Solubilization of polycyclic aromatic hydrocarbon mixtures in micellar nonionic surfactant solutions

Abstract

This study sought to examine the solubilization of mixtures of the polycyclic aromatic hydrocarbons (PAHs) in solutions of the nonionic surfactants: Tween 20, Tween 80, Triton X 100, Brij 35, and Brij 58. When pyrene (PYR), fluoranthene (FLA), and phenanthrene (PHE) were solubilized from two-PAH mixtures, the PAH concentrations and molar solubilization ratios deviated very little from those as found in the single-PAH systems. When these PAHs were solubilized from the three-PAH mixtures, however, not all three PAHs reached their single-PAH solubilities. When the PAHs were added sequentially to surfactant solution, the PAH added last reached its single-PAH solubility, while the concentration of other two PAHs were lowered by 14–45%. When the PAHs were added simultaneously to the surfactant solution, the composition of the solid phase influenced which PAH reached its single-PAH solubility. For solids containing equal mole fractions of all three PAHs, FLA and PHE dissolved in surfactant solution to a lesser extent than the single-PAH systems. In similar systems containing no surfactant, only FLA solubility decreased. As the mole fraction of a PAH in the solid phase increased, its solubility in the micelle phase (and in the aqueous phase) increased up to the solubility limit. Based on these studies, both PAH–PAH interactions and micelle–PAH interactions should be taken into account when predicting the concentrations of PAH mixtures in micellar surfactant solutions. This should be done because PAH–PAH interactions can influence aqueous solubility, while micelle–PAH interactions can affect the distribution of PAHs in the micellar phase, which may change as the mixture composition changes.