Conversion Of Waste Plastics Research Articles

Fabrication of MnAlNiO to boost the conversion of plastic wastes to CNTs for the supercapacitor application

Conversion of plastic wastes to carbon nanotubes (CNTs) with excellent electrochemical properties is promising to alleviate the environmental and energy crisis. Herein, MnAlNiO were prepared by the co-precipitation method, and used for CNTs synthesis from polyethylene (PE). It was found that Mn0.7Al0.2Ni0.1O obtained a CNTs yield of 966 mg/gcatalyst, which exhibited high aspect ratio and uniformity. Mn0.7Al0.2Ni0.1O/CNTs composite exhibited a specific capacitance of 170F/g at 0.3A/g, which was significantly higher than pristine Mn0.7Al0.2Ni0.1O (54F/g). The superiority of Mn0.7Al0.2Ni0.1O/CNTs composite in the energy storage was closely related to the in-situ growth of CNTs that effectively reduced the electrochemical impedance and improved the charge transport. It was deduced that the synergistic effect between MnAlNiO and CNTs improved the electrochemical performance in the supercapacitor application.

PP upcycling employing FCC spent catalyst: The role of contaminants, atmosphere and pressure

Innovative and sustainable approaches are being pursued to convert plastic waste into high-value fuels, particularly without using noble metal catalysts or external hydrogen sources. In this scenario, we explored the utilization of a spent fluid catalytic cracking (FCC) catalyst (ECAT), aiming to enhance the yield and quality of products through catalytic cracking of Polypropylene (PP) under different reaction conditions. Under a 20 bar H2 atmosphere, ECAT efficiently cracked PP into alkanes (71.6 %) and aromatics (25.5 %), with minimal alkenes (2.2 %) production. Similarly, under a 20 bar N2 atmosphere, ECAT achieved comparable conversion levels, producing mainly saturated hydrocarbons, which was intriguing. However, tests conducted at 1 bar N2 pressure showed that PP conversion remains unaffected but presents higher olefins’ yield and lower aromatics than ECAT. Thus, pressure seems to favor aromatization and in situ hydrogen transfer. By comparing the performance of ECAT with commercial CBV 712 zeolite, we propose that PP acts as an internal hydrogen source, eliminating the need for external supply improving efficiency and selectivity. Interestingly, mechanistic insights suggested that dehydroaromatization and hydrogen transfer within zeolite pores were dominant, and pressure (H2 or N2) could have helped it. In addition, contrary to previous studies that claim that metal contaminants in ECAT are essential for the hydrogenation process, our findings suggest that for this particular ECAT composition, we do not observe any boost in alkane yield due to the presence of these metals. Hence, our study comprehensively evaluates different strategies that can be employed to promote PP upcycling promoted by ECAT.

Waste Polyethylene-Derived Carbon Dots: Administration of Metal-Free Oxidizing Agents for Tunable Properties and Photocatalytic Hyperactivity.

The possibility of converting waste plastics into carbon dots (CDs) with 100% efficiencies using KMnO4 has emerged as a significant discovery in mitigating plastic pollution and upcycling. However, the lack of tunability of their properties, viz. aerial O2 harvesting, light-induced autophagy, and photoactivity using air as a free oxidant, has remained a bottleneck. Besides, the toxicity of KMnO4 makes the process less sustainable. Attempting to bridge these gaps, herein, we demonstrate the preparation of CDs using polyethylene with enormous controllability of their properties by utilizing less-toxic and metal-residue-free oxidizers, e.g., H2O2, HNO3, HClO4, and NaClO. We obtain structurally diverse CDs with controllable luminescent quantum yields (∼0.5-8%), excitonic lifetimes (1.3-2.3 ns), and binding energies (147-290 meV). These CDs exhibit a hugely extended range of molecular O2 harvesting (∼405-650 μM) with different amounts of strongly and weakly surface-bound O2 molecules within an estimated ratio of ∼0.77-2.51. Autophagy varied from 14 days to a nearly "no-autophagy" show. We efficiently utilized their oxygen harvesting and photocatalytic abilities to synthesize imine compounds from the corresponding amines in the open air (rate constant of ∼0.055 min-1), surpassing the literature efficiencies achieved using an O2 flow and noble metals. Notably, due to oxygen harvesting by CDs, no additional rate enhancement was observed after O2 purging, establishing the role of CDs in making free air an excellent oxidizing agent.

