Decolorization and reusing of PET depolymerization waste liquid by electrochemical method with magnetic nanoelectrodes.

This work is aimed at electrochemical decolorization of real waste liquid which obtained in the PET depolymerization process. Firstly, PET fabrics were glycolysized by utilizing excess ethylene glycol (EG). Then, the glycolysis product was mixed with water and purified through repeated crystallization to get bis(2-hydroxyethyl) terephthalate (BHET) crystal. At last, the waste liquid of the depolymerization process was electrochemical decolorized by utilizing chitosan/Fe3O4 nanoparticles as the dispersed electrodes under a DC voltage. The UV-Vis absorptions at 338, 531, and 635 nm which were due to the dyes in the waste liquid decreased with the electrolysis time. In contrast, slight change of absorption of EG (at 322 nm) indicated that EG was not destroyed in the electrolytic process. The variation of color removal efficiency with dosage of chitosan/Fe3O4 nanoparticles, applied voltage, concentration of electrolyte, pH and electrolytic time were investigated. The max color removal efficiency was 87.24%. PET fabrics were depolymerized by using the decolorized waste liquid or mixture of decolorized waste liquid and EG (1:1 v/v), and the yields of BHET were 72.3% and 76.6%, respectively. The products were BHET without dyes which were confirmed by DSC and FTIR spectroscopy. Graphical abstract.