Upcycling of poly(ethylene terephthalate) waste plastics to terephthalonitrile

Abstract

Chemical upcycling of plastic waste represents an emerging approach to generate value-added chemicals and mitigate environmental impacts. Despite the significant role of terephthalonitrile in the production of bioactive compounds and high-value materials, sustainable and efficient methods for its production from plastic waste remain underexplored. In this work, we present a tandem process for the transformation of poly(ethylene terephthalate) (PET) waste into terephthalonitrile under mild conditions (≤120 °C). The process involves PET ammonolysis with ethylene glycol and ammonia, followed by liquid-phase dehydration of terephthalamide using Pd catalysts via a water-transfer mechanism. The dehydration step achieves complete conversion of terephthalamide with up to 68% selectivity for the dinitrile and 32% for the mononitrile. Using electrospray ionization mass spectrometry, we identified Pd complexes, predominantly Pd dimers, as the catalytic species, regardless of the Pd precursor used. Application of the tandem system to commercial PET bottles and fibers resulted in terephthalonitrile yields of 39–51 mol% based on the PET feedstock, even in the presence of pigments and chlorine. Life cycle analysis indicated that this process reduces CO₂ emissions by at least 28% compared to conventional terephthalonitrile production from p-xylene. This work introduces a promising strategy for the upcycling of PET waste into organonitrogen compounds with high selectivity and low environmental impact.