Production Of Polyethylene Terephthalate Research Articles

Techno-Economic Analysis of a Carbon Molecular Sieve-Based Xylene Isomer Purification Process.

The separation and purification of xylene isomers is critical to the production of polyethylene terephthalate (PET). These separations are complex to operate and demand tremendous amounts of energy and thus are an opportunity for reducing industrial energy consumption. Membranes provide a low-energy footprint technology with simpler operation, and recently, membrane materials have been developed that are capable of separating xylene isomers. While these materials have demonstrated the ability to separate xylenes, they have yet to be commercially deployed. This work conducts a techno-economic analysis (TEA) to provide insight on the commercial attractiveness of a p-xylene selective carbon molecular sieve (CMS) membrane from both a cost and energy standpoint. This TEA was conducted through the pairing of a Maxwell-Stefan transport framework for rigid microporous materials with process modeling. Single-stage organic solvent reverse osmosis (OSRO) and pervaporation processes were used to evaluate the effects of recovery, selectivity, and diffusivity on the energy intensity and cost of the xylene separation. The final analysis used two systems, a single pervaporation stage followed by two OSRO stages, which was compared against a three-stage OSRO cascade. These were benchmarked against the commercial Parex process. We estimate that the membrane processes have the potential to enable impressive cost savings compared to the Parex process. While both systems outperformed the Parex process in terms of cost, the pervaporation/OSRO hybrid process was able to achieve the lowest cost of all due to its reduced membrane surface area compared to standalone OSRO. These findings demonstrate the potential of membrane systems in the field of difficult small molecule solvent separations.

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.

Degradation of polyethylene terephthalate (PET) plastics by wastewater bacteria engineered via conjugation.

Wastewater treatment plants are one of the major pathways for microplastics to enter the environment. In general, microplastics are contaminants of global concern that pose risks to ecosystems and human health. Here, we present a proof-of-concept for reduction of microplastic pollution emitted from wastewater treatment plants: delivery of recombinant DNA to bacteria in wastewater to enable degradation of polyethylene terephthalate (PET). Using a broad-host-range conjugative plasmid, we enabled various bacterial species from a municipal wastewater sample to express FAST-PETase, which was released into the extracellular environment. We found that FAST-PETase purified from some transconjugant isolates could degrade about 40% of a 0.25 mm thick commercial PET film within 4 days at 50°C. We then demonstrated partial degradation of a post-consumer PET product over 5-7 days by exposure to conditioned media from isolates. These results have broad implications for addressing the global plastic pollution problem by enabling environmental bacteria to degrade PET.

Biodegradation of combined pollutants of polyethylene terephthalate and phthalate esters by esterase-integrated Pseudomonas sp. JY-Q with surface-co-displayed PETase and MHETase

The waste pollution problem caused by polyethylene terephthalate (PET) plastics poses a huge threat to the environment and human health. As plasticizers, Phthalate esters (PAEs) are widely used in PET production and become combined pollutants with PET. Synthetic biology make it possible to construct engineered cells for microbial degradation of combined pollutants of PET and PAEs. PET hydroxylase (PETase) and monohydroxyethyl terephthalate hydroxylase (MHETase) isolated from Ideonella sakaiensis 201-F6 exhibit the capability to depolymerize PET. However, PET cannot enter cells, thus enzymatic degradation or cell surface displaying technology of PET hydrolase are the potential strategies. In this study, Pseudomonas sp. JY-Q was selected as a chassis strain, which exhibits robust stress tolerance. First, a truncated endogenous outer membrane protein cOmpA and its variant Signal (OprF)-cOmpA were selected as anchor motifs for exogenous protein to display on the cell surface. These anchor motifs were fused at the N-terminal of PET hydrolase and MHETase and transformed into Pseudomonas sp. JY-Q, the mutant strains successfully display the enzymes on cell surface, after verification by green fluorescent protein labeling and indirect immunofluorescence assay. The resultant strains also showed the catalytic activity of co-displaying PETase and MHETase for PET biodegradation. Then, the cell surface displaying PET degradation module was introduced to a JY-Q strain which genome was integrated with PAEs degrading enzymes and exhibited PAEs degradation ability. The resultant strain JY-Q-R1-R4-SFM-TPH have the ability of degradation PET and PAEs simultaneously. This study provided a promising strain resource for PET and PAEs pollution control.

