Modelling and Control of Sustained Oscillations in the Continuous Emulsion Polymerization of Vinyl Acetate

Abstract

<p>The population balance model of Kiparissides (1978) for the continuous emulsion polymerization of vinyl acetate, has been extended to predict molecular weight moments and has been corrected for induction time and particle shrinkage due to density changes. The developed model was successfully able to simulate experimental results from Kiparissides (1978) and Greene et al.(1976) for the continuous emulsion polymerization of vinyl acetate. Application of the model to the batch data of Keung (1974) had reasonable access as well. The model was extended to the continuous emulsion polymerization of styrene which follows different nucleation kinetics and was able to predict the average conversions and particle diameters for the data of Brooks et al.(1978). Little success was achieved in predicting the small experimentally observed oscillations for the styrene system.</p> <p>To eliminate the sustained property oscillations in the vinyl acetate system Linear-Quadratic stochastic optimal control theory was applied to the model. Due to extreme non-linearities inherent in the system, this approach was shown to be inadequate. Instead, the reaction system was redesigned to include a small continuous seeding reactor with monomer and water bypass. Model predictions indicated that the redesigned system eliminated the oscillations. Experimental testing of the redesigned system verified that a dramatic improvement in stability was possible. The redesigned reactor configuration was also shown to be more flexible in controlling particle sizes and conversion through use of the bypass.</p> <p>A method for selecting the optimum sensors was developed. It was shown that the measurement combination providing the most information would be conversion (as currently available from an on-line density meter) and some measure of weight average molecular weight.</p>