CN110627050A - Method for preparing microcrystalline graphene capacitor carbon by taking lignin as raw material - Google Patents
Method for preparing microcrystalline graphene capacitor carbon by taking lignin as raw material Download PDFInfo
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Abstract
The invention discloses a method for preparing capacitance carbon with a graphene microcrystalline structure by taking lignin as a raw material, and relates to the technical field of preparation of activated carbon and capacitance carbon. The invention comprises the following steps: (1) purifying the lignin raw material; (2) vitrification (softening) of lignin: (3) thermal cracking of lignin; (4) high-temperature carbonization of lignin; (5) microcrystalline graphene of lignocene carbon; (6) and (5) activating the microcrystalline graphene capacitor carbon. The method utilizes waste lignin of a paper mill or other industries as a raw material, has the advantages of environment-friendly and safe production process, simple manufacturing method and good operability, and the produced capacitor carbon has a graphene microcrystalline structure, higher hardness and strength, reasonable hole distribution, large specific surface and specific capacitance, high conductivity and good economic benefit, is beneficial to ecological and environmental protection and can be produced in large quantities.
Description
Technical Field
The invention relates to the technical field of preparation of capacitor carbon, in particular to a method for preparing capacitor carbon with a graphene microcrystalline structure by taking lignin as a raw material.
Background
The super capacitor is a high-tech product developed in the last 10 years, is used as a storage and auxiliary or independent power supply of electric energy, plays a role in substitution during power utilization peak or power peak, is used as a high-power supply of electrical appliances in short time, can be used for high-speed locomotives, automobiles, warships and all machines and tools with large power conversion range, and can also be used as a power supply of small electrical appliances, such as electric toys. The super capacitor can be used for storing electric energy of photovoltaic power generation and wind power generation, can also play roles in energy buffering, short-time power supply and power grid quality improvement in an intelligent power grid, has important effects on energy conservation and environmental protection, and is expected to increase the demand of the nation and the society on the super capacitor rapidly. The capacitance carbon is a medium for storing electric energy in the super capacitor, is high-quality activated carbon, has high conductivity, large specific surface area and specific capacitance, and has special mechanical properties such as hardness, strength, granularity and the like, and has important influence on the capacitance and internal resistance of the super capacitor, and accounts for 30% of the cost of the super capacitor. With the ever-increasing market demand of super capacitors, the demand of capacitor carbon is also increasing, and the capacitor carbon has a wide growing market.
The biomass capacitive carbon is a mainstream product of the super-capacitor carbon, and is used for producing biomass activated carbon and capacitive carbon which are high in quality, granular, have certain mechanical properties and physical properties, and particularly hard biomass raw materials, such as coconut shells, walnut shells and other wood raw materials with high lignin content are required, but the quantity of the resources in China is very limited.
The lignin is the second major component of biomass resources, and is separated from cellulose in the paper industry, the cellulose is used for manufacturing paper pulp, and the lignin is discharged in the form of black liquor and is a main pollutant of water in China. After the national pollution discharge is limited, the paper mill generally burns the concentrated lignin, which not only causes huge waste, but also becomes a heavy burden for the paper mill.
The literature has already been studied on the production of activated carbon or capacitive carbon from lignin, and for example, the invention patent "a method for producing activated carbon with a biomass-based porous graphene structure" (CN201810344875.1) is significantly different from the present invention. (1) The invention patent (CN201810344875.1) uses unseparated powder biomass as raw material, and the invention uses purified lignin as raw material; (2) the invention patent (CN201810344875.1) manufactures powdered activated carbon which can not meet the strict requirements of capacitance carbon on strength and granularity; (3) the activated carbon of the invention patent (CN201810344875.1) may contain a small amount of components of nano-scaled graphene in powder state, and the capacitive carbon of the invention is a hard bulk graphene microcrystal structure.
The "direct activation of lignin for preparing activated carbon for super capacitor" (Yu Bao et al) published in carbon (third stage 2015), in which KOH is directly added to lignin, then the mixture is fired into activated carbon, and the carbonization and activation are carried out in one step. Our studies found that monovalent alkali metal ions (K) were present in the preparation of graphene microcrystals from lignin+、Na+) The extension of the graphene network can be prevented, the formation of a graphene microcrystal structure is seriously interfered, the conductivity of the graphene is reduced, and the structure and the mechanical property of the capacitance carbon are influenced. Therefore, the method of Baojun et al cannot generate graphene microcrystals, and the capacitor carbon has no graphene structure.
