Bis(2-hydroxyethyl) Terephthalate Research Articles

Enhanced degradation of polyethylene terephthalate (PET) microplastics by an engineered Stenotrophomonas pavanii in the presence of biofilm.

Polyethylene terephthalate (PET) microplastics pose significant environmental and human health risks due to their resistance to degradation and accumulation in ecosystems. In this study, we engineered Stenotrophomonas pavanii JWG-G1, a robust biofilm-forming bacterium, to overexpress the PET hydrolase (DuraPETase) for PET microplastics degradation at ambient temperature. Nine endogenous PET hydrolases were identified through genome sequencing of S. pavanii, and were successfully expressed in Escherichia coli BL21(DE3). Among them, hydrolase Est_B achieved 100 % degradation of bis(2-hydroxyethyl) terephthalate (BHET) at an initial concentration of 0.23 mg/mL at 30 °C within 4 h, identifying it as a novel BHETase. However, the PET degradation performance of all endogenous PET hydrolases was inferior to that of DuraPETase. The engineered strain overexpressing DuraPETase demonstrated a significant enhancement in PET degradation, achieving a 38.04 μM total product release of high-crystallinity PET microplastics after 30 days at 30 °C. The degradation extent was greater than that of low biofilm-forming engineered strains, attributing to the aggregation of DuraPETase on the PET surface in the presence of biofilm. Additionally, this engineered strain also maintained PET degradation activity across various water environments and demonstrated effectiveness in degrading other polyester plastics. This is the first report demonstrating that an engineered strain of Stenotrophomonas species is capable of simultaneously secreting exogenous hydrolase and degrading polyester microplastics, representing a novel approach in the development of engineered bacteria with potential applications in bioreactor systems and environmental remediation.

Unravelling biochemical and molecular mechanism of a carboxylesterase from Dietzia kunjamensis IITR165 reveal novel activities against polyethylene terephthalate

Plastics and plasticizers accumulate in the ecological niches affecting biodiversity, and human and environmental health. Bacteria degrading polyethylene terephthalate (PET) were screened and PETases involved in PET degradation were characterized. Here, we identified a carboxylesterase Dkca1 of 48.44 kDa molecular mass from Dietzia kunjamensis IITR165 shown to degrade amorphous PET film into bis(2-hydroxyethyl) terephthalate (BHET) and terephthalic acid (TPA) formed 64.35 μM and 35.26 μM, respectively within 96 h at 37 °C as revealed by LC-MS analysis showed significant PET hydrolase activity similar to reported PETases. SEM analysis confirms the surface erosion as cavities and holes. Dkca1 also hydrolysed BHET and dibutyl phthalate (DBP) at a concentration of 1 mM within 3 h indicating its versatility. Fluorescence quenching shows Dkca1 protein has a maximum affinity (Kd) towards BHET (86.55 μM) than DBP (134.2 μM). The protein demonstrated high stability under temperatures above 40 °C and at the pH range of 6.0–9.0. Moreover, Amino acid composition showed that the Dkca1 enzyme belongs to family VII carboxylesterase containing conserved catalytic triad of Ser183-Glu289-His378 with pentapeptide motif GXSAG and an oxyanion hole H103GGG106, sharing 37.47 % and 32.44 % similarity with a PET hydrolase TfCa from Thermobifida fusca and PAE hydrolase CarEW from Bacillus sp. K91, respectively. A docking study revealed that ligand PET, BHET, and DBP showed favourable binding in the catalytic pocket of the Dkca1 protein.

