Hydrolysis of waste polyethylene terephthalate catalyzed by easily recyclable terephthalic acid

Hydrolysis of polyethylene terephthalate (PET) is an efficient strategy for the depolymerization of waste PET to terephthalic acid (TPA), which can be used as a fundamental building block for the repolymerization of PET or for the synthesis of biodegradable plastics and metal-organic frameworks. However, most of the reported hydrolysis catalysts are strong acids or bases, which are soluble in reaction media and difficult to separate after the reaction, leading to high production costs and a profound influence on the environment. Herein, we propose the use of TPA, the basic unit of PET, as an acid catalyst to promote the hydrolysis of PET. Under optimized conditions, i.e., 2.5 g of PET, a TPA concentration of 0.1 g/mL, mass ratio PET:H2O of 1:8, 220 °C of temperature, and 180 min of reaction time, a PET conversion of up to 100.0% and a TPA yield of 95.5% were achieved. Furthermore, the produced TPA exhibited a high purity of 99%, similar to that of fresh TPA, and was easily recoverable for PET hydrolysis without tedious workup and purification processes. More importantly, the hydrolysis efficiency was maintained over eight consecutive reaction cycles. Overall, this study provides a green, easy, and low-cost technology to recover and reuse TPA for waste PET hydrolysis.