Thermochemical conversion of waste tyres-a review

Flash Pyrolysis of Waste Tires in an Entrained Flow Reactor-An Experimental Study

In this study, a flash pyrolysis process is developed using an entrained flow reactor for recycling of waste tires. The flash pyrolysis system is tested for process stability and reproducibility of the products under similar operating conditions when operated continuously. The study is performed with two different feedstock materials, i.e., passenger car (PCT) and truck tire (TT) granulates, to understand the influence of feedstock on the yield and properties of the pyrolysis products. The different pyrolytic products i.e., pyrolytic carbon black (pCB), oil, and pyro-gas, are analyzed, and their key properties are discussed. The potential applications for the obtained pyrolytic products are discussed. Finally, a mass and energy balance analysis has been performed for the developed pyrolysis process. The study provides insight into the governing mechanisms of the flash pyrolysis process for waste tires, which is useful to optimize the process depending on the desired applications for the pyrolysis products, and also to scale up the pyrolysis process.

End-of-life tyre conversion to energy: A review on pyrolysis and activated carbon production processes and their challenges

The number of end-of-life waste tyres has increased enormously worldwide, which is one of the non-biodegradable Municipal Solid Waste (MSW) piling up in an open space for a long time. Every year, various types of tyres are released in the environment from different vehicles, such as trucks, buses, cars, motorcycles, and bicycles, which negatively impact the environment. Nowadays, waste tyres are treated in several ways, whereas thermochemical conversion is one of them, including combustion, gasification, incineration, and pyrolysis. Many literatures revealed that pyrolysis is a more environmentally friendly process than others since it can convert waste tyres into crude oil, char, and syngas without emitting harmful gases. In this study, the pyrolysis of tyres and the chemical activation of tyres are reviewed in terms of their kinetic behaviour. According to the literature, the most influential factors of the pyrolysis process are reactors, temperature, heating rate, residence time, feedstock size and catalyst. As the main ingredient of the tyre is rubber, tyre pyrolysis starts from 300 °C and completely decomposed nearly 550 °C. It can be found from literature that Pyrolysed tyre can produce 30-65% oil, 25-45% char and 5-20 % gas. It is also explained how the properties of active carbon (AC) are affected by activating conditions, including activation temperature, agent, the ratio of reagent mixture and others. Generally, pyrolytic char has surface area between 20 and 80 m2/g, whereas tyre-derived activated carbon's (TDAC) surface area varied from 90 to 970 m2/g. For large surface area and porous structure, TDAC has large application in purification and energy storage sector. The individuality of this article is to depict the entire pathway of AC production from waste tyres. The findings of this literature review help to improve technologies for producing activated carbon from waste tyres pyrolysed char.

Review in Waste Tire Management-Potential Applications in Mitigating Environmental Pollution

Increasing year-by-year vehicle production is related to the expanding volume of used tires; therefore, exploring waste management strategies is strongly recommended. The global tire market reached 2.27 billion units in 2021 and is expected to reach 2.67 billion units by 2027. Dumping tires in landfills can cause significant environmental impacts, so waste tire utilisation plays an important role. Predominantly, the following three directions are employed for waste tire disposal: retreading, energy recovery and material recovery. The review shows that used tires can remove environmental pollution from both aqueous solutions containing heavy metal ions, dyes, pharmaceutical compounds, and benzene, toluene, ethylbenzene and xylene (BTEX). Particularly high efficiency was achieved in the removal of dyes (72%), taking into account the high initial concentration of impurities. The adsorption process depends on multiple factors, including, in particular, the following: pH, initial concentration of pollution, contact time and the properties of the sorbent used. The optimal pH range was identified to be between 6 and 7. Considering the principles of circular economy as well as based on the current state of knowledge, it can be concluded that the solid fraction obtained from the combustion of waste tires can be practically utilised for various environmental purposes.

Waste tire pyrolysis and desulfurization of tire pyrolytic oil (TPO) - A review

The presence of waste tires on open fields or households creates an ideal breeding ground for disease-carrying vermin, threatening human well-being. There are various technologies studied for efficient use of waste tires, such as pyrolysis, which results in char, oil, and non-condensable gases. Tire pyrolytic oil (TPO) has been reported to be similar to commercial diesel fuel. The current hurdle for using TPO in commercial diesel engines is the available sulfur content (>1.0 wt%). The disadvantages of sulfur in liquid fuels are its ability to reduce the engine's life due to corrosion and the undesirable emission of SO_x that subsequently damages public health and property. There is a rising need to develop efficient technologies for the desulfurization of such liquid fuels. Besides conventional hydrodesulfurization, other emerging technologies include adsorption, oxidation, photocatalytic degradation, and biological desulfurization. This paper reviews the status of pyrolysis of waste tires and desulfurization technologies for TPO.Implications: The nature of tires makes them extremely challenging to recycle due to the available chemically cross-linked polymer and, therefore, they are neither fusible nor soluble and, consequently, cannot be remolded into other shapes without serious degradation. The presence of tire waste on open fields or households creates an ideal breeding ground for disease-carrying vermin which pose a threat to humans. Also, disposal in landfills can lead to groundwater pollution by heavy metals and cause hazardous and uncontrolled fires. Owing to the growing environmental concerns, the exploration of economically viable and environmentally friendly techniques for the management of waste tires has been intensified in the recent past. Thermochemical routes such as combustion, gasification, and pyrolysis are important in the management of waste tires, reducing the environmental impacts of tire volarization, and allowing for the recovery of products. Given the depletion of fossil fuels and to meet the ever-growing demand for fuel energy, several initiatives to find alternative fuel sources are currently being taken. Fuel oil obtained from the pyrolysis of waste tires is becoming a promising alternative source of energy given its availability and higher heating value. Pyrolysis, an eco-friendly process, is the heating of matter in the absence of oxygen and is normally practiced for the thermochemical decomposition of different types of feedstock including biomass, coal, tires, and municipal solid waste. This paper reviews the current studies for pyrolysis of waste tires and multiple desulfurization technologies used for treating TPO globally. The detailed specification on operating conditions for the pyrolysis reactor in achieving desirable products in terms of composition and ratios are discussed.

