Solubilization by Various Surfactant Solutions and Applications to Separation Technology

Abstract

Solubilization phenomena of various organic solutes by surfactant solution was reviewed. The interpretation of intramicellar solubilization data obtained from semi-equilibrium dialysis (SED), head-space gas chromatography (HSGC), and solute vapor pressure methods (SVP) are presented for determining equilibrium constants for the solubilization of organic species by aqueous surfactant solutions as well as activity coefficients of both the organic solute and the surfactant within the micelle. The solubilization equilibrium constant of an organic solute in an aqueous micellar solution (K) is defined as the ratio of the mole fraction of organic solute in the micellar 'pseudophase' (X) to the concentration of the unsolubilized monomeric organic solute in the aqueous phase (Cp). The simple empirical expression K=K0 (1-αX+βX2) is used to correlate the solubilization equilibrium constant (K) with the mole fraction of the organic solute in the surfactant aggregates (X). Water-soluble polyelectrolyte/surfactant complexes, involving oppositely charged species, can form at quite low thermodynamic activities of the surfactant. This fact is exploited in colloid-enhanced ultrafiltration separations, where both molecular organic pollutants and toxic ions are to be removed from contaminated aqueous streams.