Liquefaction of ground tire rubber at low temperature

A comparative study of the pyrolysis and hydrolysis conversion of tire

In the present study, we pyrolyzed a waste tire at various temperatures under an N2 atmosphere and a water environment in an autoclave reactor to investigate the effect of water on tire degradation. The analysis involved a comparison of product distribution, char properties, oil composition, and the behavior of heteroatom elements (especially oxygen, nitrogen, and sulfur) under different atmospheres. Elemental analysis, functional-group identification, and chemical state analysis of sulfur were performed for chars. In addition, the chemical composition, elemental composition, and molecular weight of the produced oils were evaluated. The heavy fraction of oils, not detectable by gas chromatography-mass spectrometry (GC-MS), was analyzed through Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The findings revealed that high temperatures promoted oil cracking, resulting in the formation of light oils in both pyrolysis and hydrolysis processes. Compared to pyrolysis, hydrolysis generated a higher yield of low molecular-weight oil. Elevated hydrolysis temperatures promoted aromatization, yielding an oil with a low H/C ratio and a high double bond equivalent number. Consequently, the concentration of aromatics in the light fraction of oils generated from the hydrolysis process exceeded that in oils from the pyrolysis process. Temperature exhibited a limited impact on oil composition during the pyrolysis process. Hydrolysis promoted the release of heteroatom-containing compounds at low temperatures. During pyrolysis, nitrogen was gradually released from the solid phase, whereas nitrogen-containing compounds were released early during hydrolysis, with gas-phase nitrogen accounting for more than 50 wt% at 320 °C. A maximum D-limonene yield of 45.58% was obtained at 360 °C within 0 min of hydrolysis, with the potential conversion of D-limonene into aromatics at higher hydrolysis temperatures. These results contribute to the understanding of tire valorization via hydrolysis.

Beneficial migration of sulfur element during scrap tire depolymerization with supercritical water: A molecular dynamics and DFT study

Complete depolymerization of scrap tires (ST) to valuable oil products and fuel gas could be achieved by supercritical water (SCW) technology. For implementing this promising technology, migration mechanism of sulfur element during the entire ST-SCW depolymerization process was identified to reduce the sulfur pollutions. In the depolymerization process of ST, OH radicals released from SCW molecules could enhance cleavage of CS bonds, resulting sulfur-containing intermediates. The intermediates could be further oxidized by free OH radicals and transformed into inorganic sulfur molecules mainly consisting of SO₄^2-, S₂O₃^2-, SO₃^2- and S^2-. In this study, a combined ReaxFF-MD and DFT method was performed to study the detailed sulfur migration mechanism during ST depolymerization in the presence of SCW and provided a strategy to fix low-valent sulfur in aqueous solution for separation of sulfur from the oil & gas products. This work provides a guidance to make ST-SCW technology cleaner and cheaper.

Current progress in waste tire rubber devulcanization

Vulcanized rubber, due to its superior mechanical properties, has long been used in various industries, especially automotive. The rubber industry has evolved and expanded over the years to meet the increasing global demands for tires. Today tires consist of about 19% natural rubber and 24% synthetic rubber, while plastic polymer and metal, filler and additives make up the rest. Over 1.6 billion new tires are produced annually and around 1 billion waste tires are generated. Tires are extensively designed with several complex processes to make them virtually indestructible. Since tire rubber does not decompose easily, their disposal at the end of service life creates a monumental environmental impact. However, waste tire rubber (WTR) consist of valuable rubber hydrocarbon, making its recovery or regeneration highly desirable. The conventional recovery method of WTR tends to produce undesirable products due to the destruction of the polymeric chain and exponentially degenerates the vulcanizates' physical properties. Since then, multiple devulcanization processes were introduced to effectively and selectively cleave vulcanizate's crosslinks while retaining the polymeric networks. Different devulcanization methods such as chemical, mechanical, irradiation, biological and their combinations that have been explored until now are reviewed here. Besides, an overview of the latest development of devulcanization by ionic liquids and deep eutectic solvents are also described. While such devulcanization technique provides new sustainability pathway(s) for WTR, the generated devulcanizate also possesses comparable physical properties to that of virgin products. This further opens the possibility of novel circular economic opportunities worldwide.

