A method for rapidly preparing high graphitized porous carbon

Abstract

The application discloses a method for rapidly preparing high-graphitized porous carbon, and belongs to the technical field of carbon material preparation. The method uses the Joule heat generated by the graphite felt to provide instant high temperature, makes the lignin sulfonate to crack, uses the metal inorganic salt generated by the cracking as an in-situ template agent, and then after simple acid washing and water washing processes, the porous carbon with high conductivity, high specific surface area and rich micro-mesopore structure can be obtained. The instant high temperature can improve the graphitization degree of the porous carbon, control the growth rate of the metal inorganic salt, produce a large number of micro-mesopore structures with uniform size distribution, improve the conductivity of the porous carbon, and also ensure high porosity. Moreover, the process can shorten the several or even dozens of hours required by the traditional tube furnace sintering to dozens of seconds, and has the advantages of simple process, high efficiency, low raw material cost, easy popularization and the like.

Description

Technical Field

[0001] This invention discloses a method for rapidly preparing highly graphitized porous carbon, belonging to the field of carbon material preparation technology. Background Technology

[0002] Porous carbon electrode materials have become the most typical and practical electrode materials for supercapacitors due to their large specific surface area, rich and controllable pore structure, stable chemical properties, and certain conductivity. Carbon material precursors include non-renewable fossil raw materials such as coal, petroleum coke, and asphalt, as well as synthetic resins such as phenolic resins. In recent years, biomass and its derivatives have received widespread attention due to their advantages such as wide availability, renewability, and environmental friendliness. Lignin is the second most abundant natural polymer after cellulose, but it is currently mainly used as a low-concentration fuel, leading to resource waste and secondary pollution. Therefore, developing high-value-added applications of lignin has significant economic and social value.

[0003] Lignosulfonate is a type of industrial lignin, obtained by cooking lignin in sulfite solution and / or sulfite solution containing sodium, calcium, magnesium, or ammonium. Using liggnosulfonate as a precursor, porous carbon materials with a hierarchical pore structure can be prepared through a one-step carbonization method without adding any additional template agents or activators. However, there are few reports on the synthesis of porous carbon using liggnosulfonate as a precursor. Chen et al. (Electrochimica Acta, 2012, 71, 92-99) obtained a specific surface area of ​​1362 m² by one-step carbonization of calcium liggnosulfonate. 2 The porous carbon material produced has a high density of macropores (>50 nm), but these macropores are less conducive to improving specific capacitance compared to mesopores, and also reduce volumetric energy. The pore structure of this porous carbon mainly originates from the hard template and activation effect of inorganic salts obtained from the decomposition of lignin sulfonate. However, traditional calcination processes typically involve heating rates below 10 °C / min and calcination times exceeding 2 hours. The decomposed inorganic salts grow over time, making it difficult to effectively control the size of the inorganic solid products and the confined space of the carbon framework, thus hindering the regulation of its pore structure.

[0004] Porous carbon rich in micro and mesoporous structures and with high electronic conductivity is the core of supercapacitor research and development. Various porous carbons prepared using traditional low-temperature calcination methods (<1000℃, activated carbon prepared by physical or chemical activation methods, and template methods) generally have an amorphous structure with well-developed pores and high specific surface area, resulting in high specific capacitance for supercapacitors. However, the material's conductivity is relatively low, leading to high internal resistance and significant voltage drop during high-rate charge and discharge, resulting in a decrease in electrode output power density. Although increasing the calcination temperature can significantly improve the graphitization degree of porous carbon, it reduces its porosity due to pore structure collapse. Furthermore, traditional calcination methods suffer from the difficulty in controlling the pore structure, especially the macropore structure, due to the crystal growth of the activator caused by prolonged calcination at high temperatures. Therefore, the traditional carbonization method for preparing porous carbon presents a difficult contradiction in reconciling high porosity and high graphitization degree. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems and provide a method for rapidly preparing highly graphitized porous carbon. This method employs a Joule heating technique to rapidly raise the temperature, thereby controlling the growth rate and activation of the metal inorganic salts / oxides from the lignin sulfonate pyrolysis products, achieving controllable preparation of porous carbon micro / nanopore structures. By adding sodium hydroxide as an activator to the lignin sulfonate, the activator melts into small droplets under instantaneous high temperature, effectively generating a large number of uniformly sized pores. This facilitates the interaction between carbon and the activator to form controllable, dense, and microporous structures.

