Recovery of VOCs from surfactant solutions by pervaporation

Abstract

Surfactant-based processes are emerging as promising technologies to enhance conventional pump-and-treat methods for remediating soils contaminated with nonaqueous phase liquids (NAPLs), primarily due to the potential to significantly reduce the remediation time. In order to reuse the surfactant, thereby making the process more economical, the NAPLs must be separated from the surfactant solution. Pervaporation was identified as a potential technology for removing volatile NAPLs from surfactant solutions. Initial tests with 1,1,1-trichloroethane (TCA) in an aqueous solution of the non-ionic surfactant Triton X-100 showed that the surfactant had a negligible effect on both flux and selectivity at concentrations of up to four times the critical micelle concentration (4×CMC). Further tests with a 40×CMC surfactant solution yielded moderately lower TCA fluxes and selectivities than comparable aqueous solutions without surfactant. The reduced pervaporation performance at higher surfactant and TCA concentrations were found to result from two effects: (1) increases in the viscosity of the solution, which increases the liquid-side boundary layer mass transfer resistance and (2) partitioning of TCA into the micelles, thereby reducing the effective extramicellar concentration. Despite these reductions in performance, pervaporation was found to be quite capable of removing this volatile NAPL from the surfactant solutions.