Chemical Upcycling Research Articles

One-pot Hydrogenolysis of Polyethylene Terephthalate (PET) to p-xylene over CuZn/Al2O3 Catalyst.

Chemical upcycling of plastic wastes into valuable chemicals is a promising strategy for resolving plastic pollution, but economically viable methods currently are still lacking. Here, we report one-pot hydrogenolysis of PET plastic into p-xylene with an excellent yield (99.8 %) over a robust non-precious Cu-based catalyst, CuZn/Al2O3, in the absence of alcohol solvents. The presence of Zn species promotes the dispersion of Cu0 and increases the ratio of Cu+/Cu0, whereas the synergistic effect of Cu0 and Cu+ leads to a superior performance in the conversion of PET. The combination of GC-MS, 13C CP MAS NMR, 2D 1H-13C CP HETCOR NMR spectroscopy and kinetic studies for the first time demonstrates 4-methyl benzyl alcohol as an important reaction intermediate in the hydrogenolysis of PET. Mechanistic studies indicate that the conversion of PET mainly follows a hydrogenolysis process, involving the cleavage of ester bonds to alcohols and the C-O bond cleavage of alcohols to alkanes. This work not only brings new insight for understanding the upgrading pathway of PET, but also provides a guidance for the design of high-performance non-precious catalysts for the chemical upcycling of plastic wastes.

Alanine Production by Chemical Upcycling of Polylactic Acid Waste Over Fe-Doped Ru/CeO2.

Biodegradable polyesters, such as polylactic acid (PLA), is one of the most promising plastics with great potential to contribute to enabling a sustainable global circular economy. However, the efficient chemical upcycling of PLA plastic waste into high-value chemicals remains a grand challenge. Herein, a series of Ru/CeFeOx catalysts with varying Ru loadings were developed for the catalytic amination of PLA plastic waste to alanine in the presence of ammonia. The as-prepared catalysts exhibited exceptional catalytic activity, high selectivity, and excellent recyclability, achieving an alanine yield of 70.5 % at 180 °C for 18 h, significantly surpassing previous reports. The outstanding catalytic performance can be primarily attributed to the presence of Fe species in Ru/CeFeOx, which generated more oxygen vacancies, provided abundant base sites, and enhanced reducibility, therefore accelerating the reaction rate and enhancing catalytic efficiency. This study presents an alternative strategy for the sustainable chemical upcycling of PLA plastic waste into alanine and the realization of a circular economy.

Chemical Upcycling of Expired Pharmaceuticals as a Source of Value-Added Chemicals for Organic Synthesis and Medicinal Chemistry.

Pharmaceutical and veterinary products are a class of contaminants of emerging concern, and their presence in the environment is due to continuous and incorrect disposal. Environmental scientists have been accumulating data on their adverse effects on animal populations since toxicological effects on wildlife were first published. Therefore, recycling strategies are needed. Valuable active ingredients can be extracted from expired pharmaceuticals and recycled according to various strategies. In an effort to reveal the potential of the chemical upcycling of expired pharmaceuticals, the active ingredients gabapentin and pregabalin were extracted and used as starting materials to prepare a small collection of promising substrates endowed with functionalities and structural three-dimensionality. Gabapentin 1 was transformed into aminoalcohol 3, spiroamine 4, and the bioactive azaspirolactam 5. The lactam analog 6 was synthesized from pregabalin 2. Due to the biological profile of 5 and the structural similarity of the N-alkylated derivatives 5l and 6b with the drug piracetam, a collection of potentially bioactive structural analogs 5a-l and 6a-b were also prepared. Simple extraction, synthesis, and purification procedures were used as a means of chemical and economic revaluation, resulting in moderate to good yields at a low cost.

Integrating thermodynamic and kinetic approaches for the design of effective and sustainable PET chemical upcycling systems

