(321u) On Solubility Extrema in Solid-Fluid Equilibrium and the Effect on Thermodynamic Modeling

The solubility of solids in compressed gases or supercritical fluids is the basis for a variety of industrial processes. Much research has been presented to model these systems using equations of state and various mixing rules. More recently from the Brennecke and Stadtherr groups, reliable computation has been introduced which includes the necessary step of thermodynamic stability analysis. Extrema in the solubility of solids in gases with pressure has been known for quite some time. While the solubility minimum was well-established decades ago, a sufficient quantity of experimental solubility maximum data has been absent from the literature until recently. These data confirm that maxima occur at quite elevated pressures. However, in the many reports in the literature, modeling results are presented with solubility maxima at relatively low pressures. This presentation will illustrate the thermodynamics of extrema and illustrate how these parameters may guide the proper regression of various models to qualitatively and quantitatively model Solid-Fluid equilibria data. The Peng-Robinson equation of state will be utilized with various mixing rules and regression objective functions to avoid improper extrema predictions. Understanding the physical interpretation of solubility extrema, the role of the objective function, and capabilities and limitation of equation of state models and mixing rules with be combined for the first time here.