State Estimation and Control for Semi-Batch Polymerization Reactors

A strategy is proposed for estimating and controlling properties of a styrene/butadiene rubber (SBR) latex produced in a semi-batch reactor operation. The suboptimal nonlinear strategy features a nonlinear state estimator, a nonlinear open-loop feedforward compensator, and a linear feedback controller to correct for errors in the feedforward control actions. In arriving at a nonlinear state estimator, three approaches, extended Kaiman filtering, extended Kaiman filtering with global reiteration, and a nonlinear optimization approach were considered. The second approach was found to be the most effective and was therefore adopted. The importance of introducing sufficient meaningful nonstationary states is discussed in order to have consistent state estimates when nonideal conditions exist. Using the knowledge of the modelled chemical reaction mechanisms, open-loop feedforward actions are proposed based on establishing conditions for maintaining fixed instantaneous copolymer properties. These open-loop/feedforward policies establish quasi-steady state conditions on the instantaneous copolymer properties to be controlled. This allows the application of conventional linear feedback control to correct for errors remaining after the open-loop/feedforward actions. Simulation results are presented to demonstrate the effectiveness of the proposed scheme.