The Shuozhi paper (Zhang Ziming) "preparation of porous carbon material by thermal cracking of lignin and its application in super capacitor" (http:// www.docin.com/p-2113348706.html) reports a method for preparing capacitive carbon by using lignin, wherein the capacitive carbon is prepared by catalytic thermal cracking of lignin, catalysts used are NaOH and KOH, and the structure of graphene cannot be generated substantially the same as the method of "direct activation of lignin with KOH" in Bao Jun.
The patent (application number: 201911031406.5) discloses a method for preparing special-shaped activated carbon and capacitive carbon from lignin-modified poor biomass, which has the core content that lignin is used for modifying powdery poor biomass, the proportion of lignin components is increased, chemical bonds are formed between the lignin components and cellulose and hemicellulose, the lignin components are converted into a hard biomass raw material, and coconut shells are replaced to prepare granular activated carbon and capacitive carbon.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a method for preparing microcrystalline graphene capacitor carbon with excellent mechanical properties and electrical properties by using waste pollutant lignin as a raw material and purifying the raw material.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the method for preparing the microcrystalline graphene capacitance carbon by taking lignin as a raw material comprises the following steps:
(1) treating the lignin raw material: removing organic impurities and inorganic impurities in the lignin raw material to obtain a pure lignin raw material;
(2) vitrification of the lignin raw material: keeping the lignin raw material at the temperature of 150-220 ℃ for 1-2 hours in an inert gas environment, expelling water and small molecular substances in the lignin raw material treated in the step (1), and simultaneously fully softening and vitrifying the lignin to form a glass body with uniform texture;
(3) thermal cracking of lignin raw material: keeping the temperature of 300-450 ℃ for 180min under the environment of inert gas and ammonia gas to ensure that the lignin is subjected to thermal cracking reaction;
(4) carbonizing lignin: keeping the temperature of 600-800 ℃ for 220min under the environment of inert gas and ammonia gas to ensure that lignin undergoes carbonization reaction to obtain lignin carbon;
(5) microcrystalline graphene of lignin carbon: in an inert gas and ammonia gas environment, maintaining the lignin carbon at a temperature of more than 1000 ℃ for 60-300min to convert the lignin carbon into graphene microcrystals to obtain microcrystalline graphene capacitive carbon;
(6) activation of microcrystalline graphene capacitor carbon: with KOH-H2O2And (3) activating the microcrystalline graphene capacitive carbon by a hydrothermal method.
Further, the lignin raw material in the step (1) is lignin separated from paper mill black liquor, and different methods for purifying lignin are adopted according to the pulping method of the paper mill: acid precipitation separation and purification method or organic solvent dissolution separation and purification method. Most of lignin in the market is crude lignin from different paper mills, and in order to ensure the product quality, the lignin raw material with high purity and less impurities is preferably selected, and pretreatment such as strict impurity removal, purification and the like is performed to remove various organic and inorganic impurities, so that the lignin can be used. The water soluble alkaline lignin can be modulated by dilute acid, and the lignin precipitate is separated and washed to obtain pure lignin; for non-alkaline lignin, it can be dissolved in organic solvent such as ethanol, separated lignin-ethanol solution, evaporated and recovered ethanol.
Further, the vitrification of the lignin raw material in the step (2) is carried out in a program temperature controlled inert atmosphere electric furnace, the glass point temperature of the lignin raw material is tested in advance, the vitrification temperature is determined according to the measurement of the glass point of the used lignin raw material, and the lignin is kept in the temperature range of 150-220 ℃ for 2 hours in an inert gas environment to be fully softened and vitrified.
Further, the thermal cracking operation of the lignin raw material in the step (3) is as follows: the method is carried out in an electric furnace with a programmed temperature control atmosphere, the temperature is raised to 300-450 ℃ in inert gas and ammonia gas, the temperature is kept for 120min, the lignin raw material is fully cracked, and the generated tar, smoke and volatile micromolecules are fully escaped.
