A review on thermal and catalytic pyrolysis of plastic solid waste (PSW)

Catalytic flash pyrolysis for recovery of gasoline-range hydrocarbons from electric cable residue using a low-cost natural catalyst: An analytical Py-GC/MS study

This investigation's novelty and objective reside in exploring catalytic flash pyrolysis of cross-linked polyethylene (XLPE) plastic residue in the presence of kaolin, with the perspective of achieving sustainable production of gasoline-range hydrocarbons. Through proximate analysis, thermogravimetric analysis, and heating value determination, this study also assessed the energy-related characteristics of cross-linked polyethylene plastic residue, revealing its potential as an energy source (44.58 MJ kg-1) and suitable raw material for pyrolysis due to its low ash content and high volatile matter content. To understand the performance as a low-cost catalyst in the flash pyrolysis of cross-linked polyethylene plastic residue, natural kaolin was subjected to characterization through thermogravimetric analysis, X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). Cross-linked polyethylene plastic residue was subjected to thermal and catalytic pyrolysis in an analytical microreactor coupled to gas chromatography-mass spectrometry (Py-GC/MS system), operating at 500 °C, to characterize the distribution and composition of volatile reaction products. The application of kaolin as a catalyst resulted in a decline of the relative concentration of hydrocarbons in the diesel range (C8-C24) from approximately 87 % to 28 %, and a reduction in lubricating oils (C14-C50) from about 70 % to 13 %, while concomitantly increasing the relative concentration of lighter hydrocarbons in the gasoline range (C8-C12) from around 28 % to 87 %. Therefore, catalytic flash pyrolysis offers the potential for converting this plastic waste into a new and abundant chemical source of gasoline-range hydrocarbons. This process can be deemed viable and sustainable for managing and valorizing cross-linked polyethylene plastic residue.

Bioplastic derived from corn stover: Life cycle assessment and artificial intelligence-based analysis of uncertainty and variability

Exploring feasible and renewable alternatives to reduce dependency on traditional fossil-based plastics is critical for sustainable development. These alternatives can be produced from biomass, which may have large uncertainties and variabilities in the feedstock composition and system parameters. This study develops a modeling framework that integrates cradle-to-grave life cycle assessment (LCA) with a rigorous process model and artificial intelligence (AI) models to conduct uncertainty and variability analyses, which are highly time-consuming to conduct using only the process model. This modeling framework examines polylactic acid (PLA) produced from corn stover in the U.S. An analysis of uncertainty and variability was conducted by performing a Monte Carlo simulation to show the detailed result distributions. Our Monte Carlo simulation results show that the mean life-cycle Global Warming Potential (GWP) of 1 kg PLA is 4.3 kgCO2eq (P5-P95 4.1-4.4) for composting PLA with natural gas combusted for the biorefinery, 3.7 kgCO2eq (P5-P95 3.4-3.9) for incinerating PLA for electricity with natural gas combusted for the biorefinery, and 1.9 kgCO2eq (P5-P95 1.6-2.1) for incinerating PLA for electricity with wood pellets combusted for the biorefinery. Tradeoffs for different environmental impact categories were identified. Based on feedstock composition variations, two AI models were trained: random forest and artificial neural networks. Both AI models demonstrated high prediction accuracy; however, the random forest performed slightly better.

Enhancing sustainable waste management: Hydrothermal carbonization of polyethylene terephthalate and polystyrene plastics for energy recovery

Hydrothermal carbonization (HTC) of single plastic polymers such as polyethylene terephthalate (PET) and polystyrene (PS) has not yet been explored on a large scale, particularly their thermal behavior, chemical transformations under subcritical conditions, and the energy properties of the resultant hydrochar. This study investigated these aspects by employing techniques, such as thermogravimetric analysis (TGA), Fourier transformed infrared spectroscopy (FTIR), elemental and calorific analysis. The results show that PET hydrochar has a superior energy densification (1.37) and energy yield (89 %) compared to PS hydrochar (1.13, 54 %). Hydrothermal carbonization modifies the chemical structure of the polymers by increasing the number of carbonyl groups (CO) in PET and forming new ones in PS, and by enhancing hydroxyl groups (OH) in PET while retaining them in PS. Both materials preserve their aromatic and aliphatic structures, with the introduction of alkenes groups (CC) in the PET hydrochar. PET hydrochar begins to decompose at lower temperatures (150-270 °C) than PS hydrochar (242-283 °C) but reaches higher peak temperatures (420-585 °C vs. 390-470 °C), with both types achieving similar burnout temperatures (650-800 °C). PET hydrochar recorded a higher activation energy (121-126 kJ/mol) than PS hydrochar (67-74 kJ/mol) with the Mampel first-order reaction model as the best fit.

Activated Carbon Based on Recycled Epoxy Boards and Their Adsorption toward Methyl Orange

With the swift progress of the electronics industry, discarded circuit boards have become an important source of non-degradable waste. In this work, discarded epoxy resin was collected as a precursor to prepare activated carbon (AC) through stepwise carbonization/activation methods. The rough carbon materials with a certain graphite and amorphous structure reveal the multiple oxygen-containing groups on their surface. In the process of studying the adsorption of methyl orange by activated carbon, it is found that the adsorption is in accordance with the quasi-secondary kinetic model, and equilibrium adsorption amounts can reach 41.051 mg/g. The adsorption isotherm of AC is more in line with the Langmuir model, and the saturation adsorption amount at three different temperatures is 23.137 mg/g, 30.358 mg/g, and 37.202 mg/g, respectively. The enthalpy (ΔH) is 17.30 KJ/mol in the adsorption process, which indicates that is a physical process with heat-absorbing capabilities. This work is of great significance with regard to the recycling of waste to reduce pollution and in terms of gaining economic benefits.

Plastic Waste Conversion by Leveraging Renewable Photo/Electro-Catalytic Technologies

Plastics have revolutionized our lives; however, the exponential growth of their usage has led to a global crisis. More sustainable strategies are needed to address this dilemma and transform the plastics economy from a linearity to a circular model. Herein, we systematically summarize the recent progress in renewable energy-driven plastic conversion strategies, including photocatalysis, electrocatalysis, and their integration. By introducing the significant works, the design principles, mechanisms, and system regulations, we decipher and compare the various aspects of plastic conversion. These approaches show high reactivity and selectivity under environmentally benign conditions and provide alternative reaction pathways for plastic conversion. Plastic upcycling as a chemical feedstock can yield value-added chemicals and fuels, contributing to the establishment of a sustainable and circular economy. Additionally, several innovations in reaction engineering and system designs are presented. Finally, the challenges and perspectives of sustainable energy-driven plastic conversion technologies are comprehensively discussed.

Effect of Feed Mass, Reactor Temperature, and Time on the Yield of Waste Polypropylene Pyrolysis Oil Produced via a Fixed-Bed Reactor

This paper presents the results of investigations into the pyrolysis of waste polypropylene in a laboratory fixed-bed batch reactor. The experiments were designed and verified in such a way as to allow the application of the response surface methodology (RSM) in the development of an empirical mathematical model that quantifies the impacts mentioned above. The influence of the mass of the raw material (50, 100, and 150 g) together with the reactor temperature (450, 475, and 500 °C) and the reaction time (45, 50 and 75 min) was examined. It has been shown that the mass of the raw material, i.e., the filling volume of the reactor, has a significant influence on the pyrolysis oil yield. This influence exceeds the influence of reactor temperature and reaction time. This was explained by observing the temperature change inside the reactor at three different spots at the bottom, middle, and top of the reactor. The recorded temperature diagrams show that, with greater masses of feedstock, local overheating occurs in the middle part of the reactor, which leads to the overcracking of volatile products and, from there, to an increased formation of non-condensable gases, i.e., a reduced yield of pyrolytic oil.

