Method for preparing porous carbon for CVD (Chemical Vapor Deposition) silicon carbon by multi-element doping with low cost and mass production

Abstract

The invention discloses a low-cost mass-production method for preparing porous carbon for CVD (chemical vapor deposition) silicon carbon by multi-element doping, which comprises the following steps: melting and mixing modified pitch and ethylene tar to form a uniform molten raw material; the preparation method comprises the following steps: pre-melting urea and sulfur to form a nitrogen-sulfur composite melt; then adding the nitrogen-sulfur composite melt, ammonium dihydrogen phosphate and boric acid into the molten raw material step by step according to the reaction temperature windows of the nitrogen-sulfur composite melt, ammonium dihydrogen phosphate and boric acid; introducing pulse air into the mixed system, and carrying out pre-crosslinking reaction in an intermittent oxygen supply mode to obtain a pre-crosslinked product with a uniform structure; performing carbonization treatment on the pre-crosslinked product in the step S3 in a mixed inert atmosphere composed of nitrogen and argon by adopting a stepped heating program to obtain a carbonized product; mixing the carbonized product with KOH, and performing high-temperature activation to obtain a coarse porous carbon material; the coarse porous carbon material is subjected to acid pickling, washing, drying and crushing, and the asphalt-based porous carbon material is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of asphalt-based carbonized material preparation, and specifically relates to a high-purity and high-structural-stability carbonized product preparation process based on a modified asphalt and ethylene tar composite raw material. BACKGROUND

[0002] Asphalt-based carbonized products are widely used in the fields of lithium ion battery negative materials, high-performance activated carbon adsorption materials, high-temperature insulation / structural materials, etc., and their core performances (such as purity, pore structure, mechanical strength, and electrical and thermal conductivity) directly depend on the optimization of raw material selection, pretreatment process, cross-linking reaction control, and carbonization system.

[0003] The current asphalt-based carbonized material preparation field has the following technical status and pain points:

[0004] Insufficient raw material adaptability: traditional processes mostly use single modified asphalt or pure ethylene tar as raw materials - pure modified asphalt has the advantages of "low ash content (usually <0.3%) and high coking value (>18%)", but has poor flowability in the molten state (especially when QI value control is poor, agglomeration easily occurs), and local overheating easily occurs during processing; pure ethylene tar has high impurity content (ash content is usually >0.5%) and large coking value fluctuations (<15%), and separate carbonization easily leads to loose product structure and insufficient purity, making it difficult to meet high requirement application scenarios (such as battery electrode materials requiring ash content <0.1%).

[0005] Low efficiency of additive action: in existing processes, functional additives such as urea (cross-linking agent), sulfur (vulcanizing agent), ammonium dihydrogen phosphate (catalyst / pore-forming agent), and boric acid (fluxing agent / structure adjusting agent) mostly use "dry powder direct mixing" or "synchronous addition" methods, which have two major problems: first, urea and sulfur have poor dispersion at room temperature, easily forming local agglomeration and leading to uneven cross-linking reaction; second, if ammonium dihydrogen phosphate (thermal decomposition temperature about 190°C) and boric acid (melting temperature about 169°C) are added synchronously, the former easily decomposes and loses effectiveness at low temperatures, and the latter easily melts too early, causing raw material adhesion, and failing to accurately match the temperature window of the cross-linking reaction.

[0006] Difficult cross-linking reaction control: the pre-cross-linking stage mostly uses a "continuous air intake" method to adjust the degree of oxidative cross-linking, but the continuous air flow is difficult to match the reactivity of the asphalt in the molten state - if the flow is too low, the cross-linking is insufficient and the subsequent carbonization is prone to cracking; if the flow is too high, local over-oxidation occurs, generating a large amount of small molecule volatile components, leading to a decrease in product yield (usually <60%).

[0007] The carbonization process to be optimized: traditional carbonization mostly adopts "single inert atmosphere (pure nitrogen or pure argon) + single heating rate": although the pure nitrogen atmosphere has low cost, there is still a trace amount of residual oxygen at high temperature (>600℃), which is easy to cause surface oxidation of the product; although pure argon is inert, the cost is 8-10 times that of nitrogen, which is not suitable for large-scale production; and the single heating rate (such as 5℃ / min throughout) either causes stress concentration in the raw material (product cracking rate >15%) due to too fast heating at low temperature, or causes low production efficiency (total carbonization time >8h) due to too slow heating at high temperature.

[0008] In summary, the existing process cannot simultaneously achieve the goals of "good raw material fluidity, high additive efficiency, uniform crosslinking reaction, low carbonization cost, and excellent product performance", and a more adaptable and more precise preparation process needs to be developed. SUMMARY

[0009] The purpose of the present application is to overcome the above-mentioned defects in the existing preparation technology of pitch-based carbon materials, and to provide a method for preparing a porous carbon for CVD silicon-carbon by multi-element doping at low cost and in large quantities. Specifically, the present application aims to solve at least one of the following four technical problems:

[0010] The purpose is to solve the problem of matching the raw material composite ratio and fluidity. By providing a composite carbon source system of modified pitch and ethylene tar, the processing fluidity of the molten raw material is significantly improved under the premise of ensuring high coking value and high purity, and agglomeration or stratification is avoided.

[0011] The purpose is to solve the problem of mismatching of additive mixing uniformity and action timing. By pre-melting treatment of urea and sulfur and stepwise temperature control addition strategy of ammonium dihydrogen phosphate and boric acid, efficient and precise use of functional additives is realized, the uniformity of crosslinking reaction is improved, and the introduction of impurities is reduced.

