Rozprawy doktorskie na temat „Chemical reactors Mathematical models”

Orientador: Rubens Maciel Filho
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: Os processos de polimerização são de grande importância, pois através destes, são produzidos uma grande diversidade de produtos de utilidade no mercado mundial, entre os quais plásticos, borrachas, tintas, etc. A simulação, a análise e o controle adequado dos processos são fundamentais para a operação e o desenvolvimento seguro de uma planta, garantindo e atendendo à demanda de competitividade atual com a fabricação de produtos de alta qualidade. O objetivo deste trabalho é o desenvolvimento de um modelo matemático determinístico detalhado e a elaboração de um software através da solução numérica do sistema de equações utilizando o Método dos Volumes Finitos. O caso de estudo considerado é a polimerização de eteno em solução em um reator tubular com catálise de Ziegler-Natta com e sem micromistura. Neste estudo é desenvolvido um modelo que simula o processo de polimerização de eteno em solução com catalisador Ziegler-Natta em uma seqüência de reatores PFR (Plug Flow Reactor - Reator de Fluxo Empistonado) e CSTR (Continuous Stirred Tank Reactor - Reator Tanque de Agitação Contínua), concentrando-se principalmente nos resultados do PFR. Os parâmetros desconhecidos necessários para a obtenção dos resultados quantitativos do modelo, como constantes cinéticas, foram estimados a partir de dados do processo industrial da Politeno SA. A partir das simulações deste modelo foram avaliados os efeitos das principais variáveis de entrada do processo no desempenho do reator e nas propriedades do polímero. Os resultados obtidos demonstram convergência para o processo sem micromistura.
Abstract: Polymerization process are important because of their large applications in the world market, for example, rubber, ink, plastic, etc. Appropriate simulation, analysis and control of a floor plan are fundamental for it safety operation and developing, providing the actual competitiveness with high quality production. This work intend to developing a detailed and deterministic mathematical model and elaborating of software using the numerical solution of a equations system obtained by Finite Volumes Method. Study case considered is the ethane polymerization in solution in a tubular reactor with catalysis Ziegler-Natta with and without micromixing. In this study were developed a model that simulates the ethane polymerization process in solution with catalysis Ziegler-Natta in a sequence of reactors PFR (Plug Flow Reactor) and CSTR (Continuous Stirred Tank Reactor), emphasizing the PFR results. The necessary parameters for model quantitative results, like kinetics constants, were calculated with Politeno SA industrial process data. The effect of the most important entrance variables in the reactor performance and in the polymer final properties were evaluated by simulations. The results show convergence for the process without micromixing.
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química

Complex optimization problems are prevalent in various fields of science and engineering. However, many of them belong to a category of problems called NP- hard (nondeterministic polynomial-time hard). On the other hand, due to the powerful capability in solving a myriad of complex optimization problems, metaheuristic approaches have attracted great attention in recent decades. Chemical Reaction Optimization (CRO) is a recently developed metaheuristic mimicking the interactions of molecules in a chemical reaction. With the flexible structure and excellent characteristics, CRO can explore the solution space efficiently to identify the optimal or near optimal solution(s) within an acceptable time. Our research not only designs different versions of CRO and applies them to tackle various NP-hard optimization problems, but also investigates theoretical aspects of CRO in terms of convergence and finite time behavior. We first focus on the problem of task scheduling in grid computing, which involves seeking the most efficient strategy for allocating tasks to resources. In addition to Makespan and Flowtime, we also take reliability of resource into account, and task scheduling is formulated as an optimization problem with three objective functions. Then, four different kinds of CRO are designed to solve this problem. Simulation results show that the CRO methods generally perform better than existing methods and performance improvement is especially significant in large-scale applications. Secondly, we study stock portfolio selection, which pertains to deciding how to allocate investments to a number of stocks. Here we adopt the classical Markowitz mean-variance model and consider an additional cardinality constraint. Thus, the stock portfolio optimization becomes a mixed-integer quadratic programming problem. To solve it, we propose a new version of CRO named Super Molecule-based CRO (S-CRO). Computational experiments suggest that S-CRO is superior to canonical CRO in solving this problem. Thirdly, we apply CRO to the short adjacent repeats identification problem (SARIP), which involves detecting the short adjacent repeats shared by multiple DNA sequences. After proving that SARIP is NP-hard, we test CRO with both synthetic and real data, and compare its performance with BASARD, which is the previous best algorithm for this problem. Simulation results show that CRO performs much better than BASARD in terms of computational time and finding the optimal solution. We also propose a parallel version of CRO (named PCRO) with a synchronous communication scheme. To test its efficiency, we employ PCRO to solve the Quadratic Assignment Problem (QAP), which is a classical combinatorial optimization problem. Simulation results show that compared with canonical sequential CRO, PCRO can reduce the computational time as well as improve the quality of the solution for instances of QAP with large sizes. Finally, we perform theoretical analysis on the convergence and finite time behavior of CRO for combinatorial optimization problems. We explore CRO convergence from two aspects, namely, the elementary reactions and the total system energy. Furthermore, we also investigate the finite time behavior of CRO in respect of convergence rate and first hitting time.
published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Chemical reaction networks are an unconventional computing medium that could benefit from the ability to form basic control systems. In this work, we demonstrate the functionality of a chemical control system by evaluating classic genetic algorithm problems: Koza's Santa Fe trail, Jefferson's John Muir trail, and three Santa Fe trail segments. Both Jefferson and Koza found that memory, such as a recurrent neural network or memories in a genetic program, are required to solve the task. Our approach presents the first instance of a chemical system acting as a control system. We propose a delay line connected with an artificial neural network in a chemical reaction network to determine the artificial ant's moves. We first search for the minimal required delay line size connected to a feed forward neural network in a chemical system. Our experiments show a delay line of length four is sufficient. Next, we used these findings to implement a chemical reaction network with a length four delay line and an artificial neural network. We use genetic algorithms to find an optimal set of weights for the artificial neural network. This chemical system is capable of consuming 100% of the food on a subset and greater than 44% of the food on Koza's Santa Fe trail. We also show the first implementation of a simulated chemical memory in two different models that can reliably capture and store information over time. The ability to store data over time gives rise to basic control systems that can perform more complex tasks. The integration of a memory storage unit and a control system in a chemistry has applications in biomedicine, like smart drug delivery. We show that we can successfully store the information over time and use it to act as a memory for a control system navigating an agent through a maze.

Orientador: Rubens Maciel Filho
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: Em reações altamente exotérmicas, uma das principais características dos reatores catalíticos de leito fixo está relacionada ao surgimento do ponto quente ou hot-spot, sendo sua prevenção de fundamental importância para o bom desempenho do reator, uma vez que ele pode levar ao aumento excessivo da temperatura no leito catalítico, o que poderia resultar em possíveis condições de instabilidade. Um fator importante para estabelecer limites de estabilidade e que, portanto, deve ser considerado dentro do projeto de reatores catalíticos de leito fixo, está relacionado à escolha da configuração de escoamento do fluido refrigerante. Desta forma, duas novas configurações de escoamento para o fluido refrigerante, empregando simultaneamente as configurações convencionais co-corrente e contra-corrente, são propostas. O objetivo é explorar e analisar a influência de diferentes configurações de refrigeração sobre o comportamento de reatores catalíticos de leito fixo monotubulares e multitubulares através de sua modelagem e simulação, reduzindo assim os efeitos do ponto-quente sobre o comportamento estacionário do reator. O emprego de modelos multitubulares é essencial quando existe a necessidade de se considerar detalhadamente todos os aspectos relacionados ao projeto mecânico do reator e também onde as interações existentes entre os tubos forem importantes. Dentre as configurações de refrigeração empregadas estão as formas convencionais, denominadas co-corrente e contra-corrente, e também as configurações mistas, que utilizam ambas as formas convencionais simultaneamente. Como caso de estudo é considerada a reação de oxidação parcial do benzeno em anidrido maleico sobre catalisador de pentóxido de vanádio (V2O5), a qual apresenta equações de taxa complexas e é altamente exotérmica, e representa uma importante classe dentro dos processos industriais. Para tanto foram desenvolvidos softwares escritos em FORTRAN 90 capazes de permitir ao usuário o estudo de diversas configurações de refrigeração e diferentes condições de operação e de projeto, tanto para o reator monotubular quanto multitubular, sendo ainda compatíveis com outras reações de interesse industrial, o que torna os procedimentos e a metodologia desenvolvidos de uso geral
Abstract: One of the main characteristics of fixed bed catalytic reactors when high exothermic reactions are carried out is the presence of the hot-spot. Prevention of hot-spot appearance is extremely important for good reactor performance, since it can lead to an excessive increase in reactor bed temperature, which could result in unstable conditions. An important factor to establish stability limits and, therefore, to be considered during the fixed bed catalytic reactor design is the choice of the coolant flow pattern. In doing so, two new coolant flow patterns are purposed using both co-current and counter-current conventional configurations simultaneously. The main objective is to explore and analyze the influence of different cooling modes on the monotubular and multitubular fixed bed catalytic reactors behavior through their modeling and simulation, reducing in this way the effects of the hot-spot on the steady state reactor behavior. The use of multitubular models is essential when there is a need to consider in detail all aspects related to the reactor mechanical design and also where the interactions between tubes are important. Among the cooling modes used are the conventional flow patterns, called co-current and counter-current, and also the mixed flow patterns, which use both conventional forms simultaneously. As a case study, the reaction of partial oxidation of benzene to maleic anhydride over a vanadium pentoxide catalyst (V2O5) is considered, which presents complex rate equations, is highly exothermic, and represent an important class of industrial processes. Bearing this in mind, FORTRAN 90 softwares that permit the user to study different cooling modes and various operational and design conditions for both mono-tubular and multitubular reactors were developed. These softwares are compatible with other reactions of industrial interest, which makes the procedures and methodology developed for general use
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química

