Low-temperature alcoholysis as a strategy for polyethylene terephthalate recycling and upcycling

Efficient Depolymerization of Polyethylene Terephthalate Waste via Mechanocatalytic Methanolysis Using the K2CO3 Catalyst

Tackling plastic waste has garnered growing attention in recent years, spurring intensified research into plastic depolymerization. Among various plastics, polyethylene terephthalate (PET) stands out as the most widely recycled. Although several depolymerization methods have been reported, many still rely on high temperatures and/or excessive amounts of toxic reagents. Herein, we study the depolymerization of PET derived from post-consumer waste bottles via mechanocatalytic methanolysis at room temperature, without any chlorinated solvents or excessive solvents/reactants. Under optimized conditions, 76% yield, 82% PET conversion, and 96% selectivity to the desired dimethyl terephthalate (DMT) were achieved within one hour of milling. Our results demonstrate a critical role of potassium carbonate (K2CO3)—used as a cost-effective, earth-abundant, and environmentally benign catalyst—in generating methoxide nucleophiles, which accelerates the mechanochemical process. To elucidate the underlying mechanism, density functional theory (DFT) calculations were performed. These simulations reveal that the formation of free methoxide anions in the solution is the primary driver of catalytic PET methanolysis under mechanochemical conditions. This work opens new avenues for sustainable plastic waste processing. The key advantage of the method is that it uses 12 times less methanol and is 24 times faster than conventional thermochemical methanolysis, while leading to nearly double the yield, offering a greener and more efficient alternative.

Transition Metal-Catalyzed Chemical Recycling and Upcycling of Polyethylene Terephthalate.

The rapid growth of the polymer industry has driven the widespread application of polyester plastics, especially polyethylene terephthalate (PET). However, the nonbiodegradability of waste PET poses persistent threats to ecosystems. Conventional mechanical recycling struggles to achieve closed-loop material circulation and preserve intrinsic material properties. Therefore, developing efficient, low-energy chemical recycling technologies that depolymerize waste PET into monomers or high-value chemicals has become a critical route toward a circular plastic economy. This review systematically presents various transition metal-catalyzed chemical depolymerization processes for waste PET, with a focused analysis of reaction mechanisms and performance of different catalytic systems in key reactions such as glycolysis, hydrolysis, hydrogenolysis, and methanolysis. Furthermore, the review outlines future research directions for enabling high-value, closed-loop recycling of waste polyesters, including rational catalyst design and process optimization and integration. Overall, this review aims to provide theoretical guidance and technological insights for the sustainable chemical recycling of polyesters.

Florisil®-Catalyzed Alcoholysis: A Sustainable Route for Plastic Waste Valorization

Chemical recycling of plastic waste into value-added chemicals represents a key strategy for advancing a circular plastics economy. Herein, we report the first systematic application of commercially available Florisil® as an inexpensive, readily available heterogeneous catalyst for the alcoholysis of polyester and polycarbonate plastic waste. Under optimized conditions, poly(lactic acid) (PLA), poly(ε-caprolactone) (PCL), poly(4-hydroxybutyrate) (P4HB), poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), and bisphenol A polycarbonate (PC-BPA) were efficiently depolymerized into valuable diesters and diols in good to excellent yields (up to ~90%). The catalytic system also maintained high performance on a larger reaction scale and proved effective for the selective depolymerization of mixed polyester waste streams, demonstrating its robustness and practical applicability. Unlike many previously reported catalytic systems that rely on metal salts or specially synthesized catalysts, Florisil® requires no prior modification and combines operational simplicity with high catalytic efficiency. These findings establish Florisil® as a sustainable and practical catalytic alternative for plastic waste valorization, broadening the range of accessible heterogeneous catalysts for chemical recycling.

Catalytic Effect on Simplified Chemical Recycling of Poly(butylene terephthalate).

Chemical recycling plays a crucial role in reducing plastic pollution, lowering CO2 emissions, and minimizing the overall carbon footprint associated with the circular economy. Poly(butylene terephthalate) (PBT) is a common candidate for chemical recycling, as it is used in various applications that benefit from closed-loop recycling. However, traditional recycling methods often require high catalyst loadings and labor-intensive purification processes. These factors increase the material and energy inputs needed, which undermines both economic viability and environmental sustainability. This study aims to closely examine the de- and repolymerization processes involved in producing recycled PBT (rPBT) within a single reactor and step. The kinetics of this recycling process were systematically investigated by evaluating the effects of depolymerization time, the stoichiometry of 1,4-butanediol, and the presence of catalysts. Both catalytic and noncatalytic conditions were analyzed to understand the intermediate composition, molecular weight development, as well as the thermal and mechanical properties of the recycled rPBT. The findings provide valuable insights for establishing baselines without an added depolymerization catalyst and highlight key parameters that enable the production of high-quality recycled materials while reducing the need for extensive purification.

Chlorine Radical Mediated Tandem Dehydrogenation-Oxidation for Upcycling Polyolefins to Functional Wax at Low Temperature in Air.

Polyolefins valued for their excellent properties are the highest produced and widely used plastics. However, their chemical stability and massive accumulation arouse severe environmental issues, necessitating urgent resolution of recycling. Current recycling strategies encounter challenges like noble metal catalyst dependence, harsh conditions, sensitivity, poor selectivity, and low-valued products. Here, we report a potentially sustainable and scalable tandem dehydrogenation-oxidation system that operates under mild conditions (120 °C, in air) without precious metals. With 1,1,2-C2H3Cl3 serving as both the solvent and chlorine radical source, polyolefins, and mixed polyethylene wastes can be efficiently converted into α,ω-functional wax under the combined action of H2O2 and phase-transfer catalyst (CP)3PW4O16 with >95% carbon utilization efficiency. The process is tolerant to water, oxygen, and common plastic additives, eliminating pre‑purification. This work offers an economically promising and potentially scalable pathway for polyolefin waste upcycling.

Study on Methanolysis of Polyethylene Terephthalate to Dimethyl Terephthalate Over Titanate Nanostructured Materials