Sustainable recovery of monomers from PET and PC waste via Thermocatalytic depolymerization for synthesis of polycarbonates and co-polycarbonates

The increasing global demand for sustainable plastics recycling methods has propelled the research and development of innovative depolymerization processes. The Thermocatalytic depolymerization (TCDP) of polyethylene terephthalate (PET) and polycarbonate (PC) has been performed at 200 ℃. Ethylene glycol (EG) is used as a reactant and as well a polymer bond-cleaving agent and Yttrium Oxide (Y2O3) is used as an effective catalyst. Y2O3 acted as a dual role during depolymerization reaction, which converts EG into cyclic ethylene oxide (CEO) and as well as to break the ester and carbonate bonds in the polymer structure of PET and PC respectively. The TCDP reaction conditions were optimized and the maximum quantity of Bis(2-hydroxyethyl) terephthalate (BHET) (80%) and (Bisphenol A (BPA)) (83%) has been recovered by TCDP reaction of PET and PC respectively. The polycarbonate and co-polycarbonate (Co-PC) were synthesized using recovered BPA and BHET with triphosgene via polycondensation reaction. The structure of monomers and polymers was confirmed by existing analytical (FTIR, NMR, XRD and GPC) techniques. The thermal properties of PC and Co-PC were performed by TG analysis. The TGA results reveal that the degradation temperature (Td) of PC and Co-PC are observed at 420.5 and 442.8 °C respectively, which shows that the Td of Co-PC has been increased by 22 ℃ than PC. The TCDP process is an effective method to recover specific value-added products from waste plastics, which could be made into a new versatile material for different applications. This research finding will provide a new direction to convert plastic waste into useful chemicals, which could reduce waste plastic and their carbon footprint and contribute to a more sustainable future by reusing plastic materials and achieving a circular economy.

Engineering dual-functional and thermophilic BMHETase for efficient degradation of polyethylene terephthalate

Polyethylene terephthalate (PET) biodegradation is hindered by the intermediates bis (2-hydroxyethyl) terephthalate (BHET) and mono (2-hydroxyethyl) terephthalate (MHET). BMHETase, a thermophilic hydrolase identified from the UniParc database, exhibits degradation activity towards both BHET and MHET. BMHETase showed higher activity on BHET than LCCICCG and FASTPETase at temperatures ranging from 50 to 70℃. To enhance its activity in degrading MHET, BMHETase was engineered to mimic Ideonella sakaiensis MHETase. The resulting 6-point mutant’s activities on MHET and BHET were 8 and 2 times those of the WT, with both optimal temperatures increased by 5℃. This enhancement may be attributed to the BMHETase6M’s intensified binding ability with MHET and enlarged binding pocket. When combined with LCCICCG, BMHETase6M achieved complete degradation of MHET in PET films to terephthalic acid, indicating broad application potential. These findings suggest that BMHETase6M holds promise as a candidate for enhancing PET biodegradation efficiency and plastic waste management.

Converting Waste Polyethylene Terephthalate to High Value Monomers by Synergistic Catalysts.

Waste plastics accumulation, such as commonly used polyethylene terephthalate (PET), has caused serious environmental pollution and resource squander. Glycolysis is a reliable closed-loop PET recycling method, which limited by the high cost and complex catalysts preparation processes. Here we report a simple synergistic catalytic strategy by premixing zinc acetate and cheap alkalis in ethylene glycol, which could achieve complete glycolysis at 180 ℃ within 2 hours, and a bis(hydroxyethyl) terephthalate (BHET) yield of 86.4%. This may be attributed to the free hydroxide ions not only enhancing the nucleophilicity of oxygen in ethylene glycol and making it easy to attack carbonyl groups, but also accelerating the swelling and dissolution of PET. Meanwhile, the in-situ generated Zn-glycolate and zinc oxide nanoparticles (ZnO NPs) activated the oxygen in the carbonyl group, making the carbon cations more electropositive. Further recycling experiments and techno-economic analysis indicated that our synergistic strategy significantly reduced industrial costs and expected to achieve large-scale industrial applications.

