High-strength honeycomb activated carbon and method for preparing the same

Abstract

The present application provides a kind of high-strength honeycomb activated carbon and its preparation method, the preparation raw material of the honeycomb activated carbon includes: powdered activated carbon, star type water-based epoxy resin, curing agent, water, surfactant, the star type water-based epoxy resin is prepared by first using alkyl sulfate to etherification of alkali lignin, then using etherified alkali lignin and epoxy compound to form branched chain by chain extension, finally using epoxy chloropropane to epoxy the end of branched chain.The specific surface area of the honeycomb activated carbon is large after curing and drying, and the adsorption capacity is strong, and it also has higher strength.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon technology, specifically relating to a high-strength honeycomb activated carbon and its preparation method. Background Technology

[0002] Honeycomb activated carbon is a new type of composite functional activated carbon with many parallel interconnected pores in its internal structure. It not only has the advantages of activated carbon such as high specific surface area, controllable pore structure and acid and alkali resistance, but also has a unique honeycomb structure with advantages such as high porosity, low pressure drop and strong resistance to dust clogging. It is widely used in gas purification, gas storage, catalysts or catalyst carriers and other fields.

[0003] Based on differences in the preparation process, honeycomb activated carbon can be divided into two types: coated honeycomb structures and monolithic honeycomb structures. Coated honeycomb structures consist of a honeycomb carrier and a carbon layer coated on the carrier. This type of structure has a lower carbon content per unit volume and stronger mechanical properties than monolithic honeycomb structures, but it suffers from severe coating peeling and has been gradually abandoned. In monolithic honeycomb structures, carbon or carbon precursors are added during the formation of the honeycomb structure, resulting in a high carbon content per unit volume. However, its mechanical properties are poor, and once the structure is damaged, the reactor must be rebuilt, which is expensive. Therefore, ensuring the overall mechanical strength of the honeycomb structure is crucial. A common method to improve mechanical strength is to use organic binders, such as polyvinyl alcohol, methylcellulose, carboxymethylcellulose, or hydroxymethylcellulose, to bond powdered activated carbon together. However, this method is not very effective. Researchers in this field have conducted extensive studies on this topic. For example, patent CN103708451B discloses a method for preparing honeycomb activated carbon bonded with asphalt. The asphalt used is aqueous emulsified asphalt, which is added in small quantities and is easy to mix. While the asphalt plays a binding role, it reduces the amount of organic binder used, thus ensuring the high specific surface area and high strength of the honeycomb activated carbon. This patent uses aqueous emulsified asphalt to replace part of the organic binder. Although this strongly bonds the powdered activated carbon together, the main component of asphalt is a high-molecular-weight hydrocarbon compound, which, when attached to the surface of the activated carbon, is not conducive to the adsorption of polar gases.

[0004] Patent CN101214957B discloses a water-resistant, high-mechanical-strength honeycomb activated carbon and its preparation method. This method involves mixing activated carbon, inorganic binder, and sintering flux. The premixed material is then kneaded with organic binder, water, and lubricating oil, extruded, dried, and heat-treated. The water-resistant honeycomb activated carbon produced by this method has high mechanical strength, good heat resistance, and good water resistance. However, in order to improve the strength, the amount of clay used accounts for about 70 wt% of the activated carbon, which greatly reduces the specific surface area and adsorption capacity of the finished honeycomb activated carbon.

[0005] In summary, there is an urgent need to develop a honeycomb activated carbon that combines high strength, large specific surface area, and good adsorption performance for polar gases. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a high-strength honeycomb activated carbon and its preparation method. A star-shaped waterborne epoxy resin is prepared using alkali lignin with a three-dimensional structure, alkyl sulfate, epoxy compounds, and epichlorohydrin as raw materials. Because the star-shaped waterborne epoxy resin contains polar groups such as ether bonds on its side chains, it endows this resin with excellent water dispersibility and adhesion to activated carbon. The honeycomb activated carbon prepared by bonding powdered activated carbon with this star-shaped waterborne epoxy resin has a large specific surface area and strong adsorption capacity after curing and drying, and also has high strength.

