Optimization of PET film glycolysis to BHET with walnut shell-derived catalysts

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A new type of environmentally friendly walnut shell matrix and efficient catalyst (denoted H-800) containing a variety of metal elements was prepared by using waste biomass walnut shell as raw material. H-800 was employed to catalyze the depolymerization of waste polyethylene terephthalate films for ethylene glycol production. The effects of key reaction parameters, including catalyst dosage, ethylene glycol dosage, reaction temperature, and reaction time, on the yield of the depolymerized product bis(2-hydroxyethyl) terephthalate (BHET) were systematically investigated. Response surface methodology experiments were designed using Design-Expert software to assess the individual and interactive effects of these parameters on BHET yield, so as to determine the optimal reaction conditions for BHET generation. Under the optimized conditions (0.48 wt% H-800 dosage, 15.18 g ethylene glycol, reaction temperature of 194.7°C, and reaction time of 2.39 h), the maximum BHET yield of 80.02% was achieved.