Preparation method of cellulose-based high-conductivity porous carbon material

Abstract

The invention provides a preparation method of a cellulose-based high-conductivity porous carbon material, and belongs to the technical field of carbon material preparation. The preparation method comprises the following steps: mixing a cellulose raw material with an acid catalyst, carrying out a stirring reaction at 40-60 DEG C, then heating to 80-120 DEG C, and carrying out a reaction to obtain a cross-linked product; washing, drying and carbonizing the cross-linked product; and carrying out graphitization treatment on the carbonized product to obtain the product. According to the method, traditional high-temperature carbonization is replaced with acid catalysis gradient dehydration, energy consumption is reduced, the structure of the precursor is regulated and controlled, then in-situ pore forming and nitrogen doping are carried out, a strong-corrosivity activating agent is avoided, the conductivity and porosity are improved, and the technical breakthrough of green and efficient preparation of the high-performance carbon material is achieved.

Description

Technical Field

[0001] This invention belongs to the field of carbon material preparation technology, and particularly relates to a method for preparing cellulose-based highly conductive porous carbon materials. Background Technology

[0002] Cellulose-based carbon materials are made from natural cellulose (such as wood, cotton, bamboo, crop straw, waste paper, etc.) as raw materials. Through a series of processes (mainly high-temperature carbonization and activation), they are transformed into functional materials with carbon as the main component. These materials typically have a porous structure, a large specific surface area, and abundant surface functional groups.

[0003] Cellulose-based carbon materials have a wide range of applications, including supercapacitors, lithium / sodium / potassium ion batteries, fuel cells, and metal-air batteries. They can also be used in environmental remediation and adsorption, catalysis, sensors, and electronic devices, and their application prospects are even broader.

[0004] In the existing technology, the preparation of cellulose-based carbon materials mainly relies on high-temperature carbonization, chemical activation or transition metal catalysis, but there are many technical defects: (1) Traditional biomass graphitization needs to be carried out at a high temperature of over 2500℃, resulting in extremely high energy consumption. Moreover, high temperature makes it difficult to optimize crystallinity and pore structure in a coordinated manner. High-temperature carbonization will destroy the original structure of cellulose, causing pore collapse or disordered arrangement of graphite microcrystals, affecting the conductivity and specific surface area of ​​the material. (2) Existing activation methods (such as KOH and phosphoric acid activation) require highly corrosive reagents and generate a large amount of waste liquid after the reaction, which has high treatment costs and pollutes the environment. Traditional methods do not have an acid recovery system, and the direct discharge of waste acid leads to resource waste and ecological risks. (3) The carbon materials generated by direct carbonization of biomass have a low degree of graphitization and poor conductivity. The conductivity of unoptimized materials is usually below 1000 S / m, and an additional graphitization process (such as microwave treatment at 3000℃) needs to be introduced. However, traditional graphitization takes a long time (>10 hours) and has high energy consumption. (4) Although transition metal catalysis (such as iron salts) can lower the graphitization temperature to below 1000℃, the alkali metals naturally present in biomass can interfere with the catalyst activity. For example, the coexistence of Na and Fe(III) will hinder the formation of FeO and inhibit the release of reducing gases (such as CO), ultimately reducing the efficiency of graphite crystal formation. (5) The raw material pretreatment efficiency is low. Cellulose requires complex pretreatment (such as enzymatic hydrolysis and high-temperature swelling) before direct carbonization. However, existing acid treatment methods (such as 70-80% sulfuric acid) require long-term heating (>4 hours) to achieve complete hydrolysis of cellulose and are prone to side reactions (such as dehydration carbonization instead of directional crosslinking), resulting in low yield. The one-step yield at room temperature is only 33%.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing cellulose-based highly conductive porous carbon materials. By replacing traditional high-temperature carbonization with acid-catalyzed gradient dehydration, energy consumption is reduced and the precursor structure is controlled. Subsequently, in-situ pore formation and nitrogen doping are performed to avoid strong corrosive activators, thereby improving conductivity and porosity. This achieves a technological breakthrough in the green and efficient preparation of high-performance carbon materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing a cellulose-based highly conductive porous carbon material, comprising the following steps:

[0009] Cellulose raw material is mixed with an acid catalyst and stirred at 40-60℃ to react, and then the temperature is raised to 80-120℃ to react and obtain cross-linked product;

[0010] The crosslinking product was washed, dried, and carbonized.

[0011] The carbonized product is then graphitized to obtain the final product.