Selective recovery of para-xylene from polyethylene terephthalate plastic

The conversion of polyethylene terephthalate (PET) plastic into low-boiling monomers like para-xylene (PX) that can be purified easier with lower energy consumption represents a promising strategy for circular economy that seamlessly integrating into current prevailing high-quality PET production chain. Herein, a selective bimetallic RuFe catalyst was successfully fabricated for hydrodeoxygenation (HDO) of dimethyl terephthalate (DMT) (a model compound of PET) and PET plastics to PX with yield as high as 88.9 % and 82.6 %, respectively, comparable to state-of-the-art examples. H2-TPR and EXAFS combined with benchmark test over model catalysts confirmed that small Ru clusters and Ru-Nx coordination are responsible for the high aromatics selectivity, on which vertical adsorption of carbonyl group (CO) is preferred. This study not only shows a promising PX-based PET recycling route, the highly selective C–O bond cleavage on Ru catalyst and corresponding structure-selectivity relationship also guide the catalyst design for other value-added biomass-based HDO reactions.

Environmental performance of different water bottles with different compositions: A cradle to gate approach

Plastic production has increased over the years and the packaging industry was responsible for 44% of the total plastic production. Polyethylene terephthalate (PET), due to its favorable properties, is one of the most used polymers in this sector.This study first aimed to compare the environmental performance related to the production of a novel recycled PET (rPET) form, namely, rPET flake, and then compare it with the production of virgin PET (vPET) and rPET pellet. Secondly, this study aimed to compare the environmental impacts of four water bottles with different compositions, namely, option A composed with only vPET, option B made with 50% vPET and 50% rPET pellet, option C made with 75% rPET pellet and 25% rPET flake, and option D made with 50% vPET, 25% rPET pellet and 25% rPET flake. Option A was designed as a single-use water bottle, while the remaining options (Options B, C and D) were thought to be reusable bottles, and for that reason were heavier and more robust compared to Option A. The environmental impact assessment followed the International Standard Rules of Life Cycle Assessment (LCA), and the impact assessment method used was the Environmental Product Declaration. Ecoibéria and Logoplaste provided the majority of the required data, and three functional units were considered. The first one was the production of 1 kg of PET, the second was the production of different water bottles, and finally, the third one was the consumption of 2 l of water with different water bottles. As a result, it was first observed that the production of rPET flake in comparison to vPET reduces, on average, 79% of the impacts, and rPET pellet reduces 10% of the impacts. Secondly, in the production of the different water bottles, Option A, the single-use bottle, presented the lowest environmental impacts in almost all categories. Finally, when taking into account the reusable factor, the use of single-use bottles presented the higher environmental impact in all categories, probably because of the dilution of the environmental impacts associated with the production of heavier and robust reusable bottles by the multiple times of uses of these bottles.

First principles investigation of manganese catalyst structure and coordination in the p-xylene oxidation process

The oxidation of p-xylene to terephtalic acid is important for the production of polyethylene terephthalate (PET). This work investigates the coordination of the Mn catalyst species under operating conditions.

Medium entropy metal oxide induced *OH species targeted transfer strategy for efficient polyethylene terephthalate plastic recycling

Increasing plastic waste is environmentally and biologically detrimental, and converting plastic waste into value-added chemicals and fuels by electrocatalytic methods is recognized as an up-cycling process that facilitates resource utilization. Here, we report a generalized medium entropy metal oxide Ni0.5Ce0.5Co2O4 induced *OH species targeted transfer strategy to selectively electrocatalytic upgrade various polyester plastics into value-added chemicals under alkaline conditions. Polyethylene terephthalate (PET) was upgraded to potassium diformate with high Faraday efficiency (95 %) and selectivity (>91 %) at a high current density of 343 mA cm−2, generating both terephthalic acid and hydrogen. The synergistic interplay between Ni and Ce in Ni0.5Ce0.5Co2O4 facilitates the adsorption of ethylene glycol molecules and hydroxide ions, prompting the directionally oriented hydroxyl (*OH) to partake in the oxidation of ethylene glycol, thereby fostering the oxidation of hydrolyzed PET products. This work not only develops an excellent electrocatalyst for the upcycling of various polyester plastics but also guides the design of medium entropy metal oxides as electrocatalysts.

