Equation of State-Mixing Rule Combinations Based Assessment of Solid-Fluid Equilibria Modelling at High Pressure for Various Systems Hassina Bezaze, Abdessalam Hassen Meniai* and Wahida Louaer Laboratoire de l’Ingénierie des Procédés d’Environnement, Universite Mentouri Route Ain El Bey Constantine, meniai@yahoo.fr The calculations of solid-fluid equilibrium at high pressure are important for the modelling and the design of processes that use supercritical carbon dioxide to extract solid solutes. However, the main difficulty is the choice of the most appropriate combination of an equation of state (EOS) and a mixing rule (MR). Consequently, this work is concerned with the modelling of the solubility of four solid compounds, namely Phenanthrene (PH), Anthracene (AN), Pentachlorophenol (PCP) and Hexachlorobenzene (HCB), in supercritical carbon dioxide. For each compound the three EOS, namely Peng Robinson (PR), Soave (S) and Redlich Kwong and Soave (RKS) were considered in combinations with van der Waals and Wong-Sandler mixing rules. For PH and AN, the operating conditions were a temperature of 313K and a pressure range of 87.5-200 bars. The best results for AN and PH were given by the Soave-VDW and the PR-VDW models, respectively. For PCP and HCB the solubility modeling was performed at 308 K and at pressure ranging from 72 to 200 bars, and the PR-WS and Soave-VW combinations seemed to be the most adequate, respectively. 1. Introduction Supercritical fluids have an interesting combination of liquid like density and solvency and gas like viscosity, diffusivity compressibility, etc. This has stimulated the development of the supercritical fluid technology which mainly takes advantages of these important and useful properties shown by gases, once compressed up to their critical points and then used as solvents. This is very useful for a great number of industrial sensitive applications like in food, pharmaceutical, waste treatment, polymers and monomers processing and biochemical industries, using instead of traditional organic solvents like n-hexane, environmentally safe solvents like supercritical CO 2 which is non flammable, non toxic, chemically inert, odourless, etc. The design and development of SF processes depend on the ability to model and predict accurately the solid-supercritical fluid equilibria (SFE). However, many of the existing simple predictive models are not sufficiently accurate and are subject to serious errors when used for calculations near critical points. An additional complication is that many of the solute molecules of interest are large and polar, while the solvent molecules such