[0007] To achieve the above objectives, the following technical solution is adopted:

[0008] A high-strength honeycomb activated carbon comprises the following raw materials: powdered activated carbon, star-shaped waterborne epoxy resin, curing agent, water, and surfactant. The star-shaped waterborne epoxy resin is prepared by first etherifying alkali lignin with alkyl sulfate, then extending the chain of the etherified alkali lignin with an epoxy compound to form branches, and finally epoxidizing the ends of the branches with epichlorohydrin.

[0009] Further, the raw materials include the following parts by weight: 100 parts powdered activated carbon, 10-15 parts star-shaped waterborne epoxy resin, 0.5-0.8 parts curing agent, 50-80 parts water, and 1-3 parts surfactant. The amount of alkyl sulfate ester is 25-30 wt% of alkali lignin, the amount of epoxy compound is 20-30 wt% of alkali lignin, and the amount of epichlorohydrin is 30-40 wt% of alkali lignin.

[0010] Alkali lignin has a three-dimensional spatial structure. First, the etherification reaction with alkyl sulfate esters is used to adjust and reduce the hydroxyl groups on the lignin spherical core. Then, the chain extension reaction with epoxy compounds is used to form branches, which move the active hydroxyl groups away from the spherical core, while improving the polarity and hydrogen bonding ability of the branches. Finally, epichlorohydrin is used for epoxidation to obtain a star-shaped waterborne epoxy resin with strong adhesive properties and epoxy groups at the end.

[0011] The alkyl sulfate ester is selected from one or a combination of two of dimethyl sulfate and diethyl sulfate.

[0012] The epoxy compound is selected from one or a combination of two of propylene oxide and ethylene oxide.

[0013] The star-shaped aqueous epoxy resin is prepared by a method comprising the following steps:

[0014] 4) Dissolve alkali lignin in a solvent, add alkali, add alkyl sulfate dropwise, stir at room temperature after the addition is complete, raise the temperature and keep it constant for reaction, cool to room temperature after the reaction is complete, adjust the pH, extract, distill, disperse in water, filter, wash, and dry to obtain etherified alkali lignin.

[0015] 5) Under an inert atmosphere, the etherified alkali lignin, organic solvent and catalyst of step 1) are mixed evenly, heated and vacuumed, epoxy compound is added under controlled temperature and reacted, vacuum degassing and nitrogen bubbling are performed after the reaction is completed, water and acid are added and stirred after cooling, dehydration is performed after heating, filtration is performed, and chain-extended alkali lignin is obtained by vacuum distillation.

[0016] 6) Add the chain-extended alkali lignin, epichlorohydrin and catalyst from step 2) to the reactor and mix evenly. Heat the mixture to carry out the reaction. After the reaction is completed, add alkali and continue stirring. After the reaction is completed, cool the mixture, separate the oil layer, wash with water until the pH is neutral, and rotary evaporate to obtain star-shaped waterborne epoxy resin.

[0017] Step 1) The weight average molecular weight of the alkali lignin is 1000-2000. The solvent is a mixture of water and acetone in a ratio of 1-2:1. The alkali is not particularly limited, including but not limited to one or a combination of sodium hydroxide and potassium hydroxide. The amount of alkali used is 20-25 wt% of the alkali lignin. The temperature is raised to 60-90℃. The reaction time is 1-5 h. The pH is adjusted to 1-3. The extractant is selected from one or a combination of chloroform and dichloromethane. The distillation is to remove the solvent. The washing is to wash with water 1-3 times to remove water-soluble impurities.

[0018] Step 2) The catalyst is selected from one or more of sodium hydroxide or potassium hydroxide, and the amount of the catalyst is 10-15 wt% of the epoxide compound. The solvent is selected from one or more of chloroform or dichloromethane. The heating is raised to 80-100℃, the vacuum is drawn to a pressure ≤ -0.093 MPa, the temperature is controlled at 90-120℃, the reaction time is 1-3 h, the cooling is lowered to 80-90℃, and the stirring time is 0.5-2 h. The acid is hydrochloric acid or carbonic acid.

[0019] Step 3) The catalyst is selected from one or a combination of two of boron trifluoride-diethyl ether complex, tin tetrachloride, and tetramethylammonium bromide. The amount of catalyst used is 3-5 wt% of the weight of alkali lignin and epichlorohydrin. The temperature is raised to 50-65°C. The reaction time is 1-4 h. There are no particular limitations on the alkali, including but not limited to one or a combination of two of sodium hydroxide and potassium hydroxide. The amount of alkali used is 40-50 wt% of epichlorohydrin. The reaction time after adding the alkali is 5-8 h. The rotary evaporation is to remove epichlorohydrin and water.

