Solubilization mechanism and mass-transfer model of anionic-nonionic gemini surfactants for chlorinated hydrocarbons

Accurate prediction and modeling of the quantitative recovery of chlorinated hydrocarbons in an aquifer by anionic-nonionic gemini surfactants requires estimates of their mass-transfer models and capture mechanisms. In this work, a series of synthesized anionic-nonionic gemini surfactants (GEOnS-m) with different molecular structures were used to solubilize different chlorinated hydrocarbons that contaminate the aquifer. GEOnS-m aggregate showed vesicle, rodlike micelle, and spherical micelle as the ethylene oxide content (EO) number increases. Non-polar chlorinated hydrocarbons (PCE, CT) mainly solubilized in the hydrophobic interior of micelles, and polar chlorinated hydrocarbons (TCE, MCB) mainly solubilized in the palisade layer of micelles. Solubilization processes were followed employing first-order and second-order kinetics. The solubilization rate increases with the decrease of EO number of GEOnS-m molecules. In essence, lower interfacial tension reduces the mass-transfer resistance of chlorinated hydrocarbons at the two-phase interface. The diameter of vesicles and spherical micelles increases, and rodlike micelles evenly changed to vesicles as chlorinated hydrocarbons transfer into micelles. The solubilization process of GEOnS-m for chlorinated hydrocarbons conforms to a novel oil diffusion & micelle reformation model that represents the coupling to two pre-existing models. And the solubilization mass-transfer mathematical model demonstrated the solubilization mass-transfer coefficient is affected by the combination of surfactant and solubilized organic properties. This study advances the application of solubilization for chlorinated hydrocarbons using anionic-nonionic gemini surfactants in surfactant-enhanced aquifer remediation (SEAR) design.

Automated summary

This study investigates the solubilization of chlorinated hydrocarbons using synthesized anionic-nonionic gemini surfactants (GEOnS-m) in an aquifer. The results show that the solubilization rate increases with the decrease of ethylene oxide content (EO) of the surfactant molecules, and the solubilization process and form depend on the polarity of the chlorinated hydrocarbons. The study advances the application of anionic-nonionic gemini surfactants in surfactant-enhanced aquifer remediation (SEAR) for chlorinated hydrocarbon solubilization, providing important insights for the design and modeling of such processes.