A review on value-addition to plastic waste towards achieving a circular economy

Plastic and mixed plastic waste (PW) has received increased worldwide attention owing to its huge rate of production, high persistency in the environment, and unsustainable waste management practices. Therefore, sustainable PW management and upcycling approaches are imperative to achieve the objectives of the United Nations Sustainable Development Goals. Numerous recent studies have shown the application and feasibility of various PW conversion techniques to produce materials with better economic value. Within this framework, the current review provides an in-depth analysis of cutting-edge thermochemical technologies such as pyrolysis, gasification, carbonization, and photocatalysis that can be used to value plastic and mixed PW in order to produce energy and industrial chemicals. Additionally, a thorough examination of the environmental impacts of contemporary PW upcycling techniques and their commercial feasibility through life cycle assessment (LCA) and techno-economical assessment are provided in this review. Finally, this review emphasizes the opportunities and challenges accompanying with existing PW upcycling techniques and deliver recommendations for future research works.

Plastic pyrolytic oils as renewable fuel: improving its physical properties and ignition patterns by waste renewable source-an experimental analysis

The increase in plastic products and disposal poses a severe environmental challenge because of their poor biodegradability and undesirable disposal by landfilling. Recycling is the best possible solution to the environmental challenges implemented by the plastic industry. Pyrolysis is a process that converts waste plastics into pyrolytic oil, and it can be used as fuel in a blended form. The viscosity and lubricity of the LDWP (low-density waste polyethylene) pyrolytic oil were lower than standard diesel. Capparis spinosa methyl ester (CME) is blended and experimented with to overcome the lubricity issue of pyrolytic oil. In this investigation, 5%, 10%, and 15% CME were blended with PD20 (20% LDWP oil + 80% diesel) blend on a volume basis. Experiments were conducted to examine the effects of CME on combustion, performance, and emissions using the combination of CME and PD20 blend tested at 0%, 25%, 50%, 75%, and 100% loading conditions. All three ternary mixtures showed enhanced combustion performance and increased NOx and smoke emissions. Due to better combustion, the efficiency of the blend PCD10 (10% CME + 20% LDWP oil + 70% diesel) was higher than the PD20 blend and significantly closer to diesel. Hence, PCD10 is suggested as an alternative to diesel fuel.

Recent advances in liquid fuel production from plastic waste via pyrolysis: Emphasis on polyolefins and polystyrene

The management of plastic waste (PW) has become an indispensable worldwide issue because of the enhanced accumulation and environmental impacts of these waste materials. Thermo-catalytic pyrolysis has been proposed as an emerging technology for the valorization of PW into value-added liquid fuels. This review provides a comprehensive investigation of the latest advances in thermo-catalytic pyrolysis of PW for liquid fuel generation, by emphasizing polyethylene, polypropylene, and polystyrene. To this end, the current strategies of PW management are summarized. The various parameters affecting the thermal pyrolysis of PW (e.g., temperature, residence time, heating rate, pyrolysis medium, and plastic type) are discussed, highlighting their significant influence on feed reactivity, product yield, and carbon number distribution of the pyrolysis process. Optimizing these parameters in the pyrolysis process can ensure highly efficient energy recovery from PW. In comparison with non-catalytic PW pyrolysis, catalytic pyrolysis of PW is considered by discussing mechanisms, reaction pathways, and the performance of various catalysts. It is established that the introduction of either acid or base catalysts shifts PW pyrolysis from the conventional free radical mechanism towards the carbonium ion mechanism, altering its kinetics and pathways. This review also provides an overview of PW pyrolysis practicality for scaling up by describing techno-economic challenges and opportunities, environmental considerations, and presenting future outlooks in this field. Overall, via investigation of the recent research findings, this paper offers valuable insights into the potential of thermo-catalytic pyrolysis as an emerging strategy for PW management and the production of liquid fuels, while also highlighting avenues for further exploration and development.

The effects of Micro/Nano-plastics exposure on plants and their toxic mechanisms: A review from multi-omics perspectives

In recent years, plastic pollution has become a global environmental problem, posing a potential threat to agricultural ecosystems and human health, and may further exacerbate global food security problems. Studies have revealed that exposure to micro/nano-plastics (MPs/NPs) might cause various aspects of physiological toxicities, including plant biomass reduction, intracellular oxidative stress burst, photosynthesis inhibition, water and nutrient absorption reduction, cellular and genotoxicity, seed germination retardation, and that the effects were closely related to MP/NP properties (type, particle size, functional groups), exposure concentration, exposure duration and plant characteristics (species, tissue, growth stage). Based on a brief review of the physiological toxicity of MPs/NPs to plant growth, this paper comprehensively reviews the potential molecular mechanism of MPs/NPs on plant growth from perspectives of multi-omics, including transcriptome, metabolome, proteome and microbiome, thus to reveal the role of MPs/NPs in plant transcriptional regulation, metabolic pathway reprogramming, protein translational and post-translational modification, as well as rhizosphere microbial remodeling at multiple levels. Meanwhile, this paper also provides prospects for future research, and clarifies the future research directions and the technologies adopted.

Investigation on effect of cerium oxide additive in waste plastic oil fueled CI engine

In this study, the effects of incorporating cerium oxide into diesel and WPO blends were investigated to determine the potential of the blend as a fuel additive. The study aimed to assess engine-performance, emission, and combustion properties of the blend. The experiments utilized a single-cylinder diesel engine, and researchers prepared two different blends of WPO with 25% WPO in diesel and 50% WPO in diesel. Cerium oxide was added to these blends at concentrations of 25 ppm and 50 ppm using an ultrasonicator. The results demonstrated that increasing cerium oxide content in the blend (50 ppm) led to reduced CO, HC, and NOx emissions at higher loads. For instance, B50 + 50 ppm exhibited lower CO and NOx emissions, while B25 + 50 ppm demonstrated lower HC and smoke emissions. Furthermore, raising the CeO2 content from 25 ppm to 50 ppm resulted in a 3% increase in brake thermal efficiency. Moreover, cerium oxide positively impacted combustion and performance properties of the blends. Among the tested blends, the B50 + 50 ppm combination showcased the highest brake thermal efficiency, optimal air-fuel ratio, and the lowest specific fuel consumption. In conclusion, employing cerium oxide as a fuel additive in diesel-WPO blends offers a promising approach for realizing a sustainable and environmentally friendly future.

Kinetics Study of PVA Polymer by Model-Free and Model-Fitting Methods Using TGA

Thermogravimetric Analysis (TGA) serves a pivotal technique for evaluating the thermal behavior of Polyvinyl alcohol (PVA), a polymer extensively utilized in the production of fibers, films, and membranes. This paper targets the kinetics of PVA thermal degradation using high three heating rate range 20, 30, and 40 K min-1. The kinetic study was performed using six model-free methods: Freidman (FR), Flynn-Wall-Qzawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink (STK), Kissinger (K), and Vyazovkin (VY) for the determination of the activation energy (Ea). TGA showed two reaction stages: the main one at 550-750 K and the second with 700-810 K. But only the first step has been considered in calculating Ea. The average activation energy values for the conversion range (0.1-0.7) are between minimum 104 kJ mol-1 by VY to maximum 199 kJ mol-1 by FR. Model-fitting has been applied by combing Coats-Redfern (CR) with the master plot (Criado's) to identify the most convenient reaction mechanism. Ea values gained by the above six models were very similar with the average value of (126 kJ mol-1) by CR. The reaction order models-Second order (F2) was recommended as the best mechanism reaction for PVA pyrolysis. Mechanisms were confirmed by the compensation effect. Finally, (∆H, ∆G, and ∆S) parameters were presented and proved that the reaction is endothermic.