Chemical recycling of polyethylene terephthalate using a micro-sized MgO-incorporated SiO2 catalyst to produce highly pure bis(2-hydroxyethyl) terephthalate in high yield

Chemical recycling is a feasible method for achieving the closed-loop recycling of polyethylene terephthalate (PET). In this strategy, post-consumer PET is depolymerized to bis(2-hydroxyethyl) terephthalate (BHET) via glycolysis, which is then repolymerized to yield recycled PET (rPET). Herein, we introduce an innovative approach for the chemical recycling of PET that focuses on glycolysis facilitated by a microsized MgO-incorporated SiO2 catalyst. This choice of catalyst is groundbreaking owing its superior glycolysis-catalysis efficiency and the ease with which it can be separated from the reaction mixture, thereby addressing the common challenges faced by traditional catalysts during PET depolymerization. By employing a heterogeneous catalyst with significantly larger particles than a conventional catalyst, we not only aimed to simplify the catalyst-removal process, thereby improving BHET purity, but also observed enhanced efficiency during the catalytic reaction that led to a superior yield of the desired product. The catalyst was synthesized using a wet impregnation method and its efficiency was evaluated at various reaction times and dosages, which revealed that the microsized MgO/SiO2 catalyst significantly outperforms traditional catalysts, to deliver a 95.1% yield of BHET with negligible amounts of metal detected in the final product. This study not only demonstrated the potential of microsized catalysts during PET glycolysis, but also contributes to the advancement of sustainable PET-recycling practices. We anticipate that the microsized MgO/SiO2 catalyst is a promising alternative for the industrial upcycling of PET waste.

PET Glycolysis to BHET Efficiently Catalyzed by Stable and Recyclable Pd-Cu/γ-Al2O3.

Glycolysis of poly(ethylene terephthalate) (PET) is a prospective way for degradation of PET to its monomer bis(hydroxyethyl) terephthalate (BHET), providing the possibility for a permanent loop recycling. However, most reported glycolysis catalysts are homogeneous, making the catalyst difficult to recover and contaminating the products. Herein, we reported on the Pd-Cu/γ-Al2O3 catalyst and applied it in the glycolysis of PET as catalyst. The formed structure gave Pd-Cu/γ-Al2O3 a high active surface area, which enabled these micro-particles to work more efficiently. The PET conversion and BHET yield reached 99% and 86%, respectively, in the presence of 5 wt% of Pd-Cu/γ-Al2O3 catalyst within 80 min at 160 °C. After the reaction, the catalyst can be quickly separated by filtration, so it can be easily reused without significant loss of reactivity at least five times. Therefore, the Pd-Cu/γ-Al2O3 catalyst may contribute to an economically and environmentally improved large-scale recycling of PET fiber waste.

Crystallization of Bis(2-hydroxyethylene) Terephthalate as a Part of a Bottle-to-Bottle Recycling Concept for Poly(ethylene terephthalate).

The chemical recycling of poly(ethylene terephthalate) (PET) is very attractive as PET bottle waste provides an abundant clean material with low levels of additives. One of the most promising processes is glycolysis, which depolymerizes PET in the presence of ethylene glycol. For this process, it is necessary to think through the whole concept, from the waste material to the newly polymerized virgin polymer. Most research ends with determining the yield of bis(2-hydroxyethyl)terephthalate (BHET) after glycolysis. Some research includes antisolvent crystallization with water to separate BHET from ethylene glycol. However, the subsequent separation of water and ethylene glycol is an energy-intensive process. Therefore, this work aims to directly crystallize BHET from ethylene glycol. For this reason, the crystallization of BHET was investigated experimentally. Crystallization was simulated using gPROMS Formulated Products with the aim of estimating kinetic parameters and using these to optimize an industrial process. Kinetic parameters were determined by model validation, including primary and secondary nucleation and crystal growth. The best-fitting set of kinetic parameters was used to optimize BHET crystallization in batch and continuous modes by minimizing equipment costs. Impeller parameters were found to have a great influence on crystallization performance. Ultimately, the continuous and batch processes gave comparable results in terms of equipment cost, with the batch process giving larger crystals and higher yields but the continuous process requiring a smaller crystallizer.

