A new two-step catalytic process has been reported in Engineering that upcycles postconsumer polyethylene terephthalate (PET) plastics with methanol into lactic acid (LA) and 1,4-cyclohexanedicarboxylic acid (CHDA) under mild conditions, using a single commercial Ru/C catalyst and without external hydrogen supply. The work, conducted by researchers from Peking University, provides an atom-economic route that valorizes both structural segments of PET waste, moving beyond traditional recycling that often valorizes only one component.

In this approach, PET is first depolymerized in a NaOH–methanol solution at 160 °C. The ethylene glycol (EG) generated from depolymerization undergoes dehydrogenative coupling with methanol to form LA and hydrogen gas, while methanol dehydrogenation provides additional hydrogen to meet the stoichiometric need for subsequent hydrogenation. The hydrogen produced in situ is collected and reused to hydrogenate terephthalic acid (TPA), the other major PET-derived monomer, into CHDA, eliminating reliance on external hydrogen cylinders. The entire sequence proceeds at a mild temperature of 160 °C without catalyst replacement, and the Ru/C catalyst functions effectively in both the dehydrogenative coupling and hydrogenation stages.

Isotopic labeling experiments using deuterated methanol and deuterated EG confirm that EG dehydrogenation contributes significantly to the rate of LA formation and the hydrogen source, while the presence of EG suppresses side reactions associated with methanol dehydrogenation. Product separation involves acidification and purification; under optimized conditions, LA is isolated with a yield of 55% and purity above 88%, and CHDA is obtained with a yield of 84% and purity exceeding 99%. Both products are higher-value chemical intermediates than the original PET monomers, supporting improved economic viability of chemical plastic recycling.

Stability tests show that catalyst activity gradually declines with repeated cycles, linked to slight agglomeration of ruthenium nanoparticles and partial metal leaching under reaction conditions. The method is validated with various real-world PET wastes, including bottles, food containers, fibers, and stained items, demonstrating compatibility with typical postconsumer feedstocks. This work establishes a practical pathway for integrated carbon–hydrogen cycling in plastic upcycling, where hydrogen generated from one monomer segment is internally recycled to upgrade the other, advancing sustainable chemical conversion of plastic waste into marketable materials.

The paper “Upcycling PET Plastics with Methanol into Lactic Acid and 1,4-Cyclohexanedicarboxylic Acid,” is authored by Zhenbo Guo, Haoyu Chen, Shuheng Tian, Meiqi Zhang, Meng Wang, Ding Ma. Full text of the open access paper: https://doi.org/10.1016/j.eng.2026.02.015. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.