Spectroscopic and thermodynamic studies of supercritical fluid solutions containing a cosolvent
Tomasko, David Lane
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Permalink
https://hdl.handle.net/2142/20315
Description
Title
Spectroscopic and thermodynamic studies of supercritical fluid solutions containing a cosolvent
Author(s)
Tomasko, David Lane
Issue Date
1992
Doctoral Committee Chair(s)
Higdon, Jonathan J.L.
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Engineering, Chemical
Language
eng
Abstract
The addition of a cosolvent to a supercritical fluid (SCF) can alter the properties of the solvent to enhance both solubilities and selectivities for particular solutes through a variety of specific and non-specific interactions. Although many cosolvent effects have traditionally been explained in terms of hydrogen bonding between cosolvents and solutes, we present spectroscopic data that suggest that these interactions may be more subtle. Specifically, fluorescence and absorption spectroscopy have been used to study structure-specific probe molecules (2-naphthol, 5-cyano-2-naphthol, and 7-azaindole) in the supercritical fluids carbon dioxide, ethane, ethylene, and fluoroform, with water, methanol, and ethanol as cosolvents. In liquid solutions, these probes exhibit well characterized spectral responses to an organized, hydrogen bonded solvent environment. The results from SCF solutions indicate significant cosolvent/solute interaction even at 0.3 mole% cosolvent yet there is no evidence for stoichiometric hydrogen bonded complexes.
The application of SCF's to the fractionation of a nonionic surfactant has been demonstrated. The surfactant consisted of a distribution of polyoxyethylene dodecyl ethers with an average ethoxylation of 3.2. Supercritical carbon dioxide, propane, ammonia, and carbon dioxide with methanol cosolvent were used to remove the non-ethoxylated alcohol and narrow the chain length distribution of the mixture.
One of the limiting factors in modeling phase behavior in solid-SCF systems is the dearth of physical property data for the solid solutes of interest. We demonstrate a simple technique for estimating one such property, the heat of fusion, from a measurement of solid-liquid-equilibria. The technique is applied to the systems phenanthrene-thianthrene, salicylic acid-phenanthrene, and 3-hydroxybenzoic acid-phenanthrene, with good results.
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