Resource and environmental assessment of pyrolysis-based high-value utilization of waste passenger tires

Waste rubber - Black pollution reframed as a global issue: Ecological challenges and sustainability initiatives

In contrast to "white pollution" originating from waste plastics, waste rubber is often referred to as "black pollution." The quantity and variety of waste rubber are increasing at an alarming rate, with a considerable fraction entering the global ecosystem via various pathways. This study presents the first critical review of waste rubber research with a focus on the risks associated with toxicant discharge and existing problems in waste rubber disposal, management, and recycling practices. We aim to obtain a comprehensive understanding of current research, particularly regarding the ecological impacts of these wastes, highlight major gaps, and propose the most significant research directions. A total of 192 studies published in journals were critically analysed. The importance of conducting long-term and large-scale experiments and developing efficient waste rubber recycling systems is also emphasised. This study highlights the need to address the challenges posed by waste rubber pollution and offers insights and references for undertaking ecological risk assessments and understanding the mechanisms underlying toxicant behaviour. Suggestions and countermeasures are proposed with ecosystem sustainability as the ultimate goal. Further long-term, comprehensive, and systematic research in this area is required.

Influences and mechanisms of pyrolytic conditions on recycling BTX products from passenger car waste tires

Pyrolysis is an effective method for waste tire disposal. However, it has rarely been used to recycle specific highly valuable components (such as benzene, toluene, and xylene (BTX)) from tire rubbers, owing to complicated pyrolytic reactions. This study investigated the pyrolysis process of passenger-car-waste-tires (PCWT) with the help of TG-DTG and Py-GC/MS. Based on response surface methodology (RSM), the effect of pyrolytic parameters on the yields of pyrolytic oil and BTX is evaluated. Furthermore, the BTX generation mechanisms are discussed from the perspective of aliphatic and aromatic hydrocarbon transformations. Additionally, pyrolytic conditions including temperature, rubber particle size, pressure, and gas flow rate were systemically investigated and the optimum pyrolytic condition for yield of BTX (26.5 g per 100 g tire rubber) was obtained [765 K, 0.7 mm, 0.52 MPa and 2.5 mL (g min)-1]. Therein, yield of benzene, toluene and xylene were 1.07, 5.03 and 20.40 g per 100 g tire rubber, respectively. During PCWT pyrolysis, BTX is primarily obtained via the Diels-Alder reactions of small-chain alkenes and transformations of limonene and aromatics. This study elucidates the BTX generation mechanisms during PCWT pyrolysis and clarifies the effects of varying pyrolytic conditions on BTX generation.

Integrated Assessment of Waste Tire Pyrolysis and Upgrading Pathways for Production of High-Value Products

Waste tire pyrolysis has received increasing attention as a promising technology recently due to the shortage of fossil resources and the severity of environmental impact. In this study, the process of waste tire pyrolysis and upgrading to obtain high-value products was simulated by Aspen Plus. Also, based on life cycle assessment, the indexes of energy, environmental, economic, and comprehensive performance were proposed to evaluate different high-value pathways. Results demonstrate that the integrated system of waste tire pyrolysis, pyrolytic oil (TPO) refining, and pyrolytic carbon black (CBp) modification has higher energy efficiency than the independent system of TPO refining, with an improvement rate of 2.6%. Meanwhile, the resource-environmental performance of the integrated system is better. However, combined with the economic benefit, the independent system is more comprehensively beneficial, with the index of comprehensive performance (BEECR) of 0.94, which increases by 3.3% compared with the integrated system. Furthermore, the comparisons of different improved high-value paths based on the independent system as the benchmark indicate that the pathway of promoting sulfur conversion during pyrolysis to reduce the sulfur content in TPO can increase the BEECR from 0.94 to 1.064, with the growth of 13.2%. Also, the physical modification of CBp to reduce the production cost and environmental impact has better performance of BEECR, increasing by 20.2%. The final sensitivity analyses show that the combined improved high-value case established by the abovementioned two paths can achieve a favorable benefit in a wide range of crude oil and waste tire prices and the environmental tax.

Study of passenger-car-waste-tire pyrolysis: Behavior and mechanism under kinetical regime

The pyrolysis of passenger-car-waste-tires (PCWT) has recently attracted widespread attention because it is a highly effective disposal method. However, a comprehensive understanding of real tire pyrolytic processes is limited owing to the complicated PCWT pyrolysis reaction system, particularly regarding the reaction mechanism. This study investigated the PCWT pyrolytic processes using a thermogravimetric analyzer coupled with mass spectrometry and analyzed all the pyrolytic products using pyrolysis-gas chromatography coupled with mass spectrometry. The composition and distribution of the PCWT pyrolytic products were investigated under a kinetic regime to eliminate other influences on the intrinsic reaction. The pyrolytic products mainly consisted of chain and cyclic alkenes, and monocylic aromatics. Importantly, an integral pyrolytic mechanism network for the PCWT was established based on the pyrolysis of single rubbers (natural, styrene butadiene, and butadiene rubbers). The reaction routes for the main products were determined according to the mechanism. Moreover, a kinetic study of the PCWT pyrolysis revealed the activation energy for this complicated reaction system.

Recycling of Rubber Wastes as Fuel and Its Additives

Economic, social, and urban developments generally require improvements in the transportation sector, which includes automobiles such as trucks, buses, trailers, airplanes, and even bicycles. All these vehicles use rubber tires. After consumption, these tires become waste, leading to enlarged landfill areas for used tires and implying additional harm to the environment. This review summarizes the growth of rubber recycling application and the sustainability of using waste rubber in the construction field. Furthermore, we provide methods to convert rubber waste to fuel or fuel additives by using tire-derived fuel and concentrate to pyrolysis, which are environmentally friendly and efficient ways. The related parameters such as temperature, pressure, and feedstock composition were studied. Most research papers observed that 500 °C is the optimal temperature at atmospheric pressure in the presence of a specific type of catalyst to improve pyrolysis rate, oil yield, and quality.

Replacing commercial carbon black by pyrolytic residue from waste tire for tire processing: Technically feasible and economically reasonable

Decades of researches have proved that pyrolysis can not only realize the harmless disposal of waste tire, but also carry out the goal of waste resource utilization via recycling pyrolytic products (e.g. pyrolytic carbon black, CBp). The current work studied the effect of CBp obtained from the commercial scale pyrolysis of waste tire, on the properties of natural rubber and butadiene rubber. CBp was incorporated into a carbon black quality identification standard formula in combination with N234 commercial carbon black (cCB) first. After screening a better substitution ratio, the composite material of CBp and cCB was mixed with more additives, and the experiment was carried out with a real production formula. To restore the practical production situation, the experiment process adopts the most commonly used process to avoid major changes in commercial production. CBp was tested at increasing loading levels as partial or full replacement of cCB. The physico-mechanical properties of the rubber compounds were studied by tests of physical, mechanical, and vulcanization properties. With the increase in the amount of CBp added, the physical and mechanical properties of the rubber compound showed a trend of slightly increasing first and then rapidly decreasing. The addition of CBp can increase the yield strength and stiffness of the rubber, but it may also lead to a decrease in hardness. Meanwhile, the substitution ratio of CBp up to 50% has been proven to improve safety and achieve a more stable vulcanization process of rubber compounds. CBp can replace up to half of cCB without significantly reducing the quality of tire rubber. The economic value of partial replacement of cCB by CBp has also been evaluated, demonstrating that adding a small amount of CBp can directly reduce the cost of raw materials, indirectly reduce the use of fossil energy promoting carbon dioxide reduction worldwide.