Post-consumer Waste Plastics Research Articles

Upcycling of waste acrylonitrile butadiene styrene as N-doped carbocatalyst for peroxymonosulfate-induced degradation by solvothermal process

Advanced upcycling of post-consumer waste plastics into functional carbocatalyst has emerged rapidly as a strategy for simultaneously achieving waste plastics disposal and alternative catalysts fabrication. In this study, this type of magnetic N-doped carbocatalyst hybrid was fabricated by a facile solvothermal impregnation of metallic nitrates into waste acrylonitrile butadiene styrene polymer. The key point of the process was that solvothermal impregnation remarkably enhanced a homogeneous metal dispersion and graphitic N structure was stably introduced into carbocatalyst due to N heteroatoms in inherent structure of waste plastics. It was found that carbocatalyst with predominant encapsulation of magnetic CoFe2O4, Fe0.64Ni0.36 and CoFe possessed excellent catalytic performance to activate peroxymonosulfate with substantial degradation of 98.3% synthetic azo contaminant. Mechanism study indicated that graphitic N and metal species exhibited strong synergistic effects for peroxymonosulfate activation to generate SO4·−, ·OH and 1O2. This system achieves a dual-pathway degradation and electron transfer from azo contaminant to peroxymonosulfate to dominate degradation of azo contaminant, providing a new insight into magnetic carbocatalyst confinement from plastic scrap for peroxymonosulfate activation and its versatile application in wastewater reclamation.

Stapler Strategies for Upcycling Mixed Plastics.

Mechanical recycling is one of the simplest and most economical strategies to address ever-increasing plastic pollution, but it cannot be applied to immiscible mixed plastics and suffers from property deterioration after each cycle. By combining the amphiphilic block copolymer strategy and reactive compatibilization strategy, we designed a series of stapler strategies for compatibilizing/upcycling mixed plastics. First, various functionalized graft copolymers were accessed via different synthetic routes. Subsequently, the addition of a very small amount of stapler molecules induced a synergistic effect with the graft copolymers that improved the compatibility and mechanical properties of mixed plastics. These strategies were highly effective for various binary/ternary plastic systems and can be directly applied to postconsumer waste plastics, which can increase the toughness of mixed postconsumer waste plastics by 162 times. Most importantly, it also effectively improved the impact resistance, adhesion performance, and three-dimensional (3D) printing performance of mixed plastics, and permitted the recycling of plastic blends 20 times with minimal degradation in their mechanical properties.

Enabling plastic waste gasification by autothermal chemical looping with > 90 % syngas purity for versatile feedstock handling

The chemical looping gasification of plastics (CLGP) is a process that offers an innovative solution for transforming post-consumer waste plastics into high-value products. The process utilizes a co-current moving bed reducer reactor with iron-titanium-based oxygen carriers to gasify plastic feed and generate syngas autothermally. Its distinguishing feature is its ability to operate over a wide range of feed loadings and co-injection of mixed plastic species without any performance losses. Isothermal bench-scale experiments reveal a syngas purity of ∼95 %, aligning with the thermodynamic simulations. The moving bed reactor facilitates a deeper reduction of the oxygen carriers to the Fe+FeTiO3 phase, leading to the high syngas purity, which is then verified with additional TGA, XRD, and SEM analysis. For an autothermal operation of CLGP process, an active material content of 20 % is found to be sufficient to satisfy the kinetic and thermodynamic constraints. Further integration with downstream production of H2 is presented and compared to a steam gasification process. The process integration simulations show that the CLGP process outperforms the steam gasification system in terms of Cold Gas Efficiency (CGE), Effective Thermal Efficiency (ETE), and H2 yield. CO2 emissions are impressively reduced by ∼30 % in the CLGP system over that in the steam gasification system due to its ability to autothermally operate the process, unlike the highly endothermic steam gasification process.

Transforming Cl-Containing Waste Plastics into Carbon Resource for Steelmaking: Theoretical Insight.

The accumulation of waste plastics poses a significant environmental challenge, leading to persistent pollution in terrestrial and aquatic ecosystems. A practical approach to address this issue involves the transformation of postconsumer waste plastics into industrially valuable products. This study focuses on an example of harnessing the carbon content in these polymers for carbon-demanding industrial processes, thereby reducing waste plastics from the environment and alleviating the demand for mined carbon resources. Employing quantum simulations, we examine the viability of polychloroprene as a carburizing agent in the steelmaking process. Our simulations reveal that polychloroprene exhibits excellent carbon diffusivity in molten iron, with a theoretical diffusion coefficient of 8.983 × 10-5cm2 s-1. This value competes favorably with that of metallurgical coke and surpasses the carbon diffusivity of other polymers, such as polycarbonate, polyurethane, and polysulfide. Additionally, our findings demonstrate that the chlorine content in polychloroprene does not permeate into molten iron but instead remains confined to the molten iron and slag interface.

