Recarburization catalyst and preparation method and application thereof

Abstract

The invention belongs to the technical field of viscose-based carbon fibers, and discloses a recarburization catalyst as well as a preparation method and application thereof. The recarburization catalyst comprises urea, organic alkali, organic carboxylic acid and a hydrogen bond acceptor. The preparation method comprises the following steps: impregnating viscose fiber felt with a recarburization catalyst aqueous solution, carrying out heat treatment in a special catalytic dehydration furnace, and carrying out heat treatment in a special carbonization-graphitization furnace to obtain the viscose-based carbon fiber felt. According to the present invention, the multiple auxiliary agents in the catalyst produce the synergistic effect, such that the impurity content of the prepared viscose-based carbon fiber felt is substantially reduced, the corrosion problem of the traditional strong acid type catalyst on the equipment is reduced, and the problems of unobvious organic carboxylic acid catalysis effect and low carbon yield are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of viscose-based carbon fibers, and in particular to a carbonization catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Viscose-based carbon fiber felt has excellent properties such as heat insulation, thermal insulation, and ablation resistance. In particular, even in an inert atmosphere at a high temperature of 2000-3300°C, viscose-based carbon fiber felt can still maintain good thermal field stability. The high temperature resistance of carbon fiber makes it widely used as a thermal insulation material in high temperature thermal environments such as solar polysilicon furnaces, semiconductor single crystal silicon pulling furnaces, semiconductor silicon carbide crystal growth furnaces, and high-end metallurgical heat treatment furnaces. The precursor of viscose-based carbon fiber felt is viscose fiber, which is regenerated cellulose with a crystal structure of cellulose II type and a molecular formula of (C6H 10 O5) n , after carbonization and graphitization, it is transformed into a viscose-based carbon fiber with a graphite-like microcrystalline structure. From the structure of viscose fiber, it can be seen that if the viscose fiber can remove H and O from the molecules in the form of water, its theoretical carbon yield can reach 44%. However, in actual production, as the viscose fiber is pyrolyzed, a large amount of tar (mainly converted from 1,6-anhydro-β-D-glucose) and small molecular volatiles such as CO, CO2, CH4, HCOOH, etc. will be generated, resulting in a carbon yield of viscose-based carbon fiber of only about 15%, which is far from the theoretical carbon yield of 44.4%. The generation of tar not only reduces the carbon yield, but also contaminates the fiber and affects product performance. At the same time, it causes serious pollution to production equipment and the environment, increasing the cost of equipment maintenance and environmental protection.

[0003] In order to improve the carbon yield of viscose-based carbon fibers, catalyst impregnation pretreatment is usually performed before carbonization. After pretreatment, the viscose fiber can reduce its pyrolysis activation energy, promote the dehydration of the primary hydroxyl groups of the cellulose molecules in the viscose fiber, and reduce the formation of tar during the production process. Currently commonly used traditional inorganic acid catalysts, such as Na2SO3, AlCl3, H2SO4, (NH4)2SO4, NH4Cl, (NH4)2HPO4, NH4H2PO4, etc., promote the dehydration of the primary hydroxyl groups of cellulose molecules at low temperatures by the catalyst's own water absorption properties, prevent cellulose depolymerization and hydroxyl esterification, and reduce the formation of volatiles, thereby effectively improving the carbon yield. However, these catalysts will introduce a large number of difficult-to-remove impurities into the viscose-based carbon fiber felt. At the same time, their pyrolysis products (acidic gases such as HCl, etc.) will not only corrode equipment and significantly increase maintenance costs, but also generate a large amount of waste liquid, increase treatment costs, and are not conducive to environmental protection requirements.

[0004] Some organic carboxylic acid catalysts such as maleic acid (C4H4O4), citric acid (C6H8O7) or 1,2,3,4-butanetetracarboxylic acid (C8H10 O8) decomposition does not introduce impurities, and its main thermal decomposition products are small molecules such as CO2, CO, and H2O, which greatly reduces corrosiveness and environmental pollution. However, due to their low dissociation constant and weak thermal stability, organic carboxylic acid catalysts do not have a significant catalytic dehydration effect, resulting in generally low carbon yields for viscose-based carbon fiber felts. Therefore, how to improve the catalytic effect of organic carboxylic acid catalysts is currently an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a carbon-increasing catalyst and its preparation method and application, so as to solve the technical problems such as the introduction of a large number of impurities, serious corrosion to equipment, serious environmental pollution and low carbon yield in the existing viscose-based carbon fiber felt preparation process.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a carbon-increasing catalyst comprising the following raw materials:

[0008] Urea, organic bases, organic carboxylic acids, hydrogen bond acceptors;

[0009] Wherein, the hydrogen bond acceptor is choline chloride or betaine.