[0020] The curing agent is a water-soluble polyetheramine, such as one or a combination of two selected from D-230 and D-400.

[0021] The specific surface area of ​​the powdered activated carbon is 1500-2000 m². 2 / g, with an average particle size of 300-500 mesh, selected from one or a combination of two or more of coal-based activated carbon, wood-based activated carbon, and fruit shell activated carbon.

[0022] The surfactant is selected from one or a combination of two or more of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfate.

[0023] This invention also provides a method for preparing high-strength honeycomb activated carbon, comprising the following steps:

[0024] S1. Add star-shaped waterborne epoxy resin, surfactant, and curing agent to water to form a stable emulsion, add powdered activated carbon and mix evenly to obtain plastic slurry;

[0025] S2. Add the plastic clay to the clay mixer for pre-kneading, seal the pre-kneaded clay, let it stand and age, and then put it into the clay mixer for vacuum kneading to obtain the clay.

[0026] S3. The clay material obtained in step S2 is extruded and molded using an extruder equipped with a honeycomb mold to obtain a honeycomb preform;

[0027] S4. The honeycomb embryo is first heated to react, and then dried in hot air to obtain a dried honeycomb embryo.

[0028] The aging time in step S2 is 3-5 hours; the pre-kneading of the mud is 1-3 times before aging, and the mud is kneaded 1-3 times after aging; the vacuum degree is 0.08-0.1 MPa.

[0029] In step S4, the temperature is increased to 80-100℃ for 1-3 hours, and then further increased to 120-130℃ for 1-3 hours. The hot air temperature is 60-80℃, and the hot air drying time is 8-18 hours.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] This invention prepares a star-shaped waterborne epoxy resin using alkali lignin, alkyl sulfate, epoxy compounds, and epichlorohydrin with a three-dimensional structure as raw materials. Because the star-shaped waterborne epoxy resin contains polar groups such as ether bonds on its side chains, it endows this resin with excellent water dispersibility and adhesion to activated carbon. The honeycomb activated carbon prepared by bonding powdered activated carbon with this star-shaped waterborne epoxy resin has a large specific surface area, strong adsorption capacity, and high strength after curing and drying. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but is not limited to the contents of the specification. Unless otherwise specified, all "parts" mentioned in the embodiments of the present invention are parts by weight. All reagents used are commercially available in the art.

[0033] Alkali lignin was purchased from Hubei Shishun Biotechnology Co., Ltd., with a weight-average molecular weight of 1850.

[0034] The coconut shell-based powdered activated carbon was purchased from Fujian Xinsen Carbon Industry Co., Ltd., with a specific surface area of ​​1160 m2 / g and an average particle size of 270 mesh.

[0035] The polyetheramine D-230 was purchased from BASF in Germany.

[0036] Preparation of star-shaped waterborne epoxy resin

[0037] Preparation Example 1

[0038] 1) Dissolve 100 parts of alkali lignin in a mixture of 500 parts of water and acetone in a 1:1 ratio, add 21 parts of sodium hydroxide, and add 30 parts of diethyl sulfate dropwise. After the addition is complete, stir at room temperature, raise the temperature to 80°C and keep the temperature constant for 2.5 h. After the reaction is complete, cool to room temperature, adjust the pH to 2, extract with chloroform, remove the solvent by distillation, then disperse the obtained solid in water, filter, wash the filter residue 3 times, and dry under vacuum at 60°C to obtain etherified alkali lignin.

[0039] 2) Under a nitrogen atmosphere, the etherified alkali lignin from step 1), 500 parts of chloroform, and 3 parts of sodium hydroxide were mixed evenly, heated to 90°C and vacuumed to -0.093 MPa. The temperature was controlled at 115°C, 30 parts of propylene oxide were added, and the reaction was carried out for 3 hours. After the reaction was completed, the mixture was degassed under vacuum and bubbled with nitrogen. The mixture was cooled, water and hydrochloric acid were added, and the mixture was stirred for 1 hour. The mixture was heated to dehydrate, filtered to remove sodium hydroxide and sodium chloride, and propylene oxide was removed by vacuum distillation to obtain chain-extended alkali lignin.

