Poly(ethylene terephthalate) (PET) is a major contributor to plastic waste. Mechanical recycling can lead to additional reuses of the post-consumer PET material, but eventually the mechanical properties of the plastic deteriorate, and the landfill is its ultimate fate. PET hydrolysis is a chemical recycling approach that can convert post-consumer PET into its monomers, terephthalic acid (TPA) and ethylene glycol. PET hydrolysis occurs in neutral water without a catalyst, but the depolymerization product yields are just a few percent when operating below the PET melting point (around 250 °C). Higher temperature leads to faster rates, but at the expense of increased energy input. We have been exploring the use of different catalysts to facilitate ester bond cleavage in PET at temperatures below the melting range. Metal triflates have been employed previously as catalysts in hydrothermal systems. They are a class of water-tolerant Lewis acids. Preliminary work with metal triflates as catalysts for PET hydrolysis at 200 °C for 2 h showed TPA yields of 57%, 66%, and 75%, with PET conversions of at least 86%, 89%, and 85% when using Al(OTf)3, In(OTf)3, and Yb(OTf)3, respectively. Hydrolysis without a catalyst at similar condition gives TPA yields of less than 10%. This presentation will illustrate the effects of temperature (150 to 250 °C), reaction time (30 – 240 min), PET/water ratio (0.1-0.5 (w/w)), and catalyst loading (0.03-0.3 mmol), on PET conversions and TPA yields. We will also illustrate the efficacy of different metal triflate catalysts, demonstrate their activity maintenance and recyclability, and postulate potential reaction mechanisms for triflate-catalyzed PET depolymerization. This work could open a new avenue toward a circular economy by efficiently converting PET into TPA under mild conditions, enabling the reuse of TPA in PET production.
