Solubilization Rates of n-Alkanes in Micellar Solutions of Nonionic Surfactants

Accurate prediction of surfactant-enhanced recovery of organic contaminants in soils requires estimates of micellar solubilization rates. This study examines the influence of surfactant properties on the rates of solubilization of octane, decane, and dodecane in micellar solutions of a homologous series of purified dodecyl alcohol ethoxylates and two commercial surfactants, an ethoxylated linear alcohol (Witconol SN-120) and an ethoxylated sorbitan ester (Witconol 2722). A batch mixing technique was employed to investigate these solubilization rates. For all surfactants studied, solubilization rates were found to increase with a decrease in solute chain length. For the purified surfactants, solubilization rates also increased with ethoxylate chain length. Batch concentration data were fit with a linear driving force mass transfer model. Effective mass transfer coefficients determined from these data ranged over more than one order-of-magnitude for the systems examined (0.11−3.3 h-1). Correlations developed for the effective mass transfer coefficients exhibit a dependence on the solute micelle-water partition coefficient, solute molar volume, and surfactant hydrophile-lipophile balance or ethoxylate chain length. Although the measured coefficients are specific for this experimental system, the results demonstrate the importance of employing organic and surfactant properties in the estimation of solubilization rates.