Development of a Program for Thermodynamic Correlation of Supercritical Fluid-solid Phase Equilibrium Data

The design and development of processes involving supercritical fluids depend on how easy the phase equilibrium can be accurately modelled and predicted. In the work described herein, the supercritical fluid-solid equilibrium has been considered. Modelling the fluid-solid equilibrium is associated with a number of drawbacks, even when it is possible to obtain the experimental solubility data for the solute in the supercritical fluid. In most cases it is necessary to introduce additional adjustment parameters into the model. In this model, three cubic equations of state have been used. The developed program, realized in Visual Basic® language, is based on the fitting of two parameters – the binary interaction parameter (K12) and the solid sublimation pressure (P2). This program can be used for any fluid-solid equilibrium even when both parameters are known or supposed. The model has been applied to palmitic acid-carbon dioxide system because the sublimation pressures of this fatty acid are known and the results obtained have been compared with them. The saturation pressure values obtained show that the thermodynamic model applied to fluid-solid equilibrium calculations is useful to predict the behaviour of the palmitic acid-supercritical carbon dioxide system. INTRODUCTION The solubility of a solid (component 2) in supercritical carbon dioxide (component 1) from its thermodynamic definition is [1]: