Analysis and Applications of the Electrolyte Cubic Plus Association Equation of State

Due to the complexity and wide industrial application of the electrolyte solutions, both experimental and theoretical studies have attracted great interest. The lack of reliable thermodynamic data of aqueous electrolyte solutions with a wide range of temperature and pressure can be sometimes resolved by using thermodynamic models.

The electrolyte Cubic Plus Association (CPA) Equation of State (EOS), e CPA, is an extension of the CPA EOS to electrolytes through the addition of the Debye Hückel theory for the ion ion electrostatic interactions, and the Born term for ion solvation. The main aim of this thesis is to analyze the e CPA EOS and apply e CPA to a range of electrolyte systems.

In the first part of this thesis, thermodynamic modeling of the aqueous solutions of quaternary ammonium salts (QAS) and metal halide salts are presented. For QAS systems (single salt systems), the ion size and adjustable model parameters are obtained by fitting the experimental data of mean ionic activity coefficients and osmotic coefficients.

Several other thermodynamic properties of aqueous solutions, such as relative static permittivity, liquid density and saturation pressure, are subsequently predicted by e CPA. The results show that the model can satisfactorily correlate the mean ionic activity coefficients and osmotic coefficients. The reliability of experimental data, parameter estimation approaches and the ion size effects are extensively discussed.

For metal halide salt systems (multi salt systems), the adjustable model parameters of single salt systems are subsequently used for modeling of multi salt systems directly. The results show that e CPA can predict well the mean ionic activity coefficients of aqueous multi salt solutions using single salt interaction parameters.

The second part of this thesis presents thermodynamic modeling studies on the gas solubilities in aqueous electrolyte solutions. The adjustable parameters are obtained by fitting the experimental data of gas solubilities in single salt solutions. The results show that the model can reasonably correlate gas solubilities over a wide range of conditions for most systems.

The model is then used to predict the gas solubility in multi salt (metal halide salt) solutions, and a reasonable performance is also achieved. The salting in/salting out effects and the various factors affecting the results are finally studied. At the last part of this thesis, a modeling study is carried out for individual ion activities in aqueous electrolyte solutions with e CPA and other approaches including the ‘extended version of Debye−Hückel + Born’ model, and the ‘MSA+Born’ model.