[0006] The technical solution adopted in this invention, a method for rapidly preparing highly graphitized porous carbon, comprises the following steps:

[0007] Lignosulfonate powder or lignin sulfonate and activator powder are pressed into tablets using a 1-20 MPa hydraulic press and sandwiched between two graphite felts. The tablets are then placed in a reaction apparatus. The apparatus is evacuated twice at 1-20 MPa to remove all oxygen from the reaction chamber, and then filled with inert gas to 0.01-1 MPa. A constant current DC power supply is used to heat the graphite felts, with the power supply voltage set to 0-50V and the current set to 0-500A. The heating time is approximately 10-300 seconds, after which the circuit is disconnected. After the reaction is complete, the remaining gas in the reaction apparatus is extracted, and inert gas is added to atmospheric pressure. The door is then opened to take samples. The product is first washed with 0.1-6.0 mol / L hydrochloric acid solution to remove inorganic impurities produced during carbonization, and then washed with deionized water until neutral, thus obtaining porous carbon material.

[0008] The lignin sulfonate is one or more of sodium lignin sulfonate, potassium lignin sulfonate, calcium lignin sulfonate, and magnesium lignin sulfonate, wherein the content of the metal elements sodium, potassium, calcium, and magnesium is 1 to 25 wt%.

[0009] The activator is one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, and zinc chloride.

[0010] The mass ratio of lignin sulfonate to activator is 16-20:0.1-1.

[0011] The inert gas is one or more of nitrogen and argon.

[0012] The graphite felt used is one or more of the following: pitch-based graphite felt, polyacrylonitrile-based graphite felt, and adhesive-based graphite felt, with a thickness of 0.5–5 mm.

[0013] The acid solution is one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid.

[0014] The specific surface area of ​​the prepared porous carbon is 1000–2500 m². 2 / g, pore size is 1~50nm.

[0015] The beneficial effects of this invention are as follows: By utilizing the rapid heating characteristic of Joule heating, the growth process of inorganic solid products (hard templates such as metal inorganic salts / oxides) from the pyrolysis of different types of lignin sulfonates and the formation process of carbon skeletons are controlled, thereby achieving the adjustment of the size of inorganic solid products and the size of the confined space of carbon skeletons within a spatial scale range of less than 2 nm and 2-50 nm, and thus achieving efficient regulation of porous carbon micro-mesoporous structures.

[0016] Using industrial waste lignin sulfonate as a carbon source, and utilizing the metal inorganic salts / oxides generated from precursor pyrolysis as in-situ templates and activators, porous carbon materials with high specific surface area, high mesoporousness, and high graphitization degree are prepared in one step through carbonization.

[0017] Thanks to the advantages of Joule heating technology, such as rapid heating, high-temperature treatment, and rapid cooling, lignin sulfonate is rapidly volatilized and decomposed to form a localized high concentration of metallic inorganic salts. Furthermore, the decomposed metallic inorganic salts, at high temperatures, limit the further growth of the inorganic salt grains generated during decomposition, thereby enabling the controllable preparation of porous carbon micro- and nano-porous structures. Attached Figure Description

[0018] Figure 1 SEM images of highly graphitized porous carbon

[0019] In the figure: a is a SEM image of highly graphitized porous carbon; b is an enlarged version of the SEM image of highly graphitized porous carbon.

[0020] Figure 2 Pore ​​size distribution curve of highly graphitized porous carbon

[0021] In the figure: the vertical axis represents the volume of the pore, in cm. 3 / (g nm); the horizontal axis represents the aperture, in nm. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Example 1

[0024] Sodium lignosulfonate powder was pressed into tablets using a hydraulic press at 5 MPa and sandwiched between two 1 mm thick graphite felt sheets, then placed in the reaction apparatus. The reaction apparatus was evacuated twice at 16 MPa to remove oxygen from the reaction chamber, and then nitrogen was introduced to 0.1 MPa. A constant current DC power supply (30 V, 10 A) was used to heat the graphite felt. Heating was continued for approximately 15 seconds, after which the circuit was disconnected. After the reaction was complete, the remaining gas in the reaction apparatus was extracted, and argon was introduced to atmospheric pressure. The door was then opened for sampling. The product was first washed with 1 mol / L hydrochloric acid solution to remove inorganic impurities produced during carbonization, and then washed with sufficient deionized water until neutral, yielding a product with a specific surface area of ​​1300 m². 2 / g, pore size 0.7cm 3 / g of high electrical conductivity porous carbon material.

