Method for preparing high-purity carbon powder by step-by-step pyrolysis of waste tires
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-10
- Publication Date
- 2026-08-11
AI Technical Summary
[0028]1. The closed-loop pressure-controlled vacuum drying pretreatment process can isolate external moisture and dust, prevent secondary pollution of materials, and efficiently remove adsorbed water, residual oil and light volatiles from the surface of the rubber powder under constant temperature conditions. The volatile gas is discharged in time to avoid the backflow and residue of impurities. It can achieve deep purification of rubber powder, reduce oil and gas separation pressure, prevent carbon powder pores from being blocked by impurities, and ensure the purity and pore regularity of the finished carbon powder from the raw material end.
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Abstract
Description
Technical Field
[0001] This application relates to the technical field of carbon powder preparation, and in particular to a method for preparing high-purity carbon powder by cascade pyrolysis of waste tires. Background Technology
[0002] With the rapid development of the transportation industry, the annual output of waste tires continues to rise. Pyrolysis resource utilization technology is currently the mainstream technology for the harmless, reduced-volume, and high-value utilization of waste tires. It can decompose the rubber polymers of waste tires into three types of products under an inert atmosphere: pyrolysis oil, pyrolysis gas, and pyrolysis carbon powder. Among them, pyrolysis carbon powder has the highest added value and can be widely used in rubber reinforcement, conductive materials, adsorption materials, and other fields. However, the existing technology for preparing carbon powder from waste tire pyrolysis still has many shortcomings.
[0003] First, the existing tire raw material pretreatment drying process is crude, mostly adopting an open constant temperature drying mode. During the drying process, external moisture and dust can easily enter the equipment, causing secondary pollution of the materials. At the same time, the adsorbed water, residual oil and light volatiles inside the rubber powder cannot be completely discharged. The residual volatile impurities will continue to precipitate during the subsequent pyrolysis process, resulting in mixed components of pyrolysis flue gas. This not only increases the pressure of subsequent oil-gas separation, but also easily forms impurities in the pores of the carbon powder, reducing the purity of the finished carbon powder product.
[0004] Secondly, the current common practice of using a single-stage simple condensation method to treat pyrolysis oil and gas flue gas makes it impossible to achieve graded separation based on the boiling point differences of oil and gas components. High-boiling-point heavy oil, medium-boiling-point medium oil, and light oil and gas are mixed during condensation, which easily leads to component adhesion and incomplete condensation. This not only significantly reduces the recovery purity and utilization value of pyrolysis oil and gas, but also causes trace amounts of condensable volatiles that are not completely condensed to be emitted with the flue gas, resulting in resource waste and air pollution.
[0005] In addition, traditional carbon powder impurity removal mostly adopts a single acid washing process. Single acid washing can only remove some surface metal impurities and cannot remove the bound sulfur impurities and stable inorganic salts embedded in the carbon powder lattice. At the same time, the existing impurity removal process is mostly a static soaking reaction, which results in uneven contact between the material and the solution, low mass transfer efficiency, and easy problems such as local impurity residue and uneven impurity removal.
[0006] Application content
[0007] This application aims to address, at least to some extent, the technical problems in the related art.
[0008] To achieve the above objectives, this application proposes a method for preparing high-purity carbon powder by cascade pyrolysis of waste tires, comprising the following steps:
[0009] S1. After removing steel wires and fiber accessories from waste tires, crush them and sieve them to obtain 80-120 mesh tire rubber powder. Place the rubber powder in a vacuum drying oven and dry it for 2-4 hours to remove adsorbed water and light volatile impurities from the surface of the rubber powder to obtain dried tire rubber powder.
[0010] S2. The dried tire rubber powder is fed into a closed inert atmosphere pyrolysis furnace. High-purity nitrogen is introduced throughout the process to maintain the oxygen content in the furnace at ≤0.5%. The three-stage gradient pyrolysis of low temperature impurity removal, medium temperature pyrolysis and high temperature reconstruction is completed in sequence.
[0011] The first stage of low-temperature impurity removal: heat up to 220-280℃, keep at a constant temperature for 30-60 minutes, and directionally remove residual oils, additives, and small molecule organic impurities from the adhesive powder;
[0012] The second stage of medium-temperature deep pyrolysis: the temperature is increased to 450-520℃ at a rate of 3-5℃ / min and held at a constant temperature for 60-90min to fully break and pyrolyze the polymer chains of tire rubber, thereby separating the carbon skeleton from the oil and gas components and obtaining pyrolysis carbon slag.
[0013] The third stage is high-temperature lattice reconstruction: the temperature is increased to 650-720℃ at a rate of 2-4℃ / min, and held at a constant temperature for 40-70min to repair the lattice defects of the carbon matrix, regulate the microstructure of carbon powder, and decompose the organic impurities bound to the carbon slag surface, thus initially reducing the ash and sulfur content.
