Mathematical Modeling of the Molecular Weight Distribution in Low Density Polyethylene. I. Steady‐State Operation of Multizone Autoclave Reactors

• Published in: Macromolecular reaction engineering 2018-08, Vol.12 (4), p.n/a
• Main Authors: López‐Carpy, Bruno, Saldívar‐Guerra, Enrique, Zapata‐González, Iván, García‐Franco, César
• Format: Article
• Language: English
• Subjects: Algebra; Autoclaving; Chain scission; Cleavage; Computer simulation; Continuously stirred tank reactors; Density; low density polyethylene; Low density polyethylenes; mathematical model; Mathematical models; Molecular weight; Molecular weight distribution; multizone autoclave reactors; Parameter sensitivity; Polydispersity; Polyethylene; Reactors
• ISSN: 1862-832X; 1862-8338
• DOI: 10.1002/mren.201800013

A comprehensive mathematical model and an efficient strategy for its solution are presented to describe the complete molecular weight distribution (MWD) in the free‐radical polymerization for the production of low density polyethylene (LDPE) in continuous stirred tank reactors at steady state. The kinetic scheme includes all the relevant reactions that affect the MWD. The solution for the complete MWD is given as explicit algebraic expressions that are solved sequentially taking advantage of the algebraic structure of the equations; the strategy can simulate LDPE multizone autoclave reactors in a simple and straightforward manner. No approximation for the moment's closure is used. Model simulations reasonably match average molecular weight data from an industrial plant, as well as results from the POLYRED software. A parameter sensitivity study for key kinetic constants shows that the MWD polydispersity is predominantly affected by the transfer to polymer rate constant. The solution is applied to linear, topological and mechanical chain‐scission mechanisms. A simple and efficient strategy for the solution of the complete molecular weight distribution in the free‐radical process for producing low density polyethylene in continuous stirred tank reactors at steady state is presented. The model used includes all the known kinetic steps. The solution is given as explicit algebraic expressions and is applied to linear, topological, and mechanical chain‐scission mechanisms.