Petrobrás / Hidratos são estruturas cristalinas constituídas por moléculas de água e gás ou líquido, sendo que a estabilização dessa estrutura cristalina requer condições de altas pressões e/ou baixas temperaturas. A formação e a aglomeração de hidratos podem causar o bloqueio de linhas de transporte de óleo e/ou gás, reduzindo a eficiência do processo, danificando os equipamentos e comprometendo a segurança da parte operacional. Neste cenário, no presente trabalho é apresentado o estudo numérico-experimental de equilíbrio de fases dos hidratos para identificar as regiões de formação e adequar as condições de operação na indústria petrolífera. Para a predição das condições de formação dos hidratos é desenvolvido um modelo termodinâmico baseado na teoria de sólido ideal de van der Waals e Platteeuw. O modelo é fundamentado na igualdade dos potenciais químicos de todas as espécies em todas as fases (água líquida, hidrato e vapor). Para os cálculos de equilíbrio da fase hidrocarboneto foi utilizada a equação de estado de Soave Redlich-Kwong e o método da secante foi utilizado para solucionar o modelo iterativamente. As medidas experimentais foram realizadas utilizando metano puro e a mistura metano (90 % em mol) e dióxido de carbono e os testes foram realizados em duas bancadas distintas, sendo os procedimentos realizados semelhantes, baseados no método isocórico pela monitoração da resposta da pressão do sistema com a variação da temperatura. Os resultados experimentais e numéricos obtidos foram comparados com dados da literatura com a finalidade de validar o modelo termodinâmico proposto, o aparato experimental e o procedimento adotado. O erro absoluto máximo entre os resultados obtidos experimentalmente e do modelo termodinâmico desenvolvido foi de 0,57%. Desta forma, nota-se os resultados apresentaram boa concordância entre os dados experimentais e os da modelagem numérica. / Hydrates are crystalline structures composed by molecules of water or liquid and gas, and the crystal structure that requires stabilization conditions of high pressure and/or low temperatures. The formation and agglomeration of hydrates can cause blockage of transmission lines oil and / or gas, reducing process efficiency, damaging the equipment and compromise the safety of the operating part. In this scenario, in this paper the numerical-experimental study of phase equilibria of hydrates is presented to identify the regions of formation and adjust the operating conditions in the oil industry. To predict hydrate formation conditions of a thermodynamic model based on the ideal solid solution theory by van der Waals and Platteeuw is developed. The model is based on the equality of the chemical potentials of all species in all phases (liquid water, vapor and hydrate). The SoaveRedlich-Kwong equation of state was employed for the phase equilibrium properties of the hydrocarbon fluid phase and the secant method was used to solve the model iteratively. Experimental measurements were performed using pure methane and methane mixture (90 mol%) and carbon dioxide, and the tests were performed on two separate stands, and similar procedures performed based on the isochoric method by monitoring the pressure response of the system with changes in the temperature. The experimental and numerical results were compared with literature data in order to validate the proposed thermodynamic model, the experimental apparatus and procedure adopted. The maximum absolute error between the experimental results and thermodynamic model was 0.57%. Thus, the results showed good agreement between experimental data and numerical modeling.