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.

Fabrication of Fe-Zr, Co-Zr, and Ni-Zr Catalysts to Boost CNTs Synthesis from Plastic Wastes and the Electrocatalytic Oxygen Evolution Reaction.

The efficient conversion of plastic wastes to high-value carbon materials like carbon nanotubes (CNTs) is one important issue about the rational recycling, reduction, and reuse of solid wastes. Herein, Fe-, Co-, and Ni-Zr catalysts were prepared and used for CNTs synthesis from polyethylene (PE) waste via a two-stage reaction system. At the same time, the effects of the PE/catalyst ratio and reaction temperature on CNTs synthesis have been studied. Compared with Co-Zr and Ni-Zr, Fe-Zr exhibited the best activity in CNTs synthesis from PE, and it achieved the highest CNTs yield of 806.3 mg/g (per gram of Fe-Zr) at 800 °C with a PE/catalyst ratio of 4. Furthermore, the obtained Fe-Zr/CNTs composite exhibited a low overpotential of 267 mV for the electrocatalytic oxygen evolution reaction (OER) at 20 mA/cm2 in 1 M KOH electrolyte solution, which was 21 mV lower than commercial RuO2 (288 mV) and 50 mV lower than Fe-Zr (317 mV). It was deduced that the in situ growth of CNTs reduced the charge transfer resistance and improved the electron transport efficiency of the Fe-Zr/CNTs composite, leading to superior activity in the electrocatalytic OER. This work provided detailed information for the preparation of the metal/CNTs composite from plastic wastes, which contributed positively to alleviate the environment and energy crisis.

An Industrial Perspective for Sustainable Polypropylene Plastic Waste Management via Catalytic Pyrolysis—A Technical Report

Recycling plastics on an industrial scale is a key approach to the circular economy. This study presents a techno-economic analysis aimed at recycling polypropylene waste, one of the main consumer plastics. Specifically, it evaluates the technical and economic feasibility of achieving a large-scale cracking process that converts polypropylene waste into an alternative fuel. Pyrolysis is considered as a promising technique to convert plastic waste into liquid oil and other value-added products, with a dual benefit of recovering resources and providing a zero-waste solution. This study concerns a fast catalytic pyrolysis in a fluidized bed reactor, with the presence of a fluid catalytic cracking catalyst of low acidity for high heat transmission, for an industrial plant with a capacity of 1 t/h of polypropylene waste provided by the Greek Petroleum Industry. From the international literature, the operational conditions were chosen pyrolysis temperature at 430 °C, pressure at 1atm, heating rate at 5 °C/min, and yields of products to 71, 14, and 15 wt.%, for liquid fuel, gas, solid product, respectively. The plant design includes a series of apparatuses, with the main one to be the pyrolyzer. The catalytic method is selected over the non-catalytic because the presence of catalyst increases the quantity and quality of the liquid product, which is the main product of the plant. The energy loops of recycling pyrolysis gas and char as a low-carbon fuel in the plant were considered. The production cost, annual revenue, for 2023, are anticipated to reach €13.7 million (115 €/t) and €15 million (15 €/t), respectively, with an estimated investment equal to €5.3 million. The Payback Time is estimated to 2.4 years to recover the cost of investment. The endeavor is rather economically sustainable. A critical parameter for large scale systems is securing feedstock with low or negligible price.

Photochemical Aerobic Upcycling of Polystyrene Plastics.