Orientadores: Rubens Maciel Filho, Aline Carvalho da Costa
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Por mais de um século, a principal fonte de combustível e produtos químicos para a sociedade humana tem vindo a partir de recursos fósseis, os quais são limitados e estão concentrados em poucas regiões do mundo. Biomassa, como a única fonte de carbono renovável, mostra-se promissora para a produção de combustíveis e produtos químicos em grande escala. Na última década, a produção de bioetanol a partir de biomassa lignocelulósica através de hidrólise enzimática tem sido estudada intensamente a nível de bancada. Reatores contínuos, nos quais a fração celulósica e a hemicelulósica de substratos lignocelulósicos são convertidos em açúcares redutores (para serem fermentados a bioetanol), são o tema desta dissertação. As principais questões consideradas aqui são: a cinética, o padrão de contato sólido-líquido, o comportamento fluidodinâmico da lama durante a hidrólise, configurações alternativas de reatores contínuos, e estratégias de operação contínua com relação ao substrato e a enzima. Foram revisados os modelos cinéticos mais recentes para a hidrólise enzimática de substratos lignocelulósicos, dando especial atenção aos modelos úteis para projeto de reatores. Foi proposto um esquema de classificação de modelos cinéticos baseado no número de reações consideradas. Com respeito à utilidade de um modelo cinético na otimização do sistema de reação, é desejável que este inclua a adsorção das enzimas na fração celulósica do substrato e na lignina, a inibição das enzimas por produto final, a reatividade do substrato e a desativação das enzimas. Neste trabalho, um modelo de uma reação foi ajustado a perfis experimentais de glicose e xilose obtidos na hidrólise enzimática de bagaço de cana prétratado com peróxido de hidrogênio alcalino. O modelo cinético apresentado difere de outros modelos em que este inclui a predição do perfil de xilose por meio de uma relação algébrica que faz uso do perfil de glicose, e é especialmente útil na ausência de dados experimentais de adsorção e reatividade do substrato. O comportamento fluidodinâmico da lama de biomassa durante a hidrólise enzimática é complexo devido à ampla distribuição de tamanhos de partícula, às formas incomuns das partículas de biomassa e às mudanças na reología que experimenta o material ao longo da reação. Neste trabalho é apresentado um levantamento detalhado da fluidodinâmica de suspensões de polpas fibrosas e lamas com tendência à sedimentação, devido a que o comportamento fluidodinâmico de lamas de biomassa pode ser entendido a partir dessas duas situações limite. Além disso, foi desenvolvido um modelo fluidodinâmico com balanços microscópicos e solucionado com um software de fluidodinâmica computacional para estudar o escoamento de lamas de biomassa em reatores tubulares com e sem defletores angulares internos. Por outro lado, a micromixtura do material dentro dos reatores foi considerada em duas situações limite: um material que é fracionado em cúmulos discretos que reagem como reatores batch durante o tempo que estejam no sistema de reação, e um material que imediatamente ingressa no sistema de reação entra em contato íntimo com outros elementos de fluido ao nível molecular. As conversões em reatores continuous para as anteriores situações limite de micromistura foram obtidas. Os reatores contínuos considerados foram reatores de tanque agitado em serie, reatores tubulares e combinação entre eles. Devido a que a biomassa adsorve água, no começo da reação de hidrólise a fase móvel pode desaparecer a concentrações de substrato maiores de 10% w/w, aproximadamente. A alimentação distribuída de substrato numa serie de reatores de tanque agitado foi uma alternativa proposta neste trabalho para incrementar a produtividade volumétrica dos reatores. Consequentemente, uma série de reatores de tanque agitado com alimentação distribuída, seguida de um reator tubular, foi a melhor alternativa para incrementar a reatividade volumétrica dos reatores e diminuir o volume de reação. O presente trabalho é em grande parte exploratório sendo que não há procedimentos detalhados de projeto e escalonamento de reatores de hidrólise enzimática de biomassa lignocelulósica na literatura científica atual. Consequentemente, reatores contínuos alternativos assim como procedimentos de modelagem mais detalhados são brevemente discutidos ao final do trabalho. De vital importância são experimentos para elucidar aspectos tais como a reutilização de enzimas por recirculação ou re-adsorção em substrato fresco, adsorção de enzimas a altas concentrações iniciais de substrato (>10% w/w), e a relação entre as propriedades reológicas da lama e a extensão da reação de hidrólise.
Abstract: For ever a century, the main source of fuel and chemicals for human society has come from fossil resources, which are limited and concentrated in a few regions of the world. Biomass, as the only source of renewable carbon, shows great promise for largescale economical production of renewable transportation and fuel chemicals. In the last decade the bioethanol production from lignocellulosic biomass via, enzymatic hydrolysis, has been intensively studied at laboratory level. Continuous reactors in which the cellulose and hemicellulose fractions of lignocellulosic substrates convert to reducing sugars (which are fermented to bioethanol) are the theme of this dissertation. The main issues considered are kinetics, contacting pattern and fluid dynamics, alternative configurations of continuous reactors, and continuous operating strategies with respect to substrate and enzyme. The most recent kinetic models for the enzymatic hydrolysis of lignocellulosic biomass, useful for reactor design, were reviewed and classified based on the number of reaction considered. Regarding to reactor design, the main factors that should be include a kinetic model are adsorption of enzymes on cellulose and lignin, inhibition of enzyme by glucose and cellobiose, substrate reactivity and enzyme deactivation. A kinetic model of a single reaction was fitted to experimental profiles of glucose and xylose obtained by the enzymatic hydrolysis of pretreated of sugarcane bagasse. This kinetic model differs of previous models in that it predicts xylose concentration based on glucose concentration. This kinetic model is a useful in the absence of experimental data on enzyme adsorption and substrate features others than concentration. The fluid dynamic behavior of biomass slurries during enzymatic hydrolysis is very complex due to the wide particle size distribution, the extremes shapes of particles and the significant rheological changes of the slurry with the progress of the enzymatic hydrolysis. This works reviewed the fluid dynamic behavior of fiber pulp suspensions and settling slurries because the fluid dynamic behavior of biomass through continuous reactors can be framed between these two limiting situations. In addition, a computational fluid dynamic model was developed to asses the fluid dynamic behavior of biomass slurries in tubular and baffled tubular reactors, motivated by the benefits of tubular reactors to carry out the enzymatic hydrolysis in terms of lower reaction volume and lower agitation requirements. On the other hand, the micromixing behavior of the flowing material was framed between two limiting situations: an incoming material that is broken up into discrete clumps in which the reaction proceed independently as in a batch reactor, and an incoming material that immediately comes into intimate contact with other fluid elements at molecular level. Conversions in continuous reactors corresponding to the above extreme states of micromixing were obtained. The continuous reactor considered were stirred tanks reactors in series, tubular reactors, and combination between them. As biomass adsorbs water, this may cause the bulk to become unsaturated at initial substrate concentration higher than 10% w/w, approximately. Operating the enzymatic hydrolysis in a distributed feeding mode by adding fresh substrate and enzyme at subsequent stirred tank reactors was proposed as an alternative to increase the volumetric productivity of reactors. A reactors configuration consisting of stirred tank reactors in series with continuous distributed feeding of substrate and enzyme, followed by a tubular reactor allow increasing the volumetric productivity of the reaction system overcoming mixing limitations and lowering the required reaction volume. It should be noted that this work is exploratory and that there are not major reports in open literature about the design and scale-up of continuous reactors for enzymatic hydrolysis. Some alternative continuous reactors, as well as modeling approaches for reactor design, are suggested. Of paramount importance are experiments to elucidate relevant aspects as reutilization of enzymes by recirculation of readsorption, adsorption of enzymes at high substrate concentrations (>10% w/w), and the relation between rheological properties of slurries with the extent of saccharification.
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química

