Method for preparing high-quality tire oil by catalytic cracking of waste and old tires

Abstract

This invention discloses a method for preparing high-quality tire oil through catalytic pyrolysis of waste tires. The method uses a eutectic solvent formed by choline chloride and ferric chloride hexahydrate as a low-temperature phase change medium, which functions as a heat carrier, swelling agent, catalyst, and sulfur capture agent. Waste tire rubber powder is mixed with this medium, and a low-temperature swelling and pyrolysis desulfurization reaction is carried out under an inert atmosphere. The Lewis acidity of iron ions in the medium preferentially breaks the C-S and S-S bonds in the rubber crosslinking bonds. The sulfur-containing active species generated by the breakage are captured in situ as inorganic sulfides and retained in the liquid phase. The escaped oil vapor is condensed to directly obtain ultra-low sulfur, light-colored, transparent, high-quality tire oil. The used medium can be oxidized and regenerated by introducing air under heating conditions, and the sulfur is recovered in the form of elemental sulfur, allowing the medium to be recycled. This invention achieves synergistic unity of low-temperature pyrolysis and deep desulfurization at the source, with a simple process flow that is economical and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of waste rubber resource utilization technology, specifically to a method for preparing high-quality tire oil by catalytic cracking of waste tires. Background Technology

[0002] Thermochemical cracking of waste tires is a recognized method for recovering carbon black, fuel oil and steel resources. However, traditional thermochemical cracking is usually carried out at high temperatures of 400-500℃, and the resulting tire oil generally has the following prominent problems: (1) The sulfur content is as high as 0.8-1.5wt%, containing a large amount of malodorous organic sulfur compounds such as thiophene and mercaptans, which will cause serious pollution when burned; (2) The content of gum and olefins is high, the oil is black in color, has poor chemical stability, and is very easy to oxidize and deteriorate during storage and heating; (3) High temperature cracking easily leads to excessive cracking of hydrocarbons into non-condensable gases, reducing the yield of liquid oil and causing serious coking of equipment.

[0003] To improve oil quality, existing technologies often employ end-of-pipe desulfurization methods such as hydrorefining or acid-base washing to further treat the cracked oil and gas. However, these post-processing techniques suffer from drawbacks such as high investment costs, high operating costs, limited hydrogen sources, and difficulty in completely removing oil-soluble macromolecular sulfides. There are also reports of using solid acid catalysts for catalytic cracking and upgrading, but these catalysts are prone to rapid deactivation at high temperatures due to coking and sulfur poisoning, and frequent regeneration increases process complexity. Therefore, there is an urgent need for a process that can effectively control sulfur at the cracking source, directly produce high-quality tire oil, and is economical and recyclable. Summary of the Invention

[0004] (a) Technical problems to be solved The purpose of this invention is to provide a method for preparing high-quality tire oil by catalytic cracking of waste tires, so as to solve the prominent problems of high energy consumption, poor product oil quality, high sulfur content and unsustainable use of catalytic media in the above-mentioned prior art.

[0005] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A method for preparing high-quality tire oil by catalytic cracking of waste tires includes the following steps: S1. Waste tires are processed by removing steel wires, crushing and separating them to obtain rubber powder; S2. Prepare a low-temperature phase change medium, wherein the low-temperature phase change medium is a eutectic solvent formed by choline chloride and ferric chloride hexahydrate in a molar ratio of 1:2. S3. Mix the rubber powder from step S1 with the low-temperature phase change medium from step S2 at a mass ratio of 1:5 to 1:8, place it in an inert atmosphere, and heat it to 200 to 240°C under stirring to carry out a pyrolysis and desulfurization reaction, so that the oil and gas generated by the pyrolysis of the rubber can escape, and at the same time, the sulfur element in the rubber is captured in situ by the iron ions in the low-temperature phase change medium to generate inorganic sulfides and remain in the liquid phase medium. S4. The oil and gas that escaped in step S3 are condensed and collected to obtain tire oil; after the reaction is completed, the remaining materials are separated into solid and liquid phases to obtain solid carbon black and low-temperature phase change medium after use. S5. The used low-temperature phase change medium obtained in step S4 is oxidized and regenerated by passing oxygen-containing gas under heating conditions, so that the inorganic sulfides captured in the medium are converted into elemental sulfur and recovered. At the same time, the reduced iron components are re-oxidized into ferric iron to obtain the regenerated low-temperature phase change medium, which is then returned to step S3 for recycling.

