Equilibrium partition of polycyclic aromatic hydrocarbons in a cloud-point extraction process

Abstract

A cloud-point extraction (CPE) process using the nonionic surfactant Tergitol 15-S-7, a secondary ethoxylated alcohol, to extract selected polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions is investigated. The CPE process is facilitated at the ambient temperature, ca. 22 °C, by the reduction of the cloud-point temperature of the surfactant solution by addition of sodium sulfate. It is observed that the preconcentration factor could be enhanced either by increasing the salt concentration or by decreasing the initial surfactant concentration in the micellar solution. A high preconcentration factor of about 40 was achieved at 1 wt% surfactant concentration with the addition of 0.6 M Na 2SO 4. It is also noted that the equilibrium partition coefficients of the model PAHs are nearly independent of surfactant concentrations, up to 3 wt%, in this study. Correlations between the equilibrium partition coefficients K p of the PAHs and their octanol–water partition coefficients K ow, as well as K p and the molar volume V x of these PAHs, indicate that the partition processes of the PAHs in the CPE processes are mainly governed by their hydrophobic affinities to the surfactant aggregates. Furthermore, the effect of added Na 2SO 4 on the equilibrium partition coefficients is also studied. It is shown that addition of more Na 2SO 4 to the surfactant solution gives more partition of the PAHs into the surfactant-rich phase.