Orientador: Eduardo Augusto Caldas Batista / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-15T20:07:25Z (GMT). No. of bitstreams: 1 Maximo_GuilhermeJose_M.pdf: 1130642 bytes, checksum: 2075f789c23ac3903cbe00e7ee7f52fc (MD5) Previous issue date: 2010 / Resumo: O equilíbrio líquido-vapor de soluções aquosas binárias formadas por açúcares presentes em sucos de fruta, D-glucose e D-frutose foi estudado através da determinação experimental da temperatura de ebulição em rotaevaporador com recirculação da fase vapor, de 20 kPa até a pressão atmosférica (93.6 kPa) e concentração entre 10 e 60 % (m/m). Os dados experimentais foram correlacionados com dados preditos a partir do cálculo do coeficiente de atividade pelo método de contribuição de grupos UNIFACLyngby utilizando diferentes modelos moleculares e parâmetros estruturais. A conformação cíclica das moléculas foi decisiva na obtenção de resultados mais precisos pela modelagem. Os resultados foram descritos com precisão através de diagramas de Dühring e o aumento da temperatura de ebulição das soluções em relação à da água pura foi considerado significativo na demanda de energia para mudança de fase. O equilíbrio termodinâmico de soluções aquosas de ácidos policarboxílicos presentes em sucos e polpas de fruta, ácido cítrico, málico, malônico, oxálico, succínico e tartárico foram estudados através da determinação experimental do pH em células isotérmicas, entre 278.15 e 323.15 K e porcentagem mássica entre 1 e 20 %. Os dados experimentais foram correlacionados com dados preditos a partir da resolução de um sistema de equações não lineares em algoritmo computacional programado em MATLAB. O coeficiente de atividade foi calculado através da utilização isolada ou combinada, do método UNIFAC-Lyngby e da equação modificada de Debye-Hückel, levando em consideração as interações de curto e longo-alcance presentes na solução. De modo geral, o modelo combinado descreveu com melhor precisão o comportamento do pH das soluções do que a utilização dos modelos isolados. Além disso, de acordo com o equilíbrio químico das soluções, a temperatura tem efeito significativo no pH das soluções, o que significa que algumas propriedades dessas misturas são alteradas durante os processos térmicos / Abstract: The vapor-liquid equilibrium of binary aqueous solutions of D-glucose and D-fructose, present in fruit juices, was evaluated by experimental boiling point measurements in a rotary evaporator with total reflux of the vapor phase from 20 kPa to atmospheric pressure (93.6 kPa) and concentration from 10 to 60 % by mass. The experimental data were correlated with predicted data by UNIFAC-Lyngby group contribution method, using different molecular approaches and structural parameters. The cyclic conformation of the sugar molecules was decisive for the accuracy of the modeling. The data were accurately described by Dühring diagrams and the rise in boiling point was considered significant for energy demand of phase change. The thermodynamic equilibrium of aqueous solutions of polycarboxylic acids present in fruit juices and pulps, citric acid, malic acid, malonic acid, oxalic acid, succinic acid and tartaric acid was evaluated by experimental pH measures in isothermic cells, from 278.15 to 323.15 K and concentration from 1 to 20 % by mass. The experimental data were correlated with predicted data by the resolution of a non-linear equation system by a computer algorithm implemented in MATLAB. The activity coefficients were calculated using the UNIFAC-Lyngby method and the modified Debye- Hückel term, taking into account the short and long-range interactions of the molecules in solution. In general, the combined model described the behavior of the pH of the solutions with higher accuracy than the isolated models. Moreover, according to chemical equilibrium of the solutions, the effect of temperature on pH was significant, meaning that some mixtures properties are affected during thermal processes / Mestrado / Mestre em Engenharia de Alimentos

Neste trabalho utilizou-se o mapa conceitual como ferramenta para analisar a estrutura conceitual de alunos de um curso de graduação em química de uma universidade pública do estado de São Paulo, sobre o tema equilíbrio químico em dois momentos distintos, o primeiro ao ingressarem na universidade e o segundo após um ano de curso. Os mapas foram analisados utilizando uma adaptação do método de Análise Estrutural de Mapas Conceituais (AEMC adaptada). Teve-se como meta do trabalho: a) Avaliar, através de mapas conceituais elaborados pelos alunos a estrutura conceitual dos mesmos referente ao conceito equilíbrio químico; b) Descrever e analisar a evolução das relações entre os principais conceitos envolvidos no tema feitas por alunos no seu ingresso no curso de graduação e após um ano de curso, quando são submetidos pela primeira vez a um estudo sistemático do tema. Pretendeu-se assim, verificar quais foram às mudanças mais significativas ocorridas em decorrência das disciplinas ministradas neste período e c) Estabelecer uma relação entre estas mudança com o processo de ensino ao qual o aluno foi submetido, ou seja, como a estrutura conceitual dos estudantes a respeito do tema mudou em função do processo de aprendizado a que foram submetidos. Concluiu-se que a ferramenta desenvolvida durante a pesquisa foi muito útil na análise proposta; onde os alunos ingressantes definem o Equilíbrio químico como o estado onde as velocidades das reações se igualam sem relacionar a conceitos da termodinâmica, estes também, demonstraram muitos conhecimentos oriundos de como o conceito é apresentado no ensino médio. Verificou-se também que os estudantes ao serem submetidos à disciplinas relacionadas ao tópico equilíbrio químico modificaram seu entendimento sobre o tema. / In this work it was used the Concept Map as a tool for analyzing the conceptual structure of students in an undergraduate degree in Chemistry from a public university in the state of São Paulo, on the subject of Chemical Equilibrium at two different times, the first at the moment when entered in the university and second after a year. The maps were analyzed using an adaptation of the method of Structural Analysis of Concept Maps (AEMC adaptada). The objectives of work were: a) Explore and modify a method of analysis of Concept Maps in order to obtain a Concept Map that shows the main conceptual connection of a group of students in order to graphically represent their conceptual structure; b) Evaluate, through Concept Maps prepared by students their conceptual framework for the Chemical Equilibrium concept; c) Describe and analyze the evolution of relations between the main concepts involved on the subject made by students in their admission to the undergraduate course and after one year course, when they are first subjected to a systematic study of the subject. Thus the intention was to verify which were most significant changes occurred as a result of the matter taught in this period and d) Establish a connection between these changes with the teaching process to which the student was submitted, ie, how the conceptual framework of students regarding the subject changed as a function of the learning process they have submitted. It was concluded that the tool developed during the research was very useful in analyzing the proposal, which the new students define the Chemical Equilibrium as state where the velocities of reactions are equal without relating the concepts of thermodynamics, they also showed a lot of knowledge from as the concept is presented in high school. It was also found that students be subjected to the disciplines related to the topic Chemical Equilibrium changed their understanding of the subject, therefore, provide a greater number of connections between the different concepts involved on the matter.