[0012] The purpose is to solve the problem of uncontrolled oxidation rate in the pre-crosslinking stage. By using pulse air assisted pre-crosslinking technology to replace the traditional continuous aeration mode, precise and gentle control of the oxidation crosslinking process is realized, the structure of the pre-crosslinked product is uniform, and the carbonization yield is improved.

[0013] The purpose is to solve the problem of balancing the cost of the atmosphere and the purity of the product in the carbonization process, and the contradiction between the heating system and the structural stability. By using a nitrogen-argon mixed atmosphere and a stepwise heating carbonization system, the production cost is significantly reduced, the product oxidation and cracking at high temperature are effectively inhibited, the production cycle is shortened, and the purity, structural integrity and production efficiency of the carbonized product are improved.

[0014] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0015] In a first aspect, the present application provides a method for preparing porous carbon for CVD silicon-carbon by multi-element doping with low cost and mass production.

[0016] A method for preparing porous carbon for CVD silicon-carbon by multi-element doping with low cost and mass production, comprising the following steps:

[0017] S1: raw material composite melting: melt and mix the carbon source and the auxiliary material to form a uniform molten raw material;

[0018] S2: additive pretreatment and stepwise addition: pretreat the nitrogen source and the sulfur source by melting to form a nitrogen-sulfur composite intermediate; then stepwise add the nitrogen-sulfur composite intermediate, the phosphorus source and the boron source to the molten raw material obtained in step S1;

[0019] S3: pulse air control pre-crosslinking: introduce pulse oxygen-containing gas into the mixed system of step S2 to perform pre-crosslinking reaction by intermittent oxygen supply mode to obtain a pre-crosslinked product with uniform structure;

[0020] S4: stepwise carbonization: carbonize the pre-crosslinked product of step S3 under a mixed inert gas atmosphere composed of nitrogen and argon by using a stepwise temperature program to obtain a carbonized product;

[0021] S5: activation and pore formation: mix the carbonized product of step S4 with KOH and then perform high-temperature activation to obtain a crude porous carbon material;

[0022] S6: post-treatment: perform acid washing, washing, drying and crushing on the crude porous carbon material of step S5 to obtain the pitch-based porous carbon material.

[0023] Preferably, in step S1, the carbon source is a mixture of one or more of modified pitch, coal tar pitch, petroleum residue pitch and biomass-based pitch.

[0024] More preferably, the ash content of the modified pitch is <0.1wt%, the coking value is >20wt%, and the quinoline insoluble QI is <5wt%.

[0025] More preferably, the ash content of the coal tar pitch is <0.3wt%, and the softening point is 80-120℃.

[0026] More preferably, the carbon content of the petroleum residue pitch is >85wt%, and the asphaltene content is 20-30wt%.

[0027] More preferably, the carbon content of the biomass-based pitch is >60wt%, and the oxygen content is <15wt%.

[0028] Preferably, in step S1, the auxiliary material is one or more of ethylene tar, onion oil or wash oil.

[0029] More preferably, the ethylene tar is pre-treated by vacuum distillation, the pre-treatment conditions are: 150-200℃, -0.08~-0.09MPa, removing 25-30wt% light fraction, retaining heavy fraction with >60wt% aromatic fraction and <1.5wt% sulfur content.

[0030] More preferably, the onion oil or washing oil satisfies 20℃ viscosity ≤100mPa·s, coking value >12wt%.

[0031] Preferably, in step S1, the mass ratio of the carbon source to the auxiliary material is 7-9:1-3.

[0032] Preferably, in step S1, the temperature of the melt mixing is 140-190℃, the stirring rate is 150-350rpm, and the holding time is 0.5-2h.

[0033] Preferably, in step S2, the nitrogen source is selected from at least one of urea, ammonium bicarbonate, melamine, and thiourea.

[0034] More preferably, the sulfur source is selected from at least one of sulfur, sodium sulfide, ammonium sulfate, and thiourea.

[0035] More preferably, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, 85wt% industrial phosphoric acid, and calcium phosphate.

[0036] More preferably, the boron source is selected from at least one of boric acid, borax, and zinc borate.

[0037] More preferably, when at least two substances are used to mix any one of the nitrogen source, the sulfur source, the phosphorus source, or the boron source, the mass ratio of the mixture is 1-3:1.

[0038] More preferably, when the coking value of the carbon source is >22wt%, the total amount of the additive is 3-4wt%.

[0039] More preferably, when the coking value of the carbon source is 18-22wt%, the total amount of the additive is 4-5wt%.

[0040] More preferably, when the coking value of the carbon source is <18wt%, 5-10wt% of phenolic resin is additionally added as a cross-linking agent.

[0041] Preferably, in step S2, the additive pre-treatment and the stepwise addition include the following steps:

[0042] (1) The nitrogen source and the sulfur source are placed in a constant-temperature container at 80-100℃ at a mass ratio of 1:1-2 for pre-melt mixing for 30-60 minutes to form a nitrogen-sulfur composite melt;

[0043] (2) cooling the nitrogen-sulfur composite melt to 120-140℃, and then mixing with a phosphorus source and a boron source, wherein the mass ratio of the phosphorus source to the boron source is 1-2:2-3;

[0044] (3) adding the phosphorus source to the molten raw material of step S1 when the system temperature is stabilized at 180℃, stirring for 30 minutes, then increasing the temperature to 220℃, and then adding the boron source, and continuing to stir for 20-40 minutes until uniform;

[0045] wherein the total amount of the nitrogen source, the sulfur source, the phosphorus source, and the boron source added is 3%-5% of the mass of the carbon source in step S1.

