A kinetic model for industrial gas-phase ethylene copolymerization (original) (raw)
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Macromolecular Reaction Engineering, 2009
A simplified kinetic scheme of eythylene/a-olefin copolymerization has been developed by adding reactions responsible for the unusual kinetic behavior to a general mechanism. The estimation of rate constants has been simplified by making physically meaningful initial guesses. Rate constants affecting yield, MWD and comonomer content have been estimated separately. Experiments were designed to investigate the effects of each rate constant independently. The obtained rate constants show that the sites which are responsible for formation of short chains with higher 1-butene content are more active at the beginning of polymerization, while the sites which are responsible for formation of longer chains with lower 1-butene units are more active at the final stages of polymerization.
Industrial & Engineering Chemistry Research, 1997
The estimation of kinetic parameters is a critical part of developing a process model for industrial polymerization processes. In transition-metal-catalyzed gas-phase olefin copolymerization processes, polymer density is a strong function of the amount of higher R-olefin comonomers incorporated into the polymer. For the calculation of copolymer composition with a process model, propagation rate constants, which vary from one catalyst system to another, must be known. In this paper, several computational methods applicable to batch, semibatch, and continuous reactors are presented to estimate the propagation rate constants and reactivity ratios in gasphase olefin copolymerization processes.
A dynamic model for ethylene copolymerization in an industrial Fluidized-Bed Reactor (FBR) is developed to describe its behavior and calculate the properties of polyethylene. The presented model considers particle entrainment and polymerization reaction in two phases. Two-site kinetic and hydrodynamic models in combination, provide a comprehensive model for the gas phase fluidized-bed polyethylene production reactor. The governing moment and hydrodynamic differential equations were solved simultaneously and the results compared with a similar work, as well as industrial data. The dynamic model showed accurate results for predicting Polydispersity Index (PDI), Molecular Weight Distribution (MWD), reactor temperature and polymer production rate.
e-Polymers, 2008
In the present work, ethylene polymerization kinetics was modeled using moment equations. According to the results obtained, the molecular weight distribution of each active center follows a Schultz-Flory distribution. However, the molecular weight distribution of polymer produced is much broader than a Schultz- Flory distribution. Besides, the order of polymerization with regard to monomer concentration is higher than unity. Moreover, the catalyst active centers deteriorate in the presence of hydrogen and consequently catalyst yield drops; nevertheless, polymerization kinetics is not mainly affected by hydrogen. Hydrogen also reduces polymer molecular weight since it is a strong transfer agent in olefin polymerizations. Notwithstanding, it does not affect polydispersity index. Last of all, although increasing cocatalyst concentration does not influence the activity of active centers, it lessens the molecular weight as a transfer agent
Industrial & Engineering Chemistry Research, 2012
A packed bed stopped flow minireactor (3 mL) suitable for performing gas phase polymerizations of olefins has been used to study the initial phases of ethylene homo-and copolymerization with two supported metallocene catalysts. The reactor can be used to perform gas phase polymerizations at times as short as 100 ms under industrially relevant conditions. It has been used to follow the evolution of the rate of polymerization, the gas phase temperature (and indirectly the particle temperature), and the polymer properties (molecular weight distribution, melting temperature, and crystallinity) for the two catalysts. It is shown that polymerization activity during the first 2−5 s of reaction can be up to 20 times higher than what is measured at longer polymerization times. The main consequence is the release of a significant amount of heat due to the rapid reaction that has to be efficiently evacuated in order to avoid particle overheating and melting. It has been seen that insufficient heat removal can strongly influence the behavior of the active sites, eventually leading to uncontrolled transfer reactions and polymers with unusually broad molecular weight distributions (MWD). It is also observed that the kinetic behavior of the two types of catalyst is similar at short times. Finally, some influence of particle size on reaction rate and molecular weight is observed between the largest and smallest catalyst particle cuts.
Journal of Applied Polymer Science, 2002
A method for quantitative evaluation of kinetic constants in Ziegler-Natta and metallocene olefin polymerizations presented previously Pinto, J. C. J Appl Polym Sci 2001, 79, 2076 is adapted to allow the estimation of kinetic constants for bulk propylene polymerizations by using a conventional fourth-generation high-activity Ziegler-Natta catalyst (HAC). In this particular case, reaction rate profiles are not available, so that estimation of kinetic data must rely on average polymer yields. The method comprises some fundamental steps, including the initial design of a statistical experimental plan, the execution of the designed experiments, the development of simple mathematical models to describe the polymeriza-tion, and the estimation of kinetic parameters from available yields, gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) data. It is shown that the proposed method allows the successful interpretation of experimental olefin polymerization data and the quantitative evaluation of kinetic parameters, which can be inserted into a process simulator to provide an accurate picture of actual industrial plant behavior.
Reactor Modeling of Gas‐Phase Polymerization of Ethylene
Chemical …, 2004
A model is developed for evaluating the performance of industrial-scale gas-phase polyethylene production reactors. This model is able to predict the properties of the produced polymer for both linear low-density and high-density polyethylene grades. A pseudo-homogeneous state was assumed in the fluidized bed reactor based on negligible heat and mass transfer resistances between the bubble and emulsion phases. The nonideal flow pattern in the fluidized bed reactor was described by the tanks-in-series model based on the information obtained in the literature. The kinetic model used in this work allows to predict the properties of the produced polymer. The presented model was compared with the actual data in terms of melt index and density and it was shown that there is a good agreement between the actual and calculated properties of the polymer. New correlations were developed to predict the melt index and density of polyethylene based on the operating conditions of the reactor and composition of the reactants in feed.