Preparation process of waste pitch-based microporous carbon with narrow pore size and high specific surface area

Abstract

This invention relates to the field of porous carbon material preparation technology, and proposes a preparation process for waste asphalt-based narrow-pore, high-specific-surface-area microporous porous carbon. The process includes step one: purifying and mechanically pulverizing waste asphalt raw materials to obtain asphalt powder with a particle size of 50–200 μm; spreading the asphalt powder evenly and feeding it into a closed pre-oxidation reactor; controlling the vacuum degree inside the reactor at -0.03–-0.06 MPa; and simultaneously introducing a low-concentration oxygen mixed atmosphere into the reactor. Step two: transferring the pre-oxidized asphalt powder to a high-pressure reactor; introducing carbon dioxide gas with a purity of 99.9% or higher into the reactor at a rate controlled at 0.3 L / min. This invention solves the technical problems of wide pore size distribution, low micropore ratio, insufficient specific surface area, and easy collapse of pore structure in existing waste asphalt-based porous carbon preparation processes. Traditional one-step rapid carbonization processes, due to concentrated thermal stress and excessively rapid gas release, result in numerous pore wall cracks, wide pore size distribution, low micropore ratio, small specific surface area, and many defects in the carbon skeleton.

Description

Technical Field

[0001] This invention relates to the field of porous carbon material preparation technology, specifically to a preparation process for waste pitch-based narrow-pore, high-specific-surface-area microporous porous carbon. Background Technology

[0002] Porous carbon materials, due to their excellent pore structure, high specific surface area, and good chemical stability, have broad application prospects in adsorption separation, catalyst support, and electrochemical energy storage. Asphalt, as an industrial by-product rich in carbon, especially waste asphalt, is widely available and inexpensive. Converting it into high-value-added porous carbon materials has significant resource utilization and environmental protection implications.

[0003] CN109052397B discloses a method for preparing pitch-based spherical activated carbon with a hierarchical porous structure. The pitch-based spherical activated carbon prepared by this method has a density of 0.4–0.85 g / cm³. 3 Specific surface area of ​​100–1600 m² 2 The composition of activated carbon is as follows: g / g, micropore content 60-75%, mesopore content 25-15%, and macropore content 15-10%. Specifically, this invention uses high-softening-point coal tar pitch (240-280℃) as raw material. A screw extrusion mixing technique is employed to uniformly mix the high-softening-point coal tar pitch, refined naphthalene, a high-temperature easily degradable substance, and a metal salt. Utilizing the different pore-forming mechanisms of refined naphthalene, the high-temperature easily degradable substance, and the metal salt, a pitch-based spherical activated carbon with a hierarchical pore structure combining macropores, mesopores, and micropores is ultimately formed. The pore structure control method of this invention is simple and can expand the wide application of pitch-based spherical activated carbon in civilian, industrial, and aerospace fields.

[0004] The above methods only achieve a micropore content of 60-75% and an upper limit of 1600 m² / g for specific surface area, with a wide pore size distribution and a lack of precise control over the narrow-pore microporous structure. The root cause of these defects lies in the fact that these technologies rely on exogenous pore-forming methods such as solvent extraction and activator etching. The formation of pores is highly random and difficult to precisely control. Furthermore, during high-temperature activation, the pore walls are susceptible to over-etching or gas release impacts, leading to micropore merging, collapse, and pore size widening. To address these issues, this solution provides a process for preparing waste bitumen-based narrow-pore, high-specific-surface-area microporous porous carbon. Summary of the Invention

[0005] This invention proposes a preparation process for waste bitumen-based narrow-pore-size, high-specific-surface-area microporous porous carbon, which solves the technical problems of wide pore size distribution, low micropore ratio, insufficient specific surface area, and easy collapse of pore structure in existing waste bitumen-based porous carbon preparation processes.

[0006] The technical solution of this invention is as follows: A process for preparing waste bitumen-based narrow-pore high specific surface area microporous porous carbon, comprising:

[0007] Step 1: The waste asphalt raw material is purified and mechanically crushed to obtain asphalt powder with a particle size of 50-200μm. The asphalt powder is spread evenly and fed into a closed pre-oxidation reactor. The vacuum degree inside the reactor is controlled at -0.03 to -0.06MPa, and a low-concentration oxygen mixed atmosphere is introduced into the furnace at the same time.

