Completed Research
Modeling of Isobutylene Polymerization Process in Agitated Reactors
Yongtai Li, MS, 2016
(Thesis: University of Pittsburgh ETD)
In this study, a comprehensive model for the IBP process in agitated reactors was developed based on the reaction mechanism by Vasilenko et al. 2010, and takes into account the reaction rate kinetics for initiation, propagation, chain transfer, and chain termination steps as well as the mixing effects. The model coupled the mass balance equations for each reaction step with those of the segregated zones model for micro- and macro-mixing effects by Villermaux 1989, and was numerically solved by Matlab. The model was then used to predict the effect of various operating variables on the IBP process performance, in terms of the three main metrics: monomer conversion (X), number average molecular weight (Mn) and polydispersity index (PDI).
In the absence of mixing, our model was used to carry out sensitivity analyses to quantify the effects of the reaction rate constants of the initiation (ki), propagation (kp), chain-transfer (ktr) and chain termination (kt) steps on the three main performance metrics. The model predictions led to: (1) Increasing ki was found to have negligible effect on the three main IBP process performance metrics; (2) Increasing kp increased X and Mn and decreased PDI; (3) increasing ktr the increased X, but decreased Mn and PDI; and (4) Increasing kt deceased X and Mn, and increased PDI.
In the presence of mixing, and at given kinetic rate constant, the model was used to conduct a parametric study to determine the effect of mixing on the IBP process performance. Eight different cases, four poor and four good mixing conditions, reactor type, and impeller type as well as design, were considered, and their effects on the three main IBP process performance metrics were investigated. The model predictions led to: (1) Mixing controls the IBP process performance due to its inherently fast reaction kinetics; (2) Mixing time and impeller type significantly affected the required mixing speed; (3) all model predictions underscored the importance of good mixing in the cationic IBP process; and (4) our model was able to predict the IBP process performance metrics and the required mixing speed in agitated reactors provided with different impellers.