Technoeconomic Feasibility of Hydrogen Production from Waste Tires with the Control of CO2 Emissions

The worldwide demand for energy is increasing significantly, and the landfill disposal of waste tires and their stockpiles contributes to huge environmental impacts. Thermochemical recycling of waste tires to produce energy and fuels is an attractive option for reducing waste with the added benefit of meeting energy needs. Hydrogen is a clean fuel that could be produced via the gasification of waste tires followed by syngas processing. In this study, two process models were developed to evaluate the hydrogen production potential from waste tires. Case 1 involves three main processes: the steam gasification of waste tires, water gas shift, and acid gas removal to produce hydrogen. On the other hand, case 2 represents the integration of the waste tire gasification system with the natural gas reforming unit, where the energy from the gasifier-derived syngas can provide sufficient heat to the steam methane reforming (SMR) unit. Both models were also analyzed in terms of syngas compositions, H₂ production rate, H₂ purity, overall process efficiency, CO₂ emissions, and H₂ production cost. The results revealed that case 2 produced syngas with a 55% higher heating value, 28% higher H₂ production, 7% higher H₂ purity, and 26% lower CO₂ emissions as compared to case 1. The results showed that case 2 offers 10.4% higher process efficiency and 28.5% lower H₂ production costs as compared to case 1. Additionally, the second case has 26% lower CO₂-specific emissions than the first, which significantly enhances the process performance in terms of environmental aspects. Overall, the case 2 design has been found to be more efficient and cost-effective compared to the base case design.

Formation Mechanism of Monocyclic Aromatic Hydrocarbons during Pyrolysis of Styrene Butadiene Rubber in Waste Passenger Car Tires

The production of aromatic hydrocarbons from the waste tire pyrolysis attracts more and more attention because of its tremendous potential. Based on styrene-butadiene rubber (SBR), which is the main rubber in the waste passenger car tires, this work studies the temperature influence on primary pyrolysis product distribution by experimental techniques (Py-GC/MS, TG-MS), and then, the formation mechanism of monocyclic aromatic hydrocarbons (MAHs) observed in the experiment was analyzed by first-principles calculations. The experimental results show that the MAHs during the pyrolysis mainly include styrene, toluene, and xylene, and subsequent calculations showed that these compounds were formed through a series of primary and secondary reactions. The formation pathways of these typical MAHs were studied via the reaction energy barrier analysis, respectively. It shows that the MAHs were not only derived from the benzene ring in the SBR chain but also generated from short-chain alkenes through the Diels-Alder reaction. The obtained pyrolysis reaction mechanism provides theoretical guidance for the regulation of the pyrolysis product distribution of MAHs.

From waste tire to high value-added chemicals: an analytical Py-GC/TOF-MS study

A Pyroprobe 5000 pyrolyzer connected to a gas chromatography-time-of-flight mass spectrometry (Py-GC-TOF-MS) was used to analyze the decomposition behavior of waste tire (WT). Effects of several typical parameters such as heating rate, atmosphere, reaction temperature, retention time, and zeolites on molecular composition and relative contents of the liquid products were investigated. Without added zeolite, the pyrolysis products mainly consisted of limonene, 1,4-pentadiene, and monocyclic aromatic hydrocarbons (MAHs) such as benzene, toluene, ethylbenzene, and xylene (BTEX). L-limonene was the dominant fraction (> 85%) of the limonene. Temperature and time presented the most significant effect on the liquid products' molecular composition and relative content, and increasing temperature and time reduced the contents of alkenes and increased the concentration of MAHs. With added zeolite, the molecular composition of the liquid products was greatly affected. All the liquid products produced with zeolite had higher MAHs and lower alkenes compared with those without added zeolite. Among the zeolites tested, Hβ was the most beneficial catalyst to the production of aromatic hydrocarbons as the MAHs reached the highest value of 53.09%. The N, S-compound mainly consisted of benzothiazole and 2-methyl-benzothiazoles-important rubber accelerators. The O, S-compound mainly consisted of sulfones or sulfoxides.

