Microwave-assisted decontamination of end-of-life tires via solvent extraction and pyrolysis

Abstract

Disclosed herein are methods for decontaminating an end-of-life (EOL) tire feedstock containing N-(1,3-dimethyl butyl)-N'-phenyl-p-phenylenediamine (6PPD) that include obtaining the EOL tire feedstock, performing at least one microwave-assisted solvent extraction on the EOL tire feedstock to create a liquid phase containing 6PPD and a decontaminated EOL tire feedstock, and separating the liquid phase containing 6PPD from the decontaminated EOL tire feedstock. Methods for converting the recovered 6PPD into commercially applicable products and systems for performing the methods are also disclosed.

Description

[0001] MICROWAVE-ASSISTED DECONTAMINATION OF END-OF-LIFE TIRES VIA SOLVENT EXTRACTION AND PYROLYSIS

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] This application claims priority to U.S. Provisional Patent Application No. 63 / 667,884 filed on July 05, 2024, the contents of which are incorporated herein by reference in their entirety for all purposes.

[0004] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0005] This invention was made with government support under Grant No. NSF EPSCoR OIA-21 19754 awarded by the National Science Foundation. The government has certain rights in the invention.

[0006] FIELD

[0007] The present disclosure relates to processes and systems for decontaminating end-of-life (EOL) tire feedstocks of harmful chemicals, such as N- (1 ,3-dimethyl butyl)-N'-phenyl-p-phenylenediamine, and processes for converting EOL tire feedstocks into recyclable resources.

[0008] BACKGROUND

[0009] Tires are an indispensable part of the modern economy but can have adverse effects during their lifetime and end-of-life (EOL). Crumb rubber, recycled rubber produced from automotive and truck scrap tires (i.e., EOL tires), is used in asphalt and recreational fields. Crumb rubber contains the tire antioxidant and antiozonant, N-(1 ,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD). 6PPD is added to tires to extend the polymer rubber lifetime. 6PPD has been shown to leach from the crumb rubber used in asphalt and recreational fields. This is a major environmental concern because 6PPD transforms, upon environmental exposure, to a highly toxic quinone form (6PPD-Q), which causes acute mortality in coho salmon. Other aquatic species have also displayed severe susceptibility to 6PPD- Q, for example, rainbow trout, brook trout, lake trout, and coastal cutthroat trout. 6PPD has also been detected in humans and linked to severe developmental, physical deformative, and behavioral health effects.

[0010] The scrap tire utilization in the US has declined from 96% in 2013 to 71 % in 2021 . This represents an ever-growing problem given 5 billion tires will be disposed of by 2030. Landfilling is the common EOL-tire management approach, but the washing of 6PPD or 6PPD-Q from EOL-tires in landfills and tire streaks on roads by rain presents a severe ecotoxicity crisis.

[0011] While determining the prevalence and toxicity of 6PPD and 6PPD-Q in the environment has gained significant traction, cost-efficient and effective methods for isolating and deconstructing 6PPD have yet to be discovered. E.U. legislation has focused on mitigating landfill accumulation via pyrolysis, recycling, retreading, and energy recovery. Though pyrolysis is one of the most feed-agnostic and common EOL tire deconstruction approaches, the fate of 6PPD during pyrolysis is unknown.

[0012] To address the foregoing issues with the fate of 6PPD after pyrolysis, in addition to its toxicity and prevalence in EOL tires, the present disclosure presents evidence that 6PPD survives pyrolysis treatments and provides novel approaches / systems for removing 6PPD from EOL tire feedstocks and converting 6PPD into commercially valued products.

[0013] SUMMARY

[0014] Disclosed herein is a method for decontaminating an EOL tire feedstock containing 6PPD, the method including (j.e., comprising) one or more of: obtaining the EOL tire feedstock; performing at least one microwave-assisted solvent extraction on the EOL tire feedstock to create a liquid phase containing 6PPD and a solid, decontaminated EOL tire feedstock; and separating the liquid phase containing 6PPD from the decontaminated EOL tire feedstock.

[0015] Also disclosed herein is a method for converting 6PPD into commercially and / or industrially applicable products, the method including one or more of: subjecting 6PPD to a catalytic hydroconversion reaction in a presence of a hydrogenation or hydrocracking catalyst, wherein the catalytic hydroconversion reaction is performed under one or more of a temperature ranging from about 130°C to about 200°C, a H2 pressure ranging from about 30 to about 50 bar, or a time period ranging from about 30 minutes to about 3 hours.

[0016] Disclosed herein is a system for decontaminating an end-of-life (EOL) tire feedstock containing 6PPD, the system including one or more of: a microwave extractor in communication with an extraction solvent mixer, wherein the microwave extractor possesses a EOL-tire feedstock import line, an extraction solvent import line; an extraction solvent export line, and a decontaminated EOL-tire feedstock export line.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Other features and advantages of the compositions, devices and methods disclosed herein will be apparent to those skilled in the art reading the following detailed description in conjugation with the exemplary embodiments illustrated in the drawings, wherein:

[0019] FIG. 1 depicts an exemplary embodiment of a system configured to decontaminate an EOL tire feedstock containing 6PPD.

[0020] FIG. 2 depicts particle size distributions of crumb rubber obtained via dynamic light scattering.

[0021] FIG. 3 depicts temperature profiles of crumb rubber in a microwave-assisted pyrolysis reactor. The temperature profiles were captured at the various powers indicated and taken at the center of the reactor (r = 0 m) and at 0.22 m from the bottom of the reactor (z = 0.22 m).

[0022] FIG. 4 depicts wall temperature profiles of crumb rubber in a microwave- assisted pyrolysis reactor. The wall temperature profiles were captured under the following pyrolysis conditions: 175 W, 125 seem N2. The outer graph depicts the wall temperature profile for 1 .3 mm crumb rubber particles subjected to the above pyrolysis conditions, while the inset depicts the wall temperature profile of 0.6 mm crumb rubber particles subjected to the above pyrolysis conditions.

[0023] FIG. 5 depicts dielectric constants and loss factors of two different crumb rubber particle sizes (1 .3 mm and 0.6 mm). Error bars represent the standard error obtained from duplicate runs.

[0024] FIG. 6 depicts th e rm ogravi metric analysis (TGA) profiles of crumb rubber particles (1.3 mm, i.e., larger and 0.6 mm, i.e., smaller) under 20 mL / min (a) air and (b) nitrogen.

[0025] FIG. 7 depicts normalized power consumption for an exemplary microwave- assisted pyrolysis of crumb rubber compared to other studies.

[0026] FIG. 8 depicts scanning electron microscopy (SEM) images of tire particles during various stages of an exemplary MW-assisted pyrolysis. FIG. 9 depicts a Raman spectra of carbon black powders obtained from an exemplary MW-assisted pyrolysis. The Raman spectra depicts the Raman shifts of the carbon black pyrolysis product for crumb rubber “as-received” (i.e., crumb rubber) and for crumb rubber that has been exposed to a solvent extraction (i.e., carbon black).

[0027] FIG. 10 depicts N2 physisorption isotherms of carbon black powders following an exemplary MW-assisted pyrolysis of crumb rubber “as-received”. All isotherms have been shifted upward in the y-direction for clarity.

[0028] FIG. 11 depicts full SEM images with magnification details from FIG. 8. Exposure to microwave radiation: a) 0 min b) 1 min c) 2 min d) 3 min e) 10 min.

[0029] FIG. 12 depicts mass yields from an exemplary MW-assisted pyrolysis of larger (1 .3 mm) and smaller (0.6mm) sized crumb rubber particles.

[0030] FIG. 13 depicts a TGA curve of 6PPD under 20 mL / min of N2 flow.