Although the introduction of plastics has improved humanity's everyday life, the fast accumulation of plastic waste, including microplastics and nanoplastics, have created numerous problems with recent studies highlighting their involvement in various aspects of our lives. Upcycling of plastics, the conversion of plastic waste to high-added value chemicals, is a way to combat plastic waste that is receiving increased attention. Herein, we describe a novel aerobic photochemical process for the upcycling of real-life polystyrene-based plastics into benzoic acid. A new process employing a thioxanthone-derivative, in combination with N-bromosuccinimide, under ambient air and 390 nm irradiation is capable of upcycling real-life polystyrene-derived products in benzoic acid in yields varying from 24-54%.

Flexural Strength of Ceiling Results from Plastic Waste Conversion

Flexural Strength of Ceiling Results from Plastic Waste Conversion

Conversion of Plastic Waste into Fuel by Pyrolysis

Abstract: Plastics have woven their way into our daily lives and now pose a tremendous threat to the environment. Over a 100 million tons of plastics are produced annually worldwide, and the used products have become a common feature at overflowing bins and landfills. Though work has been done to make futuristic biodegradable plastics, there have not been many conclusive steps towards cleaning up the existing problem. Here, the process of converting waste plastic into value added fuels is explained as a viable solution for recycling of plastics. Thus, two universal problems such as problems of waste plastic and problems of fuel shortage are being tackled simultaneously. In this study, plastic wastes (low density polyethylene) were used for the pyrolysis to get fuel oil that has the same physical properties as the fuels like petrol, diesel etc. Pyrolysis runs without oxygen and in high temperature of about 300°C which is why a reactor was fabricated to provide the required temperature for the reaction. The waste plastics are subjected to depolymerization, pyrolysis, thermal cracking and distillation to obtain different value-added fuels such as petrol, kerosene, and diesel, lube oil etc. Converting waste plastics into fuel hold great promise for both the environmental and economic scenarios. Thus, the process of converting plastics to fuel has now turned the problems into an opportunity to make wealth from waste.

Toward Building Circularity in Sustainable Plastic Waste Conversion

Toward Building Circularity in Sustainable Plastic Waste Conversion

Recycling waste plastic to construct ultra-stable and multifunctional metal-organic framework for fast efficient dye adsorption and acetone vapor detection

Plastic pollution and water pollution are currently two major environmental problems. Exploring a strategy that can convert waste plastics into high value-added functional materials will be an effective solution to relieve above issues. Herein, we realized that the waste plastic of polyethylene terephthalate (PET) was converted into ultra-stable and multifunctional 3D pillared-layer Eu-based metal-organic framework (MOF) material (labelled as Eu-PET) through one-pot solvothermal method. The effects of reaction conditions on the waste plastic PET upcycling were explored in detail. The Eu-PET exhibits excellent Congo red (CR; Concentration: 1 g/L) adsorption capacity of 2312 mg/g in 2 h at nature pH (2988.11 mg/g at pH = 4). Moreover, the influence parameters containing dye concentration, adsorbent dosage, pH, temperature and simulated dye wastewater were studied. The adsorption mechanism was explained by pseudo-second order and Langmuir models, revealing the adsorption of CR on Eu-PET was mainly defined by electrostatic interaction, hydrogen bonding interaction and π-π interaction. Furthermore, Eu-PET as fluorescent sensor, a portable Eu-PET fluorescent film was developed. Experiments have shown that a noticeable fluorescent quenching response occurred within 10 s contact to acetone vapor, and the theoretically detectable limit (LOD) was as low as 0.048 % (v/v), and Eu-PET/acetone system was static quenching. Finally, Eu-PET has excellent water, acid-base and thermal stability, and recyclability over 7 cycles of CR adsorption and acetone detection. This work opens an avenue for the green recycling/utilization of plastic waste, providing meaningful insights into the effective processing of dyes wastewater and fluorescence sensing of volatile organic compounds.