[0010] Preferably, in the above-mentioned carburizing catalyst, the organic base is one of triethanolamine, triethylenetetramine, diethylenetriamine, ethylenediamine and acrylamide.

[0011] Preferably, in the above-mentioned carbon increase catalyst, the organic carboxylic acid is one of maleic acid, citric acid, and 1,2,3,4-butanetetracarboxylic acid.

[0012] Preferably, in the above-mentioned carbon increase catalyst, the mass ratio of urea, organic base, organic carboxylic acid and hydrogen bond acceptor is 2-8:0.5-1.5:0.5-5:0.5-2.

[0013] The present invention also provides a method for preparing a carbon-increasing catalyst, comprising the following steps:

[0014] Urea, an organic base, an organic carboxylic acid and a hydrogen bond acceptor are mixed to obtain a carbon enhancement catalyst.

[0015] The present invention also provides an application of a carbonization catalyst in the preparation of viscose-based carbon fiber felt.

[0016] Preferably, in the above application, the method for preparing the viscose-based carbon fiber felt comprises the following steps:

[0017] The viscose fiber is needle-punched into a felt and then acid-washed to obtain a viscose fiber felt, and then the viscose fiber felt is impregnated with an aqueous solution of a carburizing catalyst to obtain a pretreated viscose fiber felt; or the viscose fiber is acid-washed and then impregnated with an aqueous solution of a carburizing catalyst and then needle-punched into a felt to obtain a pretreated viscose fiber felt;

[0018] The pretreated viscose fiber felt is heat-treated in a special catalytic dehydration furnace to obtain a viscose-based carbon fiber preoxidized felt;

[0019] The viscose-based carbon fiber preoxidized felt is heat-treated in a special carbonization-graphitization furnace to obtain the viscose-based carbon fiber felt.

[0020] Preferably, in the above application, the mass concentration of the carburizing catalyst in the aqueous solution of the carburizing catalyst is 3 to 20%.

[0021] Preferably, in the above application, the mass ratio of the carbonization catalyst to the viscose fiber felt in the aqueous solution of the carbonization catalyst is 8-12:1-3; and the time of the immersion treatment is 10-30 minutes.

[0022] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention uses non-strong acid organic carboxylic acid as the main catalyst and urea, organic base, and hydrogen bond acceptor as co-catalysts, which significantly reduces the corrosion problem of traditional strong acid catalysts on equipment. At the same time, the excessive hydrolysis of cellulose is avoided by not using strong acid as a catalyst.

