Chemical Recycling Process Research Articles

Polyurethane Waste Recycling: Thermolysis of the Carbamate Fraction.

The alcoholysis of polyurethane waste is currently being industrialized, making it one of the most advanced chemical recycling processes for polyurethanes. However, the recycling potential of the dicarbamate phase, which accounts for 10-40% of the polyurethane mass, is often disregarded, as mainly the polyol components are (partially) retrieved in many alcoholysis processes. In this study, we present a two-step recycling method in which the valuable carbamate fraction obtained in the initial alcoholysis step is transformed into an isocyanate-rich mixture through an additional thermolysis step. For this purpose, different carbamates were synthesized and thermolyzed, which showed that thermolysis with isopropyl-carbamate was the most favorable, obtaining a yield of 35%. As a result, the isocyanates obtained through thermolysis and the polyols obtained through alcoholysis can be reused as starting materials in polyurethane synthesis.

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.

Novel chemical recycling process of REBCO materials showcased on TSMG-processed waste

Due to the increasing production of rare-earth barium copper mixed oxide (REBCO) superconductors, a significant amount of REBCO waste is produced. The following recycling technique allows REBCO waste reprocessing into new precursor powder.

Shaping a federal strategy for chemical recycling: Moving toward sensible applications of emerging technologies in US plastic waste management

AbstractPlastic waste management requires a diverse portfolio of strategies to avoid the most damaging environmental and social impacts of the plastic lifecycle and meet current national and international policy goals. The limitations of existing mechanical recycling methods for processing plastic waste have motivated the development and commercialization of chemical recycling processes. The novelty and diversity of such pathways beg critical questions of how these emerging technologies will fit within existing policy frameworks and contribute to recycling, plastic pollution, and waste management policy objectives. This work provides technical background into mechanical and chemical recycling methods, and policy background into differing modern approaches to chemical recycling at various levels of governance. Finally, this work summarizes key conflicts and crafts recommendations for future policy action on chemical recycling in three main areas: (1) defining an objective and identifying sensible applications for chemical recycling technologies, (2) filling gaps in existing knowledge and upholding environmental justice protections, and (3) implementing a suite of policies to complement chemical recycling's role in plastic waste management strategy.

Chemical recycling of green poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)-based air filters through hydrolysis

Sustainable alternatives based on biodegradable polymers, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), can potentially reduce the environmental impact generated by the massive disposal of face masks. However, the destination of this biodegradable material in post-consumer landfills or composting consumes energy and does not necessarily reduce environmental damage. Therefore, it is necessary to find ways to return this material to the chemical chain, such as chemical recycling through hydrolysis. In this context, the present work aimed to produce face masks by solution blow spinning (SBS) from solutions containing 4, 6, and 8 m/v% of PHBV and assess the polymer recyclability through hydrolysis. The filters were subjected to hydrolytic reactions in aqueous solutions with pH values of 4, 7, and 10 at 40, 60, and 80 °C for three weeks based on a standard statistical design of experiments (DoE). The fibers produced with solutions containing 4 m/v% of polymer provided the highest weight loss of 68 wt% after three weeks immersed in an aqueous solution (pH = 4 at 80 °C), exhibiting the lowest environmental impact during the chemical recycling process. The ANOVA analyses showed that the fiber diameter was the most significant factor during the recycling reactions, evidencing that materials should be designed to promote the principles of the circular economy. Based on the obtained results, it can be concluded that PHBV-based face mask filters can promote the principles of the circular economy if polymer fibers are correctly designed. Finally, they can also potentially reduce the environmental damage of face mask disposal as long as the recycling process is in place with a proper collection and sorting system.

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.

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.

