Depolymerization Of Polyethylene Terephthalate In Supercritical And Sub-Critical Water

Depolymerization of polyethylene terephthalate (PET) in sub- and supercritical water was carried out in a batch autoclave(0.05L)under different conditions. Experiments researched the reaction temperature, reaction time, catalyst and other conditions affect on the depolymerization of PET and yield of the primary product of terephthalic acid (TPA) and ethylene glycol (EG) in detail. The depolymerization products were analyzed by Fourier-transform Infrared Spectroscopy (FT-IR), High Performance Liquid Chromatography (HPLC), Gas Chromatography- Mass Spectrometry (GC-MS) and Gas Chromatography (GC), respectively. According to the analysis of depolymerization products, combined with the segment of PET, the depolymerization mechanism of PET in supercritical and sub-critical water was proposed.Under the conditions of temperature (220⁴00℃), pressure (2.2³1.8 MPa), reaction time (5⁹0min) and ratio of water/PET (4.0¹2.0). The result showed that PET could be degraded completely in supercritical water but could not be degraded completely in sub-critical water when the temperature was low. The depolymerization of PET and yield of terephthalic acid (TPA) and Ethylene glycol depended on the reaction temperature and time. With the rising of the temperature and reaction time, the yield of TPA and EG was increased at first and then reduced. The optimal depolymerization conditions were temperature of 320℃, pressure of 11MPa, reaction time of 15min and the ratio (water to PET) of 8. In this condition, PET could be depolymerized completely and the yields of TPA and EG reached 93.23% and 53.28%, respectively.Catalytic depolymerization of PET in water was studied under the conditions of temperature (220³40℃), reaction time (5⁶0min), ratio of water/PET (8.0) and catalyst/PET (1%³%). It was found that the depolymerization of PET and yield of products were depended on the temperature, reaction time and catalyst. The optimal depolymerization conditions were temperature of 240℃, pressure of 3.2MPa, reaction time of 30min, and the Zinc Acetate concentration (zinc acetate to PET) of 1.5%. In this condition, PET could be depolymerized completely and the yields of TPA and EG could reach 90.45% and 61.51% respectively. Experimental results showed that the presence of the catalyst had an obviously promotion for PET depolymerization in sub-critical water.According to the experimental data and the Arrhenius equation, the activation energy of PET depolymerization in supercritical and subcritical water was 90.47kJ·mol^-1.