[0008] Step 2: Transfer the pre-oxidized asphalt powder to a high-pressure reactor, introduce carbon dioxide gas with a purity of 99.9% or higher into the reactor at a rate of 0.3 L / min until the pressure inside the reactor slowly rises to 0.5 MPa, then close the inlet valve and start the mechanical oscillation device installed on the outer wall of the reactor to cause the reactor body to drive the internal asphalt particles to generate periodic mechanical oscillations with a frequency of 30 Hz to 50 Hz.

[0009] After the oscillation is completed, the vessel is kept still and left to stand for 30 minutes. At this time, the pressure inside the vessel naturally drops from the initial 0.5 MPa to the range of 0.3 MPa to 0.4 MPa. High-purity nitrogen is slowly injected into the vessel through the gas injection pipe to make the pressure inside the vessel rise back to 0.5 MPa. The gas injection rate is controlled at 0.1 to 1.5 L / min. The injection of nitrogen applies a uniform isostatic pressure to the asphalt particles inside the vessel.

[0010] Step 3: After carbon dioxide permeation is completed, start the reactor heating system and heat treat the material at a slow heating rate of 0.3 to 1.0 °C / min under an inert atmosphere. After the temperature reaches the set range, maintain the temperature for 0.5 to 2 hours.

[0011] Step 4: Perform a staged, progressive pressure reduction coupled with temperature increase carbonization treatment on the reactor, including:

[0012] Step 4-1: Under inert atmosphere protection, slowly release the pressure inside the vessel by adjusting the exhaust valve. Each pressure reduction should be controlled at 0.01 to 0.05 MPa, and the duration of each pressure reduction should be controlled at 2 to 10 minutes.

[0013] Step 4-2: After completing the single pressure reduction, shut off the exhaust system and continue to increase the temperature inside the vessel at a heating rate of 0.5 to 2℃ / min. The temperature increment for each heating stage should be controlled at 5 to 20℃. After the heating is completed, maintain a constant temperature for 10 to 30 minutes.

[0014] Step 4-3: Continue the next round of depressurization, heating, and isothermal cycle operation until the system pressure gradually decreases to below 0.1 MPa and the temperature rises to the carbonization temperature range of 600-900℃.

[0015] Preferably, in step one, the furnace temperature of the closed pre-oxidation reactor is raised to the pre-oxidation temperature range of 220-280°C at a heating rate of 1-3°C / min, and maintained at a constant temperature for 1-3 hours.

[0016] Preferably, in step two, the oscillation amplitude is controlled to be 1% to 2% of the vessel diameter, and the duration is 10 minutes.

[0017] Preferably, in step two, the pressure reduction and nitrogen replenishment are repeated. Each cycle follows the following sequence: let the pressure drop naturally for 30 minutes, then replenish nitrogen to raise the pressure back to 0.5 MPa. In 3 to 4 cycles, each round of pressure replenishment applies additional compression to the carbon dioxide molecules that were partially locked in the previous cycle, forcing the carbon dioxide molecules to migrate from the surface of the particles to the more internal subsurface layer.

[0018] Preferably, in step two, after 3 to 4 cycles, carbon dioxide molecules are completely encapsulated in the core position of the entangled network of the asphalt chain segments, forming a pre-formed pore core with uniform size and fixed spatial position.

[0019] Preferably, the low-concentration oxygen mixed atmosphere in step one is a mixture of nitrogen and oxygen, wherein the volume fraction of oxygen is 5% to 15% and the volume fraction of nitrogen is 85% to 95%.

[0020] Preferably, the heat treatment temperature in step three is 180-250°C, which is lower than the softening point temperature of waste asphalt, so that the asphalt chain segments can be initially shaped without melting and flowing.

[0021] Preferably, the depressurization process in step 4-1 is a gradient depressurization, and the stabilization time of the pressure inside the vessel after each depressurization is not less than 1 minute.

[0022] Preferably, the heating process in step 4-2 is a staged heating process, and the isothermal time of each heating stage increases with the increase of carbonization temperature.

[0023] Preferably, during the multiple rounds of depressurization and heating constant temperature cycle in step 4-3, the rate of change of pressure and temperature inside the reactor is synchronously matched, so that the gasification expansion rate of the carbon dioxide pre-formed pore core inside the reactor and the shrinkage rate of the carbon skeleton are kept in dynamic balance.

