Abstract
Kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste was studied at two temperatures (300 °C and 350 °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 (k1–k6) for the individual reactions were calculated and it was observed that all reactions follow first-order kinetics.
Highlights
Introduction of Polyethylene terephthalate (PET) Waste into UsefulProducts.The global production of plastic materials is still growing and exceeded 367 million metric tons in 2020 [1], making the recycling of plastic waste an urgent global commitment
PET can be synthesized by esterification of monomers of terephthalic acid (TPA) and ethylene glycol (EG) or by transesterification of dimethyl terephthalate (DMT) and EG [6]
With further increase in temperature to 300 ◦ C, all PET waste degraded in the subcritical water (SubCW) and gave the highest yield of TPA and EG [19,21]
Summary
Introduction of PET Waste into UsefulProducts.The global production of plastic materials is still growing and exceeded 367 million metric tons in 2020 [1], making the recycling of plastic waste an urgent global commitment. Polyethylene terephthalate (PET) is the third most widely used polymer [2] in the production of packaging after polyethylene (PE) and polypropylene (PP). The primary use of PET polymer is in the textile industry, vast amounts of this material are used to make packaging in the food, medical and cosmetic industries. PET bottle is one of the most largely consumed plastic products [3]. PET bottles are durable, clear, light, inexpensive, heat-stable, and they are usually used for beverage and food applications [4]. The global production of PET bottles reached 13.1 million tons in 2020 [5]. PET is one of the main condensation polymers, which are known to be composed of different monomers. PET can be synthesized by esterification of monomers of terephthalic acid (TPA) and ethylene glycol (EG) or by transesterification of dimethyl terephthalate (DMT) and EG [6]
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