Catalytic pyrolysis of harmful plastic waste to alleviate environmental impacts

Wax is a detrimental byproduct of plastic waste pyrolysis causing challenges upon its release into the environment owing to persistence and potential toxicity. In this study, the valorization of wax materials through conversion into BTEX (i.e., benzene, toluene, ethylbenzene, and xylene) was achieved via catalytic pyrolysis using zeolite-based catalysts. The potential of two types of waxes, spent wax (SW), derived from the pyrolysis of plastic waste, and commercial paraffin wax (PW), for BTEX generation, was investigated. Using HZSM-5, higher yields of oil (54.9 wt%) and BTEX (18.2 wt%) were produced from the pyrolysis of SW compared to PW (32.3 and 14.1 wt%, respectively). This is due to the improved accessibility of lighter hydrocarbons in SW to Brønsted and Lewis acid sites in HZSM-5 micropores, promoting cracking, isomerization, cyclization, Diels-Alder, and dehydrogenation reactions. Further, the use of HZSM-5 resulted in significantly larger yields of oil and BTEX from SW pyrolysis compared to Hbeta and HY. This phenomenon is ascribed to the well-balanced distribution of Brønsted and Lewis acid sites and the identical geometric structure of HZSM-5 micropores and BTEX molecules. The addition of Ga to HZSM-5 further led to 2.24% and 28.30% enhancements in oil and BTEX yields, respectively, by adjusting the acidity of the catalyst through the introduction of new Lewis acid sites. The regeneration of the Ga/HZSM-5 catalyst by removing deposited coke on the spent catalyst under air partially recovered catalytic activity. This study not only offers an efficient transformation of undesirable wax into valuable fuels but also provides an environmentally promising solution, mitigating pollution, contributing to carbon capture, and promoting a healthier and more sustainable environment. It also suggests future research directions, including catalyst optimization and deactivation management, feedstock variability exploration, and techno-economic analyses for sustainable wax conversion into BTEX via catalytic pyrolysis.

Fractional condensation of bio-oil vapors from pyrolysis of various sawdust wastes in a bench-scale bubbling fluidized bed reactor

The use of lignocellulosic waste as an energy source for substituting fossil fuels has attracted lots of attention, and pyrolysis has been established as an effective technology for this purpose. However, the utilization of bio-oil derived from non-catalytic pyrolysis faces certain constraints, making it impractical for direct application in advanced sectors. This study has focused on overcoming these challenges by employing fractional condensation of pyrolytic vapors at distinct temperatures. The potential of five types of sawdust for producing high-quality bio-oil through pyrolysis conducted with a bench-scale bubbling fluidized bed reactor was investigated for the first time. The highest yield of bio-oil (61.94 wt%) was produced using sample 3 (damaged timber). Remarkably, phenolic compounds were majorly gathered in the 1st and 2nd condensers at temperatures of 200 °C and 150 °C, respectively, attributing to their higher boiling points. Whereas, carboxylic acid, ketones, and furans were mainly collected in the 3rd (-5 °C) and 4th (-20 °C) condensers, having high water content in the range of 35.33%-65.09%. The separation of acidic nature compounds such as acetic acid in the 3rd and 4th was evidenced by its low pH in the range of 4-5, while the pH of liquid collected in the 1st and 2nd condensers exhibited higher pH (6-7). The well-separated bio-oil derived from biomass pyrolysis facilitates its wide usage in various applications, proposing a unique approach toward carbon neutrality. In particular, achieving efficient separation of phenolic compounds in bio-oil is important, as these compounds can undergo further upgrading to generate hydrocarbons and diesel fuel.

Recent advancements in the use of plastics as a carbon source for carbon nanotubes synthesis - A review

Plastics, which majorly consist of polypropylene (PP), polyethylene (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE)), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), etc., are the most abundant municipal solid wastes (MSW). They have been utilized as a cheap carbon feedstock in the synthesis of carbon nanotubes (CNTs) because of their high hydrocarbon content, mainly carbon and hydrogen, especially for the polyolefins. In this review, the detailed progress made so far in the use of plastics (both waste and virgin) as cheap carbon feedstock in the synthesis of CNTs (only) over the years is studied. The primary aim of this work is to provide an expansive landscape made so far, especially in the areas of catalysts, catalyst supports, and the methods employed in their preparations and other operational growth conditions, as well as already explored applications of plastic-derived CNTs. This is to enable researchers to easily access, understand, and summarise previous works done in this area, forging ahead towards improving the yield and quality of plastic-derived CNTs, which could extend their market and use in other purity-sensitive applications.

Abating ammonia emission from poultry manure by Pt/TiO2 modified corn straw

Poultry manure is a significant source of ammonia (NH3) emissions, which not only poses detrimental impacts on human well-being and the ecological system, but also leads to economic losses in the agricultural industry. Herein, we modified corn straw (CS) with 1 wt% Pt/TiO2 catalysts using a low-temperature partial-oxidation technology to mitigate NH3 emissions from poultry manure. It was found that Pt/TiO2 can enable exothermic processes to occur at lower temperatures by reducing the activation energy. Under optimal modification conditions of 220 °C, the NH3 uptakes of modified CS samples were markedly greater compared to those of the original CS. Addition of 20-50% modified CS to poultry manure resulted in significant reductions of 54.1-98.6% in NH3 emissions compared to the control. Mechanistic studies indicate that NH3 adsorption on the modified CS is mainly driven by the presence of acidic and alkaline functional groups, while surface area and pore structure have a negligible effect. XPS combined with NH3-TPD reveals that the formation of amide and amine bonds contributes to the excellent stability of adsorbed NH3. H2-TPR, O2-TPD, and d-band theory suggest that strong metal-support interactions between Pt and TiO2 could be particularly crucial in catalyzing CS modification. This study proposes an environmentally sustainable and economically viable solution for abating NH3 emissions from poultry manure, thereby addressing crucial environmental and economic concerns in the agricultural sector.

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.

Global trends of pyrolysis research: a bibliometric analysis

Pyrolysis has become an interesting waste valorization method leading to an increasing number of research studies in this field in the last decade. The present study aims to provide a comprehensive knowledge map of scientific production in pyrolysis, discuss the current state of research, and identify the main research hotspots and trends in recent years. The systematic review, supported by analysis of countries and institutions, keyword co-occurrence analysis, analysis of keyword trends, journal analysis, and article impact, was carried out on 6234 journal articles from the Science Citation Index Expanded database of the Web of Science Core Collection. As a result, four main research hotspots were identified: 1) characterization techniques and pyrolysis kinetic models, 2) biochar production and its main applications, 3) bio-oil production and catalytic pyrolysis, and 4) co-pyrolysis, which has become a consolidated research hotspot since 2018. Additionally, the main challenges and opportunities for future research have been identified, such as 1) the development of multi-step kinetic models for studying complex wastes, 2) the integration of biochar into other valorization processes, such as anaerobic digestion, and 3) the development of catalytic hydropyrolysis for the valorization of organic waste. This bibliometric analysis provides a visualization of the current context and future trends in pyrolysis, facilitating future collaborative research and knowledge exchange.

Chemical recycling of plastic wastes with alkaline earth metal oxides: A review

Plastics have been widely used in daily life and industries due to their low cost and high durability, leading to huge production of plastics and tens of millions of plastic wastes every year. Chemical recycling can recycle contaminated and degraded plastics (that mechanical recycling cannot deal with) to obtain value-added products, which potentially solves the environmental problems caused by plastics and realizes a circular economy. Alkaline earth metal oxides, as a category of cost-effective and multi-functional materials, have been widely used in chemical recycling of common plastics, acting as three roles: catalyst, template, and absorbent. Among five commercial plastics, polyethylene terephthalate is suitable for pyrolysis and solvolysis. Polyethylene and polypropylene, which are ideal precursors for synthesis of carbon nanotubes, could be combined with biomass for co-pyrolysis. Polyvinyl chloride needs to be pretreated to reduce chloride content prior to pyrolysis. Depolymerization of polystyrene into monomers is attractive. This review summarized the chemical recycling approaches of commercial plastics and the strategies with alkaline earth metal oxides for the development of efficient recycling processes. It will aid understanding of the advances and challenges in the field and promote the future research.