[0040] 3) Add the chain-extended alkali lignin from step 2), 40 parts of epichlorohydrin, and 7 parts of the catalyst tetramethylammonium bromide to the reactor and mix evenly. Heat to 60°C and react for 3 hours. After the reaction is complete, add 20 parts of sodium hydroxide and continue stirring for another 7 hours. After the reaction is complete, cool and separate the oil layer. Wash with water until the pH of the oil layer is neutral. Remove epichlorohydrin and water by rotary evaporation to obtain star-shaped waterborne epoxy resin.

[0041] Preparation Example 2

[0042] The rest is the same as in Preparation Example 1, except that dimethyl sulfate is used instead of diethyl sulfate in equal amounts.

[0043] Preparation Example 3

[0044] The rest is the same as in Preparation Example 1, except that the amount of diethyl sulfate used is 25 parts.

[0045] Preparation Example 4

[0046] The rest is the same as in Preparation Example 1, except that the amount of propylene oxide used is 20 parts.

[0047] Preparation Example 5

[0048] The rest is the same as in Preparation Example 1, except that the amount of epichlorohydrin used is 30 parts.

[0049] Comparative Preparation Example 1

[0050] The rest is the same as in Preparation Example 1, except that step 1) is omitted, i.e.:

[0051] 1) Under a nitrogen atmosphere, alkali lignin, 500 parts chloroform, and 3 parts sodium hydroxide were mixed evenly, heated to 90°C and vacuumed to -0.093 MPa. The temperature was controlled at 115°C, 30 parts propylene oxide were added and reacted for 3 hours. After the reaction was completed, the mixture was degassed under vacuum and bubbled with nitrogen. The mixture was cooled, water and acid were added and stirred for 1 hour. The mixture was heated to dehydrate, filtered to remove sodium hydroxide and sodium chloride, and distilled under reduced pressure to remove propylene oxide, thus obtaining chain-extended alkali lignin.

[0052] 2) Add the chain-extended alkali lignin from step 1), 40 parts of epichlorohydrin, and 7 parts of the catalyst tetramethylammonium bromide to a reaction vessel and mix evenly. Heat to 60°C and react for 3 hours. After the reaction is complete, add 20 parts of sodium hydroxide and continue stirring for another 7 hours. After the reaction is complete, cool and separate the oil layer. Wash with water until the pH of the oil layer is neutral. Remove epichlorohydrin and water by rotary evaporation to obtain star-shaped waterborne epoxy resin.

[0053] Comparative Preparation Example 2

[0054] The rest is the same as in Preparation Example 1, except that step 2) is omitted, i.e.:

[0055] 1) Dissolve 100 parts of alkali lignin in a mixture of 500 parts of water and acetone in a 1:1 ratio, add 21 parts of sodium hydroxide, and add 30 parts of diethyl sulfate dropwise. After the addition is complete, stir at room temperature, raise the temperature to 80°C and keep it constant for 2.5 h. After the reaction is complete, cool to room temperature, adjust the pH to 2, extract with chloroform, remove the solvent by distillation, then disperse the obtained solid in water, filter, wash the filter residue 1-3 times, and dry under vacuum at 60°C to obtain etherified alkali lignin.

[0056] 2) Add the etherified alkali lignin from step 1), 40 parts of epichlorohydrin, and 7 parts of the catalyst tetramethylammonium bromide to the reactor and mix evenly. Heat to 60°C and react for 3 hours. After the reaction is complete, add 20 parts of sodium hydroxide and continue stirring for another 7 hours. After the reaction is complete, cool and separate the oil layer. Wash with water until the pH of the oil layer is neutral. Remove epichlorohydrin and water by rotary evaporation to obtain star-shaped waterborne epoxy resin.

[0057] Preparation of honeycomb activated carbon

[0058] Example 1

[0059] S1. Add 15 parts of star-shaped waterborne epoxy resin from Preparation Example 1, 3 parts of sodium dodecyl sulfate, and 0.8 parts of curing agent D-230 to water to form a stable emulsion. Add 100 parts of powdered activated carbon and mix evenly to obtain a plastic slurry.