[0006] In a preferred embodiment of the present invention, in step S2, the preparation process of the low-temperature phase change medium is as follows: choline chloride and ferric chloride hexahydrate are mixed in a specific ratio and stirred for 1-2 hours at 80-90°C under nitrogen protection to form a homogeneous liquid. This medium can solidify into a solid state at room temperature, facilitating storage and feeding. It exhibits a low-viscosity liquid state within the reaction temperature range and demonstrates good heat and mass transfer performance.

[0007] In a preferred embodiment of the present invention, in step S3, the heating procedure is as follows: first, the material is heated to 150°C and held at that temperature for 15–30 minutes to allow for swelling, and then the temperature is raised to 200–240°C to carry out the pyrolysis and desulfurization reaction. The swelling step allows the medium to fully impregnate the rubber powder, and the vulcanization crosslinking network is efficiently activated in a polar environment, creating conditions for subsequent precise desulfurization.

[0008] In a preferred embodiment of the present invention, in step S3, the inert atmosphere is a nitrogen atmosphere, and the reaction is carried out under a slight positive pressure of 0.01 to 0.05 MPa to prevent air from entering and to facilitate the smooth extraction of oil and gas.

[0009] In a preferred embodiment of the present invention, the pyrolysis desulfurization reaction in step S3 takes 1.5 to 3 hours. Within this time range, the rubber conversion rate can reach over 95%, while simultaneously obtaining a liquid oil with extremely low sulfur content.

[0010] In a preferred embodiment of the present invention, in step S5, the conditions for oxidation regeneration are: air is introduced at 80-90°C, and the reaction is carried out for 3-4 hours. During the regeneration process, the reduced ferrous ions in the medium are re-oxidized to ferric active components, while the captured sulfur precipitates as elemental sulfur powder. After filtration and separation, the sulfur can be recovered, and the activity of the medium is fully restored.

[0011] The tire oil produced by the above method has a total sulfur content of less than 0.1 wt%, a light yellow and transparent appearance, a gum content of less than 15 mg / 100mL, and a kinematic viscosity (40℃) of approximately 1.9–2.5 cSt. The diesel fraction (180–360℃) accounts for about 65% of the oil. This oil can be used directly as a high-quality fuel oil or further processed into a chemical raw material.

[0012] The present invention also claims protection for a high-quality tire oil, which is prepared by any of the methods described above.

[0013] (III) Beneficial Effects The present invention aims to provide a method for preparing high-quality tire oil by catalytic cracking of waste tires, which has the following beneficial effects: The pyrolysis temperature is significantly reduced from the traditional 400-500℃ to 200-240℃, which significantly reduces energy consumption, reduces equipment coking, inhibits excessive generation of non-condensable gases, and improves liquid oil yield.

[0014] The unique in-situ sulfur capture mechanism utilizes the high polarity of the low-temperature phase change medium and the Lewis acidity of iron ions to preferentially break the CS and SS bonds in the rubber crosslinking at a lower temperature. The sulfur-containing active species generated at the moment of breakage are captured by Fe³⁺ in the medium and converted into stable inorganic FeS, which is firmly locked in the liquid phase. This eliminates the generation of sulfur-containing gases and organic sulfides at the source, and the resulting tire oil is an ultra-low sulfur clean product as soon as it condenses, eliminating the need for costly hydrodesulfurization and other subsequent treatments.