[0046] Preferably, in step S3, the oxygen-containing gas is air.

[0047] Preferably, in step S3, the air ratio of the pulsed oxygen-containing gas is 1:2-1:4, and the air flow rate is 1.0-2.5 L / min·kg of carbon source.

[0048] More preferably, in step S3, the on-off cycle of the pulsed oxygen-containing gas is 40 seconds, wherein the air is on for 30 seconds and off for 10 seconds.

[0049] Preferably, in step S3, the pre-crosslinking reaction is to increase the temperature to 250-280℃ at a rate of 5-8℃ / min, and to keep the temperature for 1.5-4 hours, and then to naturally cool down to below 150℃.

[0050] Preferably, in step S4, the volume ratio of nitrogen to argon in the mixed inert atmosphere is 2-4:1.

[0051] Preferably, in step S4, the stepwise temperature increase program is to increase the temperature to 600℃ at a rate of 2-6℃ / min and keep the temperature for 2 hours, then to increase the temperature to 800℃ at a rate of 4-10℃ / min and keep the temperature for 1 hour, and then to naturally cool down to room temperature at a rate of ≤10℃ / min.

[0052] Preferably, in step S5, the mass ratio of the carbonized product to KOH is 1:1.5-1:5.

[0053] Preferably, in step S5, the high-temperature activation is to increase the temperature to 800-900℃ at a rate of 5-8℃ / min, and to keep the temperature for 1-4 hours.

[0054] More preferably, if the mesopore ratio of the obtained porous carbon is required to be ≥50%, the activation temperature is increased to 900-950℃, the mass ratio of the carbonized product to KOH is 1:4-1:5, and the pulsed air flow rate is 2.0-2.5 L / min·kg.

[0055] More preferably, if the obtained porous carbon micropore ratio is ≥60%, the activation temperature needs to be reduced to 800-850℃, the mass ratio of carbonization product to KOH is 1:1.5-1:2, and the holding time at 600℃ in the carbonization stage is extended to 3h.

[0056] Preferably, in step S6, the acid washing is carried out by refluxing with 1-3mol / L hydrochloric acid solution at 80-90℃ for 2-3h until the pH value of the system is 6-7.

[0057] Preferably, in step S6, the washing is carried out by washing with deionized water for 3-5 times after acid washing.

[0058] Preferably, in step S6, the drying is carried out at 80-120℃ under vacuum for 4-8h.

[0059] Preferably, in step S6, the crushing is carried out to make the particle size of the final product 100-500μm.

[0060] In a second aspect, the present application provides a pitch-based porous carbon material prepared by the method.

[0061] A pitch-based porous carbon material prepared by the method.

[0062] The pitch-based porous carbon material has a specific surface area of 1980-2520m² / g, a total pore volume of 1.62-1.85cm³ / g, a micropore volume ratio of 82.0-83.4%, a pore size distribution of 77.0-82.0% in the range of 2-5nm, a crush strength of 10.2-14.8MPa, a powder conductivity of 118-132S / m, and an activation yield of 37.0-42.0%.

[0063] In a third aspect, the present application provides applications of the pitch-based porous carbon material.

[0064] The pitch-based porous carbon material can be applied in any one or more of the following fields:

[0065] (1) Energy storage field:

[0066] As a supercapacitor electrode material, it is suitable for aqueous supercapacitors and organic supercapacitors, and can be used alone or in combination with activated carbon;

[0067] As a secondary battery negative electrode material, it is suitable for lithium ion batteries, sodium ion batteries, and potassium ion batteries;

[0068] As an energy storage auxiliary material, it is used as a battery separator coating or a supercapacitor current collector conductive coating;

[0069] (2) Adsorption and purification field:

[0070] For water pollution control, heavy metal and dye wastewater treatment;

[0071] For air pollution control, adsorption of VOCs and flue gas desulfurization and denitrification;

[0072] For water purification, remove micro-pollutants in drinking water;

[0073] (3) Catalysis and cross-border fields:

[0074] As a catalyst carrier, it is suitable for noble metal catalysts, non-noble metal catalysts and photocatalysts;

[0075] For medical field, as blood perfusion adsorbent and drug carrier;

[0076] For industrial field, as high-efficiency thermal insulation material and hydrogen production electrode material.

[0077] Beneficial effects:

[0078] The present application realizes the unity of high performance, low cost and large-scale production through raw material system design, additive process innovation and process precise control:

[0079] (1) Raw material system optimization, considering processing performance and product basic performance

[0080] By matching the carbon source with the pretreated auxiliary materials, the molten raw materials have suitable fluidity, effectively avoiding agglomeration and stratification, and ensuring the smooth progress of the subsequent process. The raw material system design ensures high coking value while optimizing the processing performance, laying a solid foundation for high carbon yield of the final product.

[0081] (2) Multi-element doping process innovation, significantly improving the utilization efficiency of additives

[0082] Through the pre-melting treatment of nitrogen source and sulfur source, uniform mixing at molecular level is realized, which significantly improves the uniformity and rate of subsequent crosslinking reaction, overcoming the inherent defects of traditional dry powder mixing.

[0083] Through the step-by-step and temperature-controlled addition strategy of phosphorus source and boron source, they precisely act on their respective reaction window period, greatly improving the effective utilization rate of additives, and effectively controlling the introduction of impurities, ensuring the characteristics of low ash content and high purity of the final product.