Photothermal Mediated Chemical Recycling to Monomers via Carbon Quantum Dots.

Plastic recycling strategies to combat rapidly increasing waste buildup are of utmost environmental importance. Chemical recycling to monomers has emerged as a powerful strategy that enables infinite recyclability through depolymerization. However, methods for chemical recycling to monomers typically rely on bulk heating of polymers, which leads to unselective depolymerization in complex polymer mixtures and the formation of degradation byproducts. Here, we report a selective chemical recycling strategy facilitated by photothermal carbon quantum dots under visible light irradiation. Upon photoexcitation, we found that carbon quantum dots generate thermal gradients that induce depolymerization of various polymer classes, including commodity and postconsumer waste plastics, in a solvent-free system. This method also provides selective depolymerization in a mixture of polymers, not possible by bulk heating alone, enabled by localized photothermal heat gradients and the subsequent spatial control imparted over radical generation. Photothermal conversion by metal-free nanomaterials facilitates chemical recycling to monomers, an important approach in addressing the plastic waste crisis. More broadly, photothermal catalysis enables challenging C-C bond cleavages with the generality of heating but without indiscriminate side reactions typical of bulk thermolysis processes.

Sustainable Approaches to Plastics

Environmental concern and awareness have led to the development of different sustainable approaches to reduce the environmental impact of waste plastics. A brief literature review was conducted to evaluate recent challenges and emerging ideas on this topic. The two most noticeable approaches identified here are the introduction of biodegradable polymers as replacements for conventional plastics and recycling post-consumer waste plastics. The sustainable approach protects the environment, reducing energy consumption and greenhouse gas emissions.

Purification and characterisation of post-consumer plastic pyrolysis oil fractionated by vacuum distillation

Valorisation of post-consumer plastic pyrolysis oil in steam crackers and their application as precursors to chemicals is currently hindered by the complexity of these oils in terms of their boiling range, the risk of fouling by unsaturated compounds, and the presence of contaminations (heteroatoms, metals, and halogens). To gain insights into which of these challenges is actually a potential showstopper, we have studied the vacuum distillation of pyrolysis oil derived from two sorted post-consumer waste plastics, i.e. polypropylene (PP) rigids and mixed polyolefins (MPO) rigids, in a batch fractionating column. The crude pyrolysis oil samples were distilled in three fractions i.e., the light fraction (final boiling point <175 °C), middle fraction (175–360 °C), and heavy fraction (initial boiling point >360 °C). Subsequently, comprehensive characterisation, such as physicochemical properties, the level of contaminations, and chemical composition, was performed. The suitability of the light and middle fractions for steam cracking and precursors to chemical feedstock was assessed. It was found that the density and viscosity values of light and middle fractions from the two pyrolysis oil samples were comparable to fossil naphtha and diesel, whereas total acid number (TAN) values were notably higher compared to petroleum-based oil fractions (>0.5 mgKOH/g). Analyses via GC-MS and ATR-FTIR revealed predominant concentrations of olefins. ICP-OES analysis showed that distillation removes more than 97.5% of metals in all fractions. The chlorine content (>3 ppm), nitrogen (≥0.1%), and oxygen (≥0.1%) exceed thresholds. Hence, this study shows that vacuum distillation effectively improved most, but not all, of the properties of the distilled fractions and can thus be an essential downstream process step for the application of post-consumer plastic pyrolysis oils as feedstock in steam crackers and precursors to chemicals.

Pyrolysis-plasma/catalytic reforming of post-consumer waste plastics for hydrogen production

Different types of single waste plastics and a range of real-world mixed waste plastics from several different industrial and commercial sources have been processed in a pyrolysis-plasma/catalytic experimental reactor system for the production of hydrogen. The hydrocarbons produced from the pyrolysis stage were catalytically (Ni/MCM-41) steam reformed in a low temperature, non-thermal plasma/catalytic reactor. The polyolefin plastics, high density polyethylene, low density polyethylene and polypropylene produced the highest yield of hydrogen at 18.0, 17.3 and 16.3 mmol g−1plastics respectively. The aromatic structured polystyrene produced a lower hydrogen yield of 11.9 mmol g−1plastics and polyethylene terephthalate with an aromatic and oxygenated structure produced only 10.2 mmol g−1plastics and a high yield of carbon oxide gases. The real-world mixed plastic waste produced yields of hydrogen in the range of 13.4–16.9 mmol g−1plastics. The lowest hydrogen yield of 13.4 mmol g−1plastics was produced from the mineral water bottle packaging waste due to the high content of polyethylene terephthalate in the plastic waste mixture.

