This study has been carried out to demonstrate the control of a reactive distillation process in which the production of biodiesel was taken as the case study using an advanced control method, which is known as dynamic matrix control. The control was accomplished by employing the transfer function model of the reactive distillation process developed, using the System Identification Toolbox of MATLAB, from the dynamic data generated when the prototype plant of the process was simulated with the aid of ChemCAD process simulator. The results obtained from the dynamic matrix control were compared with those of a proportional-integral-derivative (PID) control system tuned with Ziegler-Nichols and Cohen-Coon methods, and it was discovered that the dynamic matrix control was able to perform best among the three (dynamic matrix control method, PID tuned with Ziegler-Nichols method and PID tuned with Cohen-Coon method) because it (the dynamic matrix control) was able to make the biodiesel mole fraction response not to exceed the maximum limit value of 1 in addition to having the lowest sum of absolute errors (SAE) and sum of squared errors (SSE) from the control systems that were simulated.
In this work, the control of the mole fraction of a fuel additive being produced in a reactive distillation column has been carried out using proportional-integral-derivative (PID) control. The fuel additive considered in this case was isopropyl alcohol, which was produced from the reaction between propylene and water. To accomplish the work, a ChemCAD model of the process was first developed and simulated to convergence before it was converted to dynamic type from which the dynamic responses of the system were generated and used, with the aid of MATLAB, to develop a transfer function model having the reboiler duty, the reflux ratio and the temperature of the bottom product as the input, the disturbance and the output variables of the process, respectively. The obtained transfer function model was used to develop the open-loop and the closed-loop Simulink models of the process that were also simulated. The closed-loop simulation was carried out with the objective of achieving a fuel additive product with a mole fraction of 0.97, and this was done using a PID controller that was applied inferentially via the product temperature. The results obtained showed that the control of the fuel additive mole fraction could be achieved inferentially, with PID controller tuned with Cohen-Coon and Simulink approaches, using product temperature.
This work has been carried out to demonstrate the application of a process simulator known as CHEMCAD to the modelling and the simulation of a reactive distillation process used for the production of n-butyl acetate, with water as the by-product, from the esterification reaction between acetic acid and n-butanol. The esterification reaction, which is generally an equilibrium type, was modelled as two kinetic reaction types in the reaction section of the column used, which had 17 stages with the middle section (stages 6 – 12) being the reaction section. A reflux ratio of 3 and reboiler duty of 78 kJ/min as well as 30 mL/min of each of the reactants with 99% molar purity were used for the simulation of the column. The results obtained revealed that the developed model was a valid one because there was a very good agreement between the results and the theoretical knowledge of a distillation column based on the fact that the desired (which was the heavy) product (n-butyl acetate) was found to have the highest mole fraction in the bottom section of the column while the by-product of the process (water) was discovered to have a mole fraction higher than that of n-butyl acetate in the top (condenser) section of the column. Therefore, CHEMCAD has been applied to the steady-state simulation of the reactive distillation process used for the production of n-butyl acetate from the esterification reaction of acetic acid and n-butanol successfully.
Abstract.Reactive distillation is a process that combines chemical reaction and separation in a single piece of equipment (distillation column). The process has a lot of benefits especially for those reactions occurring at conditions suitable for the distillation of the process components, and these result in significant economic advantages. However, owing to the complexities resulting from the integration of reaction and separation, its control is still a challenge to process engineers because it requires a control method that is robust enough to handle its complexities. Therefore, in this work, model predictive control (MPC) has been applied to a reactive distillation process used for developing a renewable energy known as biodiesel. The control algorithm of the MPC was formulated with the aid of MPC toolbox of MATLAB/Simulink in which the closed-loop models of the process were developed and simulated. The analysis of the results obtained from the simulations carried out for the optimization of the tuning parameters revealed that, among the tuning parameters considered, integral absolute error of the control system was less affected by the control horizon because its p-value was greater than 0.05 based on 95% confidence level. Furthermore, the simulation of the closed-loop system of the process using model predictive control tuned with control horizon of 11, prediction horizon of 18, weight on manipulated variable rate of 0.05 and weight on output variable of 2.17, which were the optimum parameters obtained using Excel Solver, showed that the system was well handled by the controller under servo control because it was able to get settled at desired mole fractions within 60 min. However, the settling time recorded in the case of regulatory control system of the process with the same controller was found not to be encouraging. Therefore, it is recommended that further work should be carried out on this subject matter in an attempt to obtain tuning parameters that will make the settling time of the closed-loop system of the process under regulatory control simulation very reasonable. Nomenclature ANOVA
Abstract. Reactive distillation, being an intensified process of combining reaction and distillation in a single vessel, is an ongoing research. This work considered the use of this novel process to investigate how the purity of a fatty acid methyl ester (oleic acid methyl ester -methyl oleate), which is an alternative fuel that has a potential economic bedrock, vary with variations in reflux ratio and reboiler duty with the aid of Aspen Plus model of the process. The column employed in developing the model of the process was a RadFrac type having 29 stages, which was divided into five sections, namely condenser (top), rectifying, reaction, stripping and reboiler (bottom) sections. After the development, the model was simulated using UNIversal QUAsiChemical model (UNIQUAC) base method. In order to investigate the sensitivity of the system, reflux ratio and reboiler duty were varied from 2.0-5.5 and 1350-1800 W, respectively. The results obtained from the steady-state simulation of the process revealed that the developed Aspen Plus model of the system was table because it was able to converge when simulated. Furthermore, it was discovered from the sensitivity analysis carried out that a methyl oleate having a mole fraction of approximately 0.7627 could be obtained from the process when the reflux ratio and the reboiler duty were 2.0 and 1800 W respectively. Also, it was observed that the mole fraction of methyl oleate was sensitive to both reflux ratio and reboiler duty because the variations in them (reflux ratio and reboiler duty) resulted in corresponding variation in the methyl oleate mole fraction obtained from the system.
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