Green Catalytic Ionic Liquids Containing Organophosphorus for Efficient Glycolysis of Waste PET Bottle Flakes

The recycling of waste poly(ethylene terephthalate) (PET) is of great significance to alleviate environmental pollution and resource depletion. The metal-based catalysts currently used in chemical recycling often lead to metal residues and product coloration, which limits the industrialization of PET recycling. In this context, tetrabutylcarboxylate phosphate as an environmentally friendly ionic liquid catalyst containing organophosphorus was synthesized, and optimal reaction conditions for the glycolysis of PET were investigated, enabling 100% PET conversion and 40.8% bis(2-hydroxyethyl) terephthalate (BHET) yields at 200 °C and 120 min. FT-IR, 1H NMR, and XRD showed that the glycolysis products were mainly composed of BHET and a spot of dimers. The 1H NMR spectrum showed that the reaction model of PET glycolysis catalyzed by an ionic liquid is a shrink-core model, and the apparent activation energy is 89.73 kJ/mol. A possible reaction pathway was proposed subsequently. The prepared green and efficient ionic liquid is expected to replace the traditional metal salt catalyst that leaves contaminants in the product for the recovery of waste polyester products.