Further, the step (4) of carbonizing the lignin is as follows: in a programmed temperature controlled atmosphere electric furnace, in an inert gas + ammonia environment, the temperature is kept for 120min at the temperature of 600-.
Further, the step (5) of performing microcrystalline graphene on the lignin carbon comprises the following steps: in a programmed temperature control atmosphere electric furnace, under the condition of inert gas and ammonia gas, the temperature is raised to 1000 ℃, and the temperature is maintained for 60min, so that the lignin carbon is converted into a graphene microcrystal structure.
Further, the activation treatment operation of the step (6) is as follows:
A. crushing blocky microcrystalline graphene capacitance carbon into particles, and placing the particles in a hydrothermal kettle;
B. 5% of KOH by mass: 20% H2O210: 1-10: 3, preparing KOH + H2O2The mixed solution of (5%) KOH and 20% H2O2Are all the mass percentage;
C. according to the solid-liquid weight ratio of 1: 5-1: 10, microcrystalline graphene capacitive carbon and KOH + H2O2The mixed solution is added into a hydrothermal kettle, and is subjected to an activation reaction for 1 hour at the temperature of 200-220 ℃, holes are etched, and the specific surface is enlarged;
D. and filtering to obtain capacitance carbon particles after the reaction is finished, washing with deionized water, and drying to obtain the capacitance carbon with the graphene microcrystalline structure.
Further, the inert gas is one of nitrogen, argon, helium or any combination thereof.
Further, in the steps (3) to (5), the atmosphere of the inert gas and the ammonia gas is an inert gas in a volume ratio in a programmed temperature controlled atmosphere electric furnace: ammonia gas 10: 1-10: 3, adding ammonia gas into the inert gas flow. And ammonia gas is added into the inert gas and decomposed into nitrogen and hydrogen at high temperature, so that the oxygen in the lignin is reduced into water, and the purity of the microcrystalline graphene capacitive carbon is improved. Using KOH + H2O2The mixed solution activates microcrystalline graphene capacitance carbon in a hydrothermal kettle, which is beneficial to K2CO3And (4) etching larger holes.
The research mechanism of the invention is as follows: we found in the research that lignin can be carbonized and graphitized to obtain a "graphene microcrystal" material, and reported the Chinese patent (a graphene microcrystal and its preparation method, application number: 201810223709.6). The graphene crystallite is a crystalline structure consisting of sp3Bonding sp of carbon atom in state2The microcrystalline structure formed by the graphene microcrystalline fragments in the state has a long-range disordered and short-range ordered structure, is hard in texture, high in conductivity and has a large number of nano-scale holes. In order to manufacture the graphene microcrystal into capacitance carbon, the graphene microcrystal needs to be subjected to activation treatment to etch more holes of other levels, so that the specific surface and the specific capacitance are improved. Book (I)The invention is based on the former patent, and further improves to prepare the microcrystalline graphene capacitance carbon.
The invention strictly avoids K on the basis of preparing the graphene microcrystal in the previous period+And Na+Under the condition of (KOH + H), in an environment of inert gas and ammonia gas (the ammonia gas is decomposed into nitrogen gas and hydrogen gas to form inert and reducing atmosphere, which is beneficial to the formation of a graphene structure), pure lignin carbonization and graphene are used for preparing a graphene microcrystal, a large number of nano-scale holes are formed in the graphene microcrystal, and the (KOH + H) is synthesized2O2) And (3) carrying out hydrothermal activation treatment, etching holes of other levels on the basis of the nano holes to obtain the microcrystalline graphene capacitor carbon with the microcrystalline structure of graphene, wherein the holes are complete and controllable in type, and the microcrystalline graphene capacitor carbon with excellent properties such as high specific surface, specific capacitance, conductivity and hardness is obtained.
The invention has the following advantages and technical effects:
(1) according to the invention, the pollution waste lignin of the paper mill is used as a raw material instead of coconut shells, walnut shells and the like, so that waste materials are changed into valuable, the raw material source is wide, the production process is clean, environment-friendly and safe, the preparation method is simple, the operability is good, the cost is low, the economic benefit is high, and the large-scale production is facilitated.
