Low-temperature one-step synthesis of surfactant-free ZnO nanoparticles for efficient glycolysis of PET

Abstract

Among PET chemical recycling technologies, glycolysis has shown the greatest potential for achieving commercial viability on large scales. The catalyst development is always one of the challenges in PET glycolysis. Herein, surfactant-free ZnO nanoparticles (SF-ZnO) were synthesized through a one-step process in an aqueous medium at low temperatures and ambient pressure. Meanwhile, a microchannel reactor with intensified micro-mixing and mass transfer was used to finely control the synthesis of SF-ZnO with uniform size distribution and consistent production reproducibility. Compared to the modified ZnO nanoparticles (M−ZnO) treated with the surfactant KH570, SF-ZnO exhibited enhanced catalytic activity and reusability in PET glycolysis, which can be attributed to its higher concentration of acid sites and superior thermal stability. Response surface methodology (RSM) was employed to investigate the impact of four key factors (temperature, time, catalyst: PET mass ratio, EG: PET mass ratio) and their interactions on bis(2-hydroxyethyl) terephthalate (BHET) yield in PET glycolysis. Under optimal conditions (196 °C, 40 min, SF-ZnO: PET = 0.76 wt%, EG: PET = 4), PET conversion and BHET yield reached 100 % and 97.3 %, respectively. Aspen simulation and preliminary scale-up experiments confirmed the commercialization potential of PET glycolysis on SF-ZnO. Meanwhile, the environmental energy impact metric and life cycle assessment (LCA) showed that the SF-ZnO catalytic system provided an economically feasible and environmentally friendly solution to PET glycolysis.