High-strength honeycomb activated carbon and preparation method thereof

Abstract

The invention relates to high-strength honeycomb activated carbon and a preparation method thereof, and belongs to the technical field of activated carbon. The preparation method of the high-strength honeycomb activated carbon comprises the following steps: (1) crushing rice hulls, performing ultrasonic cleaning, drying, and performing pre-carbonization treatment to obtain a pre-carbonized product; (2) dipping the pre-carbonized product in a pretreated phosphoric acid solution, and activating to obtain an activated product; (3) dipping the activated product in a binder, stirring and carbonizing to obtain a carbonized product; and (4) mixing the carbonized product, basalt fiber and deionized water, pugging, pouring into a mold, carrying out extrusion molding, and drying to obtain the high-strength honeycomb activated carbon. According to the honeycomb activated carbon prepared by the preparation method disclosed by the invention, activated carbon particles are firmly combined together through earlier-stage treatment and introduction of the binder and the basalt fibers, so that the overall strength of the honeycomb activated carbon is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of activated carbon and relates to a high-strength honeycomb activated carbon and a preparation method thereof. Background Art

[0002] Most of the current air purifiers use activated carbon as the filter layer to eliminate odors, absorb toxic gases, absorb dust or other impurities, and have a good filtering effect. Among them, honeycomb activated carbon is favored by consumers due to its porous structure and large specific surface area. However, the honeycomb activated carbon on the market still faces many limitations in practical applications. For example, the activated carbon itself is not strong enough and is easily damaged during transportation, installation and operation, which affects the adsorption efficiency and service life; some manufacturers will add binders during the preparation process to improve the strength of honeycomb activated carbon. However, some binders are not compatible with the activated carbon itself, or are easily decomposed under certain conditions, causing it to lose its adhesive force, etc., which leads to poor strength of honeycomb activated carbon and affects the actual application effect. Summary of the invention

[0003] The purpose of the present invention is to provide a high-strength honeycomb activated carbon and a preparation method thereof. The honeycomb activated carbon prepared by the present invention is subjected to preliminary treatment and the introduction of a binder and basalt fiber to firmly combine the activated carbon particles together, thereby effectively improving the overall strength of the honeycomb activated carbon.

[0004] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing high-strength honeycomb activated carbon, the preparation method comprising the following steps: (1) crushing the rice husk, ultrasonically cleaning it, drying it, and then pre-carbonizing it to obtain a pre-carbonized product; (2) immersing the pre-carbonized product in a pre-treated phosphoric acid solution for activation to obtain an activated product; (3) impregnating the activated product in a binder, stirring and carbonizing the activated product to obtain a carbonized product; (4) The carbonized product, basalt fiber and deionized water are mixed and kneaded into a slurry, poured into a mold, extruded and formed, and dried to obtain high-strength honeycomb activated carbon.

[0005] Furthermore, the crushing in step (1) is crushing to 5-10 mm; the parameters of the ultrasonic cleaning step are: ultrasonic power of 500-600 W, ultrasonic frequency of 30-50 kHz, and ultrasonic time of 10-20 min; the pre-carbonization treatment is to introduce a mixed gas and heat the mixture to 200-300° C. at a heating rate of 4-6° C. / min and then keep the mixture warm for 0.5-1.5 h.

[0006] Furthermore, the mixed gas includes 67-73% nitrogen and the balance argon, and the flow rate of the mixed gas is 150-200 mL / min.

[0007] Furthermore, in step (2), the pre-carbonized product is immersed in the pre-treated phosphoric acid solution for 8-12 hours; and the activation temperature and time are 350-450° C. and 30-40 minutes, respectively.

[0008] Furthermore, the raw materials of the pretreated phosphoric acid solution in step (2) include, by percentage, 0.2-0.8wt% of sodium dodecyl sulfate, 0.5-1.5wt% of nano-silicon dioxide with an average particle size of 20-50nm, and the remainder of phosphoric acid solution with a concentration of 40-48wt%.

[0009] Furthermore, the raw materials of the binder in step (3) include, by weight, 67-85 parts of modified acrylic acid solution, 10-20 parts of surface-treated silicon dioxide and 0.8-2 parts of ethylenediaminetetraacetic acid.