Understanding and optimizing the individual contributions of recycling process components are critical in the development of effective and sustainable upcycling systems. Herein, each process component, i.e., alcohol, co-solvent, Lewis acid, and reaction conditions, is newly and holistically assessed for the alcohol-based conversion of postconsumer polyethylene terephthalate (PET) to terephthalic acid (TPA) and its precursors by integrating thermodynamic and kinetic considerations. First, an analysis based on the Flory-Huggins interaction parameter (χ1,2) establishes the importance of co-solvents in the depolymerization process due to reduction of thermodynamic potential. Second, a kinetic analysis of the catalyst component proves the vitality of the solubility of the Lewis acid source for efficient PET deconstruction. In addition, further validation experiments determine methanol as the most effective option in tandem alcoholysis given its reduced steric hindrance and relatively higher nucleophilicity, whereas process optimization tests suggest the existence of an optimum methanol molar ratio (XMetOH) of 0.16 and operation at 50 °C to realize TPA yields that exceed 90 % within 15 min across various pure and mixed PET feedstocks. Selection and implementation of greener solvents in the process is also found to reduce co-solvent based emissions by 96.3 % whilst retaining comparable monomer production efficiency. Overall, the implementation of thermodynamic considerations and kinetics-based understanding of roles played by each component is found to boost the overall depolymerization process, and the integration of these thermodynamic and kinetic approaches provides a unified avenue for optimizing and developing sustainable recycling processes for post-consumer plastic waste.

Efficient polycarbonate plastic upcycling into jet fuel cycloalkanes over a bifunctional MoCo/NiC hetero-catalyst

While there are significant economic benefits associated with plastic recycling, the practical options for treating plastic waste remain relatively limited. This study introduces a novel bimetallic MOF-derived catalyst designed specifically for upcycling polycarbonate plastic into cycloalkanes within jet fuel range. By incorporating dual metals (MoCo) onto the MOF framework, the catalyst creates single metal sites and constructs heterojunctions. Characterizations revealed that the bifunctional catalyst can chemically adsorb phenolic compounds on a highly synergistic heterogeneous surface and lower the energy barrier of hydrodeoxygenation. Integrating the catalyst into a tandem reactor facilitates the conversion of PC plastics into jet-fuels. Achieving an average cycloalkane yield of 84.5% underscores the catalyst’s potential for deep hydrodeoxygenation of actual plastic waste. Furthermore, using waste CDs as feedstock, the cycloalkanes yield remains consistent even after three regeneration cycles, demonstrating the catalyst’s stability. In the low-carbon future, this high hydrodeoxygenation performance catalyst can be applied in chemical upcycling for pursuing a circular plastic economy.

Quaternarized chitosan nanofiber and ZIF aerogel composites for synergetic CO2 cycloaddition catalysis

Chemical upcycling of CO2, a major greenhouse gas, is attracting significant attention as a crucial strategy to combat global warming. The production of cyclic carbonate using metal-organic frameworks and their composites using nanofibrous carbohydrate polymer are promising ways to convert CO2 into valuable products. However, the current role of fibrous polymers is restricted to serving as physical substrates. This study seeks to expand the functionality of quaternarized chitosan nanofibers into synergistic catalysts in addition to their physical support role. A novel aerogel composite using Co/Zn-ZIF catalyst and quaternarized chitosan nanofiber (Q-CsNF+) was fabricated, and its hierarchical pore structure was extensively discussed. The obtained ZIF/Q-CsNF+ composite can synergistically convert epoxide to cyclic carbonate by acting as a co-catalyst. Moreover, we determined the predominant factors influencing catalytic activity in CO2 cycloaddition, especially by examining the interplay between CO2 affinity and co-catalyst effects. This research provides fundamental insight into developing CO2 cycloaddition catalysts using nature-derived fibrous polymers, opening new avenues for sustainable and efficient CO2 utilization.

Catalytic recycling of polylactic acid over zirconium phosphate supported WOx active sites

Chemical upcycling of end-of-life plastics is an economically and environmentally feasible way to tackle plastics crisis. Among them, methanol alcoholysis of polylactic acid (PLA) is a promising approach, which can produce methyl lactate (MLA) that can be further converted to lactide to achieve a sustainable development. In this work, a series of WOx/ZrP catalysts with WOx active sites in low coverage and high surface area were synthesized via anchoring WOx species on the surface of zirconium phosphate (ZrP). Characterizations indicated that the strong interaction between WOx and ZrP promoted the formation of WOx active sites in low coverage. In particular, 10 %WOx/ZrP catalyst was highly active and stable for the alcoholysis of PLA plastics under mild conditions due to the abundant WOx active sites and strong acidity. The yield of MLA over 10 %WOx/ZrP catalyst reached 94.5 % within 4 h at 160 °C, which was superior to the performance of traditional solid acids (α-ZrP, HZSM-5, Hβ and Amberlyst-45). In addition, 10 %WOx/ZrP was versatile for the alcoholysis of discarded PLA-based products and could be recycled at least five times. The prominent performance of 10 %WOx/ZrP catalyst and the possible reaction mechanism were discussed.

