Background

While poly(ethylene terephthalate) (PET) is generally the most recovered landfill plastic, it still has a low recycle rate, especially given its scale of use. This leads to an increased volume of PET in landfills, with detrimental global consequences. The most commonly reported reason for low recycling rates is the inaccessibility to recycling resources, and there is therefore a need for a more accessible way of sustainably recycling PET in an environmentally friendly way. There is also a need for identifying new feedstocks in PET production, and therefore recycling of this material has dual benefit.

Technology Overview

Researchers at the University of Colorado have produced new practical methods for the chemical recycling of end-use 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. The researchers report end-use PET depolymerization in one method to be 65-75% yield of terephthalic acid in batch, depending on processing time and under microwave irradiation at 85°C.

In another method, researchers used basic conditions produced in the electrochemical reduction of protic solvents. These 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).

Further Details:

• Chemical and Electrochemical Recycling of End-Use Poly(ethylene terephthalate) (PET) Plastics in Batch, Microwave and Electrochemical Reactors - Molecules. 2020 Jun; 25(12): 2742.Published online 2020 Jun 13. doi: 10.3390/molecules25122742

Stage of Development

• Technology Readiness Level (TRL): 3

Benefits

• More accessible
• Less corrosive materials needed
• Reduced costs

Applications

• Landfill plastic recovery
• Reduces PET to useable feedstocks