The Contribution of Commercial Metal Amides to the Chemical Recycling of Waste Polyesters

Abstract

Simple and commercially available metal amides are investigated as catalysts for the chemical depolymerization of polyesters of commercial interest such as polylactide (PLA) and polyethylene terephthalate (PET) via alcoholysis. In the alcoholysis reactions performed with methanol or ethanol at room temperature, Zn, Mg, and Y amides showed the highest activities, while the amides of group 4 metals were revealed as poor catalysts. During the ethanolysis of PLA at higher temperatures and the glycolysis of PET, the good activity of the Zn amide was preserved, while for Mg and Y amides, a significant decrease was observed. The reaction temperature had an opposite effect on the performance of group 4 amides, with the Zr amide revealed to be the best catalyst in the PET glycolysis, reaching activities comparable to the best ones reported in the literature for metal catalysts (78% BHET yield within one hour at 180 °C). These studies represent new opportunities for the sustainable recycling of plastics, which are currently being used on a large scale, and provide significant contributions to the design of a circular economy model in the plastic industry.