Population-Balance Modeling of Oligomer Evolution and Reactor-Configuration Effects in Poly(ethylene terephthalate) Glycolysis

In zinc acetate-catalyzed poly(ethylene terephthalate) (PET) glycolysis in ethylene glycol, PET conversion and bis(2-hydroxyethyl) terephthalate (BHET) yield cannot resolve the oligomer distributions governing separation and reactor staging. We develop a repeat-unit-conserving population balance model resolving degree of polymerization (DP) for this reaction. It couples heterogeneous solid scission and interfacial fragment release with liquid-phase internal scission, terminal BHET formation, and reverse condensation in a shrinking-core accessibility framework. Calibrated at 140–180 °C, it reproduces conversion and BHET yield with RMSEs of 0.066 and 0.061, and semiquantitative chromatographic trends at 180 °C support the predicted shift toward dimers. At 220 °C and equal volume, replacing one stirred tank with plug flow raises BHET yield from 74.5% to 82.2% while reducing DP > 4 residues by 99.81%; two tanks capture 65.7% of this gain and a two-tank–plug-flow hybrid 96.6%. The framework links chain-length evolution to reactor screening against yield and residue specifications.