Enhancing the performance of a PtPd/HY catalyst for HDPE/VGO hydrocracking through zeolite desilication

The valorization of post-consumer waste plastic in a refinery is an attractive initiative to avoid environmental problems caused by the poor plastic waste management. The modification of a bifunctional PtPd/HY catalyst through desilication (using NaOH) of the ultrastable HY zeolite has been carried out to upgrade waste plastic (high-density polyethylene (HDPE)) dissolved in a secondary refinery stream (vacuum gas oil (VGO)) through hydrocracking. Three different catalysts have been studied: the parent (Cat-A), undergoing a desilication cycle (Cat-B), and subjected to two cycles of desilication (Cat-C). The characterization techniques employed have been: N2 adsorption–desorption, TEM, ICP-AES, tert-butylamine-TPD, pyridine FTIR, WDXRF, XRD and TPO. The hydrocracking tests have been carried out in a semi-batch reactor at: 440 °C; 80 bar; catalyst to feed ratio, 0.1 gcat (gfeed)–1; HDPE to feed ratio, 0.2 gHDPE (gfeed)–1; and reaction time, 2 h. The products have been fractioned according to their boiling point range in: gas, naphtha, light cycle oil, heavy cycle oil and coke. The composition of each fraction has been determined in terms of concentration of paraffins, olefins, naphthenes and (mono-, di- and poly-) aromatics. The results show that alkaline treated catalysts enhance the fuel production, with high HDPE and HCO conversions. The Cat-C (the one submitted to two desilication cycles) has displayed the greatest performance, reducing by half the gas yield and increasing the naphtha yield by 51 wt% respect to those obtained with the parent catalyst (Cat-A). Moreover, it has decreased the coke deposition and the coke formed has been less developed.

Front Cover: Comparative Performance of PETase as a Function of Reaction Conditions, Substrate Properties, and Product Accumulation (ChemSusChem 1/2022)

The Front Cover shows the application of poly(ethylene terephthalate) (PET) hydrolase enzymes on post-consumer waste plastic, towards the development of an enzymatic PET recycling strategy. More information can be found in the Full Paper by E. Erickson et al.

Comparative Performance of PETase as a Function of Reaction Conditions, Substrate Properties, and Product Accumulation.

Invited for this month's cover is the BOTTLE Consortium, featuring Gregg Beckham's laboratory from NREL and John McGeehan's laboratory from the University of Portsmouth. The cover image shows the application of poly(ethylene terephthalate) (PET) hydrolase enzymes on post-consumer waste plastic, towards the development of an enzymatic PET recycling strategy. The Full Paper itself is available at 10.1002/cssc.202101932.

Catalytic pyrolysis of mechanically non-recyclable waste plastics mixture: Kinetics and pyrolysis in laboratory-scale reactor

Post-consumer waste plastics that cannot be mechanically recycled represent a concerning environmental issue. According to the latest available data for Europe, as much as 25% of collected post-consumer waste plastics are landfilled, 43% is energy recovered, and 32% is recycled. One possible way of recovering non-recyclable plastics is pyrolysis, which is considered environmentally friendly technology for obtaining fuel or chemicals from plastic waste. To tackle the challenge of recovering non-recyclable plastics via pyrolysis, it is necessary to determine their actual composition. Visual separation of collected non-recyclable plastics was performed, and Fourier-transform infrared spectroscopy was used to confirm the accuracy of visual separation. A significant amount of plastics labelled as “other” was found. Since the composition of “other” waste plastics has not been sufficiently investigated, relatively few studies on their pyrolysis have been conducted. Therefore, they were characterised and added to the mixture with other found polymer types of non-recyclable plastics. Thermogravimetric analysis was conducted to determine thermochemical behaviour and kinetic parameters required for laboratory pyrolysis investigation. Kinetic analysis was conducted using the Friedman isoconversional model-free method and non-linear multivariate regression method. The goal of this paper was to analyse the kinetics, determine the product yield and characteristics of the pyrolysis process of non-recyclable plastics over zeolite catalysts. It was found how the decomposition of non-recyclable plastics occurs in two decomposition steps. The activation energy of non-recyclable plastics was 144 kJ/mol in the first stage of decomposition and 262 kJ/mol in the second stage of decomposition. It decreased by 34% and 6.5% after fresh fluid catalytic cracking catalyst was added and 41% and 18.3% with iron-modified Zeolite Socony Mobil-5 catalyst. The yield of condensate was 55% (wax) for the original sample, and it decreased to 50% (wax and oil) and 27% (mostly oil) with fresh fluid catalytic cracking and iron modified Zeolite Socony Mobil-5 catalysts. Processes with catalysts promoted the formation of olefins and aromatic compounds in pyrolytic oil. All pyrolysis products had a high value of higher heating value ranging from 39 MJ/kg to 43 MJ/kg showing good potential for further energy use.