Dual-porous ZIF-8 heterogeneous catalysts with increased reaction sites for efficient PET glycolysis

Poly (ethylene terephthalate) (PET) has been widely used for drink bottles, food packing, films, and fibers, resulting in millions of tons of waste PET. Less than 10% of that waste is recycled, and the rest is discarded or incinerated. Waste PET upcycling employs chemical recycling and particularly glycolysis to create the bis(2-hydroxyethyl) terephthalate (BHET) monomer. Herein, we report a dual-porous zeolitic imidazolate framework-8 nanoparticle (DPZIF-8) heterogeneous catalyst for efficient PET glycolysis. The DPZIF-8 nanoparticles were prepared using a triethylamine modulator, which can control the nucleation and growth mechanisms of the ZIF-8 nanoparticles. The DPZIF-8 nanoparticles include both intrinsic micropores and particle-particle adhesion-induced mesopores that can provide a larger external surface area of the zinc sites in the ZIF-8 architecture. The PET glycolysis catalyzed by DPZIF-8 at 180 °C and 1 atm for 4 h shows a PET conversion of 91.7% and a BHET yield of 76.1%, the latter particularly being much higher than with a traditional heterogeneous ZIF-8 catalyst. This dual-porous structure rational design strategy can be versatile for other metal–organic frameworks (MOFs) to increase the interfacial catalytic reaction sites between the metal–organic framework and the polymer, enhancing the PET depolymerization performance and efficiency.

Depolymerization mechanisms and closed-loop assessment in polyester waste recycling

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 (Vo)-rich catalyst under air, achieving space time yield (STY) of 505.2 gDMT·gcat−1·h−1 and 957.1 gBHET·gcat−1·h−1, these results represent 51-fold and 28-fold performance enhancements compared to reactions conducted under N2. In situ spectroscopy, in combination with density functional theory calculations, elucidates the reaction pathways of PET depolymerization. The process involves O2-assisted activation of CH3OH to form CH3OH* and OOH* species at Vo-Zn2+–O–Fe3+ sites, highlighting the critical role of Vo-Zn2+–O–Fe3+ 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.

DFT study on the depolymerization of PET by Ca-catalyzed glycolysis reaction model

Poly(ethylene terephthalate) (PET) is the most common plastics produced for applications in food and drinking containers. It is degraded to valuable product by several methods. Glycolysis of PET gains bis(2-hydroxyethylene) terephthalate (BHET) as the main product utilized as plasticizer. Calcium catalysts, Ca2+ and Ca(OH)2∙2H2O were explored to study the mechanism of PET cleavage by DFT calculations at B3LYP/6-311++G** level. Two possible pathways, coordination, and non-coordination of ethylene glycol on the calcium in glycolysis reaction, have been investigated. In addition, poly(ethylene furanoate) (PEF), considered as a sustainable polymer with the similar functional properties, was chose for the comparison of conformational structures with PET. The understanding of the relationship between PET (and PEF) structures and calcium catalysts is useful for the future development of linear sustainable polyesters.

Efficient biodegradation of Polyethylene terephthalate (PET) plastic by Gordonia sp. CN2K isolated from plastic contaminated environment

Since we rely entirely on plastics or their products in our daily lives, plastics are the invention of the hour. Polyester plastics, such as Polyethylene Terephthalate (PET), are among the most often used types of plastics. PET plastics have a high ratio of aromatic components, which makes them very resistant to microbial attack and highly persistent. As a result, massive amounts of plastic trash accumulate in the environment, where they eventually transform into microplastic (<5 mm). Rather than macroplastics, microplastics are starting to pose a serious hazard to the environment. It is imperative that these polymer microplastics be broken down. Through the use of enrichment culture, the PET microplastic-degrading bacterium was isolated from solid waste management yards. Bacterial strain was identified as Gordonia sp. CN2K by 16 S rDNA sequence analysis and biochemical characterization. It is able to use polyethylene terephthalate as its only energy and carbon source. In 45 days, 40.43 % of the PET microplastic was degraded. By using mass spectral analysis and HPLC to characterize the metabolites produced during PET breakdown, the degradation of PET is verified. The metabolites identified in the spent medium included dimer compound, bis (2-hydroxyethyl) terephthalate (BHET), mono (2-hydroxyethyl) terephthalate (MHET), and terephthalate. Furthermore, the PET sheet exposed to the culture showed considerable surface alterations in the scanning electron microscope images. This illustrates how new the current work is.

