Depolymerization of PET and Polyamide 66 Wastes Using an Iron(III) Recoverable Lewis–Brønsted Aqueous System

Abstract

The accumulation of polyethylene terephthalate (PET) and polyamide 66 (PA66) in municipal and industrial waste streams represents a major challenge to global sustainability efforts. In this work, we report the development and optimization of a low-cost, iron-recoverable, and reconstitutable Lewis–Brønsted aqueous solution (LBAS) system for the selective depolymerization of post-consumer PET and PA66 wastes. The method employs a recyclable reaction medium and operates under mild conditions (150 °C, 2 h), achieving high monomer yields with excellent selectivity. The resulting terephthalic acid, adipic acid, and hexamethylenediammonium chloride were efficiently recovered and purified using straightforward separation techniques, whereas ethylene glycol was recovered as a stream suitable for purification by conventional industrial methods. A proof-of-concept experiment confirmed that PET and PA66 can also be depolymerized in the same medium, even though cross reactions between adipic acid and ethylene glycol prevent the quantitative monomer recovery. Therefore, mixed PET/PA66 feeds require prior separation to recover the individual monomers effectively. Overall, results demonstrate a scalable and environmentally benign approach for the chemical recycling of PET and PA66, contributing to a more sustainable plastic lifecycle and circular materials economy.