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 A = 758 ± 120 L mol h /A = 1033 ± 220 L mol h and activation energies of E = 22.1 ± 1.5 kJ mol and Ea = 26.5 ± 2.1 kJ mol. 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 cm s 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.