Investigating the potential of sustainable use of green silica in the green tire industry: a review

Undoubtedly, with the increasing emission of greenhouse gases and non-biodegradable wastes as the consequence of over energy and material consumption, the demands for environmentally friendly products are of significant importance. Green tires, a superb alternative to traditional tires, could play a substantial part in environmental protection owing to lower toxic and harmful substances in their construction and their higher decomposition rate. Furthermore, manufacturing green tires using green silica as reinforcement has a high capacity to save energy and reduce carbon dioxide emissions, pollution, and raw material consumption. Nevertheless, their production costs are expensive in comparison with conventional tires. In this review article, by studying green tires, the improvement of silica-rubber mixing, as well as the production of green silica from agricultural wastes, were investigated. Not only does the consumption of agricultural wastes save resources considerably, but it also could eventually lead to the reduction of silica production expenses. The cost of producing green silica is about 50% lower than producing conventional silica, and since it weighs about 17% of green silica tires, it can reduce the cost of producing green rubber. Accordingly, we claim that green silica has provided acceptable properties of silica in tires. Apart from the technical aspect, environmental and economic challenges are also discussed, which can ultimately be seen as a promising prospect for the use of green silica in the green tire industry.

Designing an optimization model for green closed-loop supply chain network of heavy tire by considering economic pricing under uncertainty

The conditions of global competition and environmental sensitivities have made organizations and factories to collect returned products, in such a way that these organizations have tried to rehabilitate, recycle, or destroy these products in order to protect the environment. This paper propose a mathematical model for the green closed-loop supply chain network of heavy tire by considering the economic pricing of its products under conditions of uncertainty, which economically determines the price and leads to more profitability. In addition, the relevant model is a two-objective fuzzy model, the first objective of which is to minimize costs and maximize profits, and the second objective is to minimize environmental issues. The proposed model can also determine the optimal location of each center based on potential locations, the optimal amount of production, distribution, collection, recycling, as well as the reproduction of products. The ε-constraint method is used to solve the model with two objective functions; this method ensures strong Pareto optimal answers and prevents weak Pareto answers. Independent two-sample t-test is used to verify the results of certain and uncertain models in the studied model. In order to evaluate the effectiveness and profitability of the proposed method, a case study in the field of heavy tires is finally used, through which very useful results are obtained.

Biodiesel Synthesis from High Free-Fatty-Acid Chicken Fat using a Scrap-Tire Derived Solid Acid Catalyst and KOH

A heterogeneous solid acid catalyst was synthesized using tire polymer waste (TPW) for the esterification of waste chicken fat (CF) enriched with fatty acids. The TPW was carbonized and functionalized with concentrated sulfuric acid under various sulfonation conditions to obtain a sulfonated tire polymer char (TPC-SO₃H) catalyst. The TPC-SO₃H catalyst was further characterized via acid-base titration (to ascertain the total concentration of acid), X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Brunauer-Emmett-Teller (BET) analysis. The esterification reaction conditions of extracted chicken fat with methanol and the viability of catalyst reuse were also investigated. The composition of the free fatty acid (FFA) decreased to below 1% under optimum reaction conditions of 5% TPC-SO₃H catalyst, the methanol-to-CF molar-ratio of 15:1, and a reaction time of 120 min at 70 °C. The catalyst preserved its conversion efficiency above 90%, even after three cycles. The results demonstrate that the catalyst is applicable and efficient in the esterification of raw materials containing various fatty acid compositions since different carbonized materials have distinct abilities to combine acid groups. Furthermore, after de-acidification of CF-FFA by the as-prepared TPC-SO₃H catalyst, the neutral CF was transesterified completely to biodiesel and characterized via Fourier Transform Infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹H NMR) spectroscopy and physicochemical analysis. This work unveils a promising technique for utilizing tire waste generated in large quantities for the development of a novel heterogeneous acid catalyst for biodiesel production.

Comparative analysis of the characteristics of carbonaceous material obtained via single-staged steam pyrolysis of waste tires

