Properties of chemicals and their mutual phase equilibria are critical variables in process design. Reliable estimates of relevant equilibrium properties, from thermodynamic models, can form the basis of good decision making in the development phase of a process design, especially when access to relevant experimental data is limited. This thesis addresses the issue of generating and using simple thermodynamic models within a rigorous statistical mechanical framework, the so-called fluctuation solution theory, from which relations connecting properties and phase equilibria can be obtained. The framework relates thermodynamic variables to molecular pair correlation functions of liquid mixtures. In this thesis, application of the framework is illustrated using two approaches: 1. Solubilities of solid solutes in mixed solvent systems are determined from fluctuation solution theory application to expression arising fromthermodynamics. This results in neat and unusually simple expressions involving molecular correlation functions. These are determined from a combination of experimental data and molecular-based models, and their transferability is analyzed extensively. 2. Solubilities of gases in ionic liquids are described using a simple, yet physically sound, model formolecular correlation functions. Themethod addresses solubilities of supercritical gases in ionic liquids, as well as volumetric properties of pure fluids. In both cases, the models require a minimum of input data, and results are not highly sensitive towards parameter values.
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Technical University of Denmark, Department of Chemical Engineering, 2011