Effects of surfactants and salt on Henry's constant of n-hexane.

n-Hexane biological removal is intrinsically limited by its hydrophobic nature and low bioavailability. The addition of surfactants could enhance the transport of volatile organic compounds (VOCs) and change the gas-liquid equilibrium of VOCs. In this paper, the effects of four surfactants, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), tert-octylphenoxypoly-ethoxyethanol (Triton X-100), polyoxyethylene (20) sorbitan monooleate (Tween 80), and sodium nitrate on apparent Henry's constant of n-hexane in surfactant solutions were investigated. The apparent Henry's constants were significantly reduced when surfactants concentrations exceeded their critical micelle concentrations (cmc's). On a cmc basis, the anionic surfactant SDS was found to have the greatest effect on the apparent Henry's constant with CTAB succeeding, then followed by Triton X-100 and Tween 80. However, the apparent Henry's constant of n-hexane decreased even more rapidly when Triton X-100, a nonionic surfactant, was added than when the ionic surfactant of SDS or CTAB was applied under identical mass concentration and other conditions. These results suggest that Triton X-100 have the biggest solubilization of n-hexane among the four surfactants. Sodium nitrate slightly decreased the apparent Henry's constant of n-hexane in surfactant solutions, and could be considered as a cosolvent in the surfactant-(n-hexane) solution. In addition, the relationship between apparent Henry's constant and surfactant concentration was further developed.