Fabrication of mesopore-rich HZSM-5 to boost the degradation of plastic wastes

Plastic waste is causing serious environment pollution and its efficient disposal is attracting more and more attention. The use of catalysts not only reduced the degradation temperature of plastic wastes but also facilitated the production of valuable chemicals. Herein, mesopores were introduced into HZSM-5 zeolites by alkali and acid treatment, which was expected to eliminate the diffusion resistance caused by bulky polymer molecules and improve the catalytic activity. It was found that HZSM-5 zeolites enhanced PE, PP and PS degradation, and an increase of mesopore volume further improved the catalytic activity and reduced the activation energy. For example, the use of HZSM-5 in PP degradation decreased the activation energy from 146.9 kJ mol-1 to 93.1 kJ mol-1, and mesopore-rich HZSM-5 further decreased the activation energy to 84.0 kJ mol-1. The molecular diameter of the PP fragment was obtained by theoretical calculations, and it was close to 1.6 nm, which was significantly higher than the micropore diameter of HZSM-5 zeolites (0.5-0.6 nm) while lower than the mesopore diameter. It was concluded that the presence of mesopores provided the place and space for plastics degradation.

Valorization of Agricultural Waste Lignocellulosic Fibers for Poly(3-Hydroxybutyrate-Co-Valerate)-Based Composites in Short Shelf-Life Applications

Biocircularity could play a key role in the circular economy, particularly in applications where organic recycling (composting) has the potential to become a preferred waste management option, such as food packaging. The development of fully biobased and biodegradable composites could help reduce plastic waste and valorize agro-based residues. In this study, extruded films made of composites of polyhydroxybutyrate-co-valerate (PHBV) and lignocellulosic fibers, namely almond shell (AS) and Oryzite® (OR), a polymer hybrid composite precursor, have been investigated. Scanning electron microscopy (SEM) analysis revealed a weak fiber-matrix interfacial interaction, although OR composites present a better distribution of the fiber and a virtually lower presence of "pull-out". Thermogravimetric analysis showed that the presence of fibers reduced the onset and maximum degradation temperatures of PHBV, with a greater reduction observed with higher fiber content. The addition of fibers also affected the melting behavior and crystallinity of PHBV, particularly with OR addition, showing a decrease in crystallinity, melting, and crystallization temperatures as fiber content increased. The mechanical behavior of composites varied with fiber type and concentration. While the incorporation of AS results in a reduction in all mechanical parameters, the addition of OR leads to a slight improvement in elongation at break. The addition of fibers improved the thermoformability of PHBV. In the case of AS, the improvement in the processing window was achieved at lower fiber contents, while in the case of OR, the improvement was observed at a fiber content of 20%. Biodisintegration tests showed that the presence of fibers promoted the degradation of the composites, with higher fiber concentrations leading to faster degradation. Indeed, the time of complete biodisintegration was reduced by approximately 30% in the composites with 20% and 30% AS.

A feasible approach for the treatment of waste computer casing plastic using subcritical to supercritical acetone: Statistical modelling and optimization

Electronic waste (e-waste) usage has increased tremendously with the rapid evolution of technologies. The accumulated e-waste has now emerged as one of the crucial concerns regarding environmental pollution and human health. Recycling e-waste is commonly focused on metal recovery; nevertheless, a significant fraction of plastics (20-30%) are in e-waste. There is an indispensable need to focus on e-waste plastic recycling in an effective way, which has been mostly overlooked to date. An environmentally safe and efficient study is conducted using subcritical to supercritical acetone (SCA) to degrade the real waste computer casing plastics (WCCP) in the central composite design (CCD) of response surface methodology (RSM) to achieve the maximum oil yield of the product. The experiment parameters were varied in the temperature span of 150-300 °C, residence time between 30 and 120 min, solid/liquid ratio between 0.02 and 0.05 (g/ml), and NaOH amount from 0 to 0.5 g. Adding NaOH into the acetone helps to achieve efficient degradation and debromination efficiency. The study emphasized the attributes of oils and solid products recovered from the SCA-treated WCCP. The characterization of feed and formed products is performed with different characterization techniques such as TGA, CHNS, ICP-MS, FTIR, GC-MS, Bomb calorimeter, XRF, and FESEM. The highest oil yield achieved is 87.89% from the SCA process at 300 °C, in 120min, 0.05 S/L ratio, and 0.5 g of NaOH. GC-MS results disclose that the liquid product (oil) comprises single- and duplicate-ringed aromatic and oxygen-containing compounds. Isophorone is the significant component of the liquid product obtained. Furthermore, SCA's possible polymer degradation mechanistic route, bromine distribution, economic feasibility, and environmental aspect were also explored. This present work represents an environmentally friendly and promising approach for recycling the plastic fraction of e-waste and recovering valuable chemicals from WCCP.

Controlling the selectivity of the hydrogenolysis of polyamides catalysed by ceria-supported metal nanoparticles

Catalytic hydrogenolysis is a promising approach to transform waste plastic into valuable chemicals. However, the transformation of N-containing polymers, such as polyamides (i.e. nylon), remains under-investigated, particularly by heterogeneous catalysis. Here, we demonstrate the hydrogenolysis of various polyamides catalysed by platinum-group metal nanoparticles supported on CeO2. Ru/CeO2 and Pt/CeO2 are both highly active but display different selectivity; Ru/CeO2 is selective for the conversion of all polyamides into water, ammonia, and methane, whereas Pt/CeO2 yields hydrocarbons retaining the carbon backbone of the parent polyamide. Density functional theory computations illustrate that Pt nanoparticles require higher activation energy for carbon-carbon bond cleavage than Ru nanoparticles, rationalising the observed selectivity. The high activity and product selectivity of both catalysts was maintained when converting real-world polyamide products, such as fishing net. This study provides a mechanistic basis for heterogeneously catalysed polyamide hydrogenolysis, and a new approach to the valorisation of polyamide containing waste.

In-depth analysis of the effect of catalysts on plasma technologies for treatment of various wastes

Energy security and waste management are gaining global attention. The modern world is producing a large amount of liquid and solid waste as a result of the increasing population and industrialization. A circular economy encourages the conversion of waste to energy and other value-added products. Waste processing requires a sustainable route for a healthy society and clean environment. One of the emerging solutions for waste treatment is plasma technology. It converts waste into syngas, oil, and char/slag depending on the thermal/non-thermal processes. Most of all the types of carbonaceous wastes can be treated by plasma processes. The addition of a catalyst to the plasma process is a developing field as plasma processes are energy intensive. This paper covers the detailed concept of plasma and catalysis. It comprises various types of plasma (non-thermal and thermal) and catalysts (zeolites, oxides, and salts) which have been used for waste treatment. Catalyst addition improves gas yield and hydrogen selectivity at moderate temperatures. Depending on the properties of the catalyst and type of plasma, comprehensive points are listed for the selection of the right catalyst for a plasma process. This review offers an in-depth analysis of the research in the field of waste-to-energy using plasma-catalytic processes.

Carbon dioxide gasification characteristics of disposable COVID-19 masks using bubbling fluidized bed reactor

The global demand for masks has increased significantly owing to COVID-19 and mutated viruses, resulting in a massive amount of mask waste of approximately 490,000 tons per month. Mask waste recycling is challenging because of the composition of multicomponent polymers and iron, which puts them at risk of viral infection. Conventional treatment methods also cause environmental pollution. Gasification is an effective method for processing multicomponent plastics and obtaining syngas for various applications. This study investigated the carbon dioxide gasification and tar removal characteristics of an activated carbon bed using a 1-kg/h laboratory-scale bubble fluidized bed gasifier. The syngas composition was analyzed as 10.52 vol% of hydrogen, 6.18 vol% of carbon monoxide, 12.05 vol% of methane, and 14.44 vol% of hydrocarbons (C2-C3). The results of carbon dioxide gasification with activated carbon showed a tar-reduction efficiency of 49%, carbon conversion efficiency of 45.16%, and cold gas efficiency of 88.92%. This study provides basic data on mask waste carbon dioxide gasification using greenhouse gases as useful product gases.

