Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

Upcycling Waste PET: I. Ammonolysis Kinetics of Model Dimethyl Terephthalate and the Catalytic Effects of Ethylene Glycol

Chemical upcycling of waste plastics can play an important role in developing greater circularity in the material flows associated with the plastics industries. In this study, a fundamental understanding of upcycling poly(ethylene terephthalate) (PET) using ammonolysis is established. First, rate constants are determined for model studies of the ammonolysis of dimethyl terephthalate (DMT) in methanol. Ammonolysis proceeds sequentially, and a first ester group of DMT reacts with ammonia to produce methanol and the monoamide methyl 4-carbamoylbenzoate (MCB). Next, MCB reacts with ammonia to yield methanol and terephthalamide (TPD). At 100 °C, the pseudo first order rate constants are k 1 ' = 0.25 ± 0.02 h-1 and k 2 ' = 0.11 ± 0.02 h-1. Experiments conducted at 50, 75, 100, and 125 °C yield activation energies for the first and second reactions of E a1 = 27.9 ± 2.2 kJ/mol and E a2 = 37.3 ± 3.3 kJ/mol. Ammonolysis is demonstrated to be catalyzed by ethylene glycol (EG) with a first order concentration dependence. At 100 °C with EG present in a 3:1 excess, the pseudo first order rate constants are k 3 ' = 6.3 ± 0.7 h-1 and k 4 ' = 1.7 ± 0.3 h-1, representing a 22-fold increase. Demonstration experiments with reclaimed mixed postconsumer thermoform containers reveal that the ammonolysis of PET is self-catalyzed by the generated EG; the upcycling reaction on polymer substrates is autocatalytic. This new detailed understanding of the self-catalyzed chemical kinetics of ammonolysis suggests EG as the natural choice for the solvent, a topic pursued in part II of this work.

Roles of carbon dioxide in the conversion of biomass or waste plastics

Under the current trend of pursuing sustainable development and environmental protection, the important application of carbon dioxide (CO2) in the conversion process of biomass or waste plastics has become a research direction of concern. The goal of this conversion process is to achieve the efficient use of carbon dioxide, providing a process for the efficient use of biomass, and solving the environmental problems caused by plastics. Remarkable progress has been made in the study of the reaction of CO2 with other substances to produce methane, low-carbon hydrocarbons, methanol, formic acid, and its derivatives, as well as ethers, aldehydes, gasoline, low-carbon alcohols, and other chemicals. In this paper, the important role of CO2 in the conversion of alcohol, sugar, cellulose, and waste plastics was reviewed, with emphasis on the important applications of CO2 as a carbon source, reactant, reaction medium, enhancing agent, solvent, and carrier gas in the conversion of biomass or waste plastics and the basic insights of the reaction mechanism. The emerging CO2 new roles not only put forward the green application of CO2 but also have guiding significance for the utilization of biomass resources and the treatment of waste plastics.

Synthesis of Bis(isodecyl Terephthalate) from Waste Poly(ethylene Terephthalate) Catalyzed by Lewis Acid Catalysts

Increasing plastic waste generation has become a pressing environmental problem. One of the most produced waste plastics originates from post-consumer packaging, of which PET constitutes a significant portion. Despite increasing recycling rates, its accumulation has created a need for the development of new recycling methods that can further expand the possibilities of recycling. In this paper, we present the application of Lewis acid catalysts for the depolymerization of PET waste. The obtained results show the formation of diisodecyl terephthalate (DIDTP), which is used as a PVC plasticizer. For this purpose, several Lewis acid catalysts were tested, including tin, cobalt, manganese, zirconium, zinc, and calcium derivatives, alongside zinc acetate and potassium hydroxide, which were used as reference catalysts. Our results show that tin (II) oxalate is the most effective catalyst, and it was then used to synthesize two application samples (crude and purified). The physicochemical properties of PVC mixtures with the obtained samples were determined and compared to commercial plasticizers, where both plasticizers had similar plasticizing properties to PVC plasticization.

Upcycling of waste polyesters for the development of a circular economy

The rapidly increasing production and widespread application of plastics have brought convenience to our lives, but they have consumed a huge amount of nonrenewable fossil energy, leading to additional CO2 emissions and generation of an enormous amount of plastic waste (also called white pollution). Chemical recycling and upcycling of waste plastic products (also called waste plastic refineries) into recycled monomers and/or valuable chemicals can decrease the dependence on fossil energy and/or reduce the emission of CO2, enabling the full utilization of carbon resources for the development of a circular economy. Polyesters, a vital class of plastics, are ideal feedstocks for chemical recycling due to the easily depolymerizable ester bonds compared to polyolefins. Among them, polyethylene terephthalate (PET) is the most widely used product, making its chemical recycling to a circular carbon resource a hot topic with significant concerns. In this feature article, recent progress in depolymerization of waste polyesters (PET and/or PET-containing materials) and the subsequent upgrading of depolymerized monomers (or intermediates) to valuable chemicals was reviewed and prospected. Newly reported technologies, such as thermal catalysis, photocatalysis, electrocatalysis, and biocatalysis, were discussed. The achievements, challenges, and potential of industrial applications of chemical recycling of polyesters were addressed.

