Glycolysis Of Polyethylene Terephthalate Research Articles

Kinetic modelling and mechanism elucidation of catalyst-free dimethyl terephthalate hydrolysis process intensification by reactive distillation

Polyethylene terephthalate (PET) is a widely used thermoplastic polymer in the packaging and materials industries, and is predicted to have continuous market growth in the future. Methods such as glycolysis and methanolysis of PET have been identified as promising approaches in sustainable chemical recycling of PET. The latter produces dimethyl terephthalate (DMT), which can be easily hydrolyzed to terephthalic acid (TPA) at elevated temperatures and pressures, and further reused for PET production. The aim of this study was to develop a kinetic model for the hydrolysis of dimethyl terephthalate, using the experimental data. Various reaction conditions (temperature, pressure, time) have been investigated and used to calculate the activation energies and reaction rate constants, while the variation in reactor setup with methanol (MeOH) removal was conducted to show its detrimental effect on the efficiency of the reaction and selectivity towards terephthalic acid. The first reaction step of DMT to monomethyl terephthalate (MMT) is relatively irreversible, while the second reaction step of MMT to TPA ceases, as soon as the equilibrium is reached. Highest yields of TPA (76.7 %) were obtained after 40 min at 265 °C, with MeOH removal, and the activation energy was calculated to be 95 and 64 kJ mol−1 for the first and second hydrolysis reaction step, respectively.

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.

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.

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.

A new circulation in glycolysis of polyethylene terephthalate using MOF-based catalysts for environmental sustainability of plastic

The relentless growth of plastic has emerged as a significant environmental and human health concern. Catalytic glycolysis of polyethylene terephthalate (PET) has proven to be an effective solution. This study investigated a series of M−BDC (M = Ni, Co, Cu, and Zn) metal–organic frameworks as catalysts for PET glycolysis. Zn−BDC exhibited the best experimental performance. Subsequently, the effects of operating conditions were optimized for the first time through a comprehensive investigation using a model based on deep neural networks (DNNs). The guidance of the DNN model resulted in a BHET selectivity as high as 0.95, outperforming most current heterogeneous catalysts for PET depolymerization. Furthermore, the apparent activation energy was also estimated by kinetic study. In addition, our designed system exhibits high durability after five consecutive runs, reflecting its promising escalation at the industrial level. Notably, the fabrication of the M−BDC framework can utilize the organic linker terephthalic acid (TPA) derived from the BHET monomer. By applying this strategy, we have achieved a significant advancement towards closed-loop PET recycling, contributing to a more comprehensive definition of sustainable development.

Valorization of waste plastics to prepare tough, stretchable and highly conductive ionicgels

Polyethylene terephthalate (PET) is one of the most widely used polymers, and its intensive use has resulted in significant and growing environmental problems. The urgent need for a more efficient approach that avoids the cumbersome depolymerisation process and monomer purification to produce high-value products is evident. In this study, a simple and one-pot strategy was used to obtain polyurethane pre-polymer through the glycolysis of PET. The polyurethane network and the second polymer network formed by the monomers polyacrylic acid and polyacrylamide were co-introduced into the ionicgels to create a dual network structure. Glycolysis of PET was catalyzed using the ionic liquid catalyst [EMIM][DCA], resulting in a 100 % conversion. The PET alcoholysis solution consisted of 90.47 % BHET, 9.53 % oligomers containing benzene rings, and unreacted glycol. Polyurethanes synthesized through the one-pot method using PET hydrolysate, with benzene ring-containing BHETs and oligomers as the hard domains and ethylene glycol as the soft domains, exhibited excellent mechanical properties. PET-based polyurethane was employed in the preparation of dual network-structured ionicgels. As a result, the ionic gels exhibited a good stress–strain of 4.2 MPa and 990 %, along with a high conductivity (0.09 S/cm) and ultrahigh sensitivity. Furthermore, it could easily repair the broken ionicgels at 25 ℃ for 6 h, thus restoring their original tensile, and sensing properties.

Directional glycolysis of waste PET using deep eutectic solvents for preparation of aromatic-based polyurethane elastomers

Glycolysis of waste polyethylene terephthalate (PET) is a green and high-value PET recovery approach, the product of which can be used as raw materials to prepare polyurethanes.