[0024] (2) The organic carboxylic acid used in the present invention is preferably citric acid, which can promote the protonation of the primary hydroxyl groups in the cellulose molecules, so that the hydroxyl groups are removed as water molecules. At the same time, the carboxyl groups can also undergo esterification reaction with the primary hydroxyl groups, thereby reducing the dehydration of the primary hydroxyl groups (C6) and the 1,4-glycosidic bond (C1) broken at high temperature to form tar (1,6-anhydro-β-D-glucose). The organic carboxylic acid esterification reaction mechanism of cellulose is generally considered to be a cyclic anhydride mechanism, that is, the organic carboxylic acid first undergoes self-dehydration to form anhydride, and then the anhydride and the primary hydroxyl groups of cellulose undergo nucleophilic substitution reaction to form an ester bond. However, the alcoholic hydroxyl groups of citric acid will be removed in the form of water molecules at high temperatures and generate unsaturated carboxylic acids, such as aconitic acid, which reduces the degree of esterification reaction. At the same time, because cellulose is rich in intermolecular and intramolecular hydrogen bonds, it is difficult for citric acid to react with the primary hydroxyl groups of cellulose molecules in the crystalline region with a large content of hydrogen bonds. These two points together lead to the fact that the catalytic effect of citric acid on viscose-based carbon fiber felt is not obvious. Therefore, the present invention reduces the formation of unsaturated carboxylic acids by adding urea, an organic base, and a hydrogen bond acceptor, while destroying some hydrogen bonds of the cellulose molecules of viscose fibers, promoting the combination of catalyst molecules with the primary hydroxyl groups of cellulose, and ultimately improving the carbon yield of viscose-based carbon fiber felt, thereby solving the problem of low carbon yield of organic carboxylic acids. Urea, as a swelling agent, can effectively swell the fibers and promote the combination of catalyst molecules with the primary hydroxyl groups of cellulose. On the other hand, urea molecules react with cellulose at high temperatures to form cellulose carbamate, which also has the effect of promoting the improvement of carbon yield. The organic base used in the present invention is preferably triethanolamine, whose abundant hydroxyl groups can combine with the hydroxyl molecules of citric acid to form ether bonds, thereby blocking the hydroxyl groups of the citric acid molecules and inhibiting their decomposition and dehydration to generate unsaturated acids at high temperatures. The hydrogen bond acceptor used in the present invention is preferably choline chloride. On the one hand, as the catalyst solvent evaporates, the solute concentration increases, and the organic carboxylic acid and the hydrogen bond acceptor gradually form a deep eutectic solvent containing abundant hydrogen bonds, which can effectively reduce the crystallinity of cellulose. On the other hand, the chloride ions of choline chloride can also form hydrogen bonds with the hydroxyl groups of cellulose, and the two jointly promote the effective combination of catalyst molecules with cellulose molecules. The synergistic effect of multiple additives effectively solved the problems of unclear catalytic effect of organic carboxylic acid and low carbon yield of viscose-based carbon fiber felt.

[0025] (3) The present invention uses urea, organic base, organic carboxylic acid, and hydrogen bond acceptor as a metal-free, sulfur-free, phosphorus-free, silicon-free, and boron-free element catalyst, which greatly reduces the introduction of impurity elements, improves the purity of viscose-based carbon fiber felt, and reduces the requirements for subsequent high-temperature purification processes.

[0026] (4) The catalyst used in the present invention is environmentally friendly. Urea, organic bases, organic carboxylic acids, and hydrogen bond acceptors are mostly non-toxic or low-toxic raw materials, effectively reducing hazards to personnel and the environment during the production process and improving production safety. Furthermore, the pyrolysis products of the catalyst are mostly small molecular gases that are easy to capture and process, effectively solving the pollution problem of the catalytic impregnation process. DETAILED DESCRIPTION

[0027] The present invention provides a carbon-increasing catalyst comprising the following raw materials:

[0028] Urea, organic bases, organic carboxylic acids, hydrogen bond acceptors.

[0029] In the present invention, the hydrogen bond acceptor is preferably choline chloride or betaine, more preferably choline chloride.

[0030] In the present invention, the organic base is preferably one of triethanolamine, triethylenetetramine, diethylenetriamine, ethylenediamine, and acrylamide, more preferably triethanolamine or acrylamide, and more preferably triethanolamine.

[0031] In the present invention, the organic carboxylic acid is preferably one of maleic acid, citric acid, and 1,2,3,4-butanetetracarboxylic acid, more preferably maleic acid or citric acid, and more preferably citric acid.

[0032] In the present invention, the mass ratio of urea, organic base, organic carboxylic acid and hydrogen bond acceptor is preferably 2-8:0.5-1.5:0.5-5:0.5-2, more preferably 4-6:1-1.5:1-3:1-2, and more preferably 5:1.5:1:1.

[0033] The present invention also provides a method for preparing a carbon-increasing catalyst, comprising the following steps:

[0034] Urea, an organic base, an organic carboxylic acid and a hydrogen bond acceptor are mixed to obtain a carbon enhancement catalyst.

[0035] The present invention also provides an application of a carbonization catalyst in the preparation of viscose-based carbon fiber felt.

[0036] In the present invention, the method for preparing the viscose-based carbon fiber felt comprises the following steps:

[0037] The viscose fiber is needle-punched into a felt and then acid-washed to obtain a viscose fiber felt, and then the viscose fiber felt is impregnated with an aqueous solution of a carburizing catalyst to obtain a pretreated viscose fiber felt; or the viscose fiber is acid-washed and then impregnated with an aqueous solution of a carburizing catalyst and then needle-punched into a felt to obtain a pretreated viscose fiber felt;

[0038] The pretreated viscose fiber felt is heat-treated in a special catalytic dehydration furnace to obtain a viscose-based carbon fiber preoxidized felt;

[0039] The viscose-based carbon fiber preoxidized felt is heat-treated in a special carbonization-graphitization furnace to obtain the viscose-based carbon fiber felt.

