en.Wedoany.com Reported - Researchers at Peking University have developed a catalytic process for recycling waste PET plastics. The process utilizes a commercial catalyst to convert discarded bottles and containers into two high-value chemical intermediates—lactic acid and 1,4-cyclohexanedicarboxylic acid—without the need for an external hydrogen supply.
This innovative two-step method, published in the journal Engineering under the title "Upgrading PET Plastics to Lactic Acid and 1,4-Cyclohexanedicarboxylic Acid Using Methanol," reacts post-consumer polyethylene terephthalate plastics with methanol under mild conditions to upgrade them into lactic acid and 1,4-cyclohexanedicarboxylic acid. Unlike traditional recycling methods that only add value to one component of PET waste, this atom-economical route captures value from both structural fragments of the polymer simultaneously.
The research team consists of Zhenbo Guo, Haoyu Chen, Shuheng Tian, Meiqi Zhang, Meng Wang, and Ding Ma. The process they designed aims to address a fundamental limitation in the economics of plastic recycling: extracting maximum value from waste feedstocks while minimizing energy input and reliance on external reagents.
The process begins with PET depolymerization in a sodium hydroxide-methanol solution at 160°C. This initial step breaks the polymer down into its constituent units: ethylene glycol and terephthalic acid. The ethylene glycol generated during depolymerization undergoes a dehydrogenative coupling reaction with methanol to form lactic acid and hydrogen gas. Meanwhile, methanol dehydrogenation provides additional hydrogen to meet the stoichiometric requirements of the subsequent hydrogenation step. This internally generated hydrogen is collected and reused to hydrogenate terephthalic acid into 1,4-cyclohexanedicarboxylic acid, completely eliminating the need for external hydrogen cylinders.
The entire sequence proceeds at a mild temperature of 160°C without the need to change the catalyst. The commercially available Ru/C (ruthenium on carbon) catalyst functions effectively in both reaction stages. Isotopic labeling experiments using deuterated methanol and deuterated ethylene glycol confirmed that ethylene glycol dehydrogenation significantly contributes to both the rate and the hydrogen source for lactic acid formation. The researchers also found that the presence of ethylene glycol suppresses side reactions associated with methanol dehydrogenation, improving overall selectivity and yield.
Product separation involves acidification and purification steps. Under optimized conditions, the isolated yield of lactic acid is 55% with a purity exceeding 88%, while the yield of 1,4-cyclohexanedicarboxylic acid is 84% with a purity exceeding 99%. Lactic acid is a key building block for biodegradable polylactic acid plastics, food additives, pharmaceuticals, and personal care products. 1,4-Cyclohexanedicarboxylic acid is used in high-performance polyester production, coatings, and specialty chemical synthesis. Both products have higher market value than the original PET monomers, creating multiple revenue opportunities for recycling facilities.
The researchers validated the method using various real-world PET waste, including bottles, food containers, fibers, and dyed items, demonstrating compatibility with typical post-consumer feedstocks. Stability tests showed that catalyst activity gradually declined with repeated cycles, attributed to slight agglomeration of ruthenium nanoparticles and partial metal leaching. The researchers noted that Ru/C catalyst is commercially available and relatively low in cost, making periodic replacement economically feasible in industrial settings.
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