Orientador: Reginaldo Guirardello / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-19T12:38:06Z (GMT). No. of bitstreams: 1 Cunico_LarissaPeixoto_M.pdf: 3845396 bytes, checksum: d8e7fc1418bed93fc9777451bc5ab2e5 (MD5) Previous issue date: 2012 / Resumo: A demanda mundial por energia cresce a cada ano. Essa demanda pode atingir níveis que os recursos atuais de combustíveis fósseis não podem sustentar. Neste contexto, os biocombustíveis surgem como uma fonte crescente de energia primária, aumentando a oportunidade de pesquisa e desenvolvimento de tecnologia a níveis animadores. Uma importante questão relacionada com o desenvolvimento destes biocombustíveis é o equilíbrio de fases entre seus componentes. Este trabalho investiga o equilíbrio líquido-vapor (ELV) de sistemas binários e o equilíbrio líquido-líquido (ELL) de sistemas ternários e quaternários, além do equilíbrio líquido-líquido-vapor (ELLV) de sistemas ternários, compostos por óleo vegetal, álcool, glicerina e éster, envolvidos na produção do biodiesel. O modelo desenvolvido também é capaz de predizer o equilíbrio químico e de fases para vários tipos de óleos vegetais na produção de biodiesel. Para tanto houve a necessidade da estimativa das propriedades físicas destes vários componentes e uma busca por métodos de predição através de contribuição de grupos foi realizada para as propriedades físicas não encontradas na literatura. A minimização da energia de Gibbs foi utilizada para calcular cada fase presente em uma determinada condição de pressão e temperatura, assim como a composição de cada fase prevista. A equação de estado de Soave-Redlich-Kwong (SRK-EOS) com a regra de mistura de van der Waals de dois parâmetros ajustáveis (VdW-2) foi empregada. O software GAMS® 23.1.3 (General Algebraic System Model) combinado com o solver CPLEX foi utilizado para resolver numericamente o modelo matemático. Através de discretização das frações molares, a modelagem do problema pode ser desenvolvida na forma de uma programação linear. Os dados experimentais foram representados de forma satisfatória por estes modelos e utilizando SRK-EOS obteve-se desvio absoluto médio e tempo computacional para sistemas binários, ternários e quaternários respectivamente de 1,03%, 1,39% e 1,30% e 0,17s, 27s e 6s, para os sistemas utilizando metanol. Já para os sistemas que utilizam etanol, o desvio absoluto médio e tempo computacional para sistemas binários e ternários são respectivamente de 0,64% e 2,10% e 0,14s e 26s / Abstract: The worldwide energy demand increases every year. This demand will reach levels that cannot be supplied by current conventional fossil fuel resources. In this context, biofuels arise as a growing primary source of energy, raising research opportunities and encouraging technology development. An important technical issue related to biofuels development is the phase equilibrium among their components. This work investigates the vapor-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE) of binary, ternary and quaternary systems composed by vegetable oil, alcohol, glycerol and ester, involved in biodiesel production. The Gibbs energy minimization was used to calculate the amount of each phase present in a particular condition of pressure and temperature, as well as the composition of each phase predicted. The Soave-Redlich-Kwong (SRK) equation of state with van der Waals mixing rule, with two adjustable parameters (vdW-2) was employed. The GAMS® 23.2.1 (General Algebraic Model System) in combination with the solver CPLEX was used to tackle the large and complex mathematical models. The minimization of the Gibbs energy was done using a discretized procedure, so that the problem could be solved as a linear programming approach. The proposed model is also used to predict the chemical and phase equilibrium for eight types of vegetable oils in biodiesel production. For this purpose it was necessary to estimate the physical properties of these various components and a search for methods of prediction by group contribution was made to physical properties not found in the literature. The experimental data were correlated quite well by the Soave-Redlich-Kwong (SRK) equation of state, with absolute medium deviations and computational time for binary, ternary and quaternary systems using methanol as a compound of: 0.83% and 0.17s, 1.39% and 27s and 1.30% and 6s, respectively. Using ethanol as a compound, the absolute medium deviations and computational time for binary and ternary systems of: 0,64%, 2,10% , 0,14s and 26s / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

