Reaction Kinetics of Nonenzymatic and Enzymatic Hydrolysis of Mono(2-hydroxyethyl) Terephthalate and Bis(2-hydroxyethyl) Terephthalate during Poly(ethylene terephthalate) Depolymerization

Abstract

Understanding the hydrolysis kinetics of mono(2-hydroxyethyl) terephthalate (MHET) and bis(2-hydroxyethyl) terephthalate (BHET) is essential for optimizing enzymatic recycling of poly(ethylene terephthalate) (PET). Herein, a comprehensive kinetic analysis of both nonenzymatic (autohydrolysis) and enzymatic hydrolysis of MHET and BHET is provided. Autohydrolysis experiments (40–75 °C) revealed comparable activation energies of 98.1 and 96.3 kJ mol–1 for MHET and BHET, respectively. BHET autohydrolysis was 6 to 8 times faster than MHET, a difference attributed to a higher pre-exponential factor. The catalytic enhancement of LCCICCG and IsMHETase enzymes was further evaluated. While LCCICCG accelerated both reactions, its advantage diminished significantly above 60 °C as autohydrolysis began to dominate. Conversely, IsMHETase exhibited exceptional specificity for MHET, achieving nearly 3 orders of magnitude acceleration relative to autohydrolysis at 45 °C, though it was less effective toward BHET than LCCICCG. The results provide kinetic parameters as quantitative baselines for designing optimized enzyme cocktails and multizone bioreactors for efficient PET depolymerization.