Solubilization as a Separation Process

Abstract

In this paper a separation process for hydrocarbon molecules is suggested, based on solubilization in aqueous solutions by surfactant micelles. A molecular thermodynamic approach to solubilization is formulated which relates the extent of solubilization and the selectivity to the structure and properties of the surfactant and of the solubilizate molecules. An evaluation of the solubilization characteristics of benzene and hexane in aqueous solutions of non-ionic octyl glucoside, anionic sodium dodecyl sulfate and cationic cetyl pyridinium chloride is made and solubilization phase diagrams for the above systems are constructed. These diagrams indicate the formation of micelles at concentrations which are lower than the critical micelle concentration of the surfactant alone. The calculations predict, for all three surfactants, preferential solubilization of (aromatic) benzene compared to (aliphatic) n-alkanes. The preferential solubilization of benzene is caused by its smaller molecular volume and lower interfacial tension against water. Preliminary experimental results using cetyl pyridinium chloride as surfactant and an equimolar binary mixture of hexane and benzene as solubilizates indicate a selectivity of over 7 for benzene compared to hexane, and a ratio of about one molecule of benzene solubilized for every surfactant molecule in the micelle.