Efficient Methanolysis of PET toward 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 commercially available, low-cost homogeneous 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 capability of homogeneous Mn²⁺ ions to rapidly activate methanol and swell PET with the structural stability and ease of recovery inherent to the heterogeneous Mn₂O₃ oxide. Through systematic in-situ and ex-situ characterizations (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. Aspen Plus process simulation and economic analysis further validate its industrial potential: although the synergistic system introduces an additional step for homogeneous catalyst recovery, its superior product yield and lower activation energy grant it significant economic advantages and industrial potential. In summary, this work establishes a novel homo-heterogeneous catalytic system, offering a strategic approach to develop efficient and scalable solutions for polyester degradation.