[0031] FIG. 14 depicts liquid yields of products from an exemplary MW-assisted pyrolysis of “as-received” 0.6 mm crumb rubber particles. Conditions: 10 min of 175 W of microwave irradiation, 125 mL / min N2 flow, and 6 g of crumb rubber.

[0032] FIG. 15 depicts the effect temperature has on the 6PPD extraction efficiencies of different extraction cycles. An “extraction cycle” is the time period that crumb rubber is exposed to fresh extraction solvent. Cycle 1 represents a first or initial extraction cycle the crumb rubber undergoes, Cycle 2 represents an extraction cycle following Cycle 1 , and Cycle 3 represents an extraction cycle following Cycle 2. The inset depicts the 6PPD extraction efficiencies of ethanol and methanol. Experiments with 3 g of crumb rubber and 0.6 mm tire particles in 15 mL solvent.

[0033] FIG. 16 depicts the 6PPD extraction efficiency of ethanol at various extraction cycles at 50 °C. Experiments with 3 g of crumb rubber and 0.6 mm tire particles in 15 mL solvent.

[0034] FIG. 17 depicts the total additive mass losses of crumb rubber for various extraction cycles that used ethanol as the extraction solvent. The crumb rubber was subsequently dried after each extraction cycle and each extraction cycle was performed at 50 °C. Experiments with 3 g of crumb rubber and 0.6 mm tire particles in 15 mL solvent. FIG. 18 depicts the performance of various solvents for 6PPD extraction at 60 °C and 2 h. Experiments with 3 g of crumb rubber and 0.6 mm tire particles in 15 mL solvent.

[0035] FIG. 19 depicts a parity plot of various solvents’ 6PPD experimental solubilities (i.e., solubilities determined experimentally) vs. the solvents’ COSMO- RS calculated solubilities. Experiments with 3 g of crumb rubber and 0.6 mm tire particles in 15 mL solvent.

[0036] FIG. 20 depicts a schematic of an exemplary continuous flow MW-assisted solvent extraction system.

[0037] FIG. 21 depicts the temperature profiles of exemplary MW-assisted solvent extraction processes at the center of an MW-assisted solvent extraction reactor and at 0.22 m from the bed bottom of the MW-assisted solvent extraction reactor at various powers. 20 g of crumb rubber was packed in a 0.54 m tube (i.e., the reactor) with a 0.135 m ID.

[0038] FIG. 22 depicts the temperature profiles of exemplary MW-assisted solvent extraction processes at the center of an MW-assisted solvent extraction reactor and at 40 W of power at different axial locations of the MW-assisted solvent extraction reactor (z values).

[0039] FIG. 23 depicts the axial temperatures of exemplary MW-assisted solvent extraction processes at the center of an MW-assisted solvent extraction reactor in stagnant air, acetone flow, and stagnant acetone (top). Corresponding wall temperature profiles are depicted in the bottom graph.

[0040] FIG. 24 depicts a comparison between MW-assisted and conventional heating solvent extraction. Final temperature under MW and conventional heating as a function of input power supplied and absorbed.

[0041] FIG. 25 depicts the 6PPD and fatty acid extraction efficiencies at various extraction solvent flow rates, (i) Extraction of 6PPD from 0.6 mm particles at 2 mL / min and 7.5 mL / min acetone flow under ambient and microwave radiation (40 W). (ii) Extraction of 6PPD from 1 .3 mm particles at 7.5 mL / min acetone flow under ambient and microwave radiation (40 W). (iii) Extraction of fatty acids from 0.6 mm particles at 40 W and 7.5 mL / min acetone flow. FIG. 26 depicts a transmission electron microscopy (TEM) image of a 5 wt% Pd / C catalyst with particle size distribution as inset (average particle size = 3.66 nm).

[0042] FIG. 27 depicts X-ray Absorption Near Edge Structure (XANES, left) and Extended X-ray Absorption Fine Structure (EXAFS, right) spectra of 5 wt% Pd / C catalyst before and after an exemplary catalytic deconstruction reaction and Pd reference spectra. All experiments employ 1 g 6PPD and 20 mg of 5 wt% Pd / C.

[0043] FIG. 28 depicts the results of various exemplary hydroconversion reactions of 6PPD under semi-batch operation: (i) Effect of temperature at 50 bar H2, 1 .5 h; (ii) Effect of H2 pressure at 150 °C, 1 .5 h; (iii) Effect of time at 50 bar H2, 150 °C. All experiments employ 1 g 6PPD and 20 mg of 5 wt% Pd / C.

[0044] FIG. 29 depicts an exemplary reaction scheme for the hydroconversion of 6PPD.

[0045] FIG. 30 depicts the yield of products of an exemplary hydroconversion process of 6PPD at 185 °C, 2 h under batch operation. All experiments employ 1 g 6PPD and 20 mg of 5 wt% Pd / C.

[0046] FIG. 31 depicts an exemplary process development for upcycling of waste tires, including extraction of 6PPD from crumb rubber, followed by hydroconversion of 6PPD to useful products, pyrolysis of extracted crumb rubber resulting in pyrolysis oil and carbon black. Here, 50% of extracted crumb rubber is fed to the microwave-assisted (MW) pyrolysis reactor, with the remaining extracted crumb rubber being available for sale.

[0047] FIG. 32 depicts sensitivity analysis to quantify the minimum selling price of extracted crumb rubber (for a profitability index of 1 .04) (a), and results of techno- economic analysis showing the distribution of the total capital, operating, raw material, utility cost, and product sales (b).

[0048] DETAILED DESCRIPTION

[0049] All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

[0050] Unless stated otherwise, all percentages, parts, ratios, etc., are by weight.

[0051] When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

[0052] As used herein, the term “about” refers to a value that is ± 5% of the stated value. In addition, it is understood that reference to a range of a first value to a second value includes the range of the stated values, e.g., a range of about 1 to about 5 also includes the more precise range of 1 to 5. It is also understood that the ranges disclosed herein include any selected subrange within the stated range, e.g., a subrange of about 50 to about 60 is contemplated in a disclosed range of about 1 to about 100.

[0053] One aspect of the present disclosure is a method for decontaminating an EOL tire feedstock containing 6PPD, the method including one or more of: obtaining the EOL tire feedstock; performing at least one microwave-assisted solvent extraction on the EOL tire feedstock to create a liquid phase containing 6PPD and a solid, decontaminated EOL tire feedstock; and separating the liquid phase containing 6PPD from the decontaminated EOL tire feedstock.

[0054] In exemplary embodiments, the EOL tire feedstock contains one or more of crumb rubber, carbon black, silica, processing aids, vulcanizing agents, activators, accelerators, tire coolants, sealants, natural rubber, synthetic rubber, corrosion inhibitors, steel wire, fabrics, fillers, antioxidants, antiozonants or any other additive used in tire compositions known by those of ordinary skill in the art.

[0055] A tire processing aid can be any substance added during tire manufacturing to improve the ease and efficiency of the production process and enhance the tire's quality. These aids can act as lubricants and dispersion agents, helping to mix rubber compounds, fillers, and other ingredients effectively, preventing sticking to machinery, and improving the overall flow of materials. Processing aids can include, but are not limited to, plasticizers, dispersants, tackifiers, lubricants, peptizers, a metal salt modified with an aliphatic compound (e.g., a C13 to C22 fatty acid ester-based compound such as a zinc soap, a sodium soap, a potassium soap, or a zinc potassium soap), or any other processing aid used in tire compositions known by those of ordinary skill in the art.

