Lamia Zuñiga Liñan

Model predictive control of a CVD reactor for production of polysilicon rods

Production of polysilicon plays a key role in the development of hi-tech and renewable energy industry. Massive production is obtained by chemical vapor deposition (CVD) in semi-batch reactors, traditionally called Siemens reactors, where silicon rods are grown. Following recent increase in market demand for polysilicon, a fine process control on industrial processes for improving production yield and reducing energy consumption is required. In this work, a technique for a real-time model-based predictive control applied to a laboratory-scale Siemens reactor is presented; a lumped model is used for describing the CVD process. Discussion is based on numerical results.

Generalized Classes for Lower Levels of Supply Chain Management: Object-Oriented Approach

Abstract A possible and promising approach to effectively tackle the distinct optimization levels of supply chain hierarchy is to combine the object-oriented programming with the parallel computing. From this perspective, the paper proposes a generalized framework to solve the lowest levels of supply chain management paradigm by means of the BzzMath library as numerical kernel (optimizers and differential solvers) and openMP directives for exploiting shared memory machines. Also, the object-oriented approach allows the implementation of more solvers to force the same generalized class to automatically select the best one among them according to the problem and the user has not to worry about what solver and which optimizer are preferable.

Online Feasibility and Effectiveness of a Spatio-temporal Nonlinear Model Predictive Control. The Case of Methanol Synthesis Reactor

Abstract This work provides the theoretical formulation, implementation directives and validation case for the extension of the nonlinear model predictive control from the time domain to the spatio-temporal domain. Effectiveness and online feasibility are demonstrated for industrial processes of distributed nature. The case of methanol synthesis (control of hot-spot temperature and axial position) is selected.

Novel two-steps optimal control of batch polymerization reactors and application to PMMA production for the fabrication of artificial bone tissue

Abstract It is known that the applications of a material are totally dependent on their characteristics. In the particular case of the manufacture of bone tissues from polymer sources, high molecular weights are necessary to ensure optimum mechanical and optical properties. However, exothermic reactions and strong nonlinearities, which are peculiarities of such reaction systems, require rigorous control in order to achieve to the desired objectives. In this paper, an optimal control policy applied to a batch methyl methacrylate polymerization reactor is presented. The proposed methodology determines the optimal time profile of reactor temperature; if the temperature is maintained along the calculated profiles, a polymer product with desired molecular weight distribution could be obtained at the pre-specified final monomer conversion rate. The good agreement with experimental results reveals that the described control procedure is suitable to ensure that the polymer product satisfies the specifications.

Corporate Production Planning for Industrial Gas Supply Chains under Low-Demand Conditions

Abstract When the market demand significantly changes as within the ongoing worldwide economical crisis, many plants are forced to operate far from their nominal conditions. In this case, the plantwide optimization of production sites is a myopic approach that could unavoidably lead to plant inefficiencies and unconventional operation issues without preventing anyhow economical losses. A way to tackle low-demand conditions is to raise the decision-making process from the plantwide level to the corporate level by assigning a Boolean variable to each production site to manage its on/off status. By doing so, certain additional (social) constraints may become relevant. This work proposes a novel approach to the corporate production planning entirely based on MS VISUAL C++ and on specific algorithms belonging to BzzMath library.

Pilot-plant Simulation, Experimental Campaign and Rigorous Modeling of a Batch MMA Polymerization Reactor for the Fabrication of Bone Tissue

Abstract As a first crucial stage for production of PMMA scaffolds, this work provides the kinetic and dynamic characterization of the MMA/Ethyl Acetate/AIBN polymerization process. Kinetic parameters are estimated by means of experimental campaigns performed on a dedicated pilot plant (batch reactor). A novel, rigorous mathematical model is developed and implemented in Fortran 90 so as to consider the peculiar characteristics and the new structure of the pilot plant and the batch reactor: actually, the new plant configuration is designed to produce the appropriated PMMA scaffolds for medical application (with very stringent specifications for low toxicity and high biocompatibility). The good agreement between model previsions and experimental results validates the kinetic parameters and the dynamic modeling.

Pilot-scale synthesis and rheological assessment of poly(methyl methacrylate) polymers: Perspectives for medical application

This work presents the rheological assessment of poly(methyl methacrylate) (PMMA) polymers synthesized in a dedicated pilot-scale plant. This material is to be used for the construction of scaffolds via Rapid Prototyping (RP). The polymers were prepared to match the physical and biological properties required for medical applications. Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC) measurements verified that the synthesized polymers were atactic, amorphous and linear in chains. Rheological properties such as viscosity, storage and loss modulus, beyond the loss factor, and creep and recovery were measured in a plate-plate sensor within the viscoelastic linear region. The results showed the relevant influence of the molecular weight on the viscosity and elasticity of the material, and how, as the molecular weight increases, the viscoelastic properties are getting closer to those of human bone. This article demonstrates that by using the implemented methodology it is possible to synthesize a polymer, with properties comparable to commercially-available PMMA.

Optimal Fuzzy Control of Batch Polymerization Reactors: Application to PMMA Production for Biomedical Purposes

Abstract The use of polymers in the biomedical field requires that such materials have a high degree of purity and specific properties, so that their production processes must be continuously monitored and manipulated. However, the control of polymerization reactors is considered a challenging task since such systems present non-linear and transient behaviour. In this study, in order to produce poly(methyl methacrylate) scaffolds for bone tissue engineering applications, an advanced control methodology based on fuzzy models and genetic algorithms (GA) was developed to control the temperature of a pilot-scale jacketed batch reactor in which methyl methacrylate polymerization takes place. Firstly, an optimal temperature trajectory was estimated using GA. Then, a fuzzy controller was designed and applied to adjust the reactor temperature to the instantaneous profile previously calculated. The proposed control algorithm was compared to conventional PID controller, proving to be robust and more suitable and reliable for such process type.

Dynamic optimization of a MMA with VAc copolymerization reactor

Copolymerization Reactor Nadson Murilo Nascimento Lima, Lamia Zuniga Linan, Rubens Maciel Filho, Flavio Manenti, Davide Manca, Marcelo Embirucu a School of Chemical Engineering, State University of Campinas – UNICAMP, P.O. Box 6066, 13083-970, Campinas-SP, Brazil b CMIC Dept. “Giulio Natta” – Politecnico di Milano, Piazza Leonardo da Vinci, I20133, Milano, Italy c Polytechnique Institute, Federal University of Bahia – UFBA, 40210-630, SalvadorBA, Brazil * Corresponding author. E-mail: nadson@feq.unicamp.br

Cytotoxicity Assessment of a Poly(methyl methacrylate) Synthesized for the Direct Fabrication of Bone Tissues

A cytotoxicity study is performed on a poly(methyl methacrylate) polymer (PMMA) to be used for the fabrication of bone tissue by Rapid Prototyping (RP). The solution polymerization is conducted in a pilot plant reactor using more appropriated reagents in consideration of the medical application. Moreover, the polymer is efficiently handled to avoid the side effect of the monomer, reducing the concentration of this specie to 287,731 μg MMA/kg PMMA. The cytotoxicity of the polymer is determined through growth monitoring, adherence and morphology of L-929 cells. Additionally, MTT and LIVE/DEAD tests are performed. The results showed continuous and progressive growth of the cells on the surface of the specimens. Moreover, the material did not influence on the viability of mesenchymal cells and inverted fluorescence microscopy images showed a polyanionic dye calcein well retained in the cells in contact with the PMMA as well as the negative control after 72 hours. Thus, the polymer was efficiently synthesized and handled for the expected demands.