CO2-enhanced PET depolymerization by catalyst free methanolysis

Depolymerization shows promise as a strategy for converting waste plastic into monomers that can be used for repolymerization. However, catalytic approaches would be more complex and expensive due to catalyst separation, recovery, and recycling. Here, we present a CO2-enhanced subcritical methanolysis method without catalyst that can generate monomer from poly(ethylene terephthalate)(PET). The synergistic effect of CO2 on the subcritical methanolysis process for PET depolymerization was investigated including the CO2 initial pressure, reaction temperature and reaction time. Under subcritical conditions, the optimal reaction parameters with PET conversion ratio of 100% and DMT yield of 79.1% are as follows: temperature of 220℃, methanol to PET mass ratio of 6:1 and reaction time of 50 min. Moreover, through the analysis of experimental data, it was concluded that the depolymerization reaction follows a first-order kinetics, with the reaction rate being 2–3 times faster than the traditional process. However, the apparent activation energy for both reactions is found to be similar, with values of 135.1 kJ·mol−1 and 146.2 kJ·mol−1, respectively.

Development of a recycling machine for constructing synthetic yarn from plastic waste

A major challenge in plastic recycling is to convert plastic waste into a useful product. For this transformation, sustainable technologies such as plastic recycling machines are required. Current technological concepts of plastic recycling are fairly similar. This study aims to develop a small and economical plastic recycling machine to enhance microenterprise by supplying simple equipment for recycling locally processed plastic waste into thread. Starting with a hopper at the input end, the machine incorporates an auger inside a barrel, which is then linked to a metallic perforated mold at the output end. With the help of the system, the plastic flakes melting process is facilitated by maintaining temperatures between 170 °C to 211 °C at equispaced locations of a uniform barrel, while the auger spin enables the flow of molten plastic forward towards the mold.The mold reshapes the liquid plastic into strings of thread. The machine exhibits higher efficiency, reaching approximately 75 % at a decreased screw speed, as low as 28 rpm. It also achieves an average throughput of 156 gm/hour at the lowest specific mechanical energy (SME) consumption. The prototype consumes 1.5 kW for an hour operation. The entire system requires minimal space, making it appealing to individuals with limited financial resources to start a new business venture.•A sustainable technology to recycle plastic waste into plastic thread.•This optimized, portable and robust system ensures safety and lower operating costs.•This system does not require prior knowledge for operation, hence encouraging small entrepreneurs.

Utilization of non-biodegradable waste for Manufacturing of Brick along with M-sand

The exponential rise in the production of plastic and the consequential surge in plastic waste have led the scientists and researchers look out for innovative and sustainable means to reuse/recycle the plastic waste in order to reduce its negative impact on environment. Construction material, converting waste plastic into fuel, household goods, fabric and clothing are some of the sectors where waste plastic is emerging as a viable option. Out of these, construction material modified with plastic waste has garnered lot of attention. Modification of construction material with plastic waste serves a dual purpose. It reduces the amount of plastic waste going to landfills or litter and secondly lessens the use of mined construction materials, thereby mitigating the negative impact of construction industry on environment. The plastic waste is naturally available in surplus quantity and hence the cost factor comes down. Also coloring agents can be added to the mixture to attain desired shades. Hence in this thesis, an attempt is made to study regard the properties of the brick which is manufactured using plastic wastes. The present work deals with the manufacturing and analysis of bricks made with waste plastic (LDPE) and fine aggregates. The bricks produced are light weight, have smooth surface and fine edges, do not have cracks and have high crushing strength and very low water absorption. Key Words: reuse, mitigating, environment, manufacture, analysis, attempt.