[0040] In the present invention, the acid used in the pickling treatment is preferably citric acid with a mass concentration of 2%.

[0041] In the present invention, the pickling treatment further includes drying; the drying temperature is preferably 105° C.; and the drying time is preferably 40 minutes.

[0042] In the present invention, the mass concentration of the carburizing catalyst in the aqueous solution of the carburizing catalyst is preferably 3 to 20%, more preferably 10 to 15%, and even more preferably 10%.

[0043] In the present invention, the mass ratio of the carbonization catalyst to the viscose fiber felt in the aqueous solution of the carbonization catalyst is preferably 8-12:1-3, more preferably 9-11:1-2, and more preferably 10:1; the time of the immersion treatment is preferably 10-30 min, more preferably 20-30 min, and more preferably 30 min.

[0044] In the present invention, the step of impregnating the viscose fiber felt with an aqueous solution of a carburizing catalyst further includes rolling drying after the impregnation treatment, and then repeating the impregnation and rolling drying twice, and then drying at 105-140° C. until the water content is less than 5%.

[0045] In the present invention, the dedicated catalytic dehydration furnace and the dedicated carbonization-graphitization furnace adopt the equipment in patent CN116427101A.

[0046] In the present invention, the conditions for heat treatment in a dedicated catalytic dehydration furnace are preferably: heating from room temperature to 240°C in 30 minutes, heating from 240°C to 260°C in 30 minutes, heating from 260°C to 280°C in 30 minutes, and heating from 280°C to 300°C in a slightly negative pressure inert atmosphere circulating wind of -2 to -100 Pa; further preferably, a slightly negative pressure of -10 to -50 Pa; and more preferably, a slightly negative pressure of -10 Pa.

[0047] In the present invention, the conditions for heat treatment in a dedicated carbonization-graphitization furnace are preferably: in a slightly positive pressure inert atmosphere circulating wind of 2-100 Pa, heating from room temperature to 800-1400°C for 30 minutes, holding the temperature for 30 minutes, heating from 800-1400°C to 2000-2600°C for 55-80 minutes, and holding the temperature for 10 minutes; further preferably, in a slightly positive pressure inert atmosphere circulating wind of 10-40 Pa, heating from room temperature to 1000-1400°C for 30 minutes, holding the temperature for 30 minutes, heating from 1000-1400°C to 2200-2400°C for 55-60 minutes, and holding the temperature for 10 minutes; more preferably, in a slightly positive pressure inert atmosphere circulating wind of 10 Pa, heating from room temperature to 1200°C for 30 minutes, holding the temperature for 30 minutes, heating from 1200°C to 2200°C for 55 minutes, and holding the temperature for 10 minutes.

[0048] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0049] Example 1

[0050] This embodiment provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0051] S1. The viscose fiber was needle-punched into a felt, pickled with 2% citric acid, and then dried at 105°C for 40 minutes to obtain a viscose fiber felt;

[0052] S2. Urea, triethanolamine, citric acid, and choline chloride were mixed in a mass ratio of 5:1.5:1:1 to obtain a recarburizing catalyst; the recarburizing catalyst was prepared into a catalyst solution with a mass concentration of 10% using deionized water; a viscose fiber felt was immersed in the catalyst solution at a mass ratio of 10:1 between the recarburizing catalyst and the viscose fiber felt for 30 minutes, removed and rolled dry, and the immersion and rolling drying were repeated twice until the water-felt mass ratio reached 0.5. The felt was then dried in a drying oven at 110°C to a water content of 3% to obtain a pretreated viscose fiber felt;

[0053] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -10Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0054] S4. The viscose-based carbon fiber preoxidized felt was placed in a dedicated carbonization-graphitization furnace and heated from room temperature to 1200°C in 30 minutes in a slightly positive pressure inert atmosphere with circulating air at 10 Pa. The temperature was maintained constant for 30 minutes. The felt was then heated to 2200°C in 55 minutes and maintained constant for 10 minutes. The felt was then removed from the furnace and cooled to obtain the viscose-based carbon fiber felt.

