Modeling And Simulation Of The PA66 Polymerization Process

Process modeling is an important method to guide industrial production,improve existing process and solve debottleneck in industrial plants.At present,modeling the polymerization process has difficulties of physical property calculation,reaction kinetics and mass transfer kinetics.The reaction-mass transfer kinetics steady-state model based on reaction mechanism is developed for the whole PA66's continuous production process and used to analyze process parameters such as reaction temperature,pressure and residence time,which can provide guidance for the optimization of PA66 production process.The main results are as follows:1.The UNIFAC activity coefficient method was selected and the component's groups were divided for PA66 polymerization system.The new defined groups are-CH2COO-·+H3NH2C-,-CH2COOH and-CH2CONHCH2-,which characterize the component's special structure.Melting point and molar fusion enthalpy of PA66-salt as well as the equilibrium data of PA66-salt and water are experimentally determined and used to regress the group interaction parameters of UNIFAC model.The new UNIFAC model was used in Aspen to simulate the solubility of PA66-salt in aqueous solution giving a relative error of 2.1%from experimental data.The model was further employed to simulate the concentration of PA66-salt under the industrial conditions and gave a relative error as low as 5%,compared with 20%from the default UNIFAC model in Aspen.2.On the basis of inductive analysis of reported reaction mechanism,reaction kinetics and mass transfer kinetics constants of polymerization process,the kinetics constants were drawn with a reasonable range.For the polymerization process in reactor and reducer,the main reactions including the dehydration reaction of salt,polycondensation reaction and hydrolysis reaction were considered.For the polymerization process in polymerization reactor with the high temperature and the increasing viscosity of reaction material,thermal degradation reaction and mass transfer of small molecules was included.A set of kinetics constants from literature were used as original parameters.The key kinetics parameters were modified within the adjustable range to fit the experiment data including the salt content determined by water extraction method and molecular weight from intrinsic viscosity measurement.The reaction-mass transfer kinetics steady-state model based on reaction mechanism was developed and used to simulate the polymerization process at different production capacities.The simulation results agreed well with the experiment data.3.The simulation of PA66 production process was developed and applied to analyze the impacts of operating conditions of reactor,reducer and polymerization reactor,including temperature,pressure,residence time and length on the quality indexes of the product such as the mass flow of PA66,the number-average molecular weight of polymer,salt content,and the content of by-product from thermal degradation.MWN increased with the increase of temperature of reactor,the decrease of pressure of reactor and the increase of residence time of polymerization reactor to some extent.The content of salt in the product can be decreased by extending the residence time of reactor and polymerization reactor,as well as the increase of temperature of reactor and reducer.The decrease of the residence time of polymerization reactor can reduce side reactions.These results provide good reference for the optimization of production parameters in industrial process.