Low-Temperature Glycolysis of Polyethylene Terephthalate

In this work, we developed a new catalytic method of glycolysis to efficiently convert post-consumer polyethylene terephthalate (PET) into bis(2-hydroxyethyl) terephthalate (BHET). The addition of an aromatic compound possessing the alkoxy group (e.g., anisole) to the glycolysis reaction system facilitated the conversion of PET to BHET at a reaction temperature near 153 °C, which is much lower than that of catalytic glycolysis without a co-solvent (>197 °C), while overall catalytic performance remains almost unchanged. We found that an inexpensive metal salt or organic guanidine base could be used as an effective catalyst for the low-temperature glycolysis. Under the optimal reaction conditions catalyzed by alkali metal (Na or K) acetate, PET completely decomposed in 2 h with a BHET yield of 86%. We also investigated detailed reaction behaviors and possible intermolecular interactions between anisole and other chemical species that facilitate catalytic glycolysis. Based on the experimental results, the most probable reaction steps were proposed and a kinetic model mechanistically describing the overall reaction behavior was developed. The estimated apparent activation energy for PET decomposition in the co-solvent-assisted glycolysis system was found to be a low value of 80.9 kJ mol–1, which is responsible for the high reactivity even at a much lower reaction temperature than that of glycolysis without the co-solvent.