Selective Chemical Conversion of PET Wastes via FeCl₃–Amine Catalyzed Transesterification

Poly(ethylene terephthalate) (PET) is one of the most widely used plastics, and the development of efficient chemical recycling technologies is essential for establishing a sustainable circular economy. Although transesterification is a promising approach for PET depolymerization, conventional methods often require harsh reaction conditions or strong acids or bases. Herein, we investigated FeCl₃–amine catalyst system for the transesterification chemical recycling of diverse PET wastes.

PET substrates including sheets, pellets, powder, textiles, and PET mixtures such as PVC/PET and cotton/PET, were treated with alcohols in the presence of FeCl₃ and amine additives under a nitrogen atmosphere. The resulting products were isolated by filtration and characterized by GC and ¹H/¹³C NMR spectroscopy. Scale-up reactions were also performed using 20–30 g of PET waste.

Various PET substrates were efficiently depolymerized with methanol or n-octanol to afford analytically pure dimethyl terephthalate (DMT) or dioctyl terephthalate (DOT) in excellent yields (95–>99%). The addition of small amounts of amines significantly enhanced catalytic activity while maintaining outstanding product selectivity. The catalytic system also exhibited broad substrate applicability, enabling the selective depolymerization of challenging mixed and colored waste materials, including cotton/PET textiles and PVC/PET automotive leather composites. Furthermore, scale-up reactions using 20–30 g of PET waste with methanol in the presence of the FeCl₃–benzimidazole catalyst system successfully produced analytically pure DMT as white crystalline solids, with no detectable by-product formation.

The FeCl₃–amines catalyst system enables the efficient and selective conversion of diverse PET waste streams into high-purity terephthalate diesters under practical reaction conditions, highlighting its potential as a practical strategy for sustainable closed-loop PET recycling.