[0015] Catalyst regeneration and sulfur recovery in elemental form can be achieved simultaneously through air oxidation, with no significant decrease in activity even after more than 15 cycles. The entire process forms a closed loop for sulfur, resulting in no secondary pollution and extremely high atom economy.

[0016] The tire oil obtained by this invention has fundamental differences in appearance, odor, and main indicators compared with the tire oil obtained by conventional high-temperature pyrolysis, and has the technical conditions to be used directly as a high-quality fuel oil or chemical raw material. Attached Figure Description

[0017] Figure 1 This is an overall process flow diagram of the method for preparing high-quality tire oil by catalytic cracking of waste tires according to the present invention. Detailed Implementation

[0018] The following will refer to the appendix in the examples of this invention. Figure 1The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] S1. Raw material pretreatment Waste radial tires are collected, and the bead wires are extracted using a hydraulic wire extractor. The tire carcass, after the bead wires have been removed, is initially crushed into 50–80 mm pieces using a twin-shaft shredder, and then further pulverized in a fine crusher. The pulverized material is then sequentially passed through a magnetic separator to remove wire debris and an air separator to remove fiber fluff, finally sieved to obtain rubber powder with a particle size of 0.5–3.0 mm. The obtained rubber powder is dried at 105°C for 2–4 hours, controlling the moisture content to be below 1.5 wt%, and then sealed for later use.

[0020] Preferably, the particle size of the rubber powder is controlled to be 1.0 to 2.0 mm. This range can ensure sufficient contact with the medium and avoid difficulties in subsequent solid-liquid separation caused by excessively fine powder.

[0021] S2, Preparation of low-temperature phase change media The low-temperature phase change medium used in this invention is a eutectic solvent (DES), which is prepared by using choline chloride (ChCl) as a hydrogen bond acceptor and ferric chloride hexahydrate (FeCl3·6H2O) as a hydrogen bond donor, with the two being prepared in a molar ratio of 1:2.

[0022] The specific preparation process is as follows: Weigh the calculated amounts of choline chloride and ferric chloride hexahydrate, and add them to a glass or stainless steel mixing vessel equipped with a mechanical stirrer, thermometer, and nitrogen inlet / outlet. Start the stirrer at 80–120 rpm, while simultaneously introducing nitrogen to isolate it from air. Heat the mixture to 80–90°C (preferably 85°C) and continue stirring at this temperature for 1–2 hours. The two solid raw materials gradually interact, transforming from an initial heterogeneous mixture into a dark brown, homogeneous, and transparent liquid, thus obtaining the target eutectic solvent.

[0023] After preparation, the medium can be transferred to a storage tank or mold while still hot. Upon cooling to room temperature, it solidifies into a soft, dark brown solid, facilitating storage, transportation, and metered feeding. In subsequent use, it can be remelted into a low-viscosity liquid by heating to above 60°C.

[0024] The low-temperature phase change medium of this invention integrates four functions into one: (1) As a heat carrier, it efficiently transfers heat to rubber particles; (2) As a swelling agent, its high polarity allows the rubber macromolecular chains to fully expand and weaken the cross-linking network; (3) As a catalyst, it selectively activates and breaks CS and SS bonds with the Lewis acidity of Fe³⁺; (4) As a sulfur capture agent, it will combine with sulfur free radicals at the moment of fracture to generate stable inorganic sulfides, preventing them from entering the oil.

[0025] S3, pyrolysis and desulfurization reaction The rubber powder prepared in step S1 and the low-temperature phase change medium prepared in step S2 are added to a vertical stirred reactor at a mass ratio of 1:5 to 1:8 (preferably 1:6). The reactor is equipped with a nitrogen purging system, a mechanical stirring device (anchor or paddle type), an external heating jacket, and a top gas phase outlet pipeline.

