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Molecular Thermodynamics of Supercritical Fluid Mixtures

Published online by Cambridge University Press:  21 February 2011

Charles A. Eckert
Charles A. Eckert*
Affiliation:
Department of Chemical EngineeringUniversity of IllinoisUrbana, Illinois 61801, USA
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Abstract

Supercritical fluid extraction uses a dense gas as a solvent at a temperature only slightly above its critical temperature and a pressure of a few hundred bars. The process offers the advantages of both conventional distillation and solvent extraction, and permits the facile achievement of difficult separations by highly selective absorption and desorption of various solutes. A valid thermodynamic model is essential for the rational design of such processes. We have made extensive solubility measurements at pressures to about half a kilobar, and we interpret the results in terms of perturbed hard-sphere equations of state. In this, we characterize solution nonidealities in terms of enhancement factors, which are often in the range of 103−108. Even better information about the specific solvent-solute interactions are available from measurements of partial molal volumes in supercritical solutions. These are very difficult measurements, as the effects are most pronounced precisely where the solvent compressibility is greatest, and accurate data are possible only because of the advent of the high-pressure vibrating tube densitometer, which converts density determinations to highly accurate frequency measurements for determinations to a precision of ±0.0001 g/cc. The solute partial molal volumes are many liters negative in the critical region, and these data are interpreted in terms of various equations of state.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 22: Symposium NY – High Pressure in Science and Technology , 1983 , 81
Copyright
Copyright © Materials Research Society 1984

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References

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