Continuous hydrothermal processing of poly(ethylene terephthalate) (PET) under subcritical water conditions: A proof-of-principle closed-loop study

Plastics have undeniably played a crucial role in the technological and societal advancements over the past decades. However, the current linear consumption model and the reliance of the plastic industry on fossil carbon pose pressing environmental and economic challenges that cannot be ignored. In this context, poly(ethylene terephthalate) (PET) has emerged as one of the most studied plastics in the field of chemical recycling, given its extensive use in packaging and textiles, and its susceptibility to undergo solvolysis into its constituent monomers, which facilitates closed-loop recycling of PET waste. This study presents the validation of a first-of-its-kind continuous flow system that utilizes subcritical water for neutral hydrothermal processing of PET at three different reaction temperatures 250, 280 and 310 °C. Regardless of the processing conditions, PET underwent full conversion into monomers and low molecular weight esters like mono(2-hydroxyethyl) terephthalate (MHET) and bis(2-hydroxyethyl) terephthalate (BHET), with an approximate carbon distribution of 20 % and 80 % between aqueous and solid products, respectively. The product composition is strongly related to the processing conditions, with 77.5 % ethylene glycol and 94.2 % terephthalic acid recovered as monomers at 310 °C. Furthermore, solid products were repolymerized to assess the potential of reusing the heterogeneous precursor mixture as starting material for PET production. Results reveal that the solid products obtained at 250 °C yielded polymer chains with decomposition temperature, melting temperature, crystallinity, and average molecular weight (50.4 kDa) closest to commercial PET. These results underscore the potential of neutral hydrothermal processing in a future circular PET value chain.

Insight into interface chemistry of metal oxides anchored on biowaste-derived support for highly selective glycolysis of waste polyethylene terephthalate

The unprecedented rise of polyethylene terephthalate (PET) waste demands sustainable solutions like catalytic glycolysis, a promising recycling technology that mitigates environmental harm. Herein, we synthesized a series of novel Mo-Zn@SiO2 catalysts for PET glycolysis, derived from readily available rice husk ash via the wetness impregnation method. The optimum Mo-Zn@SiO2 exhibits exceptional activity, achieving complete PET conversion and a 90.4 % yield of bis(2-hydroxyethyl) terephthalate (BHET) – one of the highest performances reported for heterogeneous catalysts. Density functional theory (DFT) calculations suggest that the formation of the ZnMoO4 phase optimizes reactant and product adsorption energies, enhancing Lewis acidity and facilitating depolymerization. Kinetic studies reveal a low apparent activation energy (139.27 kJ/mol) for BHET production at 175–190 °C. Additionally, the catalyst demonstrates excellent recyclability, maintaining activity after five cycles. This work presents a viable and efficient strategy for PET waste valorization using a low-cost, readily available, and easily synthesized catalyst.

Low-temperature one-step synthesis of surfactant-free ZnO nanoparticles for efficient glycolysis of PET

Among PET chemical recycling technologies, glycolysis has shown the greatest potential for achieving commercial viability on large scales. The catalyst development is always one of the challenges in PET glycolysis. Herein, surfactant-free ZnO nanoparticles (SF-ZnO) were synthesized through a one-step process in an aqueous medium at low temperatures and ambient pressure. Meanwhile, a microchannel reactor with intensified micro-mixing and mass transfer was used to finely control the synthesis of SF-ZnO with uniform size distribution and consistent production reproducibility. Compared to the modified ZnO nanoparticles (M−ZnO) treated with the surfactant KH570, SF-ZnO exhibited enhanced catalytic activity and reusability in PET glycolysis, which can be attributed to its higher concentration of acid sites and superior thermal stability. Response surface methodology (RSM) was employed to investigate the impact of four key factors (temperature, time, catalyst: PET mass ratio, EG: PET mass ratio) and their interactions on bis(2-hydroxyethyl) terephthalate (BHET) yield in PET glycolysis. Under optimal conditions (196 °C, 40 min, SF-ZnO: PET = 0.76 wt%, EG: PET = 4), PET conversion and BHET yield reached 100 % and 97.3 %, respectively. Aspen simulation and preliminary scale-up experiments confirmed the commercialization potential of PET glycolysis on SF-ZnO. Meanwhile, the environmental energy impact metric and life cycle assessment (LCA) showed that the SF-ZnO catalytic system provided an economically feasible and environmentally friendly solution to PET glycolysis.