[0056] A vulcanizing agent can be any substance used in the chemical process of vulcanization, i.e., any chemical process which transforms rubber into a stronger, more durable material. These processes can create cross-links between the rubber molecules, enhancing its elasticity, strength, and resistance to wear and tear, making it suitable for applications like tires. Vulcanizing agents can include, but are not limited to, sulfur compounds capable of creating cross-links between rubber polymer chains (e.g., elemental sulfur), sulfenamides (e.g., CBS, TBBS), thiurams (e.g., TMTD), thiazoles (e.g., MBT), metal oxides, peroxides, or any other vulcanizing agent used in tire compositions known by those of ordinary skill in the art.

[0057] An activator can be any substance capable of enhancing a vulcanization process by promoting and / or accelerating a cross-linking reaction. Activators can include, but are not limited to, zinc oxide, stearic acid, silica-based activators, single-site activators, peroxides, activated carbon, or any other activator used in tire compositions known by those of ordinary skill in the art.

[0058] An accelerator can be any substance capable of accelerating a vulcanization process by promoting the formation of cross-links between rubber polymer chains. Accelerators can include, but are not limited to, sulfenamides, thiazoles (e.g., MBT and MBTS), thiurams (e.g., TBzTD and TMTD), MBS (NOBS), or any other accelerator used in tire compositions known by those of ordinary skill in the art.

[0059] A coolant can be any fluid substance capable of improving tire performance, increasing tire traction, and / or reducing tire wear. Coolants can include, but are not limited to, water, antifreeze (e.g., ethylene glycol or propylene glycol), calcium chloride solutions, beet juice, RV antifreeze, or any other coolant used in tire compositions known by those of ordinary skill in the art.

[0060] A sealant can be any substance capable of preventing or repairing punctures and / or leaks in tires. Sealants can include, but are not limited to, a viscous carrier fluid containing one or more of propylene glycol, polypropylene glycol or polyethylene glycol; a fibrous material containing one or more of cellulose, nylon, sisal, wool, rayon, hair, wollastonite, rock-wool, or aramid fibers; finely ground particles of one or more of marble, rubber, mica, bentonite clay, or quartz; latex-based sealants; or any other sealant used in tire compositions known by those of ordinary skill in the art.

[0061] A natural rubber can be any elastomer derived from a natural source. Natural rubber can be derived from the Hevea brasiliensis species, guayule and dandelions.

[0062] A synthetic rubber can be any synthetic elastomer capable of offering specific properties that enhance tire performance, such as improved wear resistance, low rolling resistance (for better fuel economy), and grip. Synthetic rubber can include, but are not limited to, be styrene-butadiene rubber (SBR), polybutadiene rubber (BR), butyl rubber (HR), nitrile rubber (NBR), or any other synthetic rubber used in tire compositions known by those of ordinary skill in the art.

[0063] A corrosion inhibitor can be any substance capable of preventing and / or slowing the corrosion of a tire and / or wheel rims of a tire. These inhibitors can be part of tire mounting compounds, applied as a coating, or added as a liquid sealant. They can also create a protective barrier between the tire and the rim, preventing rust and corrosion from forming. Corrosion inhibitors can include, but are not limited to, organic corrosion inhibitors, e g., those that employ carboxylate chemistry to form a protective molecular film, lanolin-based pastes, benzotriazoles and benzothiazoles; inorganic corrosion inhibitors, e.g., zinc phosphate, zinc oxide, zinc salts, aluminum salts, magnesium salts, phosphates, silicates; or any other corrosion inhibitor used in tire compositions known by those of ordinary skill in the art. A fabric can be any material that provides reinforcement and stability to a tire. Fabrics can include, but are not limited to, polyester fabrics, nylon fabrics, rayon fabrics, aramid fabrics, steel fabrics, or any other fabrics used in tire compositions known by those of ordinary skill in the art.

[0064] A filler can be any material used within tires to enhance their performance and / or durability. Fillers can include, but are not limited to, silica powders, calcium carbonate, calcium clays, zinc oxide, mica, ground coal, or any other fillers used in tire compositions known by those of ordinary skill in the art.

[0065] An antioxidant can be any substance capable of preventing degradation and / or cracking of a tire caused by exposure to oxygen, ozone, and temperature fluctuations. Antioxidants can work by reacting with free radicals, preventing the rubber from breaking down and extending the tire's lifespan. Antioxidants can include, but are not limited to, 6PPD, IPPD, DPPD, diaryl-secondary amines, acetone-amine condensation products, p-phenylenediamines, aldehyde-amine condensation products, or any other antioxidant used in tire compositions known by those of ordinary skill in the art.

[0066] An antiozonant can be any substance capable of protecting a tire from degradation caused by ozone and other factors like oxygen and heat. Antiozonants can include, but are not limited to, 6PPD, hydrocarbon waxes, styrenated phenols (SPH), styrenated and alkylated phenols (SAPH), or any other antiozonant used in tire compositions known by those of ordinary skill in the art.

[0067] In exemplary embodiments, the EOL tire feedstock is sourced from a dedicated tire recycling facility, an energy recovery plant, a tire retailer or auto shop, a recycling program, or a pyrolysis facility.

[0068] In exemplary embodiments, the EOL tire feedstock has been subjected to a pre-processing methodology before the EOL tire feedstock is obtained. The preprocessing methodology can include, but is not limited to, shredding, granulating, grinding, crumbing, devulcanization, or any other pre-processing methodology known by those of ordinary skill in the art.

[0069] In exemplary embodiments, the EOL tire feedstock contains crumb rubber particles possessing a particle size ranging from about 100pm to about 1.0 cm, about 100pm to about 1 mm, about 100pm to about 900 pm, 100pm to about 500 m, 100pm to about 300 pm, about 0.5 mm to about 2.0 mm, about 0.6mm to about 1.3mm, or any range of particle sizes or specific particle size falling within the range of 100pm to about 1 .0 cm.

[0070] In exemplary embodiments, the at least one microwave-assisted solvent extraction is conducted at a temperature of about 35°C to about 130°C, about 35°C to about 120°C, about 35°C to about 110°C, about 35°C to about 90°C, about 35°C to about 70°C, about 35°C to about 50°C, or any range of temperatures or specific temperature falling within the range of 35°C to about 130°C. The temperature that the at least one microwave-assisted solvent extraction is conducted at can depend upon the boiling point of the extraction solvent. Accordingly, the at least one microwave-assisted solvent extraction can also be conducted at a temperature above 150°C when the extraction solvent possesses a boiling point above 150°C.

[0071] In exemplary embodiments, the at least one microwave-assisted solvent extraction is performed at a power level ranging from about 40W to about 100W, about 40W to about 80W, about 40W to about 60W, or any range of power levels or specific power level falling within the range of 40W to about 100W. The power level that the at least one microwave-assisted solvent extraction is performed at can depend upon the size of the MW system and the amount of EOT-tire feedstock present during the at least one microwave-assisted solvent extraction. Accordingly, the at least one microwave-assisted solvent extraction can also be performed at a power level about 100W when large MW systems and large amounts of EOT-tire feedstock are used.

[0072] In exemplary embodiments, the at least one microwave-assisted solvent extraction is performed under an inert atmosphere, e.g., under a N2 atmosphere, under a He atmosphere, under a Ne atmosphere, under an Ar atmosphere, under a Kr atmosphere, under a Xe atmosphere, or under a CO2 atmosphere.

[0073] In exemplary embodiments, the at least one microwave-assisted solvent extraction includes subjecting the EOL tire feedstock to a flow of extraction solvent at a rate of at least 2 mL / min, at least 3 mL / min, at least 4 mL / min, at least 5 mL / min, or at least 10 mL / min. The flow rate of the extraction solvent can depend on the minimum fluidization velocity of the particles present in the EOL-tire feedstock. Accordingly, the flow rate of the extraction solvent can be below 2 mL / min if the particles in the EOL-tire feedstock are densely packed or greater than 10 mL / min if the particles in the EOL-tire feedstock in loosely packed. In exemplary embodiments, the flow rate of the extraction solvent is normalized based on the size of the MW reactor or system and / or the amount of EOL-tire feedstock or the amount of crumb rubber present during the at least one microwave-assisted solvent extraction.

