Modeling And Simulation Of Semi-batch Ethoxylation Reactor

Ethoxylation is used to produce nonionic surfactants that are ring-opening addition reactions of hydrophohic substrates containing active hydrogen with ethylene oxide. However, due to ethoxylation is highly exothermic reaction, and ethylene oxide is reactive, flammable, explosive and toxic, the experimental investigations of such commercial reactor seem to be expensive, time consuming and sometimes impossible. Thus, developing a mathematic model that can provide an alternative to detailed experimental investigations becomes very essential. In this work, the modeling and simulation of industrial ethoxylation reactor will be discussed, aiming at establishing an important foundation on the simulation and optimization of ethoxylation reactor.The approach adopted in this work consisted of the following steps:(1) The mathematical model and simulation method of semi-batch reactor were proposed. The mass transfer characteristics of ethoxylation reactors were analyzed, include well-stirred reactor and spray tower loop reactors. Based on reasonable hypothesis on the ethoxylation reactor, the mathematical model had been developed to describe the behavior of industrial reactor, which taking the kinetics, vapor-liquid equilibrium, variation of reactive volume, as well as the effect of inert gas nitrogen on the reactor into account. A numerical simulation program was developed to solve the mathematic model. Due to the non-linear dynamic characteristic of reactive process, the fourth order Runge-Kutta method and Aitken method were used, and the accuracy of the methods was validated.(2) All of the relative model parameters calculation methods and correlations were established, obtaining the corresponding parameters by taking the synthesis of polyethylene glycol as example. Firstly, a vapor-liquid equilibrium model was developed to describe the nonideality of the system. To deal with the difficulties in determining vapor-liquid equilibrium data through experimental approach due to the existence of EO, the UNIFAC based method was employed to estimate the liquid activity coefficients, in which the parameters related could be obtained by means of theoretical calculation. The results obtained show that UNIFAC equation was suitable for the description of the nonideality of the system because the predicted results from model agreed well with the experimentally measured one. Secondly, the reaction kinetic study of ethylene glycol ethoxylation under base-catalyzed conditions was carried out and the kinetic equations were established. The results showed that under the operation temperature range of 90 to 130℃, the activation energy of initiation step was 73490 J·mol^-1, the pre-exponential factor was 5.97×10⁶ m³Â·mol^-1·s^-1; The activation energy of propagation was 70840 J·mol^-1, the pre-exponential factor was 8.746×10⁷ m³Â·mol^-1·s^-1. Finally, the correlation of density was obtained by fitting experimental data.(3) With the developed mathematic model, the simulation was further performed to investigate the behaviour of stirred reactor and spray tower loop reactors in industrial production of polyethylene glycol. The effect of ethylene oxide feed flow rate on the reactor performance was investigate, so as to obtain the suitable EO feed flow rate within safety limits. The simulation results provided the typical dynamic profiles of the reactor temperature, pressure, the molar fraction of ethylene oxide in vapor and liquid, as well as the ethoxylated oligomer distributions. The simulation results were successfully validated against the experimental data, which showed the reliability of the developed mathematical model.