Hydrothermal route upcycling surgical masks into dual-emitting carbon dots as ratiometric fluorescent probe for Cr (VI) and corrosion inhibitor in saline solution

Exploration effective route to convert plastic waste into valuable carbon dots with bifunction of metal fluorescence monitoring and corrosion protection in seawater is promising. Herein, using “white-pollution” polypropylene surgical masks as a single precursor, dual-emitting carbon dots (CDs) with excellent ratiometric fluorescent sensitivity and corrosion inhibitor efficiency were fabricated with high yield (∼100 %) by a one-pot in situ acid oxidation hydrothermal strategy without post-treatment and organic solvents. Chemical, structural, morphological, optical properties and the Cr (VI) detection and Cu inhibition mechanism of the synthesized CDs had been systematically studied. Furthermore, a dual-response-OFF proportional fluorescent probe had been developed for the detection of the analyte Cr (VI) with a low detection limit of 24 nM. Additionally, the corrosion inhibition efficiency of the prepared CDs reached approximately 94.01 % for Cu substrate in 3.5 wt% NaCl electrolyte under a CDs concentration of 200 mg/L, which is higher than that of most previous reports.

Additive manufacturing for sustainability, circularity and zero-waste: 3DP products from waste plastic bottles

Polymers and their composites are now widely used in several industrial sectors, owing to their flexibility in developing customized products. The significant surge in plastic usage has led to a severe challenge in managing end-of-life plastic waste. Millions of tons of plastic waste produced annually mainly end up in landfills, leaking into the environment and posing severe threats to ecosystems. Innovative solutions to reuse/recycle/repurpose plastic waste are desired to address these global challenges. Therefore, in this study, a sustainable route to converting plastic waste into additive manufacturing (AM) feedstock is presented, where waste plastic bottles (mainly Polyethylene Terephthalate, PET) are recycled using an in-house 3D-printed filament extrusion system to produce filaments for fused filament fabrication (FFF) process. In addition to the recycled PET (rPET), virgin carbon fiber reinforced polyamide-6 (PA6-CF) polymer composites were also used to produce hybrid feedstock filaments. The rPET and rPET/PA6-CF composite filaments were extruded using an in-house filament extruder setup. The produced rPET-based filaments were characterized for their chemical and thermal properties. Subsequently, mechanical characterization was performed on 3D-printed specimens. The mechanical analysis revealed better tensile strength for rPET/PA6-CF than rPET; however, the rPET demonstrated better failure strain and young modulus, demonstrating their potential as viable materials for industrial and consumer applications. The outcomes of this study revealed promising results to promote sustainable production and consumption, complementing the circular economy practices with a straightforward production route to convert plastic waste into AM feedstock.

A comparative study of aromatic content in pyrolysis oils from waste plastics and tires: Assessing common refinery methods

The conversion of waste plastics and tires via pyrolysis to pyrolysis oil represents one of the most promising ways of chemical recycling. Determining aromatics in pyrolysis oils from these feedstocks is crucial for their utilization as both petrochemicals and fuels. In this study, we compared three standard methods commonly available in refinery laboratories (ASTM D1319 − FIA, EN12916 − HPLC-RI, ASTM D8396 − GC × GC-FID) for analyzing aromatic content across a wide range of waste plastic pyrolysis oils, their middle distillate fractions, and hydrotreated products. Using model compounds, we explained most of the observed differences in aromatic content determined by these methods. HPLC-RI and FIA resulted in significant errors. For instance, the FIA reports some dienes and heterocompounds as aromatics. The results from HPLC-RI showed that monoaromatics are overestimated, while polyaromatics are underestimated. Among the tested methods, GC × GC-FID provided the most reliable results.