[0084] (3) Precise control of pre-crosslinking process, ensuring product structure uniformity

[0085] The pulse air mode with specific space occupation ratio is adopted to replace the traditional continuous ventilation by intermittent oxygen supply, so as to realize precise and mild control on the oxidation and crosslinking rate. The mode effectively inhibits local overheating and excessive oxidation, so that the temperature fluctuation of the pre-crosslinking system is extremely small, thereby significantly improving the structure uniformity and consistency of the pre-crosslinking product.

[0086] (4) Carbonization and activation process is coordinated, balancing cost, efficiency and product structure

[0087] Through the coordinated design of nitrogen-argon mixed atmosphere and stepwise temperature program, the preparation cost is significantly reduced, the high-temperature oxidation is effectively inhibited, and the product cracking caused by internal stress is avoided, thereby shortening the production cycle and improving the production efficiency.

[0088] The finally prepared pitch-based porous carbon material exhibits excellent comprehensive performance: it has a developed hierarchical pore structure, high mechanical strength and good electrical conductivity, and various performance indicators (such as specific surface area, pore volume, electrical conductivity, ash content, etc.) are stably at an excellent level, so that it has great potential in multiple high-end application scenarios such as lithium ion battery negative electrode, supercapacitor electrode, adsorption and catalysis.

[0089] (5) The industrialization advantage is prominent, and it is easy to scale up

[0090] The specific types of carbon sources and auxiliary materials used in the application are bulk industrial by-products, which are widely available and low in cost; the process steps involved can be completed in conventional chemical equipment without special customization; the key process parameter range is wide and the fault tolerance is high, which is very conducive to stable industrial continuous production. DETAILED DESCRIPTION

[0091] The application will be further explained below in conjunction with examples.

[0092] Example 1

[0093] (I) Raw material preparation and pretreatment

[0094] 1. Modified pitch screening: select modified pitch with ash content 0.08wt%, coking value 22wt%, quinoline insoluble (QI) ≤4wt%, crush to particle size ≤3mm.

[0095] 2. Ethylene tar pretreatment: industrial-grade ethylene tar (density 1.05g / cm³, softening point 22℃) is first dried at 80℃ for 2h under vacuum for standby.

[0096] 3. Additive preparation: urea (analytical pure, purity ≥99.5%) and sulfur (industrial grade, purity ≥99%) are put into a double screw mixer at a mass ratio of 1:1.5, and are melt-mixed at 90℃ and a speed of 150rpm for 45min to obtain a uniform urea-sulfur composite melt.

[0097] 4. Ammonium dihydrogen phosphate (analytically pure, purity ≥ 99%) and boric acid (analytically pure, purity ≥ 99.5%) were separately ground into uniform powders at room temperature by a planetary ball mill (rotation speed 300 rpm, ball-to-material ratio 5:1).

[0098] 5. Substrate melting: 4.0 kg of modified pitch and 1.0 kg of ethylene tar (mass ratio 8:2) were added to a 5L high-pressure reaction kettle (with mechanical stirring and temperature control system). After sealing the reaction kettle, nitrogen was introduced to replace the air three times. The stirring speed was set to 250 rpm, and the temperature was raised to 160°C at a rate of 10°C / min. After maintaining the temperature for 72 min, a uniform pitch-ethylene tar melting system was obtained.

[0099] (B) Pre-crosslinking reaction

[0100] 6. Additives were added step by step:

[0101] First step: When the temperature of the melting system stabilized at 180°C, all the urea-sulfur complex melt prepared in step 3 was slowly added through the feeding port of the reaction kettle, and the feeding time was controlled within 10 min, maintaining a stirring speed of 250 rpm.

[0102] Second step: At 180°C, 70 g of ammonium dihydrogen phosphate powder was slowly added to the system, and the feeding time was controlled within 5 min. The stirring speed was continued at 250 rpm for 30 minutes.

[0103] 7. After completing the second step of step 6 above, the temperature was raised to 220°C at a rate of 5°C / min. After the temperature stabilized, 130 g of boric acid powder was added to the system, with a feeding time of 5 min, and the stirring speed was increased to 280 rpm, lasting for 30 minutes until the mixture was uniform.

[0104] The total amount of ammonium dihydrogen phosphate and boric acid added was 5% of the total mass of the carbon source (modified pitch) in step 5.

[0105] 8. Pulse air-assisted pre-crosslinking: The pulse air system was turned on, and compressed air with a duty cycle of 1:3 (i.e., 10 s on, 30 s off) was introduced, with a flow rate controlled at 1.8 L / min·kg of pitch. The temperature was raised to 260°C at a rate of 7°C / min, and the temperature was maintained for 2.5 h.

[0106] (III) Carbonization treatment

[0107] 9. Pre-crosslinking product crushing: After the pre-crosslinking reaction was completed, the product was cooled to room temperature, crushed to a particle size of 8 mm by a jaw crusher, and sieved for later use.

[0108] 10. Inert atmosphere carbonization: 1.0 kg of the pre-crosslinked product after crushing was loaded into a tube furnace (quartz tube, inner diameter 100 mm), and a nitrogen-argon mixed atmosphere (volume ratio 3:1, total flow rate 500 mL / min) was introduced to replace the air in the tube furnace for 3 times;

[0109] 11. First stage temperature rise: temperature rise to 600°C at a rate of 4°C / min, and holding for 2 h; second stage temperature rise: temperature rise to 800°C at a rate of 8°C / min, and holding for 1 h; after carbonization, natural cooling to room temperature (cooling rate 8°C / min), to obtain black blocky carbonized product (carbon yield about 65-70 wt%).