Computational design of highly efficient thermostable MHET hydrolases and dual enzyme system for PET recycling

Recently developed enzymes for the depolymerization of polyethylene terephthalate (PET) such as FAST-PETase and LCC-ICCG are inhibited by the intermediate PET product mono(2-hydroxyethyl) terephthalate (MHET). Consequently, the conversion of PET enzymatically into its constituent monomers terephthalic acid (TPA) and ethylene glycol (EG) is inefficient. In this study, a protein scaffold (1TQH) corresponding to a thermophilic carboxylesterase (Est30) was selected from the structural database and redesigned in silico. Among designs, a double variant KL-MHETase (I171K/G130L) with a similar protein melting temperature (67.58 °C) to that of the PET hydrolase FAST-PETase (67.80 °C) exhibited a 67-fold higher activity for MHET hydrolysis than FAST-PETase. A fused dual enzyme system comprising KL-MHETase and FAST-PETase exhibited a 2.6-fold faster PET depolymerization rate than FAST-PETase alone. Synergy increased the yield of TPA by 1.64 fold, and its purity in the released aromatic products reached 99.5%. In large reaction systems with 100 g/L substrate concentrations, the dual enzyme system KL36F achieved over 90% PET depolymerization into monomers, demonstrating its potential applicability in the industrial recycling of PET plastics. Therefore, a dual enzyme system can greatly reduce the reaction and separation cost for sustainable enzymatic PET recycling.

Synthesis and characterization of PET impregnated agro-medical waste: Novel approach for plastic substitute using hybrid composites

Composites are environmentally friendly materials made from natural fibers that have lightweight properties and improve the performance of synthetic parts. Medical waste has been identified as one of the biggest challenges recently in India due to COVID-19. More than 70% of medical waste is considered non-hazardous waste, obtained from crushing used surgical face mask (SFM) and surgical gloves (SG) as reinforcement materials chosen in this study. The research aim is to increase the strength and minimize the cost of production of polyethylene terephthalate (PET) matrix by employing hybrid waste fibers as particle reinforcement particles. Five fiber composites of 3% to 12% weight fractions of hybrid fiber (Kevlar Fiber/Glass fiber) and a constant 10% medical waste were fabricated using an injection moulding process to regulate the polymer structure and determine its thermal conductivity. Adding fibers improved mechanical properties such as tensile, flexural, and impact strength. TGA and thermal conductivity were analyzed. Tribological characteristics like a specific wear rate and coefficient of friction were conducted. Morphology is used to identify material behaviour by applying different weight fractions. Adding 9% (KF/GF) and 10% (SFM/SG) particles improves the wear and mechanical properties of the hybrid composite by 52%, respectively. Adding medical and fiber waste particles will improve the interfacial bonding between the matrix material and fillers. It is widely used as a leaf spring in ballistic and automobile applications suspension.

Progress in recycling and reutilization of waste polyethylene terephthalate

Polyethylene terephthalate (PET) is a versatile material with a wide range of applications, and the demand for PET products has been steadily increasing in recent years. This has generated large quantities of non-biodegradable PET waste. To reduce environmental pollution, recycling and reuse of waste PET is an economical solution. Different PET products vary greatly in their impurity contents, processing technology, and performance, which poses certain challenges for the recovery, purification, and reuse of PET waste in a high value-added manner. Various recycling and reutilization methods are compared, potential issues with different PET products in the recycling process are analyzed, and viscosity enhancement modification techniques and applications of recycled PET are introduced. This paper provides a reference for the recycling of various waste PET products.

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.

Intelligent Temperature Control of a Stretch Blow Molding Machine Using Deep Reinforcement Learning

Stretch blow molding serves as the primary technique employed in the production of polyethylene terephthalate (PET) bottles. Typically, a stretch blow molding machine consists of various components, including a preform infeed system, transfer system, heating system, molding system, bottle discharge system, etc. Of particular significance is the temperature control within the heating system, which significantly influences the quality of PET bottles, especially when confronted with environmental temperature changes between morning and evening during certain seasons. The on-site operators of the stretch blow molding machine often need to adjust the infrared heating lamps in the heating system several times. The adjustment process heavily relies on the personnel’s experience, causing a production challenge for bottle manufacturers. Therefore, this paper takes the heating system of the stretch blow molding machine as the object and uses the deep reinforcement learning method to develop an intelligent approach for adjusting temperature control parameters. The proposed approach aims to address issues such as the interference of environmental temperature changes and the aging variation of infrared heating lamps. Experimental results demonstrate that the proposed approach achieves automatic adjustment of temperature control parameters during the heating process, effectively mitigating the influence of environmental temperature changes and ensuring stable control of preform surface temperature within ±2 ℃ of the target temperature.