[0025] Example 2

[0026] Potassium lignosulfonate powder was pressed into tablets using a hydraulic press at 10 MPa and sandwiched between two 1 mm thick graphite felt sheets, which were then placed in the reaction apparatus. The reaction apparatus was evacuated twice at 18 MPa to remove oxygen from the reaction chamber, and then filled with nitrogen to 1 MPa. A constant current DC power supply was used to heat the graphite felt at 40 V and 5 A. Heating was continued for approximately 60 seconds, after which the circuit was disconnected. After the reaction was complete, the remaining gas in the reaction apparatus was extracted, and nitrogen was introduced to atmospheric pressure. The apparatus was then opened for sampling. The product was first washed with 1 mol / L hydrochloric acid solution to remove inorganic impurities produced during carbonization, and then washed with sufficient deionized water until neutral, yielding a product with a specific surface area of ​​1500 m². 2 / g, pore size 0.7cm 3 / g of high electrical conductivity porous carbon material.

[0027] Example 3

[0028] Potassium lignosulfonate powder was pressed into tablets using a hydraulic press at 10 MPa and sandwiched between two 1.5 mm thick graphite felt sheets, which were then placed in the reaction apparatus. The reaction apparatus was evacuated twice at 15 MPa to remove oxygen from the reaction chamber, and then filled with nitrogen to 0.5 MPa. A constant current DC power supply was used to heat the graphite felt, with the power supply voltage set to 45 V and the current set to 5 A. Heating was continued for approximately 90 seconds, after which the circuit was disconnected. After the reaction was complete, the remaining gas in the reaction apparatus was extracted, and nitrogen was added to atmospheric pressure. The door was then opened for sampling. The product was first washed with 1 mol / L sulfuric acid solution to remove inorganic impurities generated during carbonization, and then washed with sufficient deionized water until neutral, yielding a product with a specific surface area of ​​1800 m². 2 / g, pore size 0.7cm 3 / g of high electrical conductivity porous carbon material.

[0029] Example 4

[0030] Sodium lignosulfonate and sodium hydroxide powder (mass ratio 18:0.8) were pressed into tablets using a hydraulic press at 15 MPa and sandwiched between two 1 mm thick graphite felt sheets. These tablets were then placed in a reaction apparatus. The apparatus was evacuated twice at 17 MPa to remove all oxygen from the reaction chamber, and then argon gas was introduced to 0.2 MPa. A constant current DC power supply (30 V, 3 A) was used to heat the graphite felt. Heating was continued for approximately 20 seconds, after which the circuit was disconnected. After the reaction was complete, the remaining gas in the apparatus was extracted, and argon gas was introduced to atmospheric pressure. The apparatus was then opened for sampling. The product was first washed with 2 mol / L hydrochloric acid solution to remove inorganic impurities produced during carbonization, and then washed with sufficient deionized water until neutral, yielding a product with a specific surface area of ​​1450 m². 2 / g, pore size 0.7cm 3 / g of high electrical conductivity porous carbon material.

[0031] Example 5

[0032] Potassium lignosulfonate and sodium hydroxide powder (mass ratio 16:0.7) were pressed into sheets using a hydraulic press at 10 MPa and sandwiched between two 0.5 mm thick graphite felt sheets, which were then placed in a reaction apparatus. The reaction apparatus was evacuated twice at 19 MPa to remove oxygen from the reaction chamber, and then argon gas was introduced to 1 MPa. A constant current DC power supply (40 V, 5 A) was used to heat the graphite felt. Heating was continued for approximately 60 seconds, after which the circuit was disconnected. After the reaction was complete, the remaining gas in the reaction apparatus was extracted, and argon gas was introduced to atmospheric pressure. The apparatus was then opened for sampling. The product was first washed with 1 mol / L hydrochloric acid solution to remove inorganic impurities produced during carbonization, and then washed with sufficient deionized water until neutral, yielding a product with a specific surface area of ​​1750 m². 2 / g, pore size 0.7cm3 / g of high electrical conductivity porous carbon material.

