Reactive liquid-liquid extraction of lactic acid from microfiltered sweet sorghum silage press juice in an agitated extraction column using a hydrophobic natural deep eutectic solvent as modifier

Downstream processing of carboxylic acids from fermentation broths is cost-intensive and environmentally harmful, which makes methods such as reactive liquid-liquid extraction attractive separation technologies. To enhance the sustainability of liquid-liquid extraction processes, research focuses on sustainable solvents like hydrophobic natural deep eutectic solvents. However, the application of hydrophobic natural deep eutectic solvents in agitated extraction columns for continuous processing has never been investigated. This is essential to facilitate their use in industrial processes, promoting cleaner production. In this study, the application of a thymol-menthol-based deep eutectic solvent as a modifier (with the extractant tri-n-octylamine) in an agitated extraction column is evaluated for reactive liquid-liquid extraction of lactic acid from microfiltered sweet sorghum silage press juice. In addition, three-stage cross-current extractions were performed. The thymol-menthol-based deep eutectic solvent showed efficient phase separation, stable operation, and chemical stability in the agitated extraction column. In three-step cross-current operation, the extraction efficiency for lactic acid was increased from 37.0 ± 0.4 % without feed pH adjustment to 76.2 ± 0.9 % with continuously adjusting the pH value to 2.05 ± 0.02. The thymol-menthol-based deep eutectic solvent shows great potential for application in agitated extraction columns. This is highly promising because natural deep eutectic solvents can enhance the sustainability of extraction processes and reduce the reliance on fossil-based solvents.