Thermolysis of scrap tire and rubber in sub/super-critical water

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.

Evaluation on hydrothermal gasification of styrene-butadiene rubber with oxidants via ReaxFF-MD simulation

Styrene-butadiene rubber (SBR) is widely used in tires, which brings great challenge to the disposal and reclaiming of the used tires. The ring-opening reaction pathways of benzene rings in hydrothermal gasification of styrene-butadiene rubber were revealed based on reactive force field molecular dynamics (ReaxFF-MD) simulation. H-abstraction reaction that OH radicals capture H atom from the vinyl group of styrene was critical to the degrading of the styrene monomers. The energy barrier of H2O2 converted to OH radicals was lower than that of O2 and pure water converted to OH radicals. The oxidants that can urge OH radical formed in reaction were beneficial to SBR degradation, which could be assigned to confirm that SBR degradation with H2O2 was better than that with oxygen at the same concentration. The addition of oxidant could be helpful for decreasing the degradation temperature of styrene monomers. At oxidant equivalent ratio (ER) of 0.1, H2 yield at 2500 K lifted after 135 ps and increased by 75% at 500 ps compared with that without oxidants. According to the chemical equilibrium analysis, the optimal ER for H2 was 0.4 between 350 and 600 °C (real temperatures). The results could provide theoretic support and experiment guidance for adding oxidants in reclaiming waste rubber products.

Steam Pyrolysis of Oil Sludge for Energy-Valuable Products

Experimental studies of the steam pyrolysis of oil sludge were performed using a flow-type pilot plant with 300 kg/h capacity (raw material) to obtain energy-valuable products, such as liquid hydrocarbons (30.4 wt%), semi-coke (39.6 wt%), non-condensable gas-phase compounds (26.5 wt%), and bitumen (3.5 wt%). The pyrolysis process was conducted at a temperature of 650 ° C and with a steam flow rate of 150 kg/h. Liquid hydrocarbons were considered a target product. Comprehensive studies of their physicochemical characteristics, atomization process, droplet ignition, and combustion were carried out. The studied sample had physicochemical characteristics similar to traditional fuel oil (calorific value—42.6 MJ/kg, sulfur content—0.8 wt%). The jet spraying angle was 25° in view of the improved rheological properties of the test sample, with a homogeneous jet structure and a predominant droplet diameter of no more than 0.4 mm. The flame combustion process was accompanied by the formation of microexplosions, the frequency and intensity of which depended on the temperature of the air (Tg = 450–700 °C). This study, in view of its applied nature, is of interest in the design of new installations and technological systems for hydrocarbon pyrolysis.

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.

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.

Catalytic thermolysis treatment of petroleum refinery wastewater collected from effluent treatment plant

Catalytic thermolysis of petroleum refinery wastewater was investigated as a pretreatment process. Effects of various parameters like temperature, pH, dose of catalyst and time were investigated for chemical oxygen demand (COD), turbidity, and element reduction. CuSO4, FeSO4, FeCl3, and 1:1 ratio (v:v) mixture of CuSO4 and FeCl3 were used as a catalyst. The maximum reduction of COD and turbidity were 90 and 98% by mixture (1:1) of CuSO4 and FeCl3 at 70 °C, 7 pH, 1.0 kg/m3 dose in 90 min reaction time. The removal of an element like Cr, Mn, Ni, and Pb was analyzed by ICP-OES. The sludge precipitated after catalytic thermolysis was characterized using scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), Fourier transform infrared (FTIR) and thermo-gravimetric analysis (TGA)/derivative thermal analysis (DTA) analyses. Sludge from CuSO4 and mixture of CuSO4 and FeCl3 treatment has a compact structure with irregular granule which favors adsorption.