[0055] The carbon yield of the viscose-based carbon fiber felt product prepared in Example 1 was 36%, and the ash content was 35 ppm (heat treated at 900° C. for 4 h in air atmosphere). The impurity elements were measured by GDMS, and the main impurity elements were <20 ppm. The specific impurity values are shown in Table 1.

[0056] Table 1 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Example 1

[0057] element Concentration (ppmwt) P 0.06 S 3 Cl 1.6 Fe 0.07 Al 0.15 F 8.0

[0058] The production process of the embodiment of the present invention is completely corrosion-free to the equipment, the tail gas meets the discharge standards after one-time incineration, and the generated wastewater meets the discharge standards after A / O treatment.

[0059] Example 2

[0060] This embodiment provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0061] S1. The viscose fiber was needle-punched into a felt, pickled with 2% citric acid, and then dried at 105°C for 40 minutes to obtain a viscose fiber felt;

[0062] S2. Urea, acrylamide, citric acid, and choline chloride were mixed in a mass ratio of 2.5:1:1:1 to obtain a recarburizing catalyst; the recarburizing catalyst was prepared into a catalyst solution with a mass concentration of 15% using deionized water; a viscose fiber felt was immersed in the catalyst solution at a mass ratio of 10:1 between the recarburizing catalyst and the viscose fiber felt for 30 minutes, removed and rolled dry, and the immersion and rolling drying were repeated twice until the water-felt mass ratio reached 0.5. The felt was then dried in a drying oven at 110°C to a water content of 3% to obtain a pretreated viscose fiber felt;

[0063] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -30Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0064] S4. The viscose-based carbon fiber preoxidized felt was placed in a dedicated carbonization-graphitization furnace and heated from room temperature to 1400°C in 30 minutes in a 20 Pa slightly positive pressure inert atmosphere with circulating air. The temperature was maintained constant for 30 minutes. The felt was then heated to 2400°C in 60 minutes and maintained constant for 10 minutes. The felt was then removed from the furnace and cooled to obtain the viscose-based carbon fiber felt.

[0065] The carbon yield of the viscose-based carbon fiber felt product prepared in Example 2 was 29%, and the ash content was 42 ppm (heat treated at 900° C. for 4 h in air atmosphere). The impurity elements were measured by GDMS, and the main impurity elements were <10 ppm. The specific impurity values are shown in Table 2.

[0066] Table 2 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Example 2

[0067] element Concentration (ppmwt) P 0.07 S 1.2 Cl 0.07 Fe 0.05 Al 0.07 F 7.9

[0068] The production process of the embodiment of the present invention is completely corrosion-free to the equipment, the tail gas meets the discharge standards after one-time incineration, and the generated wastewater meets the discharge standards after A / O treatment.

[0069] Example 3

[0070] This embodiment provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0071] S1. The viscose fiber was needle-punched into a felt, pickled with 2% citric acid, and then dried at 105°C for 40 minutes to obtain a viscose fiber felt;

[0072] S2. Urea, acrylamide, citric acid, and betaine were mixed in a mass ratio of 5:0.5:1:1 to obtain a recarburizing catalyst; the recarburizing catalyst was prepared into a catalyst solution with a mass concentration of 15% using deionized water; viscose fiber felt was immersed in the catalyst solution at a mass ratio of 10:1 between the recarburizing catalyst and the viscose fiber felt for 20 minutes, removed and rolled dry, and the immersion and rolling drying were repeated twice until the water-felt mass ratio reached 0.5. The felt was then dried in a drying oven at 110°C to a water content of 3% to obtain a pretreated viscose fiber felt;

[0073] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -35Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0074] S4. The viscose-based carbon fiber preoxidized felt was placed in a dedicated carbonization-graphitization furnace and heated from room temperature to 1000°C in 30 minutes in a slightly positive pressure inert atmosphere with circulating air at 20 Pa. The temperature was maintained constant for 30 minutes. The felt was then heated to 2000°C in 55 minutes and maintained constant for 10 minutes. The felt was then removed from the furnace and cooled to obtain the viscose-based carbon fiber felt.

[0075] The carbon yield of the viscose-based carbon fiber felt product prepared in Example 3 was 27%, and the ash content was 40 ppm (heat treated at 900° C. for 4 h in air atmosphere). The impurity elements were measured by GDMS, and the main impurity elements were <15 ppm. The specific impurity values are shown in Table 3.

