Cover Picture: Macromol. React. Eng. 7/2014

This work is focused on the development and validation of a model accounting for the impact of the reactor residence time distribution in well‐stirred slurry‐phase catalytic polymerization of ethylene. Particle growth and morphology are described through the Multigrain model, adopting a two‐site model for the catalyst and a conventional kinetic scheme. Particle size distribution and polymer properties (average molecular weights and polydispersity) are computed as a function of particle size through a segregated model, assuming that neither breakage nor aggregation occur. Reactors are modeled by means of fundamental mass conservation equations. The model is applied to a system constituted by a series of two ideal continuous stirred tank reactors, where the synthesis of polyethylene with bimodal molecular weight distribution is performed, employing the initial catalyst size distribution as the only adjustable parameter. The model provides insights at the single particle scale for each specific size, thus highlighting the inhomogeneity which arises from the synergic effects of chemical kinetics and residence time distributions in both reactors. The satisfactory agreement between model results and experimental data, in terms of particle size distribution and average molecular weights, confirmed the suitability of the model and underlying assumptions.

Section: Model Developmentmentioning

confidence: 99%

The Effect of Residence Time Distribution on the Slurry‐Phase Catalytic Ethylene Polymerization: An Experimental and Computational Study

Casalini

Visscher

Tamaddoni

et al. 2018

“…Although the catalytic polymerization of polyolefins in gas or slurry phase is nowadays an established reality, the development of mathematical models of the overall process at the single catalyst particle scale is still underway . Even though the first modeling attempt dates back to 1971 with the work of Singh and Merrill, more comprehensive models are continuously proposed in order to improve the description of the involved phenomena .…”

Section: Introductionmentioning

confidence: 99%

Modeling of Polyolefin Polymerization in Semibatch Slurry Reactors: Experiments and Simulations

Casalini

Visscher

Janssen

et al. 2016

In this work, a well‐known single‐particle model (the multigrain model) is applied to simulate size growth and morphology evolution of polyethylene particles obtained through a slurry phase, catalytic polymerization in semibatch reactor. The model explicitly accounts for diffusion limitations within the polymer particle and between the particle and the solvent, as well as void fraction variations due to the particle growth. Catalyst behavior is described assuming a two‐site model, a good compromise between accuracy and simplicity, along with a conventional kinetic scheme, whose kinetic parameters are determined by fitting the model predictions to the experimental data. Polymer molecular weight is evaluated from population balances, solved through the method of moments. The semibatch reactor is modeled by means of fundamental mass conservation equations. Simulations show that the proposed model is able to describe not only the polymer properties of interest but also the evolution of the average particle size, thus providing a comprehensive overview of the system behavior. The model is further validated through regression‐free simulation of additional sets of experimental data, including materials with a bimodal molar mass distribution: the good agreement also found in this case confirms the robustness of the model and the estimated parameter values.

“…From the microstructural analytical results obtained by spectroscopic and fractionation techniques, we may infer weather a single‐ or multi‐site type catalyst was used during the polymerization process. As a matter of fact, putting aside the reasons behind the single‐ or multi‐site type behavior (more than one catalytic site types are active during the polymerization or mass‐ and heat‐transfer resistances broaden the MWD of polymer made by heterogeneous Z–N catalysts), multi‐site type catalysts behave as being a blend of single‐site type catalysts . As a result, all characteristic multi‐site type catalyst polyethylene distributions may be considered as the resulting sum of the corresponding single‐site type components.…”

Section: Polymer Reaction Engineeringmentioning

confidence: 99%

A Methodology for Estimating Kinetic Parameters and Reactivity Ratios of Multi‐site Type Catalysts Using Polymerization, Fractionation, and Spectroscopic Techniques

Touloupidis

Albrecht

Soares

2018

Self Cite

This work describes a polymer reaction engineering framework for understanding how catalyst kinetic parameters affect the microstructure of polyolefins made with single‐ or multi‐site catalysts. Moreover, a methodology for deconvolution and kinetic parameters estimation is presented to estimate the reactivity ratios of multi‐site catalysts based on the combination of polymerization, fractionation, and spectroscopic techniques, namely, gel permeation chromatography‐IR and carbon‐13 nuclear magnetic resonance spectroscopy. The methodology capabilities are then demonstrated and validated using a case study simulated via a Monte Carlo model including random noise in order to better represent experimental result uncertainties. The methodology can reverse engineer experimental results and estimate all relevant reaction performance parameters.