The two-stage technology of porous carbonaceous material obtained via pyrolysis in inert medium with subsequent activation by steam is well known. While steam could be a suitable substance for pyrolysis as well, single-staged technology for waste tire recycling is yet to be developed. A comparative analysis of the characteristics of the carbonaceous materials obtained by the single-staged steam pyrolysis of waste tires was carried out, which could provide a theoretical background for the development of such technology. The steam pyrolysis was performed in a tubular reactor in an overheated steam medium (500°C with 5 kg/h mass flow rate). The technical characteristics of the obtained samples were evaluated in the context of their potential for further application as absorbent and raw material for rubber production according to Chemical Abstracts Service No. 1333-86-4. The composition and physico-chemical properties of the obtained samples were studied using BET and thermogravimetric analysis, atomic emission, transmission and scanning electron microscopies, Raman, X-ray diffraction, and photoelectron spectroscopies. The results revealed that the structure and properties of all obtained carbonaceous material samples were similar. The samples consisted of amorphous carbon (with a disordered graphite lattice) and contained a significant amount of metal oxides. According to experimental data, zinc was present in the form of ZnO with a binding energy of 1022.4 eV, while sulfur was observed in the form of sulfide and oxysulfide with binding energies of 161.8 and 163.2 eV, respectively. According to electron microscopy, the morphology of samples was represented by a set of spherical agglomerates comprising nanosized particles. According to the BET analysis of the samples, the specific surface area varied in the range between 52.0 and 66.0 m²/g and the pore volume values were within a range of 0.53-0.87 cm³/g, while the average pore size varied from 412 to 527 Å.Implications: Our paper presents original research in the field of characterization of solid material obtained by single-staged steam gasification of waste tires, which were produced and exploited in conditions of Russia. Modern technology allows thermal utilization of waste tires by obtaining powders of carbonaceous material, which could be used as fuel, adsorbent, etc., but this process usually consists of two stages - pyrolysis in inert medium and activation in steam or carbon dioxide. One of the most promising directions of technological development is simplifying this process into single step, ensuring that the obtained material could be used as carbon black or adsorbent for gas steam cleansing. No data on suitability of carbonaceous material obtained by single-step steam pyrolysis of all-season waste tires to be adsorbent and/or carbon black is present in the literature. In order to evaluate the suitability of the obtained material to be adsorbent, the high specific surface area should be determined, while CAS technical standards specify many chemical and physical properties of industrial carbon black.The aim of the current article is to study the properties of carbonaceous material obtained during single-staged steam gasification of four different all-season tires (due to their widespread application worldwide) and evaluate its fitness as industrial-scale carbon black or adsorbent. The additional problem addressed was the evaluation of the variation in characteristics of carbonaceous material obtained due to different origins of tires. Experiments were conducted in a tubular lab reactor in order to simplify the experimental procedure while ensuring the applicability of the obtained results to practical conditions.The obtained results could be used for the development of the technology for closed-cycle tire processing (because black carbon is used for tire production) and adsorbent production. The characteristics of the materials obtained allow us to choose optimal parameters for such treatment and develop special policies and programs, which will integrate and regulate waste tire utilization via steam gasification.

The catalytic mechanism of intercalated chlorine anions as active basic sites in MgAl-layered double hydroxide for carbonyl sulfide hydrolysis

In order to make clear the role of intercalated anions in layered double hydroxides (LDHs) for catalytic hydrolysis of carbonyl sulfide (COS), the adsorption and reaction characteristics of COS over the simple Mg₂Al-Cl-LDH model catalyst were studied by both theoretical and experimental methods. Density functional theory (DFT) calculations by CASTEP found that the chloride ions in LDH function as the key Brønsted base sites to activate the adsorbed H₂O with enlarged bond length and angle, facilitate the dissociative adsorption of intermediates including mono-thiocarbonic acid (MTA) and hydrogen thiocarbonic acid (HTA), and participate in the formation of transient states and subsequent hydrogen transfer process with decreased energy barriers during COS hydrolysis. COS hydrolysis will preferentially go through the dissociated intermediates of mono-thiocarbonates (MT) and hydrogen thiocarbonates (HT) with dramatically decreased energy barriers, and the rate-determining step of COS hydrolysis over Mg₂Al-Cl-LDH will be the nucleophilic addition of C=O in COS by H₂O (Ea = 1.10 eV). The experimental results further revealed that the apparent activation energy (0.89 eV) of COS hydrolysis over Mg₂Al-Cl-LDH is close to theoretical value (1.10 eV), and the accumulated intermediates of MT, HT, or carbonate were also observed by FT-IR around 1363 cm^-1 on the used Mg₂Al-Cl-LDH, which are well in accordance with the theoretical prediction. The demonstrated participation of intercalated chlorine anions in the evolution of intermediates and transient states as Brønsted base sites during COS hydrolysis will give new insight into the basic sites in LDH materials.

Effect of Pyrolysis Atmosphere on the Gasification of Waste Tire Char

The aim of the study is to assess the influence of the atmosphere during pyrolysis on the course of CO2 gasification of a tire waste char. Two approaches were used: the pyrolysis step was carried out in an inert atmosphere of argon (I) or in an atmosphere of carbon dioxide (II). The examinations were carried out in non-isothermal conditions using a Rubotherm DynTherm thermobalance in the temperature range of 20–1100 °C and three heating rates: 5, 10 and 15 K/min. Based on the results of the gasification examinations, the TG (Thermogravimetry) and DTG (Derivative Thermogravimetry) curves were developed and the kinetic parameters were calculated using the KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa) methods. Additionally, the CO2 gasification of tire chars reaction order (n), was evaluated, and the kinetic parameters were calculated with the use of Coats and Redfern method. Tire waste char obtained in an argon atmosphere was characterized by lower reactivity, which was reflected in shift of conversion and DTG curves to higher temperatures and higher mean values of activation energy. A variability of activation energy values with the progress of the reaction was observed. For char obtained in an argon atmosphere, the activation energy varied in the range of 191.1–277.2 kJ/mol and, for a char obtained in an atmosphere of CO2, in the range of 148.0–284.8 kJ/mol. The highest activation energy values were observed at the beginning of the gasification process and the lowest for the conversion degree 0.5–0.7.

