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

## TL;DR

This paper introduces a detailed model explaining how PET plastic breaks down in water at neutral pH, including byproduct formation and reaction conditions.

## Contribution

A novel reaction network and kinetic model for PET hydrolysis that includes autocatalysis and byproduct generation is presented.

## Key findings

- The model accurately fits experimental data with a mean absolute error of 0.023 M.
- The highest predicted terephthalic acid yield is 94% under specific high-temperature conditions.
- 100% terephthalic acid yield is unachievable due to decomposition and equilibrium reactions.

## Abstract

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.