Closed-loop recycling for poly(ethylene terephthalate) (PET) plastic: depolymerization, monomer separation, and recycled PET (rPET)

Abstract

Closed-loop chemical recycling offers a promising solution to the end-of-life challenges of plastic waste. However, efficiently cleaving bonds to generate value-added products and develop chemically recyclable polymers remains a considerable challenge. We have developed a closed-loop upcycling strategy that depolymerizes poly(ethylene terephthalate) (PET) into bis(2-hydroxyethyl) terephthalate (BHET), followed by polycondensation to produce recycled PET (rPET). A series of xMn/Zn (x = 0, 0.5, 1, 2) catalysts, where x represents the molar ratio of Mn and Zn, were synthesized and employed to depolymerize PET plastic into the BHET monomer. The efficient PET glycolysis approach, utilizing the high surface area and weak acid sites of the 1Mn/Zn catalyst, achieved complete depolymerization of PET plastic with a BHET yield of 93.6 %. The recovered monomers can be utilized to remanufacture rPET, which exhibits competitive molecular weight, thermal stability, and rheological properties. The energy efficiency and techno-economic feasibility of the strategy for recycling PET waste plastic were assessed by constructing a lab-scale 5.0 g-grade process and simulating a 1-ton-grade process. This work introduces a closed-loop “PET-BHET-rPET” process, addressing end-of-use challenges, offering a cost-effective method, and providing a sustainable solution for upcycling plastic waste.