Depolymerization of waste PET by ChCl-based catalyst and rPET repolymerization

A composite catalytic system composed of choline chloride, p-chlorophenol, and zinc acetate was developed for the efficient glycolysis of waste polyethylene terephthalate (PET). Under optimal conditions (185°C, 4 h, 2.5 wt% catalyst), PET was depolymerized into high-purity bis(2-hydroxyethyl) terephthalate (BHET) with a yield of 96.3%. The catalyst structure was characterized by Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance. Key reaction parameters, such as temperature, ethylene glycol/PET ratio, and catalyst loading, were optimized. The obtained BHET was repolymerized by way of melt polycondensation to produce regenerated PET, which exhibited thermal and structural properties comparable with commercial PET, as confirmed by thermogravimetric analysis, differential scanning calorimetry, FTIR, and nuclear magnetic resonance. The catalyst demonstrated excellent reusability, maintaining over 82% BHET yield after six cycles. This study proposes a sustainable, highly efficient, and fully recyclable strategy for closed-loop PET recycling. Specifically, by harnessing a synergistic Lewis–Brønsted acid system, the strategy demonstrates outstanding scalability and thus holds considerable promise for near-term industrial application.