Simulation And Analysis For The Polymerization Process Of The Polycarbonate By Melt Transesterification

Polycarbonate(PC)is widely used in the automotive industry,electronic appliances,aerospace,optical media and other fields as an engineering plastic with excellent performance.As the market expands further,polycarbonate has become one of the fastest growing engineering plastics.The production method of polycarbonate is divided into phosgene method and non-phosgene method.Among them,non-phosgene production of polycarbonate realizes the recycling of by-products,which belongs to the green chemical production process and has become a hot spot in recent years.The production process is carried out under high temperature and low pressure,and the polymerization process is complicated,which becomes the core problem of the process.In this paper,the polymerization process was taken as the research object.the Aspen software and MS software are used to model and analyze the polymerization process.The main contents are as follows:(1)Based on the polymerization mechanism of polycarbonate and the tetrahedral intermediate model,the polymerization reaction is summarized as the reaction between molecular fragments.Combined with the database in Aspen,the polymerization reaction is summarized into six main reactions.At the same time,according to the existing continuous production process of polycarbonate and the characteristics of polymerization process,the idea of ??combined modeling is proposed,and the reaction process model of multi-tank series and front full mixed-flow falling film reactor is adopted.Compare with existing experimental data to verify the accuracy of the model.(2)On the basis of the polymerization model,the influence of feed ratio,polymerization pressure,polymerization temperature and residence time on the number average molecular weight of polycarbonate in the polymerization production is analyzed,and the optimum process conditions for the polymerization production are proposed(the prepolymerization temperature is maintained at 190°C to 195°C,the polycondensation temperature is maintained at 270°C to 280°C;the feed ratio is maintained at 1.01-1.03 Prepolymerization pressure is maintained at 0.4bar-0.7bar,the lower the pressure during the polycondensation phase is more conducive to the molecular weight of polycarbonate;the residence time in the prepolymerization stage is maintained at 0.8h,the best residence time of a single falling film evaporator is maintained at 0.2-0.3h).The average molecular weight is about 14,000).(3)In the polycondensation stage,the polymerization reaction is controlled by the diffusion of phenol.The diffusion coefficient of phenol in polycarbonate becomes an important factor in the study of polycondensation reaction,and it is also the key to restrict the design of polycondensation reactor,aiming at the diffusion of polycarbonate phenol molecules in polymerization.Using MS software as a platform,molecular dynamics and molecular mechanics are used to establish a unit cell model system of polycarbonate polymer and phenol.The diffusion coefficient of phenol molecules under different conditions is calculated.The results show that the diffusion coefficient increases with the increase of temperature at 190 °C-310 °C,and the phenol concentration of the unit has no effect on its own diffusion coefficient.The higher the degree of polymerization,the smaller the diffusion of phenol.Short chain provide more free volume for phenol.In actual production,high temperature and film flow in the polycondensation stage are more favorable for the polymerization reaction.