End-of-life tire management: a critical review

Environmental and social awareness are the key elements of the sustainable tire industry. End-of-life tire (ELT) waste flow is an important environmental problem worldwide since it produces severe air, water, and soil pollution issues. Significant advancements have been made in ELT management in the last few years. As a result, ELTs should not only be regarded as waste but also as a source of environmentally friendly materials. Besides, sound ELT management has vital importance for circular economy and sustainable development. Over the last decade, ELT management has attracted many researchers and practitioners. Unfortunately, a comprehensive review of the ELT management area is still missing. This study presents the first critical review of the whole ELT management area. It aims to present an extensive content analysis overview of state-of-the-art research, provide its critical analysis, highlight major gaps, and propose the most significant research directions. A total of 151 peer-reviewed studies published in the journals between 2010-2020 are collected, analyzed, categorized, and critically reviewed. This review study redounds comprehensive insights, a valuable source of references, and major opportunities for researchers and practitioners interested in not only ELT material flow but also the whole waste management area.

Possibility Routes for Textile Recycling Technology

The fashion industry contributes to a significant environmental issue due to the increasing production and needs of the industry. The proactive efforts toward developing a more sustainable process via textile recycling has become the preferable solution. This urgent and important need to develop cheap and efficient recycling methods for textile waste has led to the research community's development of various recycling methods. The textile waste recycling process can be categorized into chemical and mechanical recycling methods. This paper provides an overview of the state of the art regarding different types of textile recycling technologies along with their current challenges and limitations. The critical parameters determining recycling performance are summarized and discussed and focus on the current challenges in mechanical and chemical recycling (pyrolysis, enzymatic hydrolysis, hydrothermal, ammonolysis, and glycolysis). Textile waste has been demonstrated to be re-spun into yarn (re-woven or knitted) by spinning carded yarn and mixed shoddy through mechanical recycling. On the other hand, it is difficult to recycle some textiles by means of enzymatic hydrolysis; high product yield has been shown under mild temperatures. Furthermore, the emergence of existing technology such as the internet of things (IoT) being implemented to enable efficient textile waste sorting and identification is also discussed. Moreover, we provide an outlook as to upcoming technological developments that will contribute to facilitating the circular economy, allowing for a more sustainable textile recycling process.

Performance of activated carbons prepared from spent tyres in the adsorption of rhodamine B in aqueous solutions

Activated carbons were produced from spent tyre pyrolysis char by steam or CO₂ activation and evaluated for their performance in rhodamine B (RhB) adsorption in aqueous solutions. The effect of RhB starting concentration (80-150 mg L^-1), contact time (0-80 min), temperature (298-318 K) and initial pH on the adsorption process was examined. Pseudo-first-order and pseudo-second-order models were carried out to fit the experimental data to derive RhB adsorption kinetics. Langmuir, Freundlich and Temkin isotherm models were applied to depict RhB adsorption behaviour of the prepared activated carbons. Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) were calculated. It has been found that the activated carbons can effectively adsorb RhB due to high mesoporosity and RhB equilibrium adsorption capacity (q_e) increased almost linearly with increasing total mesopore volumes, regardless of the activation agents. When BET surface areas are similar, CO₂-activated carbon obtained higher q_e than steam due to higher mesoporosity of CO₂-activated carbon. The results show that pseudo-second-order well fitted the experimental data. RhB starting concentration increased from 80 to 150 mg L^-1 causing q_e increased from 158 to 251 mg g^-1 but RhB removal decreased from 99.7 to 84.5%. The RhB adsorption process follows the Langmuir model and thermodynamic calculation, indicating RhB adsorption is an endothermic, spontaneous process, dominated by both chemisorption and physisorption.

Experimental Analysis of Temperature Influence on Waste Tire Pyrolysis

Pyrolysis is an optimal thermochemical process for obtaining valuable products (char, oil, and gas) from waste tires. The preliminary research was done on the three groups of samples acquired by cutting the same waste tire of a passenger vehicle into cylindrical granules with a base diameter of 3, 7, and 11 mm. Each batch weighed 10 g. The heating rate was 14 °C/min, and the final pyrolysis temperature was 750 °C, with 90 s residence time. After the pyrolysis product yields were determined for all of the three sample groups, further research was performed only on 3 mm granules, with the same heating rate, but with altered final pyrolytic temperatures (400, 450, 500, 550, 600, 650, 700, and 750 °C). The results of this study show that thermochemical decomposition of the waste tire sample takes place in the temperature range of 200–500 °C, with three distinct phases of degradation. The highest yield of the pyrolytic oil was achieved at a temperature of 500 °C, but further heating of volatile matters reduced the oil yield, and simultaneously increased the yield of gas, due to the existence of secondary cracking reactions. The analysis of pyrolytic oil and char showed that these products can be used as fuel.