(2) The microcrystalline graphene capacitor carbon is prepared on the basis of a graphene microcrystal, has the excellent properties of graphene, has a large number of nano-scale holes, high hardness and strength, reasonable hole distribution, large specific surface and specific capacitance, high conductivity and good economic benefit, is beneficial to ecological and environmental protection, and can be produced in large quantities.
(3) The invention adopts a hydrothermal kettle of KOH + H2O2The mixed solution activation technology can etch holes of other levels in a controlled manner on the basis of nano-scale holes of microcrystalline graphene capacitor carbon, and the specific surface is large, and the types of the holes are complete.
(4) The microcrystalline graphene capacitor carbon has high hardness, is rarely changed into powder in the crushing process, mostly is particles with certain granularity, is favorable for improving the charging and discharging times and prolonging the service life of a super capacitor.
Drawings
FIG. 1 is a diagram showing the state of the bagasse lignin powder after purification treatment in example 1;
FIG. 2 is a Scanning Electron Microscope (SEM) image of lignin isolated from alkali lignin by precipitation with dilute acid in example 1;
FIG. 3 is a Scanning Electron Microscope (SEM) image of microcrystalline graphene capacitive carbon prepared from bagasse lignin as a raw material in example 1;
FIG. 4 is a High Resolution Transmission Electron Microscopy (HRTEM) image of microcrystalline graphene capacitive carbon prepared from bagasse lignin as a raw material in example 1;
FIG. 5 is a Scanning Electron Microscope (SEM) image of lignin separated from eucalyptus papermaking black liquor by using an ethanol solvent in example 2;
FIG. 6 is a Scanning Electron Microscope (SEM) image of microcrystalline graphene capacitive carbon prepared from eucalyptus lignin as a raw material in example 2;
FIG. 7 shows KOH + H treatment of example 22O2Scanning Electron Microscope (SEM) images of the microcrystalline graphene capacitive carbon after the activation treatment.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
Example 1
A method for preparing microcrystalline graphene capacitor carbon by taking lignin as a raw material comprises the following steps of taking alkaline lignin (pH 12) of a bagasse paper mill as an initial raw material, and performing purification treatment, vitrification, thermal cracking, carbonization, microcrystalline graphene olefination, activation and the like on the lignin to prepare the lignin microcrystalline graphene capacitor carbon, wherein the specific operation steps are as follows:
(1) treating the lignin raw material: the method comprises the following steps of (1) mixing alkaline lignin of a bagasse paper mill in a solid-liquid mass ratio: dissolving 8 in water, filtering to remove insoluble impurities, sequentially adding 10% by mass of dilute acid, adjusting pH to 6.0, separating lignin precipitate, spin-drying with a centrifuge, washing with deionized water for 3 times, and drying in an oven at 120 deg.C for 4 hr to obtain pure lignin powder;
as shown in fig. 1, the alkaline lignin of bagasse paper mill is subjected to dilute acid precipitation separation and purification in step (1) to obtain lignin powder; fig. 2 is a Scanning Electron Microscope (SEM) photograph showing that the lignin powder is fluffy flocculent.
(2) Vitrification of the lignin raw material: putting 100 g of lignin powder into a graphite crucible, heating to 220 ℃ at a heating rate of 5 ℃/min in a quartz tube type atmosphere electric furnace with program temperature control in nitrogen flow of 60mL/min, keeping for 2 hours, expelling water and small molecular substances in lignin raw materials, and simultaneously fully softening and vitrifying the lignin to form a vitreous body with uniform texture;
(3) thermal cracking of lignin raw material: heating to 400 ℃ at a heating rate of 5 ℃/min in a quartz tube type atmosphere electric furnace with a program temperature control in 40ml/min nitrogen and 10ml/min ammonia gas flow, and keeping for 2 hours to enable lignin to generate a thermal cracking reaction;
(4) carbonizing lignin: in a quartz tube type atmosphere electric furnace with program temperature control, in 40ml/min nitrogen and 10ml/min ammonia gas flow, raising the temperature to 800 ℃ at the temperature rise rate of 5 ℃/min, keeping for 2 hours, and carrying out carbonization reaction on lignin;
(5) microcrystalline graphene of lignin carbon: in a quartz tube type atmosphere electric furnace with program temperature control, in 40ml/min nitrogen and 10ml/min ammonia gas flow, raising the temperature to 1000 ℃ at the temperature rise rate of 5 ℃/min, and keeping for 1 hour to convert the temperature into a graphene microcrystal so as to obtain microcrystalline graphene capacitive carbon;
(6) activation of microcrystalline graphene capacitor carbon: roughly crushing blocky microcrystalline graphene capacitor carbon, putting deionized water and the microcrystalline graphene capacitor carbon into a high-pressure reaction kettle according to the proportion of 10:2, adding high-pressure steam to 100 atmospheres, reducing the pressure to normal pressure, vacuumizing to-1 atmosphere, repeating for 5 times, filtering capacitor carbon particles, washing with deionized water for 3 times, and drying to obtain the microcrystalline graphene capacitor carbon.