The fate of hazardous textile pollutants in an upcycling process for post-consumer garments

The environmental impact is a strong incentive for the development of upcycling processes for textile waste. However, toxic chemicals may occur in both brand-new textiles and post-consumer garments, and the chemical transfer in such routes is important to investigate. The present study applied non-target screening and quantification with liquid chromatography/mass spectrometry to follow the fate of hazardous chemicals from post-consumer polycotton garments to a new material, cellulose nanocrystals, in a chemical upcycling utilizing strongly acidic conditions. The majority of hazardous chemicals detected within the process were found to be transferred to a residual of polyester material and not to the enriched cellulose. However, phthalates were found to be mainly attached to the cellulose nanocrystals. The detected total concentration, in this case, was below 5 μg/g, at least 200 times lower than the limit set by the European Union. This indicates the importance of monitoring and controlling the phthalate content in the starting material of the process, i.e., the post-consumer garments. The chemical release into the process waste effluent could be estimated based on water solubility data for chemicals under the applied conditions. Three compounds, the water-repellent substance perfluorooctanesulfonic acid and the dyes Crystal Violet and Victoria Pure Blue, were almost entirely transferred into the process waste effluent. Although the levels detected were very low in the present pilot process, their presence eventually indicates the need for wastewater purification at further upscaling, depending on the exposure and dose in relation to toxicological relevant thresholds.

Chemical Upcycling of Polylactic Acid Plastic Waste into Alanine over Ru/CeO2 with Decoration of Indium

Chemical Upcycling of Polylactic Acid Plastic Waste into Alanine over Ru/CeO₂ with Decoration of Indium

Photochemical Aerobic Upcycling of Polystyrene Plastics via Synergistic Indirect HAT Catalysis.

Plastic pollution constitutes an evergrowing urgent environmental problem, since overaccumulation of plastic waste, arising from the immense increase of the production of disposable plastic products, overcame planet's capacity to properly handle them. Chemical upcycling of polystyrene constitutes a convenient method for the conversion of plastic waste into high-added value chemicals, suggesting an attractive perspective in dealing with the environmental crisis. We demonstrate herein a novel, easy-to-perform organocatalytic photoinduced aerobic protocol, which proceeds via synergistic indirect hydrogen atom transfer (HAT) catalysis under LED 390 nm Kessil lamps as the irradiation source. The developed method employs a BrCH2CN-thioxanthone photocatalytic system and was successfully applied to a variety of everyday-life plastic products, leading to the isolation of benzoic acid after simple base-acid work up in yields varying from 23-49 %, while a large-scale experiment was successfully performed, suggesting that the photocatalytic step is susceptible to industrial application.

Chemical upcycling of polyolefins into liquid refinery feedstock from the circularity and chemical engineering aspects

Three quarters of all plastics produced each year are discarded to landfill after a single use without proper waste management practices, causing a global environmental crisis: waste plastics suffocating our world at enormously large volumes. Discarding plastics into landfill, inefficiently processing them to lower value materials, or incinerating them cause an irreversible loss of the stored energy in plastics. These plastics, however, represent a tremendous resource for the production of chemicals and can be upcycled into high-quality value-added refinery feedstock that could be used to produce virgin polyolefins. In this article, we review pyrolysis and hydrogenolysis based chemical transformations to convert waste polyolefins into liquid hydrocarbons with a special emphasis on life cycle assessment (LCA), reactor technologies, and integration to existing refineries. Several patented technologies are described in detail to shed a light on engineering aspects of the chemical recycling. Liquid products obtained from chemical recycling are examined from the circularity point of view. Feedstock and stream locations in existing refineries and around steam crackers are recommended to feed and/or blend the products obtained from chemical recycling of polyolefins. Challenges, perspectives, and emerging areas of research and engineering are mentioned.