A new strategy for PET depolymerization: Application of bimetallic MOF-74 as a selective catalyst

Large-volume production of poly(ethylene terephthalate) (PET), especially in the form of bottles and food packaging containers, causes problems with polymer waste management. Waste PET could be recycled thermally, mechanically or chemically and the last method allows to obtain individual monomers, but most often it is carried out in the presence of homogeneous catalysts, that are difficult to separate and reuse. In view of this, this work reports for the first time, application of bimetallic MOF-74 – as heterogeneous catalyst - for depolymerization of PET with high monomer (bishydroxyethyl terephthalate, BHET) recovery. The effect of type and amount of second metal in the MOF-74 (Mg/M) was systematically investigated. The results showed increased activity of MOF-74 (Mg/M) containing Co2+, Zn2+ and Mn2+ as a second metal, while the opposite correlation was observed for Cu2+ and Ni2+. It was found that the highest catalytic activity was demonstrated by the introduction of Mg–Mn into MOF-74 with ratio molar 1:1, which resulted in complete depolymerization of PET and 91.8% BHET yield within 4 h. Furthermore, the obtained catalyst showed good stability in 5 reaction cycles and allowed to achieve high-purity BHET, which was confirmed by HPLC analysis. The as-prepared MOF-74 (Mg/Mn) was easy to separate from the post-reaction mixture, clean and reuse in the next depolymerization reaction.

Enzyme_Metal-Organic Framework Composites as Novel Approach for Microplastic Degradation.

Plastic pollution is one of the main worldwide environmental concerns. Our lifestyle involves persistent plastic consumption, aggravating the low efficiency of wastewater treatment plants in its removal. Nano/microplastics are accumulated in living beings, pushing to identify new water remediation strategies to avoid their harmful effects. Enzymes (e. g., Candida rugosa-CrL) are known natural plastic degraders as catalysts in depolymerization reactions. However, their practical use is limited by their stability, recyclability, and economical concerns. Here, enzyme immobilization in metal-organic frameworks (CrL_MOFs) is originally presented as a new plastic degradation approach to achieve a boosted plastic decomposition in aqueous systems while allowing the catalyst cyclability. Bis-(hydroxyethyl)terephthalate (BHET) was selected as model substrate for decontamination experiments for being the main polyethylene terephthalate (PET) degradation product. Once in contaminated water, CrL_MOFs can eliminate BHET (37 %, 24 h), following two complementary mechanisms: enzymatic degradation (CrL action) and byproducts adsorption (MOF effect). As a proof-of-concept, the capacity of a selected CrL_MOF composite to eliminate the BHET degradation products and its reusability are also investigated. The potential of these systems is envisioned in terms of improving enzyme cyclability, reducing costs along with feasible co-adsorption of plastic byproducts and other harmful contaminants, to successfully remove them in a single step.

Chemical recycling of post-consumer poly(ethylene terephthalate) (PET) driven by the protic ionic liquid 2-HEAA: Performance, kinetics and mechanism