Carbon nanotubes from post-consumer waste plastics: Investigations into catalyst metal and support material characteristics

Carbon nanotubes were produced from post-consumer mixed waste plastics using a pyrolysis-catalysis process. The catalysts used were Ni-Fe bimetals supported over four different porous materials. The Ni-Fe/MCM41 catalyst displayed the highest catalytic activity for the pyrolysis-catalysis of the waste plastics in terms of carbon material yield at 55.60 wt.%. The order of catalytic activity was Ni-Fe/MCM41> Ni-Fe/ZSM5> Ni-Fe/Beta > Ni-Fe/NKF5, which was closely related to their differences in catalyst pore volume and catalyst reducibility. Formation of Ni-Fe alloy with fine particle dispersion over the Ni-Fe/MCM41 catalyst is suggested to be crucial for the promotion of the decomposition of the carbon precursors and subsequent precipitation to form carbon nanotubes. Whereas, the large catalyst particle size for the Ni-Fe/Beta catalyst led to irregular carbon shapes with a simultaneous decrease in purity and graphitization of the nanotubes. By-product production of hydrogen in large quantities (38.10 mmol H2 g−1plastic) could be used as process fuel.

Open-Source Grinding Machine for Compression Screw Manufacturing

Some of the most promising distributed recycling and additive manufacturing (DRAM) technical systems use fused particle fabrication (FPF) or fused granular fabrication (FGF), where compression screws force post-consumer waste plastic through a heated nozzle for direct 3D printing. To assist the technical evolution of these systems, this study provided the details of an invention for a low-cost, easily replicable open-source grinding machine for compression screw manufacturing. The system itself can be largely fabricated using FPF/FGF following the self-replicating rapid prototyper (RepRap) methodology. This grinding machine can be made from a cordless cut-off grinder and &lt; $155 in parts. The new invention is demonstrated to be able to cut custom screws with variable (i) channel depths, (ii) screw diameters, (iii) screw lengths, (iv) pitches, (v) abrasive disk thicknesses, (vi) handedness of the screws, (vii) and materials (three types of steel tested: 1045 steel, 1144 steel, and 416 stainless steel). The results show that the device is more than capable of replicating commercial screws as well as providing makers with a much greater flexibility to make custom screws. This invention enables the DRAM toolchain to become even more self-sufficient, which assists the goals of the circular economy.

Sustainable bottled water: How nudging and Internet Search affect consumers’ choices

This study examined differences in consumer preferences and willingness to pay for sustainable bottled water based on pro-environmental guidance, Internet information search, and research setting (i.e., laboratory or online). Specifically, we investigated willingness to pay for bottled water produced with plant-based plastics and post-consumer waste plastics. Insight into willingness to pay (i.e., preferences and acceptance) for novel plastics is valuable given the potential impact of such materials regarding cleaner production of food and non-food products. Results from mixed logit models showed that searching for information increased the likelihood that consumers would choose sustainable plastic water bottles over less sustainable options, and the effect was magnified when consumers were primed to make environmentally friendly choices. Findings also revealed a considerable amount of preference heterogeneity with regard to the type of water product or type of plastic used to manufacture the bottles. Similar results were reflected in the willingness to pay. In addition, preference and willingness to pay were generally higher in the lab setting compared to the online setting. Overall, pro-environmental guidance can nudge individuals towards making more sustainable choices even if it comes at a higher cost. For stakeholders and policy makers with interests in the beverage industry, observed findings can inform recommendations for facilitating more sustainable consumer behavior.

Open Source Waste Plastic Granulator

In order to accelerate deployment of distributed recycling by providing low-cost feed stocks of granulated post-consumer waste plastic, this study analyzes an open source waste plastic granulator system. It is designed, built, and tested for its ability to convert post-consumer waste, 3D printed products and waste into polymer feedstock for recyclebots of fused particle/granule printers. The technical specifications of the device are quantified in terms of power consumption (380 to 404 W for PET and PLA, respectively) and particle size distribution. The open source device can be fabricated for less than $2000 USD in materials. The experimentally measured power use is only a minor contribution to the overall embodied energy of distributed recycling of waste plastic. The resultant plastic particle size distributions were found to be appropriate for use in both recyclebots and direct material extrusion 3D printers. Simple retrofits are shown to reduce sound levels during operation by 4dB-5dB for the vacuum. These results indicate that the open source waste plastic granulator is an appropriate technology for community, library, maker space, fab lab, or small business–based distributed recycling.

