Methanolysis of Polyethylene Terephthalate (<scp>PET</scp>) Catalyzed by Ionic Liquid [Bmim]<scp>BF₄</scp>

ABSTRACT The chemical recycling of polyethylene terephthalate (PET) faces challenges such as low depolymerization efficiency, harsh reaction conditions, and low product selectivity. In this study, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim]BF 4 ) ionic liquid (IL) was developed as a catalyst for methanolysis, achieving the efficient conversion of PET into the target monomer dimethyl terephthalate (DMT). The effects of temperature, time, IL amount, and methanol quantity on the reaction were systematically investigated. The degree of depolymerization and catalyst stability were systematically evaluated by multiscale characterization (spectroscopy, chromatography, thermal analysis, etc.). Experimental results indicated that when the PET/[Bmim]BF 4 ratio was 6:1 and the PET/methanol ratio was 1:6 (mass ratio), reaction at 200°C for 2 h, PET was completely converted (100%), and the yield of DMT reached 82.26%. [Bmim]BF 4 could be reused more than five times without significant decrease in PET conversion. The kinetic results showed that the reaction was in line with the first‐order kinetic model, and the apparent activation energy was about 43.24 kJ/mol. DFT calculations suggested that [Bmim]BF 4 efficiently catalyzed the reaction by lowering the energy barrier of the key transition state. This study provides a solution with both high efficiency and industrial potential for the green chemical recycling of PET.