PE-contaminated industrial waste ground tire rubber: How to transform a handicapped resource to a valuable one

Sustainability and enhancement of recycling differing polymer waste has become a leading driver for industries associated with this type of waste. However, polymer waste streams that have not seen as 'typical' have existed in smaller but not insignificant amounts. This study has focused on the recycling of such a waste resource that is not classified as a typical one in developed countries but appears in other locations globally where opportunities for careful waste pretreatment are hindered, therefore creating a challenge for waste handling and the application of modern techniques. Compatibilizing is a strategy employed to recycle ground tire rubber (GTR) by blending with waste high density polyethylene (w-HDPE). Such processing methods and measurement techniques have been chosen to allow easy access without extra costs. For enhanced incorporation of the filler into the matrix olefin-maleic-anhydride copolymer based additives have been synthesized and have succeeded in creating a more homogenous blend with samples having a good surface appearance and mechanical properties. Outstanding Charpy impact strength at room temperature (10.1 kJ/m²) has been achieved in compatibilized 70/30 w-HDPE/GTR (containing 20% PE-contaminant), while elongation at break and tensile strength have been 10.3% and 14.9 MPa. Morphological structure of rubber resources and blends have been assessed by SEM while analytical properties and other features of experimental compatibilizing additives have been studied by e.g. FT-IR.

Devulcanization of natural rubber industry waste in supercritical carbon dioxide combined with diphenyl disulfide

The elimination of rubber wastes without affecting the environment is one of the most important challenges of the 21st century waste management. Accordingly, the present work is focused on the recycling of natural rubber (NR) industry waste by means of devulcanization in supercritical carbon dioxide (scCO₂) atmosphere. With that aim, a novel device allowing to perform rubber devulcanization was developed. It consists of a triaxial compression reactor integrated into a dynamic hydraulic universal testing machine with a heating chamber. NR industry waste was devulcanized in the mentioned device at different temperatures, in scCO₂ by using diphenyl disulfide (DD) as devulcanizing reagent. The devulcanization degree and quality of the treated materials were evaluated by the swelling test combined with the Horikx theory. It was appeared that a successful devulcanization, with almost no degradation, was obtained, and the devulcanization degree reached maximum value of ~90%. Thermogravimetric tests and scanning electron microscopy (SEM) images strengthened these results. Finally, it was concluded that the developed device is appropriate to perform rubber recycling, which contributes to the progress in the environmental protection.

Ground Tire Rubber Modified by Ethylene-Vinyl Acetate Copolymer: Processing, Physico-Mechanical Properties, Volatile Organic Compounds Emission and Recycling Possibility

Ground tire rubber (GTR) was reclaimed and modified with 10 phr of ethylene-vinyl acetate copolymer via low-temperature extrusion process. Processing, physico-mechanical properties, volatile organic compounds emission, and recycling possibility were investigated. In order to better understand the impact of used modifiers, their efficiency was compared with trans-polyoctenamer, which is an additive that is commercially dedicated to waste rubber recycling. The results showed that a relatively small amount of ethylene-vinyl acetate copolymer improves the mechanical properties of modified reclaimed GTR and also allows further recycling by multiple processing without the deterioration of performance after three cycles.

A New Sustainable Geotechnical Reinforcement System from Old Tires: Experimental Evaluation by Pullout Tests

The tires used constitute an environmental problem that remains unsolved. It is observed that the automotive fleet and therefore the generation of tires increases year after year, so the recovery and reuse processes are insufficient. For several years, the reuse of tires as materials in the construction has been considered, and several techniques have been developed for the construction of retaining walls and road reinforcement. However, to date, their use remains sporadic. This article presents the theoretical and experimental evaluation of a new geotechnical reinforcement system from used tires. This system, suitable for the construction of containment structures and the reinforcement of roads, is characterized by the conformation of cells that do not require other elements apart from the tires and the filling material. A mathematical model was developed to describe the behavior of the system and pullout tests were carried out for validation. The tests were performed with different tire and compacted granular material with different energies. The results allow validating the theoretical model by showing an increase in pullout resistance with the density and number of tires in the arrangement. It is observed that the coincidence between the model and the tests improves as the stiffness of the soil increases, being the degree of compaction fundamental for the operation.

Preliminary Investigation on Auto-Thermal Extrusion of Ground Tire Rubber

Ground tire rubber (GTR) was processed using an auto-thermal extrusion as a prerequisite to green reclaiming of waste rubbers. The reclaimed GTR underwent a series of tests: thermogravimetric analysis combined with Fourier-transform infrared spectroscopy (TGA-FTIR), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and static headspace and gas chromatography-mass spectrometry (SHS-GC-MS) in order to evaluate the impact of barrel heating conditions (with/without external barrel heating) on the reclaiming process of GTR. Moreover, samples were cured to assess the impact of reclaiming heating conditions on curing characteristics and physico-mechanical properties. Detailed analysis of the results indicated that the application of auto-thermal extrusion is a promising approach for the sustainable development of reclaiming technologies.

