Upcycling of Waste Poly(ethylene Terephthalate): Ammonolysis Kinetics of Model Bis(2‐Hydroxyethyl Terephthalate) and Particle Size Effects in Polymeric Substrates

Chemical upcycling of poly(ethylene terephthalate) (PET) through ammonolysis is pursued. Model studies are conducted on bis(2-hydroxyethyl) terephthalate reacting with ammonia in the presence of excess ethylene glycol (EG) to form terephthalamide. Reactions conducted over the range of temperatures from 50 to 125 °C yield pre-exponential factors of A₁ = 758 ± 120 L mol^-1 h^- ¹/A₂ = 1033 ± 220 L mol^-1 h^- ¹ and activation energies of E_a1 = 22.1 ± 1.5 kJ mol^-1 and Ea₂ = 26.5 ± 2.1 kJ mol^-1. Diffusional limitations are explored using particle sizes in the ranges of 1800-2500 μm, 250-600 μm, and 150-250 μm. Data from the particle size experiments is combined with the rate constants determined from the model studies to construct an effectiveness factor. Diffusivity is used as a fitting parameter, resulting in an estimated value of 1.37 ± 0.48 E-7 cm² s^-1 for ammonia in PET at 100 °C, which compares well to related literature values. Diffusional limitations are of profound importance; for particles of only 1 millimeter in average thickness, the conversion rate is decreased by a factor of ten! The comprehensive understanding of the ammonolysis of PET in EG provided can play an important role in improving material reuse and fostering a more circular economy.