Kinetics Study of Hydrothermal Degradation of PET Waste into Useful Products

Kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste was studied at two temperatures (300 degrees C and 350 degrees C) and reaction times from 1 to 240 min. PET waste was decomposed in subcritical water (SubCW) by hydrolysis to terephthalic acid (TPA) and ethylene glycol (EG) as the main products. This was followed by further degradation of TPA to benzoic acid by decarboxylation and degradation of EG to acetaldehyde by a dehydration reaction. Furthermore, by-products such as isophthalic acid (IPA) and 1,4-dioxane were also detected in the reaction mixture. Taking into account these most represented products, a simplified kinetic model describing the degradation of PET has been developed, considering irreversible consecutive reactions that take place as parallel in reaction mixture. The reaction rate constants (k(1)-k(6)) for the individual reactions were calculated and it was observed that all reactions follow first-order kinetics.

Automated summary

The kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste were studied, and it was found that PET could be decomposed into terephthalic acid (TPA) and ethylene glycol (EG) as the main products. Further degradation of TPA to benzoic acid and EG to acetaldehyde were observed, along with the formation of by-products like isophthalic acid (IPA) and 1,4-dioxane. A simplified kinetic model was developed to describe the degradation process, and all reactions were found to follow first-order kinetics.