A complete depolymerization of scrap tire with supercritical water participation: A molecular dynamic simulation study

The growth of scrap tire (ST) has become an urgent environmental problem. In this work, the depolymerization process of ST in supercritical water (SCW) was studied with the ReaxFF molecular dynamic simulation. The depolymerization process and reaction pathway of ST in SCW were revealed. The simulation results indicated that the SCW molecules could promote the depolymerization of rubber into smaller molecules by releasing the OH radicals. After providing the OH radicals, the SCW molecules banded with the free H and turned into H₃O radicals which were the main resources to produce H₂. In the ST-SCW reaction system, more than 95% organic components in ST depolymerized into the valuable fuel (oil and fuel gas). The main compound in oil product was light oil with low viscosity. The gas products included the H₂, CO and C1-C4 gas. It was found that reaction temperature could dominate the component of final products from ST. In order to produce more oil, the optimal temperature to recycle ST with SCW participation was 647-659 K. This study demonstrates the feasibility of SCW in recovering the chemical products from ST, and provides a theoretical support for its further development.

Thermo-chemical conversion of scrap tire waste to produce gasoline fuel

Catalytic hydropyrolysis (CHP) of scrap tire was investigated for production of gasoline fuel. Effects of CHP process variables such as catalysts type ((activated carbon, AC), Ir/C, Rh/C, Pt/C, Ru/C, and Pd/C), temperature (200-450 °C), time (30-120 min), catalyst loading (0-40 wt%), and hydrogen pressure (0.1-12 MPa) on the CHP products distribution and properties of the hydropyrolysis oil (HPO) were examined. Ru/C was identified as the most suitable catalyst in terms of the HPO quality and the catalytic effect predominantly came from the noble metal. Temperature was the most influential factor affecting the yield and quality of the HPO and followed by the order of catalyst loading > H₂ pressure > time. Higher temperature, time, and catalyst loading would decrease the yield of HPO and increase the yield of gaseous product whereas contrary results were observed with increasing the H₂ pressure. With added noble metals, the hydrodenitrogenation, hydroSization, and hydrodeoxygenation reactions of the HPO were promoted and greatly lowered N, O, and S contents of the HPO with increasing the temperature, time, catalyst loading, and H₂ pressure. The lowest N, O, and S contents of 0.02, 0.41 and 0.41 wt% of HPO were achieved at 430 °C, 60 min, 10 wt% Ru/C, and 12 MPa H₂. The higher-heating value of the HPOs varied between 44 and 46 MJ/kg depending on the reaction conditions. More than half of the energy of the ST was converted into the HPO. The HPO mainly consisted of saturated and unsaturated hydrocarbons one to five benzene derivatives. The distillate fraction between 35 and 250 °C of the HPO is more than 80 wt%. Thus, we view that CHP is an alternative way to produce high quality hydro-carbon fuel from scrap tire.

A potential utilization of end-of-life tyres as recycled carbon black in EPDM rubber

End-of-life (EOL) tyres and their decomposition present severe environmental concern due to their resistance to moisture, oxygen, natural degradation, etc. Pyrolysis is considered to be the most effective and sustainable process for recycling, due to its eco-friendly process. The current work studied the effect of recycled carbon black (rCB), obtained from the pyrolysis of EOL tyres, on the properties of ethylene propylene diene rubber (EPDM). The rCB was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and chemical methods. rCB was incorporated solely, into a conventional EPDM formulation and also in combination with N550 carbon black. The physico-mechanical properties of the EPDM vulcanizates, before and after aging, were succinctly studied by SEM, TGA, Differential Scanning Calorimetry (DSC), tensile tests and cross-link density. The average particle size of rCB was observed to be 8 µm and the ash content was observed to be higher when compared to the conventional N550 carbon black, which was evident, by the TGA and SEM-EDX analyses. The reinforcing effect and the cross-link density of the rCB-filled vulcanizates were found to be marginally inferior in comparison to the conventional carbon black (N550). The morphology of the tensile- and tear-fractured surfaces were studied by SEM and it was observed that the breaking mechanism follows the rubber chain detachment from the surface mode.