A metal-free route to fully recycle PET into premium chemical feedstocks
By combining an ionic liquid catalyst with a carefully designed reaction system, the method overcomes long-standing barriers of incomplete depolymerization and low product purity, offering a promising pathway toward true closed-loop recycling of plastics.
Plastic pollution remains a persistent global challenge because most plastics are difficult to recycle without losing material quality. Polyethylene terephthalate (PET), widely used in bottles, packaging, and textiles, exemplifies this problem, as conventional mechanical recycling typically downcycles PET and limits its reuse potential. Chemical recycling offers a more sustainable alternative by breaking PET back into its original monomers, enabling the production of virgin-quality plastics. Among these strategies, methanolysis has attracted industrial interest, but existing approaches often depend on metal catalysts, high temperatures, excess solvents, and energy-intensive purification. Although ionic liquids provide a promising metal-free option, many current systems still face incomplete depolymerization and operational complexity. Overcoming these limitations is essential for scalable, energy-efficient PET recycling.
A study (DOI: 10.1016/j.plaphe.2025.100139) published in Plant Phenomics on 24 February 2025 by Qingqing Mei’s team, Zhejiang University, demonstrates a highly efficient, metal-free strategy for completely upcycling waste PET into high-value chemical feedstocks under mild conditions, offering a practical pathway toward closed-loop plastic recycling.
The study first established a systematic experimental method to explore an ionic-liquid-catalyzed PET upcycling process that couples PET methanolysis with the transesterification of the intermediate ethylene glycol (EG) using dimethyl carbonate (DMC), conducted at 130 °C over 2.5 h with methanol as the nucleophile. By varying ionic liquid structures, reaction temperature, reactant ratios, catalyst loading, and reaction time, the researchers dissected how each parameter governs depolymerization efficiency and product formation. Screening of different anions in 1-ethyl-3-methylimidazolium-based ionic liquids revealed that acetate, with the strongest hydrogen-bond-accepting ability, was essential for catalysis, while weaker anions led to reduced ethylene carbonate (EC) formation or even failed depolymerization. Fine-tuning reaction conditions showed that 130 °C, a balanced methanol-to-DMC ratio, and moderate catalyst loading maximized performance, whereas excess methanol inhibited EG cyclization despite sustaining PET methanolysis. Time-course and kinetic analyses further clarified that PET methanolysis is the rate-determining step, while EG transesterification proceeds rapidly and shifts the equilibrium toward complete depolymerization. Under optimized conditions, this method achieved complete PET conversion, delivering 99% dimethyl terephthalate (DMT) and 91% EC within 2.5 h while using less methanol than conventional systems. Extending the method to real-world substrates demonstrated its robustness, with diverse PET wastes yielding 90–99% DMT and 79–89% EC, and other polyesters and polycarbonates being efficiently transformed into corresponding dicarboxylates and cyclic carbonates. Spectroscopic analyses using NMR and FT-IR revealed that multiple hydrogen bonds between the ionic liquid and reactants activate both carbonyl and hydroxyl groups, enhancing nucleophilic attacks and stabilizing intermediates. Together, these methodical investigations show that hydrogen-bond-driven dual activation underpins the high efficiency, broad substrate scope, and energy-saving potential of this PET upcycling strategy.
Beyond laboratory-scale PET samples, the method successfully processed a wide range of real-world plastic wastes, including bottles, films, fabrics, and industrial scraps, consistently delivering high yields. It also proved applicable to other commercial polyesters and polycarbonates, converting them into corresponding dicarboxylates and cyclic carbonates with similarly impressive efficiency. Because DMT and EC are valuable feedstocks for producing new plastics, solvents, and battery electrolytes, this strategy transforms plastic waste into premium chemicals rather than low-value recyclates, strengthening the economic case for chemical recycling.
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References
DOI
Original Source URl
https://doi.org/10.1016/j.plaphe.2025.100139
About Plant Phenomics
Plant Phenomics is dedicated to publishing novel research that will advance all aspects of plant phenotyping from the cell to the plant population levels using innovative combinations of sensor systems and data analytics. Plant Phenomics aims also to connect phenomics to other science domains, such as genomics, genetics, physiology, molecular biology, bioinformatics, statistics, mathematics, and computer sciences. Plant Phenomics should thus contribute to advance plant sciences and agriculture/forestry/horticulture by addressing key scientific challenges in the area of plant phenomics.
Journal
Plant Phenomics
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
UAV-LiDAR high-throughput time-series phenotyping and genome-wide association analysis reveal the genetic basis of plant height in peanut (Arachis hypogaea L.)
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