Chemical upcycling of high-density polyethylene into upcycled waxes as rheology modifiers and paper coating materials

Chemical upcycling of plastic waste from landfills to value-added products offers both economic and environmental benefits. Reported here is a simple method to convert high-density polyethylene (HDPE) into upcycled waxes in a very high yield (up to 93%). This selectivity is achieved by reducing the degradation temperature of HDPE via the addition of an inexpensive and reusable sodium chloride. These upcycled waxes had performance comparable to those of commercial rheology modifiers. In addition, kraft paper coated with these upcycled waxes exhibited excellent water- and oil resistance. A preliminary revenue analysis showed that this innovation allows plastic-to-wax to conversion with a three-fold revenue benefit over traditional ways of producing pyrolysis waxes from plastics. Also, sodium chloride reduces the pyrolysis temperature, thus reducing energy consumption and greenhouse gas emissions, supporting cleaner production, a circular economy, and generating less environmental pollution. The underlying concept reported herein can be extended to major plastics by reducing the degradation temperatures of plastics, thereby obtaining even better control over the pyrolysis products. Thus, these findings have the potential to enhance the circular economy of plastics and protect our environment from plastic waste.

Hydrogenation of the benzene rings in PET degraded chemicals over meso-HZSM-5 supported Ru catalyst

Chemical upcycling of waste polyethylene terephthalate (PET) to value-added products can reduce the emission of CO2, microplastics and toxic chemicals. In this work, mesoporous H-type Zeolite Socony Mobil-5 (HZSM-5) supported Ru catalyst (Ru/m-HZSM-5) was synthesized and tested in the hydrogenation of PET degraded chemicals (bis(2-hydroxyethyl) terephthalate, dimethyl terephthalate, diethyl terephthalate, and terephthalic acid). Characterizations disclosed that Ru/m-HZSM-5 catalyst possesses mesopores (a dominant channel of 5.32 nm), enlarged specific surface area (404 m2·g−1), and Ru NPs dispersed highly (40.6 %) compared to that of Ru/HZSM-5. And also, it was found that Ru/m-HZSM-5 was capable for the hydrogenation of benzene rings in these PET degraded chemicals with large sizes (1.09–1.82 nm). In particular, the conversion of BHET and the selectivity of BHCD over Ru/m-HZSM-5 reached 95.5 % and 95.6 % at 120 °C within 2 h. And Ru/m-HZSM-5 could be recycled at least five times without obvious loss of activity and selectivity.

Chemical Upcycling of Polyolefin Plastics Using Structurally Well-defined Catalysts

Chemical Upcycling of Polyolefin Plastics Using Structurally Well-defined Catalysts

Recent progress of waste plastic upcycling based on multifunctional zeolite catalysts

The chemical upcycling method is a promising strategy to alleviate the pollution problem of waste plastics by tapping into their intrinsic value and converting them into high value-added products. Zeolite-based catalysts are one of the surprising and efficient classes of thermocatalytic materials that have recently attracted considerable attention for waste plastic upcycling. They are designed for targeted applications with a wide range of adjustable acidic sites, multiple pore structures, and synergistic interactions with surface metals. In this review, we categorize plastics being converted into different high-value products and introduce the role of zeolite-based catalysts in the thermal upcycling of plastics. The structure-performance relationships of zeolite-based catalysts in catalytic reactions are discussed in depth. Finally, the future development of these multifunctional catalysts applied to the upcycling of plastics is outlined.

Zinc Catalyst for Chemical Upcycling of PLA Wastes: Novel Industrial Monomer Resource toward Poly(ester–amide)

Zinc Catalyst for Chemical Upcycling of PLA Wastes: Novel Industrial Monomer Resource toward Poly(ester–amide)

Chemical upcycling of poly(ethylene terephthalate) with binary mixed alcohols toward value-added copolyester by depolymerization and repolymerization strategy

The glycolysis is one of the most promising chemical ways for the disposal of waste Poly(ethylene terephthalate) (PET) due to the relative mild conditions. However, several serious issues still remain to be solved, including complex monomer purification, elusive product components, and ambiguous depolymerized mechanism. Herein, the depolymerization-repolymerization strategy of PET with ethylene glycol (EG)/cyclohexane-1,4-dimethanol (CHDM) binary mixed alcohols was proposed to prepare the value-added Poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) (PETG/PCTG). Based on the one-pot depolymerization-repolymerization process, a series of amorphous PETG/PCTG with high molecular weight (Mn > 25,000 g/mol) and glass transition temperature can be prepared. The controlled depolymerization of PET into oligomers with higher molecular weight is of great importance to obtain high molecular weight PETG copolyesters according to the hierarchical process. The depolymerization mechanism of PET with mixed EG/CHDM was deeply elucidated, in which EG depolymerizes PET chains into the short ones, and CHDM undergoes transesterification with ester group on the end group of BHET monomers and oligomers with different molecular weight to substitute the ethylene glycol terephthalate (ET) units into 1,4-cyclohexanedimethanol terephthalate (CT) units. For post-consumer PET, the depolymerization-repolymerization of colorless PET bottle can form the rPETG with higher intrinsic viscosity, molecular weight, and thermal properties, superior to the PET film and colored bottles. The information in this work is of great importance for the upcycling of PET waste.