Experimental investigation on slow thermal pyrolysis of real-world plastic wastes in a fixed bed reactor to obtain aromatic rich fuel grade liquid oil

Plastic wastes have become one of the biggest global environmental issues and thus recycling such massive quantities is targeted. Thermal pyrolysis has been the most suitable approach to convert the waste plastic into a source of energy. This study aims to compare the thermal pyrolysis of waste plastic with that of the modal plastic compounds in a fixed bed reactor. The liquid oil, obtained from the thermal pyrolysis of HDPE, LDPE, PP and PS wastes were characterized using FT-IR, GC-MS and 1H NMR. Also, their fuel properties such as viscosity and calorific values were characterized using parallel plate rheometer and bomb calorimeter respectively. C10-C44 paraffins and C10-C22 olefins were obtained along with aromatics and alcohols in different type of plastic waste pyrolysis oil. The viscosity of the plastic oil is within kerosene and diesel range. The calorific values of the oils are at par with the Petro fuels.

Conversion of solid wastes and natural biomass for deciphering the valorization of biochar in pollution abatement: A review on the thermo-chemical processes

This overview addresses the formation of solid trash and the various forms of waste from a variety of industries, which environmentalists have embraced. The paper investigates the negative effects on the environment caused by unsustainable management of municipal solid trash as well as the opportunities presented by the formal system. This examination looks at the origins of solid waste as well as the typical treatment methods. Pyrolysis methods, feedstock pyrolysis, and lignocellulosic biomass pyrolysis were highlighted. Explain in detail the various thermochemical processes that take place during the pyrolysis of biomass. Due to its carbon content, low cost, accessibility, ubiquitousness, renewable nature, and environmental friendliness, biomass waste is a unique biochar precursor. This study looks at the different types of biomass waste that are available for treating wastewater. This study discussed a wide variety of reactors. Adsorption is the standard method that is used the most frequently to remove hazardous organic, dye, and inorganic pollutants from wastewater. These pollutants cause damage to the environment and water supplies, thus it is important to remove them. Adsorption is both simple and inexpensive to utilize. Temperature-dependent conversions explain the kinetic theories of biomaterial biochemical degradation. This article presents a review that explains how pyrolytic breakdown char materials can be used to reduce pollution and improve environmental management.

Recovery of plastic waste through its thermochemical degradation: a review

The demand to produce plastic has increased yearly; only in 2020, there was a production of approximately 368 million tons worldwide. According to Plastics Europe, from 2016 to 2018, a total of 29.1 Mt of plastic waste was generated, and 24% of this ended up in a landfill, generating problems due to accumulation. The increase in the demand for plastics has begun to contribute to the shortage of oil sources, a non-renewable resource. On the other hand, various researchers have reported effects on human health such as neurological damage, cancer in the nasal cavities, prostate, and ovarian cancer, and in animal species, destruction of the digestive and respiratory tracts due to the consumption of microplastics in food. Due to these reasons, various solutions have been proposed for recovering and recycling plastic waste. One of the most promising technologies is thermal and catalytic degradation, known as pyrolysis. This technology allows the recovery of chemical compounds of high energy value. In this work, the various environmental and social impacts caused by plastic are discussed. Worldwide consumption data is provided by sector and type of plastic, and the different routes of thermal degradation for each type of thermoplastic are shown.

Comprehensive Kinetic Study of PET Pyrolysis Using TGA

The pyrolysis of polyethylene terephthalate (PET) is a well-known process for producing high fuel value. This paper aims to study the kinetics of PET pyrolysis reactions at 4 different heating rates (2, 5, 10, and 20 K min^-1) using thermogravimetric analysis (TGA) data. TGA data show only one kinetic reaction within the temperature ranges of 650 to 750 K. Five different model-free models, namely, the Freidman (FR), Flynn-Wall-Qzawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink (STK), and distributed activation energy model (DAEM), were fitted to the experimental data to obtain the activation energy (E_a) and the pre-exponential factor (A₀) of the reaction kinetics. The Coats-Redfern (CR) model equation was fitted with the help of master plot (Criado's) to identify the most convenient reaction mechanism for this system. E_a's values were determined by the application of the five aforementioned models and were found to possess an average value of 212 kJ mol^-1. The mechanism of PET pyrolysis reaction was best described by first-order reaction kinetics; this was confirmed by the compensation. Further thermodynamic parameter analysis indicated that the reaction was endothermic in nature.

Distribution, migration, and removal of N-containing products during polyurethane pyrolysis: A review

Due to the wide applications of polyurethane (PU), production is constantly increasing, accounting for 8% of produced plastics. PU has been regarded as the 6th most used polymer in the world. Improper disposal of waste PU will result in serious environmental consequences. The pyrolysis of polymers is one of the most commonly used disposal methods, but PU pyrolysis easily produces toxic and harmful nitrogen-containing substances due to its high nitrogen content. This paper reviews the decomposition pathways, kinetic characteristics, and migration of N-element by product distribution during PU pyrolysis. PU ester bonds break to produce isocyanates and alcohols or decarboxylate to produce primary amines, which are then further decomposed to MDI, MAI, and MDA. The nitrogenous products, including NH3, HCN, and benzene derivatives, are released by the breakage of C-C and C-N bonds. The N-element migration mechanism is concluded. Meanwhile, this paper reviews the removal of gaseous pollution from PU pyrolysis and discusses the removal mechanism in depth. Among the catalysts for pollutant removal, CaO has the most superior catalytic performance and can convert fuel-N to N2 by adsorption and dehydrogenation reactions. At the end of the review, new challenges for the utilization and high-quality recycling of PU are presented.

Conversion of waste polystyrene into valuable aromatic hydrocarbons via microwave-assisted pyrolysis

The prime objective of the current research work was to understand the role of microwave-assisted pyrolysis for the upgradation of expanded polystyrene (EPS) waste into valuable aromatic hydrocarbons. Ethyl acetate solvent was used to dissolve the EPS to enhance the homogeneous dispersion of EPS with susceptor particles. Biochar obtained from the pyrolysis was used as a susceptor. The design of experiments method was used to understand the role of microwave power (300 W, 450 W, and 600 W) and susceptor quantity (5 g, 10 g, and 15 g) in the pyrolysis process. The pyrolysis was conducted till the temperature reached up to 600 °C, and this temperature was achieved in the time interval of 14-38 min based on the experimental conditions. The obtained average heating rates varied in the range of 15 to 41 °C/min to attain the pyrolysis temperature. The EPS feed was converted into char (~ 2.5 wt.%), oil (51 to 60 wt.%), and gaseous (37 to 47 wt.%) products. The specific microwave energy (J/g) was calculated to know the energy requirement; it increased with an increase in susceptor quantity and microwave power, whereas specific microwave power (W/g) was a function of microwave power and increased from 15 to 30 W/g. The predicted values calculated using the model equations closely matched the actual values showing that the developed model equations via optimization had a good fit. The obtained pyrolysis oil physicochemical properties including viscosity (1 to 1.4 cP), density (990 to 1030 kg/m³), heating value (39 to 42 MJ/kg), and flash point (98 to 101 °C) were thoroughly analyzed. The pyrolysis oil was rich in aromatic hydrocarbons and it was predominantly composed of styrene, cyclopropyl methylbenzene, and alkylbenzene derivates.