The circular economy is a paradigm for the upcoming industrial era, in which plastic wastes must be focused on as new resources. Chemical valorisation permits deepening into waste-to-gate schemes by obtaining new chemical platforms to be reintroduced in the production market. In this context, the potential of the protic ionic liquid 2-hydroxyethyl ammonium acetate (2-HEAA) to be used as a homogeneous catalytic co-solvent for the glycolytic conversion of post-consumer poly(ethylene terephthalate) (PET) was validated from different perspectives. Studies were performed for the reaction triplet framed under the experimental conditions (i) temperature T [160,170,180 ºC], (ii) plastic-to-solvent mass ratio P/S [1:3, 1:4,1:5] and (iii) plastic-to-ionic liquid mass ratio P/IL [2:1, 2:2, 2:3]. The reaction was confirmed in terms of the transformation of PET into BHET (bis(2-hydroxyethyl terephthalate) and a proposal of mechanism induced by the amine group of the 2-HEAA is given. The thermal kinetics were modelled and a first-order equation and an apparent activation energy of 60.5 kJ·mol-1 were obtained. A statistical Box-Behnken design of experiments explained the relationship between the factors of the glycolysis triplet by a response surface, with a maximum around {T = 170 ºC, P/S = 1:3.75 and P/IL = 2:1.75}, being T and P/S statistically relevant, whereas only the presence of 2-HEAA and not its amount P/IL was significant. Finally, the reusability of 2-HEAA after 90-min glycolytic chemical valorisations was confirmed up to 4 cycles. The results position 2-HEAA as a promising catalytic co-solvent for the scale-up of chemical valorisation of PET.

Efficient glycolysis of waste polyethylene terephthalate textiles over Zn-MCM-41 catalysts

Polyethylene terephthalate (PET), also known as polyester, is extensively utilized in the textile industry. The most commonly used chemical degradation method of PET is ethylene glycol (EG) glycolysis, which enables a closed-loop recovery process suitable for large-scale production. In this study, a new type of heterogeneous catalyst (Zn-MCM-41) was proposed for glycolysis of waste PET textiles, and their catalytic performance is much higher than other mesoporous zeolites. Under optimal reaction conditions, over Zn-MCM-41–25 (Si/Al molar ratio of 25) catalyst PET achieved a conversion ratio of 100 %, with bis-hydroxyethyl terephthalate (BHET) yield reaching 81.4 %. XPS results show that zinc is mainly presented as the state of Zn2+, resulting in excellent stability of the catalyst. HPLC and LCMS analyses were conducted on the products obtained from PET glycolysis, revealing that only a small amount of oligomers were generated during the process. These oligomers primarily consisted of dimer [BHET]2 and trimer [BHET]3. The Zn-MCM-41–25 catalyst also demonstrates exceptional performance in colored waste PET textiles glycolysis. Furthermore, we investigated the kinetics of PET glycolysis and determined it to follow first-order kinetics with an activation energy value of 210.03 kJ mol−1. Additionally, HPLC methods was established for analyzing glycolysis products and recovering catalysts using a simple filtration technique. The results demonstrate that even after five cycles, the catalyst maintains its high catalytic activity.

Characterization of Thermotoga maritima Esterase Capable of Hydrolyzing Bis(2-hydroxyethyl) Terephthalate.

The gene-encoding carboxylesterase (TM1022) from the hyperthermophilic bacterium Thermotoga maritima (T. maritima) was cloned and expressed in Escherichia coli Top10 and BL21 (DE3). Recombinant TM1022 showed the best activity at pH 8.0 and 85 °C and retained 57% activity after 8 h cultivation at 90 °C. TM1022 exhibited good stability at pH 6.0-9.0, maintaining 53% activity after incubation at pH 10.0 and 37 °C for 6 h. The esterase TM1022 exhibited the optimum thermo-alkali stability and kcat/Km (598.57 ± 19.97 s-1mM-1) for pN-C4. TM1022 hydrolyzed poly(ethylene terephthalate) (PET) degradation intermediates, such as bis(2-hydroxyethyl) terephthalate (BHET) and mono(2-hydroxyethyl) terephthalate (MHET). The Km, kcat, and kcat/Km values for BHET were 0.82 ± 0.01 mM, 2.20 ± 0.02 s-1, and 2.67 ± 0.02 mM-1 s-1, respectively; those for MHET were 2.43 ± 0.07 mM, 0.04 ± 0.001 s-1, and 0.02 ± 0.001 mM-1 s-1, respectively. When purified TM1022 was added to the cutinase BhrPETase, hydrolysis of PET from drinking water bottle tops produced pure terephthalic acids (TPA) with 166% higher yield than those obtained after 72 h of incubation with BhrPETase alone as control. The above findings demonstrate that the esterase TM1022 from T. maritima has substantial potential for depolymerizing PET into monomers for reuse.