Orientadores: Liliane Maria Ferrareso Lona, Fabiano Andre Narciso Fernandes
Dissertação (mestrado) - Universidade Estadual de Campinas. Faculdade de Engenharia Quimica
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Resumo: : A polimerização a alta pressão em reator autoclave é uma das tecnologias empregadas na produção de polietileno de baixa densidade (PEBD) empregam altas temperaturas, que podem variar de 150 a '300 GRAUS¿C, e altas pressões, até 3000 atm. Neste trabalho de mestrado foi desenvolvido um modelo matemático dinâmico para um reator de polimerização do tipo autoclave que opera em uma planta industrial no pólo petroquímico de Camaçari ¿ BA. O reator é dotado de múltiplos pontos de alimentação de monômero e de iniciador e possui um potente agitador, o que provoca uma natureza recirculante dentro do reator. De forma a considerar a mistura imperfeita, o reator é dividido em diversas seções. Cada seção é idealizada por um modelo de escoamento composto por um segmento de mistura perfeita, CSTR, e um segmento de mistura imperfeita, PFR. O segmento CSTR considera os pontos próximos das alimentações, enquanto que o PFR considera o resto da seção. Balanços de massa e de energia são realizados para cada segmento do reator. O método dos momentos foi utilizado para a caracterização das propriedades médias do polímero formado. Controladores do tipo PID foram implementados para controlar a temperatura e manter o reator em um ponto instável de operação. O conjunto de equações diferenciais e algébricas para cada segmento foi resolvido simultaneamente. Os resultados da simulação do modelo foram comparados com dados industriais e bons resultados foram obtidos
Abstract: High-pressure polymerization in autoclave reactors is one of the most currently technologies used for production of polyolefins, particularly polyethylene. Pressures until 3000 atm and temperatures covering the range from 150 to '300 DEGREES¿C are usually employed in this system. In the present work high-pressure ethylene polymerization process to produce low-density polyethylene (LDPE) have been considered. In this work was developed a dynamic mathematical model for an autoclave polymerization reactor that operates in an industry in Brazil. The reactor comprises multiple feed points of monomer, initiator and a powerful agitator, which cause a recirculating nature inside the reactor. In order to consider the imperfect mixing, the reactor is divided into several sections (reaction zones). Each sections is idealized as composed by segments: one CSTR and one PFR segment accounts for the imperfect mixing region. Mass and energy balance are given for each segment of the reactor. The method of moments was used to characterize the average properties of the polymer produced. PID control was used to maintain operation on an unstable steady state point. The set of differential and algebraic equations (for all segments) was solved simultaneously. The results were compared with industrial data and good agreement was obtained.
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química

Cette thèse aborde l’étude expérimentale des écoulements gaz-solide et la modélisation des réacteurs à lit fluidisé. L’application analysée concerne la carbochloration de la zircone (ZrO2), opération préliminaire indispensable à l’obtention de zirconium métallique. L’objectif principal est de mieux comprendre et de modéliser le comportement des réacteurs existants pour améliorer et optimiser leur rendement. La démarche entreprise consiste dans un premier temps à étudier et comprendre l’hydrodynamique des lits fluidisés de carbochloration. Les résultats obtenus montrent que le noir de carbone joue un rôle d’agent d’écoulement en améliorant la coulabilité de la zircone et donc le comportement du mélange ZrO2/C. De plus, une bonne dispersion du noir de carbone sur les particules de zircone est essentielle pour optimiser son rôle d’agent d’écoulement et obtenir un mélange ZrO2/C plus résistant à la ségrégation. A partir des données expérimentales, différentes méthodes et corrélations sont proposées pour prédire la taille et la densité des agglomérats, la vitesse minimale de fluidisation, l’expansion du lit fluidisé et le débit d’élutriation des particules. Les résultats obtenus lors de l’étude hydrodynamique sont ensuite utilisés pour modéliser le comportement des réacteurs industriels, par un couplage de l’hydrodynamique et de la cinétique chimique. Ce modèle permet la résolution des équations de bilan de matière, de bilan de population et de bilan thermique en régime transitoire. Il est ainsi possible de prédire les performances des réacteurs (conversion de chlore, granulométrie dans le lit fluidisé, débit d’élutriation, etc.) en fonction des conditions opératoires
This thesis deals with the experimental study of gas-solid flows and the modeling of fluidized bed reactors. The industrial application investigated in this work corresponds to the carbochlorination of zirconium dioxide (ZrO2), which is an essential step for the production of zirconium metal. The main objective is to develop a model of the industrial reactors and provide a better understanding of their behavior. The approach consists first in studying the hydrodynamics of fluidized bed carbochlorination reactors. The results show that the carbon black acts as a flow conditioner (glidant) and improves the flow properties of the ZrO2/C mixture. The presence of tiny spherical carbon nanoparticles on the surface of relatively large oxide particles reduces the interparticle forces and friction between adjacent particles. A good dispersion of the carbon nanoparticles is needed to enhance their ability to act as a glidant and also increase the resistance to segregation of the resulting mixture. From the experimental data, different methods and correlations are developed to predict the agglomerate size and density, the minimum fluidization velocity, the bed expansion and the elutriation flow rate. Then, a carbochlorination reactor model is developed by coupling hydrodynamics and kinetics. This model allows the resolution of unsteady-state mass and energy balance equations as well as population balance equations. It is thus possible to predict the chlorine conversion, the composition of the product gas, the elutriation flow rate and the particle size distribution in the bed depending on the operating conditions

A model of premixed lean Hydrogen-Oxygen flame is studied by singular perturbation techniques based on high activation energy. The model is built from four reaction steps consisting of two chain branching steps, a chain propagating step, and a recombination step. The analysis, in this case, gives rise to a layer phenomenon different from what is currently seen in combustion literature. First, there is a basic layer similar to those obtained for the one step reaction model. Then embedded in the first layer is a thinner layer giving rise to an interesting system of nonlinear boundary value problems. This system of nonlinear problems does not meet standard existence criterium and also involves an unknown parameter. Hence existence results are called for. Existence is proved for both the boundary value problem and the unknown parameter, and numerical solutions are obtained in support of the existence results. A numerical estimate of the unknown parameter is obtained. A generalization of the model for different reaction parameter ranges is made. Two new thin layers emerge. The structure of one of the new thin layers turns out to be exactly the same as that just described, hence the existence results do carry over. The boundary value problem resulting from the second of the new thin layers turned out to be quite simple and a solution could be written down explicitly.