Multigenerational effects of microplastic fragments derived from polyethylene terephthalate bottles on duckweed Lemna minor: Size-dependent effects of microplastics on photosynthesis

The 2019 global coronavirus disease pandemic has led to an increase in the demand for polyethylene terephthalate (PET) packaging. Although PET is one of the most recycled plastics, it is likely to enter the aquatic ecosystem. To date, the chronic effects of PET microplastics (MPs) on aquatic plants have not been fully understood. Therefore, this study aimed to investigate the adverse effects of PET MP fragments derived from PET bottles on the aquatic duckweed plant Lemna minor through a multigenerational study. We conducted acute (3-day exposure) and multigenerational (10 generations from P0 to F9) tests using different-sized PET fragments (PET0–200, < 200 μm; PET200–300, 200–300 μm; and PET300–500, 300–500 μm). Different parameters, including frond number, growth rate based on the frond area, total root length, longest root length, and photosynthesis, were evaluated. The acute test revealed that photosynthesis in L. minor was negatively affected by exposure to small-sized PET fragments (PET0–200). In contrast, the results of the multigenerational test revealed that large-sized PET fragments (PET300–500) showed substantial negative effects on both the growth and photosynthetic activity of L. minor. Continuous exposure to PET MPs for 10 generations caused disturbances in chloroplast distribution and inhibition of plant photosynthetic activity and growth. The findings of this study may serve as a basis for future research on the generational effects of MPs from various PET products.

GLYCOLYSIS OF WASTE PET BOTTLES USING ETHYLENE GLYCOL AS A SOLVENT AND A CALCINED SNAIL SHELL AS A CATALYST

With the increasingly widespread use of polyethylene terephthalate (PET) bottles due to their cheap and robust nature, there has been an exponential increase in waste from these bottles in landfills, dumpsites, gutters, and roadsides, which has led to a negative effect on the environment, plants, animals, and human population with land and water pollution. Chemical recycling of the waste PET bottles would reduce the menace and recover the starting monomers for PET production. In this research, waste PET bottles were chemically recycled through glycolysis to produce bis-hydroxyethyl terephthalate (BHET) using ethyl glycol (EG) as a solvent and calcined snail shell as a catalyst within the temperature range of 180-200°C at different EG:PET ratios of 5:1, 6:1, and 6.5:1, while a constant catalyst:PET of 1:100 was used. After reaction and crystallization, a yield of the glycolysis product of 39.72% was obtained. This yield recorded is not as good as using oyster shell (68.6%), sodium acetate (72%), and calcium carbonate (69%) as catalysts. TGA and FTIR indicated that the samples were composed mainly of BHET monomers as functional groups. It is recommended that longer reaction time and varying catalyst:PET ratio be used to determine the optimum temperature and reaction. Keywords: Glycolysis, Bis-Hydroxyethyl Terephthalate, Chemical Recycling, Polyethylene Terephthalate Depolymerization, Snail Shell DOI： https://doi.org/10.35741/issn.0258-2724.58.3.28

Depolymerization of polyethylene terephthalate with glycol under comparatively mild conditions

The depolymerization of polyethylene terephthalate (PET) can proceed by using ethylene glycol (EG) as an alcoholysis solvent. However, high reaction temperature (≥180℃) of glycolysis process requires high energy consumption, and unfortunately results in yellowing of monomer product, i.e., bis(2-hydroxyethyl) terephthalate (BHET), limiting the production of high-quality and colorless recycled PET (rPET). To address this problem, a strategy involving acetonitrile as cosolvent was applied to decrease glycolysis temperature to 90℃ or even lower, and solvents as well as catalyst can be recycled and reused. The glycolysis of PET is hard to proceed at 90℃. However, the swelling effect of acetonitrile caused cracks and defects on the surface of PET, which promoted the depolymerization of PET and led to an S-shaped reaction curve. Besides, adding acetonitrile could significantly accelerate the degradation of oligomers into BHET. Under the optimal reaction conditions, the conversion of PET and yield of BHET could reach 96% and 90%, respectively.

Precisely Constructed Metal Sulfides with Localized Single-Atom Rhodium for Photocatalytic C-H Activation and Direct Methanol Coupling to Ethylene Glycol.

