Production and utilization of pyrolysis oil from solidplastic wastes: A review on pyrolysis process and influence of reactors design

Effect of design parameters in nanocatalyst synthesis on pyrolysis for producing diesel-like fuel from waste lubricating oil

Converting waste lubricating oil into diesel-like liquid fuels using pyrolysis presents a dual solution, addressing environmental pollution while offering a viable response to the fossil energy crisis. However, achieving high-quality fuel with a substantial yield necessitates the utilization of highly active and cost-effective catalysts. We report the development of Fe-Ni nanocatalysts, synthesized using a green approach and supported on TiO2, as a promising strategy for converting waste lubricating oil into premium-grade diesel-like fuel. To ensure efficient and effective pyrolysis processes, tailoring the synthesis parameters of these nanocatalysts is indispensable. In this study, we investigate the effect of design parameters on nanocatalyst synthesis, such as the concentrations of pre-catalysts and reducing agents, reducing time, and the amount of support material, and evaluate their impact on the quality and quantity of pyrolysis products. Through optimization of the synthesis process, a high quality diesel-like fuel with a product yield of about 54% at a mild reaction temperature of 400 °C was obtained. This study highlights the critical role of nanocatalysis in addressing persistent environmental and energy challenges while showcasing the potential of green nanocatalysts in sustainable waste-to-energy conversion processes.

Upcycling of PVC waste to high-value sorbent with KOH-activation for efficient removal of organic dyes

Polyvinyl chloride (PVC), known for its chemical stability and flame-retardant qualities, has many uses in various fields, such as pipes, electric wires, and cable insulation. Research has established its potential recovery as a fluidic fuel through pyrolysis, but the use of PVC pyrolysis oil, which is tainted by chlorine, is constrained by its low heat value and harmful environmental effects. This study engineered a layered double hydroxide (LDH) to tackle these challenges. The LDH facilitated dechlorination during PVC pyrolysis and bolstered thermal stability via cross-linking. During pyrolysis with LDH, PVC was transformed into carbon-rich precursors to sorbents. Chemical activation of these residues using KOH created sorbents with a specific surface area of 1495.4 m2 g⁻1, rendering them hydrophilic. These resulting sorbents displayed impressive adsorption capabilities, removing up to 486.79 mg g⁻1 of methylene blue and exhibiting the simultaneous removal of cations and anions.

Efficient extraction of metals (Fe, Zn, Pb) from hazardous jarosite using ionic liquid and waste-derived solvents

The present study evaluated a solvo-metallurgical technique for metal extraction from industrial solid waste (jarosite) using ionic liquids (ILs) and waste-derived solvents. The jarosite contains a considerable amount of metal ions, namely iron, zinc, and lead. The jarosite was characterized by XRF, XRD, SEM, and FTIR techniques. The parameters affecting metal extraction, such as stirring time, acid molarity, and temperature, have been examined. Aliquat 336 was used to extract metals from fresh and roasted jarosite after equilibration with HCl. The response surface methodology (RSM) was used to optimize the parameters for the maximum metal extraction using [A336] [Cl]. Maximum extraction of iron (86.75%), zinc (51.96%), and lead (94.38%) from roasted jarosite was achieved at optimum conditions (125-min stirring time, 5 M acid molarity, and 20 ml/g liquid-to-solid ratio). Furthermore, the metal extraction was investigated using waste-derived solvents. The results show that waste-derived solvents, such as biomass and plastic pyrolysis oil, can effectively extract metals from fresh and roasted jarosite. Biomass pyrolysis oil achieved the highest extraction at 50 °C for 90 min, while plastic pyrolysis oil achieved the highest extraction at 50 °C for 60 min from roasted jarosite. These solvents are also cost-effective because they are made from waste plastic and biomass.

Stabilization of heavy metals in solid waste and sludge pyrolysis by intercalation-exfoliation modified vermiculite

Increasing amounts of solid waste and sludge have created many environmental management problems. Pyrolysis can effectively reduce the volume of solid waste and sludge, but there is still the problem of heavy metal contamination, which limits the application of pyrolysis in environmental management. The intercalated-exfoliated modified vermiculite (IEMV) by intercalators of sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide were used to control the release of Cd, Cr, Cu, Zn and Pb during pyrolysis process of sludge or solid waste. The retention of heavy metals in sludge was generally better than that in solid waste. The IEMV by octadecyltrimethylammonium bromide as the intercalator calcined 800 °C (STAB-800) was the best additive for heavy metal retention, and the retention of Cr, Cu and Zn was significantly better than that of Pb and Cd. Cr, Cu, Zn and Pb were at low risk, while Cd had considerable risk under certain circumstances. New models were proposed to comprehensively evaluate the results of the risk and forms of heavy metals, and the increasing temperature was beneficial in reducing the hazards of heavy metals by the addition of STAB-800. The reaction mechanism of heavy metals with vermiculite was revealed by simulation of reaction sites, Fukui Function and Frontier Molecular Orbital. Thermal activation-intercalated-exfoliated modified vermiculite (T-IEMV) is more reactive and had more active sites for heavy metals. Mg atoms and outermost O atoms are the main atoms for T-IEMV to react with heavy metals. The Cr, Cu and Zn have better adsorption capacity by T-IEMV than Pb and Cd. This study provides a new insight into managing solid waste and sludge and controlling heavy metal environmental pollution.

