Bis(2-hydroxyethyl) Terephthalate Research Articles

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_MOF) 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%, 24h), following two complementary mechanisms: enzymatic degradation (CrL action) and byproducts adsorption (MOF effect). As aproof-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 themin a single step.

Integrating glycolysis and enzymatic catalyst to convert waste poly(ethylene terephthalate) into terephthalic acid

The current society has an increasing demand for poly(ethylene terephthalate) (PET). Due to its high crystallinity and hydrophobicity, PET could be hardly degraded for high-value utilization. Besides, the escalating accumulation of waste PET has also led to significant environmental issues. In this study, a convenient and cost-efficient industrial strategy featuring the integration of glycolysis and enzymatic catalysis has been developed for the selective conversion of PET into terephthalic acid (TPA), which provides a method for colored waste PET degradation. Without the need for complex purifying processes, the products of glycolysis directly initiate the next round of the enzymatic system. Through this system, a total yield of 72.47 % of bis-2-(hydroxyethyl) terephthalate(BHET) and mono-(2-hydroxyethyl) terephthalate(MHET) was produced by glycolysis loading sodium bicarbonate (NaHCO3) catalyst, and the enzyme system almost completely converted a substrate concentration of 100 g/L within 48 h, producing 50.36 g/L TPA. Besides, the product problem of pink color in the air after acidification caused by cobalt ions was solved by resin adsorption. In general, the glycolysis and enzymatic catalysis system in this study has prospects for commercial application due to its value for colored waste PET recycling, which reduces the environmental burden caused by waste PET.

The comparative plastisphere microbial community profile at Kung Wiman beach unveils potential plastic-specific degrading microorganisms.

Plastic waste is a global environmental issue that impacts the well-being of humans, animals, plants, and microorganisms. Microplastic contamination has been previously reported at Kung Wiman Beach, located in Chanthaburi province along with the Eastern Gulf of Thailand. Our research aimed to study the microbial population of the sand and plastisphere and isolate microorganisms with potential plastic degradation activity. Plastic and sand samples were collected from Kung Wiman Beach for microbial isolation on agar plates. The plastic samples were identified by Fourier-transform infrared spectroscopy. Plastic degradation properties were evaluated by observing the halo zone on mineral salts medium (MSM) supplemented with emulsified plastics, including polystyrene (PS), polylactic acid (PLA), polyvinyl chloride (PVC), and bis (2-hydroxyethyl) terephthalate (BHET). Bacteria and fungi were identified by analyzing nucleotide sequence analysis of the 16S rRNA and internal transcribed spacer (ITS) regions, respectively. 16S and ITS microbiomes analysis was conducted on the total DNA extracted from each sample to assess the microbial communities. Of 16 plastic samples, five were identified as polypropylene (PP), four as polystyrene (PS), four as polyethylene terephthalate (PET), two as high-density polyethylene (HDPE), and one sample remained unidentified. Only 27 bacterial and 38 fungal isolates were found to have the ability to degrade PLA or BHET on MSM agar. However, none showed degradation capabilities for PS or PVC on MSM agar. Notably, Planococcus sp. PP5 showed the highest hydrolysis capacity of 1.64 ± 0.12. The 16S rRNA analysis revealed 13 bacterial genera, with seven showing plastic degradation abilities: Salipiger, Planococcus, Psychrobacter, Shewanella, Jonesia, Bacillus, and Kocuria. This study reports, for the first time of the BHET-degrading properties of the genera Planococcus and Jonesia. Additionally, The ITS analysis identified nine fungal genera, five of which demonstrated plastic degradation abilities: Aspergillus, Penicillium, Peacilomyces, Absidia, and Cochliobolus. Microbial community composition analysis and linear discriminant analysis effect size revealed certain dominant microbial groups in the plastic and sand samples that were absent under culture-dependent conditions. Furthermore, 16S and ITS amplicon microbiome analysis revealed microbial groups were significantly different in the plastic and sand samples collected. We reported on the microbial communities found on the plastisphere at Kung Wiman Beach and isolated and identified microbes with the capacity to degrade PLA and BHET.