Perspectives on Thermochemical Recycling of End-of-Life Plastic Wastes to Alternative Fuels

Due to its resistance to natural degradation and decomposition, plastic debris perseveres in the environment for centuries. As a lucrative material for packing industries and consumer products, plastics have become one of the major components of municipal solid waste today. The recycling of plastics is becoming difficult due to a lack of resource recovery facilities and a lack of efficient technologies to separate plastics from mixed solid waste streams. This has made oceans the hotspot for the dispersion and accumulation of plastic residues beyond landfills. This article reviews the sources, geographical occurrence, characteristics and recyclability of different types of plastic waste. This article presents a comprehensive summary of promising thermochemical technologies, such as pyrolysis, liquefaction and gasification, for the conversion of single-use plastic wastes to clean fuels. The operating principles, drivers and barriers for plastic-to-fuel technologies via pyrolysis (non-catalytic, catalytic, microwave and plasma), as well as liquefaction and gasification, are thoroughly discussed. Thermochemical co-processing of plastics with other organic waste biomass to produce high-quality fuel and energy products is also elaborated upon. Through this state-of-the-art review, it is suggested that, by investing in the research and development of thermochemical recycling technologies, one of the most pragmatic issues today, i.e., plastics waste management, can be sustainably addressed with a greater worldwide impact.

Plastic waste as pyrolysis feedstock for plastic oil production: A review

Turning plastic waste into plastic oil by pyrolysis is one of the promising techniques to eradicate plastic waste pollution and accelerate the circular economy of plastic materials. Plastic waste is an attractive pyrolysis feedstock for plastic oil production owing to its favorable chemical properties of proximate analysis, ultimate analysis, and heating value other than its abundant availability. Despite the exponential growth of scientific output from 2015 to 2022, a vast majority of the current review articles cover the pyrolysis of plastic waste into a series of fuels and value-added products, and up-to-date reviews exclusively on plastic oil production from pyrolysis are relatively scarce. In light of this void in the current review articles, this review attempts to provide an up-to-date overview of plastic waste as pyrolysis feedstock for plastic oil production. A particular emphasis is placed on the common types of plastic as primary sources of plastic pollution, the characteristics (proximate analysis, ultimate analysis, hydrogen/carbon ratio, heating value, and degradation temperature) of various plastic wastes and their potential as pyrolysis feedstock, and the pyrolysis systems (reactor type and heating method) and conditions (temperature, heating rate, residence time, pressure, particle size, reaction atmosphere, catalyst and its operation modes, and single and mixed plastic wastes) used in plastic waste pyrolysis for plastic oil production. The characteristics of plastic oil from pyrolysis in terms of physical properties and chemical composition are also outlined and discussed. The major challenges and future prospects for the large-scale production of plastic oil from pyrolysis are also addressed.

Energy Recovery and Economic Evaluation for Industrial Fuel from Plastic Waste

Plasma gasification is considered an environmentally friendly process to convert plastic waste into fuel oil; a prototype system is described to test and validate the plasma treatment of plastic waste as a strategic vision. The proposed plasma treatment project will deal with a plasma reactor with a waste capacity of 200 t/day. The annual plastic waste production in tons in all regions of Makkah city during 27 years for all months in the years 1994 to 2022 is evaluated. A statistics survey of plastic waste displays the average rate generation ranging from 224 thousand tons in the year 1994 to 400 thousand tons in the year 2022, with an amount of recovered pyrolysis oil; 3.17 × 10⁵ t with the equivalent energy; 12.55 × 10⁹ MJ, and an amount of recovered diesel oil; 2.7 × 10⁵ t with an amount of electricity for sale 2.96 × 10⁶ MW.h. The economic vision will be estimated, using the results of energy generated from diesel oil as an industrial fuel extracted from plastic waste equivalent to 0.2 million barrels of diesel oil, with sales revenue and cash recovery of USD 5 million, considering the sale of each one barrel of diesel extracted from plastic waste in the range of USD 25. It is important to consider that the equivalent barrels of petroleum cost, according to the organization of the petroleum-exporting countries' basket prices, up to USD 20 million. The sales profit (2022) is as follows: for diesel with a sales revenue of diesel oil, USD 5 million, with a rate of return of 4.1%, and a payback period of 3.75 years. The generated electricity reached USD 32 million for households and USD 50 million for factories.

Effects of Ni/Al2O3 catalyst treatment condition on thermocatalytic conversion of spent disposable wipes

Municipal solid waste (MSW) management is an essential municipal service. Proper waste treatment is an important part of the waste management. Thermocatalytic waste upcycling has recently gained great interest and attention as a method to extract value from waste, which potentially substitutes traditional waste treatment methods. This study aims at demonstrating the potential for thermocatalytic waste upcycling using spent disposable wipes as an MSW surrogate. Two different Ni/Al2O3 catalysts were prepared, treated under two different atmospheres (N2 and CO2). The catalyst treated in N2 (Ni/Al2O3-N2) exhibited a higher surface metallic Ni site than the catalyst treated in CO2 (Ni/Al2O3-CO2). The use of the Ni/Al2O3-N2 increased the yield of gas pyrolysate and decreased the yield of byproduct (e.g., wax), compared with no catalyst and the Ni/Al2O3-CO2. In particular, the Ni/Al2O3-N2 catalyst affected the generation of gaseous hydrogen (H2) by increasing the H2 yield by up to 102% in comparison with the other thermocatalytic systems. The highest H2 yield obtained with the Ni/Al2O3-N2 was attributed to the most surface metallic Ni sites. However, the Ni/Al2O3-N2 catalyst led to char having a lower higher heating value than the other catalysts due to its lowest carbon content. The results indicated that the reduction treatment environment for Ni/Al2O3 catalyst influences thermocatalytic conversion product yields of spent disposable wipes, including enhanced H2 production.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at 10.1007/s11814-023-1461-8.

Carbon nanotubes production from real-world waste plastics and the pyrolysis behaviour

The investigation of the pyrolysis behaviour of real-world waste plastics (RWWP) and using them as the feedstock to produce carbon nanotubes (CNTs) could serve as an effective solution to address the global waste plastics catastrophe. This research aimed to characterize the pyrolysis behaviour of RWWP via thermogravimetric analysis (TG) and fast pyrolysis-TG/mass spectrometry (Py-TG/MS) analyses. Activation energies (131.04 kJ mol^-1 -171.04 kJ mol^-1) for RWWP pyrolysis were calculated by three methods: Flynn-Wall-Ozawa (FWO) method, Kissinger-Akahira-Sunose (KAS) method, and Starink method. Py-TG/MS results indicated that the RWWP could be identified as polystyrene (RWWP-1), polyethylene (RWWP-2), polyethylene terephthalate (RWWP-3, 4), and polypropylene (RWWP-5, 6). In addition, RWWP-1, 2, 5, 6 outperform RWWP-3 and 4 as sources of carbon for producing CNTs. The results showed a high carbon yield of 32.21 wt% and a high degree of CNT purity at 93.04%.

Selective recovery of caprolactam from the thermo-catalytic conversion of textile waste over γ-Al2O3 supported metal catalysts

The massive generation of synthetic textile waste has drawn considerable attention. Landfilling/incineration of textile waste has been widely made. To abate the environmental burdensome from the conventional management processes, a thermo-catalytic conversion was used for rapid volume reduction of textile waste and simultaneous valorization by recovering textile monomer in this study. Stockings were chosen as a model feedstock. Because stockings consisted of nylon with other contents, different products (caprolactam (nylon monomer), imines, cyclic dimers, and azepines) were recovered. The yield of caprolactam from the thermal conversion at 500 °C was 53.6 wt%. To selectively enhance the caprolactam yield, catalytic pyrolysis was done using γ-Al₂O₃ supported metal catalysts (Ni, Cu, Fe, or Co). γ-Al₂O₃ itself increased the caprolactam yield up to 69.0 wt% via a based-catalyzed reaction of nylon depolymerization and intramolecular cyclization. Under the presence of metal catalysts, the caprolactam yield increased up to 73.3 wt%. To offer desired feature of green chemistry, CO₂ was adopted as reactive gas. Under the CO₂-mediated catalytic pyrolysis, caprolactam yield was enhanced up to 77.1 wt% over Cu/Al₂O₃ (basis: stocking mass). Based on the net content of nylon in the stockings, the yield of caprolactam was deemed 95.3 wt%. This study proves that textile waste (stocking) and CO₂ are useful resources for recovery of nylon monomer, which can reduce the waste generation with simultaneous recovery of value-added product.