[0026] After feeding is completed, the reactor is sealed, and the air inside the reactor is repeatedly replaced with nitrogen three times to maintain a slightly positive nitrogen environment of 0.01–0.05 MPa (preferably 0.02 MPa). The purpose of replacement is to remove oxygen and prevent unnecessary hydrolysis of iron ions in the medium or oxidation of organic matter at high temperatures.

[0027] The heating process is divided into two stages: The first stage is the swelling stage: The material in the reactor is heated to 150°C at a stirring speed of 60–120 rpm and held at this temperature for 15–30 minutes (preferably 20 minutes). At this temperature, the medium is completely in a low-viscosity liquid state, and the rubber powder fully swells and expands within it. During this process, the high polarity and hydrogen bond network of the medium strongly interact with the CS and SS bonds in the rubber vulcanization crosslinking network, effectively activating and weakening these polar crosslinking bonds, thus preparing for subsequent selective cleavage.

[0028] The second stage is the cracking and desulfurization reaction stage: the temperature is further increased to 200-240℃ (preferably 220℃), and the reaction is maintained at this temperature for 1.5-3 hours (preferably 2 hours). During this stage: The activated and weakened CS and SS bonds break preferentially over the CC backbone, and the crosslinking network of the rubber is broken. The rubber backbone is then catalytically degraded into smaller hydrocarbon vapor molecules, which escape from the liquid medium into the gas phase. The sulfur-containing reactive species (including sulfur free radicals, HS⁻, etc.) generated at the moment of cross-linking bond breakage have not yet had time to recombine with hydrocarbon free radicals. They are instantly captured by the surrounding high concentration of [FeCl4]⁻ complexed anions and free Fe³⁺ through coordination and redox reactions, and transformed into stable inorganic ferrous sulfide (FeS), which is firmly locked in the liquid medium.

[0029] The oil and gas are discharged from the gas phase outlet at the top of the reactor. They first pass through a cyclone separator to remove any trace amounts of carbon black dust that may be entrained, and then sequentially enter a three-stage condensation system: a first-stage indirect water cooling (condensation temperature approximately 25–30°C), a second-stage indirect air cooling (condensation temperature approximately 5–10°C), and a third-stage cryogenic cooling (condensation temperature approximately -5–0°C). The liquids obtained from the three-stage condensation are combined to form crude tire oil, which can be collected and used directly. A small amount of non-condensable gases (mainly methane, ethane, and other low-carbon hydrocarbons) are washed with alkaline solution and then sent to the burner as a supplementary heat source for the reaction system.

[0030] After the reaction reaches the preset time, heating is stopped, stirring is continued, and nitrogen gas is introduced to assist in cooling. When the temperature inside the vessel drops to 80-100℃, solid-liquid separation is prepared.

[0031] S4, Product Separation After the reaction in step S3 is completed and the mixture is cooled, the material in the reactor (which is a black paste or slurry mixture) is subjected to solid-liquid separation. The separation method can be hot vacuum filtration, pressure filtration, or horizontal centrifuge separation, with hot pressure filtration being preferred to balance separation efficiency and ease of operation.

[0032] The resulting filtrate is the used low-temperature phase change medium, which is dark brown-black in color and contains dissolved and finely suspended ferrous sulfide, as well as some ferrous species (Fe²⁺) that were reduced during the reaction. This filtrate is then transferred to the regeneration process.

[0033] The resulting filter cake mainly consists of recovered carbon black, mixed with a small amount of residual media and trace amounts of incompletely pyrolyzed rubber particles. The filter cake is washed several times with anhydrous ethanol or deionized water at a concentration equivalent to 2-3 times its mass. The washing liquid is collected and the ethanol is recovered through simple distillation for recycling. The distillation residue concentrate is combined with the filtrate and sent to the regeneration process. The washed filter cake is dried at 105°C to constant weight to obtain the recovered carbon black product, whose iodine absorption value, oil absorption value, and other indicators meet the recycling standards for rubber-grade carbon black.