Catalytic function of ionic liquids in polyethylene terephthalate glycolysis by molecular dynamics simulations

This computational work provides an atomic description of the solvation scenario of PET glycolysis using ionic liquid catalysts, showing the distinct role of anions and cations in the process.

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.

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.

Conversion of polyethylene terephthalate (PET) plastic particles in a microwave-assisted heating reactor

Abstract With the rapid economic development, PET (polyethylene terephthalate) plastic is widely used in various fields, i.e., clothing, food, housing and transportation. However, PET has a very strong chemical inertia, which makes it difficult to be degraded by microorganisms, thereby occupying a lot of space. Therefore, the recycling of waste PET has become one of the most important topics of environmental protection. Glycolysis requires the most mild and safe reaction environment among chemical recycling methods, and the ethylene glycol used in the reaction can be reused. Using glycolysis to recycle PET undoubtedly conforms to the green and sustainable concept, and glycolysis recycling is undoubtedly a low-cost, low-consumption and low-harm path for PET recycling. The heating and glycolysis characteristics of microwave-assisted PET glycolysis, and the energy analysis of glycolysis were studied. The aim was to produce BHET (bis(2-hydroxyethyl) terephthalate) as the target product from PET waste. In this study, the effects of reaction temperature, reaction time, and PET particle size on the performances of PET conversion rate, oligomeric BHET yield, and BHET yield were examined, and the energy efficiency and recovery efficiency also were presented. The results showed that the optimal conditions for microwave-assisted PET glycolysis were reaction temperature of 180 °C, reaction time of 30 min, and PET particle size of 75 μm, and the maximum PET conversion rate was 66.71 ± 9.71 wt%, the maximum yield of BHET was 48.08 ± 0.68 wt% and the maximum BHET yield was 19.83 ± 5.40 wt%. The energy efficiency and recovery efficiency were 11.88 % and 17.89 %, respectively.

Insight the influence of the catalyst basicity on glycolysis behavior of Polyethylene terephthalate (PET)

Although polyethylene terephthalate (PET) is one of the most prevalent plastics, a cumulative disposal of PET waste has caused adverse effects on both economy and environment. Catalytic glycolysis of PET waste has emerged as a prevalent and sustainable pathway to address this problem. Due to the limitations of recovery and recycling, the catalytic development trend for PET glycolysis has recently changed from homogenous to heterogeneous designs. Herein, metal oxides with different basicity, including calcium, cerium, and cobalt, were supported on alumina and first employed in the glycolysis process of waste PET plastic. A plausible mechanism is proposed and reveals the correlation between the basicity of as-prepared catalyst and glycolysis performances. Among these catalysts, 10%Ce/Al2O3 exhibited a complete conversion of waste PET with the highest selectivity to the main product BHET. There is no significant drop in catalytic activity after five consecutive runs. Furthermore, the excellent quality of the monomer product BHET was confirmed via different analysis techniques. This work has contributed to a promising notion for engineering efficient heterogeneous catalysts of PET recycling technology.

Magnetic ionic liquid catalyst functionalized with antimony (III) bromide for effective glycolysis of polyethylene terephthalate

In a previous study, we demonstrated the efficient depolymerization of polyethylene terephthalate (PET) through glycolysis using antimony (III) oxide, a commonly used catalyst in PET synthesis. In the present research, we introduce a novel approach involving the synthesis of a magnetic bifunctional ionic liquid, Fe3O4@PMIM.SbBr4, containing only 2.2 wt% of antimony. The aim is to reduce the required antimony dosage for the reaction and enable its facile recovery and reuse. By employing this catalyst in PET chemical recycling through glycolysis to generate bis (2-hydroxyethyl) terephthalate (BHET) monomer, we achieved 100% PET conversion with a 96.4% yield and selectivity for BHET. This outcome was obtained using a catalyst loading of 6.0 wt% at 200 °C and 0.6 bar in a high-pressure reactor. We explored the impact of catalyst loading on BHET yield and conducted a comparative assessment of the Fe3O4@PMIM.SbBr4 catalyst against antimony (III) bromide, and another synthesized unsupported antimony-containing ionic liquid. Our results revealed the superior catalytic activity of the magnetic ionic liquid catalyst in PET glycolysis. The utilization of this catalyst offers promising potential for PET glycolysis due to its effortless separation using an external magnet, ability to produce highly pure BHET, and recyclability for repetitive use.

