Chemical and Electrochemical Recycling of End-Use Poly(ethylene terephthalate) (PET) Plastics in Batch, Microwave and Electrochemical Reactors

• Published in: Molecules (Basel, Switzerland) Vol. 25; no. 12; p. 2742
• Main Authors: Myren, Tessa H T, Stinson, Taylor A, Mast, Zachary J, Huntzinger, Chloe G, Luca, Oana R
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 13-06-2020; MDPI
• Subjects: Chemical reactions; Chemical reduction; Depolymerization; electrochemical reactor; Electrochemical Techniques; Electrochemistry; Electrolysis; Ethylene; Irradiation; Low cost; Methods; microwave; Microwaves; Oxidation-Reduction; Plastics; Polyethylene terephthalate; Polyethylene Terephthalates - chemistry; polymer recycling; Polymers; quaternary recycling; Reactors; Reagents; Recycling; Refluxing; Silver chloride; Sodium chloride; Sodium hydroxide; Solvents; Temperature; Terephthalic acid; United States > US; polymer recycling; quaternary recycling; depolymerization; microwave; electrochemical reactor
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules25122742

This work describes new methods for the chemical recycling of end-use poly(ethylene terephthalate) (PET) in batch, microwave and electrochemical reactors. The reactions are based on basic hydrolysis of the ester moieties in the polymer framework and occur under mild reaction conditions with low-cost reagents. We report end-use PET depolymerization in refluxing methanol with added NaOH with 75% yield of terephthalic acid in batch after 12 h, while yields up to 65% can be observed after only 40 min under microwave irradiation at 85 °C. Using basic conditions produced in the electrochemical reduction of protic solvents, electrolytic experiments have been shown to produce 17% terephthalic acid after 1 h of electrolysis at -2.2 V vs. Ag/AgCl in 50% water/methanol mixtures with NaCl as a supporting electrolyte. The latter method avoids the use of caustic solutions containing high-concentration NaOH at the outset, thus proving the concept for a novel, environmentally benign method for the electrochemical recycling of end-use PET based on low-cost solvents (water and methanol) and reagents (NaCl and electricity).