[0074] In exemplary embodiments, wherein the at least one microwave-assisted solvent extraction is performed for at least 30 seconds, at least 1 minute, at least 5 minutes, at least 10 minutes, at least 15 minutes, at least 30 minutes, at least 1 hour, at least 2 hours, at least 5 hours, at least 10 hours, or at least 24 hours. The amount of time that the at least one microwave-assisted solvent extraction is performed can depend on whether the at least microwave-assisted solvent extraction is performed as a continuous process or batch-wise process and / or the extraction solvent. Since the at least one microwave-assisted solvent extraction can be performed either a continuous process, a batch-wise process, or a combination thereof, the amount of time the at least one microwave-assisted solvent extraction is performed can, in exemplary embodiments, be less than 30 seconds or greater than 24 hours. The amount of time that the at least one microwave-assisted solvent extraction is performed can also be dependent upon the size of the MW reactor or system and the amount of EOL-tire feedstock present during the at least one microwave-assisted solvent extraction.

[0075] In exemplary embodiments, the extraction solvent is selected from carbonyls (e.g., ketones, aldehydes, esters), alcohols, hexanes, nitriles, ethers, esters, and combinations thereof. In exemplary embodiments, the extraction solvent is or includes acetone. In exemplary embodiments, the extraction solvent is or includes methanol, ethanol, butanone, ethyl acetate, MIBK, 2-hexanone, hexanes, acetonitrile, 1-propanol, 1-butanol, or isopropyl alcohol.

[0076] In exemplary embodiments, the extraction solvent is a solvent that has a 6PPD solubility of at least 500g 6PPD / L of extraction solvent, at least 1000g 6PPD / L of extraction solvent, at least 1500g 6PPD / L of extraction solvent, or at least 2000g 6PPD / L of extraction solvent. In exemplary embodiments, the extraction solvent is a solvent capable of penetrating into the crumb rubber, natural rubber and / or synthetic rubber of the EOL-tire feedstock to remove 6PPD, and optionally other tire additives, from the rubber materials without disrupting the crosslinked network of the rubber materials. Extraction solvents capable of penetrating into the rubber materials and removing 6PPD and other tire additives, without causing damage to the cross-link network of the rubber materials, can cause the rubber materials to swell. Accordingly, in exemplary embodiments, the extraction solvent is a solvent that causes crumb rubber, natural rubber, and / or synthetic rubber in the EOL-tire feedstock to swell at a swelling degree of at least 10%, at least 20%, at least 30%, at least 40%, or at least 50%. Swelling degree can be calculated by determining the weight or volume of the rubber material before solvent exposure and monitoring the change in weight (mass swelling ratio) or volume (volume swelling ratio) of the rubber material after solvent exposure.

[0077] In exemplary embodiments, the decontaminated EOL tire feedstock contains no detectable levels of 6PPD. The level or concentration of 6PPD in the decontaminated EOL tire feedstock can be detected according to any routinely practiced analytical method in the art, for example, a gas chromatography-mass spectrometry (GCMS) analytical method or other mass spectrometry analytical methods, such as those disclosed in Evans et al. (Environmental Science & Technology Letters 2025 12 (1 ), 79-84). In exemplary embodiments, the decontaminated EOL tire feedstock contains levels of 6PPD below a detection limit of a GCMS analytical method. A detection limit, also known as the limit of detection (LOD), is the lowest concentration of an analyte that can be reliably detected, but not necessarily quantified, with a specific analytical method. In exemplary embodiments, the decontaminated EOL tire feedstock contains levels of 6PPD below 1 ppb, 10 ppb, 100 ppb, or 1000 ppb.

[0078] In exemplary embodiments, the liquid phase contains one or more fatty acids, processing aids, vulcanizing agents, activators, accelerators, tire coolants, sealants, corrosion inhibitors, antioxidants or antiozonants.

[0079] In exemplary embodiments, the method includes subjecting the decontaminated EOL tire feedstock to a pyrolysis process. The pyrolysis process can include one or more of: heating the decontaminated EOL tire feedstock at temperatures ranging from about 300°C to about 800°C, optionally in a low-oxygen or oxygen-free environment; heating the decontaminated EOL tire feedstock under a pressure ranging from about 0.1 MPa to about 2.0 MPa; heating the decontaminated EOL tire feedstock in a presence of a pyrolysis catalyst (e.g., a zeolite catalyst (such as HZSM-5 and HY), a metal oxide (such as MgO / CaCOs, AI2O3), a metal-based catalyst (such as Ni / Al2O3, Ni / Fe bimetallic catalysts, Cu- doped catalysts, and Pd / H|3 catalysts), FOO catalysts, Biochar); and / or heating the decontaminated EOL tire feedstock in a pyrolysis reactor for a range of residence times or a specific residence time falling withing the range of about 1 second to about 24 hours. In exemplary embodiments, the pyrolysis process is performed with conventional heating. In exemplary embodiments, the pyrolysis process is performed with MW-assisted heating.

[0080] In exemplary embodiments, the method is performed continuously, i.e., the method is performed without interruption between steps. In exemplary embodiments, the method is performed batch-wise, i.e., the method is performed with distinct breaks in the method that prevent the method from being performed without interruption or as an uninterrupted flow.

[0081] Another aspect of the present disclosure is a method for converting 6PPD into commercially and / or industrially applicable products, the method including one or more of: subjecting 6PPD to a catalytic hydroconversion reaction in a presence of a hydrogenation or hydrocracking catalyst, wherein the catalytic hydroconversion reaction is performed under one or more of a temperature ranging from about 130°C to about 200°C, a H2 pressure ranging from about 30 to about 50 bar, or a time period ranging from about 30 minutes to about 3 hours.

[0082] As used herein, a “commercially and / or industrially applicable product” is a product that possesses a commercial value which can be marketed as it stands or marketed as a component of another product, and / or is a product that possesses an industrial value that can be used to aid in the creation of other commercial products and / or used to aid in the operation of an industrial process. In exemplary embodiments, the method uses a catalytic cracking process instead of a catalytic hydroconversion reaction to convert 6PPD into commercially and / or industrially applicable products.

[0083] In exemplary embodiments, the catalytic hydroconversion reaction produces one or more of the following commercially and / or industrially applicable products: cyclohexylamine, cyclohexane, triethylamine, dicyclohexylamine, and / or dimethyl butylamine.

[0084] In exemplary embodiments, the metal-supported hydrogenation catalyst is a 5 wt% Pd / C catalyst, a metal catalyst (e.g., a catalyst containing Pt, Pd, Ni, Ru, Co, and combinations thereof), a solid acid catalyst (e.g., a zeolite catalyst, silica- alumina catalyst, and acidic mixed oxide catalysts (such as WOs / ZrC^)), a sulfide catalyst (e.g., nickel-tungsten sulfides or M0S2), a metal-supported hydrogenation catalyst, a metal-supported / acid hydrocracking catalyst, or any catalyst that can be used in hydroconversion processes known by those of ordinary skill in the art.

[0085] In exemplary embodiments, the method includes obtaining a liquid phase containing 6PPD produced from any one of the methods for decontaminating an EOL tire feedstock containing 6PPD disclosed herein; subjecting the liquid phase to the catalytic hydroconversion reaction in the presence of a hydrogenation or hydrocracking catalyst to create a product mixture; and isolating 2,2 ,4-trimethyl- 1 ,2,3,4-tetrahydroquinoline from the product mixture. In exemplary embodiments, the isolating of 2,2, 4-trimethyl-1 ,2,3,4-tetrahydroquinoline from the product mixture includes removing any one or more solid materials from the product mixture; and rinsing the solid materials with methanol to isolate 2, 2, 4-trimethyl-1 ,2,3,4- tetrahydroquinoline.