In this example, the steps (2) to (5) are carried out in a quartz tube furnace, and the temperature rise and the temperature decrease are automatically and continuously operated under the control of a program.
As shown in fig. 3, it is a Scanning Electron Microscope (SEM) photograph of the microcrystalline graphene capacitive carbon prepared in example 1, which is in a hard block shape; as shown in fig. 4, a High Resolution Transmission Electron Microscope (HRTEM) photograph of the microcrystalline graphene capacitive carbon prepared in example 1 shows a large number of randomly arranged graphene crystallite fragments with a large number of nano-scale pores.
In this example, about 25 g of microcrystalline graphene capacitive carbon product is finally obtained by using 100 g of bagasse pith-lignin raw material, and the yield is about 25%.
Example 2
In south China, especially Guangxi, there are artificial fast-growing eucalyptus forests in the wild of the mountain, which are mainly used for paper making and plywood production. In the embodiment, lignin in a eucalyptus paper mill is used as an initial raw material, the eucalyptus paper mill is used for pulping by a chemical-mechanical method, the pH value of the lignin is 9, and the lignin is weak in alkaline; the operation steps for preparing the microcrystalline graphene capacitor carbon are as follows:
(1) treating the lignin raw material: the solid-liquid mass ratio of lignin of eucalyptus paper mill is 1: adding 8 of the lignin into 75 mass percent of ethanol, fully stirring, filtering insoluble impurities, sucking ethanol in an ethanol-lignin solution by using a cyclone condensing device, recovering the ethanol, washing lignin precipitate by using deionized water for 3 times, drying by using a centrifugal machine, and drying for 4 hours in an oven at 120 ℃ to obtain pure lignin powder.
As shown in fig. 5, the Scanning Electron Microscope (SEM) photograph of the lignin separated from the eucalyptus papermaking black liquor by using the ethanol solvent in the step (1) is roughly spherical.
(2) Putting 20 g of lignin powder into a graphite crucible, heating to 220 ℃ at a heating rate of 5 ℃/min in a quartz tube type atmosphere electric furnace with program temperature control in nitrogen flow, keeping for 2 hours, expelling water and small molecular substances in the lignin raw material, and simultaneously fully softening and vitrifying the lignin;
(3) thermal cracking of lignin raw material: heating to 400 ℃ at a heating rate of 5 ℃/min in a quartz tube type atmosphere electric furnace with a program temperature control in 40ml/min nitrogen and 8ml/min ammonia gas flow, and keeping for 2 hours to enable lignin to generate a thermal cracking reaction;
(4) carbonizing lignin: in a quartz tube type atmosphere electric furnace with program temperature control, in 40ml/min nitrogen and 8ml/min ammonia gas flow, raising the temperature to 800 ℃ at the temperature rise rate of 5 ℃/min, keeping for 2 hours, and carrying out carbonization reaction on lignin;
(5) microcrystalline graphene of lignin carbon: in a quartz tube type atmosphere electric furnace with program temperature control, in 40ml/min nitrogen and 8ml/min ammonia gas flow, raising the temperature to 1000 ℃ at the temperature rise rate of 5 ℃/min, and keeping for 1 hour to convert the temperature into a graphene microcrystal so as to obtain microcrystalline graphene capacitive carbon;
(6) activation of microcrystalline graphene capacitor carbon:
A. crushing blocky microcrystalline graphene capacitance carbon into particles, and placing the particles in a hydrothermal kettle;
B. 5% of KOH by mass: 20% H2O210:2, preparing KOH + H2O2The mixed solution of (1);
C. according to the solid-liquid weight ratio of 1: 8 ratio of KOH + H2O2Adding the mixed solution into a hydrothermal kettle, and carrying out activation reaction for 1 hour at the temperature of 200 ℃;
D. and filtering to obtain capacitance carbon particles after the reaction is finished, washing for 3 times by using deionized water, and drying to obtain the capacitance carbon with the graphene microcrystalline structure.