[0010] Furthermore, the preparation method of the modified acrylic acid solution is: 33-41 parts by weight of methyl acrylate, 3-8 parts by weight of γ-methacryloxypropyltrimethoxysilane, 0.5-2 parts by weight of nonylphenol polyoxyethylene ether, 0.03-0.07 parts by weight of potassium persulfate and 40-50 parts by weight of deionized water are mixed, and stirred at 70-80° C. for 2-4 hours to obtain a modified acrylic acid solution; The preparation method of the surface-treated modified silicon dioxide is as follows: the silicon dioxide is crushed into 80-120 meshes and then fully immersed in a treatment liquid, stirred at a speed of 400-600 rpm for 20-30 minutes, then stirred at a speed of 150-250 rpm for 10-20 minutes, and allowed to stand for 0.6-1 hour to obtain the surface-treated silicon dioxide; the treatment liquid is composed of 1-3 wt% of γ-aminopropyltriethoxysilane and the remainder of anhydrous ethanol.

[0011] Furthermore, the stirring time in step (3) is 30-50 min; the temperature and time of the carbonization are 500-600° C. and 0.8-1.2 h, respectively.

[0012] Furthermore, in step (4), the mass ratio of the carbonized product, basalt fiber and deionized water is 9-13:0.5-1.5:30-40.

[0013] Furthermore, in step (4), the mud kneading is carried out at -0.01 MPa for 0.6-1 h; the pressure of the extrusion molding is 12-18 MPa; and the temperature and time of the drying are 100-140° C. and 16-20 h, respectively.

[0014] Beneficial effects of the present invention: (1) The present invention pre-treats the raw materials through steps such as ultrasound and pre-carbonization to form a preliminary carbon skeleton structure, thereby providing more contact sites for subsequent reactions. The raw materials are then impregnated with the pre-treated phosphoric acid solution, in which the phosphoric acid molecules can interact with the carbon atoms in the carbon skeleton to etch micropores and mesopores, thereby increasing the specific surface area of ​​the activated carbon, further allowing the sodium dodecyl sulfate molecules and nano-silicon dioxide to better penetrate into the carbon structure. The small-particle size nano-silicon dioxide can support and enhance the pore structure during the activation process, thereby improving the strength of the activated carbon.

[0015] (2) The polymer structure formed by the polymerization of methyl acrylate in the modified acrylic acid solution in the binder of the present invention provides a supporting matrix for the surface-treated silica. The surface-treated silica can be evenly dispersed in the polymer network formed by the modified acrylic acid solution due to its good dispersibility and compatibility with activated carbon. The silane coupling agent on the surface of silica interacts with the components in the modified acrylic acid solution, further enhancing the stability of silica in the binder. At the same time, the polymer structure in the modified acrylic acid solution can also limit the movement of silica. The complexation of ethylenediaminetetraacetic acid can remove metal ions that may affect the dispersibility and compatibility of silica, so that it can better play the role of reinforcement and filling. The synergistic effect of the three enables the binder to more firmly combine the activated carbon particles together, thereby improving the overall strength of the honeycomb activated carbon.

[0016] (3) The present invention also adds basalt fiber, which has the characteristics of high strength, high modulus and good corrosion resistance. The basalt fiber is randomly distributed in the carbonized product and intertwined with the particles of the carbonized product. When the honeycomb activated carbon is subjected to external forces, such as compression, stretching or bending, the basalt fiber can bear part of the stress. In addition, the basalt fiber has high fracture toughness and can absorb the energy released during the crack propagation process, preventing the crack from propagating, thereby improving the overall strength and toughness of the honeycomb activated carbon. DETAILED DESCRIPTION

[0017] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0018] Example 1 A method for preparing high-strength honeycomb activated carbon, the preparation method of this embodiment comprises the following steps: (1) crushing the rice husk, ultrasonically cleaning it, drying it, and then pre-carbonizing it to obtain a pre-carbonized product; (2) immersing the pre-carbonized product in a pre-treated phosphoric acid solution at a volume ratio of 1:3 to activate the product and obtain an activated product; (3) impregnating the activated product in a binder at a volume ratio of 1:1.8, stirring and carbonizing to obtain a carbonized product; (4) The carbonized product, basalt fiber and deionized water are mixed and kneaded into a slurry, poured into a mold, extruded and formed, and dried to obtain high-strength honeycomb activated carbon.