[0060] S2. Add the plastic clay to the clay mixer for pre-kneading 3 times. After sealing the pre-kneaded clay, let it stand and age for 5 hours. Then put it into the clay mixer for vacuum kneading 3 times with a vacuum degree of 0.1MPa to obtain the clay.

[0061] S3. The clay material obtained in step S2 is extruded and molded using an extruder equipped with a honeycomb mold to obtain a honeycomb preform with an outer diameter of 29 mm, a cylindrical pore shape of 200 pores / square inch, and an inner wall thickness of 0.3 mm.

[0062] S4. First, heat the honeycomb preform to 80℃ for 3 hours, then continue to heat it to 115℃ for 3 hours to carry out the reaction, and finally dry it in hot air at 80℃ for 16 hours to obtain a dried honeycomb preform.

[0063] Examples 2-5

[0064] The rest is the same as in Example 1, except that the star-shaped waterborne epoxy resin used was prepared in Examples 2-5.

[0065] Example 6

[0066] The rest is the same as in Example 1, except that the amount of star-shaped waterborne epoxy resin used in Example 1 is 10 parts.

[0067] Comparative Example 1

[0068] The rest is the same as in Example 1, except that an equal amount of polyvinyl alcohol is used to replace the star-shaped waterborne epoxy resin used in Example 1.

[0069] Comparative Example 2

[0070] The rest is the same as in Example 1, except that the star-shaped waterborne epoxy resin used is the same as that prepared in Comparative Preparation Example 1.

[0071] Comparative Example 3

[0072] The rest is the same as in Example 1, except that the star-shaped waterborne epoxy resin used was prepared in Comparative Preparation Example 2.

[0073] The honeycomb activated carbon prepared in the above examples and comparative examples was tested for the following properties:

[0074] 1. Compressive strength: Tested in accordance with standard GB / T 5072-2008.

[0075] 2. Specific surface area: determined using the Brunauer-Emmett-Teller (BET) method, with N2 as the adsorbed gas.

[0076] 3. Sulfur Penetration Capacity: Tested according to standard ASTM / D 6646-2014. Cylindrical honeycomb activated carbon (180 pores / square inch, 0.4mm inner wall thickness) with an outer diameter of 25.4mm and a height of 10mm was prepared and filled into the test tube to a height of 230mm. The absorption tube was made of glass with an inner diameter of 25.4mm and a height of 230mm. Sulfur penetration capacity: This refers to the amount of sulfur that a unit volume of desulfurizing agent can absorb while ensuring the process purification level. A higher sulfur penetration capacity indicates a better sulfur adsorption capacity of the desulfurizing agent.

[0077] Table 1

[0078]

[0079]

[0080] As can be seen from Table 1, the honeycomb activated carbon prepared by this invention has a large specific surface area after curing and drying, strong adsorption capacity for the polar gas hydrogen sulfide, and also has high strength.

[0081] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A high-strength honeycomb activated carbon, the raw materials for the preparation of which comprise: 100 parts of powdered activated carbon, 10-15 parts of star-shaped waterborne epoxy resin, 0.5-0.8 parts of curing agent, 50-80 parts of water, 1-3 parts of surfactant, the star-shaped waterborne epoxy resin is prepared by etherification of alkali lignin with sulfuric acid alkyl ester, then chain extension of the etherified alkali lignin with an epoxy compound to form branches, and finally epoxidation of the ends of the branches with epichlorohydrin; The amount of the sulfuric acid alkyl ester is 25-30 wt% of the alkali lignin, the amount of the epoxy compound is 20-30 wt% of the alkali lignin, and the amount of the epichlorohydrin is 30-40 wt% of the alkali lignin; the sulfuric acid alkyl ester is selected from dimethyl sulfate, diethyl sulfate, or a combination of the two.

2. The high-strength honeycomb activated carbon of claim 1, wherein the epoxy compound is selected from propylene oxide, ethylene oxide, or a combination of the two.