[0024] The working principle and beneficial effects of this invention are as follows:

[0025] 1. In this invention, carbon dioxide molecules are precisely encapsulated within the core of the pitch chain entanglement network through high-pressure carbon dioxide permeation coupled with mechanical oscillation and pressure-cycle air-locking technology, forming pre-formed pore cores with uniform size and fixed spatial position. During subsequent carbonization, the carbon dioxide within the core vaporizes and expands upon heating, directly opening up the chain segment locking region from the inside, transforming it into a microporous structure with a uniform pore size. The average pore size is controlled within the range of 0.6–1.2 nanometers, effectively solving the problem of wide pore size distribution in traditional processes.

[0026] 2. In this invention, a staged, gradual pressure reduction coupled with heating carbonization is employed. The carbonization process is controlled by slowly reducing pressure and gradually increasing temperature, avoiding sudden pressure drops and rapid temperature increases that could cause instantaneous impact and rupture on the pore walls. This process results in a specific surface area of ​​1800–2200 m² / g for the obtained porous carbon material, far exceeding that of traditional one-step carbonization processes. Simultaneously, the slow heating promotes the gradual pyrolysis and condensation of the asphalt matrix and the reconstruction of the carbon skeleton, ensuring the stable preservation of the microporous structure during continuous carbonization.

[0027] 3. In this invention, by setting a negative pressure pre-oxidation treatment, the vacuum degree is controlled at -0.03 to -0.06 MPa, reducing the risk of sudden gas release during subsequent heat treatment. During the carbonization stage, a slow release method is adopted, with each round of pressure reduction ranging from 0.01 to 0.05 MPa and lasting for 2 to 10 minutes. This is combined with a buffer process of 5 to 20°C temperature increment and 10 to 30 minutes of constant temperature in each heating stage, effectively reducing the degree of instantaneous stress concentration on the pore walls. Compared with traditional rapid heating carbonization processes, the optimal group exhibits intact pore walls with no obvious collapse or breakage, fewer carbon skeleton defects, and an ID / IG ratio of 0.70 to 0.80.

[0028] 4. This invention allows for precise control of key parameters, from pre-oxidation temperature, vacuum level, carbon dioxide permeation pressure, mechanical oscillation frequency, and pressure cycle count, to the depressurization rate, heating rate, and final carbonization temperature during the carbonization stage. Experimental comparisons verified the influence of different parameters on material properties, providing clear data support and theoretical basis for parameter optimization based on target product performance requirements in industrial production. This facilitates the stable mass production of narrow-pore, high-specific-surface-area microporous porous carbon. Attached Figure Description

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0030] Figure 1 This is a flowchart of the carbon dioxide embedding and three-stage pressure cycle pre-forming hole core process of the present invention;

[0031] Figure 2 The curves showing the changes in pressure inside the vessel and carbon dioxide embedding rate during the three pressure cycles of this invention are shown.

[0032] Figure 3 This is a flowchart of the phased pressure reduction coupled with heating carbonization cycle of the present invention; Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figures 1-2 As shown in the figure, this embodiment proposes a preparation process for waste bitumen-based narrow-pore high specific surface area microporous porous carbon, including the following steps:

[0036] Step 1: The waste asphalt is pre-treated and purified to remove solid impurities such as sand, gravel, and metal, achieving a purity ≥95%. This purification process prevents impurities from disrupting the uniformity of the asphalt powder during crushing, pre-oxidation, and carbonization, preventing pore blockage or localized overheating, and ensuring the stable operation of subsequent CO2 infiltration, pre-pore formation, and carbonization processes. The waste asphalt raw material is then mechanically crushed to obtain a uniform powder with a particle size of 50–200 μm. This powder is then spread evenly in a high-temperature resistant tray and fed into a closed pre-oxidation reactor. The vacuum regulation system is activated to maintain a relative negative pressure within the furnace, with the vacuum degree controlled at -0.03 to -0.06 MPa. Simultaneously, a volume fraction of 5%–1% is introduced into the furnace. A low-concentration oxygen atmosphere of 5% is used to balance the removal of volatiles and the pre-oxidation cross-linking reaction. Under these conditions, the furnace temperature is raised to the pre-oxidation temperature range of 220-280℃ at a heating rate of 1-3℃ / min and maintained at this temperature for 1-3 hours. The negative pressure environment is conducive to the continuous escape of low-molecular-weight volatile components in waste asphalt, reducing the risk of sudden gas release during subsequent heat treatment. The low oxygen partial pressure condition can promote the slow diffusion of oxygen inside the asphalt particles, causing the asphalt molecules to undergo moderate oxidation cross-linking and condensation reactions, thereby improving the softening point and thermal stability of the material. After pre-oxidation treatment, the asphalt particles can maintain a relatively stable solid structure during subsequent heating, reducing the collapse of the pore structure caused by local melting flow.