The influence of preliminary processing of end-of-life tires on transportation cost and vehicle exhausts emissions

Recovery and recycling end-of-life tires (ELT) incur a significant cost of collection and transportation. Improperly conducted ELT collection contributes to excessive vehicle exhaust emissions and high transportation costs. This study investigates the collection and transportation costs of ELT including preliminary processing of waste tires like cutting, baling and packing tires to reduce the volume of each shipment. Waste collection vehicles exhaust emissions were examined in the collection scenarios. In this study a novel approach of multi-criteria decision support - coupled analytical hierarchy process (AHP) and Preference Ranking Organization METHod for Enrichment of Evaluations (PROMETHEE) methods have been applied for selecting the best scenario, considering costs and environmental impacts in the collection of ELT. The results show the most profitable method of the ELT collection by routing of heavy truck and pickup of waste tires from a local network after preprocessing. Packing the tires in the collection points reduces the total cost between 20-30% and vehicles' exhaust emissions up to 40 %, compared to other methods in the Polish case study. The proposed decision support method is useful for evaluating environmental and cost factors, especially in regions where transport costs due to distances constitute the largest share of costs. This method and the results are useful for the ELT collection companies in promoting sustainable methods of transportation of waste including emission and economic factors. The study encourages using the compacting of ELT at the collection points for more efficient transportation.

Developments in waste tyre thermochemical conversion processes: gasification, pyrolysis and liquefaction

Fossil fuels, particularly crude oil, have proven to be a source of energy to households, transportation and power industries over the past decades. This natural reserve is diminishing at an alarming rate with crude oil having reserves to last the earth for the next half a century. As a result, researchers are constantly seeking remedial technologies to close this gap. Thermochemical conversion processes such as pyrolysis, gasification and liquefaction (PGL) offer an alternative solution to mitigating the world's high reliance on crude oil. These processes can be employed to provide energy, fuel and high-end value-added products. This paper aims to highlight all the research and development advancements and trends that have been made over the past three decades while employing waste tyres and other feedstock. In addition, the prominent countries and their associated researchers who have made novel discoveries in the field of thermochemical conversion are extensively discussed. The research findings show that significant research outputs such as the utilization of vast types of feed materials, the reaction mechanisms, the factors affecting the processes, and the application of the different end-products for thermochemical processes are well documented in the literature. Also, the collected data showed that significant advancements have been achieved in developing PGL technologies. The following conclusions were drawn: (i) PGL technologies show a generally increasing percentage interest from 1990 to 2020, (ii) many authors have identified the end-products obtained from waste feedstocks, such as; waste tyres, biomass, plastics, food waste, microalgae and animal manure to yield promising application benefits, (iii) China has shown the greatest interest in investing into waste to energy initiatives and has demonstrated the vast applications of waste derived products and, (iv) employing waste tyres as a feedstock has shown potential for producing high-end value products in their crude form or refined form. Some of the shortcomings identified during the study are the modest interest shown by most African regions as well as the lack of regulatory frameworks developed by certain countries.

Fossil fuels, particularly crude oil, have proven to be a source of energy to households, transportation and power industries over the past decades.

Waste Refinery: The Valorization of Waste Plastics and End-of-Life Tires in Refinery Units. A Review

This review collects a wide range of initiatives and results that expose the potential of the refineries to be converted into waste refineries. Thus, they will use their current units for the valorization of consumer society wastes (waste plastics and end-of-life tires in particular) that are manufactured with petroleum derivatives. The capacity, technological development, and versatility of fluid catalytic cracking (FCC) and hydroprocessing units make them appropriate for achieving this goal. Polyolefinic plastics (polyethylene and polypropylene), the waxes obtained in their fast pyrolysis, and the tire pyrolysis oils can be cofed together with the current streams of the industrial units. Conventional refineries have the opportunity of operating as waste refineries cofeeding these alternative feeds and tailoring the properties of the fuels and raw materials produced to be adapted to commercial requirements within the oil economy frame. This strategy will contribute in a centralized and rational way to the recycling of the consumer society wastes on a large scale. Furthermore, the use of already existing and, especially, depreciated units for the production of fuels and raw materials (such as light olefins and aromatics) promotes the economy of the recycling process.

A Review on Management of End of Life Tires (ELTs) and Alternative Uses of Textile Fibers

Annually, approximately 3 billion tires are commercially transacted worldwide each year and an equivalent amount is disposed of by the end of their life. Despite the increase in the life of tires and the global economic and pandemic crisis, the number of discarded tires is going to rise further due to the increasing demand for vehicles worldwide (approximately 5 billion tires by the end of 2030). The obsolete methods of tire disposal, including landfill, burning, etc., are a responsible for environmental issues (harmful substances production, air and soil pollution) and for the transmission of various diseases. Nowadays, approximately 70% of the total tires at the end of their life (ELTs) is recovered. The largest percentage of the recovered ELTs is intended for energy production or recovery as a fuel in cement industries or can be used for the production of various materials. A significant amount (approximately 95%) of the discarded ELTs can be reused. The products from the processing of ELTs can be fragments of different sizes and types, including: Trimmed rubber (70% by weight), steel wire (5–30% by weight), and fluff or textile fibers (up to 15% by weight). From the aforementioned materials, rubber and steel wires are mainly recovered and used for numerous applications. However, current ways of utilizing these materials will have to adapt or change in the near future, in order to comply with stricter regulations. The purpose of the current study is to sufficiently review recent progress on the management of ELTs, focusing on alternative uses of textile fibers such as additive for sound absorbing materials, bituminous conglomerates, concrete production, plastic materials, soil reinforcement, etc.