[0110] (Four) KOH activation to form pores

[0111] 12. Activator mixing: the carbonized product was crushed to a particle size of 3-5 mm, mixed with KOH particles (analytical pure, purity ≥ 85%) at a mass ratio of 1:3, and deionized water was added (solid-liquid ratio 1:2), and stirred at 60°C and a rotation speed of 200 rpm for 30 min, so that the KOH was fully soaked into the carbonized product;

[0112] 13. High temperature activation: the mixed material was transferred to a corundum boat and placed in a tube furnace, and nitrogen was introduced (flow rate 400 mL / min) to heat to 850°C at a rate of 6°C / min, and holding for 2 h;

[0113] 14. Cooling of the crude product: after the activation was completed, nitrogen was continuously introduced to cool to below 100°C, and the crude pitch-based porous carbon material was taken out.

[0114] (Five) Post-treatment (acid washing-drying-crushing)

[0115] 15. Acid washing to remove impurities: the crude porous carbon material was placed in a 7.1 wt% hydrochloric acid solution (solid-liquid ratio 1:10), and refluxed at 85°C and a rotation speed of 150 rpm for 2.5 h; then repeatedly washed with deionized water until the filtrate pH=7;

[0116] 16. Drying: the porous carbon material after acid washing was placed in a vacuum drying oven, and dried at 100°C and -0.09 MPa for 8 h;

[0117] 17. Crushing and grading: the dried porous carbon was crushed by an air flow crusher, and the product with a particle size of 50-75 mesh (200-300 μm) was screened out, i.e. the final pitch-based porous carbon material (activation yield about 45-50 wt% based on the mass of modified pitch).

[0118] Example 2

[0119] The steps are consistent with Example 1, and the difference is:

[0120] Step S4: carbonization product and KOH mass ratio 1:2, activation heating rate 5°C / min, activation temperature 800°C, holding time 2.5 hours;

[0121] The remaining steps: Step S1 (modified pitch-ethylene tar 7:3), Step S1 (urea-sulfur 1:1.2), Step S2 (ammonium dihydrogen phosphate-boric acid 1.5:2.5), S3-S5 same as Example 1.

[0122] Example 3

[0123] The same as the steps of Example 1, the difference is: in step S4, the carbonization product and KOH mass ratio is 1:4, the activation heating rate is 8°C / min, the activation temperature is 900°C, and the holding time is 1.5 hours

[0124] Example 4

[0125] The same as the steps of Example 1, the difference is: in step S5, the activation heating rate is 7°C / min, the activation temperature is 880°C, and the holding time is 2 hours (KOH ratio 1:2.5)

[0126] Comparative Example 1

[0127] The same as the steps of Example 1, the difference is: omit step S4 (KOH activation), directly perform acid washing (same as Example 1), drying, and crushing on the carbonization product of step S3;

[0128] Comparative Example 2

[0129] The same as the steps of Example 1, the difference is: in step S4, KOH (mass ratio 1:3 with modified pitch) is mixed with the pre-crosslinked crushed product, and carbonization and activation are performed simultaneously (i.e. 4°C / min to 600°C for 2h, 8°C / min to 800°C for 1h, no subsequent 850°C separate activation)

[0130] Comparative Example 3

[0131] The same as the steps of Example 1, the difference is: in step S5, only 85°C deionized water is used to wash the crude porous carbon material (pH is measured every 30 minutes), until pH=6-7 (without hydrochloric acid), and the remaining post-processing parameters (drying, crushing) are the same as Example 1.

[0132] Comparative Example 4

[0133] The same as the steps of Example 1, the difference is: in step S3, the carbonization product is directly heated to 800°C at a rate of 5°C / min, and held for 3 hours (without the 600°C holding step), and the activation parameters in step S5 are the same as Example 1.

[0134] The porous carbon obtained in the above examples and comparative examples is tested as follows.

[0135] Test method notes: ① Specific surface area / pore volume / micropore volume: liquid nitrogen adsorption-desorption method (BET model, micropore definition <2 nm); ② Crushing strength: after powder tabletting (pressure 5 MPa), the compressive strength is measured by a universal mechanical testing machine; ③ Powder conductivity: four-probe method (sample pressing density 1.0 g / cm³); ④ Activation yield: (final porous carbon mass / initial modified pitch mass) × 100%; ⑤ Pore size distribution concentration: the proportion of 2-5 nm pore size to total pore volume.

[0136] The test results are shown in Table 1.

[0137] Table 1

[0138] Evaluation index Unit Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Total pore volume cm³ / g 1.85 1.62 1.78 1.70 0.55 1.18 1.64 1.35 Specific surface area (BET) m² / g 2350 1980 2520 2410 580 1650 2320 1820 Proportion of micropore volume % 83.4 83.1 82.0 82.9 80.0 79.2 83.0 80.3 Crushing strength MPa 12.5 14.8 10.2 11.8 28.5 8.5 12.2 9.0 Powder conductivity S / m 125 118 132 128 140 105 122 110 Activation yield % 41.0 42.0 37.0 39.0 - (no activation) 32.0 39.0 34.0 Pore size distribution concentration (proportion of 2-5 nm) % 80.0 77.0 82.0 81.0 50.0 65.0 79.0 70.0

[0139] Data regularity explanation:

[0140] Pore structure parameters: Examples 1-4 are activated by KOH alone and have a stepwise carbonization, and the total pore volume and specific surface area are significantly higher than those of the comparative examples (the lowest in Comparative Example 1 without activation, and insufficient in Comparative Example 2 with simultaneous activation); Example 3 has the highest pore volume and specific surface area due to high KOH ratio (1:4) and high activation temperature (900°C), but the lowest activation yield (excessive KOH leads to increased carbon loss).

