Catalytic depolymerization of polyethylene terephthalate in hot compressed water

Zinc acetate (Zn(Ac)2) catalyzed depolymerization of polyethylene terephthalate (PET) in hot compressed water (HCW) was carried out in a batch autoclave reactor, as a potential method for chemical recycling of waste PET. The effects of the ratio of Zn(Ac)2 to PET (0–3%), temperature (220–300 °C), and reaction time (5–60 min) were investigated. The optimal conditions for complete catalytic depolymerization of PET were temperature 240 °C, pressure 3.2 MPa, reaction time 30 min, and Zn(Ac)2/PET ratio 1.5%. The main products of catalytic depolymerization were identified and quantified as terephthalic acid and ethylene glycol by Fourier-transform infrared spectroscopy, high-performance liquid chromatography, gas chromatography/mass spectrometry, and gas chromatography. The maximum yield of terephthalic acid reached 90.5%. The phase behavior of PET with or without a catalyst in water during heating and cooling was studied in a fused-silica capillary reactor. According to the phase change data, the temperature of PET dissolution in HCW to form a homogeneous aqueous solution was decreased by adding Zn(Ac)2.