Ce travail de thèse a pour ambition d’apporter des solutions et des perspectives innovantes aux travaux de recherche actuels sur la méthanisation en voie solide, en s’appuyant sur les outils numériques. Les livrables de cette thèse s’organisent en « boîte à outils numériques » pour l’ingénieur, le chercheur et l’exploitant d’installation. Tout comme la boîte à outils de l’ouvrier, ils se structurent en plusieurs parties représentant les trois principales applications du numérique pour la méthanisation : l’optimisation, la caractérisation hydrodynamique et la modélisation. Le lien entre ces parties s’articule naturellement autour d’une approche systémique identifiant les échanges entre chacune de ces parties afin d’en former une solution complète dépassant leur somme. Ce travail a été réalisé autour de deux substrats : le fumier bovin pailleux et la tonte d’herbe, mais a été réalisé dans un esprit de transposition à tout autre substrat. La première étape de ce travail a été la conception des réacteurs et compteurs de gaz permettant de réaliser chacune des parties ultérieures à moindre coût. Ce matériel a été conçu par ordinateur après avoir déterminé les caractéristiques nécessaires par le calcul. La seconde étape a été d’utiliser une approche différente des plans d’expériences afin d’accroître l’efficacité des optimisations réalisées à l’aide de cet outil. Cette approche permet d’optimiser à la fois la composition de chaque substrat et la valeur de différents paramètres opératoires en un seul plan d’expériences combinant plans factoriels et plans de mélanges. L’outil du Bootstrapping a été également utilisé afin de minimiser les expériences réalisées en conservant la même significativité des résultats obtenus. Dans cette étude, la composition de deux substrats et deux paramètres opératoires ont été étudiés pour maximiser la production de méthane : la composition en fumier bovin et en tonte d’herbe, l’immersion du massif solide et la fréquence de recirculation de la phase liquide. La problématique de percolation est également un sujet d’étude : à quoi cela sert-il d’optimiser les paramètres opératoires si la phase liquide ne peut percoler au sein du massif solide ? La troisième étape de ce travail réside dans l’étude de l’écoulement de la phase liquide au sein d’un massif en conditions de codigestion en fonction de sa composition et de sa stratification. Cette étape permet de fournir des paramètres caractéristiques de l’écoulement, de proposer une nouvelle approche de la stratification et de mettre en évidence l’effet de la codigestion sur l’évolution des microporosités et macroporosités. Enfin, l’impact de l’évolution des microporosités et macroporosités sur la biologie a été injecté dans un modèle à un seul substrat afin de fournir un outil de compréhension du phénomène et un premier pas vers la prédiction du phénomène. L’ensemble de cette démarche permet donc d’optimiser les paramètres opératoires, de s’assurer de l’aspect fonctionnel d’une expérience et de proposer un modèle de compréhension globalisant les connaissances. Ce n’est pas une solution définitive mais une solution à étayer, tout comme la boîte à outils se renouvelle en outils toujours plus performants
This work aims to provide innovative solutions and perspectives to the current research work on solid state anaerobic digestion, using digital tools. The deliverables of this study are organized into a “digital toolbox” for engineers and researchers. Like the worker’s toolbox, this solution consists of several sections representing the three main digital applications for anaerobic digestion: optimization, hydrodynamics and modeling. Each part is linked with others to build a systemic approach identifying exchanges between them in order to form a complete solution exceeding the sum of its parts. This work was carried out around two substrates: straw cattle manure and damp grass. It was however designed to be transposed to any substrates. The first step in this work was the reactors and gas counters conception to perform each of these steps at lower cost. This equipment was computer-aided designed after the characteristics were determined by calculation. The second step was to determine a different approach from experimental designs to increase the optimization efficiency using this tool. This method allows tooptimize both the composition of each substrate and the different operating parameters values in a single experimental design combining factor design and mix design. The bootstrapping tool is also used to minimize the number of experiments while maintaining the results significance. In this study, the two substrates composition and two operating parameters were studied to maximize methane yield. The two substrates were cattle manure and damp grass, and the two studied parameters were immersion of the substrates and recirculation frequency of the liquid phase. The percolation is also a study subject: what is the purpose of optimizing the operating parameters if the liquid phase cannot percolate within the solid part? Therefore, the third step of this work is to study the liquid phase flow within the solid part under codigestion conditions according to its composition and stratification. This step allows to provide the flow characteristic parameter to propose a new stratification approach and to highlight the codigestion effect on the microporosity and macroporosity evolution. Finally, the microporosity and macroporosity evolution impact on biology was modeled in a single substrate model to provide an understanding tool and a first work step on a prediction tool integrating these phenomena. The whole study allows to optimize the operating parameters, to ensure the functional aspect of an experiment and bring forward an understanding model of porosities evolution. It is not a definitive solution but a solution to substantiate, just as the toolbox is continuously renewed in innovative and more efficient tools

Thesis (M.S. in Operations Research)--Naval Postgraduate School, September 1990.
Thesis Advisor(s): Johnson, Laura. Second Reader: Parry, Sam H. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): Chemical Warfare Casualties, Chemical Warfare Agents, Mathematical Models. Author(s) subject terms: Chemical Casualties, Chemical Warfare, Regression, CHEMCAS. Includes bibliographical references (p. 36-37). Also available in print.

Current enzyme kinetic equations are inadequate for modelling enzymatic reactor systems because they fail to take into account the interactions between that various process parameters. They also are unable to predict reaction rates in complex solute systems. A quasi-native kinetic model was developed that predicts enzyme activity by examining the effect of solute addition on the overall protein structure. The theory was tested using the enzyme urease (urea aminohydrolase EC 3.5.1.5).
The quasi-native model was found to accurately predict both the activation and inhibition phenomena observed with urease and could also predict enzymatic activity in complex solute systems. The quasi-native isomerization constant was shown to be a function of hydrophobic effects characterized by the Sechenov theory and electrostatic effects characterized by the DeBye-Huckel theory. The Sechenov constant was found to be independent of temperature and pH.
The urease denaturation rate constant displayed a response to solute addition similar to that observed with the quasi-native isomerization equilibrium constant. However, the effect of pH on urease kinetics was a complex function of the ionization of active-site ligands and enzyme surface charge interactions.

A model for the hot slab ignition problem is analyzed to determine critical conditions based on the parameters of the system. Activation energy asymptotics, a singular perturbation approach, is applied to the governing equation resulting in a Volterra integral equation of the second kind whose solution represents the temperature perturbation at the surface of the hot slab. The system is said to be supercritical for given parameter values when the temperature perturbation blows up in small finite time, an indication of ignition, or subcritical when the blow up time is large, indicating that heat loss effects overcome the hot slab ignition mechanisms. Comparison principles for integral equations are used to construct upper and lower solutions of the equation. The exact solution as well as the upper and lower solutions depend on two parameters ε, the Zeldovich number a measure of the heat release and λ, the scaled hot slab size. Upper and lower bounds on the transition region, delineating the super-critical from the sub-critical region, are derived based upon the lower and upper solution behavior. The product integration method is used to compute solutions of the Volterra equation for values of ε and λ in the transition region. The computations indicate that a critical curve, λ(c) lying between the analytic bounds, exists.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Atmospheric particulate matter is known to have significant effects on human health, visibility, and global climate. The magnitudes of these effects, however, depend in complex ways on chemical composition, relative humidity, temperature, phase state, and other parameters. Current regional air quality models such as CMAQ (Community Multiscale Air Quality model) ignore many of these considerations, and consider that the formation of secondary organic aerosol (SOA) can be calculated by assuming thermodynamic ideality in the organic particulate matter (OPM) phase as well as negligible uptake of water into the OPM phase. Theoretical predictions and model simulations considering non-ideality and water uptake show that the standard model assumptions can lead to large errors in predicted SOA mass, and that the magnitude of these errors is sensitive to the composition of the OPM phase. The SOA module in CMAQ v4.7.1 has been revised in this work to allow consideration of the effects of both non-ideality and water uptake. First, a reasonable specific surrogate structure was assigned to each of the lumped products assumed to be produced by reaction of the different precursor hydrocarbons considered in CMAQ (e.g., isoprene, benzene, and toluene). Second, the CMAQ code was modified to allow iterative calculation (at each point in space and time) of the gas/particle partitioning coefficient for each of the SOA-forming products and for water. Third, model simulations were performed for the Eastern US at a resolution of 36-km x 36-km for late summer 2006, under a range of relative humidity conditions. When compared with an appropriate base case, the modified code produced increases in SOA ranging from 0.17 to 0.51 micrograms per cubic meter. The average change was 0.30 micrograms per cubic meter, corresponding to a 37% increase in SOA formation. Incorporation of phase separation effects would likely lead to further increases in predicted SOA levels.