[0037] Step Two: Transfer the pre-oxidized asphalt powder to a high-pressure reactor. Start the vacuum pump to evacuate the reactor until the absolute pressure inside the reactor is below -0.06 MPa. Maintain this vacuum state for 15 minutes to completely remove oxygen and water vapor adsorbed between the powder particles and on their surfaces. Close the vacuum valve and introduce carbon dioxide gas with a purity of 99.9% or higher into the reactor at a rate of 0.3 L / min until the pressure inside the reactor slowly rises to 0.5 MPa. Then close the inlet valve and start the mechanical vibration device installed on the outer wall of the reactor. This will cause the reactor to drive the internal asphalt particles to generate periodic mechanical vibrations at a frequency of 30 Hz to 50 Hz. The oscillation amplitude is controlled at 1% to 2% of the reactor diameter and the duration is 10 minutes. During this oscillation, there is a slight relative motion between the asphalt particles and between the particles and the reactor wall. The particle surface is subjected to alternating shearing, stretching and compression, which temporarily reduces the local entanglement density of the polymer chain segments on the asphalt surface, forming instantaneous molecular-level channels. Carbon dioxide molecules use these channels to quickly pass through the dense area of ​​the asphalt surface and enter the free volume area inside the particles. When the oscillation stops, the asphalt chain segments retract and close under the action of elastic restoring force, physically encapsulating the carbon dioxide molecules that have entered the free volume between the chain segments, preventing the carbon dioxide from escaping in reverse during subsequent operations.

[0038] Immediately after the oscillation ends, stop the mechanical disturbance and keep the reactor body stationary for 30 minutes. During the stationary period, no gas replenishment or venting is performed inside the reactor. At this time, the carbon dioxide molecules embedded inside the asphalt particles will cause the particle volume to expand slightly due to occupying free volume space, which in turn causes the free gas volume inside the reactor to decrease. The pressure inside the reactor will naturally drop from the initial 0.5 MPa to the range of 0.3 MPa to 0.4 MPa. This natural pressure drop directly reflects the total amount of carbon dioxide molecules that are effectively embedded.

[0039] When the pressure drop rate approaches zero, i.e., when the 30-minute settling period ends, high-purity nitrogen is slowly injected into the reactor through the gas injection pipe to raise the pressure inside the reactor back to 0.5 MPa. The gas injection rate is controlled at 0.1–1.5 L / min to avoid impact. The injection of nitrogen applies uniform isostatic pressure to the asphalt particles inside the reactor, causing the asphalt chain segments with embedded carbon dioxide molecules to be compressed a second time, further increasing the degree of chain segment entanglement. The complete process from the natural pressure drop during settling to the pressure increase after nitrogen injection is recorded as one pressure cycle.

[0040] The above-mentioned static depressurization and nitrogen replenishment were repeated three times. Each cycle followed the following sequence: allowing the pressure to drop naturally for 30 minutes, then replenishing nitrogen to raise the pressure back to 0.5 MPa. In each of the three cycles, each round of replenishment applied additional compression to the carbon dioxide molecules that were partially locked in the previous cycle, forcing the carbon dioxide molecules to migrate from the particle surface to the more internal subsurface layer. At the same time, each natural depressurization phase verified that there was no significant gas leakage.

[0041] After three cycles, carbon dioxide molecules are completely encapsulated in the core of the entangled network of asphalt segments, forming pre-formed pore cores with uniform size and fixed spatial position. These pre-formed pore cores will not merge, migrate, or escape prematurely during the subsequent heating and carbonization process. When the temperature reaches the asphalt carbonization range, the carbon dioxide molecules in the core are heated, vaporized, and expanded, which just opens up the local area locked by the chain segments from the inside, directly transforming into a microporous structure with uniform pore size and intact pore walls.

