Upcycling of Waste Poly(ethylene terephthalate) : Ammonolysis Kinetics of Model Bis(2-hydroxyethyl terephthalate) and Particle Size Effects in Polymeric Substrates.

Abstract

Upcycling of poly(ethylene terephthalate) (PET) through ammonolysis is pursued.  Model studies on bis(2-hydroxyethyl) terephthalate (BHET) reacting with ammonia in excess ethylene glycol (EG) to form terephthalamide (TPD) are presented. Sequential ester conversion is characterized by the pseudo reaction rate constants of  = 1.02±0.09 h-1 and  = 0.44±0.08 h-1 at 100 ⁰C; these values correspond to second order rate constants of  = 0.60±0.05 L mol-1 h-1 and  = 0.26±0.05 L mol-1 h-1. Reactions conducted over a range of temperatures yield preexponential factors of A1 = 758±120 L mol-1 h⁻¹ / A2 = 1033±220 L mol-1 h⁻¹ and activation energies of Ea1 = 22.1±1.5 kJ mol-1 / Ea2 = 26.5±2.1 kJ mol-1. Diffusional limitations are explored using particle sizes of 1800-2500 μm, 250-600 μm, and 150-250 μm. Conversion data from the particle size experiments is combined with the rate constants determined from the model studies to construct an effectiveness factor.  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.