Upcycling of PET oligomers from chemical recycling processes to PHA by microbial co-cultivation

Polyethylene terephthalate (PET) is the most widely consumed polyester plastic and can be recycled by many chemical processes, of which glycolysis is most cost-effective and commercially viable. However, PET glycolysis produces oligomers due to incomplete depolymerization, which are undesirable by-products and require proper disposal. In this study, the PET oligomers from chemical recycling processes were completely bio-depolymerized into monomers and then used for the biosynthesis of biodegradable plastics polyhydroxyalkanoates (PHA) by co-cultivation of two engineered microorganisms Escherichia coli BL21 (DE3)-LCCICCG and Pseudomonas putida KT2440-ΔRDt-ΔZP46C-M. E. coli BL21 (DE3)-LCCICCG was used to secrete the PET hydrolase LCCICCG into the medium to directly depolymerize PET oligomers. P. putida KT2440-ΔRDt-ΔZP46C-M that mastered the metabolism of aromatic compounds was engineered to accelerate the hydrolysis of intermediate products mono-2-(hydroxyethyl) terephthalate (MHET) by expressing IsMHETase, and biosynthesize PHA using ultimate products terephthalate and ethylene glycol depolymerized from the PET oligomers. The population ratios of the two microorganisms during the co-cultivation were characterized by fluorescent reporter system, and revealed the collaboration of the two microorganisms to bio-depolymerize and bioconversion of PET oligomers in a single process. This study provides a biological strategy for the upcycling of PET oligomers and promotes the plastic circular economy.

Controlling PET oligomers vs monomers via microwave-induced heating and swelling

The production of polyethylene terephthalate (PET) bottles and fibers, and their subsequent mismanagement, have created an urgent need to develop strategies to handle the resulting waste. Here, glycolysis of PET using manganese oxide catalysts under microwave-assisted heating is demonstrated to form oligomers and the monomer bis(2-hydroxyethyl) terephthalate (BHET) at moderate conditions. Higher surface area catalysts achieve faster overall rates of depolymerization to the monomer. Oligomers form homogeneously and depolymerize to monomers over manganese oxide. The polymer-to-solvent ratio and reaction temperature affect the overall oligomer yield. The swelling of PET, caused by the diffusion of ethylene glycol into the polymer matrix, causes the dissolution of the PET to form oligomers. Oligomers are characterized and show similar physical properties to the starting PET despite having 1/20th of the molecular weight.

Amino alcohols as recycling-catalysts for degradation of PET to oligoethylene terephthalates

Polyethylene terephthalate (PET) is an essential component of daily life. However, due to PET's resistance to natural degradation, a plethora of life in the ecosystem is swimming in discarded plastic causing a serious environmental disaster. Using glycolysis, a chemical recycling method, PET is largely recycled to bis(2-hydroxyethyl) terephthalate (BHET) monomers. BHET is polymerized back to a pre-polymer (∼25-35 DPn) followed by polycondensation for higher molecular weight PET, hence an energy-intensive and cost-inefficient method. This study demonstrates glycolysis of PET using Amino alcohols (AmOH's) for generating oligoethylene terephthalate (OET) of DPn value of ∼30 in high yields (98%) under mild reaction conditions; 180°C temperature, atmospheric pressure, with recyclability. PET-to-PET cycle was closed by preparing PET from generated OETs. A comparative model study on methyl benzoate (in EG) revealed the efficiency of AmOH's over Hünig's base; N, N-Ethyldiisopropylamine (DIPEA) despite being more basic. Similarly, N-Butyl-N-methylbutane-1-amine (MDBA) demonstrated slower PET conversion than Methyl diethanolamine (MDEA) AmOH. Although AmOH's such as MDEA also act as nucleophile and add to the polymer chain, to our surprise, our NMR studies revealed that there is no sign of insertion of AmOH's indicating that the AmOH's may function as catalysts. Morphological studies conducted under different reaction conditions unveiled the method of OET generation. The computational studies and Kinetic Isotopic studies explained facilitation of hydroxy group of AmOH in the degradation. Following the shrinking core model, the calculated activation energy for degradation was estimated to be 45.4 kJ mol−1.

Oxygen Vacancy Promoted Generation of Monatomic Oxygen Anion over Ni2+ -Doped MgO for Efficient Glycolysis of Waste PET.