[0014] S3. The oil and gas flue gas generated during the pyrolysis process are treated by staged condensation to separate and recover the pyrolysis oil and pyrolysis gas.
[0015] S4. Cool the pyrolysis solid carbon slag to room temperature, and then use dilute acid washing, deionized water rinsing, weak alkali desulfurization, and pure water repeated rinsing processes to remove metal ash, sulfides, and inorganic salt impurities from the carbon slag until the pH value of the filtrate after rinsing is 6.5-7.5.
[0016] S5. Place the purified carbon powder filter cake in an inert atmosphere drying furnace and dry it at 150-200℃ under nitrogen protection for 3-5 hours. Then grind it at low speed and sieve it through a 150-200 mesh screen to remove agglomerated particles and obtain high-purity carbon powder.
[0017] In addition, the application may also include the following additional technical features:
[0018] Specifically, in the three-stage isothermal pyrolysis process of step S2, the heating rate decreases step by step, with rapid impurity removal in the low-temperature stage, uniform pyrolysis in the medium-temperature stage, and slow lattice reconstruction in the high-temperature stage.
[0019] Specifically, the multi-stage wet purification process in step S4 is as follows: rinsing and soaking in 3%-5% dilute hydrochloric acid for 20-30 minutes to remove metallic ash such as iron, zinc, and calcium; then soaking in 2%-4% sodium bicarbonate weak alkaline solution for 15-25 minutes to directionally remove sulfur impurities bound to carbon powder; and finally rinsing with deionized water 3-5 times.
[0020] Specifically, in step S1, the vacuum drying oven is sealed and pressure controlled throughout the process, and the drying temperature is kept constant at 80-100℃. During the drying process, a small amount of exhaust is performed every 30 minutes to release volatile gases.
[0021] Specifically, in step S2, the high-purity nitrogen gas is introduced in a manner that involves uniform gas distribution at the bottom and uniform exhaust at the top, with the continuous nitrogen gas flow rate being stably controlled at 8-15 L / min throughout the process.
[0022] Specifically, in step S2, the precise temperature control and heating endpoint of the first stage of low-temperature impurity removal is 240-260℃, the constant temperature and stable holding time is 40-50min, and the temperature fluctuation error during the heating process is ≤±3℃.
[0023] Specifically, in step S2, the fixed heating rate of the second stage of medium-temperature deep pyrolysis is 4℃ / min, the precise heating endpoint is 480-500℃, the constant temperature holding time is 70-80min, and the furnace temperature does not fluctuate during the holding stage.
[0024] Specifically, in step S2, the fixed heating rate for the third stage of high-temperature lattice reconstruction is 3℃ / min, the precise heating endpoint is 680-700℃, the constant temperature holding time is 50-60min, and the furnace pressure remains constant during the high-temperature reconstruction stage.
[0025] Specifically, step S3, staged condensation, adopts a series three-stage gradient condensation process. The oil and flue gas pass through the first-stage condensation unit, the second-stage condensation unit, and the third-stage condensation unit in sequence. The first-stage condensation has a constant temperature of 80-100℃, the second-stage condensation has a constant temperature of 40-60℃, and the third-stage condensation has a constant temperature of 0-10℃. The temperature fluctuation of each stage of condensation is ≤±2℃.
[0026] Specifically, during the dilute hydrochloric acid pickling process, a magnetic stirring device is used to stir at a constant speed of 60-100 r / min throughout the process; during the weak alkali desulfurization soaking process, the stirring is carried out synchronously and at a constant speed of 40-70 r / min to ensure that the material and the solution are in full contact and react.
[0027] The beneficial effects of the method for preparing high-purity carbon powder by cascade pyrolysis of waste tires disclosed in this application are as follows:
[0028] 1. The closed-loop pressure-controlled vacuum drying pretreatment process can isolate external moisture and dust, prevent secondary pollution of materials, and efficiently remove adsorbed water, residual oil and light volatiles from the surface of the rubber powder under constant temperature conditions. The volatile gas is discharged in time to avoid the backflow and residue of impurities. It can achieve deep purification of rubber powder, reduce oil and gas separation pressure, prevent carbon powder pores from being blocked by impurities, and ensure the purity and pore regularity of the finished carbon powder from the raw material end.
[0029] 2. The three-stage gradient series condensation process is adopted to separate heavy, medium and light oil and gas components based on the difference in boiling points. This can effectively avoid the problems of incomplete oil and gas condensation and component adhesion and mixing, and significantly improve the recovery purity and utilization value of pyrolysis oil and pyrolysis gas. At the same time, multi-stage condensation can deeply capture condensable volatiles, reduce oil and gas tail gas emissions, improve resource utilization, and optimize the environmental protection of the process.