[0019] The crushing in step (1) of this embodiment is crushing to 5 mm; the parameters of the ultrasonic cleaning step are: ultrasonic power of 500 W, ultrasonic frequency of 30 kHz, and ultrasonic time of 10 min; the pre-carbonization treatment is to introduce a mixed gas and heat it to 200 ° C at a heating rate of 4 ° C / min and then keep it warm for 0.5 h.

[0020] The mixed gas in this embodiment includes 67% nitrogen and the balance argon. The flow rate of the mixed gas in this embodiment is 150 mL / min.

[0021] The pre-carbonized product in step (2) of this embodiment is immersed in the pre-treated phosphoric acid solution for 8 hours; the activation temperature and time are 350° C. and 30 minutes, respectively.

[0022] The raw materials of the pretreated phosphoric acid solution in step (2) of this embodiment include, by percentage, 0.2 wt % of sodium dodecyl sulfate, 0.5 wt % of nano-silicon dioxide with an average particle size of 20 nm, and the remainder of a phosphoric acid solution with a concentration of 40 wt %.

[0023] The raw materials of the binder in step (3) of this embodiment include, by weight, 67 parts of modified acrylic acid solution, 10 parts of surface-treated silicon dioxide and 0.8 parts of ethylenediaminetetraacetic acid.

[0024] The modified acrylic acid solution of this embodiment is prepared by mixing 33 parts by weight of methyl acrylate, 3 parts by weight of γ-methacryloxypropyltrimethoxysilane, 0.5 parts by weight of nonylphenol polyoxyethylene ether, 0.03 parts by weight of potassium persulfate and 40-50 parts by weight of deionized water, and stirring at 70° C. for 2 hours to obtain a modified acrylic acid solution; The preparation method of the surface-treated modified silica of this embodiment is as follows: the silica is crushed into 80 meshes and then fully immersed in a treatment liquid, stirred at a speed of 400 rpm for 20 minutes, then stirred at a speed of 150 rpm for 10 minutes, and allowed to stand for 0.6 hours to obtain the surface-treated silica; the treatment liquid of this embodiment is composed of 1 wt% of γ-aminopropyltriethoxysilane and the remainder of anhydrous ethanol.

[0025] The stirring time in step (3) of this embodiment is 30 minutes; the temperature and time of carbonization are 500° C. and 0.8 hours respectively.

[0026] The mass ratio of the carbonized product, basalt fiber and deionized water in step (4) of this embodiment is 9:0.5:30.

[0027] The mud kneading in step (4) of this embodiment is carried out at -0.01 MPa for 0.6 h; the pressure of extrusion molding is 12 MPa; the temperature and time of drying are 100° C. and 16 h respectively.

[0028] Example 2 A method for preparing high-strength honeycomb activated carbon, the preparation method of this embodiment comprises the following steps: (1) crushing the rice husk, ultrasonically cleaning it, drying it, and then pre-carbonizing it to obtain a pre-carbonized product; (2) immersing the pre-carbonized product in a pre-treated phosphoric acid solution at a volume ratio of 1:3 to activate the product and obtain an activated product; (3) impregnating the activated product in a binder at a volume ratio of 1:1.8, stirring and carbonizing to obtain a carbonized product; (4) The carbonized product, basalt fiber and deionized water are mixed and kneaded into a slurry, poured into a mold, extruded and formed, and dried to obtain high-strength honeycomb activated carbon.

[0029] The crushing in step (1) of this embodiment is crushing to 10 mm; the parameters of the ultrasonic cleaning step are: ultrasonic power of 600 W, ultrasonic frequency of 50 kHz, and ultrasonic time of 20 min; the pre-carbonization treatment is to introduce a mixed gas and heat it to 300 ° C at a heating rate of 6 ° C / min and then keep it warm for 1.5 h.

[0030] The mixed gas in this embodiment includes 73% nitrogen and the balance argon. The flow rate of the mixed gas in this embodiment is 200 mL / min.