[0034] The liquid collected by the three-stage condensation system in step S3 is the high-quality tire oil of the present invention. It can be used directly as the final product, or the fractions can be purified by simple adsorption (such as by short-range adsorption filtration with activated clay or activated carbon) to obtain a nearly colorless premium product.

[0035] S5, Media Regeneration and Sulfur Recovery The used low-temperature phase change medium (filtrate, possibly mixed with washing liquid concentrate) obtained in step S4 is transferred to the regeneration reactor. The regeneration reactor is equipped with a heating jacket, a stirring device, a bottom gas distributor, and an exhaust port.

[0036] At a stirring speed of 150 rpm, the medium is heated to 80–90°C. Oxygen-containing gas, preferably air, is introduced from the bottom through a gas distributor. The gas flow rate is measured as 0.2–0.5 vvm (volume of gas introduced per minute per volume of liquid) of the liquid phase. The reaction is carried out at this temperature for 3–4 hours.

[0037] The main reactions that occur during the oxidative regeneration process are: The ferrous ions (Fe²⁺) generated during the pyrolysis stage in the medium are re-oxidized into highly active ferric ions (Fe³⁺), and the catalytically active components are fully restored.

[0038] The ferrous sulfide (FeS) locked in the medium reacts with oxygen in the acidic DES system and is oxidized into high-purity elemental sulfur (rhombic sulfur) that is insoluble in the system, and gradually precipitates out from the liquid medium in the form of a pale yellow powder.

[0039] The reaction system gradually returns from a deep brownish-black color to the initial deep brown of freshly prepared DES, while the formation and suspension of a pale yellow solid powder can be observed. After the oxidation reaction is complete, the material is centrifuged or filtered under reduced pressure, and the collected solid phase is elemental sulfur product with a purity of over 99%. The resulting liquid phase is the completely regenerated low-temperature phase change medium. After sampling and testing its Fe³⁺ content and acidity, a small amount of fresh DES is added as needed to compensate for minor mechanical losses during operation. The system can then be directly returned to step S3 for the next batch of waste tires in the pyrolysis and desulfurization cycle.

[0040] This regeneration process can be completed at low temperature (80-90℃) and normal pressure, without the need for high-temperature roasting or complex chemical treatment, and is highly economical and environmentally friendly. Specific Implementation The following specific embodiments further illustrate the implementation process and effects of the present invention.

[0042] Example 1 (1) Take waste steel radial tires and pretreat them according to the above method to obtain 300 g of rubber powder with a particle size of 1.0-2.0 mm and a moisture content of 1.2 wt%.

[0043] (2) Weigh 139.6 g (1 mol) of choline chloride and 540.6 g (2 mol) of ferric chloride hexahydrate, and stir at 85°C under nitrogen protection for 1.5 hours to obtain a dark brown homogeneous DES low-temperature phase change medium. Cool and solidify.

[0044] (3) Add 300 g of rubber powder and 1800 g of solidified DES medium (mass ratio 1:6) into a 5 L stirred reactor, seal, purge with nitrogen three times, and maintain a slight positive pressure of 0.02 MPa. Start stirring at 80 rpm, raise the temperature to 150℃ and hold for 20 minutes to allow swelling; continue to raise the temperature to 220℃ and hold for 2 hours. The generated oil and gas are collected by three-stage condensation to obtain tire oil. The non-condensable gas is washed with alkali and then burned for heating.

[0045] (4) After the reaction is complete, the temperature is lowered to 90°C, and the remaining material is subjected to pressurized hot filtration. The filter cake is washed twice with 200 mL of anhydrous ethanol and then dried to obtain recovered carbon black. The filtrate is transferred to the regeneration reactor.

[0046] (5) The filtrate was stirred and reacted with air at 0.3 vvm at 85°C for 3.5 hours. The light yellow elemental sulfur powder separated by centrifugation was the liquid phase, which is the regenerated DES medium.