Transesterification of Bis 2-Hydroxyethyl Terephthalate for Production of Bis 4-Hydroxybutyl Terephthalate over Homogenous Catalysts

Transesterification of Bis 2-Hydroxyethyl Terephthalate for Production of Bis 4-Hydroxybutyl Terephthalate over Homogenous Catalysts

Improving the Sustainability of Catalytic Glycolysis of Complex PET Waste through Bio-Solvolysis.

This work addresses a novel bio-solvolysis process for the treatment of complex poly(ethylene terephthalate) (PET) waste using a biobased monoethylene glycol (BioMEG) as a depolymerization agent in order to achieve a more sustainable chemical recycling process. Five difficult-to-recycle PET waste streams, including multilayer trays, coloured bottles and postconsumer textiles, were selected for the study. After characterization and conditioning of the samples, an evaluation of the proposed bio-solvolysis process was carried out by monitoring the reaction over time to determine the degree of PET conversion (91.3-97.1%) and bis(2-hydroxyethyl) terephthalate (BHET) monomer yield (71.5-76.3%). A monomer purification process, using activated carbon (AC), was also developed to remove the colour and to reduce the metal content of the solid. By applying this purification strategy, the whiteness (L*) of the BHET greatly increased from around 60 to over 95 (L* = 100 for pure white) and the Zn content was significantly reduced from around 200 to 2 mg/kg. The chemical structure of the purified monomers was analyzed via infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC), and the composition of the samples was measured by proton nuclear magnetic resonance (1H-NMR), proving a high purity of the monomers with a BHET content up to 99.5% in mol.

Morphology control of waste polyesters for enhanced glycolysis reactivity and minimization of side reactions

Effective pretreatment routes using dimethyl sulfoxide (DMSO) as solvent were accomplished to enhance the polyethylene terephthalate (PET) glycolysis rate. Highly ordered structure PET flakes were dissolved in DMSO at high temperatures, followed by solid–liquid separation using two different methods to generate micro-sized powders. Under identical glycolysis conditions, the reaction time of pretreated PET powders was gradually reduced by approximately five times that of PET flakes. During the glycolysis of PET with ethylene glycol (EG), diethylene glycol-containing terephthalate compounds (DCTC) are formed as undesired byproducts at high temperatures. These byproducts significantly affect the overall quality of BHET. Consequently, pretreated PET degradation under mild conditions was employed as a preventive measure against EG dehydration, leading to the production of DCTC. PET powders with controlled morphology exhibit outstanding performance and achieve a 100 % PET conversion at 180 °C to DCTC-free bis(2-hydroxyethyl) terephthalate (BHET). The purity of the obtained BHET was characterized using proton–NMR spectroscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The utilization of this technology presents a potential solution for overcoming the technical and economic challenges associated with current PET upcycling methodologies.

Envisioning a BHET Economy: Adding Value to PET Waste

Poly(ethylene terephthalate), the fifth most produced polymer, generates significant waste annually. This increased waste production has spurred interest in chemical and mechanical pathways for recycling. The shift from laboratory settings to larger-scale implementation creates opportunities to explore the value and recovery of recycling products. Derived from the glycolysis of PET, bis(2-hydroxyethyl) terephthalate (BHET) exhibits versatility as a depolymerization product and valuable monomer. BHET exhibits versatility and finds application across diverse industries such as resins, coatings, foams, and tissue scaffolds. Incorporating BHET, which is a chemical recycling product, supports higher recycling rates and contributes to a more sustainable approach to generating materials. This review illuminates the opportunities for BHET as a valuable feedstock for a more circular polymer materials economy.

