Stirring-assisted cloud-point extraction of polycyclic aromatic hydrocarbons

A novel cloud-point extraction (CPE) process, namely, stirring-assisted cloud-point extraction (S-CPE), was developed with a stirring rate over 380 rpm in a PEG/PPG-18-18 dimethicone aqueous solution at a temperature over its cloud point. Compared with a general CPE process with centrifugation (C-CPE), the stirring process successfully accelerated the phase separation, where the whole process was able to be finished in 15 min and a lower water content in the surfactant-rich phase was also obtained, e.g., the water content was as low as 52 wt % at a 2 wt % surfactant solution, indicating a higher resulting distribution coefficient. The phase separation of the process was studied with dynamic lighting scattering. Because of the increasing contact chances between micelles and extractable species, the stirring operation is also in favor to increase the extractability of the CPE process, where higher recoveries of polycyclic aromatic hydrocarbons (PAHs) were obtained even with a lower surfactant concentration, e.g., a 98.9% recovery of anthracene was obtained in a I wt % surfactant solution. What is more important is that the stirring operation is suitable for a scaling-up process, and the surfactant-rich phase floating upon the solution is more easily collected and removed. In addition, the extractant used in the S-CPE, PEG/PPG-18-18 dimethicone, has little UV absorbance, avoiding the disturbance to the signal of PAHs in UV or fluorescence detector, so it is convenient to determine PAHs concentration in every phase during S-CPE process by high-performance liquid chromatography (HPLC) directly. The stirring operation successfully avoids the low phase-separation efficiency like in the CPE process with heating and has no treatment capacity limitation like in C-CPE. Therefore, S-CPE offers an efficient possibility for scaling up a typical CPE process to be applied in the separation of PAHs in the water treatment.