Co-upcycling of Plastic Waste and Biowaste via Tandem Transesterification Reactions

Polyethylene terephthalate (PET) and glycerol are prevalent forms of plastic and biowaste, necessitating facile and effective strategies for their upcycling treatment. Herein, we present an innovative one-pot reaction system for the concurrent depolymerization of PET plastics and the transesterification of glycerol into dimethyl terephthalate (DMT), a valuable feedstock in polymer manufacturing. This process occurs in the presence of methyl acetate (MA), a byproduct of the industrial production of acetic acid. The upcycling of biowaste glycerol into glycerol acetates renders them valuable additives for application in both the biofuel and chemical industries. This integrated reaction system enhances the conversion of glycerol to acetins compared with the singular transesterification of glycerol. In this approach, cost-effective catalysts, based on perovskite-structured CaMnO3, were employed. The catalyst undergoes in situ reconstruction in the tandem PET/glycerol/MA system due to glycerolation between the metal oxides and glycerol/acetins. This process results in the formation of small metal oxide nanoparticles confined in amorphous metal glycerolates, thereby enhancing the PET depolymerization efficiency. The optimized coupled reaction system can achieve a product yield exceeding 70% for glycerol acetates and 68% for PET monomers. This research introduces a tandem pathway for the simultaneous upcycling of PET plastic waste and biowaste glycerol with minimal feedstock input and maximal reactant utilization efficiency, promising both economic advantages and positive environmental impacts.

Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

Polyesters carrying polar main-chain ester linkages exhibit distinct material properties for diverse applications and thus play an important role in today's plastics economy. It is anticipated that they will play an even greater role in tomorrow's circular plastics economy that focuses on sustainability, thanks to the abundant availability of their biosourced building blocks and the presence of the main-chain ester bonds that can be chemically or biologically cleaved on demand by multiple methods and thus bring about more desired end-of-life plastic waste management options. Because of this potential and promise, there have been intense research activities directed at addressing recycling, upcycling or biodegradation of existing legacy polyesters, designing their biorenewable alternatives, and redesigning future polyesters with intrinsic chemical recyclability and tailored performance that can rival today's commodity plastics that are either petroleum based and/or hard to recycle. This review captures these exciting recent developments and outlines future challenges and opportunities. Case studies on the legacy polyesters, poly(lactic acid), poly(3-hydroxyalkanoate)s, poly(ethylene terephthalate), poly(butylene succinate), and poly(butylene-adipate terephthalate), are presented, and emerging chemically recyclable polyesters are comprehensively reviewed.

Depolymerization within a Circular Plastics System

The societal importance of plastics contrasts with the carelessness with which they are disposed. Their superlative properties lead to economic and environmental efficiency, but the linearity of plastics puts the climate, human health, and global ecosystems at risk. Recycling is fundamental to transitioning this linear model into a more sustainable, circular economy. Among recycling technologies, chemical depolymerization offers a route to virgin quality recycled plastics, especially when valorizing complex waste streams poorly served by mechanical methods. However, chemical depolymerization exists in a complex and interlinked system of end-of-life fates, with the complementarity of each approach key to environmental, economic, and societal sustainability. This review explores the recent progress made into the depolymerization of five commercial polymers: poly(ethylene terephthalate), polycarbonates, polyamides, aliphatic polyesters, and polyurethanes. Attention is paid not only to the catalytic technologies used to enhance depolymerization efficiencies but also to the interrelationship with other recycling technologies and to the systemic constraints imposed by a global economy. Novel polymers, designed for chemical depolymerization, are also concisely reviewed in terms of their underlying chemistry and potential for integration with current plastic systems.

Comparsion of Catalyst Effectiveness in Different Chemical Depolymerization Methods of Poly(ethylene terephthalate)

This paper presents an overview of the chemical recycling methods of polyethylene terephthalate (PET) described in the scientific literature in recent years. The review focused on methods of chemical recycling of PET including hydrolysis and broadly understood alcoholysis of polymer ester bonds including methanolysis, ethanolysis, glycolysis and reactions with higher alcohols. The depolymerization methods used in the literature are described, with particular emphasis on the use of homogeneous and heterogeneous catalysts and ionic liquids, as well as auxiliary substances such as solvents and cosolvents. Important process parameters such as temperature, reaction time, and pressure are compared. Detailed experimental results are presented focusing on reaction yields to allow for easy comparison of applied catalysts and for determination of the most favorable reaction conditions and methods.

