Operation and control of a semibatch reactive distillation column

Reactive distillation integrates reaction and separation into one apparatus and offers the possibility to overcome restrictions given by chemical and phase equilibria. The batch and semibatch modes permit a more flexible operation compared to the continuous case especially for multi product plants. Here the heterogeneously catalysed esterification of methanol and acetic acid in a reactive distillation column which is operated in semibatch mode is investigated. The solution of a minimum batch time problem defines the optimal trajectory of the process. The task of feedback control is to track this trajectory in the presence of disturbances and model uncertainties. Due to the nonlinear plant behaviour, robustness properties have to be taken into consideration in the design. The nonlinearity of the system is considered as an uncertainty of the linear nominal model in the optimal operating region. A robust controller is designed using a combination of a loop shaping procedure and frequency response approximation. The linear closed-loop system is stable for the nominal model as well as for the models containing uncertainties. The controller also shows good tracking performance when used with the nonlinear model.