[0086] In exemplary embodiments, the catalytic hydroconversion reaction is performed at a weight ratio of 6PPD to the metal-supported hydrogenation catalyst of 1 :0.01 , 1 : 0.02, 1 :0.03, 1 :0.04, 1 :0.05 or any range of weight ratios or any specific weight ratio falling within the range of 1 :0.01 . Those of ordinary skill in the art will appreciate that the weight ratio is dependent upon the kinetics of the catalytic hydroconversion reaction. Accordingly, the weight ratio can exceed 1 :0.05 when the kinetics of the catalytic hydroconversion reaction are low and can be below 1 :0.01 when the kinetics of the catalytic hydroconversion reaction are high. In exemplary embodiments, the catalytic hydroconversion reaction is performed a temperature ranging from about 130°C to about 200°C, 150°C to about 200°C, 170°C to about 200°C, 190°C to about 200°C, or any temperature range or specific temperature falling within the range of 130°C to about 200°C. Those of ordinary skill in the art will appreciate that the temperature of the catalytic hydroconversion reaction can depend upon the catalyst present during the reaction and what other components are present in the reaction mixture (e.g., organic solvents).

[0087] In exemplary embodiments, the catalytic hydroconversion reaction is performed at a H2 pressure ranging from about 30 to about 50 bar, about 40 to about 50 bar, or any pressure range or specific pressure falling within the range of about 30 to about 50 bar.

[0088] In exemplary embodiments, the catalytic hydroconversion reaction is performed for a time period ranging from about 30 minutes to about 3 hours, from about 1 hour to 3 hours, from about 2 hours to 3 hours, or any time range or specific time falling within the range of 30 minutes to 3 hours.

[0089] Another aspect of the present disclosure is a system for decontaminating an end-of-life (EOL) tire feedstock containing 6PPD, the system including one or more of: a microwave extractor in communication with an extraction solvent mixer, wherein the microwave extractor possesses a EOL-tire feedstock import line, an extraction solvent import line; an extraction solvent export line, and a decontaminated EOL-tire feedstock export line.

[0090] The microwave extractor can be a monomode or multimode reactor. Monomode reactors can utilize a single, well-defined microwave mode for irradiation, leading to a highly focused and homogenous energy field. Multimode reactors can employ a larger cavity where microwaves reflect off the walls of the reactor, creating a more chaotic and less focused energy distribution.

[0091] The extraction solvent mixer is configured to store an extraction solvent and, optionally, mix two or more solvents together (e.g., via an impeller).

[0092] In exemplary embodiments of the system, the extraction solvent export line is in communication with a separation unit configured to separate an extraction solvent from any additives contained in an EOL-tire feedstock. The separation unit can be a flash chromatography column configured to separate an extraction solvent from other products in a liquid mixture, a distillation column, or any thermal separation unit such as, but not limited to, thermal diffusion columns and dividing wall columns.

[0093] In exemplary embodiments of the system, the separation unit possesses a purified extraction solvent export line and an additive export line, the purified extraction solvent export line being in communication with a recycled extraction solvent unit and the additive export line being in communication with an additive purification unit.

[0094] The recycled extraction solvent unit can be configured to store recycled extraction solvent and transfer the extraction solvent to a downstream waste removal system and / or to the extraction solvent mixer.

[0095] The additive purification unit can be an absorption column configured to separate 6PPD from a mixture containing other additives found in EOL-tires. In exemplary embodiments, the additive purification unit is configured to distill and / or evaporate any remaining extraction solvent and / or other low boiling point compounds to assist in the separation of 6PPD from a mixture. In exemplary embodiments, the additive purification unit possesses a membrane that selectively permeates 6PPD and / or any remaining extraction solvent. Possible membranes include, but are not limited to, polydimethylsiloxane (PDMS) membranes, permeable pavements, biologically active soil media, bioretention systems, nanofiltration membranes, reverse osmosis membranes and any other membrane system or membrane capable of permeating 6PPD known by those of ordinary skill in the art.

[0096] In exemplary embodiments of the system, the additive purification unit possesses a 6PPD export line in communication with a hydroconversion reactor containing a hydrogen gas import line and a hydroconversion product export line. The hydrogen gas import line can be in communication with a hydrogen gas storage unit. The hydroconversion product export line can be in communication with a downstream purification system.

[0097] The hydroconversion reactor can be configured to perform any one of the catalytic hydroconversion reactions disclosed herein. In exemplary embodiments of the system, the recycled extraction solvent unit possesses a recycled extraction solvent export line in communication with the extraction solvent mixer, and a waste export line in communication with a downstream waste processing system.

[0098] In exemplary embodiments of the system, the decontaminated EOL-tire feedstock export is in communication with a microwave pyrolysis reactor containing a pyrolysis oil export line and a carbon black export line. In exemplary embodiments, the decontaminated EOL-tire feedstock export is in communication with a crumb rubber separation unit configured to remove crumb rubber from a decontaminated EOL-tire feedstock and transport crumb rubber to the microwave pyrolysis reactor. The crumb rubber separation unit can also possess a solid waste export line that is in communication with a downstream solid waste removal system. The pyrolysis oil export line can be in communication with a downstream pyrolysis oil processing system. The carbon black export line can be in communication with a downstream carbon black processing system.

[0099] FIG. 1 depicts an exemplary system for decontaminating an end-of-life (EOL) tire feedstock containing 6PPD. The system includes a microwave extractor (100) in communication with an extraction solvent mixer (102). The microwave extractor (100) also possesses a EOL-tire feedstock import line (104), an extraction solvent import line (106), an extraction solvent export line (108), and a decontaminated EOL-tire feedstock export line (110). In exemplary embodiments, the EOL-tire feedstock import line (104) is in communication with an EOL-tire feedstock source (112). The extraction solvent export line (108) is in communication with a separation unit (114) configured to separate an extraction solvent from any additives contained in a EOL-tire feedstock. The separation unit (114) possesses a purified extraction solvent export line (116) and an additive export line (118), the purified extraction solvent export line (116) being in communication with a recycled extraction solvent unit (120) and the additive export line (118) being in communication with an additive purification unit (122). The additive purification unit (122) possesses a 6PPD export line (124) in communication with a hydroconversion reactor (126) containing a hydrogen gas import line (128) and a hydroconversion product export line (130). In exemplary embodiments, the hydroconversion product export line (130) is in communication with one or more systems configured to isolate individual hydroconversion products formed from a hydroconversion reaction and, optionally, convert isolated individual hydroconversion products into commercially applicable products. The recycled extraction solvent unit (120) possesses a recycled extraction solvent export line (132) in communication with the extraction solvent mixer (102), and a waste export line (134). In exemplary embodiments, the waste export line (134) is in communication with one or more systems configured to remove and / or convert waste separated from an extraction solvent in the recycled extraction solvent unit (120). The decontaminated EOL-tire feedstock export (110) is in communication with a crumb rubber separation unit (136) configured to separate decontaminated crumb rubber from other solid waste materials. The crumb rubber separation unit (136) possesses a solid waste export line (138) and a decontaminated crumb rubber export line (140). The solid waste export line (138) can be in communication with one or more systems configured to remove solid waste from the system and / or convert solid waste into commercially applicable products. The decontaminated crumb rubber export line (140) is in communication with a microwave pyrolysis reactor (142) containing a pyrolysis oil export line (144) and a carbon black export line (146). The carbon black export line (146) can be in communication with one or more systems configured to purify carbon black material and / or convert carbon black into commercially applicable products. The pyrolysis oil export line (144) can be in communication with one or more systems configured to purify pyrolysis oil and / or convert pyrolysis oil into commercially applicable products. Examples

[0100] The present disclosure will be described in more detail with reference to the following Examples, which shows exemplary embodiments in accordance with the present disclosure. The present disclosure is not limited to these exemplary embodiments.