[0031] The pre-carbonized product in step (2) of this embodiment is immersed in the pre-treated phosphoric acid solution for 12 hours; the activation temperature and time are 450° C. and 40 minutes, respectively.

[0032] The raw materials of the pretreated phosphoric acid solution in step (2) of this embodiment include, by percentage, 0.8 wt % of sodium dodecyl sulfate, 1.5 wt % of nano-silicon dioxide with an average particle size of 50 nm, and the remainder of phosphoric acid solution with a concentration of 48 wt %.

[0033] The raw materials of the binder in step (3) of this embodiment include, by weight, 85 parts of modified acrylic acid solution, 20 parts of surface-treated silicon dioxide and 2 parts of ethylenediaminetetraacetic acid.

[0034] The modified acrylic acid solution of this embodiment is prepared by mixing 41 parts by weight of methyl acrylate, 8 parts by weight of γ-methacryloxypropyltrimethoxysilane, 2 parts by weight of nonylphenol polyoxyethylene ether, 0.07 parts by weight of potassium persulfate and 50 parts by weight of deionized water, and stirring at 80° C. for 4 hours to obtain a modified acrylic acid solution; The preparation method of the surface-treated modified silica of this embodiment is as follows: the silica is crushed into 120 meshes and then fully immersed in a treatment liquid, stirred at a speed of 600 rpm for 30 minutes, then stirred at a speed of 250 rpm for 20 minutes, and allowed to stand for 1 hour to obtain the surface-treated silica; the treatment liquid of this embodiment is composed of 3 wt% of γ-aminopropyltriethoxysilane and the remainder of anhydrous ethanol.

[0035] The stirring time in step (3) of this embodiment is 30-50 minutes; the temperature and time of carbonization are 600° C. and 1.2 hours respectively.

[0036] The mass ratio of the carbonized product, basalt fiber and deionized water in step (4) of this embodiment is 13:1.5:40.

[0037] The mud kneading in step (4) of this embodiment is kneading at -0.01 MPa for 1 hour; the pressure of extrusion molding is 18 MPa; the temperature and time of drying are 140° C. and 20 hours respectively.

[0038] Example 3 A method for preparing high-strength honeycomb activated carbon, the preparation method of this embodiment comprises the following steps: (1) crushing the rice husk, ultrasonically cleaning it, drying it, and then pre-carbonizing it to obtain a pre-carbonized product; (2) immersing the pre-carbonized product in a pre-treated phosphoric acid solution at a volume ratio of 1:3 to activate the product and obtain an activated product; (3) impregnating the activated product in a binder at a volume ratio of 1:1.8, stirring and carbonizing to obtain a carbonized product; (4) The carbonized product, basalt fiber and deionized water are mixed and kneaded into a slurry, poured into a mold, extruded and formed, and dried to obtain high-strength honeycomb activated carbon.

[0039] The crushing in step (1) of this embodiment is crushing to 7.5 mm; the parameters of the ultrasonic cleaning step are: ultrasonic power of 550 W, ultrasonic frequency of 40 kHz, and ultrasonic time of 15 min; the pre-carbonization treatment is to introduce a mixed gas and heat it to 250 ° C at a heating rate of 5 ° C / min and then keep it warm for 1 hour.

[0040] The mixed gas in this embodiment includes 70% nitrogen and the balance argon. The flow rate of the mixed gas in this embodiment is 175 mL / min.

[0041] The pre-carbonized product in step (2) of this embodiment is immersed in the pre-treated phosphoric acid solution for 10 hours; the activation temperature and time are 400° C. and 35 minutes, respectively.

[0042] The raw materials of the pretreated phosphoric acid solution in step (2) of this embodiment include, by percentage, 0.5 wt % of sodium dodecyl sulfate, 1 wt % of nano-silicon dioxide with an average particle size of 35 nm, and the remainder of phosphoric acid solution with a concentration of 44 wt %.

[0043] The raw materials of the binder in step (3) of this embodiment include, by weight, 76 parts of modified acrylic acid solution, 15 parts of surface-treated silicon dioxide and 1.4 parts of ethylenediaminetetraacetic acid.