Although there are many studies on photocatalytic environmental remediation, hydrogen evolution, and chemical transformations, less success has been achieved for the synthesis of industrially important and largely demanded bulk chemicals using semiconductor photocatalysis, which holds great potential to drive unique chemical reactions that are difficult to implement by the conventional heterogeneous catalysis. The performance of semiconductors used for photochemical synthesis is, however, usually unsatisfactory due to limited efficiencies in light harvesting, charge-carrier separation, and surface reactions. The precise construction of heterogeneous photocatalysts to facilitate these processes is an attractive but challenging goal. Here, single-atom rhodium-doped metal sulfide nanorods composed of alternately stacked wurtzite/zinc-blende segments are successfully designed and fabricated, which demonstrate record-breaking efficiencies for visible light-driven preferential activation of C-H bond in methanol to form ethylene glycol (EG), a key bulk chemical used for the production of polyethylene terephthalate (PET) polymer. The wurtzite/zinc-blende heterojunctions lined regularly in one dimension accelerate the charge-carrier separation and migration. Single-atom rhodium selectively deposited onto the wurtzite segment with photogenerated holes accumulated facilitates methanol adsorption and C-H activation. The present work paves the way to harnessing photocatalysis for bulk chemical synthesis with structure-defined semiconductors.

Can we improve the environmental benefits of biobased PET production through local biomass value chains? – A life cycle assessment perspective

The transition to a bioeconomy is one of the ambitions of the European Union for 2030. Biobased industries play an essential role in this transition. However, there has been an on-going discussion about the actual benefit of using biomass to produce biobased products, specifically the use of agricultural materials (e.g., corn and sugarcane). This paper presents the environmental impact assessment of 30% and 100% biobased polyethylene terephthalate production using European biomass supply chains (e.g., sugar beet, wheat, and miscanthus). An integral assessment between the life cycle assessment methodology and the global sensitivity assessment is presented as an early-stage support tool to propose and select supply chains that improve the environmental performance of biobased polyethylene terephthalate production. From the results, miscanthus is the best option for the production of biobased polyethylene terephthalate: promoting European local supply chains, reducing greenhouse gas emissions (process and land-use change), and generating lower impacts in midpoint categories related to resource depletion, ecosystem quality, and human health. This tool can help improving the environmental performance of processes that could boost the shift to a bioeconomy.

Efficient depolymerization of polyethylene terephthalate (PET) and polyethylene furanoate by engineered PET hydrolase Cut190

The enzymatic recycling of polyethylene terephthalate (PET) can be a promising approach to tackle the problem of plastic waste. The thermostability and activity of PET-hydrolyzing enzymes are still insufficient for practical application. Pretreatment of PET waste is needed for bio-recycling. Here, we analyzed the degradation of PET films, packages, and bottles using the newly engineered cutinase Cut190. Using gel permeation chromatography and high-performance liquid chromatography, the degradation of PET films by the Cut190 variant was shown to proceed via a repeating two-step hydrolysis process; initial endo-type scission of a surface polymer chain, followed by exo-type hydrolysis to produce mono/bis(2-hydroxyethyl) terephthalate and terephthalate from the ends of fragmented polymer molecules. Amorphous PET powders were degraded more than twofold higher than amorphous PET film with the same weight. Moreover, homogenization of post-consumer PET products, such as packages and bottles, increased their degradability, indicating the importance of surface area for the enzymatic hydrolysis of PET. In addition, it was required to maintain an alkaline pH to enable continuous enzymatic hydrolysis, by increasing the buffer concentration (HEPES, pH 9.0) depending on the level of the acidic products formed. The cationic surfactant dodecyltrimethylammonium chloride promoted PET degradation via adsorption on the PET surface and binding to the anionic surface of the Cut190 variant. The Cut190 variant also hydrolyzed polyethylene furanoate. Using the best performing Cut190 variant (L136F/Q138A/S226P/R228S/D250C-E296C/Q123H/N202H/K305del/L306del/N307del) and amorphous PET powders, more than 90 mM degradation products were obtained in 3 days and approximately 80 mM in 1 day.Graphical

Synthesis of Unsaturated Polyester Resin Based on Pet Waste

Abstract: Polyethylene terephthalate (PET) flakes are widely used as raw material for manufacturing of packaging materials. The worldwide production of PET is 30.5 million metric tons/year. With such a large consumption, the effective application of PET waste is of considerable commercial and technological significance. In this paper we used PET flakes for the synthesis of unsaturated polyester resin to go green. PET flakes were depolymerized by using Neopentyl glycol (NPG) and propylene glycol (PG). Glycolyzed product was reacted with maleic anhydride and phthalic anhydride. Then it was mixed with styrene monomer to get unsaturated polyester (UP) resins. Molecular weight, Hydroxyl value and Acid value of all synthesized UP resins were studied.