Parameter Estimation in a Simplified MWD Model for HDPE Produced by a Ziegler-Natta Catalyst Duncan E. Thompson, Kim B. McAuley,* P. James McLellan Introduction Engineers want to predict end-use properties of polyolefins from reactor operating conditions so that they can optimize reactor operations and design new products. In our previous work, [1] we developed a simplified mathe- matical model to predict molecular weight distributions (MWDs) of ethylene/hexene copolymers, and used indus- trial data to obtain parameter estimates. This simplified model predicts MWD from reactor operating conditions (hydrogen concentration, ethylene partial pressure, hex- ene concentration) but does not account for temperature effects. In this work, we include temperature effects, and we extend the model to include both butene and hexene comonomers. Many end-use properties of high-density polyethylene (HDPE), such as tensile strength, impact strength, melting point, and Young’s modulus, are influenced by the MWD. The model proposed in this paper predicts MWD, and can be used in combination with other models [2] to predict end-use properties from reactor operating conditions. The extended non-isothermal model has many more parameters than the original isothermal model, [1] and not all of these parameters can be readily estimated using the available industrial data set. [3] Estimability analysis [4–6] is used to determine which parameters can be estimated from the available data. The unestimable parameters are either left at their initial guesses, or are removed from the model by further simplification. In deciding which parameters can be estimated, the estimability analysis technique accounts for the model structure, for correlated effects of model parameters, and for the level of uncertainty in each of the initial parameter guesses. The Full Paper D. E. Thompson, K. B. McAuley, P. J. McLellan Department of Chemical Engineering, Queen’s University, Kingston, ON K7L 3N6, Canada Fax: þ1 613 533 6637; E-mail: kim.mcauley@chee.queensu.ca A simplified steady-state model to predict MWDs of ethylene/butene and ethylene/hexene copolymers produced industrially using heterogeneous Z-N catalysts is developed. Estim- ability 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 infor- mation about their uncertainties ensures that appropriate results are obtained from the estim- ability 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. 160 Macromol. React. Eng. 2009, 3, 160–177 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mren.200800052