Thermodynamic behavior of supercritical fluid mixtures

Conference · Sat Mar 01 04:00:00 EST 1986 · Int. J. Thermophys.; (United States)

OSTI ID:7017214

Sengers, J M.H.; Chang, R F; Everhart, C M; Morrison, G; Nielson, G; Hauley, H J.M.; Cezairliyan, A

The recent surge of interest in supercritical extraction has brought the unusual properties of supercritical mixtures into the focus of attention. We discuss some of the properties of binary mixtures in a range around the gas-liquid critical line from the point of view of supercritical solubility. The general thermodynamic relationships that govern the enhancement of supercritical solubility are readily derived by a mathematical method introduced by Ehrenfest. The enhancement is governed by a strong divergence centered at a critical end point. We give the classical and nonclassical power-law behavior of the solubility along the experimental paths of constant temperture or pressure. The factor multiplying the strong divergence contains the partial molar volume or enthalpy of the solute in the supercritical phase. These partials are quite anomalous, especially if the mole fraction of the solute is small. They diverge at the solvent's critical point. We cite experimental evidence of these divergences, especially the results of recent experiments in dilute near-critical salt solutions. The anomalies found in these salt solutions are common to all dilute near-critical mixtures with a nonvolatile second component. We show that on experimentally convenient paths the solubility in a binary liquid mixture near its consolute points is not strongly enhanced. Finally, we sketch a nonclassical model based on the decorated lattice gas that can be used to describe supercritical solubility enhancement at low solubility, with the pure solvent used as a reference.

• Research Organization: National Bureau of Standards, Gaitherburg, MD
• OSTI ID: 7017214
• Report Number(s): CONF-850617-
• Conference Information: Journal Name: Int. J. Thermophys.; (United States) Journal Volume: 7:2
• Country of Publication: United States
• Language: English

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ALKENES
ALKYLATED AROMATICS
AROMATICS
BINARY MIXTURES
CONDENSED AROMATICS
CRITICAL PRESSURE
CRITICAL TEMPERATURE
CRYSTAL MODELS
DISPERSIONS
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ORGANIC COMPOUNDS
PARTIAL MOLAL VOLUME
PHYSICAL PROPERTIES
SEPARATION PROCESSES
SOLUBILITY
SOLVENT EXTRACTION
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SUPERCRITICAL GAS EXTRACTION
SUPERCRITICAL STATE
THERMODYNAMIC PROPERTIES
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TOLUENE
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