Catalyst-mediated pyrolysis of waste plastics: tuning yield, composition, and nature of pyrolysis oil

With ever-increasing plastic waste, a robust and sustainable methodology to valorize the waste and tweak, the composition of the value added product is the need of the hour. The present study describes the effect of different heterogeneous catalyst systems on the yield, composition and nature of the pyrolysis oil produced from various waste polyolefins like high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and polypropylene (PP). The waste polyolefins were subjected to thermal as well as catalytic pyrolysis. Liquid, gas, and solid products were obtained during the pyrolysis. Various catalysts such as activated alumina (AAL), ZSM-5, FCC catalyst, and halloysite clay (HNT) were used. Usage of catalysts has reduced the temperature of the pyrolysis reaction from 470 to 450 °C with better liquid product yield. PP waste generated higher liquid yield compared to LLDPE and HDPE waste. The highest liquid yield of 70.0% was achieved with PP waste using AAL catalyst at 450 °C. The sulfur and chloride content was found to be < 10 and < 20 ppm respectively in all the pyrolysis liquid. Pyrolysis liquid products were analyzed using gas chromatography (GC), nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray fluorescence (XRF) spectroscopy, and gas chromatography coupled with mass spectrophotometry (GC-MS). The obtained liquid products consist of paraffin, naphthene, olefin and aromatic components. Catalyst regeneration experiments with AAL showed that the product distribution profile remains the same up to three cycles of regeneration.

On the use of plastic precursors for preparation of activated carbons and their evaluation in CO2 capture for biogas upgrading: a review

In circular economy, useful plastic materials are kept in circulation as opposed to being landfilled, incinerated, or leaked into the natural environment. Pyrolysis is a chemical recycling technique useful for unrecyclable plastic wastes that produce gas, liquid (oil), and solid (char) products. Although the pyrolysis technique has been extensively studied and there are several installations applying it on the industrial scale, no commercial applications for the solid product have been found yet. In this scenario, the use of plastic-based char for the biogas upgrading may be a sustainable way to transform the solid product of pyrolysis into a particularly beneficial material. This paper reviews the preparation and main parameters of the processes affecting the final textural properties of the plastic-based activated carbons. Moreover, the application of those materials for the CO₂ capture in the processes of biogas upgrading is largely discussed.

Combustion, Chemistry, and Carbon Neutrality

Combustion is a reactive oxidation process that releases energy bound in chemical compounds used as fuels─energy that is needed for power generation, transportation, heating, and industrial purposes. Because of greenhouse gas and local pollutant emissions associated with fossil fuels, combustion science and applications are challenged to abandon conventional pathways and to adapt toward the demand of future carbon neutrality. For the design of efficient, low-emission processes, understanding the details of the relevant chemical transformations is essential. Comprehensive knowledge gained from decades of fossil-fuel combustion research includes general principles for establishing and validating reaction mechanisms and process models, relying on both theory and experiments with a suite of analytic monitoring and sensing techniques. Such knowledge can be advantageously applied and extended to configure, analyze, and control new systems using different, nonfossil, potentially zero-carbon fuels. Understanding the impact of combustion and its links with chemistry needs some background. The introduction therefore combines information on exemplary cultural and technological achievements using combustion and on nature and effects of combustion emissions. Subsequently, the methodology of combustion chemistry research is described. A major part is devoted to fuels, followed by a discussion of selected combustion applications, illustrating the chemical information needed for the future.

An assessment of the impact of structure and type of microplastics on ultrafiltration technology for microplastic remediation

Microplastic, which is of size less than 5 mm, is gaining a lot of attention as it has become a new arising contaminant because of its ecophysiology impact on the aquatic environment. These microplastics are found in freshwater or drinking water and are the major carriers of pollutants. Removal of this microplastic can be done through the primary treatment process, secondary treatment process, and tertiary treatment process. One approach for microplastic remediation is ultrafiltration technology, which involves passing water through a membrane with small pores to filter out the microplastics. However, the efficiency of this technology can be affected by the structure and type of microplastics present in the water. New strategies can be created to improve the technology and increase its efficacy in removing microplastics from water by knowing how various types and shapes of microplastics react during ultrafiltration. The filter-based technique, that is, ultrafiltration has achieved the best performance for the removal of microplastic. But with the ultrafiltration, too some microplastic that are of sizes less than of ultrafiltration membrane passes through the filter and enters the food chain. Accumulation of this microplastic on the membrane also leads to membrane fouling. Through this review article, we have assessed the impact of the structure, size, and type of MPs on ultrafiltration technology for microplastic remediation, with that how these factors affect the efficiency of the filtration process and challenges occur during filtration.

Post-pandemic micro/nanoplastic pollution: Toward a sustainable management

The global health crisis caused by the COVID-19 pandemic has resulted in massive plastic pollution from the use of personal protection equipment (PPE), with polypropylene (PP) being a major component. Owing to the weathering of exposed PPEs, such contamination causes microplastic (MP) and nanoplastic (NP) pollution and is extremely likely to act as a vector for the transportation of COVID-19 from one area to another. Thus, a post-pandemic scenario can forecast with certainty that a significant amount of plastic garbage combined with MP/NP formation has an adverse effect on the ecosystem. Therefore, updating traditional waste management practices, such as landfilling and incineration, is essential for making plastic waste management sustainable to avert this looming catastrophe. This study investigates the post-pandemic scenario of MP/NP pollution and provides an outlook on an integrated approach to the recycling of PP-based plastic wastes. The recovery of crude oil, solid char, hydrocarbon gases, and construction materials by approximately 75, 33, 55, and 2 %, respectively, could be achieved in an environmentally friendly and cost-effective manner. Furthermore, the development of biodegradable and self-sanitizing smart PPEs has been identified as a promising alternative for drastically reducing plastic pollution.

Plastic-Waste-Derived Char as an Additive for Epoxy Composite

Tremendous amounts of plastic waste are generated daily. The indiscriminate disposal of plastic waste can cause serious global environmental issues, such as leakages of microplastics into the ecosystem. Thus, it is necessary to find a more sustainable way to reduce the volume of plastic waste by converting it into usable materials. Pyrolysis provides a sustainable solution for the production of carbonaceous materials (e.g., char). Plastic-waste-derived char can be used as an additive in epoxy composites to improve the properties and performance of neat epoxy resins. This review compiles relevant knowledge on the potential of additives for epoxy composites originating from plastic waste. It also highlights the potential of plastic-waste-derived char materials for use in materials in various industries.

A Thermo-Catalytic Pyrolysis of Polystyrene Waste Review: A Systematic, Statistical, and Bibliometric Approach

Global polystyrene (PS) production has been influenced by the lightness and heat resistance this material offers in different applications, such as construction and packaging. However, population growth and the lack of PS recycling lead to a large waste generation, affecting the environment. Pyrolysis has been recognized as an effective recycling method, converting PS waste into valuable products in the chemical industry. The present work addresses a systematic, bibliometric, and statistical analysis of results carried out from 2015 to 2022, making an extensive critique of the most influential operation parameters in the thermo-catalytic pyrolysis of PS and its waste. The systematic study showed that the conversion of PS into a liquid with high aromatic content (84.75% of styrene) can be achieved by pyrolysis. Discussion of PS as fuel is described compared to commercial fuels. In addition, PS favors the production of liquid fuel when subjected to co-pyrolysis with biomass, improving its properties such as viscosity and energy content. A statistical analysis of the data compilation was also discussed, evaluating the influence of temperature, reactor design, and catalysts on product yield.