[0012] The dehydration and crosslinking process is carried out in stages with controlled temperature. The first stage involves a reaction at a low temperature of 40-60℃ for 1-3 hours, which promotes partial hydrolysis of cellulose into oligosaccharides and releases bound water, while simultaneously regulating the acid concentration. The second stage involves raising the temperature to 80-120℃ and maintaining it for 1-2 hours, which enables intramolecular dehydration to form a graphite-like precursor rich in COC-bonded crosslinked networks. This process, through gradient control of acid concentration and temperature, directionally generates graphite-like microcrystalline precursors, avoiding pore collapse caused by direct high-temperature carbonization. It also significantly shortens the pretreatment time to less than one-third of that of traditional acid hydrolysis processes, increasing the yield to over 60%.

[0013] Optionally, the cellulose raw material includes one or more of bamboo pulp, microcrystalline cellulose, waste paper pulp, cotton fiber, or lignocellulose.

[0014] Optionally, the acid catalyst includes concentrated sulfuric acid and / or sulfonic acid catalysts.

[0015] Furthermore, the cellulose raw material and the acid catalyst are prepared in a solid-liquid ratio of 1:(3-8).

[0016] Furthermore, the washing is performed by washing with deionized water or ethanol until neutral; the drying is performed by freeze drying, wherein the freeze drying temperature is 0-5°C.

[0017] Furthermore, the carbonization temperature is 600-900℃.

[0018] Furthermore, a mixture of NH3 and H2 is introduced into the carbonization process.

[0019] Furthermore, the flow rate of the mixed gas is 0.1-5 L / min.

[0020] Preferably, the flow rate of NH3 in the mixed gas is 10-30%.

[0021] More preferably, during the heating process of carbonization, the flow rate of the mixed gas is 2-5 L / min when the temperature is below 180°C, and 0.1-1 L / min when the temperature is above 180°C. The etching effect of NH3 forms a microporous-mesoporous hierarchical structure in the carbon framework, while in-situ nitrogen doping is achieved through gas-phase reaction, enhancing the surface wettability and electron transport efficiency of the material. This process requires no additional chemical activators, avoiding the corrosion problems of equipment caused by traditional KOH activation, and nitrogen doping improves the surface wettability and electron transport efficiency of the material. The etching effect in the low-temperature range below 180°C is optimal for forming the microporous-mesoporous hierarchical structure, while the subsequent high-temperature range above 180°C mainly involves nitrogen doping reactions.

[0022] Preferably, the graphitization process is carried out in a microwave graphitization furnace.

[0023] Furthermore, the graphitization treatment is carried out at a temperature of 2500-3000℃ for 10-30 minutes, with the microwave power density controlled at 5-15kW / kg. Microwave heating directly acts on the interior of the carbon material through molecular polar vibration, causing the graphite microcrystals to align along the (002) crystal plane, increasing the degree of graphitization to over 90% (traditional processes require more than 10 hours), while simultaneously increasing the electrical conductivity to over 4800S / m.

[0024] Preferably, the acid catalyst is recovered by vacuum distillation after the reaction is completed and recycled, which can reduce waste liquid discharge by more than 90% and reduce raw material costs.

[0025] Compared with existing technologies, this invention replaces traditional high-temperature carbonization with acid-catalyzed gradient dehydration, reducing energy consumption and regulating the precursor structure. On this basis, in-situ pore formation and nitrogen doping are performed, avoiding strong corrosive activators and improving conductivity and porosity. Microwave-assisted graphitization shortens the processing time and increases the degree of graphitization, achieving a technological breakthrough in the green and efficient preparation of high-performance carbon materials.

[0026] The carbon material obtained by this invention has both a high specific surface area (2000-2500 m²) and... 2With its hierarchical porous structure (40-60% micropores and 20-30% mesopores) and excellent conductivity (4800-6000 S / m, tested using the four-probe method), it is suitable for applications such as supercapacitor electrodes, lithium-ion battery anodes, and adsorption materials. Furthermore, compared to existing technologies, it reduces energy consumption by over 40%, waste acid emissions by over 88%, and does not rely on metal catalysts, demonstrating significant environmental and industrialization advantages.

[0027] Among them, in the testing of supercapacitors, the capacity retention rate is ≥95% after 10,000 cycles at a current of 10A / g. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] It should be noted that all raw materials used in this invention are commercially available products. Any proportions not explicitly stated in this invention can be arbitrary. All proportions not explicitly stated in this invention are by mass ratios. All technical details not elaborated upon in this invention are prior art.

