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In the present paper, a dynamic optimization problem regarding grade transitions in bulk poly(propylene) polymerization processes is formulated and solved for the first time. Initially, a detailed dynamic process model is presented and implemented, comprising mass and energy balances, some of the polymer properties (such as the melting flow index and the xylene solubles) and regulatory control loops. Additionally, the effects of cocatalyst and electron donor on the propagation rate constant are taken into account. Then, the dynamic optimization problem is formulated and an evolutionary algorithm is used to solve the resulting nonlinear programming problem. It is shown that there is significant coupling among the manipulated variables and the controlled performance and polymer property variables, which adds complexity to the grade transition problem and demands the simultaneous manipulation of multiple variables during transitions. Despite the inherent open‐loop unstable nature of the analyzed process, it is shown that smooth grade transition trajectories can be accomplished through proper adjustment of the objective function weights. Finally, it is shown that the obtained optimum trajectories can significantly diminish the transition time, which can be of paramount importance for the plant economics. [ABSTRACT FROM AUTHOR]

The effect of adding hydrogen and/or electron donor on the microstructure of polypropylene polymerized with a 4th generation Ziegler-Natta catalysts at two temperatures on the molecular weight distribution, tacticity, and crystallinity of polypropylene is thoroughly investigated in this article. Polypropylene tacticity and crystallinity increases not only when external donors are added, but also when hydrogen is used as a chain transfer agent. The molecular weight distribution of the resins is deconvoluted into several Flory's most probable distributions to show how different active site types respond to the presence of electron donor and hydrogen. [ABSTRACT FROM AUTHOR]

Apparent kinetic rate constants and activation energies for catalyst activation, deactivation, and propylene propagation with a 4th-generation Ziegler-Natta catalyst are estimated. The rate of polymerization in the presence of donor and hydrogen is higher than in their absence. Catalyst activation and propagation rate constants increase with the addition of hydrogen, likely because hydrogen frees 2-1-terminated dormant sites. The deactivation term was the highest without electron donor, presumably because the nonspecific sites deactivate faster than the specific sites. Apparent activation energies for catalyst activation, deactivation, and propagation are not significantly influenced by the presence of hydrogen or external donor, indicating that they do not affect these mechanisms substantially. [ABSTRACT FROM AUTHOR]