Assessment of carbon recovery from solid organic wastes by supercritical water oxidation for a regenerative life support system

The carbon recovery from organic space waste by supercritical water oxidation (SCWO) was studied to support resource recovery in a regenerative life support system. Resource recovery is of utmost importance in such systems which only have a limited total amount of mass. However, the practical waste treatment strategies for solid space wastes employed today are only storing and disposal without further recovery. This work assesses the performance of SCWO at recovering organic wastes as CO₂ and water, to discuss the superiority of SCWO over most present strategies, and to evaluate the different SCWO reactor systems for space application. Experiments were carried out with a batch and a continuous reactor at different reaction conditions. The liquid and gas products distribution were analyzed to understand the conversion of organics in SCWO. Up to 97% and 93% of the feed carbon were recovered as CO₂ in the continuous and the batch reactor, respectively. Residual carbon was mostly found as soluble organics in the effluent. Compared with the batch reactor, the continuous reactor system demonstrated a ten times higher capacity within the same reactor volume, while the batch reactor system was capable of handling feeds that contained particulate matter though suffering from poor heat integration (hence low-energy efficiency) and inter-batch variability. It was concluded that SCWO could be a promising technology to treat solid wastes for space applications. A continuous reactor would be more suitable for a regenerative life support system.

A study on the performance of coke resistive cerium modified zeolite Y catalyst for the pyrolysis of scrap tyres in a two-stage fixed bed reactor

Catalytic pyrolysis is a useful technique for the conversion of scrap tyres into liquid fuels. Zeolite catalysts were employed in the pyrolysis of scrap tyres for the production of aromatic rich fuel. Deactivation of zeolite catalysts during pyrolysis reaction was investigated which played an important role in the product quality and composition. Herein, the performance of microporous zeolite catalysts and mesoporous MCM-41 catalyst was evaluated in a two-stage fixed bed reactor for the pyrolysis of scrap tyres. Comparative studies showed the increase in the production of aromatic compounds up to 23.7% over zeolite catalyst as compared to 18.7% over MCM-41 catalyst. However, Zeolite Y catalyst exhibited higher coke formation led to the rapid deactivation. The stability of zeolite catalysts is addressed by the incorporation of Cerium metal within the framework of two zeolite catalysts namely Zeolite Y and ZSM-5 through the ion-exchange technique. Parent and spent catalysts were characterised using synchrotron FT-IR spectroscopy, temperature-programmed desorption of ammonia (NH₃-TPD), N₂ Physisorption, scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), energy-dispersive X-ray spectroscopy (EDX), and hydrogen temperature-programmed reduction (H₂-TPD). A higher percentage of aromatics were produced over the large pore Zeolite Y. Cerium ion-exchange decreased the formation of coke from 8.1% to 5.7% over submicron and large pore Zeolite Y catalyst. Moreover, naphthalene production decreased over both Ce-Zeolite Y and Ce-ZSM-5.

Pyrolytic preparation and modification of carbon black recovered from waste tyres

The medium temperature pyrolysis process using a fixed-bed reactor at atmospheric pressure was utilised to recover carbon black from motorcycle and automobile tyres. Experimental results have shown that the ash and volatile contents of several recovered carbon blacks are high, the elongation at break of the vulcanised natural rubber filled with recovered carbon blacks from motorcycle tyres is better than that from motorcycle tyres and standard carbon black 7#, while the other mechanical properties are worse. In order to improve the reinforcing effect of recovered carbon blacks, the modification of recovered carbon black was performed by high-energy electron bombardment and non-oxidising acid. The specific surface area of the pyrolytic carbon blacks increased after high-energy electron bombardment. The ash content of the pyrolytic carbon black was reduced from 22.5% to 8.4% after rinsing with hydrochloric acid, and the tensile stress at 300% was increased by about 2.2 MPa.

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.

Experimental Study on Spent FCC Catalysts for the Catalytic Cracking Process of Waste Tires

Research on the synergistic high-value reuse of waste tires and used catalysts in spent fluid catalytic cracking (FCC) catalysts was carried out in this study to address the serious ecological and environmental problems caused by waste tires and spent FCC catalysts. The experiment, in which a spent FCC catalyst was applied to the catalytic cracking of waste tires, fully utilized the residual activity of the spent FCC catalyst and was compared with a waste tire pyrolysis experiment. The comparative experimental results indicated that the spent FCC catalyst could improve the cracking efficiency of waste tires, increase the output of light oil in pyrolysis products, and improve the quality of pyrolysis oil. It could also be used for the conversion of sulfur compounds during cracking. The content of 2-methyl-1-propylene in catalytic cracking gas was found to be up to 65.59%, so a new method for producing high-value chemical raw materials by the catalytic cracking of waste tires with spent FCC catalysts is proposed.

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.