José Carlos Pinto

The use of particle swarm optimization for dynamical analysis in chemical processes

Particle swarm optimization is employed here to evaluate the parametric regions where different dynamic phenomena (periodic oscillations, double-period oscillations, chaos) can be expected in dynamic models. The proposed algorithm comprises two fundamental steps: the rough evaluation of regions where the desired solutions can be found and solution refining. The refining step allows the search for unstable solutions that may coexist with the other stable attractors. No preliminary bifurcation analysis is required. Simulations performed for distinct dynamic models show that the proposed algorithm is indeed able to locate different dynamic phenomena in the parameter space and that the algorithm may be of help for those interested in increasing the speed of more traditional dynamic bifurcation analysis.

Monitoring and Control of Polymerization Reactors Using NIR Spectroscopy

Abstract: The development and use of microprocessor-based devices improved the speed and reliability of transmission and manipulation of data. More recently, some monitoring techniques were greatly improved by the combination of spectroscopic methods and fiber optics technology, which allow for the in situ and in-line acquisition of process data, consequently allowing for reduction of time delays normally involved with sample preparation. Among them, techniques based on the near infrared spectroscopy (NIRS) have certainly become the most important ones. The main objective of this paper is to review the use of NIR spectroscopy as an alternative technique for polymerization process monitoring and control, presenting and discussing successful applications of NIR spectroscopy as a tool for in situ and in-line monitoring and control of solution, suspension, and emulsion polymerization processes.

Modeling and optimization of the combined carbon dioxide reforming and partial oxidation of natural gas

The optimization of the combined carbon dioxide reforming and partial methane oxidation over a 1% Pt/-Al2O3 catalyst was studied in order to produce synthesis gas with hydrogen/carbon monoxide ratio close to 1, for applications in metallurgical and polycarbonates processes and for production of oxygenated compounds and hydrocarbons. The study was performed with the help of experimental design and two mathematical modeling approaches: empirical and phenomenological. Empirical polynomial models were employed to analyze the effects of the process variables on the response factors and the final correlation coefficients obtained were above 95%. The phenomenological model was obtained from individual mass balances and the obtained correlation coefficients were above 95% for CH4 and N2, 90% for CO2 and H2O and near 70% for H2 and CO. The empirical modeling approach was found to be more efficient, simpler and led to better results than those obtained with the phenomenological model approach. Therefore, the empirical modeling was used for optimization of the process operation conditions. At an oxygen/methane ratio of 0.55 gmol/gmol and temperature of 950 ◦ C, optimized process conditions were obtained with complete methane conversion, maximum carbon monoxide selectivity of 43% and minimum hydrogen/carbon monoxide ratio of 1.3, in absence of water.

In‐line evaluation of average particle size in styrene suspension polymerizations using near‐infrared spectroscopy

The main objective of this article is evaluating the influence of average polystyrene particle size upon the near-infrared (NIR) spectra collected during suspension polymerization experiments and observing whether NIR spectroscopy may be used for in-line monitoring and control of average particle size. It is shown that NIR spectra are sensitive to changes of the average particle size, and that standard empirical models (PLS—partial least squares—and NN—neural networks) may be built to correlate average particle size and light absorbance at certain wavelengths fairly well. Finally, it is shown that these models allow the in-line evaluation of average particle size in styrene suspension polymerizations with NIR spectroscopy.

Modeling of end-use properties of poly(propylene/ethylene) resins

The objective of the present work is to develop empirical models to predict end-use properties of poly(ethylene/propylene) resins as functions of more fundamental molecular and morphological properties of the polymer resins. The final properties analyzed are two mechanical properties, rigidity and impact strength, and one thermal property, glass transition temperature. Two additional properties of practical importance are also modeled: the melt index and the xylene soluble content. Molecular and morphological properties selected for resin characterization are molecular weight distribution, polymer composition, degree of crystallinity, spherulite size distribution and rubbery phase dispersion. End-use, molecular and morphological properties were evaluated experimentally for 19 different commercial polypropylene copolymer grades. Statistical correlation analysis was performed for all variables and used as the basis for proper choice of inputs to each output model. Models developed are able to reproduce and predict experimental data within experimental accuracy and show that both polymerization and final resin processing variables may be of fundamental importance for definition of the final property balance of the polymer material.

