Easily recoverable and reusable p-toluenesulfonic acid for faster hydrolysis of waste polyethylene terephthalate

Abstract

Common technologies for waste polyethylene terephthalate (PET) hydrolysis generally use strong acids or alkalis as catalysts; however, these processes are costly and generate a large amount of acid, alkali, and salt wastewater. In addition, these catalysts are difficult to recycle and reuse, which is not in line with the concept of sustainable development. This study describes the use of concentrated p-toluenesulfonic acid (PTSA) as an acid catalyst for PET hydrolysis under relatively mild conditions, enabling the degradation of approximately 100% of PET into 96.2% of terephthalic acid (TPA) within 90 minutes at 150 °C. A similar degradation efficiency can only be achieved at 150 °C using concentrated sulfuric acid for over 5 h. The generated TPA was easily separated from the hydrolysis system via filtration. The used PTSA was easily recovered from the filtrate after TPA collection using simple concentration and crystallization technologies. The recovered PTSA still maintained excellent catalytic efficiency for PET hydrolysis after five consecutive cycles. Furthermore, the kinetics of the reaction confirmed that the PET hydrolysis catalyzed by concentrated PTSA conforms to a first-order reaction with a relatively low apparent activation energy of 76.4–125.4 kJ mol⁻¹. Finally, the technical feasibility and environmental impact of a scale-up were evaluated using Aspen Plus simulations. Overall, this work proposes a feasible and green strategy for the low-cost and environmentally friendly hydrolysis of waste PET.