A sustainable extraction process for removing dyes and metals from glycolyzed polyester textiles using deep eutectic solvent

During the glycolysis of waste polyester textiles for the recovery of bis(2-hydroxyethyl terephthalate) (BHET), residual color impurities and Zn 2+ in the product significantly restrict the high-value application of recycled PET. In this study, deep eutectic solvents (DESs) were employed as extractants to simultaneously remove dyes and metal ions from waste PET glycolysis solution. A DES composed of decanoic acid and oleic acid was identified as effective, achieving a decolorization efficiency of 90.5%, a BHET loss of 5.9%, and a Zn 2+ removal ratio of 42.3% in a single extraction from a model system dyed with Disperse Blue 56 under optimal operating conditions. Quantum chemical calculations and spectroscopic characterization revealed that dye extraction occurs mainly through a physical process dominated by van der Waals interactions, while Zn 2+ removal follows an ion-exchange mechanism, resulting in the formation of a Zn 2 + - [DecA] 2 − - OleA ${\text{Zn}}^{2+}\text{-}{\text{[DecA]}}_2^{-}\text{-}\text{OleA}$ complex in the oil phase. The extraction of Zn 2+ was found to be thermodynamically limited due to the high stability of the tetradentate complex formed between BHET and Zn 2+ . This work aims to propose a practical strategy for impurity removal in the closed-loop recycling of colored PET textiles.