[0030] 3. A dilute hydrochloric acid pickling-weak alkali desulfurization-multiple pure water rinsing and graded purification system is adopted. Then, the embedded sulfur impurities and inorganic salt impurities in the carbon powder lattice are removed by sodium bicarbonate weak alkali solution. At the same time, differentiated magnetic stirring is provided. During the pickling stage, high-speed stirring is used to disperse the material and enhance the dissolution of metal impurities. During the desulfurization stage, low-speed stirring is used to balance the desulfurization effect and the integrity of the carbon powder structure. Attached Figure Description
[0031] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:
[0032] Figure 1 This is a flowchart illustrating a method for preparing high-purity carbon powder by cascade pyrolysis of waste tires, as described in this application. Detailed Implementation
[0033] To make the technical means, inventive features, objectives, and effects of this application easier to understand, the application is further described below with reference to specific illustrations. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.
[0034] The present application will now be described in further detail with reference to the accompanying drawings.
[0035] like Figure 1 As shown in the embodiment of this application, a method for preparing high-purity carbon powder by cascade pyrolysis of waste tires includes the following steps:
[0036] S1. After removing steel wires and fiber accessories from waste tires, crush them and sieve them to obtain 80-120 mesh tire rubber powder. Place the rubber powder in a vacuum drying oven and dry it for 2-4 hours to remove adsorbed water and light volatile impurities from the surface of the rubber powder, and obtain dried tire rubber powder.
[0037] It should be noted that the finished waste tires contain a large amount of non-rubber components such as metal wires, chemical fibers, and rubber additives. These impurities will seriously interfere with the subsequent pyrolysis reaction, resulting in increased carbon powder ash content, structural damage, and substandard purity. Therefore, fine pretreatment is required.
[0038] First, the waste tires are mechanically dismantled and sorted, thoroughly removing the internal steel wire skeleton, surface fiber auxiliary materials, and various impurities, retaining only the pure rubber matrix. Then, a rubber pulverizer is used to ultrafinely pulverize the pure rubber material. After pulverization, it is graded and sieved through a standard sieve to select tire rubber powder in the 80-120 mesh range. Rubber powder in this mesh range has uniform particle size and a suitable specific surface area, ensuring rapid and uniform heat transfer during subsequent pyrolysis, avoiding incomplete pyrolysis of large particles and excessive pulverization of small particles, while effectively improving the pyrolysis reaction efficiency.
[0039] The sieved and qualified tire rubber powder is evenly spread in a vacuum drying oven and subjected to constant temperature vacuum drying for 2-4 hours. At room temperature, the surface of the tire rubber powder will absorb moisture from the air, and some light volatile matter and trace dust impurities will remain on the surface. The low-pressure environment of vacuum drying can remove the adsorbed water and free light volatile matter impurities from the surface of the rubber powder under low temperature and non-oxidizing conditions. This effectively avoids the problems of pressure fluctuations in the furnace caused by moisture vaporization during subsequent pyrolysis and the decrease in carbon powder purity caused by volatile matter impurities, resulting in dry, clean, and stable tire rubber powder.
[0040] S2. The dried tire rubber powder is fed into a closed inert atmosphere pyrolysis furnace. High-purity nitrogen is introduced throughout the process to maintain the oxygen content in the furnace at ≤0.5%. The three-stage gradient pyrolysis process of low-temperature impurity removal, medium-temperature pyrolysis, and high-temperature reconstruction is completed in sequence.
[0041] The first stage is low-temperature impurity removal: the temperature is raised to 220-280℃ and kept at a constant temperature for 30-60 minutes to remove residual oils, additives, and small molecule organic impurities from the adhesive powder.
[0042] The second stage of medium-temperature deep pyrolysis involves heating to 450-520℃ at a rate of 3-5℃ / min and holding at that temperature for 60-90 minutes to fully break down the polymer chains of the tire rubber, thereby separating the carbon skeleton from the oil and gas components and obtaining pyrolysis carbon slag.
[0043] The third stage involves high-temperature lattice reconstruction: heating to 650-720℃ at a rate of 2-4℃ / min and holding at that temperature for 40-70min to repair lattice defects in the carbon matrix, regulate the microstructure of the carbon powder, and decompose bound organic impurities on the surface of the carbon slag, thus initially reducing ash and sulfur content.
[0044] It should be noted that a low-oxygen, inert atmosphere can prevent the rubber raw materials and pyrolytic carbon matrix from oxidizing and burning at high temperatures, thus avoiding loss of performance. It also prevents impurities from undergoing oxidation reactions to form difficult-to-remove oxides, ensuring the integrity and basic purity of the pyrolytic carbon from the source. A three-stage gradient pyrolysis process—low-temperature impurity removal, medium-temperature pyrolysis, and high-temperature reconstruction—is employed to achieve impurity removal, polymer pyrolysis, and carbon structure modification step by step.
