Reaction Kinetics In The Systhesis Of Dimethylureaand Industrial Optimization

As an important organic synthesis intermediate,dimethylurea has been widely used in many fields.In particular,with the development of pharmaceutical industry,the requirements for the production process of dimethyl urea are getting higher and higher,so the improvement of the existing production process has attracted much attention.This paper studied the gas-liquid reaction kinetics of the urea ammonolysis system in order to provide basic data for the continuous transformation of the synthesis process and the design of the gas-liquid reactor.The influence of each process condition on the conversion rate and yields of the reaction were explored by single-factor experiments.On these basis,the response surface methods were used to optimize the process conditions,the best reaction conditions as follows: reaction temperature was 155℃,the MMA ventilation speed was 135ml/min,stirring speed was 620r/min,MMA:urea(molar ratio)=4.3:1.Under these conditions,the conversion rate of urea was 99.54%,and the selectivity of dimethylurea was about46.86%.The results of the kinetic experiments showed that the urea ammonolysis reaction was a instantaneous reaction.The main mass transfer effects of temperature,stirring speed,ventilation speed,and the diameter of the stirring blade under the influence of gas film mass transfer resistance are discussed.Comprehensively considering the effects of various factors,we use the dimensionless number group analysis method to obtain the correlation formula of the gas/liquid volume mass transfer coefficient.The calculation and experimental results showed that the two correlation equations can better reflect the experimental values.Then,we studied the methylurea aminolysis reaction,The results showed that the overall rate of methylurea aminolysis reaction was extremly slow,and the mass transfer has little effect on the overall reaction rate.We found a new intermediate and the structure was determined by means of thin-layer chromatography,column chromatography and HPLC.Accroding to the results,we proposed a new reaction route that methylurea may be directly converted into this intermediate,and then the intermediate transformed into dimethylurea.The purification crafts of this intermediate was optimized by response surface methods.The order of the three factors affecting the yield of intermediates was established,as: Silica gel volume>volume flow>chloroform volume fraction...