[0047] (6) Results of this embodiment: 138 g of tire oil was collected, with a yield of 46.0 wt% (relative to the mass of rubber powder). The oil was light yellow and transparent in appearance, with a total sulfur content of 0.05 wt%, a rubber content of 8 mg / 100 mL, a kinematic viscosity of 2.1 cSt at 40℃, and a diesel fraction (180~360℃) accounting for 67%. 159 g of carbon black was recovered, with an iodine adsorption value of 78 g / kg. The purity of the recovered elemental sulfur was 99.2%.

[0048] Example 2 The procedure was the same as in Example 1, except that the amount of rubber powder was kept at 300 g, and the amount of DES medium was adjusted to 1500 g, i.e., a mass ratio of 1:5. The pyrolysis temperature was 220°C, and the reaction time was 2 hours.

[0049] Results: 141 g of tire oil was collected, with a yield of 47.0 wt%. The oil was light yellow and transparent, with a total sulfur content of 0.07 wt% and a gum content of 11 mg / 100 mL. The medium was recycled after oxidation regeneration, and its activity did not decrease. This example demonstrates that sufficient desulfurization can still be achieved at a mass ratio of 1:5, which is beneficial for reducing the amount of medium added at one time.

[0050] Example 3 The operation is the same as in Example 1, except that the pyrolysis desulfurization temperature is set to 200°C and the reaction time is extended to 3 hours.

[0051] Results: The rubber conversion rate was approximately 93%, and 132 g of tire oil was collected, with a yield of 44.0 wt%. The oil was light yellow and transparent, with a total sulfur content of 0.06 wt% and a rubber content of 9 mg / 100 mL. The amount of non-condensable gas generated was reduced by approximately 15% compared to Example 1. This example demonstrates that the method of the present invention can still be carried out smoothly at extremely low temperatures of 200°C, and that the liquid oil has higher selectivity.

[0052] Example 4 Following the procedure in Example 1, the same batch of DES low-temperature phase change medium underwent repeated cycles of pyrolysis desulfurization, solid-liquid separation, oxidation regeneration, and return to pyrolysis, for a total of 20 cycles. Key indicators of the tire oil were sampled and analyzed at the 5th, 10th, 15th, and 20th cycles, and the results are shown in Table 1.

[0053] Table 1. Effect of media circulation number on tire oil quality As shown in Table 1, after 20 consecutive cycles of the medium, the total sulfur content of the obtained tire oil remained stable at less than 0.10 wt%, and the oil remained transparent. There was no sudden increase in sulfur content or blackening and deterioration of the oil, indicating that the low-temperature phase change medium of the present invention has excellent cycle stability and long-lasting desulfurization activity.

[0054] Several comparative examples are provided below to highlight the technical advantages of the present invention.

[0055] Comparative Example 1: Using a conventional horizontal pyrolysis furnace, 300 g of pretreated rubber powder of the same specifications was heated to 450°C under nitrogen protection and pyrolyzed for 2 hours. The resulting oil and gas were condensed to obtain tire oil. This tire oil was opaque brownish-black in appearance and had a strong, foul odor. Testing revealed: total sulfur content 1.28 wt%, rubber content 215 mg / 100mL, kinematic viscosity (40°C) 3.6 cSt, and diesel fraction only 40%. Compared with all the above examples, the product quality showed a fundamental difference.

[0056] Comparative Example 2: The procedure was the same as in Example 1, but the low-temperature phase change medium was replaced with pure choline chloride. After reacting at 220°C for 2 hours, the rubber powder showed only limited swelling, with almost no oil or gas generation. This comparative example demonstrates that without the Lewis acid catalytic effect of Fe³⁺, effective rubber pyrolysis cannot be achieved at 220°C alone. This indicates that the acidic catalytic function of FeCl₃ in the DES is indispensable, and only a combination of both can achieve the low-temperature, high-efficiency pyrolysis of this invention.