3. The high-strength honeycomb activated carbon of claim 1, wherein the star-shaped waterborne epoxy resin is prepared by a method comprising the following steps: dissolving alkali lignin in a solvent, adding alkali, adding sulfuric acid alkyl ester dropwise, stirring at room temperature after dropping, warming and constant temperature reaction, cooling to room temperature after reaction, adjusting pH, extraction, distillation, dispersing in water, filtering, washing, and drying to obtain etherified alkali lignin; mixing the etherified alkali lignin of step 1), an organic solvent, and a catalyst uniformly under an inert atmosphere, warming and vacuumizing, controlling temperature to add an epoxy compound and perform reaction, vacuum degassing and nitrogen bubbling after reaction, adding water and acid and stirring after cooling, dehydrating by warming, filtering, and distilling under reduced pressure to obtain chain-extended alkali lignin; mixing the chain-extended alkali lignin of step 2), epichlorohydrin, and a catalyst uniformly in a reaction kettle, warming to perform reaction, adding alkali and continuing stirring after reaction, cooling, separating oil layer, washing with water until pH is neutral, and rotary evaporation to obtain star-shaped waterborne epoxy resin.

4. The high strength honeycomb activated carbon of claim 3, wherein, In step 1), the weight average molecular weight of the alkali lignin is 1000-2000, the solvent is a mixture of water and acetone in a ratio of 1-2:1, the alkali is selected from sodium hydroxide, potassium hydroxide, or a combination of the two, the amount of the alkali is 20-25 wt% of the alkali lignin, the warming is to 60-90°C, the reaction time is 1-5 h, the pH adjustment is to 1-3, the extraction agent for extraction is selected from chloroform or dichloromethane, or a combination of the two; the distillation is to remove the solvent, and the washing is with water for 1-3 times to remove water-soluble impurities.

5. The high strength honeycomb activated carbon of claim 3, wherein, In step 2), the catalyst is selected from sodium hydroxide or potassium hydroxide, or a combination of two or more, the amount of the catalyst is 10-15 wt% of the epoxy compound, the solvent is selected from chloroform or dichloromethane, or a combination of the two, the warming is to 80-100°C, the vacuumizing is to a pressure ≤-0.093 MPa, the temperature control is to control the temperature at 90-120°C, the reaction time is 1-3 h, the cooling is to 80-90°C, and the stirring time is 0.5-2 h.

6. The high strength honeycomb activated carbon of claim 3, wherein, Step 3) the catalyst is selected from one or a combination of boron trifluoride-ethyl ether complex, tin tetrachloride, tetramethylammonium bromide, the catalyst is used in an amount of 3-5wt% of the weight of alkali lignin and epichlorohydrin, the temperature is raised to 50-65℃, the reaction time is 1-4h, the base is selected from one or a combination of sodium hydroxide, potassium hydroxide, the base is used in an amount of 40-50wt% of epichlorohydrin, the reaction time after adding the base is 5-8h, and the rotary evaporation is to remove epichlorohydrin and water.

7. The high strength honeycomb activated carbon of any of claims 1-6, wherein, The curing agent is a water-soluble polyether amine.

8. The high strength honeycomb activated carbon of any of claims 1-6, wherein, The specific surface area of the powdered activated carbon powder is 1500-2000 m 2 / g, the average particle size is 300-500 mesh, and the powdered activated carbon is selected from one or a combination of two or more of coal-based activated carbon, wood-based activated carbon, and fruit shell-based activated carbon. The surfactant is selected from one or a combination of two or more of sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, and sodium dodecyl sulfate.

9. The method for preparing high-strength honeycomb activated carbon according to any one of claims 1-8, comprising the following steps: S1. Adding star-shaped waterborne epoxy resin, surfactant, and curing agent to water to form a stable emulsion, adding powdered activated carbon and mixing uniformly to obtain plastic paste; S2. Adding the plastic paste to a paste mill for pre-paste, sealing the pre-paste and standing for aging, then feeding into the paste mill for vacuum paste to obtain the paste; S3. Extruding the paste obtained in step S2 using an extruder equipped with a honeycomb mold to obtain a honeycomb-shaped embryo; S4. First heating the honeycomb-shaped embryo to react, and then drying in hot air to obtain a dried honeycomb-shaped embryo; The aging time in step S2 is 3-5h; the pre-paste is 1-3 times before aging, and the paste is 1-3 times after aging; the vacuum degree of the vacuum is 0.08-0.1MPa; The temperature in step S4 is raised to 80-100℃ / 1-3h, and then continuously raised to 120-130℃ / 1-3h, the hot air temperature is 60-80℃, and the hot air drying time is 8-18h.

Images