Catalytic Chemical Recycling of Waste Polyethylene Terephthalate (PET) Via Microwave-Assisted Glycolysis and Repolymerization of Bis(2-Hydroxyethyl) Terephthalate (BHET)

One of the most prominently used plastics is polyethylene terephthalate (PET). However, PET is often designed for single use only, thus lots of waste is generated, leading to plastic pollution. Thus, a novel catalytic chemical recycling method was created to glycolyze waste PET bottles, recover bis(2-hydroxyethyl) terephthalate (BHET), and subsequently repolymerize the BHET to produce back the PET material. The study emphasized using microwave and cost-effective reagents as catalysts to recycle waste PET. The process was carried out initially via the glycolysis method in normal atmospheric pressure, with ethylene glycol and an economical catalyst, Na2CO3, used to depolymerize PET and produce BHET. The process was done in two ways: (1) via conventional heating using hotplates and (2) via commercial microwave heating. The highest BHET yield obtained from conventional heating method was 87.59%, using 1.0% Na2CO3 catalyst concentration, temperature at 196 °C, with 8 hours reaction time. Meanwhile, the microwave-assisted glycolysis method resulted to a higher yield of 89.55%, utilizing only 1.5% Na2CO3, 280 W microwave power, and 30 minutes of irradiation time. Afterwards, the BHET was polymerized into PET using a microwave-assisted process, further improved with the aid of the catalyst, para-toluenesulfonic acid (p-TSA). Results showed that the highest PET yield was 97.52%, with the optimized conditions of 120 W microwave power, 90 minutes irradiation time, and 1.0% p-TSA catalyst concentration via the Box- Behnken design. The methods were based on the circular economy approach: to recover monomers from PET bottles, which can be used to reproduce PET and generate new products such as polymer film composites for various applications, thereby closing the loop. This study sought to optimize the chemical recycling process by lessening the reaction time and energy requirement through the aid of simple and environment-friendly catalysts, making it more sustainable in the long run.