[0045] The first stage is a low-temperature impurity removal process: the pyrolysis furnace is heated uniformly to 220-280℃ and held at this temperature for 30-60 minutes. This temperature range is the removal temperature zone for light organic impurities. The temperature is below the breakage temperature of the rubber polymer backbone, which will not damage the carbon skeleton structure of tire rubber. It can directionally and selectively remove residual processing greases, softeners, antioxidants, plasticizers, and other rubber additives, as well as various small-molecule organic impurities and residual volatiles from the rubber powder. Sufficiently long holding time at this temperature ensures that trace amounts of organic impurities inside and on the surface of the rubber powder are fully extracted and removed, eliminating soluble organic impurities from the raw material and preventing the generation of large amounts of impurities during subsequent high-temperature pyrolysis.
[0046] The second stage is the medium-temperature deep pyrolysis process: After low-temperature impurity removal, the furnace temperature is raised to 450-520℃ at a uniform heating rate of 3-5℃ / min and held at this temperature for 60-90 minutes. This heating rate is gentle and controllable, avoiding the drawbacks of excessively rapid heating leading to excessive temperature differences between the inside and outside of the rubber powder, excessive surface pyrolysis, and incomplete internal pyrolysis. It also avoids the problems of high energy consumption and low efficiency caused by excessively slow heating. 450-520℃ is the optimal pyrolysis temperature for the cross-linked network of tire rubber polymers. Under this constant temperature condition, the long-chain polymer structure and cross-linked elastic network of tire rubber can be fully broken and degraded, disrupting the original macromolecular structure of the rubber and achieving complete separation of the solid carbon skeleton from the gaseous and liquid oil and gas components. This maximizes the release of pyrolysis oil and gas while preserving the complete carbon matrix, ultimately yielding pure and structurally stable pyrolysis carbon slag.
[0047] The third stage is the high-temperature lattice reconstruction process: After the intermediate-temperature pyrolysis, the heating rate is further reduced to a low-speed heating mode of 2-4℃ / min to raise the furnace temperature to 650-720℃, and then held at that temperature for 40-70 minutes. This low-speed heating allows the carbon matrix to be heated uniformly and stress to be released gradually, effectively repairing lattice defects, pore collapse, and structural disorder generated in the carbon matrix during intermediate-temperature pyrolysis. It also reorganizes the microcrystalline and pore structures of the carbon powder, improving its structural stability and regularity. Simultaneously, the high-temperature environment can completely decompose the stubborn organic residues and macromolecular pyrolysis byproducts bound to the carbon slag surface, and also achieve the thermal decomposition and removal of some bound sulfur and ash, initially reducing the ash and sulfur content of the pyrolysis carbon slag. This completes the initial modification and upgrading of the carbon powder, significantly reducing the processing pressure of subsequent chemical refining processes.
[0048] S3. The oil and gas flue gas generated during the pyrolysis process are treated by staged condensation to separate and recover the pyrolysis oil and pyrolysis gas.
[0049] It should be noted that during the entire gradient pyrolysis reaction process, a mixed oil and gas flue gas containing heavy oil, light oil, combustible gas, and trace amounts of volatiles will be continuously generated in the furnace. In order to achieve resource utilization and clean production, the oil and gas flue gas generated by pyrolysis is subjected to online graded condensation treatment.
[0050] A gradient cooling condensation process is employed, utilizing the boiling point differences of various components in the oil and gas mixture. Different condensation temperatures are set through a multi-stage condensation unit to separate the mixed oil and gas in stages. High-boiling-point, large-molecule hydrocarbon components are condensed and enriched to form pyrolysis oil, which can be recycled as fuel oil and basic chemical feedstock. Low-boiling-point, small-molecule combustible gases, which cannot be condensed and liquefied, are collected and recycled as auxiliary fuel for the pyrolysis furnace. This process enables the resource recovery of byproducts from waste tire pyrolysis, improving the economic efficiency of the process while ensuring its environmental friendliness.
[0051] S4. Cool the pyrolysis solid carbon slag to room temperature, and then use dilute acid washing, deionized water rinsing, weak alkali desulfurization, and pure water repeated rinsing processes to remove metal ash, sulfides, and inorganic salt impurities from the carbon slag until the pH value of the filtrate after rinsing is 6.5-7.5.
[0052] It should be noted that after the solid carbon slag is naturally cooled to room temperature after pyrolysis, it still retains a small amount of stubborn impurities such as metal oxides, inorganic salts, and bound sulfides accumulated during the pyrolysis process. These are the core factors affecting the purity, whiteness, and stability of the carbon powder. Therefore, a refined chemical impurity removal process is required for deep purification. This process employs a multi-stage refining process, sequentially using dilute acid washing, deionized water rinsing, weak alkali desulfurization, and repeated rinsing with pure water, to remove various impurities step by step.
[0053] First, a dilute acid pickling treatment is carried out. Low-concentration inorganic dilute acid is used to soak and stir the carbon slag, which can fully dissolve the residual iron, zinc, calcium, magnesium and other metal ash and various insoluble inorganic salt impurities in the carbon slag, and convert solid metal impurities into soluble ions that enter the liquid phase. After pickling, deionized water is used for preliminary rinsing to remove the acidic waste liquid and dissolved metal ion impurities attached to the surface of the carbon slag.