Integrating experimental and computational approaches for deep eutectic solvent-catalyzed glycolysis of post-consumer polyethylene terephthalate

To achieve a sustainable and circular economy, developing effective plastic recycling methods is essential. Despite advances in the chemical recycling of plastic waste, modern industries require highly efficient and sustainable solutions to address environmental problems. In this study, we propose an efficient glycolysis strategy for post-consumer polyethylene terephthalate (PET) using deep eutectic solvents (DESs) to produce bis(2-hydroxyethyl) terephthalate (BHET) with high selectivity. Choline chloride (ChCl)- and urea-based DESs were synthesized using various metal salts and were tested for the glycolysis of PET waste; ChCl–Zn(OAc)2 exhibited the best performance. The DES-containing solvent system afforded a complete PET conversion, producing BHET at a high yield (91.6%) under optimal reaction conditions. The degradation mechanism of PET and its interaction with DESs were systematically investigated using density functional theory-based calculations. Furthermore, an intuitive machine learning model was developed to predict the PET conversion and BHET selectivity for different DES compositions. Our findings demonstrate that the DES-catalyzed glycolysis of post-consumer PET could enable the development of a sustainable chemical recycling process, providing insights to identify the new design of DESs for plastic decomposition.

The “De−Re Polymerization” Strategy: From Nondegradable Pet to Degradable Peat

AbstractPolyethylene terephthalate (PET) is a widely used plastic, but its short service life and non‐degradable features make it a major source of white pollution. In this context, the efficient recycling and rational reuse of PET have become a global research priority. In this paper, a deep eutectic solvent（DES）is prepared using methylurea and zinc chloride to catalyze the efficient PET glycolysis, which produces a high purity product bis(2‐hydroxyethyl) terephthalate (BHET), in 83.75% of yield. The product is condensed with diethyl adipate to produce Poly (ethyleneadipate‐co‐terephthalate) (PEAT). The relationships between the structural, thermal, mechanical, and degradation properties of PEAT with different intrinsic viscosities and composition ratios are studied. The addition of benzene ring improves the thermal properties and tensile strength of PEAT, but also makes them stiffer and less degradable. An increase in intrinsic viscosity can improve the thermal and mechanical properties to some extent but has little effect on the degradation. In general, the PEAT produced by the above process has good thermal properties, controllable degradation properties, and better mechanical properties than Poly (butyleneadipate‐co‐terephthalate) (PBAT). This work achieves the conversion of waste PET to high value‐added PEAT and has potential development prospects in recycling of PET.

Enhancing polyethylene terephthalate conversion through efficient microwave-assisted deep eutectic solvent-catalyzed glycolysis

Chemical recycling of plastics is a promising approach for effectively depolymerizing plastic waste into its constituent monomers, thereby contributing to the realization of a sustainable circular economy. Glycolysis, which converts polyethylene terephthalate (PET) into the monomer bis(2-hydroxyethyl) terephthalate (BHET), has emerged as a cost-effective and commercially viable chemical recycling process. However, glycolysis requires long reaction times and high energy consumption, limiting its industrialization. In this study, we develop an energy-efficient microwave-assisted deep eutectic solvent-catalyzed glycolysis method to degrade PET effectively and rapidly, resulting in a high BHET yield. This combined approach enables the quantitative degradation of PET within 9 min, achieving a high BHET yield of approximately 99% under optimal reaction conditions. Furthermore, the proposed approach has a low specific energy consumption (45 kJ/g) and minimizes waste generation. The thermal behavior of PET and its degradation mechanism are systematically investigated using scanning electron microscopy and density functional theory-based calculations. The results obtained suggest that the proposed straightforward, swift, and energy-efficient strategy has the potential to offer a sustainable solution to plastic waste management challenges and expedite the industrialization of chemical recycling.

Expression and engineering of PET-degrading enzymes from Microbispora, Nonomuraea, and Micromonospora.

Mismanagement of PET plastic waste significantly threatens human and environmental health. Together with the relentless increase in plastic production, plastic pollution is an issue of rising concern. In response to this challenge, scientists are investigating eco-friendly approaches, such as bioprocessing and microbial factories, to sustainably manage the growing quantity of plastic waste in our ecosystem. Industrial applicability of enzymes capable of degrading PET is limited by numerous factors, including their scarcity in nature. The objective of this study is to enhance our understanding of this group of enzymes by identifying and characterizing novel enzymes that can facilitate the breakdown of PET waste. This data will expand the enzymatic repertoire and provide valuable insights into the prerequisites for successful PET degradation.

