Single-Step Electrochemical Upcycling of PET: Waste to Value-Added Chemicals, Oral Presentation

Globally, an estimated 7.4 billion tons of plastic have accumulated, with projections suggesting this could escalate to 40 billion metric tons by 2050. Unfortunately, only about 10% of this plastic is recycled, due to the lack of sustainable and economical solutions [1]. Alarmingly, over 70% of plastic waste ends up in landfills or oceans where it gradually decomposes into small particles (average diameter less than 5 mm), often referred to as microplastics (MPs). This widespread presence of microplastics poses a significant hazard to global ecosystems and human health. Microplastics can be ingested by organisms through various pathways including consumption of contaminated food, inhalation of polluted air, and dermal contact [2]. Polyethylene terephthalate (PET), is the second most abundant plastic produced worldwide due to its extensive use in consumer packaging. Conventional mechanical recycling of PET often leads to the loss of its desirable properties [3]. Therefore, there is significant interest in chemical recycling technologies capable of depolymerizing PET. Through chemical hydrolysis at high temperatures, PET can be broken down into its constituent monomers, terephthalic acid and ethylene glycol. Nonetheless, the subsequent chemical separation of these products, particularly ethylene glycol (EG), presents challenges due to its high boiling point, viscosity, and water solubility, necessitating energy-intensive distillation processes. In response to this challenge, electrochemical methods have gained popularity for oxidizing PET hydrolysates into valuable products such as formic acid and glycolate, thereby offering a more sustainable pathway for upcycling [4]. However, most studies on electrochemical upcycling of PET still utilize a two-stage process. Initially, PET is hydrolyzed in a potassium hydroxide KOH solution at temperatures exceeding 80°C. Subsequently hydrolysate is used as an electrolyte to produce formate at the anode while hydrogen is produced at the cathode. Botte's group is investigating electrochemical approaches to convert plastics into valuable chemicals [5]. An effective enhanced electrocatalytic hydrolysis process for recycling PET waste into value-added chemicals was developed. This novel approach integrates the hydrolysis of PET with the concurrent electrochemical oxidation of ethylene glycol employing transition metals as catalyst and using mid temperature conditions. The effect of different variables on the overall conversion and the product distribution were evaluated. Operating time, voltage and particle size were varied, and the end products were characterized by FTIR, SEM, NMR, and IC. Our studies indicate that the electrochemical approach enhanced PET hydrolysis in comparison to traditional chemical hydrolysis [6] along with the oxidation of ethylene glycol into formic acid/formate in a single process eliminating the need for separate hydrolysis. Optimization of this process could be a sustainable approach for upcycling of PET microplastic into valuable products. [1] Li, M. and S. Zhang, Tandem Chemical Depolymerization and Photoreforming of Waste PET Plastic to High-Value-Added Chemicals. ACS Catal. 2024. 14(5): p. 2949-2958,doi: 10.1021/acscatal.3c05535. [2] E. Bäckström, K. Odelius, and M. Hakkarainen, “Trash to Treasure: Microwave-Assisted Conversion of Polyethylene to Functional Chemicals,” Ind. Eng. Chem. Res. , vol. 56, no. 50, pp. 14814–14821, Dec. 2017, doi: 10.1021/acs.iecr.7b04091. [3] R. K. Brizendine et al. , “Particle Size Reduction of Poly(ethylene terephthalate) Increases the Rate of Enzymatic Depolymerization But Does Not Increase the Overall Conversion Extent,” ACS Sustain. Chem. Eng. , vol. 10, no. 28, pp. 9131–9140, Jul. 2022, doi: 10.1021/acssuschemeng.2c01961. [4] Y. Li, L. Q. Lee, H. Zhao, Y. Zhao, P. Gao, and H. Li, “Alcohol–alkali hydrolysis for high-throughput PET waste electroreforming-assisted green hydrogen generation,” J. Mater. Chem. A , vol. 12, no. 4, pp. 2121–2128, Jan. 2024, doi: 10.1039/D3TA05522A. [5] G. G. Botte, “Processes for electrochemical up-cycling of plastics and systems thereof,” WO2021257972A1, Dec. 23, 2021 Accessed: Jul. 21, 2023. [Online]. Available: https://patents.google.com/patent/WO2021257972A1/en [6] F. Lu and G. G. Botte, “Understanding the Electrochemically Induced Conversion of Urea to Ammonia Using Nickel Based Catalysts,” Electrochimica Acta , vol. 246, pp. 564–571, Aug. 2017, doi: 10.1016/j.electacta.2017.06.055.