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.

Production of light olefins and monocyclic aromatic hydrocarbons from the pyrolysis of waste plastic straws over high-silica zeolite-based catalysts

Owing to the ever-increasing generation of plastic waste, the need to develop environmentally friendly disposal methods has increased. This study explored the potential of waste plastic straw to generate valuable light olefins and monocyclic aromatic hydrocarbons (MAHs) via catalytic pyrolysis using high-silica zeolite-based catalysts. HZSM-5 (SiO2/Al2O3:200) exhibited superior performance, yielding more light olefins (49.8 wt%) and a higher MAH content than Hbeta (300). This was attributed to the increased acidity and proper shape selectivity. HZSM-5 displayed better coking resistance (0.7 wt%) than Hbeta (4.4 wt%) by impeding secondary reactions, limiting coke precursor formation. The use of HZSM-5 (80) resulted in higher MAHs and lower light olefins than HZSM-5 (200) because of its higher acidity. Incorporation of Co into HZSM-5 (200) marginally lowered light olefin yield (to 44.0 wt%) while notably enhancing MAH production and boosting propene selectivity within the olefin composition. These observations are attributed to the well-balanced coexistence of Lewis and Brønsted acid sites, which stimulated the carbonium ion mechanism and induced H-transfer, cyclization, Diels-alder, and dehydrogenation reactions. The catalytic pyrolysis of plastic straw over high-silica and metal-loaded HZSM-5 catalysts has been suggested as an efficient and sustainable method for transforming plastic waste materials into valuable light olefins and MAHs.

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.

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.

Study on synergistic pyrolysis and kinetics of mixed plastics based on spent fluid-catalytic-cracking catalyst

At present, disposable plastic products such as plastic packaging are very common in our daily life. These products are extremely easy to cause serious damage to the soil and marine environment due to their short design and service life, difficulties in degradation, or long degradation cycles. Thermochemical method (pyrolysis or catalytic pyrolysis) is an efficient and environmentally friendly way to treat plastic waste. In order to further reduce the energy consumption of plastic pyrolysis and improve the recycling rate of spent fluid catalytic cracking (FCC) catalysts, we adopt the "waste-to-waste" approach to apply the spent FCC catalysts as catalysts in the catalytic pyrolysis of plastics, exploring the pyrolysis characteristics, kinetic parameters, and synergistic effects between different typical plastics (polypropylene, low-density polyethylene, polystyrene). The experimental results show that the spent FCC catalysts used in the catalytic pyrolysis of plastics are beneficial to reduce the overall pyrolysis temperature and activation energy, in which the maximum weight loss temperature decreases by about 12 ℃ and the activation energy decreases by about 13%. The activity of spent FCC catalysts is improved after modification by microwave and ultrasonic, which further improve the catalytic efficiency and reduce the energy consumption of pyrolysis. The co-pyrolysis of mixed plastics is dominated by positive synergistic effect, which is conducive to improving the thermal degradation rate and shortening the pyrolysis time. This study provides relevant theoretical support for the resource application of spent FCC catalysts and "waste-to-waste" treatment of plastic waste.

Economic analysis of the circular economy based on waste plastic pyrolysis oil: a case of the university campus

Recently, the concept of a circular economy for carbon neutrality is emerging. In particular, waste plastics are one of the key wastes, and efforts are being made to recycle them as energy rather than dispose of them. Accordingly, the technology of producing and utilizing pyrolysis oil from waste plastics attracts attention. As it is an early stage of technology development, however, there are not many demonstrations and papers that analyze the technology broadly. The goal of this study is to propose building a circular economy on a university campus through waste plastic pyrolysis oil technology. To show its feasibility, waste plastic pyrolysis oil technology is analyzed comprehensively from economic, environmental, and policy perspectives using the scenario analysis technique on the university campus level. A methodology of the scenario analysis technique enables predicting the uncertainties. Since plastic pyrolysis oil technologies and carbon neutrality are accompanied by many uncertainties, this technique is expected to be an appropriate methodology for this study. First, the amount of pyrolysis oil production from waste plastics from the campus is estimated. Then, the cost and carbon emissions from waste plastics are estimated if the pyrolysis oil technology is used instead of the traditional waste disposal process. As a result, the total economic profits of up to 425,484,022 won/year (354,570.01 $/year) are expected when a circular economy is built using waste plastic pyrolysis oil. In addition, it is also confirmed that greenhouse gas (GHG) emissions can be reduced by up to 840,891 kgCO2eq/year. The waste plastic pyrolysis oil satisfies Korea's gas pollutant standards and is consistent with the GHG reduction policy. It can be concluded that building a circular economy at the university campus level using waste plastic pyrolysis oil technology is suitable from economic, environmental, and policy perspectives.