Synergism of solar-driven interfacial evaporation and photo-Fenton Cr(VI) reduction by sustainable Bi-MOF-based evaporator from waste polyester

The integration of interfacial solar steam generation and photocatalytic degradation technology has provided a promising platform to simultaneously produce freshwater and degrade pollutants. However, constructing low-cost, multi-functional evaporators for treating Cr(VI)-polluted water remains challenging, and the synergistic mechanism on Cr(VI) reduction is fuzzy. Herein, we propose the combined strategy of ball milling and solution mixing for the sustainable production of Bi-MOF microrod from waste poly(ethylene terephthalate), and construct Bi-MOF-based solar evaporators for simultaneous photo-Fenton Cr(VI) reduction and freshwater production. Firstly, the evaporator comprised of Bi-MOF microrod and graphene nanosheet possesses high light absorption, efficient photothermal conversion, and good hydrophilic property. Attributing to the advantages, the hybrid evaporator exhibits the evaporation rate of 2.16 kg m−2 h−1 and evaporation efficiency of 87.5% under 1 kW m−2 of irradiation. When integrating with photo-Fenton reaction, the Cr(VI) reduction efficiency is 91.3%, along with the reaction kinetics of 0.0548 min−1, surpassing many advanced catalysts. In the outdoor freshwater production and Cr(VI) reduction, the daily accumulative water yield is 5.17 kg m−2 h−1, and the Cr(VI) reduction efficiency is 99.9%. Furthermore, we prove that the localization effect derived from the interfacial solar-driven evaporation enhances H2O2 activation for the photo-Fenton reduction of Cr(VI). Based on the result of density functional theory, Bi-MOF microrod provides rich active centers for H2O2 activation to produce active sites such as e− or ·O2−. This study not only proposes a new strategy to construct multi-functional solar evaporators for freshwater production and catalytic reduction of pollutants, but also advances the chemical upcycling of waste polyesters.

Enhanced catalytic hydrogenolysis of natural rubber to natural gas over Ru/ZrO2 via phase control strategy

The inert CC and C-C bonds is a major limitation for the degradation and utilization of rubber wastes, which has resulted in the increasingly serious environmental crisis. Here we developed an efficient strategy to catalyze complete cleavage of CC and C-C bonds in natural rubber by the enhanced reaction activity of Ru-based catalysts with the modulated ZrO2 crystal phases. And 95.0% of gas carbon yield with 98.6 mol% of CH4 and 1.4 mol% of C2-C4 hydrocarbons was achieved over Ru/m-ZrO2, which was more than 3 times higher than gas carbon yield over Ru/c-ZrO2 and Ru/t-ZrO2. The investigation on reaction pathway displayed that the primary hydrogenation of CC bonds with high bond energy would promote the transformation of natural rubber. The Ru0 species and spill-over hydrogen in Ru/m-ZrO2 catalyst acted in synergy for the catalytic hydrogenolysis of natural rubber. Ultimately, various rubber wastes were directly converted to natural gas, it could provide a new perspective for the chemical upcycling of the accumulated rubber wastes.

Recent Progresses and Challenges in Upcycling of Plastics through Selective Catalytic Oxidation.

Chemical upcycling of plastics provides an important direction for solving the challenging issues of plastic pollution and mitigating the wastage of carbon resources. Among them, catalytic oxidative cracking of plastics to produce high-value chemicals, such as catalytic oxidation of polyethylene (PE) to produce fatty dicarboxylic acids, catalytic oxidation of polystyrene (PS) to produce benzoic acid, and catalytic oxidation of polyethylene terephthalate (PET) to produce terephthalic acid under mild conditions has attracted increasing attention, and some exciting progress has been made recently. In this article, we will review recent progresses on the catalytic oxidation upcycling of plastics and provide our understanding on the current challenges in catalytic oxidation upcycling of plastics.