[0101] Example 1 : Decontamination of EOL Tire Feedstock with Microwave-Assisted Solvent Extraction

[0102] Microwave-assisted Pyrolysis ofEOL Tires Initial testing of the abatement of 6PPD by icrowave-assisted pyrolysis was first investigated as a possible decontamination strategy. Two batches of crumb rubber with different average particle sizes were used in this investigative study (FIG. 2). Initially, the effect of the microwave’s power level on the pyrolysis reactor bed's temperature was investigated. The temperature profiles obtained from this study (FIG. 3) show a temperature upshot at varying power levels at the center of the crumb rubber bed reaching a temperature up to 500 °C. The upshot trend indicated a polymer material degradation in which the mass ratio of polymer to susceptor was decreasing. This suggests an optimal power level is needed to initiate pyrolysis. The crumb rubber particle size had a noticeable effect on the temperature profile during pyrolysis (FIG. 4). First, the wall temperature at the bottom of the bed (z = 0 cm) increased faster than the top of the bed (z = 8.5 cm from the reactor bottom) for both particle sizes. At longer reaction times, the two profiles converged, indicating an axial temperature differential was only present at the beginning. Second, the larger particles heat faster than the smaller ones. This was due to the higher loss tangent tan5 of the larger particles (FIG. 5). Under conventional heating using TGA (FIG. 6), the 1.3 mm particles exhibited a similar degradation curve to the smaller particles. This indicated that the heating differences observed in FIG. 4 were truly due to microwave radiation rather than thermal conduction. Lastly, the reflected power for both particle sizes was similar, with -50% coupling efficiency at t = 0. Once the rubber particle degraded, coupling reached 100% due to the forward power being entirely absorbed by the carbon black phase. The superior energy efficiency relative to other microwave pyrolysis systems (FIG. 7) was due to the excellent coupling, tuning, and penetration of the microwave radiation. For example, Song et al. (Song, Z. et al. Microwave pyrolysis of tire powders: Evolution of yields and composition of products. J Anal Appl Pyrolysis 123, 152-159 (2017)) achieved similar product yields but employed much higher power levels (450 W). The other microwave pyrolysis systems depicted in FIG. 7 are Bing et al. (Bing, W. et al. Microwave fast pyrolysis of waste tires: Effect of microwave power on product composition and quality. J Anal Appl Pyrolysis 155, 104979 (2021) and Simon et al. (Simon, D. et al. Microwave Devulcanization of Ground Tire Rubber and Its Improved Utilization in Natural Rubber Compounds. ACS Sustain Chem Eng (2023)).

[0103] The degradation of the tire particle under microwave irradiation was monitored using SEM (FIG. 8). Initially, the surface of the tire particle was smooth with no significant defects. After one minute, the particle surface became rough and non-uniform. Macropores and defects were seen after 2-3 minutes of microwave irradiation, consistent with the temperature profiles (FIG. 4), where pyrolysis conditions were reached by then. Lastly, the remaining pyrolyzed char formed a much finer powder than the original crumb rubber particles. The observed evolution of carbon black indicates that microwave irradiation can be absorbed uniformly by the tire particles.

[0104] The carbon black powders produced using different particle sizes displayed similar surface areas and characteristics. Raman spectroscopy (FIG. 9 & Table 1 ) suggested that the carbon black structure remained unaltered throughout the MW- pyrolysis reaction.

[0105] Table 1 : ID / IG Band Ratio from Raman Spectra

[0106] N2 physisorption analyses (FIG. 10) revealed that carbon black obtained from tires had a surface area and pore volume of 40-45 m2 / g and 0.35 cm3 / g, respectively. SEM images and XRF (FIG. 11 & Table 2) indicated significant sulfur, zinc, and other atoms were still present on the carbon surface.

[0107] Table 2: Mass % of Different Atoms on the Surface of Carbon Black obtained from Pyrolysis TGA-MS revealed very little organic impurities were present. Although the product was not fully enriched carbon black, several applications can utilize the recovered carbon black. Additionally, the conventional production of carbon black was tied to high greenhouse gas emissions, indicating alternative processes are critical.

[0108] The liquid pyrolysis oil product distribution and solid carbon black powder from the 1 .3 mm and 0.6 mm particles are independent of starting particle size (FIG. 12). However, GCMS of the oil product showed that 6PPD survived appreciably after pyrolysis. This demonstrated the recalcitrant nature of 6PPD under harsh pyrolysis conditions and suggests solvent extraction is necessary for its removal. The TGA curve of 6PPD showed a maximum degradation at about 300 °C and suggests that some 6PPD in the tires may sublime into the liquid product before the rubber degrades (FIG. 13). The liquid products (FIG. 14) are mostly benzene, toluene, and xylene (BTX)-derived chemicals and limonene; the latter forming via Diels-Alder cyclization of isoprene (monomer of natural rubber). Small quantities of larger fused aromatic compounds, such as indanes and naphthalene, were observed by GCMS. The lack of these compounds was due to the low power which dictates product formation in the liquid stream.

[0109] Decontamination of Waste Tires from 6PPD

[0110] Since pyrolysis is ineffective for 6PPD decontamination, use of microwave- assisted solvent extraction was investigated. All solvent extractions were conducted in batch mode to reveal the effects of time and temperature using methanol, a polar, common extraction solvent (FIG. 15) that is also a good microwave susceptor for converting electromagnetic energy into heat. As expected, the amount of 6PPD removed at 35 °C was less than at 50 °C, indicating high temperatures are more effective. At longer times, 6PPD in the organic solvent and the crumb rubber (solid) phase reached equilibrium, determined by the 6PPD solubility in methanol. Fresh methanol was needed to increase the extraction driving force. Indeed, “cycle” concentration profiles demarcated repeat extractions of the rubber crumb with fresh solvent and a significant drop in 6PPD concentration from the first to the second to the third cycle. The inset in FIG. 15 showed that ethanol, a similar solvent, was slightly better for extraction than methanol. The concentration profile of 6PPD in ethanol at 50 °C plateaued again at longer times (FIG. 16); multiple batches with fresh solvent can fully remove 6PPD from the waste tires. The extraction kinetics followed a 1st-order profile with the rate constant decreasing after each cycle with the model and data agreeing well. Interestingly, extraction removed 6PPD (typically 2 wt% in passenger vehicles) and other additives (quinolines, stearic acid, and palmitic acid) (FIG. 17 ), some unidentifiable due to proprietary compositions.

[0111] The extraction yield differences between ethanol and methanol suggested that organic solvents have different efficacy, and solvent screening was necessary. Common organic solvents under the same conditions (2 h, 60 °C) were compared (FIG. 18). Interestingly, the extraction efficiency of alcohols was practically identical, whereas that of ketones and esters varied. Smaller ketones, like acetone and butanone, had higher extraction efficiency than larger ketones, like methyl isobutyl ketone (MIBK) and 2-hexanone. Water contained no measurable 6PPD post-extraction. The varying extraction efficiency and the plateaus at longer times in extraction profiles underscored solubility as a key thermodynamic property. The multiscale COSMO-RS software can rapidly calculate solubility in thousands of solvents. This has been demonstrated for plastic waste separation / recycling and antioxidant extraction. A parity plot of the measured extraction efficiency vs. the calculated 6PPD solubility (FIG. 19) corroborates that the solubility is a crucial determinant of the solvent’s ability to remove 6PPD from waste rubber and confirmed that acetone an effective solvent while being inexpensive and non-toxic. Hildebrand solubility parameters were also investigated but did not show a well- defined trend (Table 3).