[0054] Following this, a weak-alkali desulfurization process is carried out, using a mild weak-alkali solution for soaking and modification. This precisely removes stubborn sulfur-containing impurities such as bound sulfur, sulfur oxides, and sulfides from the carbon powder structure, avoiding the carbon matrix structure damage and excessive corrosion problems caused by strong acid and strong alkali desulfurization. This ensures the desulfurization effect while preserving the complete microstructure of the carbon powder. Finally, the desulfurized carbon slag is repeatedly rinsed with high-purity water to remove residual alkaline waste liquid and salt byproducts generated by the neutralization reaction, until the pH value of the filtrate after rinsing stabilizes in the neutral range of 6.5-7.5. This ensures that there are no acid or alkali residues in the carbon powder and that soluble impurities are completely removed, completing the refining and purification of high-purity carbon powder.
[0055] S5. Place the purified carbon powder filter cake in an inert atmosphere drying furnace and dry it at 150-200℃ under nitrogen protection for 3-5 hours. Then grind it at low speed and sieve it through a 150-200 mesh screen to remove agglomerated particles and obtain high-purity carbon powder.
[0056] It should be noted that the carbon powder after multi-stage chemical refining is a wet filter cake containing a large amount of moisture. During the drying process, it is prone to particle agglomeration and oxidation, thus requiring inert atmosphere drying modification treatment. The purified carbon powder filter cake is fed into an inert atmosphere drying furnace and dried for 3-5 hours under constant temperature conditions of 150-200℃ while continuously purging nitrogen to create an oxygen-free protective atmosphere. The nitrogen inert environment completely prevents oxidation, burn-off, and structural changes of the carbon powder during high-temperature drying. Simultaneously, this drying temperature efficiently removes free moisture and trace amounts of residual volatile impurities from the carbon powder filter cake without damaging the already well-defined carbon powder lattice structure, resulting in a dry, loose, high-purity carbon powder raw material.
[0057] After drying, the carbon powder undergoes low-speed fine grinding. This low-speed grinding mode avoids the damage to the microstructure and pores of the carbon powder caused by the high temperature and shear force of high-speed grinding, only breaking up minor agglomerates formed during drying, thus ensuring the integrity of the individual carbon powder particles. After grinding, the powder is graded and sieved through a 150-200 mesh standard sieve to thoroughly remove large, undispersed agglomerates and trace impurities, standardizing the particle size and obtaining the finished high-purity carbon powder.
[0058] In one embodiment of this application, during the three-stage isothermal pyrolysis process in step S2, the heating rate decreases step by step, with rapid impurity removal in the low-temperature stage, uniform pyrolysis in the medium-temperature stage, and slow lattice reconstruction in the high-temperature stage.
[0059] It should be noted that the low-temperature section uses a faster heating rate, which can break through the critical temperature for impurity volatilization in a short time, quickly remove excess components such as adsorbed water, light organic impurities, and low-boiling-point ash from the material surface, while avoiding the problem of impurity adhesion and residue caused by prolonged low-temperature heating, thus efficiently completing the material purification pretreatment.
[0060] The medium-temperature section adopts a uniform heating mode to ensure that the material is heated evenly and the internal and external temperatures rise simultaneously. This precisely matches the cracking reaction characteristics of the organic matrix inside the material, allowing the macromolecular organic components to break down and decompose stably and fully, and preventing local overheating, incomplete cracking, or overburning and carbonization.
[0061] The high-temperature section further reduces the heating rate, providing sufficient reaction time for the evolution of the carbon powder lattice structure by heating slowly. This enables the repair of lattice defects and the regularization and reconstruction of the pore structure of carbon-based materials, effectively improving the structural stability and physicochemical properties of the finished carbon powder. Through three-stage differentiated temperature control, the efficiency of impurity removal, the integrity of pyrolysis, and the structural quality of the finished product are all taken into account.
[0062] In one embodiment of this application, the specific process of step S4, multi-stage wet purification, is as follows: pickling and soaking in 3%-5% dilute hydrochloric acid for 20-30 minutes to remove metal ash such as iron, zinc, and calcium; then soaking in 2%-4% sodium bicarbonate weak alkaline solution for 15-25 minutes to directionally remove sulfur impurities bound to carbon powder; and finally rinsing with deionized water 3-5 times.
[0063] It should be noted that, firstly, a 3%-5% (w / w) dilute hydrochloric acid solution is used to acid wash and soak the pyrolyzed carbon powder material for 20-30 minutes. This concentration and duration of dilute hydrochloric acid system can fully neutralize and replace the inorganic metal ash such as iron, zinc, and calcium mixed in the material, converting solid metal oxides and metal salt impurities into soluble ions and stripping the metal impurity components from the carbon powder matrix. At the same time, the mild acidic system will not cause corrosion or damage to the carbon powder structure.
