Depolymerization of polyesters by in situ generated alkali metal alkoxides

Abstract

The ubiquitous use of plastic has resulted in an undeniable global impact on the environment. Glycolysis of polyethylene terephthalate (PET) is a promising plastic recycling approach, but the use of heavy metal catalysts may pose tremendous risks to both our environment and human health. In this work, we developed a method for the in situ generation of alkali metal catalysts, which generated magnesium alcoholate (MgEG) through ligand exchange between acetylacetone and ethylene glycol (EG). By optimizing the reaction conditions, we achieved complete conversion of PET bottle flakes at 180 °C and obtained a bis(2-hydroxyethyl) terephthalate (BHET) yield of 85.9%. Structural characterization and density functional theory calculations demonstrated that EG in magnesium alcoholate formed a quaternary ring with the carbonyl group, reducing the reaction energy barrier. Moreover, this catalytic strategy exhibited reasonable catalytic activities on colored PET, PET mixed with other plastics and various polyesters, indicating the considerable potential for degradation of polyesters using non-heavy metal catalysts.