PET depolymerization using deep eutectic solvents

Polyethylene terephthalate plastic (PET) is one of the most extensively used materials worldwide due to its affordability, lightweight nature, and high durability. Proper end-of-life management is essential to address growing environmental concerns. In recent years, there has been an increasing focus on the chemical breakdown and recycling of PET materials. The primary goal of this process is the recovery of the polymer components both as ethylene glycol and as the more expensive terephthalic acid, with the purpose of using them to synthesize the virgin polymer, thus fully recycling the original waste. The standard depolymerization reactions, albeit yielding the starting PET monomer, usually require high temperatures and long reaction times (180 °C, 24 h)1, making the recycling process economically burdenly. Several types of DES have been demonstrated to catalyze PET depolymerization through different mechanisms, with the effect of lowering the critical energy demand2. In this study, fast and simple depolymerization of PET flakes with two different DES is presented. In the first case, less than 5 minute microwave irradiation of PET flakes mixed with a 1:3.5 ZnCl2:urea DES was carried out, whereas in the second one microwave and conventional heating (150°C) of PET in a KF:ethylene glycol 1:6 DES was compared. The fast microwave treatment hydrolyzed around 10% of PET flakes in zinc-based DES, whereas complete consumption of flakes was obtained in the KF-based DES. Conventional heating in KF DES produced pure terephthalic acid with a yield of 45 %. The reaction products were characterized by FTIR-ATR, NMR, and XRD3