In this example, the steps (2) to (5) are carried out in a quartz tube furnace, and the temperature rise and the temperature decrease are automatically and continuously operated under the control of a program.
Fig. 6 is a Scanning Electron Microscope (SEM) photograph of the microcrystalline graphene capacitive carbon obtained in example 2, which shows that the microcrystalline graphene capacitive carbon looks like hard detritus. Fig. 7 is a Scanning Electron Microscope (SEM) photograph of the microcrystalline graphene capacitive carbon of example 2, which shows that there are a large number of pores with various dimensions.
This example uses 100 grams of eucalyptus lignin as the starting material to obtain about 20 grams of activated carbon product at about 20% yield.
Example 3
The method for preparing the microcrystalline graphene capacitance carbon by taking lignin as a raw material comprises the following steps:
(1) treating the lignin raw material: the same lignin as in example 1 was selected and the procedure was the same as in example 1;
(2) vitrification of the lignin raw material: keeping the lignin raw material at the temperature of 150 ℃ for 2 hours in an argon atmosphere of 60ml/min, and expelling water and small molecular substances in the lignin raw material treated in the step (1) to fully soften and vitrify the lignin;
(3) thermal cracking of lignin raw material: keeping the temperature of 450 ℃ for 120min under the environment of 40ml/min argon and 4ml/min ammonia gas to ensure that the lignin is subjected to a thermal cracking reaction;
(4) carbonizing lignin: keeping the temperature of the mixture at 600 ℃ for 220min under the environment of 40ml/min argon and 4ml/min ammonia gas to ensure that lignin is subjected to carbonization reaction to obtain lignin carbon;
(5) microcrystalline graphene of lignin carbon: in an environment of 40ml/min argon gas and 4ml/min ammonia gas, maintaining the lignin carbon at 1050 ℃ for 300min to convert the lignin carbon into graphene microcrystal, so as to obtain microcrystalline graphene capacitive carbon;
(6) activation of microcrystalline graphene capacitor carbon:
A. crushing blocky microcrystalline graphene capacitance carbon into particles, and placing the particles in a hydrothermal kettle;
B. 5% of KOH by mass: 20% H2O210: 3, preparing KOH + H2O2The mixed solution of (1);
C. according to the solid-liquid weight ratio of 1: 10 ratio of KOH + H2O2Adding the mixed solution into a hydrothermal kettle, and carrying out activation reaction for 1 hour at the temperature of 220 ℃;
D. and filtering to obtain capacitance carbon particles after the reaction is finished, washing with deionized water, and drying to obtain the capacitance carbon with the graphene microcrystalline structure.
Part of the property parameters of the microcrystalline graphene capacitor carbon prepared in the embodiments 1 and 2 are summarized in table 1, and part of the indexes are obviously higher than those of the product of the company of clony, japan.
TABLE 1
High-pressure steam activation;
**KOH—H2O2activating by a hydrothermal method;
and after ball milling and crushing, the mass percentage of the particles is larger than 100 meshes.
