Modeling Ethylene/1-Butene Copolymerizations in Industrial Slurry Reactors

Abstract

In this work, a comprehensive model is developed for the ethylene/1-butene copolymerization in an industrial slurry polymerization reactor for linear low-density polyethylene synthesis. The model is able to describe the dynamic evolution of the molecular weight averages, comonomer content, particle size averages, melt index, and density of the final polymer resin and extends modeling results available in the open literature. A new modeling approach is used to describe the evolution of particle sizes, which is based on the definition of a joint distribution of mass and catalyst concentration of solid polymer particles. It is shown that the model successfully describes the operation of an industrial slurry polymerization reactor. For this reason, the model is used to analyze how sensitive the final polymer properties are to variations of the feed conditions and to development of segregated mixing zones inside the reactor vessel. It is shown that the ethylene feed flow rate is the most influential process variable and that the existence of very small segregated reactor zones can lead to very serious operation problems, such as particle agglomeration.

A Simplified Comprehensive Kinetic Scheme for Modeling of Ethylene/1‐butene Copolymerization Using Ziegler‐Natta Catalysts

“…Polymerization initiates with addition of the first monomer unit to the stable Ti–Et compound, and subsequently continues. While in most previous mechanisms6–11 no differences were taken into accounts between active centers formed from chain transfer to ethylene or 1‐butene, in this work, transfer to ethylene makes the stable Ti–Et compound, but transfer to 1‐butene avoids formation of Ti–Et, by‐passing this step by forming an initiated chain of P 1 . Chain transfer to hydrogen forms a different type of active center, Ti–H, while chain transfer to TEAL still forms the stable Ti–Et compound.…”

“…The three series of variables are Flory parameters of each site, their weight fractions and the number of sites. It is typical to consider five active centers for deconvolution of MWD27 while fewer numbers have also applied without problems 8. In this paper, no differences were noticed between errors come from considering four or five sites, so four sites were taken into account.…”

“…The balance equations for moments of live chains, λ n and dead chains, µ n are also given in Table 3. Using well‐established particle models at industrial operation conditions, it has been proved that mass‐ and heat‐transfer resistances might be neglected in the slurry polymerization of ethylene 8. It can be assumed that all chemical components present in the gas and liquid phases are in thermodynamic equilibrium and, especially because the catalyst particles used in this work had no defined spherical morphology, concentrations at the surface of active centers might be equal to the concentrations at the bulk of liquid phase.…”

“…In the terminal group model, polymerization kinetic constants depend on the type of monomer participating in the reaction and the type of monomer at the polymer chain end. This comprehensive engineering approach has been recently reviewed by Soares and traditionally used by different groups 6–11. This type of reaction scheme takes about 20 reactions into account that, by considering 5 active center types, needs at least 100 rate constants for an isothermal modeling of the process 12.…”

Control of Bulk Propylene Polymerizations Operated with Multiple Catalysts through Controller Reconfiguration

“…[26,27] The weight-average molecular weight (M w ), the number-average molecular weight (M n ), and the polydispersity index (PD) can be obtained from the statistical moment balances of the polymer chains. [28] Based on the averages, and remaining compositions, the MI [26] and the XS [27] can also be calculated, as shown in Equation (28)- (32).…”