid as catalyst.However,it is difficult to separate and recover the catalyst,which has a short catalytic life and pollutes the environment.For this reason,the preparation of phosphotungstic acid supported on carbon was studied by reflux method.The synthesized heterogeneous acid catalyst was characterized by Fourier transform infrared spectroscopy?FTIR??specific surface area?BET?and solid ultraviolet?UV-vis?.The results show that when the loading capacity of phosphotungstic acid is less than 26.68%,the surface of the activated carbon shows a high degree of dispersion.When the catalyst load is 26.68%,the catalytic activity of the catalyst is higher,and the reaction has a good esterification yield.In this paper,Activated Carbon Supported phosphotungstic Acid?TPA/AC?as catalyst was used to optimize the synthesis process of n-butyl Gallate under different heating methods.In the conventional oil bath heating,through single factor experiment and the response surface method for optimum synthesis cosnditions:the amount of catalyst is 1.28g,the molar ratio of 1:11.92,reaction temperature 132.2?,reaction time is 120min,the maximum yield of n-butyl gallate was up to 84.33%.The experimental results of the optimum technological conditions are close to the predicted maximum yield of 84.33%,which proves the reliability of the experimental results.In the microwave radiation heating,through the single factor experiment and response surface methodology to optimize the optimal synthesis conditions are:catalyst dosage 1.02 g,the molar ratio of 1:11.06,reaction temperature 127.1?,reaction time is 34.2min,the maximum is 90.33%of the yield of n-butyl gallate.It was found that microwave heating could yield higher esterification yield in less time than conventional heating.Kinetic studies showed that use TPA/AC as catalyst,when the reaction time was110min,the conversion rate of gallic acid reached 85%,and the reaction was basically balanced.Under microwave irradiation,the conversion rate of gallic acid was up to90%at the reaction time of 35min.At this point,the chemical reaction equilibrium was basically established.The intrinsic reaction kinetics equations of two different heating modes were obtained.Compared with the traditional heating,microwave heating is faster and more efficient.From the intrinsic kinetic equation,the activation energy E and the pre exponential factors A for the conventional oil bath heating and microwave heating are found to be 51.39 kJ/mol?16.27kJ/mol and1.251x10⁵mol.L^-1.min^-1?10.023mol.L^-1.min^-1,respectively.That the conventional oil bath heating method under the reaction activation energy of E is 3.16 times the microwave,visible under microwave irradiation,the reaction activation energy decreased obviously,which also explains why the reaction under microwave irradiation can achieve faster chemical reaction equilibrium.