[0044] The modified acrylic acid solution of this embodiment is prepared by mixing 37 parts by weight of methyl acrylate, 5.5 parts by weight of γ-methacryloxypropyltrimethoxysilane, 1.25 parts by weight of nonylphenol polyoxyethylene ether, 0.05 parts by weight of potassium persulfate and 45 parts by weight of deionized water, and stirring at 75° C. for 3 hours to obtain a modified acrylic acid solution; The preparation method of the surface-treated modified silica of this embodiment is as follows: the silica is crushed into 100 mesh and then fully immersed in the treatment liquid, stirred at a speed of 500 rpm for 25 minutes, then stirred at a speed of 200 rpm for 15 minutes, and allowed to stand for 0.8 hours to obtain the surface-treated silica; the treatment liquid of this embodiment is composed of 2 wt% of γ-aminopropyltriethoxysilane and the remainder of anhydrous ethanol.

[0045] The stirring time in step (3) of this embodiment is 40 minutes; the temperature and time of carbonization are 550° C. and 1 hour respectively.

[0046] The mass ratio of the carbonized product, basalt fiber and deionized water in step (4) of this embodiment is 11:1:35.

[0047] The mud kneading in step (4) of this embodiment is performed at -0.01 MPa for 0.8 h; the pressure for extrusion molding is 15 MPa; and the drying temperature and time are 120° C. and 18 h, respectively.

[0048] Comparative Example 1 On the basis of Example 3, the pre-carbonization treatment in step (1) was removed, and the other conditions were consistent with those in Example 3.

[0049] Comparative Example 2 On the basis of Example 3, the pretreated phosphoric acid solution in step (2) was removed and replaced with a 44 wt % phosphoric acid solution. Other conditions were the same as those in Example 3.

[0050] Comparative Example 3 On the basis of Example 3, the nano-silicon dioxide in the phosphoric acid solution pretreated in step (2) was removed and replaced with an equal weight of sodium dodecyl sulfate. Other conditions were the same as those in Example 3.

[0051] Comparative Example 4 On the basis of Example 3, the modified acrylic acid solution of the binder in step (3) was removed and replaced with an equal weight of deionized water. Other conditions were the same as those in Example 3.

[0052] Comparative Example 5 On the basis of Example 3, the surface-treated silica in the binder in step (3) was removed and replaced with an equal weight of silica, and the other conditions were the same as those in Example 3.

[0053] Comparative Example 6 On the basis of Example 3, the surface-treated silica of the binder in step (3) was removed and replaced with an equal weight of deionized water. Other conditions were the same as those in Example 3.

[0054] Comparative Example 7 On the basis of Example 3, the basalt fiber in step (4) was removed and replaced with an equal weight of deionized water, and the other conditions were the same as those in Example 3.

[0055] The high-strength honeycomb activated carbon prepared in the above Examples 1-3 and Comparative Examples 1-7 was used as a sample, and its transverse compressive strength (MPa) and longitudinal compressive strength (MPa) were tested with reference to the standard GB / T 5072-2008. The specific results are recorded in Table 1 below.

[0056] Table 1

[0057] As can be seen from Table 1, the honeycomb activated carbon prepared by the present invention has high strength and is not easy to collapse. Among them, the pre-carbonization treatment is removed in Comparative Example 1, which may affect the formation of the preliminary carbon skeleton structure, thereby affecting the contact site of the subsequent treatment and affecting the carbon strength; Comparative Example 2 replaces the pretreated phosphoric acid solution with a 44wt% phosphoric acid solution, and Comparative Example 3 replaces the nano-silicon dioxide in the pretreated phosphoric acid solution, and the pretreated phosphoric acid solution not only contains phosphoric acid to activate, but also contains sodium dodecyl sulfate and nano-silicon dioxide, etc., which can improve wettability, support pore structure, etc. The treatment of Comparative Examples 2 and 3 may cause the specific surface area and pore structure of activated carbon to be unsatisfactory, thereby affecting the carbon strength; Comparative Examples 4-6 all remove or replace a certain component in the binder, and the modified acrylic acid solution, surface-treated silica and ethylenediaminetetraacetic acid interact with each other to synergistically improve the performance of the binder, thereby affecting the carbon strength; Comparative Example 7 removes basalt fiber, and the excellent performance of basalt fiber itself can effectively improve the strength of activated carbon, prevent the expansion of cracks, and thereby affect the carbon strength.