Resource recovery from discarded COVID-19 PPE kit through catalytic fast pyrolysis

During the COVID-19 pandemic, the world saw an exponential surge in the production of Personal Protective Equipment (PPE) kits, which eventually got discarded in the biomedical waste stream. In this study, thirteen different polymer samples from the PPE kit were collected and characterized using Fourier transform infrared spectrometer, thermogravimetric analysis, and analytical pyrolysis-gas chromatograph/mass spectrometry. The characterization data showed that about 94 % by mass of components were made of only three polymers, viz. polypropylene (PP, 75.6 wt %), polyethylene terephthalate (PET, 12.5 wt %), and polycarbonate (PC, 6 wt %). The analytical pyrolysis of the PPE coverall suit (PP) yielded mainly alkenes containing 2,4-dimethyl-1-heptene as the major compound with 17 wt % yield at 600 °C. The pyrolysates from face shield (PET) were rich in benzoic acid (5.8 wt %) and acetophenone (4.8 wt %), while those from safety goggles (PC) were rich in phenol (17.6 wt %) and p-cresol (12.4 wt %) at 600 °C. HZSM-5 and HY zeolites were used for the catalytic upgradation of pyrolysates especially from PP, PET and PC. The temperature and feed-to-catalyst ratio were optimized by performing catalytic fast pyrolysis experiments at 500 °C, 600 °C and 700 °C with different feed-to-catalyst ratios 1:2, 1:4, and 1:6 (w/w). The yield of aromatic hydrocarbons, viz., BTEX (benzene, toluene, ethylbenzene, xylenes) and naphthalene, was maximum (∼25.7 wt %) from PP coverall when HY catalyst was used at 600 °C and 1:6 (w/w) loading. In the case of PET face shield, the total yield of BTEX, naphthalene and biphenyl was maximum (27.9 wt %) at 600 °C and 1:4 (w/w) of HZSM-5, while in the case of PC goggles, it was maximum (18.6 wt %) at 700 °C and 1:4 (w/w) of HY. This study shows that the entire PPE kit can be valorized via catalytic fast pyrolysis to generate petrochemical products and platform molecules like monoaromatic hydrocarbons at high selectivities.

Chemical Upcycling of Waste Plastics to High Value-Added Products via Pyrolysis: Current Trends, Future Perspectives, and Techno-Feasibility Analysis

Chemical upcycling of waste plastics into high-value-added products is one of the most effective, cost-efficient, and environmentally beneficial solutions. Many studies have been published over the past few years on the topic of recycling plastics into usable materials through a process called catalytic pyrolysis. There is a significant research gap that must be bridged in order to use catalytic pyrolysis of waste plastics to produce high-value products. This review focuses on the enhanced catalytic pyrolysis of waste plastics to produce jet fuel, diesel oil, lubricants, aromatic compounds, syngas, and other gases. Moreover, the reaction mechanism, a brief and critical comparison of different catalytic pyrolysis studies, as well as the techno-feasibility analysis of waste plastic pyrolysis and the proposed catalytic plastic pyrolysis setup for commercialization is also covered.

Pyrolytic conversion of waste plastics to energy products: A review on yields, properties, and production costs

In recent years, about 370 million tonnes of waste plastic are generated annually with about 9 % recycled, 80 % landfilled and 11 % converted to energy. As recycling of waste plastics are quite expensive and labour-intensive, the focus has now been shifted towards converting waste plastics into energy products. Pyrolysis of waste plastic generates liquid oil (crude), gas, char and wax among which liquid oil is the most valuable product. In this review, emphasis has been given on the pyrolysis products yield from both thermal and catalytic pyrolysis and the factors that affect pyrolysis products yield. The use of homogenous catalysts, for example AlCl₃, can significantly improve the quality of waste plastic pyrolytic oil (WPPO), reduce time and energy consumption of the process, and help remove the contaminants of waste plastic. This study also thoroughly reviewed physico-chemical properties of WPPO to understand their thermal stability, elemental composition, and functional groups. Although liquid oil exhibits comparable heating value with commercial fuel (diesel/petrol), for example higher heating value of Polypropylene (PP) and Polyethylene (PE) are 50 and 42 MJ/kg which is between 42 and 46 MJ/kg for commercial diesel the other properties depend on several parameters such as plastic and pyrolysis reactor types, temperature, feed size, reaction time, heating rate and catalysts. A techno-economic analysis indicate that the liquid oil production cost could be about 0.6 USD/l if plant capacity is ≥175,000 million litres/year with a breakeven of 1 year. After-treatment of WPPO through distillation and hydrotreatment is recommended for improving the physio-chemical properties comparable to commercial fuel to use in automobile applications. This paper will be a valuable guide for stakeholders, and decision and policy makers for proper utilization of waste plastics.

Conversion of Polyethylene to High-Yield Fuel Oil at Low Temperatures and Atmospheric Initial Pressure

The transformation of waste plastics into fuels via energy-efficient and low-cost pyrolysis could incentivize better waste plastic management. Here, we report pressure-induced phase transitions in polyethylene, which continue to heat up without additional heat sources, prompting the thermal cracking of plastics into premium fuel products. When the nitrogen initial pressure is increased from 2 to 21 bar, a monotonically increasing peak temperature is observed (from 428.1 °C to 476.7 °C). At 21 bar pressure under different atmosphere conditions, the temperature change driven by high-pressure helium is lower than that driven by nitrogen or argon, indicating that phase transition is related to the interaction between long-chain hydrocarbons and intercalated high-pressure medium layers. In view of the high cost of high-pressure inert gases, the promotion or inhibition effect of low-boiling hydrocarbons (transitioning into the gaseous state with increasing temperature) on phase transition is explored, and a series of light components are used as phase transition initiators to replace high-pressure inert gases to experiment. The reason that the quantitative conversion of polyethylene to high-quality fuel products is realized through the addition of 1-hexene at a set temperature of 340 °C and the initial atmospheric pressure. This discovery provides a method for recycling plastics by low energy pyrolysis. In addition, we envisage recovering some of the light components after plastic pyrolysis as phase change initiators for the next batch of the process. This method is able to reduce the cost of light hydrocarbons or high-pressure gas insertion, reduce heat input, and improve material and energy utilization.

A State-of-the-Art Review on the Technological Advancements for the Sustainable Management of Plastic Waste in Consort with the Generation of Energy and Value-Added Chemicals

Plastic waste poses a serious threat to the environment and it has been increasing at an alarming rate. In 2022, global plastic waste generation was reported to be around 380 million tonnes as compared to 353 million tonnes in 2019. Production of liquid fuel from plastic waste is regarded as a viable method for disposing of the plastic and utilizing its energy. Currently, a wide range of technologies have been explored for turning plastic waste into fuel, including the conventional pyrolysis, incineration, gasification and advanced oxidation. However, a systematic summary and comparative analysis of various technologies has still not reported. Traditional non-biodegradable plastic waste (NPW) treatment methods include landfilling and incineration, but these methods encounter bottlenecks and are unable to adequately address NPW issues. This review attempts to present a thorough summary of treatment methods for plastic waste (both conventional and novel treatment technologies that have recently been reported), examine their mechanism and their current state of development. Furthermore, the superiority and drawbacks of each technology are analysed and the prospects of technology application are proposed. By tackling the problems of white pollution and energy scarcity, this review intends to inspire the use of solid waste as a source of energy.