[0112] Table 3: COSMO Solubility of 6PPD in Tested Solvents and HSP Distances of 6PPD from each Solvent

[0113]

[0114] HSP values for 6PPD are dD = 18.8, dP = 4.1 , and dH = 6.3.

[0115] Acetone’s lower boiling point (56 °C) than 6PPD (260 °C) made solvent recovery much less energy intensive. While acetone can readily dissolve many classes of molecules, acetone did not degrade the cross-linked rubber phase. This is crucial for producing a 6PPD-free crumb rubber product that is safe for various applications. Similarly, solvent centrifugation separated polystyrene from rubber in high-impact polystyrene without compromising the materials.

[0116] The mass fraction of 6PPD and 6PPD-Q in relevant solvents is shown in Table 4. All values were calculated using COSMO-RS. Interestingly, across all solvents, the mass fraction for the quinone structure is several orders of magnitude lower than the parent structure. The mass fraction in water is meager and the significant drop in mass fraction from 6PPD to 6PPD-Q in hexane suggests the loss in aromaticity greatly reduces dissolution. Table 4: Mass Fractions of 6PPD and 6PPD-Q in Various Solvents

[0117] Calculated by COSMO-RS

[0118]

[0119] 6PPD-free crumb rubber is essential for re-introducing crumb rubber to municipal applications. Harmful chemicals in scrap tire pellets in turf fields and tire additives in urban runoff underscore an urgent need for additive removal from crumb rubber. A continuous-phase microwave heating setup was constructed to extract 6PPD rapidly and completely from a higher volume (20 g) of crumb rubber. The extraction setup involved a fixed bed filled with rubber (FIG. 20). Using 0.6 mm particles, time-dependent temperature profiles of the packed bed of crumb rubber under N2 flow were gathered and showed that higher temperatures were achieved with higher powers at the same location (at the center, r = 0, z = 0.22 m from the bottom), all of which eventually reached equilibrium (FIG. 21 ). At a given power, temperature gradients exist down the packed bed's length (FIG. 22). Similar temperature profiles have been observed in other tubular microwave systems. The axial temperature profile changed dynamically after turning the acetone flow on and eventually reached an equilibrium (FIG. 23). This was due to the excellent microwave-absorbing properties of acetone. Lastly, comparisons between MW and conventional heating (CH) indicated that MWs are more efficient at heating the crumb rubber (FIG. 24). CO2 emissions arising from the MW case were 0.26 g CC>2 / g tire whereas the CH case was 0.38 g CCh / g tire based on an emissions equivalent of 0.39 kg CO2 per kWh. Since MWs represent an electrified process, the emissions can be further driven down if the electricity is supplied by renewable sources.

[0120] Time-dependent extraction data for MW heating is shown in FIG. 25. Higher flow rates enhanced efficiency as the transport rate (external mass transfer) from the solid to the liquid increases. MW radiation also increased the extraction rate from the tire particle toward the surface, where the acetone removed the particle (FIG. 25). The dielectric constant of 6PPD was measured to be 1 .79, comparable to that of crumb rubber. Thus, the migration of 6PPD within the rubber particle was possibly due to rubber particle’s MW activity. This finding indicates that heat from MWs enhances the release rate of additives from the crumb rubber due to the heating of the solid rubber domains by solvent penetration and volumetric heating. After the extraction, the total mass loss from the crumb rubber bed was approximately 5 wt%. The removal capacity was 0.3 g crumb rubber / mL acetone based on concentration profiles and bed loadings. The relative nitrogen content also decreased (Table 5), further confirming additive removal.

[0121] Table 5: Weight % of C, H, N and S Atoms in the Starting Crumb Rubber and Solvent Extracted Crumb Rubber

[0122] Extraction from 1 .3 mm larger particles showed similar characteristics (FIG.

[0123] 25) but was slower than smaller particles (0.6 mm). This indicates intraparticle mass transfer limitations for solid-liquid extraction, consistent with the flow rate results. Lastly, fatty acids, palmitic and stearic acid, were also extracted upon heating. These are typically used as vulcanization accelerators during the rubbermaking process. MWs improve 6PPD extraction relative to ambient conditions and remove other additives during solvent extraction. The concentration profiles of each fatty acid (FIG. 25) paralleled those of 6PPD. Importantly, MWs removed 6PPD quickly (10 min) with no detectable 6PPD at the exit. This indicates complete decontamination of 6PPD from the crumb rubber, demonstrating MWs can electrify the removal of toxic chemicals. Likewise, when investigating the pyrolysis of fully decontaminated crumb rubber, 6PPD was not detected in the oil product, demonstrating solvent extraction before pyrolysis is necessary. Lastly, the solvent extraction did not affect the morphology of the carbon black.

[0124] Catalytic Upgrading of 6PPD

[0125] Upon isolation of 6PPD from waste rubber, a management strategy was investigated to prevent 6PPD’s re-introduction into the ecosystem. Catalytic destruction technologies remediate various contaminants, e.g., per- and polyfluoroalkyl substances, in drinking water. Thus, catalytic catalysis was investigated to determine if this process could convert 6PPD into safe, value-added products. A 5 wt% Pd / C catalyst (BET surface area = 940 m2 / g) was chosen due to its ability to catalyze hydrogenation readily. Hydroconversion was performed in batch at high hydrogen pressure and mild temperatures. TEM images of the catalyst showed metallic Pd particles of about 3.7 nm in diameter (FIG. 26) with a lattice spacing of 2.3 A. Post reaction characterization was done for understanding catalyst stability. FIG. 27 displayed XAS catalyst data before and after the reaction, indicating a change in the oxidation state consistent with a Pd (II) species in the spent Pd / C. The d-d spacing in the EXAFS region remained unchanged, consistent with TEM images. XPS corroborated the changes to Pd / C post-reaction. Overall, the reaction conditions altered the catalyst by reducing the carbon support while the Pd nanoparticles underwent partial and full oxidation with a small fraction of metallic Pd remaining.

[0126] Reaction condition optimization (FIG. 28) indicated that the reaction temperature and H2 pressure strongly affected the 6PPD conversion. This was consistent with the hydrogenation of aromatic compounds using metal-supported catalysts. Under semi-batch conditions, the hydrogen consumed increased with time (FIG. 31). The product distribution changed with time due to breaking of C-N bonds of the ring-hydrogenated 6PPD molecule. Pd catalyzed the hydrogenolysis of C-N bonds at milder conditions than other metals. A general reaction scheme for the hydroconversion of 6PPD is shown in FIG. 29. Higher temperatures and longer reaction times (185 °C, 2 h) produced smaller end products (FIG. 30). The primary pathway for 6PPD hydroconversion proceeded via initial aromatic ring hydrogenation followed by hydrogenolysis of the C-N bonds to produce two cyclohexylamine compounds. This is supported by the formation of 1a and 1 b at early reaction times and the ability of Pd / C to catalyze hydrogenation over hydrogenolysis. The detected end hydrocarbon and amine-based products, cyclohexylamine (3a), cyclohexane (5a), and triethylamine (5b), are platform chemicals with various industrial applications. The other pathway produced small quantities of dicyclohexylamine (4a) and dimethyl butylamine (4b).

[0127] Reactions were then performed with the extracted oil after separating the solvent acetone. Unlike the neat 6PPD, the real extract produced approximately 60% liquid (soluble in methanol) and 40% solid products. The only product made was 2,2,4-trimethyl-1 ,2,3,4-tetrahydroquinoline, a starting material for the synthesis of retinoids.

