(563f) Stages and Kinetics of Poly(ethylene terephthalate) Depolymerization in a Ball Mill Reactor

The deconstruction of post-consumer plastics into monomers provides the potential to both reduce the carbon intensity of chemicals and materials, as well as reduce the accumulation of environmentally harmful waste. Mechanochemistry, commonly performed in electrically driven ball mill reactors, offers a promising approach to chemically recycle plastics by avoiding the use of solvents and high reaction temperatures.¹ To this end, the progression and kinetics of the mechanochemical hydrolysis of PET under dry conditions at room temperature is investigated.² The rapid and complete depolymerization of PET is demonstrated with 20 min via ball milling with stoichiometric amounts of sodium hydroxide. Over the duration of the reaction, the yield of monomers increases steadily, while the molecular weight of the unreacted PET remains unchanged, indicating a reaction where PET completely depolymerizes within a local reaction environment, while chains outside this region are unaffected. A rapid increase in the depolymerization rate is observed when approximately 50% conversion of the PET, which corresponds to a transition of the PET powder into a homogenous wax. The transition to a wax increases accessibility of the PET chains, facilitating the more rapid hydrolysis. Finally, the rate of depolymerization is studied while adjusting milling parameter, specifically milling frequency, ball-to-powder ratio, and vessel temperature. From this, a unified kinetic expression to describe the conversion of PET is developed based on the milling energy dose.

References

1. K. J. Ardila-Fierro, J. G. Hernandez, ChemSusChem 2021, 14, 2145-2162
2. A. W. Tricker, A. A. Osibo, Y. Chang, J. X. Kang, A. Ganesan, E. Anglou, F. Boukouvala, S. Nair, C. W. Jones, ACS Sustain. Chem. Eng. 2022, 10, 11338-11347