Equilibrium model analysis of waste plastics gasification using CO2 and steam.

Utilization of carbon dioxide (CO2) in thermochemical treatment of waste plastics may significantly help to improve CO2 recycling, thus simultaneously curtailing dioxins/furans and CO2 emissions. Although CO2 is not such an effective gasifying agent as steam, a few investigations have explored the utilization of CO2 in conjunction with steam to achieve somewhat higher carbon conversion. This work presents a comparative evaluation study of CO2 and steam gasification of a typical post-consumer waste plastics mixture using an Aspen Plus equilibrium model. The effect of flow rate of gasifying medium (CO2 and/or steam) and gasification temperature on product gas composition, carbon conversion, and cold gas efficiency has been analyzed. Simulation results demonstrate that CO2 can serve as a potential gasifying agent for waste plastics gasification. The resulting product gas was rich in CO whereas CO2-steam blends yield a wider H2/CO ratio, thus extending the applications of the product gas.

Numerical Analyses of Loaded Strip Footing Resting on Cellular Mattress and Strips: Reinforced Fly Ash Slope

In this paper, unreinforced and cellular reinforced fly ash slopes were analyzed using numerical modelling to simulate the laboratory model studies by applying similar geometry and reinforcement parameters to understand its deformation behavior on rigid foundation. Small scale laboratory experimental models were performed on fly ash slopes by applying strip loading at a 60° inclination. In the current study an approach was made to use cellular reinforcement (CR) material which is made up of from post-consumer waste plastic water bottles along with steel grid-jute geotextile composite reinforcement at slope facia. A numerical analyses using finite-element analysis (FEA) PLAXIS 3D was conducted to validate the experimental laboratory model test results. In FEA, fly ash as backfill material and reinforcing materials like steel grid-jute geotextile and cellular/geocell reinforcement were modeled systematically. Here, fly ash modeled with Mohr–Coulomb failure criteria as linear elastic plastic material and, for cellular/geocell reinforcement it was modeled as elastoplastic material. The numerical model analyses were consistently substantiated with experimental results. Parametric analysis were conducted by using validated numerical model to evaluate the influence of various cellular properties along with steel grid-jute geotextile composite reinforcement on the performance of reinforced fly ash slopes. The numerical finite element simulation (FES) results are in good agreement with the model test results.

Polymer Recovery through Selective Dissolution of Co-mingled Post-Consumer Waste Plastics

It still remains a challenge to the recycling industry to develop an efficient and economical large-scale plastic waste recycling system, in spite of growing environmental concerns in waste disposal. Selective dissolution and precipitation (SDP) is a mechanical recycling technique that eliminates pre-sorting of mixed waste plastics and recycling polymer of high-grade quality. In this preliminary investigation, recycling of a comingled post-consumer waste plastic mixture of low-density polyethylene (LDPE), polystyrene (PS), high-density polyethylene (HDPE), and polyethylene terephthalate (PETE) using a lab-scale SDP setup was examined. A few experimental runs performed on the representative samples using Xylene/Toluene as solvents and acetone/2-propanol as anti-solvents demonstrated the sorting and recycling efficiency of this technique. FT-IR analysis of the reclaimed products revealed that the structural properties being very similar to virgin materials.

Catalytic Thermal Cracking of Postconsumer Waste Plastics to Fuels. 2. Pilot-Scale Thermochemical Conversion

Synthetic gasoline and diesel fuels were prepared via catalytic and noncatalytic pyrolysis of waste polyethylene and polypropylene plastics followed by distillation of plastic crude oils. Reaction conditions optimized using a 2 L batch reactor were applied to pilot-scale production of plastic crude oil from polypropylene. The optimum conditions on the pilot-scale system were a reaction temperature of 500 °C and a residence time of 4.7 min. Plastic crude oil yields at pilot scale were comparable to those of the batch scale (70–80%). Plastic crude oils obtained from pyrolysis were distilled into the boiling point range of motor gasoline, diesel no. 1, gas oil, and vacuum gas oil range fractions. The elemental composition of the crude oil and its distillates were similar to the starting plastic material. Fuel properties were studied for both neat and in blends (5% and 20%) with ultralow sulfur diesel fuel (ULSD). Excellent low temperature properties were obtained for some of the samples, as indicated by a po...