Valorization of neem seeds biomass to biofuel via non-catalytic and catalytic pyrolysis process: Investigation of catalytic activity of Co-Mo/Al2O3 and Ni-Mo/Al2O3 for biofuel production

Biofuel production from neem seeds have been evaluated via non-catalytic and catalytic pyrolysis process. Co-Mo/Al₂O₃ and Ni-Mo/Al₂O₃ industrial catalysts have been applied in upgrading process of pyrolysis oil to biofuel. The catalytic activity test revealed that these catalysts succeeded in converting fatty acids content of pyrolysis oil into low oxygen content compounds such as alcohols, alkanes, cyclic compounds, and esters via deoxygenation route. Enhancement of temperature and catalyst loading lead to increase of bio-gas production yield, significantly. The highest yield of pyrolysis oil (60.2%) was obtained at 450 °C, heating rate of 40 °C.min^-1 via non-catalytic pyrolysis. Using 40% catalyst loading of Ni-Mo/Al₂O₃, the content of alcohol, cyclic and alkane compounds in the bio-oil were reached 12.65%, 21.74% and 15%, respectively. The highest selectivity using 40% catalyst loading of Co-Mo/Al₂O₃ catalyst at 450 °C was related to fatty acids (62.5%), esters (18.2%) and alkanes (6.25). It is inferred that the addition of Ni to Mo causes more progress of decarbonylation and decarboxylation reactions, and the addition of Co to Mo generates more ester compounds. Sensitivity analysis indicated that the effect of Ni-Mo/Al₂O₃ catalyst through catalytic pyrolysis process was more severe than Co-Mo/Al₂O₃ catalyst.

Plastic and Waste Tire Pyrolysis Focused on Hydrogen Production—A Review

In this review, we compare hydrogen production from waste by pyrolysis and bioprocesses. In contrast, the pyrolysis feed was limited to plastic and tire waste unlikely to be utilized by biological decomposition methods. Recent risks of pyrolysis, such as pollutant emissions during the heat decomposition of polymers, and high energy demands were described and compared to thresholds of bioprocesses such as dark fermentation. Many pyrolysis reactors have been adapted for plastic pyrolysis after successful investigation experiences involving waste tires. Pyrolysis can transform these wastes into other petroleum products for reuse or for energy carriers, such as hydrogen. Plastic and tire pyrolysis is part of an alternative synthesis method for smart polymers, including semi-conductive polymers. Pyrolysis is less expensive than gasification and requires a lower energy demand, with lower emissions of hazardous pollutants. Short-time utilization of these wastes, without the emission of metals into the environment, can be solved using pyrolysis. Plastic wastes after pyrolysis produce up to 20 times more hydrogen than dark fermentation from 1 kg of waste. The research summarizes recent achievements in plastic and tire waste pyrolysis development.

Upcycling Polystyrene

Several environmental and techno-economic assessments highlighted the advantage of placing polystyrene-based materials in a circular loop, from production to waste generation to product refabrication, either following the mechanical or thermochemical routes. This review provides an assortment of promising approaches to solving the dilemma of polystyrene waste. With a focus on upcycling technologies available in the last five years, the review first gives an overview of polystyrene, its chemistry, types, forms, and varied applications. This work presents all the stages that involve polystyrene's cycle of life and the properties that make this product, in mixtures with other polymers, command a demand on the market. The features and mechanical performance of the studied materials with their associated images give an idea of the influence of recycling on the structure. Notably, technological assessments of elucidated approaches are also provided. No single approach can be mentioned as effective per se; hybrid technologies appear to possess the highest potential. Finally, this review correlates the amenability of these polystyrene upcycling methodologies to frontier technologies relating to 3D printing, human space habitation, flow chemistry, vertical farming, and green hydrogen, which may be less intuitive to many.

Exploring the Valorization of Buckwheat Waste: A Two-Stage Thermo-Chemical Process for the Production of Saccharides and Biochar

To realize the utilization of the valorization of buckwheat waste (BW), a two-stage thermal-chemical process was explored and evaluated to produce saccharides and biochar. During the first stage, BW underwent a hydrothermal extraction (HTE) of varying severity to explore the feasibility of saccharides production; then, the sum of saccharides yields in the liquid sample were compared. A higher sum of saccharides yields of 4.10% was obtained at a relatively lower severity factor (SF) of 3.24 with a byproducts yield of 1.92 %. During the second stage, the contents of cellulose, hemicellulose, and lignin were analyzed in the residue after HTE. Enzymatic hydrolysis from the residue of HTE was inhibited. Thus, enzymatic hydrolysis for saccharides is not suitable for utilizing the residue after HTE of BW. These residues with an SF of 3.24 were treated by pyrolysis to produce biochar, providing a higher biochar yield of 34.45 % and a higher adsorption ability (based on methyl orange) of 31.11 % compared with pyrolysis of the raw BW. Meanwhile, the surface morphology and biomass conversion were analyzed in this study. These results demonstrate that the two-stage thermal-chemical process is efficient for treating BW and producing saccharides and biochar. This work lays a foundation for the industrial application of BW, and for improving the economic benefits of buckwheat cultivation.