Orientadores: Rubens Maciel Filho, Maria Regina Wolf Maciel
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: Para a síntese do acrilato de etila, foi desenvolvido um modelo contínuo bidimensional estacionário para um reator tubular, considerando transferência de calor e massa por dispersão radial e convecção axial. Foi assumido o modelo pseudo-homogêneo sendo do tipo ¿plug-flow¿, o qual se mostrou adequado para as condições de escoamento utilizadas. Todos os elementos necessários à modelagem detalhada do processo foram estabelecidos, incluindo informações experimentais, bem como as correlações para cálculo das propriedades físicas dos componentes puros, os métodos de cálculo respectivos à mistura, as correlações para estimativa dos parâmetros de transferência de massa e energia e a perda de carga. O modelo foi desenvolvido para trabalhar com diferentes métodos numéricos. Uma adimensionalização das variáveis foi realizada antes da discretização das equações diferenciais parciais pelo Método de Colocação Ortogonal. A solução numérica é baseada na implementação do Método das Linhas, o qual é uma combinação de um método de colocação ortogonal na dimensão radial e uma integração axial pelo método de Runge- Kutta de 4 ª ordem. Um método baseado na Quadratura de Gaus-Jacobi foi utilizado para o cálculo das médias das propriedades físicas na radial para cada intervalo de integração. O comportamento do reator é investigado em função de sua sensibilidade a um grupo de parâmetros de projeto e operação. Este software, que na verdade é uma planta virtual, foi utilizado para representar a produção do acrilato de etila em escala industrial em um reator multitubular. O catalisador utilizado foi ácido sulfúrico e as informações sobre a cinética foram suficientes para abordar várias operações compatíveis com as condições industriais. A reação é endotérmica, homogênea, possui uma cinética de segunda ordem e ocorre na fase líquida. A temperatura de reação utilizada foi em torno de 80 ºC, e o fluido de aquecimento utilizado foi o Dowterm A. Para etapa de separação utilizou-se um software comercial, no caso o Aspen Plus. Esta etapa compreendeu primeiramente a caracterização termodinâmica da mistura reacional, e em seguida, a simulação dos principais equipamentos utilizados na separação, visando a otimização do processo. O Acrilato de etila é um éster produzido a partir do ácido acrílico e do etanol. Ésteres acrílicos como este, são mundialmente utilizados para a produção de polímeros, os quais por sua vez, são utilizados principalmente na indústria de tintas e vernizes, adesivos, couro, papel, e tecidos. O que motivou este trabalho, foram os recentes avanços no desenvolvimento de uma rota bioquímica para a síntese do ácido acrílico, utilizando a cana de açúcar como matéria prima. Hoje o ácido acrílico é produzido pela oxidação do propeno, ou seja, uma rota petroquímica. Como o etanol também é produzido no Brasil a partir da cana de açúcar, com um preço muito competitivo comparado à via petroquímica, é possível desenvolver uma ¿rota verde¿, a qual pelos resultados encontrados, é interessante tanto do ponto de vista financeiro quanto ambiental
Abstract: For the synthesis of ethyl acrylate, a continuous bi-dimensional steady-state model for a tubular reactor is developed, considering heat and mass transfer by radial dispersion and axial convection. The model is pseudo-homogeneous and is assumed a plug flow type, which it quite reasonable for the used flow conditions. All the elements necessary to the detailed process modeling were established, including experimental information as well as the correlations to calculate the pure-component physical properties, the respective mixture properties calculations methods, the correlations to estimate heat and mass transfer parameters and pressure drop. The model is built and rearranged to be solved for different numerical methods. An adimensionalization of the variables was carried out before the discretization of the partial differential equations by Orthogonal Collocation method. The numerical solution is based on the method of lines implementation, which is a combination of an orthogonal collocation method in the radial dimension and an axial integration by an explicit 4th order Runge-Kutta method. A Gauss-Jacobi quadrature based method for the radial mean physical properties calculations is used as an internal procedure for each integration interval. This software, in fact a virtual plant, was used to represent the industrial scale production in a multitubular reactor. The catalyst used was sulfuric acid and the information about kinetic was available to cover a broad range of operations compatible with industrial conditions. The kinetic is of second order, homogeneous and the reaction is endothermic and it takes place in the liquid phase. The reactor temperature was about 80 ºC, and Dowtherm A was used as heater fluid. The commercial software Aspen Plus, was used for the separation step. This step includes firstly a thermodynamic characterization of reaction mixture, and after, the simulation of the major equipments used in the separation step, aiming the process optimization. Ethyl acrylate is an ester produced from acrylic acid and ethyl alcohol. Acrylic esters such this, are worldwide used, primarily for polymers production, mainly for coatings, paints, adhesives, and binders for leather, paper, and textiles. The motivation of this work, was the recent advances in the development of biochemical route for the synthesis of acrylic acid by the sugar cane. Today the acrylic acid is produced by the propene oxidation, or a petrochemical route. As the ethyl alcohol is already produced in Brazil by the sugar cane, in a very competitive price compared to petrochemical via, it is possible to develop a ¿green route¿, which by the results found, is both interesting in a financial and environmental point of view
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

This thesis describes the research conducted by t he author in completion of a Doctor of Philosophy in the Centre for Advanced Macromolecular Design(CAMD), Univcrsity of New South Wales (UNSW) , Sydney, Australia; under the supervision of Professor Christopher Barner-Kowollik and Doctor Michelle L. Coote (Australian National University). The research has led to the creation of new knowledge in the fields of free radical polymerisation and chemical kinetics. Research was conducted in two main thrusts: (1) investigation into the governing kinetic processes behind star polymer synthesis via what has become known as a reversible addition fragmentation chain transfer (RAFT), R-group approach and (2) an entirely new mode of living free radical (LFR) polymerisation which has been named thioketone mediated polymerisation (TKMP). In the first broad area of the described research, a novel kinetic modelling scheme has been developed in which only the reactions of a single arm star are simulated explicitly. Subsequently, the molecular weight distributions (MWDs) arising from the single arm star simulation are convolved, using probabilistic calculations, to generate the MWD appropriate to a multi-arm star polymerisat ion bearing t he same kinetic parameters as the single arm one. This model is validated against experimental data, enabling, for the first time, the use of rigorous theoretical reasoning to distill a set of synthetic guidelines for star polymer synthesis via a RAFT, R-group approach. Subsequently, the product spectra resulting from RAFT, R-group approach polymerisations of para-acetoxystyrene have been analysed via mass spectrometry. This has led to direct evidence for many of the complex species whose existence had, up until this point, been inferred from gel permeation chromatography (GPC) measured MWDs. The menagerie of species identified includes, but is not limited to, star-star couples, initiator fragment terminated stars, initiator fragment terminated star-star couples and linear chains -- both living and terminated. Using a kinetic model devised specifically for application in mass spectrometry analysis, the experimentally observed abundances of each of the above species have been compared to t hose predicted by simulation. The qualitative agreement between the predicted and observed abundances has provided additional evidence that t he proposed mechanism for RAFT, R-group approach polymerisations is correct and operative. Further, it seems unlikely that significant, undiscovered kinetic phenomena exist. Due to (a) long simulation times encountered using the state of the art, commercial partial differential equation solver for polymerisation kinetics (i.e. PREDICI, Computing in Technology (CiT), GmbH; see http://www.cit-wulkow.de) and (b) the limited flexibility this software provides with respect to the types of chemical species that can be simulated, fundamental research has been conducted into the kinetic Monte Carlo method to (i) examine fundamental aspects of this simulation approach; (ii) determine the maximum speed attainable through a combination of optimisations including run-time generation of problem specific code and parallelisation; and, therefore (iii) find out what the potential of this method may be as a replacement for t he existing methods. In terms of speed, the developed code outperforms previous Monte Carlo benchmarks in the literature by a factor of 2.6 and the latest developments in the commercial tool, PREDICI that took place during the author's Ph.D. candidature give it similar performance to the herein described Monte Carlo code; however, the latter is required to run on multiple processors in order to compete with the serial algorithm implemented in PREDICI. The Monte Carlo method does, however, provide complete freedom with respect to the chemical species whose kinetics can be simulated, allowing for complex species with many chain lengths and, in principal copolymer compositions and branched structures. The Monte Carlo approach is the method of choice for these types of simulations and for the first time competes with the commercial tool in terms of speed. In the second broad area of the described research, an experimental investigation has been conducted into the applicability of thioketones, S=C (R1) (R2), as mediating agents for free radical polymerisations. The compound di-tert-butyl thioketone (DTBT), S=C-(C(CH3)3)2, has been chosen as a model reagent and this, when incorporated into a free radical polymerisation of styrene has led to a linear increase of the average molecular weight as conversion of monomer into polymer takes place - demonstrating control. A reversible radical trapping mechanism has been proposed and evidence for this has been provided in the form of an ab initio calculation of the equilibrium constant for the trapping of a styryl dimer radical by DTBT. This equilibrium constant was approximately K = 105 L mol-1 and is close to the value which is expected on the basis of the experimental results. To aid future experimental investigations intoTKMP, a quantum chemical survey has, been conducted with the aim of discovering the radical affinities of a large range of thioketones. It has been demonstrated that there is ample scope within this class of compound for potent radical trapping - far above that of DTBT. The affinities of various thioketone substrates for radicals have been understood in terms of the radical stabilising and thioketone destabilising effect of the two substituents R1 and R2 on, respectively, the adduct radical, R-S-C???(R1) (R2), and the parent thioketone. All results appearing in this thesis have been published previously in peer-reviewed scientific journals.

