Researchers from Peking University have unveiled a groundbreaking catalytic method that transforms postconsumer polyethylene terephthalate (PET) plastic waste into valuable chemical compounds, offering a promising solution to the growing issue of plastic pollution. Published in the journal Engineering, this innovative two-step process leverages methanol and a commercial ruthenium-on-carbon (Ru/C) catalyst to convert PET into lactic acid (LA) and 1,4-cyclohexanedicarboxylic acid (CHDA) under mild reaction conditions without requiring an external supply of hydrogen gas. The approach not only enhances the sustainability of plastic upcycling but also maximizes atom economy by valorizing both major PET monomer fragments—ethylene glycol and terephthalic acid—simultaneously.
The key to this process lies in the catalytic cycle which begins with the depolymerization of PET in a sodium hydroxide and methanol solution at a moderate temperature of 160 °C. During this stage, PET is broken down into its core structural constituents, with ethylene glycol liberated in situ. Rather than discarding this byproduct, the system ingeniously employs it for a subsequent dehydrogenative coupling reaction with methanol to yield lactic acid and molecular hydrogen. This internally generated hydrogen is then harnessed effectively within the same reaction vessel to hydrogenate the terephthalic acid fraction of PET into 1,4-cyclohexanedicarboxylic acid, a high-value chemical intermediate with numerous industrial applications. This closed-loop hydrogen cycling obviates the need for pressurized hydrogen cylinders, significantly improving process safety, cost-efficiency, and environmental footprint.
What distinguishes this catalytic process from conventional chemical recycling methods is its capability to perform both depolymerization and selective hydrogenation reactions with a single Ru/C catalyst under uniform reaction conditions—160 °C and 1 MPa of argon atmosphere to exclude oxygen. The catalyst remains active through both reaction stages without requiring regeneration or replacement, showcasing remarkable operational simplicity. The use of argon serves a dual purpose: to prevent air-induced catalyst deactivation and to act as an internal standard for precise quantification of hydrogen produced during the reaction. The researchers conducted extensive reaction optimizations involving variables such as PET loading, NaOH concentration, temperature, and reaction time, demonstrating robust and tunable performance.
Isotopic labeling experiments using deuterated methanol (CD3OD) and deuterated ethylene glycol provided compelling mechanistic insights. These experiments confirmed that ethylene glycol’s dehydrogenation significantly drives lactic acid formation and constitutes a primary hydrogen source. Moreover, the presence of ethylene glycol was found to suppress undesirable side reactions typically associated with methanol dehydrogenation, enhancing the selectivity toward target products. Such rigorous characterization underlines the catalytic efficiency and specificity critical for industrial viability, minimizing waste and maximizing product purity.
Product recovery from the reaction mixture involves strategic acidification followed by purification steps that yield high-purity lactic acid and 1,4-cyclohexanedicarboxylic acid. Under optimal conditions, lactic acid was isolated with a commendable 55% yield and a purity exceeding 88%, while cyclohexanedicarboxylic acid was obtained with an exceptional 84% yield and purity above 99%. Both products hold significant industrial value, especially lactic acid as a precursor for biodegradable polymers such as polylactic acid (PLA), and CHDA as a critical monomer in specialty polymers and resins. This upcycling strategy thereby transitions PET waste from a low-value environmental burden into lucrative feedstocks for the chemical and materials sectors.
Catalyst longevity remains an important consideration in scaling up new chemical methodologies. Over repeated reaction cycles, the Ru/C catalyst exhibited gradual activity decline attributed primarily to slight agglomeration of ruthenium nanoparticles and partial metal leaching. This phenomenon, typical of heterogeneous catalysts operating under aqueous alkaline conditions, necessitates further research into catalyst stabilization techniques. Nonetheless, the catalyst’s durability demonstrated in this study offers a solid foundation for development towards industrial-scale applications, balancing efficiency with practical longevity.
Real-world applicability was further demonstrated by testing this methodology on an array of postconsumer PET wastes including beverage bottles, food packaging containers, textile fibers, and dyed or stained items. The compatibility across diverse feedstock types validates the robustness and adaptability of the process within existing plastic recycling streams, addressing challenges posed by contamination and varied polymer compositions. This versatility is crucial for integrating such chemical upcycling technologies into present-day waste management infrastructures.
Beyond environmental benefits, this catalytic system signifies a strategic advancement in chemical recycling, emphasizing integrated carbon–hydrogen cycling. The internal generation and utilization of hydrogen from ethylene glycol not only eliminates dependency on external hydrogen sources but also maximizes resource efficiency and reduces overall carbon footprint. Such innovation aligns with global priorities toward circular economy principles, fostering sustainable materials management and reducing reliance on fossil resources.
The study’s implications extend into economic realms as well. By producing higher-value chemical intermediates rather than merely recovering monomers, this two-step catalytic process potentially offers superior commercial viability. The dual valorization strategy mitigates economic disadvantages often associated with traditional chemical recycling, improving profitability and encouraging wider adoption. This integrative approach exemplifies how catalytic science can reshape plastic waste into versatile precursors for advanced manufacturing.
As the global community intensifies efforts to combat plastic pollution, this research embodies a timely, technologically sophisticated advance that addresses both environmental and economic challenges. The ability to chemically transform PET waste into valuable, market-ready products under mild conditions using accessible catalysts epitomizes the progress achievable through innovative catalysis and reaction engineering. Such forward-thinking scientific endeavors broaden the horizon for sustainable plastic recycling with tangible benefits for industry and society alike.
In conclusion, the novel upcycling pathway combining methanol-mediated depolymerization, dehydrogenative coupling, and in situ hydrogenation with a single Ru-based catalyst represents a significant milestone in plastic waste valorization. By uniting mechanistic understanding with practical processing considerations, the researchers have forged a scalable, atom-efficient route that could revolutionize how postconsumer PET is managed globally. This work not only advances catalytic plastic recycling but also contributes importantly to the overarching mission of developing circular, low-carbon chemical manufacturing paradigms.
Subject of Research: Chemical upcycling of postconsumer PET plastics into lactic acid and 1,4-cyclohexanedicarboxylic acid using methanol and Ru/C catalysis.
Article Title: Upcycling PET Plastics with Methanol into Lactic Acid and 1,4-Cyclohexanedicarboxylic Acid
News Publication Date: April 4, 2026
Web References:
- Full paper: https://doi.org/10.1016/j.eng.2026.02.015
- Journal website: https://www.sciencedirect.com/journal/engineering
References:
Guo, Z., Chen, H., Tian, S., Zhang, M., Wang, M., & Ma, D. (2026). Upcycling PET Plastics with Methanol into Lactic Acid and 1,4-Cyclohexanedicarboxylic Acid. Engineering. https://doi.org/10.1016/j.eng.2026.02.015
Image Credits: Zhenbo Guo, Haoyu Chen et al.
Keywords
Chemical recycling, PET upcycling, Ruthenium catalyst, Lactic acid synthesis, 1,4-cyclohexanedicarboxylic acid, Dehydrogenative coupling, Hydrogenation, Sustainable catalysis, Plastic waste valorization, Circular economy, Methanol chemistry, Catalyst stability