[0141] Crushing strength: Comparative Example 1 has no pore structure and the highest strength (28.5 MPa); Example 2 has a low KOH ratio (1:2) and a relatively dense pore structure, and the strength is higher than that of Example 3 (14.8 MPa vs. 10.2 MPa); Comparative Example 2 has the lowest strength (8.5 MPa) due to loose structure caused by simultaneous activation.

[0142] Conductivity: Example 3 has the highest conductivity (132 S / m) due to high activation temperature (900°C) and slightly higher graphitization degree; Comparative Example 2 has the lowest conductivity (105 S / m) due to loose structure.

[0143] Pore size concentration: Examples 1-4 have a 2-5 nm pore size ratio of 72%-78% due to stepwise carbonization and precise activation, which is significantly higher than that of the comparative examples (45% in Comparative Example 1), reflecting the precise control ability of the process on the pore structure.

[0144] In summary, the present application focuses on the following four core technical problems to address the pain points of the prior art, and through precise design of process parameters and step innovation, the performance of the carbonized product and the preparation efficiency are synergistically improved:

[0145] 1. Raw material compound matching and flowability problem: Solve the contradiction of "poor flowability and unstable coking value" of traditional single raw material (pure modified asphalt / pure ethylene tar) - by limiting the mass ratio of "modified asphalt: ethylene tar = 7-9:1-3", and clearly defining the key indicators of modified asphalt (ash content <0.1%, coking value >20%, QI <5%), both retain the advantages of "high purity and high coking value" of modified asphalt, and adjust the melt viscosity through ethylene tar (rich in light aromatic hydrocarbons) to meet the stirring (200-300 rpm) requirements after melting at 150-180℃, avoiding agglomeration or stratification.

[0146] 2. Additive mixing uniformity and timing mismatch problem: Solve the problem of traditional "poor dispersion of dry powder mixing and simultaneous addition failure" - ① By "pre-melting and mixing urea and sulfur at 80-100℃ in a mass ratio of 1:1-2", the molecular diffusion of the melt is used to achieve uniform dispersion of both, improving the crosslinking reaction activity; ② Limit "ammonium dihydrogen phosphate added at 180℃ (match its thermal decomposition temperature, avoid premature failure), boric acid added at 220℃ (match the fluxing demand in the middle of the crosslinking reaction)", and control the total amount of both to 3%-5% of the asphalt mass (avoid excessive introduction of impurities), achieve "precise action on the reaction window period" of additives.

[0147] 3. Oxidation rate out of control in pre-crosslinking stage: Solve the problem of "excessive oxidation / insufficient crosslinking caused by continuous air intake" in traditional process - use "pulse air with air occupation ratio 1:3 (flow rate 1.5-2 L / min·kg asphalt)", precisely control the oxidation rate through "air intake-air stop" pulse mode: air intake stage provides oxygen needed for crosslinking, air stop stage releases local reaction heat, avoids local temperature rise caused by continuous air intake (temperature difference can be controlled within ±5℃), ensures uniform structure of pre-crosslinking product, no local carbonization or uncrosslinked area.

[0148] 4. Carbonization atmosphere cost and product purity balance, heating schedule and structure stability contradiction problem: ① Solve the problem of "high cost of pure argon and insufficient purity of pure nitrogen" - use "nitrogen:argon = 3:1 (V:V) mixed atmosphere", nitrogen can quickly replace air in the system and inhibit high-temperature oxidation, argon can make up for the deficiency of nitrogen inertness, reduce the cost of the atmosphere by more than 60% on the premise of ensuring the ash content of the product <0.1%; ② Solve the problem of "cracking / low efficiency caused by single heating rate" - design "3-5℃ / min heating to 600℃ (2h holding, slowly release small molecule volatile, avoid internal stress cracking) → 5-10℃ / min heating to 800℃ (1h holding, quickly complete deep carbonization, improve production efficiency)" stepwise heating schedule, reduce the cracking rate of the product to less than 5%, shorten the total carbonization time to 5-7h (20%-30% shorter than traditional process).

[0149] The pitch-based porous carbon material prepared by the specific process described in the above examples exhibits a series of excellent comprehensive performance, making it have broad application prospects in multiple high-tech fields.

[0150] (I) Excellent comprehensive performance

[0151] Excellent basic physicochemical performance: The product has a high specific surface area (1800-2800 m² / g), a large total pore volume (1.2-2.0 cm³ / g), good electrical conductivity (powder electrical conductivity ≥ 80 S / m), and high mechanical strength (crushing strength ≥ 10 MPa), and the production process is stable, the activation yield is ≥ 35%, and the key index deviation between batches is small.

[0152] Excellent purification and stability: The product is high in purity after acid washing, has a neutral pH value (6-7), and has very low residual ion content. At the same time, the product shows excellent environmental tolerance, and its structure and performance can still remain highly stable under harsh conditions such as high temperature (300°C), strong acid (pH = 1), and strong base (pH = 13).

[0153] Reliable long-term use performance: In the main application scenarios of the product, it shows good long-term stability. As an electrode material, the capacity retention rate is still excellent after 10,000 cycles in supercapacitors, and the capacity decay is controllable after 500 cycles in lithium-ion batteries; as an adsorbent, it can still maintain most of the initial adsorption capacity after multiple adsorption-desorption cycles.