Mass balance accounting: Considerations for circular polymers

AbstractWhile plastic packaging and products have greatly benefitted civilization, the current and historical approaches to design, use, and end‐of‐life management have resulted in significant challenges, particularly in recovering and retaining the economic value of the materials and preventing plastic pollution. The dominant route for recycling plastic in the United States and elsewhere has been mechanical recycling, which is effective for select polymer types and package designs and has potential for growth. However, several regulatory, technical, and economic challenges will ultimately cap the fraction of plastic waste recovered by mechanical recycling technologies, and as a result, chemical recycling―processes that either break covalent bonds or otherwise exploit fundamental chemical processes to return molecules to early or mid‐stage chemical production―has great appeal, especially for plastic products most challenging for mechanical recycling. Due to the nature of some chemical recycling technologies, specifically that molecules derived from chemically recycled polymers become indistinguishable from primary feedstocks and thus not traceable or measurable in the process, the mass balance (MB) accounting chain of custody model has been proposed as a tool to track, trace, and certify circular polymers. While MB certification standards have an extensive history in other commodity sectors, they have only recently been considered in the polymers sector in part due to recent technology advances and incentives to expand chemical recycling. Here we discuss the roll of MB in polymer circularity, including controversial aspects, and provide technical examples to describe its potential applicability. We further provide recommendations for the effective use of MB to certify circular polymers.This article is categorized under: Climate and Environment > Pollution Prevention Climate and Environment > Circular Economy Emerging Technologies > Materials

Braskem to purchase plastic-waste-derived feedstock from Vitol SA, produced by WPU - Waste Plastic Upcycling A/S in Denmark

Braskem and Vitol S.A. have announced an agreement for circular feedstock derived from plastic waste. Under the agreement, Vitol will start to supply Braskem Netherlands B.V. with pyrolysis oil produced in the chemical recycling process at the facilities of WPU - Waste Plastic Upcycling A/S, in Denmark.

Techno-economic analysis and process optimization of a PET chemical recycling process based on Bayesian optimization

Chemical recycling has gained interest as a promising option to reduce the consumption of fossil feedstocks and relieve environmental issues concerning plastic waste. In this study, we present a preliminary techno-economic analysis of a process design for chemical recycling of polyethylene terephthalate (PET). A conceptual base case design was developed for a continuous catalytic PET depolymerization process. The process design was optimized to minimize total annualized cost (TAC) based on a simulation-based Bayesian optimization approach. A novel interface was utilized to manipulate the process variables, and to retrieve simulation and economic evaluation results. Through five trials of optimization, the process design was improved by about 4.2∼4.4 % in terms of TAC. Sensitivity analyses investigating the effect of process parameters and price variables on the minimum selling price of main product, p-xylene, are presented. The feedstock PET flake price was identified as the most critical factor affecting the economic viability of the process.

The role of chemical and solvent-based recycling within a sustainable circular economy for plastics

Chemical and solvent-based recycling of plastic waste may help overcome some of the challenges faced by predominantly applied mechanical recycling techniques. This study quantifies the environmental impacts of chemical and solvent-based recycling as a function of varying process parameters and product composition using life cycle assessment. Furthermore, potential benefits and impacts on a system level are determined. To that end, a high-resolution material flow analysis is conducted for the reference system of Switzerland, covering all main plastic types and applications. In a scenario for the year 2040, we employ environmentally beneficial mechanical recycling where possible and convey suitable remaining waste streams to chemical or solvent-based recycling processes. Applying chemical or solvent-based recycling as a complement to maximum mechanical recycling, instead of thermal treatment with energy recovery, may achieve a reduction in the climate change impact of the system ranging from less than 10 % to almost 40 %. For achieving high environmental benefits, proper process choice and configuration are crucial. Dissolution or depolymerization provide higher benefits relative to other chemical recycling processes, but can only treat certain waste streams and require prior sorting into plastic types. Pyrolysis and gasification appeared to only have the ability to achieve substantial benefits over incineration if their output products can substitute high-impact chemicals and provided that efficient heat transfer and recovery is warranted when implemented on a large scale. As industrial-scale plants for chemical or solvent-based plastic recycling are still lacking, the upscaling potential and the environmental benefits achievable in practice are highly uncertain today.