Dissertation (PhD)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: A mathematical model is presented which conceptualises fluid flow and heat transfer in cellular metallic foams completely saturated with a fluid in motion. The model consists of a set of elliptic partial differential governing equations describing, firstly, a momentum balance in the fluid by the spatial distribution of its locally mean velocity, and secondly, an energy balance in the fluid and in the solid matrix of the metallic foam, by the spatial and temporal distribution of their locally mean temperatures. The separate energy balance descriptions for the fluid and the solid matrix extend the application of the model to conditions of thermal equilibrium and thermal non-equilibrium between the fluid and the solid matrix. A computational solution algorithm is presented which allows the universal application of the model to porous domains of arbitrary shape, with spatially and temporally variable heat loads in a variety of forms.
AFRIKAANSE OPSOMMING: 'n Wiskundige model word voorgestel wat vloei en warmteoordrag voorspel in sellulêre metaalsponse wat in geheel gevul is deur 'n bewegende vloeier. Die vloeier kan in gasof vloeistoffase verkeer. Die model bestaan uit 'n stel elliptiese parsiële differensiaalvergelykings wat in die eerste plek 'n momentum-ewewig in die vloeier beskryf in terme van 'n ruimtelike, lokaal-gemiddelde snelheidsveld, en wat tweedens 'n energie-ewewig in die vloeier en in die soliede matriks van die metaalspons beskryf in terme van ruimtelike en tydelike lokaal-gemiddelde temperatuur verspreidings. Die aparte energie-ewewig beskrywings vir die vloeier en vir die soliede matriks van die metaalspons brei die aanwending van die model uit na gevalle waar die vloeier en die soliede matriks in termiese ewewig of in termiese onewewig verkeer. 'n Numeriese oplossingsalgoritme word ook voorgestel vir die universele toepassing van die model op ruimtelik-arbitrêre metaalspons geometrië wat onderwerp word aan 'n aantal verskillende ruimtelik-en tydveranderlike termiese laste.

Traditionally the reactor is recognised as the `heart' of a chemical process system and hence the focus on this part of the system is usually quite detailed. Steam reforming, however, due to the `building block' nature of its reaction products is unusual and generally is perceived as a `utility' to other reaction processes and hence the focus is drawn " towards the 'main' reaction processes of the system. Additionally as a `mature' process, steam reforming is often treated as sufficiently defined for the requirements within the overall chemical process. For both primary and secondary steam reformers several models of varying complexity were developed which allowed assessment of issues raised about previous models and model improvements; drawing on the advancements in modelling that have not only allowed the possibility of increasing the scope of simulations but also increased confidence in the simulation results. Despite the complex nature of the steam reforming systems, a surprisingly simplistic model is demonstrated to perform well, however, to improve on existing designs and maximise the capability of current designs it is shown that more complex models are required. After model development the natural course is to optimisation. This is a powerful tool which must be used carefully as significant issues remain around its employment. Despite the remaining concerns, some simple optimisation cases showed the potential of the models developed in this work and although not exhaustive demonstrated the benefits of optimisation.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Traditionally the reactor is recognised as the `heart' of a chemical process system and hence the focus on this part of the system is usually quite detailed. Steam reforming, however, due to the `building block' nature of its reaction products is unusual and generally is perceived as a `utility' to other reaction processes and hence the focus is drawn " towards the 'main' reaction processes of the system. Additionally as a `mature' process, steam reforming is often treated as sufficiently defined for the requirements within the overall chemical process. For both primary and secondary steam reformers several models of varying complexity were developed which allowed assessment of issues raised about previous models and model improvements; drawing on the advancements in modelling that have not only allowed the possibility of increasing the scope of simulations but also increased confidence in the simulation results. Despite the complex nature of the steam reforming systems, a surprisingly simplistic model is demonstrated to perform well, however, to improve on existing designs and maximise the capability of current designs it is shown that more complex models are required. After model development the natural course is to optimisation. This is a powerful tool which must be used carefully as significant issues remain around its employment. Despite the remaining concerns, some simple optimisation cases showed the potential of the models developed in this work and although not exhaustive demonstrated the benefits of optimisation.

As redes poliméricas são materiais amplamente estudados, pois suas propriedades especiais permitem que sejam aplicadas em áreas como indústria de fertilizantes, medicina, bioquímica, análises químicas dentre outras. A microestrutura de uma rede polimérica, em geral, exerce grande influência sobre as propriedades macroscópicas desses materiais e o interesse da influência dessa microestrutura nas propriedades finais são de interesse estratégico. As reações de ciclização influenciam no controle da microestrutura das redes poliméricas, é sabido que um aumento na diluição do sistema aumenta a incidência deste tipo de reações. A modelagem matemática da copolimerização do estireno-divinilbenzeno é um assunto amplamente estudado, porém poucos estudos foram realizados considerando as reações de ciclização com uma cinética definida e não um problema tipo caixa-preta. Este trabalho teve como principal objetivo o estudo da copolimerização de estireno-divinilbenzeno em solução e sua modelagem matemática com a inclusão das reações de ciclização intramoleculares. Sendo assim, reações de copolimerização de estireno-divinilbenzeno em soluções com baixas concentrações de monômeros foram realizadas em batelada em um reator de vidro, inicialmente foram utilizados dois modelos matemáticos para estudar o comportamento do sistema nestas condições, denominados: Modelo A e Modelo B. O Modelo A foi desenvolvido através do balanço de massa de todas as espécies no meio reacional e inclusão das reações de ciclização. O tamanho máximo dos polímeros mortos considerados neste modelo foi de 300 unidades monoméricas, pois devido à diluição acreditava-se que este tamanho máximo abrangesse todos os tamanhos de polímeros mortos, porém sua comparação com dados experimentais mostrou o contrário. O Modelo B foi baseado no modelo desenvolvido por Aguiar (2013) e utiliza o balanço de massa para as espécies não poliméricas e método dos momentos para as espécies poliméricas (radicais poliméricos e polímeros mortos). Este modelo utiliza também o Fracionamento Numérico para determinação das massas moleculares e ponto de gel, as reações de ciclização foram incluídas através do Método dos Caminhos. Quando comparados aos dados experimentais, o Modelo B mostrou-se mais realista com menores tempos de simulação e com menores problemas numéricos que o Modelo A, portanto este foi utilizado para o estudo do sistema em questão. Os resultados apresentados através do Modelo B indicam que o parâmetro atribuído à cinética das ligações cruzadas (Cp) foi de 0,05 e o valor do parâmetro de ciclização do menor segmento ciclizável (3 unidades monoméricas) foi de 130 s-1 para a temperatura de 90ºC, os valores para os demais tamanhos foram calculados através da equação de Rolfes e Stepto. Este trabalho é uma continuação ao trabalho de Aguiar (2013) e seus resultados mostraram que as simulações das variáveis: concentração de duplas ligações pendentes, Massa Molecular Mássica Média (Mw) e polidispersidade aproximaram-se mais dos dados experimentais quando as ciclizações são incluídas no modelo quando comparadas à abordagem sem a inclusão das reações de ciclização.
Polymer networks are widely studied materials; their especial properties allow them to be applied in areas such as the fertilizer industry, medicine, biochemistry, chemical analysis among others. In general, the polymer network microstructure has influence in macroscopic properties of materials, hence the interest of such microstructure in final properties are of strategic interest. The cyclization reactions influence in the microstructure control of polymer networks. It is known that an increase in systems dilution can increase the cyclization reactions incidence. Mathematical modeling of copolymerization of styrene-divinylbenzene is a widely studied subject, but few studies have been conducted considering the cyclization reactions with a defined kinetic and not a problem black-box type. This work aimed to study the styrene-divinylbenzene copolymerization solutions and their mathematical modeling with the inclusion of intramolecular cyclization reactions. Thus, solution copolymerization of styrene and divinylbenzene was carried out at low concentration of monomers in batch reactor. Two mathematical models were initially used to analize the behavior of the system, which were called: Model A and Model B. The Model A was developed by molar balance of species in the reaction medium and includes cyclization reactions, which were considered to happen in polymer chains with 300 or less monomer units. Due the dilution was believed that this number of units covering all sizes of dead polymers, but comparison between Model A an experimental data proved otherwise. The Model B was based in model of Aguiar (2013), and uses the mass balance for non-polimerics species and moments methods for polimerics species. Model B also uses numerical fractionation for average molecular weight and gel point determination, and the method of paths to approach cyclization reactions. When compared to experimental data, Model B proved more realistic, presenting shorter simulation times and less numerical problems than Model A. Therefore Model B was chosen to represent the system. The results presented by Model B indicate that the parameter assigned to the kinetics os crosslink (Cp) was fitted at 0,05 and cyclization rate constant for paths with 3 monomer units was fitted 130 s-1 at temperature of 90°C. The cyclization rate constants for longer paths were calculated trough Rolfes and Steptos equation. This work is a follow up to Aguiars work (2013) and the results showed that the simulation of variables: concentration of pendant double bonds, average molecular weight and polidispersity better predicted when the cyclization rate constants are greater than zero.