The Namibian Physical Science Higher Level Syllabus requires students to study the topic on chemical equilibrium. This section has proven to be one of the most difficult for Namibian learners as reflected by their poor responses to questions in the Grade 12 NSSC ‘H’ examinations. Triggered by these discoveries, I decided to conduct a research on how teachers mediate learning of the topic on chemical equilibrium in a Namibian context. Conducted at a private school in Windhoek, the study involved two experienced Grade 11 Physical Science teachers renowned for good results. I adopted a qualitative case study underpinned by an interpretive paradigm. Sense making of concepts on chemical equilibrium was my unit of analysis. To generate data, I used document analysis, semi-structured interviews, lesson observations, which were videotaped as well as stimulated recall interviews. Vygotsky’s mediation of learning and social constructivism blended with Shulman’s pedagogical content knowledge (PCK) were the theoretical frameworks adopted in the study. During the analysis process, there was grouping of data into categories. These included teacher-learner interactions as emphasized by Vygotsky’s mediation of learning and learners’ challenges according to PCK. I used an inductive approach to identify emerging themes from my data. The themes were colour coded and the developed into analytical statements. Data triangulation, member checking, and peer review ensured data validity and trustworthiness. Stimulated recall interviews conducted while watching the videos with the two teachers, complemented these approaches. My findings were that teachers extensively used various meditational tools such as prior knowledge, language, analogies and an equilibrium game to mediate learning. The teachers experienced numerous challenges during mediation of learning, including language difficulties and learners’ failure to comprehend complex chemical equilibrium concepts. Notwithstanding, the teachers in this study managed to some extent to overcome the challenges by exhibiting facets of advanced PCK.

The fuel industry in many parts of the world is blending alcohols with motor fuel either to extend the fuel or to improve its octane rating or both. Unfortunately alcohols are hygroscopic and as a result, water becomes a component of the fuel. This can lead to phase separation and the formation of a water-rich layer which could have serious corrosion consequences. In an attempt to understand the phase-splitting in alcohol-petrol-water blends, phase equilibria in ternary systems (alcohol-hydrocarbon-water) have been determined by experiment. The phase equilibria in these ternary systems are also discussed in terms of modern theories of liquid mixtures and the UNIQUAC theory is applied to the "ethanol + benzene + water" ternary system. The alcohols are all the C₁, C₂, C₃ and C₄ alcohols, and the hydrocarbons include those typically found in petrol, e.g. cyclohexane, benzene and substituted benzenes.

Association constants for the formation of lead (II) chloride complexes were studies in aqueous solutions also containing copper (II) and cadmium (II) ions. The ionic strength was adjusted with sodium perchlorate to resemble that of sea water. The temperature was set at fixed values between 5° and 35° C to determine the effect on the equilibria in these systems. The total metal concentration was less than 10-8 M. Differential pulse anodic striping voltammetry was used with a conventional three electrode system and a thin-film working electrode of Pt/Hg. Complex formation was followed as a function of the ligand concentration by observing the shift in the stripping peak potential Ep. The measured Ep and temperature data were used to obtain thermodynamic information on the formation of the complex ions. The activity coefficients were assumed constant at a given temperature. The values for the base ten logarithm of the overall formation constants at 25.0° are 1.11, 1.48 and 1.83 for PbCl+, PbCl°2 and PbCl-3 complexes respectively. These results are in good agreement with literature values. The Δ H of formation values for those complexes in solution were found to be positive. Tentative results were obtained for copper (II) which was only weakly complexed with Cl - under the present conditions.