Dynamic optimization of semicontinuous emulsion copolymerization reactions: composition and molecular weight distribution

Abstract Iterative dynamic programming (IDP) is used to compute optimal monomer and chain transfer agent feed profiles to produce polymer with specified copolymer composition and molecular weight distribution. The approach used allows the implementation of constrained optimization procedures for systems described by complex mathematical models, as those needed for proper description of emulsion copolymerization reactors, especially when the computation of the whole molecular weight distribution is desired. The proposed approach is applied to the semicontinuous methyl methacrylate (MMA)/butyl acrylate (BuA) emulsion copolymerization in stirred tank reactors, using dodecanethiol as chain transfer agent (CTA). It is shown that this technique allows the effective computation of feed policies for the production of copolymers with constant composition and well-defined molecular weight distributions.

Control and design of average particle size in styrene suspension polymerizations using NIRS

In a previous paper, Santos et al. (J Appl Polym Sci 1998, 20, 1737) showed that NIRS may be used efficiently for in-line evaluation of average particle sizes in styrene suspension polymerizations if proper calibration is carried out with the help of both multivariate techniques and nonlinear models. In the present work, the technique presented by Santos et al. was used for in-line evaluation and for control and design of average particle sizes during styrene suspension polymerizations carried out in the batch mode. The effects of agitation speed and stabilizer concentration on the particle-size Distribution (PSD) were investigated. It is shown here that this technique allows the successful design and real-time control of particle sizes in lab-scale styrene suspension polymerization reactors.

Steady-state modeling of slurry and bulk propylene polymerizations

A mathematical model for steady-state slurry and bulk propylene polymerizations is developed and implemented. The model is based on the detailed formulation of mass balances for all chemical species present in the reaction environment, of energy balances for the reactor mixture and cooling water and of momentum balances. The model allows the computation of mass and energy inventories and the prediction of polymer molecular structure and morphology, including the molecular weight distribution, the chain composition distribution, the particle size distribution and the stereo-block distribution. Besides, end-use properties, such as the melting-flow index, the impact strength and the flexural modulus, are described through empirical models that depend on the molecular and morphological properties of the polymer resins, as described by Latado et al. (Polymer Testing 20(4) (2001) 419-439). The model also allows the simulation of the extrusion operation and is validated with actual operation data for two different polymerization plants, using different Ziegler-Natta catalysts.

Dynamic optimization of non-linear emulsion copolymerization systems: Open-loop control of composition and molecular weight distribution

Time optimal monomer and chain-transfer agent feed profiles were computed and implemented experimentally for the simultaneous control of copolymer composition and molecular weight distribution in non-linear emulsion copolymerization systems. Iterative dynamic programming was used for the off-line calculation of the optimal feed policies. This approach can deal with constrained optimization of systems described by complex mathematical models, as those needed for the emulsion copolymerization kinetics, especially when the computation of the whole molecular weight distribution is included. The proposed approach was applied to the semibatch methylmethacrylate (MMA)/n-butylacrylate (n-BA) emulsion copolymerization, using n-dodecanethiol as chain-transfer agent, and allowed the production of copolymers with constant composition and with well-defined molecular weight distributions.

Modeling particle size distribution (PSD) in emulsion copolymerization reactions in a continuous loop reactor

A detailed dynamic mathematical model that describes the evolution of particle size distributions (PSD) during emulsion copolymerization reactions in a continous loop reactor is developed and compared with experimental data. The model is based on the assumption that two distinct particle populations exist: precusor particles and stable latex particles. Precursor particles are colloidally unstable and therefore may undergo coagulation with other precursors and be absorbed by stable latex particles. It is shown that the kinetic model is able to reproduce the rather complex dynamic behavior of the vinyl acetate/Veova 10 emulsion copolymerization in a continuous loop reactor.