[0033] Example 6

[0034] Sodium lignosulfonate powder was pressed into tablets using a hydraulic press at 10 MPa and sandwiched between two 1 mm thick graphite felt sheets, which were then placed in the reaction apparatus. The reaction apparatus was evacuated twice at 14 MPa to remove oxygen from the reaction chamber, and then filled with nitrogen to 1 MPa. A constant current DC power supply (30 V, 3 A) was used to heat the graphite felt. Heating was continued for approximately 20 seconds, after which the circuit was disconnected. After the reaction was complete, the remaining gas in the reaction apparatus was extracted, and nitrogen was introduced to atmospheric pressure. The apparatus was then opened for sampling. The product was first washed with 1 mol / L hydrochloric acid solution to remove inorganic impurities produced during carbonization, and then washed with sufficient deionized water until neutral, yielding a product with a specific surface area of ​​1350 m². 2 / g, pore size 0.7cm 3 / g of high electrical conductivity porous carbon material.

[0035] As can be seen from the above examples, the content, size, particle size, pore structure, and oxygen-containing functional groups of the cathode carbon additive have a significant impact on the rate performance of the battery. For this invention, a suitable carbon additive has a specific surface area of ​​10–2500 m². 2 / g, carbon aerogel with a mesopore size of 2-50nm, its content is 1-10%, and the oxygen-containing functional group content of carbon aerogel is 1-10%.

Claims

1. A method for rapidly preparing highly graphitized porous carbon, characterized in that... The steps for rapidly preparing highly graphitized porous carbon are as follows: Lignosulfonate powder or lignin sulfonate and activator powder are pressed into tablets using a 1-20 MPa hydraulic press and sandwiched between two graphite felts. The tablets are then placed in a reaction apparatus. The apparatus is evacuated twice at 1-20 MPa to remove all oxygen from the reaction chamber, and then filled with inert gas to 0.01-1 MPa. A constant current DC power supply is used to heat the graphite felts, with the power supply voltage set to 0-50V and the current set to 0-500A. The heating time is approximately 10-300 seconds, after which the circuit is disconnected. After the reaction is complete, the remaining gas in the reaction apparatus is extracted, and inert gas is added to atmospheric pressure. The door is then opened to take samples. The product is first washed with 0.1-6.0 mol / L hydrochloric acid solution to remove inorganic impurities produced during carbonization, and then washed with deionized water until neutral, thus obtaining porous carbon material.

2. The method for rapidly preparing highly graphitized porous carbon as described in claim 1, characterized in that... The lignin sulfonate is one or more of sodium lignin sulfonate, potassium lignin sulfonate, calcium lignin sulfonate, and magnesium lignin sulfonate, wherein the content of the metal elements sodium, potassium, calcium, and magnesium is 1 to 25 wt%.

3. The method for rapidly preparing highly graphitized porous carbon as described in claim 1, characterized in that... The activator is one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, and zinc chloride.

4. The method for rapidly preparing highly graphitized porous carbon as described in claim 1, characterized in that... The mass ratio of lignin sulfonate to activator is 16-20:0.1-1.

5. The method for rapidly preparing highly graphitized porous carbon as described in claim 1, characterized in that... The inert gas is one or more of nitrogen and argon.

6. The method for rapidly preparing highly graphitized porous carbon as described in claim 1, characterized in that... The graphite felt used is one or more of the following: pitch-based graphite felt, polyacrylonitrile-based graphite felt, and adhesive-based graphite felt, with a thickness of 0.5–5 mm.

7. The method for rapidly preparing highly graphitized porous carbon as described in claim 1, characterized in that... The specific surface area of ​​the prepared porous carbon is 1000–2500 m². 2 / g, pore size is 1~50nm.

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