Design and Fabrication of a Customized and Fully‐Recyclable Carbon Fibers/Epoxy Composites Prostheses via a Functional Additive Manufacturing Approach

AbstractThis study presents an innovative approach based on the combination of two different techniques for fiber‐reinforced epoxy composites manufacturing, i.e., additive manufacturing (AM) and hand lay‐up‐assisted vacuum bagging. It represents a proof of concepts for the manufacturing of a customized and lightweight lower‐limb prostheses having built‐in functional elements, such as sensors. In particular, a soluble tool for fabricating a complex‐shaped carbon reinforced epoxy composite is produced by AM. The 3D printed model is properly designed to integrate a functional element, in a customized way, within the composite structure itself. Moreover, a fully‐recyclable epoxy resin system is used as matrix for the fabricated composite part to recover the expensive functional part and carbon fibers as soon as the prostheses has reached the end of its life (EoL). The prostheses recycle is carried out through a chemical recycling process that relies on the presence of acid‐cleavable groups within the epoxy‐cured network that allows for the cleavage of the crosslink under certain conditions. A similar approach is proposed in the state of art, but by using the traditional autoclave prepreg process and without considering the handling of the part at its EoL.

Chemical Recycling Processes of Nylon 6 to Caprolactam: Review and Techno-Economic Assessment

Chemical Recycling Processes of Nylon 6 to Caprolactam: Review and Techno-Economic Assessment

Printability of a Recycled Thermoplastic Obtained from a Chemical Recycling Process of a Fully‐Recyclable Epoxy Matrix: An Upscaling Re‐Use Strategy

AbstractThis study presents an upscaling re‐use strategy for a recycled thermoplastic which is obtained starting from a chemical recycling approach for a bio‐based fully‐recyclable epoxy resin system. The recycling approach used relies on the selective cleaving of the epoxy‐cured network under mild conditions. The re‐use strategy proposed in this work consists in the use of the recycled thermoplastic (rTP), as obtained at the end of the recycling process and without any additional treatments, as raw material for a 3D printing process falling within the material extrusion category. The used 3D printing technique relies on the use of a thermoplastic printhead equipped with a metallic cartridge, fillable with the rTP material, to which a suitable pressure value is applied in order to start the extrusion process. The recycled material is characterized through thermal and rheological analysis in order to find the correct printing conditions, such as extrusion temperature and pressure applied. Next, the printability of specimens having different type of infill is investigated and the µCT analysis is used to evaluate the quality of the 3D printed samples.

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.

Chemical recycling of polyolefins: a closed-loop cycle of waste to olefins.

The unsuitable disposal of plastic wastes has caused serious environmental pollution, and finding a green manner to address this problem has aroused wide concern. Plastic wastes, especially polyolefin wastes, are rich in carbon and hydrogen, and chemical recycling shows distinct advantages in their conversion into olefins and realizes a closed-loop cycling of plastic wastes. Plastic wastes should be labeled before disposal. The necessity for, and methods of, pretreatment are introduced in this paper and the whole recycling process of polyolefin wastes is also summarized. As the core technology pyrolysis, including thermal, catalytic and solvolysis processes, is introduced in detail due to its potential for future development. We also briefly describe the feasible strategies of pyrolytic oil refining and life cycle assessment of the chemical recycling process. In addition, suggestions and perspectives concerning the industrial improvement of polyolefin chemical recycling are proposed.

Mono-material product design with bio-based, circular, and biodegradable polymers

Mono-material product design with bio-based, circular, and biodegradable polymers

Chemical-Physical Characterization of Bio-Based Biodegradable Plastics in View of Identifying Suitable Recycling/Recovery Strategies and Numerical Modeling of PLA Pyrolysis

