Polyethylene terephthalate monomerization via glycolysis and methanolysis using metal-free basic carbocatalyst

The giant amount of disposed Polyethylene Terephthalate (PET) has become a big environmental challenge. Waste PET is herein catalytically depolymerized and monomerized via glycolysis (using ethylene glycol as a solvent) as well as by methanolysis (using Methanol as a solvent). For this purpose, a novel, sustainable, metal-free basic carbocatalyst in pellet form was synthesized. Employing this catalyst in pure PET glycolysis led to a yield of bis(hydroxyethyl) terephthalate (BHET) of 76.3 mol% under optimal conditions (468 K, 1 h reaction time). Using flakes of a real PET bottle waste, a 58.9 mol% was achieved but required 3 h, attributed to altered partial crystallinity (proved by XRD). In other hand, the use of the same basic carbocatalyst in methanolysis produces a dimethyl terephthalate (DMT), with a maximum yield of 98.9 mol% at 468 K. Whereas 89.7 mol% was obtained using flakes of a real PET bottle waste in 2 h. These results highlight the potential for using the metal-free basic carbocatalyst for efficient PET recycling processes.