Reaction Network Analysis and Kinetic Modeling of BHET Depolymerization as (Sub-)Network of PET

Introduction

Polyethylene terephthalate (PET) is widely used in fibers, films, and containers. Due to the low cost of virgin PET and the inferior properties of recycled PET [1-3], recycling remains economically unattractive in many regions [4]. Consequently, large amounts of PET are incinerated or end up in the environment, causing significant ecological damage [5]. Enzymatic depolymerization offers a sustainable alternative with mild conditions, energy efficiency, and environmental benefits [4]. While most studies focus on total depolymerization to terephthalic acid (TPA), this work targets the selective production of intermediates such as MHET and BHET, which are increasingly in demand for PET re-synthesis [6].

Experimental and Modeling

Two enzymes identified from prior screenings [6] were tested in different reaction media to analyze their effects on kinetics, equilibria, and product distribution. Ethylene glycol and DMSO shifted the product spectrum toward MHET. Mechanistic kinetic modeling, considering substrate, enzyme, and product inhibition, was performed to describe the reaction sub-network of BHET depolymerization with high accuracy.

Results and Outlook

A simplified reaction network for enzymatic PET depolymerization was established based on HPLC analysis. Reaction kinetics for BHET depolymerization were successfully modeled, providing a foundation for process design and optimization. Future work will extend the modeling to trimers and dimers and adapt the findings to PEF systems.