REVERSE MICELLES IN SUPERCRITICAL FLUIDS .3. AMINO-ACID SOLUBILIZATION IN ETHANE AND PROPANE

The solubilization of the amino acids tryptophan and proline in bis(2-ethylhexyl) sodium sulfosuccinate (AOT) reverse micelles and microemulsions is described for the solvents supercritical fluid (SCF) ethane and liquid propane. Two different types of condensed phases, a solid crystalline amino acid phase and an aqueous phase, are investigated at 37°C from 73 to 325 bar. The concentration of surfactant in both the aqueous and dense fluid phases is reported for the first time, giving insight into the natural curvature of the micelles. In regions where pressure has little effect on the water-to-surfactant ratio, W0, solubilization in the micelles is relatively constant. At lower pressures, there is a pronounced effect of pressure on the partitioning of surfactant and water, and thus on solubilization. The partitioning of an amino acid between the water pool inside the micelles and the micellar interfacial region is described by a surface monolayer model. This partitioning is influenced by pressure in regions where W0 and thus the curvature and rigidity of the interface are variable. The model explains the experimental result that the micelles are highly selective for proline versus tryptophan. Based on the measured concentrations of AOT and tryptophan in both the fluid and aqueous phases, a process is presented for separating hydrophilic substances from water. © 1990 American Chemical Society.