Evaluation of Tributyl Phosphate-Based Hydrophobic Deep Eutectic Solvent as an Alternative Diluent for Reactive Extraction of Lactic Acid

The separation of lactic acid from the fermentation medium by using green solvents is crucial for both process efficiency and product purity. In the extraction process with deep eutectic solvents, a more selective and environmentally friendly separation can be achieved, minimizing energy consumption and waste generation. In this study, the effect of hydrophobic deep eutectic solvents (HDES) on the reactive extraction of lactic acid from an aqueous solution was investigated. HDES, prepared with different molar ratios of DL-menthol and tributyl phosphate, were used as a diluent, while tri-n-octylamine (TOA) was selected as the extractant. The physical properties of the prepared solvents were analyzed, and structural analysis was performed using FTIR and NMR. The effect of temperature on the structure of HDES was examined by TGA. The effects of initial acid concentration, amine concentration, HDES molar ratio, and temperature on extraction efficiency were evaluated. The success of the reactive extraction was demonstrated by calculating the distribution coefficient, loading factor, and extraction efficiency. It was observed that the highest extraction efficiency (E%) of 94.18% was achieved using HDES with a high mole fraction of TBP (X_t = 0.8) at the maximum TOA concentration (0.85 mol/L).