Potential of deep eutectic solvents as green and sustainable solvents for the recovery of carboxylic acids from aqueous solution: a review

This paper presents an in-depth exploration of the potential of deep eutectic solvents (DESs) as green and sustainable solvents in the reactive extraction process for the recovery of carboxylic acids from fermentation broth/aqueous waste stream. It delves into the eco-friendly nature and cost-effectiveness of DESs, highlighting their high solvation capabilities and aligning with sustainable practices. The various hydrophobic DESs/NADESs, examining their suitability for the extraction of carboxylic acids as the replacements of conventional solvents along with their preparation, are explored. The study emphasizes the appropriate selection of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) in DES formulations to enhance the extraction efficiency. The role of physical properties of DESs such as viscosity, density, surface tension and ionic conductivity, which impact the mass transfer efficiency in the extraction of acids are discussed. In this review, the effect of various process parameters such as type of DES/carboxylic acid, initial acid concentration, pH, DES to aqueous phase ratio, temperature, stirring speed on the extraction of carboxylic acid along with possible extraction mechanism are extracted out. With exploration of recent studies on the extraction of acids using DESs, the efficient recovery of carboxylic acids and the excellent reusability of the DES for multiple extraction cycles is also discussed. The paper concludes with recommendations for future prospects, emphasizing the need to optimize DES compositions and intensified reactive extraction technologies with scale up for practical and efficient carboxylic acid recovery. © 2025 Society of Chemical Industry (SCI).