Rate-limited mass transfer of octane, decane, and dodecane into nonionic surfactants solutions under laminar flow conditions

A key component to predicting the success of utilizing surfactants to enhance the removal of organic liquids from soil system is quantifying micellar solubilization kinetics. In this study, a flow reactor was employed to investigate the influence of surfactant ethoxylate chain length on the rates of solubilization of octane, decane, and dodecane in micellar solutions of a homologous series of purified dodecyl alcohol ethoxylates. Effluent concentration data were fit using a finite element model utilizing a linear-driving-force model to represent mass transfer at the interface. For flow rates between 0.1 and 2 ml min−1, mass transfer coefficients ranged from 5 × 10−8 to 7 × 10−7 m s−1 and did not vary in a systematic way with either solute structure or surfactant ethoxylate chain length and were lower than those found in pure water. Correlations developed for the Sherwood number based on diffusion coefficients of surfactant micelles containing organic material (organic-laden micelle) exhibit a velocity dependence similar to that found for systems based on aqueous diffusion. These results suggest that under gentle flowing conditions, the mass transfer is limited by diffusion of the organic-laden micelle. Although these trends are specific for this experimental system, the results demonstrate the importance of selecting the proper diffusion coefficient when modeling surfactant solubilization processes.