(408a) Reaction Pathways and a Kinetics Model for Hydrolysis of Post-Consumer PET

Transforming post-consumer polyethylene terephthalate (PET) into its primary monomer, terephthalic acid (TPA), is a strategy to reduce PET waste and the environmental impact of PET production and use. This process can be performed by hydrolyzing PET, where water molecules cleave the ester bonds, providing TPA and ethylene glycol (EG) as the ultimate products. The TPA can be purified and then repolymerized with EG to create virgin PET, fostering a circular economy.

Kinetics models are important for engineering work as they facilitate the design, control, assessment, and optimization of chemical reaction processes. This presentation will focus on a newly developed reaction engineering model for PET hydrolysis in neutral water. The model is based on a reaction network that comprises seven different pathways that account for formation of the main products (terephthalic acid (TPA), ethylene glycol) and numerous byproducts (e.g., mono-hydroxyethyl terephthalate (MHET), bis(2-hydroxyethyl) terephthalate (BHET), benzoic acid). The network includes random hydrolytic scission of the ester bonds in PET, reversible hydrolysis of BHET and MHET, and decomposition of both TPA and ethylene glycol. The network was deduced by using published studies and results from preliminary modeling work. Autocatalysis by TPA and diffusion and reaction of water within solid PET particles when below its melting point are features of the model.

Parameter estimation was performed by fitting literature data for PET hydrolysis over a wide range of batch holding times (15 s - 4 h) and reaction temperatures (170 - 570 ˚C). The model fits the experimental product concentrations and demonstrated the ability to predict accurately product yields from additional published studies of PET neutral hydrolysis. We conclude by using the model to assess more completely the hydrolysis parameter space and to better understand the relative rates of the different pathways.