Synergistic catalysis of ionic liquids and metal salts for facile PET glycolysis

Polyethylene terephthalate (PET), a thermoplastic engineering polyester, is one of the most widely used polymers today. However, PET can be recycled and difficult to degrade under atmospheric conditions due to high chemical stability, causing problems such as environmental pollution and waste of resources. Through comparative experiments, it was found that protic ionic liquids (PIL) and transition metal salts have a synergistic catalytic effect, under optimal reaction conditions, PET was subjected to glycolysis at 180 °C for 20 min by using PIL-Zn(OAc)2 as a catalyst, PET was almost completely converted and the yield of monomeric BHET reached a peak of 91.25 %, this is much higher than the yield using ionic liquids or metal salts alone. In this paper, protic ionic liquids were synthesized and compounded with transition metal salts as catalysts for PET glycolysis. Through FT-IR, NMR, TG and SEM analysis of the experimental product, it can be determined that the target product is bis-hydroxyethyl terephthalate (BHET). The composite catalyst still exhibited excellent catalytic activity after 8 cycles. Further, this study explored the reaction kinetics of PIL-Zn(OAc)2 catalyzed PET glycolysis to obtain an apparent activation energy Ea = 120.59 kJ/mol of the reaction. Finally, this paper also discussed the possible reaction pathway of the composite catalyst, hoping this composite catalyst can provide a reference for the industrialization of PET recycling.

Sustainable PET Waste Recycling: Labels from PET Water Bottles Used as a Catalyst for the Chemical Recycling of the Same Bottles.

We report using a waste material, poly(ethylene terephthalate) (PET) water bottle labels, for the chemical recycling of the same PET water bottles. The solid fillers used for the manufacturing of the packaging labels were recovered by thermolysis in an electrical furnace at 600, 800, and 1000 °C with 13.5, 12.0, and 10.4 wt % recovery. Characterization of the solid residue showed the presence of calcium carbonate, calcium oxide, and titanium dioxide, which are typical fillers used for packaging film manufacturing, such as water bottle labels. These solid residues were then used as a catalyst for PET depolymerization by glycolysis, in which the catalyst recovered from bottle labels and shredded PET reacted in the presence of excess ethylene glycol at 200 °C. The reaction mixtures were analyzed for PET conversion and the yield of the bis(2-hydroxyethyl)terephthalate (BHET) monomer as the final product of the glycolysis reaction to determine the efficiency of the catalyst. Our results show that the catalyst prepared at 800 °C (Cat-800) has the best performance and provides a 100% PET conversion with a 95.8% BHET yield with a 1.0 wt % loading in 1.5 h. The catalyst from the PET water bottle labels is nontoxic, readily available, cost-effective, environmentally friendly, and can be used as a model for the self-sufficient chemical recycling of PET via glycolysis.

Chemical recycling of polyethylene terephthalate (PET) to monomers: Mathematical modeling of the transesterification reaction of bis(2-hydroxyethyl) terephthalate to dimethyl terephthalate

The accumulation of plastic waste in the environment is making recycling a compelling issue, particularly for polyethylene terephthalate (PET), used in products with a short shelf-life. An appealing route to chemical recycling of PET is glycolysis, leading to bis(2-hydroxyethyl) terephthalate (BHET). Its subsequent transesterification with methanol to dimethyl terephthalate (DMT) is crucial for the recovery of polymer-grade monomers. To favor the industrial applicability of this process, this work investigates the influence of three main parameters, i.e. the methanol to ethylene glycol molar ratio, the solvent to oligomers molar ratio and the mass fraction of the catalyst, on the transesterification of BHET to DMT. A kinetic model has been proposed, and the reaction rates evaluated by comparison with the experimental data. The model was used to predict the performances of the process in a wide range of operating conditions, in order to establish the optimal ones for high yield to DMT.

Two-Step Chemo-Microbial Degradation of Post-Consumer Polyethylene Terephthalate (PET) Plastic Enabled by a Biomass-Waste Catalyst.

