Efficient PET Depolymerization Using Cost-Effective Alkali and Alkaline Earth Metal-Based Salts for High Monomer Yield

Catalytic glycolysis of polyethylene terephthalate (PET) into its monomer, bis(2-hydroxyethyl) terephthalate (BHET), is a major focus of chemical research in recent decades. Metal catalysts, especially heavy metal salts, are recognized for their efficiency in degrading this widely used thermoplastic. However, concerns over the non-biodegradable and toxic nature of heavy metal catalysts like Zn and Pb salts, along with their limited selectivity, have led researchers to seek alternative, more environmentally friendly, and cost-effective catalysts. This study explores alternatives such as lithium, sodium, and calcium acetate/formates, demonstrating that selected benign metal salts not only accelerate PET degradation but can also surpass traditional heavy metal acetate catalysts (e.g., Zn acetate) in terms of activity and BHET yield. More importantly, complete PET conversion is achieved within 3 h at ≈188 °C, with excellent BHET yield. The catalytic reactions using lithium and calcium acetate show a superior initial reaction rate under optimized conditions.