[0030] Example 1

[0031] A method for preparing cellulose-based highly conductive porous carbon materials:

[0032] (1) Bamboo pulp cellulose (purity ≥95%) and 98% concentrated sulfuric acid were mixed at a solid-liquid ratio of 1:5. The mixture was first stirred and reacted in a 50℃ water bath for 2 hours, and then the temperature was raised to 100℃ and the reaction was continued for 1 hour to obtain the precursor. The waste sulfuric acid was recovered by vacuum distillation (-0.09MPa, 100℃) with a recovery rate of 92%, and was reused for the next batch of pretreatment.

[0033] (2) After washing the precursor with water until neutral, freeze-dry it at 0°C, place it in a tube furnace and introduce an NH3 / H2 mixture with 20% NH3 content. The flow rate of the mixture is 1L / min. The temperature is increased to 800°C at 5°C / min and carbonized for 2 hours to form a nitrogen-doped porous carbon framework (nitrogen content 3.2%).

[0034] (3) The carbonization product is placed in a microwave graphitization furnace and treated at 2800℃ for 20 minutes under argon protection (power density 10kW / kg) to obtain graphitized porous carbon material.

[0035] The specific surface area, as measured by testing, is 2235 m². 2 / g (BET test), (micropore content 55%, mesopore content 28%, BJH method (Barrett-Joyner-Halenda)); used as electrode material for supercapacitors, conductivity: 5100S / m (four-probe method); specific capacitance: 320F / g at 1A / g, 95% capacity retention after 10,000 cycles at 10A / g.

[0036] Example 2

[0037] A method for preparing cellulose-based highly conductive porous carbon materials:

[0038] (1) Microcrystalline cellulose (particle size 50 μm) and p-toluenesulfonic acid were mixed at a solid-liquid ratio of 1:6. The mixture was stirred in a water bath at 60°C for 1.5 hours, and then heated to 90°C for another 1.5 hours to obtain the crosslinking precursor.

[0039] Waste acid recovery: p-Toluenesulfonic acid recovery rate 94%, distillation temperature 85℃, vacuum degree -0.08MPa.

[0040] (2) After the precursor is washed with ethanol, it is freeze-dried at 0°C and placed in a tube furnace. A NH3 / H2 mixture with 15% NH3 is introduced at a flow rate of 2L / min. The temperature is increased to 700°C at 5°C / min and carbonized for 2.5 hours to form a nitrogen-doped porous carbon framework (nitrogen content 2.5%).

[0041] (3) The carbonization product is placed in a microwave graphitization furnace and treated at 2600℃ for 15 minutes under argon protection (power density 10kW / kg) to obtain highly crystalline carbon material.

[0042] Tested results show that when used as the negative electrode of lithium / sodium-ion batteries, the initial coulombic efficiency is 89% (0.1C charge / discharge); the reversible capacity is 420mAh / g at 0.5C; and the cycle stability is 91% capacity retention after 500 cycles at 1C.

[0043] Example 3

[0044] A method for preparing cellulose-based highly conductive porous carbon materials:

[0045] (1) Waste paper pulp (cellulose content 80%) is mixed with 95% sulfuric acid / benzenesulfonic acid (volume ratio 3:1) at a solid-liquid ratio of 1:4. The mixture is stirred and reacted in a water bath at 45°C for 3 hours, and then heated to 110°C and reacted for another hour to obtain the precursor, thereby achieving the simultaneous degradation of impurities (lignin, ink).

[0046] Waste acid recovery: Mixed acids are recovered through fractionation, with sulfuric acid recovery rate of 88% and benzenesulfonic acid recovery rate of 91%.

[0047] (2) The carbonization stage adopts a stepped heating method: first, the temperature is raised to 600℃ (N2 protection) at 10℃ / min and held for 1 hour to form a basic framework. Then, the temperature is switched to NH3 / H2 mixed gas with 25% NH3 and heated to 850℃ at 10℃ / min for 2 hours to form a micropore-macropore composite structure.

[0048] (3) The carbonized product was placed in a microwave graphitization furnace and treated at 2400℃ for 25 minutes under argon protection (power density 10kW / kg) to balance the conductivity and adsorption performance.

[0049] Tests showed that when used as an adsorbent material for wastewater treatment, the methylene blue adsorption capacity was 980 mg / g (initial concentration 500 mg / L). The material also exhibits an electrical conductivity of 4800 S / m (four-probe method) and a compressive strength of 12 MPa.

