Timothy F. L. McKenna

Single particle modelling for olefin polymerization on supported catalysts: A review and proposals for future developments

In the present article, we review the state-of-the-art models for single particle olefin polymerization models. Special attention is paid to particle growth, polymerization rates, concentration and temperature radial profiles, polymer microstructure, and particle morphology. It is proposed that these models can be conveniently classified as polymer property and particle morphology models, according to their most important predictive abilities, even though particle morphology characteristics will influence polymer properties and vice versa. Currently, there is no single model that incorporates all of these modelling aspects into a unified formulation. A great deal of progress has been made toward understanding the relationship between the important phenomena involved in modelling single particle growth. It seems that the basic understanding on modelling polymer properties is quite substantial, but there is still significant contributions to be made when modelling the morphology evolution of these complex polymer particles. Some of these areas are discussed and suggestions for future development are made.

Silica Encapsulation by Miniemulsion Polymerization: Distribution and Localization of the Silica Particles in Droplets and Latex Particles

The impact of including hydrophobically modified silica on the morphology of miniemulsified monomer mixtures and that of the resulting polymer particles was investigated, with emphasis placed on the distribution and localization of the inorganic phase. Silica nanoparticles with diameters of 20 and 78 nm were first modified with γ-methacryloxypropyl trimethoxysilane (γ-MPS) to favor their dispersion in methyl methacrylate (MMA)/n-butyl acrylate (BuA) and mixtures of varying MMA to BuA weight ratios. The monomer-silica dispersions were then emulsified by ultrasonication, and the resulting silica-loaded droplets were examined using cryo-transmission electron microscopy (cryo-TEM). This represents the first time such silica-loaded nanodroplets were examined in this way. The results of the cryo-TEM show that whereas the silica particles could easily be dispersed in MMA or a mixture of MMA and BuA to produce stable dispersions, the emulsification step promotes the (re)localization of the silica at the oil-water interfaces. It was also shown that not all droplets are equal; some droplets and particles contain no silica whereas others contain many silica particles. After the subsequent polymerization step, the silica was buried inside the latex particles.

Emulsion copolymerization of styrene and n‐butyl acrylate in presence of acrylic and methacrylic acids: Effect of pH on kinetics and carboxyl group distribution

The batch emulsion copolymerization of styrene with n-butyl acrylate in the presence of acrylic and methacrylic acids was investigated. Values of reaction rate and conversion observed at different pH values were examined. The effect of pH on the glass transition temperature of the polymers was also investigated and the results compared with model predictions. Its effect on the distribution of the carboxyl groups at different positions within the emulsion system (surface and core of particles, and in the aqueous phase) was also analyzed. Three methods were used to measure the number of carboxyl groups: conductimetry, organic phase potentiometry, and titration with a solution of sodium hydroxide in methanol.

The interaction between mass transfer effects and morphology in heterogeneous olefin polymerization

The interaction between mass transfer effects and morphology in heterogeneous olefin polymerization

Modeling of transfer phenomena on heterogeneous Ziegler catalysts. III. Modeling of intraparticle mass transfer resistance

The use of equations such as Dpore = DBulk (ϵ/τ) to predict pore diffusivities in the modeling of liquid phase polymerizations on heterogeneous Ziegler-type catalysts leads to highly unrealistic results when applied to situations with activities greater than 10,000 g/g/h or higher (polyethylene in suspension). A simple, isothermal model of mass transfer with reaction is presented and is used to examine the slurry polymerization of ethylene at activities higher than those previously studied in order to explore the major tendencies in the development of concentration gradients and average molecular weight of the polymer and to evaluate accepted estimates of monomer diffusivity in the catalyst pores. Experimental results are compared with the predictions of the classic reaction diffusion model, and it is shown that values of monomer diffusivity commonly used to model slurry polymerizations are not high enough in order to correctly simulate the activity levels obtained in this work. The modeling study shows that the effect of mass transfer resistance on the molecular weight is not all together negligible and that either estimates of the diffusion coefficient of ethylene in the catalyst pores need to be revised, or that more complete description of mass transfer is required than is provided by the classic reaction/diffusion equations.

Evolution of Particle Morphology During Polymerisation of High Impact Polypropylene

The particle morphology of impact polypropylene was examined experimentally in order to understand how the rubber phase produced in the second step of the polymerisation is distributed inside the growing polymer particles, and how the quantity of rubber produced influences the overall morphology of the final product. It was found that the rubber can pool on the surface of the growing particles, but that this pooling is not uniform. In addition, it was observed that the rubber phase does not flow out of the large pore openings on the surface of the particles. A possible mechanism for the distribution of rubber was proposed. #An earlier version of this paper was presented at ECOREP II, 2nd European Conference on Reaction Engineering of Polyolefins, Lyon, France, July 1–4, 2002.

Progress in describing particle growth for polyolefins : A look at particle morphology

Discussion focuses on the strengths and weaknesses of current methods of modelling particle growth, and heat and mass transfer during the polymerisation of olefins on supported Ziegler-Natta Catalysts. It is demonstrated that improvements need to be made in the area of mass transfer models in the form of a mechanistic description of particle morphology. Scanning electron microscopy (SEM) is used to examine particle morphology. Simplified models of particle growth demonstrate the need to include convection in gas phase processes and a better description of particle morphology.

Modelling of heat and mass transfer during the polymerisation of olefins on heterogeneous Ziegler catalysts

Abstract The modelling of heat and mass transfer during the gas and slurry phase polymerisation of olefins is examined. It is demonstrated that it might not be necessary in many cases to calculate concentration gradients in the growing catalyst/polymer complex, and that the currently used representation of heat transfer from small, highly active particles using standard chemical engineering correlations might not be accurate. Close examination of the morphology of catalyst particles shows that it is unlikely that the particles should be treated as a pseudo-homogeneous medium, and in fact the critical length scale for mass transfer is not the particle radius, but is much smaller. Furthermore, computational fluid dynamic simulations of single and interacting particles shows that convection is not the dominant heat transfer mechanism during the critical stages of the reaction.

An Integrated Approach to Polymer Reaction Engineering: A Review of Calorimetry and State Estimation

ABSTRACT In order to completely master a polymerisation process, it is necessary to take a pluri-disciplinary approach that incorporates the use of kinetic and polymer property models (e.g. of Rp, the rate of polymerisation and of copolymer composition distribution, CCD), hardware and software sensors, non-linear observers for the data interpretation, and easily tuneable, robust controllers for the optimal and safe operation of reactors that produce polymer of a pre-specified quality. An overview of the results obtained in this area show that such an approach allows not only to follow and control production rates and the evolution of the CCD, but to obtain other useful process information on the evolution of such properties as the number of particles per litre of emulsion (Np) and the number of radicals per particle () in emulsion polymerisation, or the overall termination rate constant in solution reactions. It is also shown that this method can be used not only for reactor control, but also for fault detection and process optimisation.

A combined hardware/software sensing approach for on-line control of emulsion polymerisation processes

In the present work, a new strategy for the on-line determination of information concerning a free radical polymerisation (overall and individual monomer conversions, and the product of the number of radicals per particle multiplied by the number of particles) is presented. It is based on the construction of a non-linear observer that uses information obtained via a new adaptive inferential calorimetric measurement scheme. The results, presented for the case of the emulsion copolymerisation of methyl methacrylate (MMA) and vinyl acetate (VAc), show that with only a rough model of the physical process, it is possible to obtain reliable estimates of the evolution of the polymerisation reaction.