Hydrothermal Depolymerization of Waste PET

The widely use of PET (poly(ethyleneterephthalate)) results in that resource recovery of waste PET is urgent and its hydrolysis in high temperature water to produce terephthalic acid (TPA) and ethylene glycol (EG) is a very important method. Hydrothermal diamond anvil cell (HDAC) was used to in situ observe transformation of PET in water up to 240°C. The result shows that PET melts at 217°C, and then hydrolyzes to produce low molecular dissoluble compounds such as TPA and EG from cleavage of ester bond. Different from the microrector (about 0.075μl) of HDAC, degradation of PET in hydrothermal vessel of 50 ml is far slow, so the higher temperatures of 240, 260, and 280°C are tried. As for hydrothermal vessel runs, solid products after degradation are mainly composed of TPA. With increasing temperature, although it is benefit for the degradation rate of PET, TPA will decomposes at higher temperature, thus, it is very important to determine an appropriate condition for high yield of TPA and EG. The optimum hydrolysis conditions for TPA are as follows: ratio of H ₂ O/PET (W/W) is 10, reaction temperature is 260°C, reaction time is 15 min, and at the optimum condition the degradation rate of PET is almost 100% and the yield of TPA is 91.64%.