The Simulation And Optimization Of Catalytic Distillation Based On The Rate-based Model

With the purpose of process intensification,Catalytic distillation(CD)technology is developed and applied in roomy area,which combines the distillation and a heterogeneous catalyzed reaction in a single vessel.Comparing to the traditional distillation process,CD process is more complicated.It is necessary to utilize the method of process simulation to make a good understanding of the interaction between the catalytic reaction and the distillation process,which is crucial to give guides to practical design and production process.Since the catalytic packing put in the catalytic distillation column,the processes of mass and heat transfer,pressure drop,liquid holdup and effective phase interface area are totally different from those in the traditional distillation column which equipped with the structure packing without the catalyst layer.It is significant to set up the mathematics model for catalytic distillation to take the difference of mass and heater transfer,pressure drop,liquid holdup and effective phase interface area into account.Resultly,this research focuses on the non-equilibrium model to simulation and optimization the CD process using the Rate-based method.The major research contents are as follows:(1)Set up the mathematics equations model based on the Rate-based model by adopting the RateFrac model in the chemical engineering process simulation software Aspen Plus and programming the mass transfer coefficients,interface area,liquid holdup model and macro-kinetics external Fortran subroutines,which can be compiled to calculate at the same time.The method of Newtons was adopted to calculate the process.(2)The catalytic distillation process of hydrolysis of methyl acetate was choose to be the test system to confirm the proposed model.The 5 different depth models were set up to simulate the process,namely:Equilibrium stage model assuming chemical equilibrium.(EQ-EQ model);Equilibrium stage model using the power law type kinetics form.(A-EQ model);Equilibrium stage model using the user kinetics.(p-EQ model);Rate-based model using the user kinetics with mass transfer coefficients correlation of Bravo et al.(p-Rate-based-B model);Rate-based model using the user kinetics with effective experimental correlations.(p-Rate-based-E model).The simulation results were validated by experimental data from literature.Finally,the results show that the p-Rate-based-E model can predict the catalytic distillation process in accuracy.(3)Using the proposed model to simulate the catalytic distillation process of hydrolysis of methyl acetate to make a good understanding of the mass and heat transfer rates profile,vapor and liquid concentration profile,temperature and reaction profile.The results show that the mass transfer resistance was concentrated on the liquid film and the height of the reaction zone in the existing catalytic distillation column still needs optimization.Therefore,the p-Rate-based-E model was adopted to optimize the catalytic distillation internals and the process parameters in catalytic distillation column.It is found that the 4mm catalytic packing shows the excellent performance in pressure drop,mass and heat transfer,reaction,liquid holdup and effective phase area comparing to the 8mm,12mm,19mm and 25mm catalytic packing.Results show that the conversion of methyl acetate is up to 99%under the condition of 4mm catalytic distillation internals;5.5 of the ratio of methyl acetate to water in feed;0.8 of ratio of reflux to feed rates;1.5m of the height of reaction zone;0.9m of the height of stripping zone.The P-Rate-based-E model proposed in this research takes account carefully of mass and heat transfer,reaction,pressure drop,liquid holdup and effective phase area in catalytic distillation process and shows the good prediction performance,which can provide the basically theory guides to design and optimization of engineering problem and catalytic packing development.