[0154] (II) Broad application scenarios

[0155] Based on the above excellent performance, the pitch-based porous carbon material of the present application can be widely used in the following fields:

[0156] (1) Energy storage field

[0157] Supercapacitors: can be used as high-performance electrode materials, suitable for water-based supercapacitors (6M KOH, 3M H2SO4 electrolyte), organic supercapacitors (1 mol / L TEABF4 / acetonitrile, EMIMBF4 ionic liquid electrolyte), which can be used alone or in combination with activated carbon (mass ratio 1-3:1), and the prepared electrode has a high compaction density (≥0.8 g / cm³).

[0158] Secondary batteries: suitable for lithium-ion batteries (as a graphite composite negative electrode additive, the addition amount is 5-10 wt%), sodium-ion batteries (as a single negative electrode, the initial discharge capacity is ≥ 300 mAh / g), and potassium-ion batteries (as a negative electrode, the capacity is ≥ 250 mAh / g at 0.1C rate), and has good compatibility with common electrolytes.

[0159] Energy storage auxiliary materials: can be used as battery separator coating material (coating thickness 5-10 μm, significantly improve the wettability of electrolyte, the liquid absorption rate of the separator is greater than or equal to 200%), supercapacitor current collector conductive coating (coating thickness 1-3 μm, effectively reduce the contact resistance less than or equal to 1 Ω).

[0160] (2) Adsorption and purification field

[0161] Water pollution control: can efficiently adsorb heavy metal ions (such as Pb2+, Cd2+, Hg2+) in industrial wastewater and printing and dyeing wastewater dyes (such as methylene blue, rhodamine B), the treatment capacity is greater than or equal to 500L / kg material, and the adsorption equilibrium time is less than or equal to 60min.

[0162] Air pollution control: has high adsorption capacity (fixed bed adsorption, breakthrough time is greater than or equal to 10h) to VOCs (benzene, toluene, xylene), and can be used for flue gas desulfurization and denitrification (adsorption SO2 capacity is greater than or equal to 100mg / g, NOx capacity is greater than or equal to 50mg / g), and can be regenerated at 150-200℃.

[0163] Advanced water purification: suitable for advanced removal of micro-pollutants (such as antibiotics, algal toxins) in drinking water, the removal rate is greater than or equal to 90%, and the material itself has no leachables, which ensures the safety of drinking water.

[0164] (3) Catalysis and cross-border field

[0165] Catalysis field: as an excellent catalyst carrier, it is suitable for noble metal catalysts (such as Pt, Pd, loading capacity 1-5wt%) for catalytic hydrogenation reaction (conversion rate greater than or equal to 95%), non-noble metal catalysts (such as Fe-N-C, Co-N-C) for oxygen reduction reaction (half-wave potential greater than or equal to 0.8V vs RHE), and light catalysts (such as TiO2, g-C3N4) carrier for photocatalytic degradation of organic matter.

[0166] Medical field: can be used as blood perfusion adsorbent, and can efficiently adsorb bilirubin, creatinine and other toxins; also can be used as drug carrier, and can load ibuprofen and other drugs and realize controllable slow release.

[0167] Industrial field: due to its porous structure and thermal stability, it can be used as high-efficiency heat insulation material (porosity greater than or equal to 80%, thermal conductivity less than or equal to 0.05W / (m·K)); its good electrical conductivity also makes it show application potential as electrode material in water electrolysis hydrogen production and other energy conversion technologies.

[0168] In summary, the asphalt-based porous carbon material provided by the application not only has excellent core performance indicators, but also has structural stability under extreme conditions, long service life, and can meet the stringent requirements of carbon material performance in energy storage, environmental protection, catalysis, medical treatment and other high-end fields, and has very broad application prospect.

[0169] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing porous carbon for CVD silicon-carbon using multi-element doping with low cost mass production, characterized in that: Comprise the following steps: S1: raw material composite melting: melt mixing carbon source and auxiliary materials to form a uniform melt raw material; S2: additive pretreatment and stepwise addition: pre-melt treatment of nitrogen source and sulfur source to form a nitrogen-sulfur composite intermediate; then the nitrogen-sulfur composite intermediate, phosphorus source and boron source are added stepwise to the melt raw material obtained in step S1; S3: Pulse air control pre-crosslinking: pulse oxygen-containing gas is introduced into the mixing system of step S2, and pre-crosslinking reaction is carried out by intermittent oxygen supply mode to obtain a pre-crosslinked product with uniform structure; S4: Stepwise carbonization: the pre-crosslinked product of step S3 is carbonized under a mixed inert gas atmosphere composed of nitrogen and argon using a stepwise temperature program to obtain a carbonized product; S5: Activation and pore forming: the carbonized product of step S4 is mixed with KOH and then high-temperature activated to obtain a crude porous carbon material; S6: Post-processing: the crude porous carbon material of step S5 is subjected to acid washing, washing, drying and crushing to obtain the pitch-based porous carbon material.

2. The method of claim 1, wherein: In step S1, The carbon source is a mixture of one or more of modified pitch, coal tar pitch, petroleum residue pitch, and biomass-based pitch; Wherein, the ash content of modified pitch is <0.1wt%, the coking value is >20wt%, and the quinoline insoluble QI is <5wt%; the ash content of coal tar pitch is <0.3wt%, and the softening point is 80-120℃; the carbon content of petroleum residue pitch is >85wt%, and the asphaltene content is 20-30wt%; the carbon content of biomass-based pitch is >60wt%, and the oxygen content is <15wt%; The auxiliary material is one or more of ethylene tar, onion oil or wash oil; Wherein, the ethylene tar is pretreated by vacuum distillation, and the pretreatment conditions are: 150-200℃, -0.08~-0.09MPa, removing 25-30wt% light fraction, retaining heavy fraction with >60wt% aromatic fraction and <1.5wt% sulfur content; the onion oil or wash oil satisfies 20℃ viscosity ≤100mPa·s, and the coking value is >12wt%. The mass ratio of the carbon source to the auxiliary material is 7-9:1-3; The temperature of melt mixing is 140-190℃, the stirring rate is 150-350rpm, and the holding time is 0.5-2h.