[0064] After pickling, the material is soaked in a 2%-4% sodium bicarbonate weak alkaline solution for 15-25 minutes. Compared to strong alkaline solutions, the sodium bicarbonate weak alkaline system is mild and can directionally remove bound sulfur impurities from the surface and interior of the carbon powder, break the bonds between sulfur and the carbon matrix, and efficiently remove fixed sulfur components that are difficult to remove by pyrolysis without causing pore collapse or structural damage to the carbon powder. Finally, the treated material is rinsed repeatedly with deionized water 3-5 times to gradually wash away residual hydrochloric acid, sodium bicarbonate solution, and dissolved impurity ions from the surface of the material.
[0065] In one embodiment of this application, in step S1, the vacuum drying oven is sealed and pressure controlled throughout the process, and the drying constant temperature is set to 80-100℃. During the drying process, a small amount of exhaust is performed every 30 minutes to release volatile gases.
[0066] It should be noted that the drying constant temperature is set to 80-100℃. This temperature range is the low-temperature constant temperature drying range, which can not only meet the conditions for the volatilization and precipitation of free water, adsorbed water and light volatiles inside the material, but also avoid problems such as premature pyrolysis, component denaturation and surface carbonization caused by high-temperature drying, thus preserving the original structure and effective components of the material to the greatest extent.
[0067] Meanwhile, a micro-venting operation is performed every 30 minutes during the drying process. Through intermittent micro-venting, the mixed gases such as water vapor and volatile organic compounds accumulated inside the chamber are discharged in a timely manner, preventing the volatile gases from saturating and flowing back into the chamber and being re-adsorbed onto the material surface. This effectively improves the drying efficiency and drying uniformity, ensuring that the material moisture content and impurity content in the subsequent pyrolysis process are stable and controllable.
[0068] In one embodiment of this application, the high-purity nitrogen gas introduced in step S2 is introduced by uniformly distributing gas at the bottom and uniformly exhausting gas at the top, with the continuous nitrogen gas flow rate being stably controlled at 8-15 L / min throughout the process.
[0069] It should be noted that the uniform gas distribution at the bottom allows high-purity nitrogen to diffuse evenly from the bottom of the furnace to all areas of the furnace chamber, covering the material accumulation layer without dead corners, quickly replacing the air in the furnace, isolating oxygen, and effectively preventing the carbon powder material from oxidizing, burning, or deteriorating during high-temperature pyrolysis.
[0070] Uniform top exhaust can simultaneously remove oil, flue gas, and trace impurities generated during pyrolysis in the furnace, maintaining a clean atmosphere inside the furnace. A constant airflow rate ensures that the pressure and concentration of the inert atmosphere inside the furnace remain stable, avoiding temperature fluctuations and increased energy consumption caused by excessive flow.
[0071] In one embodiment of this application, the precise temperature control endpoint of the first stage of low-temperature impurity removal in step S2 is 240-260℃, the constant temperature and stable holding time is 40-50min, and the temperature fluctuation error during the heating process is ≤±3℃.
[0072] It should be noted that this temperature range is the optimal range for low-temperature impurity removal of materials. It can accurately remove residual crystal water, low-boiling-point organic impurities, and surface-adhered light impurities from materials, while not triggering the cracking reaction of the organic matrix inside the material, and accurately distinguishing the reaction boundary between the impurity removal stage and the cracking stage.
[0073] A constant temperature holding time of 40-50 minutes ensures that the overall temperature of the material is uniform and meets the standard, allowing various light impurities to fully and thoroughly volatilize and be removed, avoiding incomplete impurity removal caused by uneven heating inside and outside the material. The ultra-low temperature fluctuation control standard effectively ensures the consistency of impurity removal effect of the entire furnace, eliminating premature cracking caused by excessively high local temperatures and impurity residue caused by excessively low local temperatures.
[0074] In one embodiment of this application, the fixed heating rate of the second stage of the medium-temperature deep pyrolysis in step S2 is 4℃ / min, the precise heating endpoint is 480-500℃, the constant temperature holding time is 70-80min, and the furnace temperature does not fluctuate during the holding stage.
[0075] It should be noted that the uniform heating rate of 4℃ / min is adapted to the thermal conductivity characteristics of the organic matrix of the material, which can achieve uniform heating of the material from the outside to the inside, avoiding the problems of overheating of the material surface and failure of internal cracking caused by rapid heating, or low process efficiency caused by slow heating, and ensuring that the macromolecular organic components undergo bond breaking, cracking and gasification reactions in a gradual and orderly manner.
