MODELLING, SIMULATION AND CONTROL OF THE REACTIVE DISTILLATION OF BIODIESEL PRODUCTION

ABSTRACT
In this work, the production of biodiesel via reactive distillation process has been modelled and simulated with the aid of ChemCAD for both steady state and dynamics. Also, the control of the process has been carried out using MATLAB/Simulink. In order to achieve this aim, dynamics data showing the response of biodiesel mole fraction in the column bottoms (controlled variable) to a change in reboiler duty (manipulated variable) and reflux ratio (selected disturbance variable) were extracted from the ChemCAD dynamic simulation of the developed process model and used to obtain the first-order-plus-dead-time transfer function relation between biodiesel mole fraction in the column bottoms, reboiler duty and reflux ratio with the aid of MATLAB. The open loop simulation was done by applying steps to the input variables (reboiler duty and reflux ratio). Furthermore, the set-point tracking and disturbance rejection control of the system were carried out using a PID controller tuned with Zeigler- Nichols, Cohen-Coon and trial-and-error techniques. It was observed that the controller parameters obtained by Zeigler-Nichols and Cohen-Coon tuning were not able to achieve the set-point tracking control of the system, and this necessitated the use of trial-and-error technique that was used to obtain the controller parameters used to handle the system in the desired manner for set-point tracking of maintaining the mole fraction of biodiesel at 0.9. Nonetheless, Zeigler-Nichols and Cohen-Coon tuning techniques were sufficient to successfully tune the process controller to carry out the disturbance rejection of the process. However, it was observed that the performance of Cohen-Coon tuning technique was better than that of Zeigler-Nichols tuning technique in the disturbance rejection control simulation as it had lower Integral Square Error and lower Integral Absolute Error values. It has, thus, been discovered that biodiesel could be produced in high purity via reactive distillation process, and the system could be efficiently handled to behave as desired using PID control system.