[0050] Example 4

[0051] A method for preparing cellulose-based highly conductive porous carbon materials:

[0052] The difference from Example 1 is in step (2): after washing the precursor with water until neutral, freeze-dry it at 0°C, place it in a tube furnace, and introduce an NH3 / H2 mixture with 20% NH3 at a flow rate of 2.5 L / min, while simultaneously raising the temperature to 180°C at 5°C / min. Then, introduce the same mixture at a flow rate of 0.5 L / min and continue to raise the temperature to 800°C at 5°C / min for 2 hours to form a nitrogen-doped porous carbon framework (nitrogen content 3.9%).

[0053] The specific surface area of ​​the obtained porous carbon material was measured to be 2378 m². 2 / g (BET test), (micropore content 58%, mesopore content 24%, BJH method (Barrett-Joyner-Halenda)); used as electrode material for supercapacitors, conductivity: 5500 S / m (four-probe method); specific capacitance is the same as in Example 1: 320 F / g at 1 A / g, capacity retention of 97% after 10,000 cycles at 10 A / g.

[0054] Comparative Example 1

[0055] Unlike Example 1, in step (1), bamboo pulp cellulose (purity ≥95%) and 98% concentrated sulfuric acid were mixed at a solid-liquid ratio of 1:5, and the mixture was directly heated to 100°C and reacted for 3 hours to obtain the precursor. The waste sulfuric acid was recovered by vacuum distillation (-0.09MPa, 100°C) with a recovery rate of 92%, and reused for the next batch of pretreatment.

[0056] The specific surface area of ​​the obtained porous carbon material was measured to be 1279 m². 2 / g (BET test), (micropores account for 33%, mesopores account for 49%, BJH method (Barrett-Joyner-Halenda)); the specific surface area is too small to be used in supercapacitors.

[0057] Comparative Example 2

[0058] Unlike Example 1, in step (2) the carbonization process, nitrogen was used to replace the NH3 / H2 mixture with 20% NH3 content.

[0059] The specific surface area of ​​the obtained porous carbon material was measured to be 570 m². 2 / g (BET test); Specific surface area is too small to be used in supercapacitors.

[0060] As can be seen from Examples 1-3, the porous carbon material of the present invention can be used in a variety of application scenarios, including the fields of new energy materials and environmental protection. As can be seen from Example 4, using a mixed gas flow rate that is initially high and then gradually decreases in the low-temperature and high-temperature stages of the carbonization process can significantly improve the etching effect of the carbon framework and the nitrogen doping effect.

[0061] Comparative Example 1 shows that without gradient acid catalytic dehydration, mesopores and macropores predominate. Comparative Example 2 shows that without NH3 / H2 mixed gas carbonization, the carbon material activation effect is poor, and the specific surface area is significantly reduced.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. In addition, those skilled in the art can understand that although some embodiments here include certain features included in other embodiments but not other features, the combination of features of different embodiments means that they are within the scope of the present invention and form different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in this background section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form implying that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a cellulose-based highly conductive porous carbon material, characterized in that, Includes the following steps: Cellulose raw material is mixed with an acid catalyst and stirred at 40-60℃ to react, and then the temperature is raised to 80-120℃ to react and obtain cross-linked product; The crosslinking product was washed, dried, and carbonized. The carbonized product is then graphitized to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The cellulose raw materials include one or more of bamboo pulp, microcrystalline cellulose, waste paper pulp, cotton fiber, or lignocellulose; And / or, the acid catalyst includes concentrated sulfuric acid and / or sulfonic acid catalysts.

3. The preparation method according to claim 1, characterized in that, The cellulose raw material and acid catalyst are prepared in a solid-liquid ratio of 1:(3-8).

4. The preparation method according to claim 1, characterized in that, The washing process involves rinsing with deionized water or ethanol until neutral. And / or, the drying is freeze-drying.

5. The preparation method according to claim 1, characterized in that, The carbonization temperature is 600-900℃.

6. The preparation method according to claim 1 or 5, characterized in that, The carbonization process is carried out by a mixture of NH3 and H2.

7. The preparation method according to claim 6, characterized in that, The flow rate of the mixed gas is 0.1-5 L / min; And / or, the flow rate of NH3 in the mixture is 10-30%.

8. The preparation method according to claim 7, characterized in that, During the heating process of carbonization, the flow rate of the mixed gas is 2-5 L / min when the temperature is below 180℃; And / or, the flow rate of the mixed gas is 0.1-1 L / min when the temperature is above 180°C.

9. The preparation method according to claim 1, characterized in that, The graphitization process is carried out in a microwave graphitization furnace; The graphitization treatment is carried out at a temperature of 2500-3000℃ for 10-30 minutes, and the microwave power density is controlled at 5-15kW / kg.

10. The preparation method according to claim 1, characterized in that, The acid catalyst is recovered by vacuum distillation after the reaction is completed and recycled.