Technological Research And Simulation On Synthesis Of Dimethyl Carbonate Catalyzed By Potassium Methoxide

Transesterification method of propylene carbonate and methanol is the basic method for industrial production of dimethyl carbonate.Due to the good catalytic effect and high solubility of sodium methoxide,sodium methoxide is mainly used as the homogeneous catalyst for transesterification method.However,sodium methoxide catalyst easily reacts with water and carbon dioxide causing deactivation,the catalytic activity of the sodium methoxide not lasting and the final effect of reaction affected.This paper compared the catalytic activity of potassium methoxide and sodium methoxide for transesterification under various reaction conditions.Potassium methoxide,which is also the methoxide,have the greater catalytic activity and faster dissolution rate than sodium methoxide,with high solubility;When the amount of catalyst is low,potassium methoxide also show excellent catalytic effect;the catalytic effect of it is more lasting.And the potassium carbonate produced by potassium methoxide with water,carbon dioxide has good catalytic activity for the synthesis of dimethyl carbonate by transesterification.It has little effect on the progress of transesterification.Therefore,potassium methoxide can be used as a catalyst for synthesizing dimethyl carbonate by transesterification instead of sodium methoxide.Under the catalysis of potassium methoxide,the effects of the feed molar ratio of methanol to propylene carbonate,the amount of catalyst and the reaction temperature on the transesterification to synthesis dimethyl carbonate were studied,and finally the appropriate batch reaction conditions were determined.The thermodynamic and kinetic on the transesterification of propylene carbonate reacting with methanol were studied.The equilibrium concentration at different temperatures was obtained through experiments,from which reaction equilibrium constant K was calculated.According to the linear relationship between ln K and 1/T,the reaction enthalpy(35)_rH is-21.28k J/mol;According to the reaction mechanism,the reaction rate equation was established.Matlab software integrated the reaction rate equation to obtain the calculated value of propylene carbonate concentration.The calculated value compared with the experimental data to simulate the reaction rate constant k_+at different temperatures;It can be deduced from the relationship between k_+and T that the reaction activation energy E_ais 40.37 k J/mol,and the pre-exponential factor A is22811.04 mol/(L·min).At last,Aspen Plus software was used to simulate the reactive distillation column and pressurized distillation column in the technology of transesterification to synthesis dimethyl carbonate.The operation parameters such as feed molar ratio of methanol to propylene carbonate,number of theoretical stages,feedboard position,total feed flow and reflux ratio of the reactive distillation column were mainly studied the effects on the conversion of propylene carbonate and the mass fraction of dimethyl carbonate at the overhead,obtaining the optimized operation conditions.Under this operation condition,the conversion of propylene carbonate reached 99.80%,and mass fraction of dimethyl carbonate at the overhead was 31.85%;At the same time,the effects of conditions such as bottom flow,number of theoretical stages,feed position,reflux ratio and operation pressure of the pressurized rectification column were studied to obtain optimized operation conditions.Under this operation condition,the mass fraction of dimethyl carbonate at the bottom is as high as 99.9968%,which meets the requirements of battery-grade dimethyl carbonate.The methanol and dimethyl carbonate azeotrope which the mass fraction of dimethyl carbonate is14.39%was obtained at the overhead.