[0076] The 480-500℃ mid-temperature range is the core temperature range for deep pyrolysis of the material's organic framework, which can efficiently decompose most of the medium-boiling-point organic impurities and high molecular weight components in the material. Combined with a long-term constant-temperature stable holding period of 70-80 minutes, and precise control with zero temperature fluctuations during the holding period, the pyrolysis reaction can be fully carried out, eliminating residual organic macromolecular impurities inside the material, achieving the initial formation of the carbon-based framework, and significantly improving the purification degree and structural regularity of the material.
[0077] In one embodiment of this application, the fixed heating rate of the third stage of high-temperature lattice reconstruction in step S2 is 3℃ / min, the precise heating endpoint is 680-700℃, the constant temperature holding time is 50-60min, and the furnace pressure is kept constant during the high-temperature reconstruction stage.
[0078] It should be noted that compared to the intermediate-temperature pyrolysis stage, the lower heating rate of 3℃ / min effectively reduces the thermal stress impact during the high-temperature heating process. The high-temperature range of 680-700℃ is the optimal temperature for carbon powder lattice reconstruction, which can activate the migration and recombination of carbon atoms inside the carbon-based material, repair lattice defects generated during the early pyrolysis process, regulate the pore structure, and improve the crystallinity of the carbon powder. The isothermal holding time of 50-60 minutes provides sufficient reaction time for lattice reconstruction and structural shaping, ensuring that the reconstruction process is fully completed. At the same time, the constant furnace pressure during the high-temperature stage can stabilize the furnace atmosphere density and heat transfer efficiency, avoiding temperature deviations and uneven structural reconstruction caused by pressure fluctuations, thus obtaining a carbon powder matrix material.
[0079] In one embodiment of this application, step S3, staged condensation, adopts a series three-stage gradient condensation process. The oil and gas flue gas pass through a primary condensation unit, a secondary condensation unit, and a tertiary condensation unit in sequence. The primary condensation unit has a constant temperature of 80-100℃, the secondary condensation unit has a constant temperature of 40-60℃, and the tertiary condensation unit has a constant temperature of 0-10℃. The temperature fluctuation of each stage of condensation is ≤±2℃.
[0080] Understandably, the constant temperature of the primary condensation unit is set at 80-100℃, mainly to condense and retain high-boiling-point heavy oil and gas components in the pyrolysis flue gas. This temperature can accurately match the condensation critical point of heavy oil components, realize the rapid liquefaction and separation of heavy components, and at the same time avoid the mixing and adhesion of light and heavy components caused by low-temperature condensation.
[0081] The secondary condensation unit has a constant temperature set at 40-60℃, focusing on the condensation and recovery of medium-boiling-point oil and gas components, further separating the residual medium-quality oil in the flue gas, and purifying the flue gas components step by step.
[0082] The three-stage condensation unit is set to a constant temperature of 0-10℃, which is used for deep condensation and capture of light oil and gas and trace amounts of condensable volatiles. This maximizes the recovery of pyrolysis oil and gas products, reduces the emission of pollutants in flue gas, and ensures the separation accuracy of each condensation unit by precise temperature control. This avoids problems such as incomplete condensation and low purity of component separation caused by temperature fluctuations, and achieves efficient graded recovery of pyrolysis oil and gas and deep purification of flue gas.
[0083] In one embodiment of this application, a magnetic stirring device is used to stir at a constant speed of 60-100 r / min during the dilute hydrochloric acid pickling process; and the stirring is carried out synchronously and at a constant speed of 40-70 r / min during the weak alkali desulfurization soaking process to ensure that the material and the solution are in full contact and react.
[0084] It should be noted that metal ash mostly adheres to the surface and pores of carbon powder particles. A high uniform stirring rate can break up the agglomeration of material particles, allowing carbon powder particles to be fully dispersed in the acidic solution, continuously renewing the contact interface between the material and the solution, enhancing the reaction mass transfer efficiency between hydrochloric acid and metal impurities, and ensuring uniform removal of metal impurities.
[0085] During the sodium bicarbonate weak alkali desulfurization soaking process, uniform stirring is carried out simultaneously. The combined sulfur impurities are mostly embedded in the micro-crystalline structure of the carbon powder. The low stirring rate can ensure that the material and the weak alkali solution are in full contact and react, while avoiding the shear force generated by high-speed stirring from damaging the pores and crystalline structure of the carbon powder that has been initially formed.
[0086] The present application and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present application. The actual structure is not limited to this. In conclusion, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of the present application, such design should fall within the protection scope of the present application.