[0042] Step 3: After carbon dioxide permeation is completed, start the reactor heating system and heat treat the material at a slow heating rate of 0.3-1.0℃ / min under an inert atmosphere to reduce the temperature gradient inside the reactor and local overheating. The heat treatment temperature is 180-250℃, which is lower than the softening point of waste asphalt. This allows the asphalt chain segments to be initially shaped without melting and flowing, keeping the asphalt matrix in a highly viscoelastic or semi-solid stable range. This ensures that the molecular chain segments have a certain mobility while avoiding significant melting and flow of the material.

[0043] Once the temperature reaches the set range, it is maintained at a constant temperature for 0.5–2 hours. During this constant temperature process, carbon dioxide molecules adsorbed in the free volume region inside the asphalt particles gradually induce local microstructural rearrangement, and the asphalt molecular chains undergo slow orientation and condensation. The initial microporous structure inside the particles begins to form and gradually stabilizes. At the same time, the relatively low heating rate facilitates uniform heat transfer, keeping the internal and external thermal stress of the particles at a low level, thereby reducing the risk of pore wall cracking and collapse caused by internal stress concentration during the subsequent high-temperature carbonization stage. Since the temperature during this stage remains below the significant softening and flow temperature of the asphalt, the material as a whole maintains a relatively stable solid skeleton structure.

[0044] Step 4: After Step 3 is completed, begin the staged, progressive pressure reduction coupled with temperature increase carbonization treatment on the reactor.

[0045] Step 4-1: Under inert atmosphere protection, slowly release the pressure inside the vessel by adjusting the exhaust valve. Each pressure drop should be controlled at 0.01 to 0.05 MPa, and the duration of each pressure drop should be controlled at 2 to 10 minutes to avoid rapid escape of gas from the particles due to sudden pressure drop, which could cause pore wall rupture.

[0046] Step 4-2: After completing the single pressure reduction, shut off the exhaust system and continue to increase the temperature inside the vessel at a heating rate of 0.5 to 2℃ / min. The temperature increment of each heating stage is controlled at 5 to 20℃. After the heating is completed, maintain a constant temperature for 10 to 30 minutes to gradually stabilize the heat distribution and gas diffusion state inside the particles.

[0047] Step 4-3: Continue to perform the next round of depressurization, heating, and isothermal cycle operation until the system pressure gradually decreases to below 0.1MPa and the temperature rises to the carbonization temperature range of 600-900℃.

[0048] In this gradual process, pressure release and temperature increase are not synchronous and drastic, but are carried out in a phased and slow coupling manner, thereby reducing the instantaneous impact of gas expansion inside the particles on the pore walls under high temperature conditions; at the same time, slow heating can promote the gradual pyrolysis and condensation of the asphalt matrix and the reconstruction of the carbon skeleton, so that the initial microporous structure is stably preserved during the continuous carbonization process, and reduce the problems of pore structure collapse, uncontrolled pore size distribution and local ablation that are prone to occur in traditional rapid carbonization processes.

[0049] The following example illustrates the cyclic control process from steps 4-1 to 4-3 using a set of specific process parameters. It should be noted that the following examples are only used to explain the synergistic relationship between pressure regulation, temperature control, and pore structure stabilization in this invention, and are not intended to limit the specific implementation scope of this solution. In this example, the waste bitumen-based precursor after the low-temperature stabilization treatment in step three is used as the object to illustrate its carbonization behavior under progressive pressure reduction and staged temperature increase conditions, as detailed below:

[0050] Example Step 4-1: After the low-temperature stabilization treatment in Step 3, the asphalt-based precursor in the reactor is in a carbon dioxide adsorption state. At this time, the initial system pressure is 0.80 MPa and the temperature is 260℃. The exhaust valve is opened to slowly reduce the pressure for the first time, lowering the system pressure from 0.80 MPa to 0.76 MPa, a pressure reduction of 0.04 MPa. The entire pressure reduction process lasts for about 5 minutes, and its average pressure reduction rate is expressed as: ;

[0051] in, This refers to the magnitude of a single pressure drop. Assuming the duration of the voltage drop, after substituting the parameters of this embodiment, the average voltage drop rate is approximately... Because the depressurization process is carried out in a small, gradual manner, the adsorbed gas inside the particles can be released gradually to the outside, thereby reducing the risk of pore wall rupture caused by excessive instantaneous pressure difference. After the depressurization is completed, the current pressure state is maintained for about 2 minutes to allow the local pressure inside and between the particles to return to equilibrium, thus weakening the impact of the internal pressure gradient on the stability of the microporous structure.