Polyethylene terephthalate (PET) pollution has significant environmental consequences; thus, new degradation methods must be explored to mitigate this problem. We previously demonstrated that a consortium of three Pseudomonas and two Bacillus species can synergistically degrade PET in culture. The consortium more readily consumes bis(2-hydroxyethyl) terephthalate (BHET), a byproduct created in PET depolymerization, compared to PET, and can fully convert BHET into metabolically usable monomers, namely terephthalic acid (TPA) and ethylene glycol (EG). Because of its crystalline structure, the main limitation of the biodegradation of post-consumer PET is the initial transesterification from PET to BHET, depicting the need for a transesterification step in the degradation process. Additionally, there have been numerous studies done on the depolymerization reaction of PET to BHET, yet few have tested the biocompatibility of this product with a bacterial consortium. In this work, a two-step process is implemented for sustainable PET biodegradation, where PET is first depolymerized to form BHET using an orange peel ash (OPA)-catalyzed glycolysis reaction, followed by the complete degradation of the BHET glycolysis product by the bacterial consortium. Results show that OPA-catalyzed glycolysis reactions can fully depolymerize PET, with an average BHET yield of 92% (w/w), and that the reaction product is biocompatible with the bacterial consortium. After inoculation with the consortium, 19% degradation of the glycolysis product was observed in 2 weeks, for a total degradation percentage of 17% when taking both steps into account. Furthermore, the 10-week total BHET degradation rate was 35%, demonstrating that the glycolysis products are biocompatible with the consortium for longer periods of time, for a total two-step degradation rate of 33% over 10 weeks. While we predict that complete degradation is achievable using this method, further experimentation with the consortium can allow for a circular recycling process, where TPA can be recovered from culture media and reused to create new materials.

Novel dragon fruit peel ash-derived solid catalyst for biodiesel production and PET waste recycling

The present protocol demonstrates the development of an affordable methodology for synthesizing biodiesel and depolymerizing PET waste using dragon fruit (Hylocereus costaricensis or Hylocereus polyrhizus) peel ash derived solid catalyst. The reported catalytic process yielded 99 % biodiesel at room temperature in 5 h with 8 wt% catalyst amounts and 12 M equivalents of methanol, while requiring just 20 min of run time at an elevated temperature (65 °C). The reaction was found to be endothermic pseudo-first order reaction having activation energy of 56.36 kJ mol−1. Meanwhile, PET waste was depolymerized to bis(2-hydroxyethyl) terephthalate (BHET) in 1.5 h at 190 °C with 16 equivalents of ethylene glycol and 4 wt% of the catalyst, giving 84 % of the desired monomer. The developed catalyst and the resultant products are thoroughly characterized using a variety of techniques to determine the catalyst's chemical composition and to confirm the formation of the desired products.

NIR light-induced functionalized MXene as a dynamic-crosslinker for reinforced polyurethane composites with shape memory and self-healing

Near infrared (NIR) light-driven shape memory can expand the potential of polyurethane as advanced materials. Herein, polyurethane composites (PU/B-THDI/FMXene) with Diels-Alder (D-A) reversible crosslinking feature were fabricated in combination with internal crosslinker bis(2-hydroxyethyl) terephthalate (BHET) modified hexamethylene-diisocyanate trimer (B-THDI), and functionalized MXene (FMXene). FMXene was prepared via 3-isocyanatopropyltriethoxysilane (IPTS) as a coupling agent between MXene and furfuryl alcohol (FA) through covalent bonds, thereby enabling dynamic crosslinking. FMXene can not only form D-A dynamic-crosslinked network with PU chain, but also retain excellent thermal conductivity. Only containing 2 wt% FMXene endows PU/B-THDI/FMXene2 composites with fast shape memory (<15 s, shape-fixity and recovery rates are 88.1 % and 97.8 %, respectively), self-healing (<100 s, the healing efficiency for tensile strength and elongation at break are 88.0 % and 91.0 %, respectively), good self-healing repeatability (79.1 %) and thermal conductivity (0.661 W m−1 K−1). Moreover, PU/B-THDI/FMXene2 exhibits remarkable mechanical performances (tensile strength of 16.9 MPa and elongation at break of 233.9 %) and thermal stability. In addition, B-THDI with crosslinking and toughening effects provides certain strength and flexibility for PU. Thus, this work may open new approaches for developing photothermal-induced shape memory polyurethane.