[0058] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing high-strength honeycomb activated carbon, characterized in that: The preparation method comprises the following steps: (1) crushing the rice husk, ultrasonically cleaning it, drying it, and then pre-carbonizing it to obtain a pre-carbonized product; (2) immersing the pre-carbonized product in a pre-treated phosphoric acid solution for activation to obtain an activated product; (3) impregnating the activated product in a binder, stirring and carbonizing the activated product to obtain a carbonized product; (4) The carbonized product, basalt fiber and deionized water are mixed and kneaded into a slurry, poured into a mold, extruded and formed, and dried to obtain high-strength honeycomb activated carbon.

2. The method for preparing high-strength honeycomb activated carbon according to claim 1, characterized in that: The crushing in step (1) is crushing to 5-10 mm; the parameters of the ultrasonic cleaning step are: ultrasonic power of 500-600 W, ultrasonic frequency of 30-50 kHz, and ultrasonic time of 10-20 min; the pre-carbonization treatment is to introduce a mixed gas and heat the mixture to 200-300° C. at a heating rate of 4-6° C. / min and then keep the mixture warm for 0.5-1.5 h.

3. The method for preparing high-strength honeycomb activated carbon according to claim 2, characterized in that: The mixed gas includes 67-73% nitrogen and the balance argon, and the flow rate of the mixed gas is 150-200 mL / min.

4. The method for preparing high-strength honeycomb activated carbon according to claim 1, characterized in that: In step (2), the pre-carbonized product is immersed in the pre-treated phosphoric acid solution for 8-12 hours; the activation temperature and time are 350-450° C. and 30-40 minutes, respectively.

5. The method for preparing high-strength honeycomb activated carbon according to claim 1, characterized in that: The raw materials of the pretreated phosphoric acid solution in step (2) include, by percentage, 0.2-0.8wt% of sodium dodecyl sulfate, 0.5-1.5wt% of nano-silicon dioxide with an average particle size of 20-50nm, and the remainder of phosphoric acid solution with a concentration of 40-48wt%.

6. The method for preparing high-strength honeycomb activated carbon according to claim 1, characterized in that: The raw materials of the binder in step (3) include, by weight, 67-85 parts of modified acrylic acid solution, 10-20 parts of surface-treated silicon dioxide and 0.8-2 parts of ethylenediaminetetraacetic acid.

7. The method for preparing high-strength honeycomb activated carbon according to claim 6, characterized in that: The preparation method of the modified acrylic acid solution is as follows: 33-41 parts by weight of methyl acrylate, 3-8 parts by weight of γ-methacryloxypropyltrimethoxysilane, 0.5-2 parts by weight of nonylphenol polyoxyethylene ether, 0.03-0.07 parts by weight of potassium persulfate and 40-50 parts by weight of deionized water are mixed, and then stirred at 70-80° C. for 2-4 hours to obtain a modified acrylic acid solution; The preparation method of the surface-treated modified silicon dioxide is as follows: the silicon dioxide is crushed into 80-120 meshes and then fully immersed in a treatment liquid, stirred at a speed of 400-600 rpm for 20-30 minutes, then stirred at a speed of 150-250 rpm for 10-20 minutes, and allowed to stand for 0.6-1 hour to obtain the surface-treated silicon dioxide; the treatment liquid is composed of 1-3 wt% of γ-aminopropyltriethoxysilane and the remainder of anhydrous ethanol.

8. The method for preparing high-strength honeycomb activated carbon according to claim 1, characterized in that: The stirring time in step (3) is 30-50 minutes; the temperature and time of the carbonization are 500-600° C. and 0.8-1.2 hours respectively.

9. The method for preparing high-strength honeycomb activated carbon according to claim 1, characterized in that: In step (4), the mass ratio of the carbonized product, basalt fiber and deionized water is 9-13:0.5-1.5:30-40.

10. The method for preparing high-strength honeycomb activated carbon according to claim 1, characterized in that: The step (4) comprises kneading the clay at -0.01 MPa for 0.6-1 h; the extrusion molding pressure is 12-18 MPa; the drying temperature and time are 100-140° C. and 16-20 h, respectively.

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