Enhancing sustainability in PET glycolysis by closed-loop recycling

Glycolysis is a mild process for the chemical recycling of poly(ethylene terephthalate) (PET), but still lacks efficiency due to high waste streams. The aim of this work therefore is to facilitate recycling of ethylene glycol (EG) reactant/solvent and homogeneously dissolved zinc acetate (ZnAc2) catalyst as well as dissolved product bis(2-hydroxyethyl)terephthalate (BHET) in the water-free PET glycolysis process. Through a combined approach of re-dosing and washing we saved 48.6 +/- 0.5% of EG and 50.0 +/- 5.2% of ZnAc2. By incorporating the collection of evaporated EG during BHET drying/re-polymerization, additional 35% of EG could further be saved in each of the five duplicate runs. While applying an optimized washing procedure in the recycling experiments, an equilibrium PET conversion was consistently reached after 150min of reaction time. Furthermore, the overall process yield was maintained at 80.6 +/- 1.8% in the recycling runs and the waste stream generation was reduced to a minimum. This study highlights the viability and environmental advantages of internal recycling, paving the way for a more sustainable and cost-effective PET glycolysis process.