Characterization of a novel esterase and construction of a Rhodococcus-Burkholderia consortium capable of catabolism bis (2-hydroxyethyl) terephthalate

Bis (2-hydroxyethyl) terephthalate (BHET) is one of the main compounds produced by enzymatic hydrolysis or chemical depolymerization of polyethylene terephthalate (PET). However, the lack of understanding on BHET microbial metabolism is a main factor limiting the bio-upcycling of PET. In this study, BHET-degrading strains of Rhodococcus biphenylivorans GA1 and Burkholderia sp. EG1 were isolated and identified, which can grow with BHET as the sole carbon source. Furthermore, a novel esterase gene betH was cloned from strain GA1, which encodes a BHET hydrolyzing esterase with the highest activity at 30 °C and pH 7.0. In addition, the co-culture containing strain GA1 and strain EG1 could completely degrade high concentration of BHET, eliminating the inhibition on strain GA1 caused by the accumulation of intermediate metabolite ethylene glycol (EG). This work will provide potential strains and a feasible strategy for PET bio-upcycling.

Immobilization of the Lipase B from Candida antarctica on Urban Solid Waste

The adsorption of the lipase B from Candida antarctica (CALB) over polyethylene terephthalate (PET), polypropylene (PP), and derivatives, abundant components of urban solid waste (USW), was investigated. The characterization of the supports and biocatalysts synthesized by SEM-EDS and FTIR is presented. Two immobilization strategies were evaluated, conventional and total adsorption. The adsorbed protein was determined by Bradford and through high-resolution inductively coupled plasma atomic emission spectroscopy (ICP-AES). In this sense, the adsorption of CALB in all the proposed supports was evidenced, obtaining the highest protein loads in bis-(2-hydroxyethyl) terephthalate (BHET). Subsequently, the biocatalysts were applied to the esterification of rac-ibuprofen with ethanol. CALB immobilized in BHET showed remarkable activity, achieving conversions of 30%. In this context, immobilization on this support was optimized, studying the addition of sorbitol-glycerol. Thus, in the presence of 0.91 g of polyols, a catalyst with a protein load of 33.3 mg·g−1 was obtained, achieving productivity of 0.298 mmol min−1 mg−1. Additionally, no differences were found when using BHET from USW bottles of various colors. This research shows the potential of materials derived from PET as enzymatic supports, unreported materials, that we can use as tools to achieve sustainable biotechnological applications.

Performance of Plastic Waste-Based Polyionic Liquid toward the Dehydration of Crude Oil Emulsions

Polyethylene terephthalate (PET) is one of the most widely used plastics in the world. Due to the large production and use of this plastic, its waste represents one of the most critical environmental problems. The purpose of this study is to convert PET waste into a valuable material. The consumed PET was transformed into a precursor to synthesize a polyionic liquid (PIL) that was used for dehydrating crude oil emulsions. To do so, the consumed PET was converted to bis(2-hydroxyethyl) terephthalate (BHET). First, BHET and tetraethylene glycol were reacted separately with thionyl chloride, obtaining the corresponding alkyl halides, bis(2-chloroethyl) terephthalate, BCET, and TEC, respectively. Next, the obtained alkyl halides, BCET and TEC, were reacted with 1,5-pentanediamine, yielding a polymer (BTP). Finally, BTP was reacted with acetic acid to produce the corresponding PIL (BTP–PIL). The structure and thermal stability of BTP–PIL were characterized using nuclear magnetic resonance spectroscopy and thermal gravimetric analysis. The dehydration performance of PIL and the original polymer was investigated using the bottle test method, including several factors such as demulsifier dose, brine content, temperature, and settling time. Results indicated that PIL achieved high performance in dehydrating crude oil emulsions.