High-value utilization of waste tires: A review with focus on modified carbon black from pyrolysis

Recently, the recycling of waste tires has caused widespread concern for its environmental issues. The experience of the producer responsibility and tax system is of great beneficial to developing countries. The article also elaborates on the efforts of Chinese government to focus on establishing and perfecting waste tire treatment system by strengthen legislation. The main reasons such as immature market, non-uniform policy and repeated taxation for the survival difficulties of waste tire recycling enterprises in China are summarized. Among numerous resource methods, pyrolysis has been considered as a promising thermochemical process to deal with the waste tires. Unlike other similar reviews that mainly focus on its liquid phase, special attention has been given to solid char, pyrolysis carbon black, due to its wide application and high-value utilization in the future. We summarize the available research on application of pyrolysis carbon black as an alternative to commercial carbon black in rubber manufacture, as activated carbon in pollution control and as biochar for soil improvement. Analysis of the available data revealed that 1) the influence of temperature and time has been basically established; 2) catalyst type, dosage and reactor selection should be adjusted according to product demand; 3) pickling has become the primary means of improving pyrolysis carbon black; 4) the type of modifier and modification method must be adjusted according to the specific characteristics of the raw materials and needs to be combined with the experimental results to realize resource utilization and give full play to its economic value.

Quality protocol and procedure development to define end-of-waste criteria for tire pyrolysis oil in the framework of circular economy strategy

The requirements to define End-of-Waste Criteria (EWC) were set in the Waste Framework Directive (WFD), Article 6 and the detailed data collected are considered to be the baseline for the elaboration of the operational EWC through several steps. Such waste stream (which is produced from End of Life Tires-ELT) could be a valuable source for energy recovery and can be used on a pan-European basis as an alternative fuel, for co-incineration in cement plants or furthermore in internal compunctions engines. The exploration for sustainable energy is one of the most dynamic areas of research currently. This study aims to investigate the ability to manage and exploit the energy content of Tire Pyrolysis Oil (TPO), through pyrolysis technology as incineration/co-incineration technology for ELTs presents significant environmental issues. However, TPO, must be declassified from waste in order to be able to be use as an alternative fuel in internal combustion engines for power generation participating in the loop of circular economy and industrial symbiosis. This paper focus on the development of a Quality Protocol (QP) and the procedure how to develop EWC for the declassification of TPO in order to replace Light Fuel Oil (LFO).

Modeling and economic analysis of waste tire gasification in fluidized and fixed bed gasifiers

Waste tires have an organic-matter composition of more than 90% and have been proposed as an excellent calorific fuel material. The objective of this study is to find an economic and efficient pathway for producing syngas by waste tires gasification. To achieve this goal, two most commonly used gasifier types of fluidized bed and fixed bed have been simulated and compared by using a semi-empirical model and a one-dimensional kinetics model, respectively. Moreover, economic analysis of the levelized cost of syngas is used to compare economic indicators of different gasifiers. Results show that the lower heating value of the tire-syngas product is 2.5-7.4 MJ/Nm³, moreover, equivalence ratio and tire mixture ratio have negative impacts on syngas heating value and syngas efficiency. Furthermore, the levelized cost of syngas of tire gasification is 0.33-0.60 ¢/kWh that is lower than the market price of natural gas at 0.68 ¢/kW, which indicates tire gasification is a potential technology for syngas production. Finally, compared with the fluidized bed tire gasification, the fixed bed tire gasification has worse performance but better economic indicators, indicating that fixed bed gasification is an economic pathway for the syngas product.

Study of waste tire pyrolysis in a rotary kiln reactor in a wide range of pyrolysis temperature

Thermal pyrolysis of waste tires without metals has been studied in a rotating kiln reactor under nitrogen atmosphere. The pyrolysis temperature was varied in a wide range from 400 up to 1050 °C to investigate the effect of temperature on pyrolysis products. The pyrolytic oil during each pyrolysis process was reported in different pyrolysis times. It was found that the maximum yield of pyrolytic oil was 44 wt% in 550 °C. However, by raising the temperature of the pyrolysis process, the yield of produced gas increased, while the yield of produced char decreased. In addition, Fourier transform infrared spectroscopy (FT-IR) was performed in order to specify functional groups and types of bonds at different temperatures. FT-IR analysis showed the presence of some undesired compounds with sulphur and nitrogen functionalities in pyrolytic oil. Also, the properties of maximum produced oil were analyzed. The distillation data of maximum pyrolytic oil revealed that there was 14%, 4%, and 36% of light naphtha (>160 °C), heavy naphtha (160-200 °C) and middle distillate (200-350 °C), respectively and the fraction of VGO (<350 °C) was 46%.

