Kinetic modeling of slurry propylene polymerization using a heterogeneous multi-site type Ziegler-Natta catalyst

摘要

The semi-batch slurry polymerization of propylene using a heterogeneous multi-site type Ziegler-Natta catalytic system was studied. A simple kinetic model including initiation, propagation, spontaneous chain transfer, chain transfer to hydrogen, chain transfer to monomer and chain transfer to cocatalyst, and spontaneous deactivation was developed to predict instantaneous rates of polymerization and average molecular weights of final products. Estimation of kinetic parameters was performed using online measurements of polymerization rate and end of batch measurements of average molecular weights. The multivariable nonlinear optimization problem was solved using the Nelder-Mead simplex method for three different site types at three levels of temperatures. The model predicts that the propagation reaction has a lower activation energy than chain transfer reactions which leads to a decrease of molecular weight at elevated temperatures. The deactivation reaction has a higher activation energy than the propagation reaction, which results in decreasing the final rate of polymerization at higher temperatures.