Model Predictive Control of Free Surfactant Concentration in Emulsion Polymerization

Abstract: In emulsion polymerization processes, the surfactant concentration plays an important role in the latex stability, reaction kinetics and particle size distribution (PSD). Controlling the free surfactant concentration in the aqueous phase ensures the stability of the latex and the control of the micellar nucleation rate. The PSD is determined by particle nucleation, growth and stability which are highly nonlinear behaviors. The PSD affects the polymer rheology, adhesion, optical properties and mechanical strength. This work deals with the model predictive control (MPC) of free surfactant concentration using the surfactant feed rate as a control variable. The used strategy is a global method that aims to reduce the on-line calculation time due to the partial differential equations (PDE) model based optimization task resolution. In order to decrease the computational burden, the nonlinear PDE system is solved off-line. Then, a linearized PDE model around the previous off-line behavior is used to find the optimal variations for the on-line predictive control.