Hydrothermal Catalytic Depolymerization of Poly(ethylene terephthalate) into Value-Added Functional Molecules Using Crednerite-Type CuMnO2 Catalyst

The rapid increase in non-biodegradable polyethylene terephthalate (PET) usage has resulted in serious environmental problems due to excessive plastic waste accumulation. Sustainable recycling, upcycling and conversion of value-added products is an effective and eco-friendly method to reduce plastic waste in the environment. In this work, hydrothermally synthesized crednerite-type CuMnO2 was investigated as a catalyst for the hydrothermal catalytic depolymerization (HTCD) of post-consumer PET. HTCD experiments were performed at 200 °C for 6 h by using ethylene glycol (EG), NaOH and water as co-reactants and only 0.1 wt% CuMnO2 catalyst. Depending on the reaction pathway, the process enabled the selective recovery of the valuable monomers bis(2-hydroxyethyl) terephthalate (BHET) through glycolysis and terephthalic acid (TPA) through alkaline hydrolysis followed by acidification. The obtained results from this study indicate that crednerite-type CuMnO2 is an effective catalyst for enhancing the depolymerization reaction rate, and the remaining catalysts can be easily recovered from the reaction mixture by simple filtration, highlighting its practical advantages for catalyst recycling and reuse. Moreover, the recovered BHET and TPA can be further used as organic linkers for MOF synthesis in energy storage applications; this is an aspect that has already been reported in our previous work. The HTCD method using crednerite-type CuMnO2 could therefore represent a promising approach for reducing plastic waste in solid waste streams, while extending this method to other types of plastic waste may provide a new roadmap for addressing environmental challenges and improving waste management systems in society.