[0076] Table 3 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Example 3

[0077] element Concentration (ppmwt) P 0.54 S 3 Cl 1.3 Fe 0.09 Al 0.13 F 8.3

[0078] The production process of the embodiment of the present invention is completely corrosion-free to the equipment, the tail gas meets the discharge standards after one-time incineration, and the generated wastewater meets the discharge standards after A / O treatment.

[0079] Example 4

[0080] This embodiment provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0081] S1. The viscose staple fibers were pickled with 2% citric acid and then dried at 105°C for 40 minutes to obtain viscose staple fibers.

[0082] S2. Urea, triethanolamine, citric acid, and choline chloride were mixed in a mass ratio of 5:1.5:1:1 to obtain a recarburization catalyst. The recarburization catalyst was prepared into a catalyst solution with a mass concentration of 10% using deionized water. Viscose fiber staples were completely immersed in the catalyst solution for 30 minutes, removed, and dried in a drying oven at 110°C to a water content of 3%. The staples were then needle-punched into a felt to obtain a pretreated viscose fiber felt.

[0083] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -10Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0084] S4. The viscose-based carbon fiber preoxidized felt was placed in a dedicated carbonization-graphitization furnace and heated from room temperature to 1200°C in 30 minutes in a slightly positive pressure inert atmosphere with circulating air at 10 Pa. The temperature was maintained constant for 30 minutes. The felt was then heated to 2200°C in 55 minutes and maintained constant for 10 minutes. The felt was then removed from the furnace and cooled to obtain the viscose-based carbon fiber felt.

[0085] The carbon yield of the viscose-based carbon fiber felt product prepared in Example 4 was 32%, and the ash content was 51 ppm (heat treated at 900° C. for 4 h in air atmosphere). The impurity elements were measured by GDMS, and the main impurity elements were <20 ppm. The specific impurity values are shown in Table 4.

[0086] Table 4 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Example 4

[0087] element Concentration (ppmwt) P 0.42 S 2.6 Cl 2.1 Fe 0.06 Al 0.13 F 9.8

[0088] The production process of the embodiment of the present invention is completely corrosion-free to the equipment, the tail gas meets the discharge standards after one-time incineration, and the generated wastewater meets the discharge standards after A / O treatment.

[0089] Example 5

[0090] This embodiment provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0091] S1. The viscose fiber filaments were pickled with 2% citric acid and then dried at 105°C for 40 minutes to obtain viscose fiber filaments;

[0092] S2. Urea, triethanolamine, citric acid, and choline chloride were mixed in a mass ratio of 5:1:0.5:0.5 to obtain a recarburization catalyst. The recarburization catalyst was prepared into a catalyst solution with a mass concentration of 15% using deionized water. Viscose filaments were completely immersed in the catalyst solution for 30 minutes, removed, and dried in a drying oven at 110°C to a water content of 3%. The fibers were then chopped into 38 mm pieces and needle-punched into a felt to obtain a pretreated viscose fiber felt.

[0093] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -20Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0094] S4. The viscose-based carbon fiber preoxidized felt was placed in a dedicated carbonization-graphitization furnace and heated from room temperature to 1400°C in 30 minutes in a slightly positive pressure inert atmosphere with circulating air at 20 Pa. The temperature was maintained constant for 30 minutes. The felt was then heated to 2400°C in 55 minutes and maintained constant for 10 minutes. The felt was then removed from the furnace and cooled to obtain the viscose-based carbon fiber felt.

[0095] The carbon yield of the viscose-based carbon fiber felt product prepared in Example 5 was 31%, and the ash content was 45 ppm (heat treated at 900° C. for 4 h in air atmosphere). The impurity elements were measured by GDMS, and the main impurity elements were <20 ppm. The specific impurity values are shown in Table 5.

