Sustainable Ammonium Metallates Enabling Efficient PET Waste Depolymerization

The increasing volume and heterogeneity of post-consumer PET waste highlight the need for efficient and sustainable chemical recycling technologies capable of providing monomers of sufficient purity for closed-loop applications. In this work, we report a solvolytic process enabled by ammonium metallate catalysts, and in particular [TMA][FeCl4], designed to operate under less severe conditions than conventional depolymerization routes. The methodology employs methanol as the sole solvent at 170 °C, without acidic or basic additives, and affords DMT yields up to 90% at 1 mol % catalyst loading, while complete disappearance of insoluble PET is maintained even at loadings as low as 0.1 mol %. A systematic experimental plan, including catalyst screening, optimization, PET concentration effects, and mechanical-stirring assisted scale-up to 48 g of PET, demonstrates high robustness and excellent isolated yields across operating conditions. The process shows broad tolerance toward common polymeric contaminants and real post-consumer waste streams, including colored packaging and mixed textile substrates, yielding high-purity DMT after a single recrystallization. The recovered DMT was successfully reused for PET synthesis and further validated as a polyester-grade feedstock through the preparation of a PBT-based thermoplastic copolyester elastomer with properties comparable to appropriate benchmark materials. Overall, the less severe reaction conditions, low catalyst loading and cost, operational simplicity, waste-stream compatibility, and recovery of polymer-grade DMT highlight the potential of this approach for PET chemical recycling and monomer valorization.