[0128] Techno-economic analysis

[0129] The economic feasibility of the exemplary process was evaluated. FIG. 31 depicts the process flowsheet incorporating microwave-assisted solvent-based extraction of 6PPD from crumb rubber, solvent recycling, hydro-conversion of 6PPD, and microwave-assisted pyrolysis of extracted crumb rubber. An adsorption / desorption unit was included to enhance the 6PPD purity prior to entering the reactor. 50% of the extracted crumb rubber from the extraction unit was sold, and 50% was fed to the pyrolysis unit. FIG. 32(a) shows the profitability index for identifying the minimum selling price of the extracted crumb rubber. The minimum selling price for a profitability index 1.03 is $1 ,2 / kg. The profitability index rises with increasing the selling price of the crumb rubber extracted. The total capital cost was $ 5,991 ,785 and the annual operating cost was $ 22,939, 100 at a throughput of 50,000 tons / year. FIG. 32(b) shows the distribution of costs along with the total raw material, product sales, and utility costs. A large fraction of the overall costs is associated with raw material costs and product sales.

[0130] Conclusions of Example 1

[0131] The elimination of 6PPD from newly produced and landfilled tires is necessary due to its harmful environmental effects and unintended consequences on human health. Example 1 demonstrated an effective approach for decontaminating 6PPD from waste tires using microwave-assisted heating. Computer-aided solubility calculations using COSMO-RS indicated the 6PPD solubility in various solvents is a key descriptor for the extraction capacity of 6PPD. A scaled-up, continuous-flow microwave-powered extraction setup can rapidly remove 6PPD and other additives from waste tires under acetone flow. 6PPD can be catalytically converted to value-added products, such as cyclohexylamine, using a conventional Pd / C catalyst under hydrogen pressure. The crumb rubber can then rapidly be pyrolyzed under MW irradiation to a pyrolysis oil of aromatic compounds and a solid carbon black phase. 6PPD emerged in the pyrolysis oil of the as- received crumb rubber, causing product contamination, but was absent in the solvent-extracted crumb rubber. These findings indicate that pyrolysis alone is not a standalone solution for6PPD decontamination and EOL tire upcycling, and solvent extraction is critical for isolating 6PPD. The full rubber degradation and carbon black recovery represent an exciting opportunity to recycle this material for new tires or other materials. Lastly, the exemplary process for 6PPD decontamination is economically feasible with a minimum selling price of $1 ,2 / kg of extracted crumb rubber.

[0132] It will be appreciated by those skilled in the art that the present disclosure can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the disclosure is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.

Claims

CLAIMS:1 . A method for decontaminating an end-of-life (EOL) tire feedstock containing N-(1 ,3-dimethyl butyl)-N'-phenyl-p-phenylenediamine (6PPD), the method comprising: obtaining the EOL tire feedstock; performing at least one microwave-assisted solvent extraction on the EOL tire feedstock to create a liquid phase containing 6PPD and a solid, decontaminated EOL tire feedstock, wherein the least one microwave-assisted solvent extraction uses an extraction solvent that possess a 6PPD solubility of at least 500 geppo / Lsoivent; and separating the liquid phase containing 6PPD from the decontaminated EOL tire feedstock.

2. The method of claim 1 , wherein the EOL tire feedstock contains one or more of carbon black, silica, processing aids, vulcanizing agents, activators, accelerators, tire coolants, sealants, natural rubber, synthetic rubber, corrosion inhibitors, steel wire, fabrics, fillers, antioxidants or antiozonants.

3. The method of claim 1 , wherein the EOL tire feedstock contains crumb rubber particles possessing a particle size ranging from about 100pm to 1 .0 cm.

4. The method of claim 1 , wherein the at least one microwave-assisted solvent extraction is conducted at a temperature of about 35°C to about 130°C.

5. The method of claim 1 , wherein the at least one microwave-assisted solvent extraction is performed at a power level ranging from about 40W to about 100W.

6. The method of claim 1 , wherein the at least one microwave-assisted solvent extraction is performed under an inert atmosphere.

7. The method of claim 1 , wherein the at least one microwave-assisted solvent extraction comprises: subjecting the EOL tire feedstock to a flow of extraction solvent at a rate of at least 2 mL / min.

8. The method of claim 1 , wherein the at least one microwave-assisted solvent extraction is performed for at least 30 seconds.

9. The method of claim 1 , wherein the extraction solvent is selected from the group consisting of carbonyls (ketones, aldehydes, esters), alcohols, hexanes, nitriles, ethers, esters, and combinations thereof.

10. The method of claim 1 , wherein the extraction solvent includes acetone.11 . The method of claim 1 , wherein the extraction solvent causes tire rubber in the EOL-tire feedstock to swell at a swelling degree of at least 20%.

12. The method of claim 1 , wherein the decontaminated EOL tire feedstock contains no detectable levels of 6PPD according to gas chromatography-mass spectrometry (GCMS).

13. The method of claim 1 , wherein the decontaminated EOL tire feedstock contains levels of 6PPD below a detection limit of a GCMS analytical method.

14. The method of claim 1 , wherein the liquid phase contains one or more fatty acids, processing aids, vulcanizing agents, activators, accelerators, tire coolants, sealants, corrosion inhibitors, antioxidants or antiozonants.

15. The method of claim 1 , comprising: subjecting the decontaminated EOL tire feedstock to a pyrolysis process.

16. The method of claim 1 , wherein the method is performed continuously.

17. The method of claim 1 , wherein the method is performed batch-wise.

18. A method for converting N-(1 ,3-dimethyl butyl)-N'-phenyl-p- phenylenediamine (6PPD) into commercially and / or industrially applicable products, the method comprising: subjecting 6PPD to a catalytic hydroconversion reaction in a presence of a metal-supported hydrogenation catalyst, wherein the catalytic hydroconversion reaction is performed under one or more of the following conditions:- a temperature ranging from about 130°C to about 200°C,- a H2 pressure ranging from about 30 to about 50 bar, or a time period ranging from about 30 minutes to about 3 hours.

19. The method of claim 18, wherein the catalytic hydroconversion reaction produces one or more of the following commercially and / or industrially applicable products: cyclohexylamine, cyclohexane, triethylamine, dicyclohexylamine, and / or dimethyl butylamine.

20. The method of claim 18, wherein the metal-supported hydrogenation catalyst is a 5 wt% Pd / C catalyst.21 . The method of claim 18, wherein the method produces 2, 2,4-trimethy I- 1 ,2,3,4-tetrahydroquinoline.

22. The method of claim 18, wherein the catalytic hydroconversion reaction is performed at a weight ratio of 6PPD to the metal-supported hydrogenation catalyst of 1 : 0.02.

23. A system for decontaminating an end-of-life (EOL) tire feedstock containing N-(1 ,3-dimethyl butyl)-N'-phenyl-p-phenylenediamine (6PPD), the system comprising:a microwave extractor in communication with an extraction solvent mixer, wherein the microwave extractor possesses a EOL-tire feedstock import line, an extraction solvent import line, an extraction solvent export line, and a decontaminated EOL-tire feedstock export line.

24. The system of claim 23, wherein the extraction solvent export line is in communication with a separation unit configured to separate an extraction solvent from any additives contained in a EOL-tire feedstock.

25. The system of claim 24, wherein the separation unit possesses a purified extraction solvent export line and an additive export line, the purified extraction solvent export line being in communication with a recycled extraction solvent unit and the additive export line being in communication with an additive purification unit.

26. The system of claim 25, wherein the additive purification unit possesses a 6PPD export line in communication with a hydroconversion reactor containing a hydrogen gas import line and a hydroconversion product export line.

27. The system of claim 25, wherein the recycled extraction solvent unit possesses a recycled extraction solvent export line in communication with the extraction solvent mixer, and a waste export line.

28. The system of claim 23, wherein the decontaminated EOL-tire feedstock export is in communication with a microwave pyrolysis reactor containing a pyrolysis oil export line and a carbon black export line.

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