Economical Chemical Recycling of Complex PET Waste in the Form of Active Packaging Material

Since millions of tons of packaging material cannot be recycled in conventional ways, most of it ends up in landfills or even dumped into the natural environment. The researched methods of chemical depolymerization therefore open a new perspective for the recycling of various PET materials, which are especially important for packaging. Food preservative packaging materials made from PET plastics are complex, and their wastes are often contaminated, so there are no sophisticated solutions for them in the recycling industry. After integrating the biopolymer chitosan, which is derived from natural chitin, as an active surface additive in PET materials, we discovered that it not only enriches the packaging material as a microbial inhibitor to reduce the bacteria Staphylococcus aureus and Escherichia coli, thus extending the shelf life of the contained food, but also enables economical chemical recycling by alkaline or neutral hydrolysis, which is an environmentally friendly process. Alkaline hydrolysis at a high temperature and pressure completely depolymerizes chitosan-coated PET packaging materials into pure terephthalic acid and charcoal. The products were characterized by Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and elemental analysis. The resulting reusable material represents raw materials in chemical, plastic, textile, and other industries, in addition to the antimicrobial function and recyclability itself.

Catalytic Transformation of PET and CO2 into High-Value Chemicals

Polyethylene terephthalate (PET) and CO₂ , two chemical wastes that urgently need to be transformed in the environment, are converted simultaneously in a one-pot catalytic process through the synergistic coupling of three reactions: CO₂ hydrogenation, PET methanolysis and dimethyl terephthalate (DMT) hydrogenation. More interestingly, the chemical equilibria of both reactions were shifted forward due to a revealed dual-promotion effect, leading to significantly enhanced PET depolymerization. The overall methanol yield from CO₂ hydrogenation exceeded the original thermodynamic equilibrium limit since the methanol was in situ consumed in the PET methanolysis. The degradation of PET by a stoichiometric ratio of methanol was significantly enhanced because the primary product, DMT was hydrogenated to dimethyl cyclohexanedicarboxylate (DMCD) or p-xylene (PX). This synergistic catalytic process provides an effective way to simultaneously recycle two wastes, polyesters and CO₂ , for producing high-value chemicals.

Mechanistic aspects of poly(ethylene terephthalate) recycling-toward enabling high quality sustainability decisions in waste management

Since plastic waste pollution is a severe environmental concern in modern life, the demand for recycling poly(ethylene terephthalate) (PET) has increased due to its versatile applications. Taking advantage of plastic recycling methods creates the chances of minimizing overall crude oil-based materials consumption, and as a result, greenhouse gasses, specifically CO₂, will be decreased. Although many review articles have been published on plastic recycling methods from different aspects, a few review articles exist to investigate the organic reaction mechanism in plastic recycling. This review aims to describe other processes for recycling bottle waste of PET, considering the reaction mechanism. Understanding the reaction mechanism offers practical solutions toward protecting the environment against disadvantageous outgrowths rising from PET wastes. PET recycling aims to transform into a monomer/oligomer to produce new materials from plastic wastes. It is an application in various fields, including the food and beverage industry, packaging, and textile applications, to protect the environment from contamination and introduce a green demand for the near future. In this review, the chemical glycolysis process as an outstanding recycling technique for PET is also discussed, emphasizing the catalysts' performance, reaction conditions and methods, degradation agents, the kinetics of reactions, and reprocessing products. In general, a correct understanding of the PET recycling reaction mechanism leads to making the right decisions in waste management.

Strategic Possibility Routes of Recycled PET

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

Molecular catalyst systems as key enablers for tailored polyesters and polycarbonate recycling concepts

A transition metal catalyst system for the selective catalytic depolymerization of various polyester- and polycarbonate-based materials is presented. The use of a molecular ruthenium catalyst with selected triphos ligands enabled a selective hydrogenolysis of a large diversity of polymeric consumer products, paving the way to innovative and sustainable recycling strategies within a circular economy.

Scanning electron microscopic study of hazardous waste flakes of polyethylene terephthalate (PET) by aminolysis and ammonolysis

Polyethylene terephthalate (PET) waste flakes were degraded with aqueous methylamine and aqueous ammonia, respectively at room temperature in the presence and absence of quaternary ammonium salt as a catalyst for different periods of time. The aminolysed and ammonolysed PET samples were investigated for the surface morphology with the help of scanning electron micrograph (SEM). It shows that the semi-crystalline PET waste samples reduce to monodisperse rods before fully degradation to the end products. The presence of the catalyst provides site for degradation of PET waste and enhances the rate of degradation. The SEM shows early developments of fissures in comparison to the one in absence of quaternary ammonium salt used as catalyst.

Recycling of waste PET into useful textile auxiliaries

Polyethylene terephthalate (PET) waste fibers were initially depolymerized using a glycolysis route in the presence of sodium sulfate as a catalyst, which is a commonly used chemical and ecofriendly as compared to heavy metal catalysts. Good yield of the pure monomer bis(2-hydroxyethylene terephthalate) (BHET) was obtained. Further, to attempt its reuse, the purified BHET was converted to different fatty amide derivatives to obtain quaternary ammonium compounds that have a potential for use as softener in the textile finishing process. The products were characterized by infrared spectroscopy. Application of these synthesized compounds was carried out on cotton fabric; they were evaluated for performance and were found to give good results. The chemicals used during depolymerization and reuse of PET are inexpensive and comparatively less harmful to the environment, and thus offer advantages in the chemical recycling of polyester waste fibers.