Claims
1. A method for preparing high purity carbon powder from waste tires by step pyrolysis, characterized in that, Includes the following steps: S1. After removing steel wires and fiber accessories from waste tires, crush them and sieve them to obtain 80-120 mesh tire rubber powder. Place the rubber powder in a vacuum drying oven and dry it for 2-4 hours to remove adsorbed water and light volatile impurities from the surface of the rubber powder to obtain dried tire rubber powder. S2. The dried tire rubber powder is fed into a closed inert atmosphere pyrolysis furnace. High-purity nitrogen is introduced throughout the process to maintain the oxygen content in the furnace at ≤0.5%. The three-stage gradient pyrolysis of low temperature impurity removal, medium temperature pyrolysis and high temperature reconstruction is completed in sequence. The first stage of low-temperature impurity removal: heat up to 220-280℃, keep at a constant temperature for 30-60 minutes, and directionally remove residual oils, additives, and small molecule organic impurities from the adhesive powder; The second stage of medium-temperature deep pyrolysis: the temperature is increased to 450-520℃ at a rate of 3-5℃ / min and held at a constant temperature for 60-90min to fully break and pyrolyze the polymer chains of tire rubber, thereby separating the carbon skeleton from the oil and gas components and obtaining pyrolysis carbon slag. The third stage is high-temperature lattice reconstruction: the temperature is increased to 650-720℃ at a rate of 2-4℃ / min, and held at a constant temperature for 40-70min to repair the lattice defects of the carbon matrix, regulate the microstructure of carbon powder, and decompose the organic impurities bound to the carbon slag surface, thus initially reducing the ash and sulfur content. S3. The oil and gas flue gas generated during the pyrolysis process are treated by staged condensation to separate and recover the pyrolysis oil and pyrolysis gas. S4. Cool the pyrolysis solid carbon slag to room temperature, and then use dilute acid washing, deionized water rinsing, weak alkali desulfurization, and pure water repeated rinsing processes to remove metal ash, sulfides, and inorganic salt impurities from the carbon slag until the pH value of the filtrate after rinsing is 6.5-7.
5. S5. Place the purified carbon powder filter cake in an inert atmosphere drying furnace and dry it at 150-200℃ under nitrogen protection for 3-5 hours. Then grind it at low speed and sieve it through a 150-200 mesh screen to remove agglomerated particles and obtain high-purity carbon powder.
2. The method of claim 1, wherein the method further comprises the step of: In the three-stage isothermal pyrolysis process of step S2, the heating rate decreases step by step, with rapid impurity removal in the low-temperature stage, uniform pyrolysis in the medium-temperature stage, and slow lattice reconstruction in the high-temperature stage. 3. The method of claim 1, wherein the method further comprises the step of: The specific process of step S4, multi-stage wet purification, is as follows: pickling and soaking in 3%-5% dilute hydrochloric acid for 20-30 minutes to remove metal ash such as iron, zinc, and calcium; then soaking in 2%-4% sodium bicarbonate weak alkaline solution for 15-25 minutes to directionally remove sulfur impurities bound to carbon powder; and finally rinsing with deionized water 3-5 times. 4. The method of claim 1, wherein the method further comprises the step of: In step S1, the vacuum drying oven is sealed and pressure controlled throughout the process, and the drying temperature is kept constant at 80-100℃. During the drying process, a small amount of exhaust is performed every 30 minutes to remove volatile gases. 5. The method of claim 1, wherein the method further comprises the step of: In step S2, the high-purity nitrogen gas is introduced in a manner that involves uniform gas distribution at the bottom and uniform exhaust at the top, with the continuous nitrogen gas flow rate being stably controlled at 8-15 L / min throughout the process. 6. The method of claim 1, wherein the method further comprises the step of: The precise temperature control endpoint of the first stage of low-temperature impurity removal in step S2 is 240-260℃, the constant temperature and stable holding time is 40-50min, and the temperature fluctuation error during the heating process is ≤±3℃. 7. The method of claim 1, wherein the method further comprises the step of: The fixed heating rate of the second stage of the intermediate-temperature deep pyrolysis in step S2 is 4℃ / min, the precise heating endpoint is 480-500℃, the constant temperature holding time is 70-80min, and the temperature inside the furnace does not fluctuate during the holding stage. 8. The method of claim 1, wherein the method further comprises the step of: The fixed heating rate for the third stage of high-temperature lattice reconstruction in step S2 is 3℃ / min, the precise heating endpoint is 680-700℃, the constant temperature holding time is 50-60min, and the pressure inside the furnace is kept constant during the high-temperature reconstruction stage. 9. The method of claim 1, wherein the method further comprises the step of: The step S3 staged condensation adopts a series three-stage gradient condensation process. The oil and flue gas pass through the first-stage condensation unit, the second-stage condensation unit, and the third-stage condensation unit in sequence. The first-stage condensation has a constant temperature of 80-100℃, the second-stage condensation has a constant temperature of 40-60℃, and the third-stage condensation has a constant temperature of 0-10℃. The temperature fluctuation of each stage of condensation is ≤±2℃. 10. The method of claim 3, wherein the method further comprises the step of: During the dilute hydrochloric acid pickling process, a magnetic stirring device is used to stir at a constant speed of 60-100 r / min throughout the process; during the weak alkali desulfurization soaking process, the stirring is carried out simultaneously at a constant speed of 40-70 r / min to ensure that the material and the solution are in full contact and react.