Managing water quality aspects requires the use of integrative tools that allow a holistic approach to this problem. Water quality models coupled to hydrodynamic models are these tools. This study presents the application of the water quality model WASP coupled to the hydrodynamic model DYNHYD for two distinct reservoirs: Lake Texoma and Tocoma Reservoir. Modeling the former included simulations of water velocities, water level, and four chemical and physical compounds: chlorides, dissolved oxygen (DO), biochemical oxygen demand (BOD), and total suspended solids (TSS); and validation of the results by comparing with observed values during March - May, 1997. The latter is still under project status and the simulation was performed in a prospective way. The analysis included simulations of water velocities under current and for expected conditions, DO and BOD. Both models, DYNHYD and WASP, fitted pretty well to observed conditions for Lake Texoma and for where Tocoma Reservoir has been planned. Considering management and decision support purposes, the role of boundary and loading conditions also was tested. For Lake Texoma, controlling boundary conditions for chlorides is a determinant factor for water quality of the system. However, DO and TSS in the reservoir are governed by additional process besides the condition of the boundary. Estimated loadings for this system did not provided significant effects, even though the allocation of a load for chlorides resulted in significant changes in the trend for expected chloride concentrations at the Washita River Arm of Lake Texoma. For Tocoma Reservoir, the expected concentration of DO all over the reservoir is going to driven by boundary conditions, as well as by the management of autochthonous BOD loadings provided by vegetation decomposition. These two factors will be determinant for the resulting water quality of the future reservoir.

Le bicarbonate de soude raffiné, produit industriellement par la société Solvay, est fabriqué dans des colonnes à bulles de grande taille, appelées les colonnes BIR.

Dans ces colonnes, une phase gazeuse contenant un mélange d’air et dioxyde de carbone (CO2) est dispersée sous forme de bulles dans une solution aqueuse de carbonate et de bicarbonate de sodium (respectivement Na2CO3 et NaHCO3). Cette dispersion donne lieu à un transfert de CO2 des bulles vers la phase liquide. Au sein des colonnes, la phase gazeuse se répartit dans deux populations de bulles :des petites bulles (diamètre de quelques mm) et des grandes bulles (diamètre de quelques cm). Le transfert bulle-liquide de CO2 est couplé à des réactions chimiques prenant place en phase liquide, qui conduisent à la conversion du Na2CO3 en NaHCO3. Une fois la concentration de saturation dépassée le NaHCO3 précipite sous forme de cristaux et un mélange liquide-solide est recueilli à la sortie de ces colonnes.

Ce travail, réalisé en collaboration avec la société Solvay, porte sur l’étude et la modélisation mathématique des phénomènes de transfert de matière entre phases, couplés à des réactions chimiques, prenant place au sein d’une colonne BIR. L’association d’études sur des colonnes à bulles à l’échelle industrielle ou réduite (pilote) et d’études plus fondamentales sur des dispositifs de laboratoire permet de développer une meilleure compréhension du fonctionnement des colonnes BIR et d’en construire un modèle mathématique détaillé.

L’objectif appliqué de ce travail est la mise au point d’un modèle mathématique complet et opérationnel d’une colonne BIR. Cet objectif est supporté par trois blocs de travail, dans lesquels différents outils sont développés et exploités.

Le premier bloc est consacré à la modélisation mathématique du transfert bulle-liquide de CO2 dans une solution aqueuse de NaHCO3 et de Na2CO3. Ce transfert est couplé à des réactions chimiques en phase liquide qui influencent sa vitesse. Dans un premier temps, des modèles sont développés selon des approches unidimensionnelles classiquement rencontrées dans la littérature. Ces approches passent par une idéalisation de l’écoulement du liquide autour des bulles. Une expression simplifiée de la vitesse du transfert bulle-liquide de CO2, est également développée et validée pour le modèle de colonne BIR.

Dans un second temps, une modélisation complète des phénomènes de transport (convection et diffusion), couplés à des réactions chimiques, est réalisée en suivant une approche bidimensionnelle axisymétrique. L’influence de la vitesse de réactions sur la vitesse de transfert est étudiée et les résultats des deux approches sont également comparés.

Le deuxième bloc est consacré à l’étude expérimentale du transfert gaz-liquide de CO2 dans des solutions aqueuses de NaHCO3 et de Na2CO3. A cette fin, un dispositif expérimental est développé et présenté. Du CO2 est mis en contact avec des solutions aqueuses de NaHCO3 et de Na2CO3 dans une cellule transparente. Les phénomènes provoqués en phase liquide par le transfert de CO2 sont observés à l’aide d’un interféromètre de Mach-Zehnder.

Les résultats expérimentaux sont comparés à des résultats de simulation obtenus avec un des modèles unidimensionnels développés dans le premier bloc. De cette comparaison, il apparaît qu’une mauvaise estimation de la valeur de certains paramètres physico-chimiques apparaissant dans les équations de ce modèle conduit à des écarts significatifs entre les grandeurs observées expérimentalement et les grandeurs estimées par simulation des équations du modèle.

C’est pourquoi une méthode d’estimation paramétrique est également développée afin d’identifier les valeurs numériques de ces paramètres physico-chimiques sur base des résultats expérimentaux. Ces dernières sont également discutées.

Dans le troisième bloc, nous apportons une contribution à l’étude des cinétiques de précipitation du NaHCO3 dans un cristallisoir à cuve agitée. Cette partie du travail est réalisée en collaboration avec Vanessa Gutierrez (du service Matières et Matériaux de l’ULB).

Nous contribuons à cette étude par le développement de trois outils :une table de calcul Excel permettant de synthétiser les résultats expérimentaux, un ensemble de simulations de l’écoulement au sein du cristallisoir par mécanique des fluides numérique et une nouvelle méthode d’extraction des cinétiques de précipitation du NaHCO3 à partir des résultats expérimentaux. Ces trois outils sont également utilisés de façon combinée pour estimer les influences de la fraction massique de solide et de l’agitation sur la cinétique de germination secondaire du NaHCO3.

Enfin, la synthèse de l’ensemble des résultats de ces études est réalisée. Le résultat final est le développement d’un modèle mathématique complet et opérationnel des colonnes BIR. Ce modèle est développé en suivant l’approche de modélisation en compartiments, développée au cours du travail de Benoît Haut. Ce modèle synthétise les trois blocs d’études réalisées dans ce travail, ainsi que les travaux d’Aurélie Larcy (du service Transferts, Interfaces et Procédés de l’ULB) et de Vanessa Gutierrez. Les équations modélisant les différents phénomènes sont présentées, ainsi que la méthode utilisée pour résoudre ces équations. Des simulations des équations du modèle sont réalisées et discutées. Les résultats de simulation sont également comparés à des mesures effectuées sur une colonne BIR. Un accord raisonnable est observé.

A l’issue de ce travail, nous disposons donc d’un modèle opérationnel de colonne BIR. Bien que ce modèle doive encore être optimisé et validé, il peut déjà être utilisé pour étudier l’effet des caractéristiques géométriques des colonnes BIR et des conditions appliquées à ces colonnes sur le comportement des simulations des équations du modèle et pour identifier des tendances.

//

The refined sodium bicarbonate is produced by the Solvay company using large size bubble columns, called the BIR columns.

In these columns, a gaseous phase containing an air-carbon dioxyde mixture (CO2) is dispersed under the form of bubbles in an aqueous solution of sodium carbonate and sodium bicarbonate (Na2CO3 and NaHCO3, respectively). This dispersion leads to a CO2 transfer from the bubbles to the liquid phase. Inside these columns, the gaseous phase is distributed in two bubbles populations :small bubbles (a few mm of diameter) and large bubbles (a few cm of diameter).

The bubble-liquid CO2 transfer is coupled with chemical reactions taking places in the liquid phase that leads to the conversion of Na2CO3 to NaHCO3. When the solution is supersaturated in NaHCO3, the NaHCO3 precipitates under the form of crystals and a liquid-solid mixture is extracted at the outlet of the BIR columns.

This work, realized in collaboration with Solvay, aims to study and to model mathematically the mass transport phenomena between the phases, coupled with chemical reactions, taking places inside a BIR column. Study of bubble columns at the industrial and the pilot scale is combined to a more fundamental study at laboratory scale to improve the understanding of the BIR columns functioning and to develop a detailed mathematical modeling.

The applied objective of this work is to develop a complete and operational mathematical modeling of a BIR column. This objective is supported by three blocks of work. In each block, several tools are developed and used.

The first block is devoted to the mathematical modeling of the bubble-liquid CO2 transfer in an NaHCO3 and Na2CO3 aqueous solution. This transfer is coupled with chemical reactions in liquid phase, which affect the transfer rate.

In a first time, mathematical models are developed following the classical one-dimensional approaches of the literature. These approaches idealize the liquid flow around the bubbles. A simplified expression of the bubble-liquid CO2 transfer rate is equally developed and validated for the BIR column model.

In a second time, a complete modeling of the transport phenomena (convection and diffusion) coupled with chemical reactions is developed, following an axisymmetrical twodimensional approach. The chemical reaction rate influence on the bubble-liquid transfer rate is studied and the results of the two approaches are then compared.