[0052] Example Step 4-2: After pressure stabilization, close the exhaust valve and start the heating system to raise the reactor temperature from 260℃ to 270℃ at a heating rate of 1℃ / min, with a temperature increment of 10℃. The heating time must meet the following requirements:

[0053] in, This refers to the temperature increase in a single stage. The heating rate;

[0054] In this embodiment, the heating duration is about 10 minutes, and after reaching the target temperature, the temperature is kept constant for 15 minutes to make the heat distribution inside the asphalt matrix gradually uniform, while promoting the continuous pyrolysis, polycondensation and aromatization reactions.

[0055] During the isothermal phase, the gas diffusion process inside the particle due to the temperature increase follows Fick's diffusion law:

[0056] in, For diffusion flux, The diffusion coefficient is... For concentration gradient;

[0057] Because of the use of a lower heating rate and a staged isothermal method, the internal thermal stress and gas diffusion rate of the particles can be maintained in a relatively gentle state, thereby reducing the phenomenon of local pore structure collapse and pore size abrupt change.

[0058] Example Step 4-3: After completing the above pressure reduction, pressure stabilization, temperature increase, and isothermal processes, continue with the next cycle. In this embodiment, in the second cycle, the system pressure is further reduced from 0.76 MPa to 0.72 MPa, and the temperature is increased from 270°C to 280°C; as the number of cycles increases, the system pressure gradually decreases while the temperature gradually increases. When the cycle reaches the 20th cycle, the internal pressure of the reactor has decreased to 0.18 MPa, and the temperature has increased to 760°C, and the asphalt matrix gradually completes pyrolysis and carbonization, forming a stable carbon skeleton. Finally, the system pressure decreases to 0.08 MPa, the temperature reaches 820°C, and the final carbonization is completed at this temperature for 40 minutes. During the entire cycle, the pressure change inside the pore structure can be approximated as: ;

[0059] That is, the change in pore wall stress is positively correlated with the change in system pressure difference. Since this scheme adopts a small-amplitude, gradual pressure reduction method, it can effectively reduce the degree of instantaneous stress concentration on the pore wall and mitigate the risk of pore structure shrinkage and collapse under high temperature conditions. The specific surface area of ​​the obtained porous carbon material can reach 1200-2200 m² / g, the average pore size is controlled in the range of 0.8-1.2 nm, the proportion of micropores is significantly increased, and the pore size distribution is more concentrated and stable.

[0060] By setting a stabilization buffer process between each cycle stage, the problems of pore structure collapse, pore size widening and specific surface area reduction caused by rapid accumulation of internal stress in the traditional continuous carbonization process can be effectively mitigated, and it is conducive to forming microporous porous carbon materials with more concentrated pore size and more stable structure.

[0061] To verify the effect of the process of this invention on the regulation of the pore structure and properties of the material, the following comparative analysis is conducted on the key indicators, micromorphology, and structural characteristics of the traditional carbonization process and the optimized process of this invention, systematically explaining the influence of different process parameters on the properties of waste bitumen-based microporous carbon:

[0062] The control group used a traditional carbonization process, using the same batch and pretreated waste asphalt-based precursor as raw material. It directly carried out rapid heating carbonization at atmospheric pressure under an inert atmosphere without step-by-step pressure reduction, staged heating, or isothermal buffering. Specifically, it rapidly heated from the low-temperature stable end temperature of 260°C to 820°C at a rate of 5°C / min, and then held at this temperature for 40 minutes to complete the carbonization. The remaining raw material usage, equipment type, and environmental conditions were consistent with the experimental group. This was used to compare and verify the advantages of the present invention's staged gradual pressure reduction coupled heating carbonization process in suppressing pore structure collapse, controlling narrow pore size distribution, and improving high specific surface area.