3. The method of claim 1, wherein: In step S2, The nitrogen source is selected from at least one of urea, ammonium bicarbonate, melamine, and thiourea; The sulfur source is selected from at least one of sulfur, sodium sulfide, ammonium sulfate, and thiourea; The phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, 85wt% industrial phosphoric acid, and calcium phosphate; The boron source is selected from at least one of boric acid, borax, and zinc borate; When at least two substances are used to mix any of the nitrogen source, sulfur source, phosphorus source or boron source, the mixed mass ratio is 1-3:1; When the coking value of the carbon source is >22wt%, the total additive amount is 3-4wt%; when the coking value is 18-22wt%, the additive amount is 4-5wt%; when the coking value is <18wt%, 5-10wt% of phenolic resin needs to be additionally added as a crosslinking agent.

4. The method according to claim 1 or 3, characterized in that: In step S2, The additive pretreatment and stepwise addition comprise the following steps: (1) Put the nitrogen source and the sulfur source in a constant-temperature container at 80-100℃, with a mass ratio of 1:1-2, and pre-melt and mix for 30-60 minutes to form a nitrogen-sulfur composite melt; (2) After cooling the nitrogen-sulfur composite melt to 120-140℃, mix it evenly with the phosphorus source and the boron source, wherein the mass ratio of the phosphorus source to the boron source is 1-2:2-3; (3) To the molten raw material of step S1, when the system temperature is stabilized at 180℃, add the phosphorus source, stir for 30 minutes, then raise the temperature to 220℃, and then add the boron source, continue to stir for 20-40 minutes until uniform; wherein the total amount of the nitrogen source, the sulfur source, the phosphorus source, and the boron source added is 3%-5% of the mass of the carbon source in step S1.

5. The method of claim 1, wherein: In step S3, the oxygen-containing gas is air; the air flow rate of the pulse oxygen-containing gas is 1.0-2.5 L / min·kg of carbon source, with an air-to-gas ratio of 1:2-1:4; the pre-crosslinking reaction is to raise the temperature to 250-280℃ at a rate of 5-8℃ / min, and keep the temperature at this level for 1.5-4 hours, and then naturally cool to below 150℃.

6. The method of claim 1, wherein: In step S4, the volume ratio of nitrogen to argon in the mixed inert atmosphere is 2-4:1; the stepwise temperature program is: raise the temperature to 600℃ at a rate of 2-6℃ / min and keep the temperature for 2 hours, then raise the temperature to 800℃ at a rate of 4-10℃ / min and keep the temperature for 1 hour, and then naturally cool to room temperature at a rate of ≤10℃ / min.

7. The method of claim 1, wherein: In step S5, the mass ratio of the carbonized product to KOH is 1:1.5-1:5; the high-temperature activation is to raise the temperature to 800-900℃ at a rate of 5-8℃ / min, and keep the temperature for 1-4 hours; if the mesopore ratio of the obtained porous carbon is required to be ≥50%, the activation temperature needs to be increased to 900-950℃, the mass ratio of the carbonized product to KOH is 1:4-1:5, and the pulse air flow rate is 2.0-2.5 L / min·kg; if the micropore ratio of the obtained porous carbon is required to be ≥60%, the activation temperature needs to be reduced to 800-850℃, the mass ratio of the carbonized product to KOH is 1:1.5-1:2, and the carbonization stage 600℃ keeps the temperature for 3 hours.

8. The method of claim 1, wherein: In step S6, the acid pickling is to use 1-3 mol / L hydrochloric acid solution to treat at 80-90℃ for 2-3 hours until the pH value of the system is 6-7; the washing is to wash 3-5 times with deionized water after acid pickling; the drying is to be carried out at 80-120℃ under vacuum for 4-8 hours; the crushing is to make the final product particle size 100-500 μm.

9. A pitch-based porous carbon material prepared by the method of any one of claims 1-8.

10. Use of the pitch-based porous carbon material according to claim 9, characterized in that: It can be applied to any one or more of the following fields: (1) Energy storage field: As a supercapacitor electrode material, it is suitable for water-based supercapacitors and organic supercapacitors, and can be used alone or in combination with activated carbon; As a secondary battery negative electrode material, it is suitable for lithium ion batteries, sodium ion batteries, and potassium ion batteries; As an energy storage auxiliary material, it is used as a battery separator coating or a supercapacitor current collector conductive coating; (2) Adsorption and purification field: Used for water pollution treatment, heavy metal and dye treatment of industrial wastewater and dyeing wastewater; For air pollution control, adsorption of VOCs and flue gas desulfurization and denitrification; For water purification, removal of micro-pollutants in drinking water; (3) Catalysis and cross-border fields: As a catalyst carrier, it is suitable for noble metal catalysts, non-noble metal catalysts and photocatalysts; Used in medical field as blood perfusion adsorbent and drug carrier; Used in industrial field as high-efficiency thermal insulation material and water electrolysis hydrogen production electrode material.