(632c) Polymerization Process Reconfiguration from Molecular Weight Distribution

Authors: 
Zhang, C., Carnegie Mellon University
Biegler, L. T., Carnegie Mellon University
Shao, Z., Zhejiang University
Chen, X., Zhejiang University
Gu, X., Zhejiang University
Yao, Z., Zhejiang University

To meet the market requirements, a polymerization process is expected to be capable of producing a number of polymer grades with different end-use properties. Due to the limitations of the conventional process structures, many polymer grades, especially some high-quality grades, may not be available even under a wide range of operating conditions. Hence, a more flexible process configuration needs to be considered and designed. On the other hand, molecular weight distribution (MWD) is at the core in establishing key quality indices for polymers. Toughness, hardness, stiffness, strength, and viscoelasticity are among the properties dependent on MWD. Few research efforts, however, have been made to determine the optimal structure and operating conditions of polymerization processes from different specifications on MWD due to the complexity of MWD modeling and calculation.

Reactor network plays a central role in determining the characteristics of polymerization processes. In our study, we develop and analyze a comprehensive superstructure of series and parallel reactor configurations. First, on the basis of the superstructure model, several steady-state optimization problems with specified MWDs, like polymer productivity maximization, will be studied to obtain the optimal steady-state structure and operating conditions. Next, dynamic reconfiguration problems will be further proposed and solved to show the optimal time-dependent process structure and control trajectories. For polymer grade transitions, a time-varying process configuration is expected to help minimize the transition time or the quantity of waste products. A high-density polyethylene (HDPE) slurry process with several continuous stirred-tank reactors (CSTRs), together with other units including flash drums, coolers, compressors, and pumps, is considered as an example to illustrate the feasibility and advantages of the proposed reactor network synthesis method. The polymerization process reconfiguration from MWD could lead to the development of new polymer grades, the improvement of the end-use properties and productivity of products, and the improvement of process operating policies.

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