Upcycling of polyethylene to gasoline through a self-supplied hydrogen strategy in a layered self-pillared zeolite

Conversion of plastic wastes to valuable carbon resources without using noble metal catalysts or external hydrogen remains a challenging task. Here we report a layered self-pillared zeolite that enables the conversion of polyethylene to gasoline with a remarkable selectivity of 99% and yields of >80% in 4 h at 240 °C. The liquid product is primarily composed of branched alkanes (selectivity of 72%), affording a high research octane number of 88.0 that is comparable to commercial gasoline (86.6). In situ inelastic neutron scattering, small-angle neutron scattering, solid-state nuclear magnetic resonance, X-ray absorption spectroscopy and isotope-labelling experiments reveal that the activation of polyethylene is promoted by the open framework tri-coordinated Al sites of the zeolite, followed by β-scission and isomerization on Brönsted acids sites, accompanied by hydride transfer over open framework tri-coordinated Al sites through a self-supplied hydrogen pathway to yield selectivity to branched alkanes. This study shows the potential of layered zeolite materials in enabling the upcycling of plastic wastes.

Maximizing waste plastic oil yield and enhancing energy and environmental metrics through pyrolysis process optimization and fuel modification

The accumulation of plastic waste poses a major environmental challenge, while the conversion of waste plastics into oil via pyrolysis holds promise as an alternative energy solution. Despite numerous investigations into this area, none have focused on optimizing pyrolysis process parameters for higher oil yield and enhancing the overall performance of plastic oil through suitable fuel modification. The present study aims to optimize the pyrolysis process parameters, including heating rate (HR), process temperature (PT), and reaction time (RT), to achieve a higher yield of waste plastic oil (WPO) and enhance the overall performance by blending optimal quantities of water. Fuel characterization and properties measurement were conducted using Fourier Transform Infrared and ASTM methods. WPO was blended with conventional diesel fuel (CDF) and different volume concentrations of water (5%, 10%, and 15%). The performance metrices were assessed under various engine conditions. The study findings indicate that the optimum condition of process parameters is an HR of 17.3 °C/min, PT of 403 °C, and RT of 96.30 min, and the fuel quality confirms its suitability as an alternative fuel source. The performance metrics revealed that WPO has a 5.4% lower brake-thermal efficiency than CDF, and the inclusion of 10% water in WPO (WPO10W) enhances the efficiency by 11.5%. The in-cylinder pressure and net-heat release rate of WPO are 1.3% and 12.9% lower than CDF, respectively, and WPO10W emulsion promotes efficient combustion. WPO10W emulsion fuel reduces oxides of nitrogen, hydrocarbon, and carbon monoxide emissions by 21.2%, 9.8%, and 22.2%, respectively, compared to WPO.

A comprehensive comparison of plastic derived and commercial Pt/C electrocatalysts in methanol oxidation, hydrogen evolution reaction, oxygen evolution and reduction reaction

This work utilized an innovative and economical remediation method to convert inexpensive waste feedstock into extremely useful catalysts. The procedure centered on polyethylene (PE), an easily accessible substance, and effectively transformed it at a mild temperature utilizing a new solvothermal technique, which entailed the reaction of sulfuric acid with PE chains at 120 °C. Throughout this process, the polymer experienced a pivotal cross-linking stage, resulting in its conversion into carbon materials when exposed to temperatures above 500 °C. To improve the catalytic characteristics, platinum (Pt) was effectively integrated into the resultant carbon matrix using the existing impregnation technique. Further, the catalyst's physicochemical properties were thoroughly analyzed utilizing SEM, FTIR, and XRD techniques. After that, the catalyst's performance was thoroughly evaluated in several electrocatalytic reactions, such as methanol oxidation, oxygen evolution and reduction reactions, and hydrogen evolution. The results of this investigation reveal the impressive electrocatalytic ability of the Pt/C catalyst made from waste plastic. It was found to be comparable to the best commercially available Pt/C catalysts in all the reactions that were examined. This research not only demonstrates the possibility of using waste plastic for catalyst production, but also serves as the first documented example, based on successfully converting waste plastic bags into Pt/C through the conventional Liquid Phase Reduction (LPR) process. This novel method has great potential for sustainable and ecologically responsible catalytic applications.