Parameter Estimation in a Simplified MWD Model for HDPE Produced by a Ziegler-Natta Catalyst

A simplified steady-state model to predict MWDs of ethylene/butene and ethylene/hexene copolymers produced industrially using heterogeneous Z-N catalysts is developed. Estimability analysis is used to guide model simplification and to determine which parameters can be estimated using the available data. Scaling of response variables and parameters using information about their uncertainties ensures that appropriate results are obtained from the estimability analysis. Parameter estimates are obtained to provide good predictions of the measured MWDs. Although the parameter values obtained are specific to the Z-N catalyst of our industrial sponsor, the method should be useful for parameter estimation and model simplification in other catalytic polymerization systems.