[0063] Experimental group A is the heating rate variable group, used to investigate the effects of different heating rates on the accumulation of thermal stress, the degree of pore structure collapse and the uniformity of pore size distribution of waste asphalt-based microporous carbon. All samples adopted the same raw material pretreatment, pre-oxidation, high-pressure CO2 permeation adsorption, low-temperature stabilization and staged gradual pressure reduction coupled heating carbonization cycle process as the optimal process. Only the heating rate parameter in step four was adjusted, and the other process parameters were kept constant.

[0064] Experimental group A consisted of three temperature gradients: a slow heating rate of 0.5℃ / min, a standard heating rate of 1.0℃ / min, and a rapid heating rate of 2.0℃ / min. The standard heating rate of 1.0℃ / min represents the optimal process parameter for this invention.

[0065] By comparing the specific surface area, micropore ratio, pore size distribution and micromorphological characteristics of materials under different heating rates, the correlation between heating rate and pore structure stability is clarified.

[0066] Experimental group B is the depressurization rate variable group, used to investigate the effects of different depressurization rates on the gas release rate, instantaneous stress of pore walls and integrity of microporous carbon based on waste asphalt. All samples adopted the same raw material pretreatment, pre-oxidation, high-pressure CO2 permeation adsorption, low-temperature stabilization and staged gradual heating coupled isothermal process as the optimal process. Only the single depressurization amplitude and depressurization time in step four were adjusted to change the depressurization rate, and the other process parameters were kept constant.

[0067] Experimental group B consisted of three gradients: a slow depressurization group with a single depressurization of 0.01 MPa and a depressurization time of 5 min; a standard depressurization group with a single depressurization of 0.04 MPa and a depressurization time of 5 min; and a rapid depressurization group with a single depressurization of 0.05 MPa and a depressurization time of 5 min. Among these, the standard depressurization group with a single depressurization of 0.04 MPa and a depressurization time of 5 min represents the optimal process parameters for this invention.

[0068] By comparing the specific surface area, micropore ratio, pore size distribution and micromorphological characteristics of materials under different pressure reduction rates, the correlation between pressure reduction rate and stress concentration in pore walls is clarified.

[0069] Experimental group C is the carbonization final temperature variable group, used to explore the regulation of different carbonization final temperatures on the degree of reconstruction of microporous carbon skeleton, micropore development perfection, pore size and specific surface area of ​​waste asphalt-based microporous carbon skeleton. All samples adopted the same raw material pretreatment, pre-oxidation, CO2 high-pressure permeation adsorption, low-temperature stabilization and staged gradual pressure reduction coupled heating cycle process as the optimal process. Only the carbonization final temperature parameter in step four was adjusted, and the other process parameters were kept constant.

[0070] Experimental group C has three gradients: low temperature carbonization group 700℃, standard carbonization group 820℃, and high temperature carbonization group 900℃. Among them, the standard carbonization group 820℃ is the optimal process parameter of this invention.

[0071] By comparing the carbon element crystal structure, specific surface area, micropore ratio and pore size distribution characteristics of materials at different carbonization final temperatures, the correlation between carbonization final temperature and carbon skeleton densification, micropore shrinkage or pore expansion effect is clarified.

[0072]

[0073] The above experiments show that traditional one-step carbonization processes are prone to pore structure collapse, wide pore size distribution, low specific surface area, and numerous carbon skeleton defects due to concentrated thermal stress and rapid gas release. In contrast, the optimal process of this invention can precisely control thermal stress and gas release rate, effectively suppressing pore wall collapse and cracking, and obtaining high-performance porous carbon materials with a specific surface area of ​​1800–2200 m² / g, a micropore ratio of 88%–95%, a highly concentrated pore size distribution, and a stable carbon skeleton with few defects. At the same time, it is verified that deviations from the optimal parameter values ​​will lead to a significant decrease in material performance, providing direct data support and theoretical basis for the optimization of process parameters and industrial applications.

