Upcycling of poly(ethylene terephthalate) waste plastics to terephthalonitrile

Abstract

Despite the significant role of terephthalonitrile in the production of bioactive compounds and high-value materials, methods for its production from alternative carbon resources remain underdeveloped. 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. We identified Pdx(CH₃CN)y(H₂O)z(OH)t species, predominantly present in a dimeric form, 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. 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 a lower environmental impact.