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The chemical recycling of polyethylene terephthalate (PET) via glycolysis is a promising pathway for the circular economy; however, it often requires harsh conditions or expensive catalysts. This study investigates the depolymerization of waste PET using ethylene glycol (EG) mediated by a deep eutectic solvent (DES) synthesized from zinc acetate dihydrate (Zn(OAc)2·2H2O) and urea. The formation of the DES via hydrogen bonding was confirmed by Fourier transform infrared analysis. Experimental results demonstrated a remarkable enhancement in catalytic activity owing to the DES, increasing the depolymerization efficiency from negligible levels (using only EG) to complete conversion. Under optimal conditions, a Zn(OAc)2·2H2O : urea molar ratio of 1 : 1.5, reaction temperature of 180°C, and reaction time of 90 min, the PET conversion reached 100% with a bis(2-hydroxyethyl) terephthalate (BHET) yield of 63.8%. The structure of the recovered BHET monomer was verified by 1Hnuclear magnetic resonance spectroscopy. Furthermore, a synergistic mechanism involving the Lewis acidity of Zn2+ and the hydrogen-bonding network of urea is proposed to explain the superior catalytic performance. This work presents a cost-effective, green and highly efficient protocol for PET waste valorization.

The polyethylene terephthalate (PET) application has many challenges and potential due to its sustainability. The conventional PET degradation was developed for several technologies to get higher yield products of ethylene glycol, bis(2-hydroxyethyl terephthalate) and terephthalic acid. The chemical recycling of PET is reviewed, such as pyrolysis, hydrolysis, methanolysis, glycolysis, ionic-liquid, phase-transfer catalysis and combination of glycolysis–hydrolysis, glycolysis–methanolysis and methanolysis–hydrolysis. Furthermore, the reaction kinetics and reaction conditions were investigated both theoretically and experimentally. The recycling of PET is to solve environmental problems and find another source of raw material for petrochemical products and energy.

Alcoholysis of poly(ethylene terephthalate) (PET) waste to produce monomers, including methanolysis to yield dimethyl terephthalate (DMT) and glycolysis to generate bis-2-hydroxyethyl terephthalate (BHET), is a promising strategy in PET waste management. Here, we introduce an efficient PET-alcoholysis approach utilizing an oxygen-vacancy ( V o )-rich catalyst under air, achieving space time yield (STY) of 505.2 g DMT ·g cat −1 ·h −1 and 957.1 g BHET ·g cat −1 ·h −1 , these results represent 51-fold and 28-fold performance enhancements compared to reactions conducted under N 2 . In situ spectroscopy, in combination with density functional theory calculations, elucidates the reaction pathways of PET depolymerization. The process involves O 2 -assisted activation of CH 3 OH to form CH 3 OH * and OOH * species at V o -Zn 2+ –O–Fe 3+ sites, highlighting the critical role of V o -Zn 2+ –O–Fe 3+ sites in ester bond activation and C–O bond cleavage. Moreover, a life cycle assessment demonstrates the viability of our approach in closed-loop recycling, achieving 56.0% energy savings and 44.5% reduction in greenhouse-gas emissions. Notably, utilizing PET textile scrap further leads to 58.4% reduction in initial total operating costs. This research offers a sustainable solution to the challenge of PET waste accumulation. Polyester waste is increasingly accumulating in the environment, and alcoholysis recycling offers a sustainable management solution. This study demonstrates the use of an oxygen vacancy-rich catalyst to transform waste blended polyester/textiles into high-value monomers.