[0096] Table 5 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Example 5

[0097] element Concentration (ppmwt) P 0.63 S 3.5 Cl 1.8 Fe 0.08 Al 0.25 F 11.3

[0098] The production process of the embodiment of the present invention is completely corrosion-free to the equipment, the tail gas meets the discharge standards after one-time incineration, and the generated wastewater meets the discharge standards after A / O treatment.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0101] S1. The viscose fiber was needle-punched into a felt, pickled with 2% citric acid, and then dried at 105°C for 40 minutes to obtain a viscose fiber felt;

[0102] S2. Ammonium sulfate, ammonium chloride, and triethanolamine were mixed in a mass ratio of 1:1:1.25 to obtain a recarburizing catalyst; the recarburizing catalyst was prepared into a catalyst solution with deionized water to form an 8% mass concentration; viscose fiber felt was immersed in the catalyst solution at a mass ratio of 10:1 between the recarburizing catalyst and the viscose fiber felt for 30 minutes, removed and rolled dry, and the immersion and rolling drying were repeated twice until the water-felt mass ratio reached 0.5. The felt was then dried in a drying oven at 110°C to a water content of 3% to obtain a pretreated viscose fiber felt;

[0103] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -10Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0104] S4. The viscose-based carbon fiber preoxidized felt is sent into a dedicated carbonization-graphitization furnace and heated from room temperature to 800°C in 30 minutes in a 20Pa slightly positive pressure inert atmosphere circulating air (the temperature is too high and the acidic gas will corrode the equipment severely). The temperature is maintained for 30 minutes. The viscose-based carbon fiber preoxidized felt is then heated to 2200°C in 55 minutes and maintained at this temperature for 10 minutes. The felt is then removed from the furnace and cooled to obtain the viscose-based carbon fiber felt.

[0105] The carbon yield of the viscose-based carbon fiber felt product prepared in Comparative Example 1 was 28%, the ash content was 188 ppm (heat treated at 900°C for 4 h in an air atmosphere), and the impurity elements were measured by GDMS. The main impurity elements were <150 ppm. The specific impurity values are shown in Table 6.

[0106] Table 6 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Comparative Example 1

[0107] element Concentration (ppmwt) P 0.67 S 120 Cl 1.5 Fe 0.2 Al 0.34 F 8.5

[0108] Comparative Example 2

[0109] This comparative example provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0110] S1. The viscose fiber was needle-punched into a felt, pickled with 2% citric acid, and then dried at 105°C for 40 minutes to obtain a viscose fiber felt;

[0111] S2. Ammonium dihydrogen phosphate, ammonium chloride, and triethanolamine were mixed in a mass ratio of 1:1.25:1 to obtain a recarburizing catalyst; the recarburizing catalyst was prepared into a catalyst solution with deionized water to form an 8% mass concentration; viscose fiber felt was immersed in the catalyst solution at a mass ratio of 10:1 between the recarburizing catalyst and the viscose fiber felt for 30 minutes, removed and rolled dry, and the immersion and rolling drying were repeated twice until the water-felt mass ratio reached 0.5. The felt was then dried in a drying oven at 110°C to a water content of 3% to obtain a pretreated viscose fiber felt;

[0112] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -20Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0113] S4. Send the viscose-based carbon fiber preoxidation felt into a dedicated carbonization-graphitization furnace and heat it from room temperature to 800°C in 30 minutes in a 40Pa slightly positive pressure inert atmosphere circulating air (the temperature is too high and the acidic gas will corrode the equipment severely). Keep the temperature constant for 30 minutes. Then heat it to 2200°C in 60 minutes and keep the temperature constant for 10 minutes. Then take it out of the furnace and cool it to obtain the viscose-based carbon fiber felt.

[0114] The carbon yield of the viscose-based carbon fiber felt product prepared in Comparative Example 2 was 28%, the ash content was 373 ppm (heat treated at 900°C for 4 h in an air atmosphere), and the impurity elements were measured by GDMS. The main impurity elements were <120 ppm. The specific impurity values are shown in Table 7.

[0115] Table 7 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Comparative Example 2

[0116] element Concentration (ppmwt) P 103 S 7 Cl 2.1 Fe 0.14 Al 0.52 F 7.6

[0117] Comparative Example 3

[0118] This comparative example provides a method for preparing a viscose-based carbon fiber felt, comprising the following steps:

[0119] S1. The viscose fiber was needle-punched into a felt, pickled with 2% citric acid, and then dried at 105°C for 40 minutes to obtain a viscose fiber felt;

[0120] S2. A catalyst solution with a mass concentration of 6% was prepared by mixing citric acid and deionized water. Viscose fiber felt was immersed in the catalyst solution at a mass ratio of 10:1 between the carburizing catalyst and the viscose fiber felt for 30 minutes. The mixture was then removed and rolled dry. The immersion and rolling drying process was repeated twice until the water-felt mass ratio reached 0.5. The mixture was then dried in a drying oven at 110°C to a water content of 3%, thereby obtaining a pretreated viscose fiber felt.