The second block is devoted to the experimental study of the gas-liquid CO2 transfer to NaHCO3 and Na2CO3 aqueous solutions. An experimental set-up is developed and presented. CO2 is put in contact with NaHCO3 and Na2CO3 aqueous solutions in a transparent cell. The phenomena induced in liquid phase by the CO2 transfer are observed using a Mach-Zehnder interferometer.

The experimental results are compared to simulation results that are obtained using one of the one-dimensional model developed in the first block. From this comparison, it appears that a wrong estimation of some physico-chemical parameter values leads to significative differences between the experimentally observed quantities and those estimated by simulation of the model equations. Therefore, a parametric estimation method is developed in order to estimate those parameters numerical values from the experimental results. The found values are then discussed.

In the third block is presented a contribution to the NaHCO3 precipitation kinetic study in a stirred-tank crystallizer. This part of the work is realized in collaboration with Vanessa Gutierrez (Chemicals and Materials Department of ULB).

Three tools are developed :tables in Excel sheet to synthetize the experimental results, a set of simulations of the flow inside the crystallizer by Computational Fluid Dynamic (CFD) and a new method to extract the NaHCO3 precipitation kinetics from the experimental measurements. These three tools are combined to estimate the influences of the solid mass fraction and the flow on the NaHCO3 secondary nucleation rate.

Finally, the synthesis of all these results is realized. The final result is the development of a complete and operational mathematical model of BIR columns. This model is developed following the compartmental modeling approach, developed in the PhD thesis of Benoît Haut. This model synthetizes the three block of study realized in this work and the studies of Aurélie Larcy (Transfers, Interfaces and Processes Department of ULB) and those of Vanessa Gutierrez. The equations modeling the phenomena taking place in a BIR column are presented as the used method to solve these equations. The equations of the model are simulated and the results are discussed. The results are equally compared to experimental measurement realized on a BIR column. A reasonable agreement is observed.

At the end of this work, an operational model of a BIR column is thus developed. Although this model have to be optimized and validated, it can already be used to study the influences of the geometrical characteristics of the BIR columns and of the conditions applied to these columns on the behaviour of the model equation simulations and to identity tendencies.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

The kinetics of reduction by free flavin semiquinones of the individual components of 1:1 complexes of yeast cytochrome c peroxidase and the cytochrome c from horse, tuna, and yeast, including several site-specific mutants of either the cytochrome c or cytochrome c peroxidase, have been studied. The orientations of the various cytochromes c within electrostatically-stabilized complexes with the peroxidase are not equivalent. This is shown by differential decreases in the rate constants for cytochrome reduction by neutral flavin semiquinones upon complexation which are in the order: tuna ≫ horse > yeast iso-2 > yeast iso-1. We have also directly measured the physiologically-significant intracomplex one-electron transfer rate constants from the ferrous cytochromes c to the peroxide-oxidized species of the peroxidase at several ionic strengths. The rate constants at low ionic strength are highly species dependent, again consistent with the contention that the orientations of the various cytochromes within the complex with CcP are not the same. Increasing the ionic strength in all cases resulted in an increase in the rate constant for the first-order process which controls electron transfer from cytochrome c to the peroxidase Compound I species of the peroxidase. When the two proteins are immobilized by covalent cross-linking, no such rate enhancement is observed, suggesting that the ionic strength effect is manifested by an increase in the number of geometric orientations between the two proteins which results in more rapid electron transfer. Similar rate enhancing effects are observed when positively charged residues on the surface of cytochrome c are converted to electrostatically neutral amino acids by site-specific mutagenesis. The effect of site-specific mutagenesis of two residues of cytochrome c peroxidase have also been studied. His-181, when converted to a glycine has little effect on the electron transfer rate constant, whereas when Trp-191 is converted to a phenylalanine no intracomplex electron transfer could be observed, indicating an obligatory role of this residue in the electron transfer process.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Orientador: Elias Basile Tambourgi
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: A utilização do método Monte Carlo na simulação do transporte de partículas em reatores nucleares é crescente e constitui uma tendência mundial. O maior inconveniente dessa técnica, a grande exigência de capacidade de processamento, vem sendo superado pelo contínuo desenvolvimento de processadores cada vez mais rápidos. Esse contexto permitiu o desenvolvimento de metodologias de cálculo neutrônico de reatores nas quais se acopla a parte do transporte de partículas, feita com um código de Monte Carlo, ao cálculo de queima e decaimento radioativo. Neste trabalho tal metodologia de simulação é implantada, validada para reatores de pesquisas, notadamente os do tipo TRIGA e finalmente utilizada na simulação neutrônica do reator TRIGA IPR ¿ RI do CDTN/CNEN. O sistema de códigos empregados é constituído pelos amplamente utilizados códigos MCNP4B (transporte por método Monte Carlo) e ORIGEN2.1 (queima e decaimento radioativo). Apesar dos esforços recentes no sentido de agrupar as duas etapas de cálculo, transporte e queima, em um único código, até o momento esta opção não está disponível e, portanto, um terceiro código é utilizado para realizar o acoplamento transporte/queima. Neste trabalho utilizou-se para tal o código MONTEBURNS. O sistema formado por estes três códigos permitiu obter os parâmetros neutrônicos de interesse do IPR ¿ R1 através apenas de simulação teórica, sem a necessidade de qualquer tipo de ajuste baseado em dados experimentais, em boa concordância com os valores medidos... Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital
Abstract: The use of Monte Carlo methods in particles transport simulations of nuclear reactor is growing fast and constitutes a strong tendency all over the world. The major inconvenient of such techniques is the huge demand of processing power which has been surpassed the development of reactor physics calculation methodologies in which the particles transport part, made by a Monte Carlo transport code, is linked with the burnup and radioactive decay part of the simulation. On this work a such simulation methodology is made operational, validated for research reactors, mainly for TRIGA reactor and finally utilized for reactor physics simulation of the CDTN¿s TRIGA IPR ¿ R1. The adopted codes system is constituted by the widespreadly used codes MCNP4B (Monte Carlo transport) and ORIGEN2.1 (burnup and radioactive decay). In spite of the very recent efforts toward get together both, transport and burnup, in only one code at the moment this is a not available option and therefore, a third code is needed to carry out the linkage transport/burnup. MONTEBURS code was used to this purpose. This three codes system has allowed to obtain the physical parameters of IPR ¿ R1 calculated using only theoretical simulation without any kind of experimental adjustment or interaction between experiments and calculation in good agreement with measured values... Note: The complete abstract is available with the full electronic digital thesis or dissertations
Doutorado
Sistemas de Processos Quimicos e Informatica
Doutor em Engenharia Química

In the present study syngas-air diffusion flames are simulated using LES with artificial neural network (ANN) based chemical kinetics modeling and the results are compared with previous direct numerical simulation (DNS) study, which exhibits significant extinction-reignition and forms a challenging problem for ANN. The objective is to obtain speed-up in chemistry computation while still having the accuracy of stiff ODE solver. The ANN methodology is used in two ways: 1) to compute the instantaneous source term in the linear eddy mixing (LEM) subgrid combustion model used within LES framework, i.e., laminar-ANN used within LEMLES framework (LANN-LEMLES), and 2) to compute the filtered source terms directly within the LES framework, i.e., turbulent-ANN used within LES (TANN-LES), which further dicreases the computational speed. A thermo-chemical database is generated from a standalone one-dimensional LEM simulation and used to train the LANN for species source terms on grid-size of Kolmogorov scale. To train the TANN coefficients the thermo-chemical database from the standalone LEM simulation is filtered over the LES grid-size and then used for training. To evaluate the performance of the TANN methodology, the low Re test case is simulated with direct integration for chemical kinetics modeling in LEM subgrid combustion model within the LES framework (DI-LEMLES), LANN-LEMLES andTANN-LES. The TANN is generated for a low range of Ret in order to simulate the specific test case. The conditional statistics and pdfs of key scalars and the temporal evolution of the temperature and scalar dissipation rates are compared with the data extracted from DNS. Results show that the TANN-LES methodology can capture the extinction-reignition physics with reasonable accuracy compared to the DNS. Another TANN is generated for a high range of Ret expected to simulate test cases with different Re and a range of grid resolutions. The flame structure and the scalar dissipation rate statistics are analyzed to investigate success of the same TANN in simulating a range of test cases. Results show that the TANN-LES using TANN generated fora large range of Ret is capable of capturing the extinction-reignition physics with a very little loss of accuracy compared to the TANN-LES using TANN generated for the specific test case. The speed-up obtained by TANN-LES is significant compared to DI-LEMLES and LANN-LEMLES.