Using new solvents for removal of phenolic compounds present in industrial wastewater

Resumo

The development of industrial activity has associated a considerable increase in the volume of wastewater that, depending on their source, may contain large amount of organic and / or inorganic substances in concentrations which are harmful to the environment. Among these substances are the phenols, highly polluting substances and present in a large number of industrial activities (paper, food, photography, paints and explosives industries, synthesis of pharmaceuticals, petrochemical processes...). The removal of these compounds from wastewater streams before discharge is fundamental to the environmental protection. In this way, the Spanish legislation on industrial emissions limits the content of phenols in the wastewater to a maximum of 1 mg /l. The techniques used to remove or reduce the content of phenolic compounds in aqueous streams are biodegradation, thermal decomposition, and absorption, but none of them is effective when the wastewater contains a high concentration of phenols. Regarding the methods for liquid extraction with solvents, one of the main advantages is that they allow treating wastewater streams containing a high concentration of phenols. However, the more important limitation is that the solvents used in traditional liquid-liquid extraction are usually volatile organic compounds (VOCs), which are toxic, flammable and, in many cases, highly polluting substances. Therefore, it is desirable to consider alternative solvents that are equally effective but cleaner and more friendly with the environment. In this way, in recent years ionic liquids (ILs) and deep eutectic solvents (DESs) have attracted much attention from the scientific community due in particular to their combination of unique characteristics that make a difference with the conventional solvents. In particular their negligible vapor pressure and their physicochemical properties, such as polarity, viscosity and affinity for many organic and inorganic compounds, make them potential candidates for their use in multiphase systems as separation agents. Within this context, the main objective of this project is the application of hydrophobic ILs and DESs as extraction agents in the removal/reduction of phenol and its derivatives compounds (2-methylphenol, 2,4-dimethylphenol, 4-chlorophenol, 2-chlorophenol, 4-nitrophenol, 2,3-dichlorophenol, 2.4-dichlorophenol, pentachlorophenol, 2-benzyl-4-chlorophenol, etc.) present in wastewater streams generated at industrial level. This will require performing a solubility study of different ILs with the phenolic compounds, as well as the phase equilibria of ternary systems IL or DES + phenolic compound + water. These results will allow us to select the more appropriated solvent, which can perform an effective removal of phenolic compounds from water. Once selected the best solvent that allow to carry out an effective extraction, the next step will be its application to aqueous mixtures formed by a large number of phenolic compounds, in order to approach, insofar as possible, the real behavior of a residual stream generated in industry. With all these experimental data, the process simulation using commercial software will be carried out and the continuous extraction process at lab scale will be performed.