The possibility of drug incompatibilities is a matter of serious concern when administering two or more therapeutic agents. This is especially true in the case of parenteral administration when one must be aware not only of therapeutic interactions but also chemical and physical reactions that might occur. In order to avoid incompatibilities, drug manufacturers have suggested that parenteral solutions be used immediately after reconstitution and that admixtures of parenteral products not be administered wherever possible (1,2). Physicians have also stressed the importance in avoiding multiple drug therapy (3,4). In spite of these suggestions, the practice of multiple drug therapy is prevalent. Because of this, there has been an increase in awareness of the number of drug admixtures administered in the hospital. At the University of Michigan Hospital over two thirds of the intravenous fluids administered contained two or more therapeutic agents (5). Holysko and Ravin (6) report that 48% of the intravenous fluids contain one additive, 30% contain two additives, and 22% contain three or more additives. The survey taken by Patterson and Nordstrom (7) showed that 24% of the solutions administered intravenously contained two drugs 1 and that 16% of the intravenous solutions contained three or more additives. The increased awareness of the problems in admixtures of parenterals has contributed to the increased use of centralized intravenous additive programs at various hospitals. The hospital pharmacist is now becoming more responsible for the preparation of intravenous admixtures (8). The need for additional information concerning potential interactions when admixtures of therapeutic agents for intravenous use are administered is evident. The lack of information includes, in addition to incompatibilities, areas of interest such as stability, sterility, and clinical effectiveness (8,9). This report will discuss a method to detect potential chemical interactions. The drugs under investigation are sodium ethacrynate (Edecrina) in combination with selected cardiovascular and psychotherapeutic agents when in admixture in normal saline solution. Possible therapeutic interactions and physical incompatibilities of these combinations will also be discussed.

Amorphous calcium carbonate (ACC) precipitation is modeled using particle nucleation, growth, and aggregation. The particles are tracked in terms of their radial size and particle density using direct quadrature method of moments (DQMOM). Four separate nucleation models are implemented and are compared to experimental data. In discord with a recent study, it is shown that classical nucleation, coupled with equilibrium chemistry, is in good agreement with experimental data. Novel nucleation mechanisms are presented which fit the experimental data with slightly greater accuracy. Using equilibrium chemistry it is shown that the equilibrium value of ACC is pKeq = 7.74 at 24C, which is a factor of two smaller than the originally published equilibrium constant. Additionally, legacy equilibrium chemistry expressions are shown to accurately capture the fraction of calcium carbonate ions formed into ACC nano-clusters. The density, solubility, and water content of ACC are discussed in a brief review, finding that a wide variety of properties are reported in the literature. Based on literature findings, it is proposed that the broad variety of reported properties may be due to ACC having several unique thermodynamic states. Compelling evidence is presented exposing errors made by experimentalists studying the calcium carbonate system. The errors correct for mistakes of experimental kinetic data of the chemical-potential cascade of calcium carbonate due to the formation of meta-stable phases. Correlations are presented which correct for these mistakes. A time-scale analysis shows the overlapping of kinetic scales and mixing scales within the calcium carbonate system. The kinetic scales are based on classical nucleation theory, coupled with diffusion limited growth. The mixing scales were computed using one-dimensional turbulence (ODT).

This thesis is concerned with the numerical simulation of mixtures of chemically reacting fluids at high pressures. Mixture rules are established, accommodating components that do not follow the thermally perfect Equation of State (EoS), and including formulas for the fugacities. Particular attention has been given to the species EoS originally developed by Hirschfelder, Buehler, McGee and Sutton. The Law of Mass Action that governs chemical equilibrium of mixtures of fluids is presented. The common assumption of neglecting fugacities contributions when calculating the equilibrium composition is assessed by comparing complete thermochemical predictions with those obtained by reduced models. For air mixtures at high pressures and moderate temperatures, species thermally imperfect EoS effects are significant. However, the contribution of fugacities to the Law of Mass Action is found to be small, at least for mixtures of super-critical dissociating gases. Similar conclusions apply to combustion mixtures (involving hydrogen and oxygen).