Solubility of solids in Supercritical Fluids

For the design of extraction processes of mostly high boiling liquid or solid compounds with the help of supercritical fluids, for example, the extraction of caffeine from coffee beans using carbon dioxide the phase equilibrium behavior as a function, of the pressure without or in the presence of co-solvents is required. As in the case of all other phase equilibria, the isofugacity condition has to be fulfilled  

The fugacity of the pure solid compound 2 can be described by the sublimation pressure, the fugacity coefficient in the saturation state and the Poyntin.g factor, so that the following phase equilibrium relation is obtained for the calculation of the solubility of the solid 2 in the supercritical fluid  

Since the sublimation pressure of the solid is low, the fugacity coefficient in the saturation state shows values which are nearly unity, so that finally the following 

For the calculation of the solubility y2 reliable sublimation pressures are required. For the calculation of the Poynting factor, additionally the molar volume of the solid compound is required. Then the equation of state only has to describe the fugacity coefficient in the gas phase 02 as a function of pressure. 

For the pure compound 2, this means at the vapor (sublimation) pressure 2 the mole fraction y2 is equal to unity. With the addition of CO2 the vapor phase concentration of component 2 decreases. Since at low pressures the fugacity coefficient and the Poynting factor are approximately unity, the mole fraction y2 at moderate pressure becomes approximately  

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General overview of several studies of transport and intermolecular interactions in compressed supercritical fluids is presented. The unique aspects of the instrumentation used in these studies are emphasized. First, the results of NMR studies of self-diffusion in supercritical ethylene and toluene are discussed. These experiments used the fixed field gradient NMR spin-echo technique. Second, the novel NMR technique for the determination of solubility of solids in supercritical fluids is described. 

A serious test of mixture equations of state is shown to be their application for prediction of solubility of solutes in supercritical fluids (JJ. ). In the present report, we apply the Redl ich-Kwong and the Peng-Robinson equations of state for supercritical fluid extraction of solids and study the effect of choosing different mixing rules on prediction of solubility of solids in supercritical fluids -Figures 1-5. 

Solubility of solids in supercritical fluids using equations of state - excess Gibbs free energy models. 

Kwiatkowski, J., Lisicki, Z., and Majewski, W., An Experimental Method for Measuring Solubilities of Solids in Supercritical Fluids, Ber. Bunsenges. Phys. Chem. 88 865-869 (1984)... 

The solubility of solids in supercritical fluids is a very sensitive function of temperature and pressure. Unlike liquids, supercritical fluids are highly compressible and minor temperature or pressure changes lead to large changes in density and, therefore, solvent power QJ. The expansion of supercritical solutions, therefore, results in a substantial solubility decrease. The solubility of Naphthalene in carbon dioxide at 45 C, for example, decreases by about two orders of magnitude upon reducing the pressure from 127 to 62 bars (21. If this... 

In the last one and a half to two decades, the KB theory of solutions was successfully used to predict the solubility in numerous systems. Indeed, it is quite impressive that one method was successful for such different systems as those examined in this chapter the solubility of gases and drugs and hydrophobic organic pollutants in binary and multicomponent mixed solvents and the solubility of protein. In addition, this method was successfully applied to the solubility of solids in supercritical fluids, to the solubility of mixed gases in individual solvents, to the explanation of salting-out phenomena (Ruckenstein and Shulgin 2009). In some cases (multicomponent mixtures) the KB theory of solutions constitutes the most powerful theoretical method for investigating the thermodynamic properties. 

Kumar, S. K. and K. P. Johnston. 1988. Modelling the solubility of solids in supercritical fluids with density as the independent variable. Journal of Supercritical Fluids. 1, 15. 

Kwiatkowski, J., Z. Lisicki, and W. Majewski. 1984. An experimental-method for measuring solubilities of solids in supercritical fluids. Berichte der Bunsen-Gesellschc -Physical Chemistry Chemical Physics. 88, 865. 

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