Purification of lactide by deep eutectic solvent assisted phase-change extraction technology

Impurities such as lactic acid and its oligomers in crude lactide (LT) significantly impair the quality of polylactide products. This study introduces a novel deep eutectic solvent assisted phase-change extraction (DES-PCE) method for efficient LT purification. By forming deep eutectic solvents (DESs) through the interaction of amides and acids, this method enables the separation of acid impurities during a temperature-driven phase transition, where LT crystallizes and impurities remain in the liquid phase. Centrifugation of the mixture yields high-purity LT, with N,N-Dimethylformamide (DMF) identified as the optimal amide, enhancing LT purity from 83.82% to 99.91% while achieving a yield of 95.97%. Mechanistic studies using FT-IR, NMR, and quantum chemical calculations elucidate the formation and function of DESs, as well as their impact on solubility and viscosity. Compared to conventional distillation, the DES-PCE process significantly reduces energy consumption and carbon dioxide emissions by 91% and 94%, respectively, showcasing its potential as a sustainable and cost-effective solution for LT purification.