Efficient methanolysis of PET to produce high-purity DMT via homo-heterogeneous Mn2+/Mn2O3 synergistic catalysis

Abstract

The depolymerization of waste polyethylene terephthalate (PET) has predominantly focused on zinc-based catalysts, benefiting from their stable Lewis acidity derived from unique 3d orbital electronic configurations. In contrast, manganese-based catalytic materials, which share similar electronic structural features, have rarely been explored. This study developed a synergistic catalytic system using MnCl₂·4H₂O and heterogeneous Mn₂O₃ for the methanolysis of PET which achieved complete PET conversion within 1 hour at 180 °C with a dimethyl terephthalate (DMT) yield of 95.35%. Compared with other catalytic systems for PET depolymerization, the present system uniquely integrates the low-cost and commercially available homogeneous Mn²⁺ ions and heterogeneous Mn₂O₃ oxide, combining the capability of rapid methanol activation and PET swelling with the structural stability and ease of recovery inherent to the heterogeneous component. Through systematic in situ and ex situ characterization studies (XRD, XPS, in situ DRIFTS, etc.), it was revealed that the essence of the synergistic effect originates from a dynamic composite active center formed at the interface between Mn²⁺ and Mn₂O₃, which efficiently stabilizes key reaction intermediates and promotes product desorption. The Aspen Plus process simulation and economic analysis further validate its industrial potential: despite the introduction of an additional step for homogeneous catalyst recovery, the synergistic system achieves superior product yield and process efficiency, translating into compelling economic advantages and strong commercial viability. In summary, this work establishes a novel homo-heterogeneous catalytic system, offering a strategic approach to develop efficient and scalable solutions for polyester degradation.