Hydrolysis of post-consume poly(ethylene terephthalate) with sulfuric acid and product characterization by WAXD, 13C NMR and DSC

Chemical recycling of polymer contaminated poly(ethylene terephthalate) by neutral hydrolysis

Plastic recycling is gaining traction to reduce the demand for fossil resources for plastic production. Poly(ethylene terephthalate) (PET), mainly used in the packaging and textile sectors, is often isolated in the sinking fraction during the density-based separation of mixed plastic waste streams. The heterogeneity of the sinking fraction makes direct mechanical recycling of PET impossible. Therefore, neutral hydrolysis of PET was investigated in the presence of other polymer contaminants to study their impact on the neutral hydrolysis of PET. PA6, PC, POM, and PVC were found to decompose during hydrolysis, whereas ABS, PMMA and a mixture of PE, PP and PS was chemically inert during the hydrolysis treatment. The subsequent BHET synthesis with excess ethylene glycol was performed directly on a mix of the polymer contaminated hydrolysis products or a hydrolyzed post-consumer plastic waste fraction. BHET was successfully formed in the plethora of decomposition products in the synthesis, and a subsequent recrystallization recovered the BHET in high purity with only water being used as solvent. This demonstrated a robust method to handle PET fractions in mixed plastic waste that can be applied without purification prior to BHET synthesis - enabling chemical recycling of PET. Abbreviations: ABS, Poly(acetonitrile-butadiene-styrene); ATR-FTIR, Attenuated Total Reflectance Fourier Transformed Infrared Spectroscopy; BC, Bis(2-Hydroxyethyl) terephthalate crystals; BHET, Bis(2-Hydroxyethyl) terephthalate; DMSO, Deuterated dimethyl sulfoxide; DSC, Differential Scanning Calorimetry; EG, Ethylene glycol; 1H NMR, Proton Nuclear Magnetic Resonance; Hm, Melting enthalpy; Oligo, Oligomers; PA6, Polyamide 6; PC, Polycarbonate; PE, Polyethylene; PET, Poly(ethylene terephthalate); PMMA, Poly(methyl methacrylate); POM, Polyoxymethylene; PP, Polypropylene; PS, Polystyrene; P, Purity; PVC, Poly(vinyl chloride); rpm, Revolutions per minute; SPHP, Solid Phase Hydrolysis Product; Ti(IV)OBu, Titanium(IV) butoxide; Tm, Melting temperature; TPA, Terephthalic acid; Wt, Weight; Y, Solid Phase Hydrolysis Product yield; Yt, Bis(2-Hydroxyethyl) terephthalate yield; ν, IR stretching mode; δ, IR bending mode; ω, IR wagging mode.

Innovative approaches to chemical recycling of polyethylene terephthalate waste: Investigating key components and their emerging applications

Polyethylene Terephthalate, a widely recognized thermoplastic, is used in numerous sectors including packaging, textiles, electronics, construction, and medical due to its lightweight, cost-efficiency, transparency, flexibility, quick drying, durability and excellent gas/moisture barrier properties. However, its non-biodegradable nature poses significant environmental concerns, necessitating effective recycling and reuse methods. Over the past decades, scientists have focused on both mechanical and chemical recycling methods for PET waste to produce new molecules with potential applications. This review provides a comprehensive account of utilizing PET waste as a feedstock for synthesizing new molecules through various recycling techniques. An up-to-date and comparative overview of different chemical recycling techniques, including ammonolysis, aminolysis, glycolysis, alcoholysis, and hydrolysis in terms of reactants, reaction conditions, products, and yields are outlined. Applications of depolymerized end products like terephthalamide, NN'-bisallyl-terephthalamide, terephthalic dihydrazide, NN'-diphenyl-terephthalamide, dimethyl-terephthalate, dimethyl terephthalate, bis-hydroxyethyl-terephthalate (BHET), bis-hydroxy ethylene terephthalamide (BHETA), terephthalic acid etc. are succinctly presented. These products found potential industrial applications including thermostabilizers, surfactants, hardeners, peptisers, photoinitiators, crosslinkers, plasticizers, adsorbents, sealants, catalysts, etc. Additionally, the conversion of these depolymerized end products into other useful compounds like terephthalonitrile, para-xylylenediamine, 1,4-bis(aminomethyl)cyclohexane, lanthanum complexes, acrylates, BHET and BHETA derivatives, oxadiazole derivatives, 2,2'-(1,4-phenylene)-bis(2-oxazoline), 1,4-cyclohexanedimethanol, dyes, dioctyl terephthalate, butylene-adipate-co-terephthalate, terephthaloyl dichloride etc. has also been detailed along with their potential applications.

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.

Theoretical studies on glycolysis of poly(ethylene terephthalate) in ionic liquids

Ionic liquids (ILs) present superior catalytic performance in the glycolysis of ethylene terephthalate (PET). To investigate the microscopic degradation mechanism of PET, density functional theory (DFT) calculations have been carried out for the interaction between ILs and dimer, which is considered to symbolize PET. We found that hydrogen bonds (H-bonds) play a critical role in the glycolysis process. In this study, 24 kinds of imidazolium-based and tertiary ammonium-based ILs were used to study the effect of different anions and cations on the interaction with PET. Natural bond orbital (NBO) analysis, atoms in molecules (AIM) and reduced density gradient (RDG) approaches were employed to make in-depth study of the nature of the interactions. It is concluded that the interaction of cations with dimer is weaker than that of anions and when the alkyl chain in the cations is replaced by an unsaturated hydrocarbon, the interaction will become stronger. Furthermore, anions play more important roles than cations in the actual interactions with dimer. When the hydrogen of methyl is replaced by hydroxyl or carboxyl, the interaction becomes weak for the amino acid anions and dimer. This work also investigates the interaction between dimer and ion pairs, with the results showing that anions play a key role in forming H-bonds, while cations mainly attack the oxygen of carbonyl and have a π-stacking interaction with dimer. The comprehensive mechanistic study will help researchers in the future to design an efficient ionic liquid catalyst and offer a better understanding of the mechanism of the degradation of PET.

Co-interaction lead to glycolysis of ethylene terephthalate (PET) in ionic liquids (ILs): H-bonds and π-stacking.

Polymeric cracking of waste polyethylene terephthalate to chemicals and energy

Polyethylene terephthalate (PET) is a widely used thermoplastic. PET residues represent on average 7.6 wt% of the different polymer wastes in Europe. Pyrolysis of these wastes is attracting increasing interest, and PET is a potential candidate for this thermal process. The paper measures and discusses the kinetics of the pyrolysis reaction in terms of the reaction rate constants as determined by dynamic thermogravimetric analysis, with special emphasis on the required heating rate to obtain relevant results. The product yields and compositions are also determined. Gaseous products represent 16-18 wt%. The amounts of condensables and carbonaceous residue are a function of the operating mode, with slow pyrolysis producing up to 24 wt% of carbonaceous residue. Major condensable components are benzoic acid, monovinyl terephthalate, divinyl terephthalate, vinyl benzoate, and benzene. The present paper complements previous literature findings by (1) the study of the influence of the heating rate on the reaction kinetics in dynamic pyrolysis tests, (2) the isothermal investigation in a fluidized bed reactor to pyrolyze PET, and (3) the assessment of upgrading and recovery of the products. The paper concludes with a proposed reactor recommendation for PET pyrolysis, in either the bubbling or circulating fluidized bed operating mode.