[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for preparing waste bitumen-based narrow-pore high specific surface area microporous porous carbon, characterized in that, include: Step 1: The waste asphalt raw material is purified and mechanically crushed to obtain asphalt powder with a particle size of 50-200μm. The asphalt powder is spread evenly and fed into a closed pre-oxidation reactor. The vacuum degree inside the reactor is controlled at -0.03 to -0.06MPa, and a low-concentration oxygen mixed atmosphere is introduced into the furnace at the same time. Step 2: Transfer the pre-oxidized asphalt powder to a high-pressure reactor, introduce carbon dioxide gas with a purity of 99.9% or higher into the reactor at a rate of 0.3 L / min until the pressure inside the reactor slowly rises to 0.5 MPa, then close the inlet valve and start the mechanical oscillation device installed on the outer wall of the reactor to make the reactor body drive the internal asphalt particles to generate periodic mechanical oscillations with a frequency of 30 Hz to 50 Hz. After the oscillation is completed, the vessel is kept still and left to stand for 30 minutes. At this time, the pressure inside the vessel naturally drops from the initial 0.5 MPa to the range of 0.3 MPa to 0.4 MPa. High-purity nitrogen is slowly injected into the vessel through the gas injection pipe to make the pressure inside the vessel rise back to 0.5 MPa. The gas injection rate is controlled at 0.1 to 1.5 L / min. The injection of nitrogen applies a uniform isostatic pressure to the asphalt particles inside the vessel. Step 3: After carbon dioxide permeation is completed, start the reactor heating system and heat treat the material at a slow heating rate of 0.3 to 1.0 °C / min under an inert atmosphere. After the temperature reaches the set range, maintain the temperature for 0.5 to 2 hours. Step 4: Perform a staged, progressive pressure reduction coupled with temperature increase carbonization treatment on the reactor, including: Step 4-1: Under inert atmosphere protection, slowly release the pressure inside the vessel by adjusting the exhaust valve. Each pressure reduction should be controlled at 0.01 to 0.05 MPa, and the duration of each pressure reduction should be controlled at 2 to 10 minutes. Step 4-2: After completing the single pressure reduction, shut off the exhaust system and continue to increase the temperature inside the reactor at a heating rate of 0.5 to 2℃ / min. The temperature increment for each heating stage should be controlled at 5 to 20℃. After the heating is completed, maintain a constant temperature for 10 to 30 minutes. Step 4-3: Continue the next round of depressurization, heating, and isothermal cycle operation until the system pressure gradually decreases to below 0.1 MPa and the temperature rises to the carbonization temperature range of 600-900℃.

2. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, In step one, the furnace temperature of the closed pre-oxidation reactor is raised to the pre-oxidation temperature range of 220-280℃ at a heating rate of 1-3℃ / min, and then maintained at a constant temperature for 1-3 hours.

3. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, In step two, the oscillation amplitude is controlled to be 1% to 2% of the vessel diameter, and the duration is 10 minutes.

4. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, In step two, the process of static pressure reduction and nitrogen replenishment is repeated. Each cycle follows the sequence of: static pressure reduction for 30 minutes, nitrogen replenishment to raise the pressure back to 0.5 MPa. In 3 to 4 cycles, each round of pressure replenishment applies additional compression to the carbon dioxide molecules that were partially locked in the previous cycle, forcing the carbon dioxide molecules to migrate from the surface of the particles to the more internal subsurface layer.

5. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, In step two, after 3 to 4 cycles, carbon dioxide molecules are completely encapsulated in the core of the entangled network of the asphalt chain segments, forming a pre-formed pore core with uniform size and fixed spatial position.

6. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, The low-concentration oxygen mixed atmosphere in step one is a mixture of nitrogen and oxygen, wherein the volume fraction of oxygen is 5% to 15% and the volume fraction of nitrogen is 85% to 95%.

7. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, The heat treatment temperature in step three is 180-250℃, which is lower than the softening point temperature of waste asphalt, so that the asphalt chain segments can be initially shaped without melting and flowing.

8. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, The depressurization process in step 4-1 is a gradient depressurization, and the stabilization time of the pressure inside the vessel after each depressurization is not less than 1 minute.

9. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, The heating process in step 4-2 is a staged heating process, and the isothermal time of each heating stage increases with the increase of carbonization temperature.

10. The preparation process of waste bitumen-based narrow-pore high specific surface area microporous porous carbon according to claim 1, characterized in that, During the multiple rounds of depressurization and heating constant temperature cycles in step 4-3, the rate of change of pressure and temperature inside the reactor is synchronously matched, so that the gasification expansion rate of the carbon dioxide pre-formed pore core inside the reactor and the shrinkage rate of the carbon skeleton are kept in dynamic equilibrium.

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