Reaction Network and Kinetics Model for Neutral Hydrolysis of Poly(ethylene terephthalate)

We present a reaction network and kinetic model that describes the hydrolytic depolymerization of poly-(ethylene terephthalate) (PET) in water with neutral pH. The network comprises seven reaction pathways. It includes autocatalysis of PET depolymerization by terephthalic acid (TPA) and the generation of monohydroxyethyl terephthalate, bis-(2-hydroxyethyl) terephthalate, benzoic acid, and decomposition products of TPA and ethylene glycol as byproducts. The model can handle PET hydrolysis in the solid state and in the molten state. Parameter estimation was performed by fitting the model to product concentrations from literature for PET hydrolysis over a wide range of times (15 s to 25 h) and nominal reaction temperatures (170-570 °C). The model fits the entire set of experimental concentrations with a mean absolute error of 0.023 M. It also demonstrated the ability to predict product yields from many published studies. The highest TPA yield predicted by the model is 94%, obtained from hydrolysis at 450 °C (instantaneous heating) after a 20 s batch holding time. TPA yields of 100% were not achievable in the model because of TPA decomposition pathways and equilibrium reactions involving byproducts.