Comparative pyrolysis behaviors of tire tread and side wall from waste tire and characterization of the resulting chars

In this study, tire tread (TT) and side wall (SW) of waste tire were separately used as feedstocks for pyrolysis treatment, and the resulting chars were thoroughly characterized to exploit the potential applications. Analytic results show that the SW contained higher fixed carbon (27.55%) and carbon content (82.30%) than those of TT (15.21% and 56.56% respectively). TGA results indicated that 400-600 °C is the main decomposition temperature range for both feeds. The char yields showed a declining trend and stabilized at 500 °C, and higher char yield of TT was achieved than that of SW. Meanwhile, the chars from TT showed a high surface area (121.47 m²/g) than that of SW (44.72 m²/g), which could be a good adsorbent or an activated carbon precursor. FT-IR results showed that leading surface functional group of TT-500 was C-O/C-O-C from alcohols, ketones or ether, whereas SW-500 from phenols, alcohols and carboxylic acids. When compared with commercial products, SW-500 showed better properties than those of a carbon black (N660, 10 μm) in terms of carbon quality and ash content. This study suggested that by pyrolyzing the distinct sections of the waste tire is a promising approach to produce chars for more specific applications.

Modeling kinetics and transport phenomena during multi-stage tire wastes pyrolysis using Comsol®

This paper is devoted to the modeling of the pyrolysis process in order to predict mass and heat loss profiles of a used tire sample and ultimately prevent eventual difficulties in pyrolysis reactors. Once assumptions are made, the thermal balances and kinetics of each reaction were written. The resolution of the differential equations allowed us to present the profile of heat variation within the sample as a function of temperature in a fixed bed reactor. The modeling is based on the energy behavior of each reaction, the rate conversion of which was also modeled and compared with that obtained experimentally. There is a satisfactory agreement between the theoretical and the experimental results in one hand and a good fit with experimental and regression results of other researchers in another hand. It was shown in particular, that some exothermic reactions intervene during the pyrolysis of the used tires. Indeed, the exothermic heat at the center of 2 cm particle exceeds 1500 kJ/kg which presents an economic and energetic payoff for the plant. It has also been noted that the small particle size can result in faster heat transfer and shorten the process completion time. At the same time, rapid heat transfer can trigger more endothermic reactions, increasing thus the overall energy consumption of the process.

Combustion of pistachio shell: physicochemical characterization and evaluation of kinetic parameters

The study of different renewable energy sources has been intensifying due to the current climate changes; therefore, the present work had the objective to characterize physicochemically the pistachio shell waste and evaluate kinetic parameters of its combustion. The pistachio shell was characterized through proximate analysis, ultimate analysis, SEM, and FTIR. The thermal and kinetic behaviors were evaluated by a thermogravimetric analyzer under oxidant atmosphere between room temperature and 1000 °C, in which the process was performed in three different heating rates (20, 30, and 40 °C min^-1). The combustion of the pistachio shell presented two regions in the derivative thermogravimetric curves, where the first represents the devolatilization of volatile matter compounds and the second one is associated to the biochar oxidation. These zones were considered for the evaluation of the kinetic parameters E _a , A, and f(α) by the modified method of Coats-Redfern, compensation effect, and master plot, respectively. The kinetic parameters for zone 1 were E _a1 = 84.11 kJ mol^-1, A ₁ = 6.39 × 10⁶ min^-1, and f(α)₁ = 3(1 - α)^2/3, while for zone 2, the kinetic parameters were E _a2 = 37.47 kJ mol^-1, A ₂ = 57.14 min^-1, and f(α)₂ = 2(1 - α)^1/2.

Emission characteristics of toxic pollutants from an updraft fixed bed gasifier for disposing rural domestic solid waste

Gasification has gained advantage as an effective way to dispose domestic solid waste in mountainous rural of China. However, its toxic emissions such as PCDD/Fs and heavy metals, as well as their potential environmental risks, were not well studied in engineering application. In this study, an updraft fixed bed gasifier was investigated by field sampling analysis. Results showed that low toxic emissions (dust, SO₂, NOx, HCl, CO, H₂S, NH₃, PCDD/Fs and heavy metals) in the flue gas were achieved when the rural solid waste was used as feedstock. The mass distribution of heavy metals showed that 94.00% of Pb, 80.45% of Cu, 78.00% of Cd, 77.31% of Cr, and 76.25% of As were remained in residual, whereas 86.58% of Hg was found in flue gas. The content of PCDD/Fs in the flue gas was 0.103 ngI-TEQ·Nm^-3, and the total emission factor of PCDD/Fs from the gasifier was 50.04 μgI-TEQ·t-waste^-1, among which only 0.04 μgI-TEQ·t-waste^-1 was found in the flue gas. The total output of PCDD/Fs was1.89 times as high as input, indicting the updraft fixed bed gasifier increased emission of PCDD/Fs during the treatment domestic solid waste. In addition, the distribution characteristics of PCDD/Fs congeners reflected that PCDD/Fs was mainly generated in the gasification process rather than the stage of flue gas cleaning, suggesting the importance to effectively control the generation of PCDD/Fs within the gasifier chamber in order to obtain a low PCDD/Fs emission level.