| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 14.68 MB | Adobe PDF |
Authors
Advisor(s)
Abstract(s)
A representação experimental e teórica de propriedades termofísicas, e do equilíbrio
de fases de sistemas contendo eletrólitos é ainda muito limitada, apesar da sua
elevada importância. Isso ocorre devido às dificuldades na representação das
interações eletrostáticas, além daquelas que derivam da utilização de diferentes
estados padrão, escalas de concentração e coeficientes de atividade. Assim, no
presente trabalho foi realizado o estudo do equilíbrio sólido-líquido em sistemas de
solventes mistos contendo eletrólitos, medindo solubilidades e desenvolvendo a
modelação termodinâmica.
Os sais estudados foram o brometo de sódio e o cloreto de lítio, nos sistemas
água/metanol, água/etanol e metanol/etanol às temperaturas de 298.15 e 323.15 K,
e em toda a gama de composições. Para a determinação da solubilidade, o método
dos frascos agitados foi usado em combinação com dois métodos analíticos
distintos, a gravimetria e medição de índice de refração. Ambos mostraram serem
fiáveis, estando em geral concordantes com os encontrados na literatura. No
entanto, há indicadores que as solubilidades obtidas por gravimetria são mais
consistentes.
Os novos dados obtidos de solubilidade, junto a informações publicadas na
literatura, sobre equilíbrio sólido-líquido, coeficientes de atividade médios iónicos e
coeficientes osmóticos constituíram uma base de dados relevante para o
desenvolvimento do modelo termodinâmico. O modelo Extended UNIQUAC foi o
selecionado, permitindo a representação da solubilidade de fases sólidas hidratadas
com elevada qualidade, obtendo erros relativos entre 1.1 e 6.7%. Foram
identificadas maiores dificuldades no cálculo da solubilidade quando as fases sólidas
são anidras e também na descrição dos coeficientes de atividade médios iónicos ou
osmóticos. Portanto, sugere-se reestimar os parâmetros do modelo quer usando
propriedades como entalpia e capacidade calorífica, bem como incluindo na base de
dados outros sais contendo os iões Li+ e Br-.
Despite of its high importance, the experimental and theoretical representation of termophysical properties, and phase equilibria of mixtures containing electrolytes is still very limited. Important difficulties that contribute to this are the representation of the electrostatic interactions, besides those derived from the use of different standard states, concentration scales and activity coefficients. Thus, in the present work, the study of solid-liquid-equilibrium in systems of mixture solvents containing electrolytes is accomplished, measuring the solubility and developing thermodynamic modeling. The studied salts were the sodium bromide and lithium chloride, in systems of water/methanol, water/ethanol and methanol/ethanol at 298.15 K and 323.15 K, in the entire composition range. To determine the solubility, the shake-flask method was combined with two analytical techniques: gravimetry and refractive index measurements. Both methods proved to be very reliable, and generally give solubility values comparable to those found in the open literature. However, there are indications that the results from gravimetric method are more consistent. The new solubility data were combined with data from literature about solid-liquid equilibrium, mean ionic activity coefficients and osmotic coefficients, creating a relevant database to develop the thermodynamic model. The Extended UNIQUAC model was selected, allowing the representation of solubility with high quality when hydrate solid phases are present, showing relative deviations between 1.1 and 6.7%. Larger difficulties were identified in the calculation of solubility when the solid phase is anhydrous, and also in the description of the mean ionic activity or osmotic coefficients. Therefore, parameter re-estimation is suggested including properties like enthalpy and heat capacity, and also to add in the database other salts containing the ions Li+ and Br-.
Despite of its high importance, the experimental and theoretical representation of termophysical properties, and phase equilibria of mixtures containing electrolytes is still very limited. Important difficulties that contribute to this are the representation of the electrostatic interactions, besides those derived from the use of different standard states, concentration scales and activity coefficients. Thus, in the present work, the study of solid-liquid-equilibrium in systems of mixture solvents containing electrolytes is accomplished, measuring the solubility and developing thermodynamic modeling. The studied salts were the sodium bromide and lithium chloride, in systems of water/methanol, water/ethanol and methanol/ethanol at 298.15 K and 323.15 K, in the entire composition range. To determine the solubility, the shake-flask method was combined with two analytical techniques: gravimetry and refractive index measurements. Both methods proved to be very reliable, and generally give solubility values comparable to those found in the open literature. However, there are indications that the results from gravimetric method are more consistent. The new solubility data were combined with data from literature about solid-liquid equilibrium, mean ionic activity coefficients and osmotic coefficients, creating a relevant database to develop the thermodynamic model. The Extended UNIQUAC model was selected, allowing the representation of solubility with high quality when hydrate solid phases are present, showing relative deviations between 1.1 and 6.7%. Larger difficulties were identified in the calculation of solubility when the solid phase is anhydrous, and also in the description of the mean ionic activity or osmotic coefficients. Therefore, parameter re-estimation is suggested including properties like enthalpy and heat capacity, and also to add in the database other salts containing the ions Li+ and Br-.