Fast and isothermal acetolysis of poly(ethylene terephthalate): Reaction pathways and kinetic modeling

Poly(ethylene terephthalate) (PET) acetolysis enables depolymerization into the monomers terephthalic acid (TPA) and ethylene glycol diacetate (EGDA). Acetic acid serves as both reaction medium and reactant. This work explores isothermal and fast (rapid heating, short time) acetolysis across a range of heat source set point temperatures (200–570 °C) and PET/acetic acid mass ratios and batch reactor holding times from 15 s to 120 min. TPA yields up to 80 % were achieved in under 3 min via rapid heating from room temperature toward 400–420 °C set points, but the yields are significantly lower at higher final set point temperatures due to decomposition of both solvent and product. A kinetics model based on a reaction network with three irreversible pathways successfully correlated both literature data and the present experimental product yields. The kinetics model, which includes the temperature-dependent density of acetic acid, correlates the TPA yields with a root-mean-square error of 16 %. The activation energy for PET acetolysis was found to be 109.5 ± 0.4 kJ/mol. Acetolysis is advantaged over hydrolysis for chemical recycling of PET by achieving higher TPA yields at comparable conditions and with reduced solvent demand relative to the PET loading. Disadvantages would include solvent decomposition and greater solvent cost.