Reaction kinetics of hydrothermal depolymerization of poly(ethylene naphthalate), poly(ethylene terephthalate), and polycarbonate with aqueous ammonia solution

Poly(ethylene naphthalate) (PEN), poly(ethylene terephthalate) (PET) and poly(carbonate) (PC) were depolymerized in a semi-batch reactor with a 0.6 M aqueous ammonia solution under hydrothermal conditions, at 433–553 K and 10 MPa, compared with aqueous alkaline (NaOH and KOH) solutions and water alone. The polymers studied were almost completely converted into monomers in an aqueous ammonia solution as well as aqueous NaOH and KOH solutions under hydrothermal conditions. The depolymerization reactions for the three polymers consisted of the initial induction stage, where the reactions proceeded very slowly, and the major depolymerization stage thereafter. The induction times were correlated with temperature. In the latter stage the overall depolymerization rate for each polymer was represented by 2/3-order reaction kinetics with respect to the amount of unreacted polymer, suggesting that the reaction occurred on the polymer surface. The depolymerization rates for PC with a 0.6 M aqueous ammonia solution were much faster than those with a 0.6 M aqueous NaOH solution.