Directing Depolymerization Of Pet With Subcritical And Supercritical Ethanol To Different Monomers Through Changes In Operation Conditions

Recycling of poly(ethylene terephthalate) (PET) wastes has become an urgent need since huge amounts of this plastic are accumulated in the environment. Unlike other chemical recycling methods, depolymerization of PET with supercritical ethanol is based on the use of a nontoxic green solvent. However, the viability of ethanolysis further depends on finding mild pressure and temperature conditions that do not interfere with the degradation efficiency. This challenge was faced in this study by performing ethanolysis of PET under unexplored pressure, temperature, reaction time, and weight ratio PET to ethanol (% wt) conditions. The variation of ethanolysis conditions revealed that besides the expected diethyl terephthalate (DET) and ethylene glycol (EG), other degradation products were also obtained, such as terephthalic acid (TPA). The exploration of the pathways involved allowed directing the process toward different degradation monomers by changing ethanolysis conditions. Long supercritical treatments completely degraded PET and essentially led to the formation of DET and EG since the primarily formed TPA reacted with ethanol under these conditions to produce further DET. Subcritical pressures and temperatures, short reaction times, and high % wt did not always result in complete degradation of PET but increased TPA formation, the main monomer regarded as the building block for PET repolymerization.