Developing efficient and eco-friendly catalysts for selective degradation of waste polyethylene terephthalate (PET) is critical to the circular economy of plastics. Herein, we report the first monatomic oxygen anion (O- )-rich MgO-Ni catalyst based on a combined theoretical and experimental approach, which achieves a bis(hydroxyethyl) terephthalate yield of 93.7 % with no heavy metal residues detected. DFT calculations and electron paramagnetic resonance characterization indicate that Ni2+ doping not only reduces the formation energy of oxygen vacancies, but also enhances local electron density to facilitate the conversion of adsorbed oxygen into O- . O- plays a crucial role in the deprotonation of ethylene glycol (EG) to EG- (exothermic by -0.6 eV with an activation barrier of 0.4 eV), which is proved effective to break the PET chain via nucleophilic attack on carbonyl carbon. This work reveals the potential of alkaline earth metal-based catalysts in efficient PET glycolysis.

Conventional and MW assisted PET glycolysis promoted by titanium based catalyst

Polyethylene terephthalate (PET) flakes from postconsumer bottles were depolymerized in the presence of ethylene glycol (EG) and titanium (IV) phosphate (TiP) as catalyst. Glycolysis was carried out both as conventional heated and under microwave (MW) irradiation. For the former method the reaction conditions were: molar ratio PET repeating unit to EG-1:2.77, without catalyst and with different amounts of TiP at 200 °C. The MW assisted process was performed under similar experimental conditions applying a power range 400–600 W. It was optimizated with respect to the catalyst concentration and yeild of bis(2-hydroxyethyl) terephthalate (BHET). The experiments showed that the optimal result was achieved in a MW reactor using 0.2 wt% TiP (based on PET weight) at 450 W for 45 min reaction time. The degradation product contained the monomer BHET (61.7%), dimers, trimers and low amounts oligomers and EG. The yield of BHET achieved was 87%. The glycolysis products were characterized by a combination of analytical techniques – chromatographic, spectroscopic and thermal methods. The comparison of both approaches showed the advantages of MW assisted degradation in view of efficiency and time saving.

Microwave-assisted depolymerization of PET over heterogeneous catalysts

The accumulation of plastic waste in the environment is rising and poses a significant environmental and health threat. Polyethylene terephthalate (PET), used mainly in single-use plastic bottles, accounts for a substantial fraction of this waste. The currently employed recycling strategies are inadequate to deal with the global plastic waste problem. PET glycolysis is a promising depolymerization method but has mainly been conducted using homogeneous catalysts; developing active and sustainable catalysts, and more energy-efficient processes remain challenges. Here, we implement microwave heating in PET glycolysis and identify ZnO as an excellent heterogeneous catalyst. We demonstrate the influence of ZnO's particle size and facet and hydrogen bonding on its activity. Finally, we demonstrate excellent performance for real-world post-consumer PET waste deconstruction with rapid depolymerization into bis(2-hydroxyethyl) terephthalate (BHET), achieving > 95% yields in less than 10 min. Cradle-to-gate life cycle assessment also indicates that BHET produced by ZnO-catalyzed glycolysis has lower global warming potential than the petrochemical-based production and homogeneously-catalyzed glycolysis.

Comparative Reactivity of Different Polyols in the PET Saponification Process

This work is concerned with polyethylene terephthalate (PET) saponification by different potassium compounds in various polyols as well as biodiesel’s main by-product, crude glycerol. It was established that reaction conditions (initial PET/K+ molar ratio, reaction time, etc.) could control the molecular weight of obtained oligomeric products. In ethylene glycol, depolymerization proceeds rapidly, and already at 10–30 min, PET is completely dissolved in the reaction mixture with the formation of liquid oligomers. Then, these oligomers react with potassium compounds, and after 200 min of the process, there are only solid, low-molecular-weight products (dipotassium terephthalate, monomers, and dimers). At the same time, PET saponification in pure glycerol is less effective, and solid polyether flakes could not fully decompose even after 200 min of the process. Crude glycerol takes the middle position between pure polyols. Based on the obtained data, an improved kinetic model was developed, and rate constants were estimated. This model takes into account PET saponification by potassium salts as well as direct PET glycolysis. Ethylene glycol is formed in situ by transesterification between fatty acid ethylene glycol esters and glycerol in the case of pure and crude glycerol.