Plastic pollution has escalated into a critical global issue, with production soaring from 2 million metric tons in 1950 to 400.3 million metric tons in 2022. The packaging industry alone accounts for nearly 44% of this production, predominantly utilizing polyethylene terephthalate (PET). Alarmingly, over 90% of the approximately 1 million PET bottles sold every minute end up in landfills or oceans, where they can persist for centuries. This highlights the urgent need for sustainable management and recycling solutions to mitigate the environmental impact of PET waste. To better understand PET’s behavior and promote its management within a circular economy, we examined its chemical and physical properties, current strategies in the circular economy, and the most effective recycling methods available today. Advancing PET management within a circular economy framework by closing industrial loops has demonstrated benefits such as reduced landfill waste, minimized energy consumption, and conserved raw resources. To this end, we identified and examined various strategies based on R-imperatives (ranging from 3R to 10R), focusing on the latest approaches aimed at significantly reducing PET waste by 2040. Additionally, a comparison of PET recycling methods (including primary, secondary, tertiary, and quaternary recycling, along with the concepts of “zero-order” and biological recycling techniques) was envisaged. Particular attention was paid to the heterogeneous catalytic glycolysis, which stands out for its rapid reaction time (20–60 min), high monomer yields (>90%), ease of catalyst recovery and reuse, lower costs, and enhanced durability. Accordingly, the use of highly efficient oxide-based catalysts for PET glycolytic degradation is underscored as a promising solution for large-scale industrial applications.

In this study, the glycolysis of polyethylene terephthalate was studied in presence of deep eutectic solvents as catalyst. In the glycolysis of PET, five different deep eutectic solvents were synthesized using different hydrogen bond donors and acceptors. Among the synthesized DESs, the most efficient catalyst was found to be DES formed by potassium carbonate and ethylene glycol. Glycolysis reaction was performed between PET and ethylene glycol. The effects of process parameters such as temperature, ratio of EG/PET and ratio of DES/PET were examined. The maximum yield for monomer product, bis(2-hydroxyethyl) terephthalate was observed as 88% at the reaction temperature of 180 °C, ethylene glycol/deep eutectic solvent ratio of 15 and deep eutectic solvent/polyethylene terephthalate ratio of 6.

The recycling of polyethylene terephthalate (PET) waste plastics has garnered global attention as an essential area of research to address. Chemical upcycling methods, such as glycolysis, offers a visible solution by directly converting PET wastes into high-valued monomers, enabling their reintegration into the plastic life cycle. However, the recovery of metal salt catalyst and the thermal stability of organic catalyst pose challenges in PET glycolysis. Zeolites with strong Brønsted acid are widely used in the degradation of polyolefins, but in PET glycolysis, they face the problems of acid site mismatch and difficult contact with PET. In this work, nanosized FAU-type zeolite catalysts (100-FAU) were employed to carry out PET glycolysis, which were green synthesized at low temperature without organic template. In comparison to commercial FAU-type catalysts, 100-FAU exhibits enhanced Lewis acidity and basicity along with increased accessibility to active sites. The 100% degradation of PET was achieved within 1 h, resulting in a BHET yield of 64.2%. Prolonging the reaction time to 1.5 h led to an enhanced BHET yield of 72.1%. The quality of the primary product bis(2-hydroxyethyl) terephthalate (BHET) was verified through IR, DSC, and NMR characterizations. Furthermore, as a solid catalyst with high thermal stability, zeolite can be easily recovered via filtration and demonstrated stable performance over at least 5 cycles, and proved effective for glycolysis of commercially waste PET plastics. The acid–base dual-functional catalytic mechanism of Na-form FAU in PET glycolysis was proposed. Under its guidance, the promoting effect of other Na-form nanosized zeolites on PET degradation was verified.

The waste management of polyethylene terephthalate (PET)–derived polyester (PES) textile is a global issue, and material recovery through chemical recycling can restore a circular economy. In our investigation, microwave-induced catalytic aminolysis and glycolysis of PES textile wastes using Ag-doped ZnO nanoparticles have been proposed. Ag-doped ZnO is prepared by the sol-gel method and characterised by XRD, FT-IR, UV-Vis, SEM-EDX and TEM. The reaction parameters such as PET-to-catalyst ratio, microwave power and irradiation time, temperature and catalyst recycling have been optimised. The catalyst was found to be more stable and could be recycled up to six times without losing its activity. Both the aminolysis and glycolysis of PES showed 100% conversion and afforded of bis (2-hydroxy ethylene) terephthalamide (BHETA) and bis (2-hydroxy ethylene) terephthalate (BHET), respectively. The depolymerisation of PES wastes using Ag-doped ZnO afforded BHETA and BHET for about 95 and 90%, respectively. The monomers BHET and BHETA confirmed by FT-IR, 1 H NMR and mass spectroscopy. According to the findings, 2 mol% Ag-doped ZnO has higher catalytic activity. Graphical abstract

