Separation of phenols from aqueous streams using terpenoids and hydrophobic eutectic solvents

The separation of phenols from wastewater, mainly in petrochemical plants, refineries, and coal processing plants context, is essential to meet discharge limits. Several technologies have been studied to separate phenols from water, being the liquid-liquid extraction one of the most used so far. Currently, the separation of phenols by extraction is done using organic solvents, such as toluene or methyl isobutyl ketone. In this work, we study the potential use of hydrophobic eutectic solvents and terpenoids as sustainable solvents in the separation of phenol, 2-nitrophenol, and 2-chlorophenol from water. Initially, a screening based on molecular simulation with the COSMO-RS method was carried out to select the most promising alternative solvents. Experimentally, the extraction of the three phenols was studied using four terpenoids, three hydrophobic eutectic solvents, and three conventional organic solvents. Also, the back-extraction of the phenols using an alkaline solution was done to regenerate the solvents, studying the chemical stability of the solvents by FTIR analyses. Among the tested solvents, the most promising extraction and back-extraction yields were obtained for geraniol and linalool. Overall phenols extraction yields of 98.0% and 96.1% for geraniol and linalool respectively, and back-extraction yields 99.5% were obtained, at solvent-to-feed ratio in volume of 0.5. Using both solvents, the extraction of phenols was performed in a packed parallel extraction column to obtain the distribution ratios of each component, further used to simulate a countercurrent extractor by the Kremser method. Finally, to evaluate the use of geraniol and linalool in this process at the industrial scale, the separation of phenols from the wastewater of petrochemical and coal processing plants was simulated using the COSMO-based/Aspen Plus methodology. A complete separation of phenols could be obtained using geraniol and linalool as solvents with a solvent-to-feed ratio of 0.5 and 10 equilibrium stages in the extractor.