Study On The Green Technology Of Benzaldehyde Production

Benzaldehyde is an important organic intermediate product which is mainly manufactured by chlorination and hydrolysis of toluene. However, the disadvantage of low yield, poor product quality and serious environment pollution is unavoidable. In this paper the effort is made to try to exploit the clean technology about chlorination and hydrolysis of toluene by systematically studying technology and kinetics of two key reaction steps.The study on the technology and kinetics of chlorination of benzyl chloride is rather essential to the design of reactive distillation column in that the new technology about combination of reaction and distillation is used in the production of benzal chloride. In the inner loop reactor, the effect of temperature and chlorine flow rate on conversion of benzyl chloride and yield of benzal chloride was studied and the rule of concentration change of benzyl chloride, benzal chloride , benzotrichloride with reaction time was measured by changing reaction temperature and chlorine flow rate. The result showed there is difference between the product distribution of benzal chloride manufactured by chlorination of benzyl chloride and by direct chlorination of toluene. The concentration of benzal chloride is higher than 65% ( benzotrichloride% >2% ),which is much higher than that of direct chlorination of toluene. It is good to produce benzal chloride and provide foundation for the ascertain of technological conditions of benzal chloride production.The kinetic model of consecutive reaction for chlorination of benzyl chloride has been built by analyzing the reaction mechanism and macroscopic stage. The reaction rate constant and activity energy of consecutive reaction was calculated by parameter estimation. The two step reaction activity energies are 28.14KJ/mol and 58.37KJ/mol in the temperature range from 950C to 1250C, and the model values and experimental values tally well.The hydrolyzation of benzal chloride is the heterogeneous phase gas-liquid-liquid reaction. A new kind of phase transfer catalyst was adapted and the study on the feasibility of hydrolyzation of benzal chloride, reaction technology and kinetics was carried out in order to get rid of heavy metal pollution caused by zinc catalysis. The result declared that this catalysis has an excellent character in reaction rate and product yield The fact that the improvement oftemperature can speed hydrolyzation rate without changing the selectivity of benzaldehyde and the proper hydrolyzation temperature is between 1000C to boiling point was obtained by using different reaction temperature. The change of hydrolyzation medium has no harmful effect on reaction rate and yield of benzaldehyde. All these experimental results lay a foundation for cleaning hydrolyzation technology.The simplified peseudo-first-order kinetic model for hydrolyzation of benzal chloride was proposed according to the character of hydrolyzation reaction and the apparent reaction rate constant and activity energy was obtained. The activity energy is 17.73KJ/mol in the temperature range from 900C to 1100C and the model values and experimental values tally well.