A pseudo-homogeneous system for PET glycolysis using a colloidal catalyst of graphite carbon nitride in ethylene glycol

• A pseudo-homogeneous system was designed for PET glycolysis. • Ultrasmall graphite carbon nitride was well dispersed in EG to form colloid. • Excellent PET conversion and BHET yield were obtained through PET glycolysis. • Graphite carbon nitride is suitable for the recycle of real polyester plastics. Glycolysis of poly (ethylene terephthalate) (PET) is a promising way to recycle waste PET and produce bis-(2-hydroxyl ethyl) terephthalate (BHET), the monomer of PET. However, traditional catalysts will cause environment pollution and economic burden. In this work, based on the green and low-cost graphitic carbon nitride colloid, we developed a pseudo-homogeneous system for PET glycolysis, and poly (bisphenol A carbonate) (BPA-PC) and polylactic acid (PLA) methanolysis. Using this system, 100% conversion of PET and 80.30% yield of BHET were achieved, and the reaction time was 2-8 times shorter than that of other metal-based catalysis systems. Catalyst and ethylene glycol were reused five times directly preserving their activity. Furthermore, the degradation of real commercial plastics has also been achieved. According to FT-IR, XPS, and 1 H NMR characterization results, the nucleophilic attack ability of ethylene glycol and electrophilicity of the PET carbonyl's carbon are enhanced by the formation of hydrogen bond between ethylene glycol, PET and catalyst.