Surfactant-enhanced Removal of Hydrophobic Oils from Source Zones

This research has demonstrated that the more hydrophobic the oil (e.g., the higher its molecular weight), the more hydrophobic the surfactant system must be to achieve desirable phase behavior. The oil hydrophobicity can be characterized by its equivalent alkane carbon number (EACN). A new approach is presented for estimating the EACN of multi-component hydrophobic nonaqueous phase liquids (NAPLs), which can be used to help guide surfactant selection. Results demonstrate that achieving middle phase microemulsions is more complicated for high EACN oils (e.g. hexadecane with an EACN of 16). An Aerosol-OT (AOT)/ Tween 80 system was identified in batch studies and evaluated in column studies. In less than five injected pore volumes, this surfactant system removed greater than 99% of residual hexadecane from a vertical glass bead column by both mobilization and supersolubilization mechanisms. Counter-flow liquid-liquid extraction conducted in porous hollow fiber membranes was shown to effectively separate hydrophobic oils from surfactant solutions, thereby regenerating the surfactant for reuse. This research thus demonstrates that surfactant enhanced remediation of hydrophobic oils is a viable technology, worthy of further development.