Currently, supercritical-fluid technology in the pharmaceutical and microelectronicsindustries is increasingly applied to solve difficult processing problems. The solubility of asolute in a supercritical fluid is the most important thermophysical property that needs to bedetermined and modeled as a first step to develop any supercritical fluids application. Thisresearch was undertaken to develop a reliable mathematical model to compute the solubility ofsolids in supercritical fluids. As a result, a new combination rule is proposed along with a novelapproach to obtain general correlations for its parameters. The new combination rule is amodification of the classical van der Waals mixing rules where the binary cohesive parametera12 is correlated in terms of the reduced pressure. A database containing experimentalsolubility data for 126 isotherms was used in this study. Half of the isotherms (63) werejudiciously selected to develop the correlations in the new combination rule. A correlation isproposed in which the crossed cohesive parameter a12 of the equation of state is expressed interms of the reduced properties and the ratio a2/a1. The rest of the isotherms (63) were thenused to validate the results. Detailed error calculations were carried out for differentthermodynamic models that included the Peng-Robinson and Patel-Teja equations of stateand van der Waals, cubic, and Rao mixing rules. The conclusion, after comparing thecalculated errors for various models, was that the best results were obtained for the Patel-TejaEoS and the new mixing rule proposed here. This work is a significant contribution in the fieldin two ways. First, it provides a specific correlation that gives excellent values of solubility.Secondly, it proposes a novel approach that can be extended to other mixing rules and mayresult in a fully predictive method.
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