[0121] S3. The pretreated viscose fiber felt was sent to a dedicated catalytic dehydration furnace for heat treatment in a -10Pa slightly negative pressure inert atmosphere circulating air, heated from room temperature to 240 ° C for 30 min, heated to 260 ° C for 30 min, heated to 280 ° C for 30 min, heated to 300 ° C for 30 min, and cooled out of the furnace to obtain a viscose-based carbon fiber preoxidation felt;

[0122] S4. The viscose-based carbon fiber preoxidized felt was placed in a dedicated carbonization-graphitization furnace and heated from room temperature to 1200°C in 30 minutes in a slightly positive pressure inert atmosphere with circulating air at 10 Pa. The temperature was maintained constant for 30 minutes. The felt was then heated to 2200°C in 55 minutes and maintained constant for 10 minutes. The felt was then removed from the furnace and cooled to obtain the viscose-based carbon fiber felt.

[0123] The carbon yield of the viscose-based carbon fiber felt product prepared in Comparative Example 3 was 19%, the ash content was 46 ppm (heat treated at 900°C for 4 h in air atmosphere), and the impurity elements were measured by GDMS. The main impurity elements were <15 ppm. The specific impurity values are shown in Table 8.

[0124] Table 8 GDMS data of main impurities of viscose-based carbon fiber felt prepared in Comparative Example 3

[0125]

[0126]

[0127] The results of the above examples and comparative examples demonstrate that the carburization catalyst used in the present invention exhibits excellent carburization performance, with a product carbon yield comparable to that of conventional catalytic processes. Furthermore, the concentration of impurities introduced by the carburization catalyst is significantly reduced. Metal elements such as Fe and Al are introduced during metal equipment or tool processing; element F is introduced as a residual purifying agent; and element S is introduced during the viscose fiber production process.

[0128] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A carbon-increasing catalyst, characterized in that: The invention comprises the following raw materials: urea, organic base, organic carboxylic acid, hydrogen bond acceptor; Wherein, the hydrogen bond acceptor is choline chloride or betaine.

2. A carbonization catalyst according to claim 1, characterized in that: The organic base is one of triethanolamine, triethylenetetramine, diethylenetriamine, ethylenediamine and acrylamide.

3. A carbon-increasing catalyst according to claim 2, characterized in that: The organic carboxylic acid is one of maleic acid, citric acid, and 1,2,3,4-butanetetracarboxylic acid.

4. A carburization catalyst according to claim 1 or 3, characterized in that: The mass ratio of the urea, the organic base, the organic carboxylic acid and the hydrogen bond acceptor is 2-8:0.5-1.5:0.5-5:0.5-2.

5. The method for preparing a carburizing catalyst according to any one of claims 1 to 4, characterized in that: The following steps are involved: Urea, an organic base, an organic carboxylic acid and a hydrogen bond acceptor are mixed to obtain a carbon enhancement catalyst.

6. Use of a carburizing catalyst according to any one of claims 1 to 4 in the preparation of viscose-based carbon fiber felt.

7. The use according to claim 6, characterized in that The preparation method of the viscose-based carbon fiber felt comprises the following steps: The viscose fiber is needle-punched into a felt and then acid-washed to obtain a viscose fiber felt, and then the viscose fiber felt is impregnated with an aqueous solution of a carburizing catalyst to obtain a pretreated viscose fiber felt; or the viscose fiber is acid-washed and then impregnated with an aqueous solution of a carburizing catalyst and then needle-punched into a felt to obtain a pretreated viscose fiber felt; The pretreated viscose fiber felt is heat-treated in a special catalytic dehydration furnace to obtain a viscose-based carbon fiber preoxidized felt; The viscose-based carbon fiber preoxidized felt is heat-treated in a special carbonization-graphitization furnace to obtain the viscose-based carbon fiber felt.

8. The use according to claim 7, characterized in that In the aqueous solution of the carbon increase catalyst, the mass concentration of the carbon increase catalyst is 3-20%.

9. The use according to claim 8, characterized in that The mass ratio of the carbonization catalyst to the viscose fiber felt in the aqueous solution of the carbonization catalyst is 8-12:1-3; and the time of the immersion treatment is 10-30 minutes.

Images