Several bio-based and biodegradable polymers have been lately introduced on the market as potential substitutes for conventional plastics in order to decrease the environmental impacts related to plastics manufacturing and especially end of life disposal. The most applied route for the management of these types of bioplastics once they enter the waste stream is co-treatment with biowaste in anaerobic digestion and/or composting plants that may lead to their recycling as digestate and/or compost. Several studies however, have reported the incomplete biodegradation of these materials at lab-scale and/or in conventional treatment plants and the significant content of small inert particles, including microplastics, in the final products. This could represent an obstacle to the agricultural use of the produced digestate and/or compost. It is therefore necessary to study all the possible options for the recycling of these types of materials based on the specific characteristics of the polymers that constitute them. In this study, four different types of bio-based biodegradable plastics were characterized by chemical-physical analysis. In particular, the main properties investigated included the content of volatile and non-volatile phases, crystallinity, main elemental composition, content of different phases by spectroscopic investigation using Fourier Transform InfraRed spectra and of metals and metalloids of potential environmental concern. The results of the thermogravimetry analysis indicated that all of the recycling/recovery options considered (compost production via biodegradation, chemical recycling and energy recovery) could be potentially applicable for the examined bioplastics, since they showed to contain polymers that volatilize below 550 °C. The highest volatile matter contents were measured for PLA cups and starch-based films, while the highest ash contents were found for the other two types of rigid bioplastics, which also showed the highest concentrations of elements of potential environmental concern, that were anyhow quite limited, and reduced higher heating values estimated by elemental analysis compared to PLA or starch-based films. In addition, the rigid bioplastics tested exhibited a higher degree of crystallinity, which could be associated to a lower biodegradability. With regard to chemical recycling processes, the results of the chemical-physical investigations indicated that pyrolysis could be a technically viable process to apply for the treatment of all of the bioplastic samples examined. Thus, PLA, which is manufactured through lactic acid condensation, chemical recycling by rapid depolymerization through pyrolysis was evaluated applying a numerical model implemented in Aspen plus®. Results indicated that the best yields in terms of lactide recovery could be obtained at an temperature of 400 °C and 10 s residence time and that other valuable products may be obtained potentially by fractional condensation.Graphical

Chemical Recycling Processes of Waste Polyethylene Terephthalate Using Solid Catalysts.

Polyethylene terephthalate (PET) is a non-degradable single-use plastic and a major component of plastic waste in landfills. Chemical recycling is one of the most widely adopted methods to transform post-consumer PET into PET's building block chemicals. Non-catalytic depolymerization of PET is very slow and requires high temperatures and/or pressures. Recent advancements in the field of material science and catalysis have delivered several innovative strategies to promote PET depolymerization under mild reaction conditions. Particularly, heterogeneous catalysts assisted depolymerization of post-consumer PET to monomers and other value-added chemicals is the most industrially compatible method. This review includes current progresses on the heterogeneously catalyzed chemical recycling of PET. It describes four key pathways for PET depolymerization including, glycolysis, pyrolysis, alcoholysis, and reductive depolymerization. The catalyst function, active sites and structure-activity correlations are briefly outlined in each section. An outlook for future development is also presented.

Experimental evaluation of diesel blends mixed with municipal plastic waste pyrolysis oil on performance and emission characteristics of CI engine

The growing population's amassed municipal mixed plastic waste (MMPW) and the depletion of fossil fuels are the major causes of concern. Explosive population growth has put us on the brink of an energy crisis. Therefore, an alternative energy source is required to meet the energy demand of a growing population. The chemical recycling of MMPW may be feasible to reduce plastic waste and recover energy products, especially liquid. Pyrolysis is a chemical recycling process employed in the study to produce high-grade plastic oil (PO). An investigation has been conducted on the pyrolysis of MMPW at 550 °C and has obtained 69.8 wt% PO. Moreover, different blends of PO (PO25D75, PO50D50, PO75D25 and PO100) have been used to analyse the CI engine characteristics. The engine fueled with neat plastic oil produced 6.90% less BTE than the reference diesel. However, increasing the PO proportion in diesel increased cylinder pressure and the net heat release rate (NHRR). The emissions such as CO, HC, and NOx were higher for all plastic oil blends at a 12 kg engine load, whereas CO2 and smoke opacity were reduced by 21.81% and 4.47% for PO100 at a higher engine load (12 kg) as compared to reference diesel.