Widely used poly(ethylene terephthalate) (PET) material induces environmental concern on its wastes. In this paper, different 1-hexyl-3-methylimidazolium (Hmim) halometallates, including [Hmim]ZnCl3, [Hmim]CoCl3, [Hmim]FeCl4 and [Hmim]CuCl3, are synthesized as Lewis acidic ionic liquids (LAIL) catalysts for PET degradation in excess ethylene glycol (EG). By using individual or mixed LAIL catalysts, product bis(hydroxyethyl) terephthalate (BHET) is characterized by FT-IR, 1H-NMR and DSC et al. From the PET conversion and yield of BHET product, a synergistic effect is found in mixed [Hmim]ZnCl3 and [Hmim]CoCl3 complexes. 87.1% BHET from original PET wastes catalyzed by equimolar [Hmim]ZnCl3 and [Hmim]CoCl3 mixture is higher than any individual IL halometallate. The filter residues after removing the BHET products with different reacting time using [Hmim]ZnCl3 and [Hmim]CoCl3 as catalyst, respectively, are characterized by 1H-NMR. The area ratio of the methylene protons of COO–CH2 (δ = 4.30 ppm) and the aromatic protons of the benzene ring (δ = 8.12 ppm) of filter residues suggests that more by-products will be produced by [Hmim]ZnCl3 because of its relatively higher catalytic activity in the chain scission stage. The glycolysis synergy comes from the balance between high reactivity of [Hmim]ZnCl3 and high selectivity of [Hmim]CoCl3.

Polyethylene terephthalate (PET) is a versatile polymer widely used in textiles because of its chemical stability, mechanical strength, and ease of processing. However, the increasing consumption of PET, particularly in the textile industry, has led to significant environmental concerns owing to its resistance to degradation. To address these issues, chemical recycling methods, particularly glycolysis, have attracted attention for depolymerizing PET into valuable monomers for repolymerization. This review focuses on recent advances in catalysts for PET glycolysis, with special emphasis on their application in textile recycling. We categorized the catalysts into homogeneous and heterogeneous types and discussed their effectiveness in reducing the reaction temperatures and times, thereby decreasing energy consumption and operational costs. Although homogeneous catalysts achieved efficient depolymerization at lower temperatures, their post-reaction separation and purification steps remain challenging and costly. In contrast, heterogeneous catalysts offer simpler separation processes but require significant energy input. Research on the application of glycolytic catalysts in fiber recycling was also highlighted, considering the substantial use of PET in the textile industry. Finally, we suggested future research directions for developing cost-effective and sustainable catalysts that are applicable to PET fibers with the aim of enhancing the efficiency and environmental sustainability of PET recycling processes.

A flame retardant unsaturated polyester resin (UPR) was prepared by methods of glycolysis of recycled polyethylene terephthalate (r-PET) via propylene glycol (PG) and diphenylsilanediol (DDS) as mixed glycolysis agent and esterification of the glycolyzed products with maleic anhydride (MA). The chemical structures of glycolyzed products and the resulted UPRs were characterized by fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (1H-NMR). The peaks at the range of 540–465 cm−1 and 1643 cm−1 on the FTIR spectrum indicated the introduction of Si–O into the main chain of UPR/Si and the reaction between glycolyzed product and MA, respectively). The different amounts of aluminum hydroxide (ATH) was added in the resulted UPRs to obtain UPR composites. The effects of DDS ratio on the flame retardancy, thermal stability, mechanical properties of the resulted UPRs and their composites were investigated. The result showed that the flame retardancy of UPR composites was further improved by addition of ATH to the UPR composites. Finally, the synergistic flame retardant mechanism between DDS and ATH was discussed based on scanning electronic microscopy (SEM) morphologies and FTIR spectra of the residual char after horizontal burning tests (UL-94). It suggested that r-PET can be glycolyzed successfully with PG and DDS as mixed glycolysis agent and the flame retardancy of the resulted UPR based on the glycolyzed products and their composites were improved due to incorporation of DDS in the main chain of UPR and the addition of ATH.