[0057] Comparative Example 3: The procedure was the same as in Example 1, but in step S3, the material was directly heated to 220°C for pyrolysis and desulfurization without swelling at 150°C, and the reaction time was 2 hours. Although the pyrolysis reaction still occurred, the liquid oil yield decreased by approximately 8 percentage points, the resulting tire oil was slightly darker in color, the total sulfur content increased to 0.15 wt%, and the rubber content increased to 25 mg / 100mL. These results indicate that swelling pretreatment can effectively activate rubber crosslinking bonds and promote the preferential breakage of subsequent highly selective CS bonds. The absence of this step affects desulfurization selectivity and oil quality.

[0058] In summary, the technical solution of this invention, through the ingenious design of a low-temperature phase change medium and a multi-stage temperature control program, achieves the synergistic unity of low-temperature, high-efficiency pyrolysis of waste tires and deep desulfurization at the source, directly producing ultra-low sulfur, light-colored, transparent, high-quality tire oil that is difficult to achieve with traditional processes. This method is simple, the medium can be recycled for a long time, sulfur is recovered in the form of elemental sulfur, it is environmentally friendly, and has good prospects for industrial application.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-quality tire oil by catalytic cracking of waste tires, characterized in that, Includes the following steps: S1. Waste tires are processed by removing steel wires, crushing and separating them to obtain rubber powder; S2. Prepare a low-temperature phase change medium, wherein the low-temperature phase change medium is a eutectic solvent formed by choline chloride and ferric chloride hexahydrate in a molar ratio of 1:

2. S3. Mix the rubber powder from step S1 with the low-temperature phase change medium from step S2 at a mass ratio of 1:5 to 1:8, place it in an inert atmosphere, and heat it to 200 to 240°C under stirring to carry out a pyrolysis and desulfurization reaction, so that the oil and gas generated by the pyrolysis of the rubber can escape, and at the same time, the sulfur element in the rubber is captured in situ by the iron ions in the low-temperature phase change medium to generate inorganic sulfides and remain in the liquid phase medium. S4. The oil and gas that escaped in step S3 are condensed and collected to obtain tire oil; after the reaction is completed, the remaining materials are separated into solid and liquid phases to obtain solid carbon black and low-temperature phase change medium after use. S5. The used low-temperature phase change medium obtained in step S4 is oxidized and regenerated by passing oxygen-containing gas under heating conditions, so that the inorganic sulfides captured in the medium are converted into elemental sulfur and recovered. At the same time, the reduced iron components are re-oxidized into ferric iron to obtain the regenerated low-temperature phase change medium, which is then returned to step S3 for recycling.

2. The method according to claim 1, characterized in that, In step S2, the preparation process of the low-temperature phase change medium is as follows: choline chloride and ferric chloride hexahydrate are mixed in a certain proportion and stirred for 1 to 2 hours under nitrogen protection at 80 to 90°C to form a homogeneous liquid.

3. The method according to claim 1, characterized in that, In step S3, the heating procedure is as follows: first, the material is heated to 150°C and kept at that temperature for 15 to 30 minutes to allow it to swell, and then the temperature is raised to 200 to 240°C to carry out the pyrolysis and desulfurization reaction.

4. The method according to claim 1, characterized in that, In step S3, the inert atmosphere is a nitrogen atmosphere, and the reaction is carried out under a slight positive pressure of 0.01 to 0.05 MPa.

5. The method according to claim 1, characterized in that, In step S3, the cracking and desulfurization reaction takes 1.5 to 3 hours.

6. The method according to claim 1, characterized in that, In step S5, the conditions for oxidation regeneration are: air is introduced at 80-90°C, and the reaction is carried out for 3-4 hours.

7. The method according to any one of claims 1 to 6, characterized in that, In step S4, the total sulfur content of the collected tire oil is less than 0.1 wt%, and its appearance is light yellow and transparent.

8. A high-quality tire oil, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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