Although the present invention has been described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (9)
1. The method for preparing the microcrystalline graphene capacitance carbon by taking lignin as a raw material is characterized by comprising the following steps:
(1) treating the lignin raw material: removing organic impurities and inorganic impurities in the lignin raw material to obtain a pure lignin raw material;
(2) vitrification of the lignin raw material: keeping the lignin raw material at the temperature of 150-220 ℃ for 1-2 hours in an inert gas environment, and expelling water and small molecular substances in the lignin raw material treated in the step (1) to fully soften and vitrify the lignin;
(3) thermal cracking of lignin raw material: keeping the temperature of 300-450 ℃ for 180min under the environment of inert gas and ammonia gas to ensure that the lignin is subjected to thermal cracking reaction;
(4) carbonizing lignin: keeping the temperature of 600-800 ℃ for 220min under the environment of inert gas and ammonia gas to ensure that lignin undergoes carbonization reaction to obtain lignin carbon;
(5) microcrystalline graphene of lignin carbon: in an inert gas and ammonia gas environment, maintaining the lignin carbon at a temperature of more than 1000 ℃ for 60-300min to convert the lignin carbon into graphene microcrystals to obtain microcrystalline graphene capacitive carbon;
(6) activation of microcrystalline graphene capacitor carbon: with KOH-H2O2Carrying out activation treatment on the microcrystalline graphene capacitance carbon by a hydrothermal method or other activation methods.
2. The method for preparing microcrystalline graphene capacitive carbon by taking lignin as a raw material according to claim 1, wherein the method comprises the following steps: the lignin raw material in the step (1) is lignin separated from black liquor of a paper mill; depending on the pulping process in the paper mill, different methods of purifying lignin are used: acid precipitation separation and purification method or organic solvent dissolution separation and purification method.
3. The method for preparing microcrystalline graphene capacitive carbon by taking lignin as a raw material according to claim 1, wherein the method comprises the following steps: and (3) vitrifying the lignin raw material in the step (2) in an inert atmosphere electric furnace with program temperature control, determining the vitrification temperature according to the measurement of the glass point of the used lignin raw material, and keeping the lignin raw material in the temperature range of 150 ℃ and 220 ℃ for 2 hours in an inert gas environment to fully soften and vitrify the lignin.
4. The method for preparing microcrystalline graphene capacitive carbon by taking lignin as a raw material according to claim 1, wherein the method comprises the following steps: the thermal cracking operation of the lignin raw material in the step (3) is as follows: the method is carried out in an electric furnace with a programmed temperature control atmosphere, the temperature is raised to 300-450 ℃ in inert gas and ammonia gas, the temperature is kept for 120min, the lignin raw material is fully cracked, and the generated tar, smoke and volatile micromolecules are fully escaped.
5. The method for preparing microcrystalline graphene capacitive carbon by taking lignin as a raw material according to claim 1, wherein the method comprises the following steps: the carbonization operation of the lignin in the step (4) is as follows: in a programmed temperature controlled atmosphere electric furnace, in an inert gas + ammonia environment, the temperature is kept for 120min at the temperature of 600-.
6. The method for preparing microcrystalline graphene capacitive carbon by taking lignin as a raw material according to claim 1, wherein the method comprises the following steps: the operation of the step (5) of performing microcrystalline graphene on the lignin carbon is as follows: in a programmed temperature control atmosphere electric furnace, under the condition of inert gas and ammonia gas, the temperature is raised to 1000 ℃, and the temperature is maintained for 60min, so that the lignin carbon is converted into a graphene microcrystal structure.
7. The method for preparing microcrystalline graphene capacitor carbon from lignin as a raw material according to claim 1, wherein the KOH-H of the step (6)2O2The hydrothermal activation treatment operation was as follows:
A. crushing blocky microcrystalline graphene capacitance carbon into particles, and placing the particles in a hydrothermal kettle;
B. 5% of KOH by mass: 20% H2O210: 1-10: 3, preparing KOH + H2O2The mixed solution of (1);
C. according to the solid-liquid weight ratio of 1: 5-1: 10, microcrystalline graphene capacitive carbon and KOH + H2O2The mixed solution is mixed in a hydrothermal kettle and is activated and reacted for 1 hour at the temperature of 200-220 ℃;
D. and filtering to obtain capacitance carbon particles after the reaction is finished, washing with deionized water, and drying to obtain the capacitance carbon with the graphene microcrystalline structure.
8. The method for preparing microcrystalline graphene capacitive carbon from lignin as a raw material according to any one of claims 1 to 7, wherein: the inert gas is one of nitrogen, argon and helium or any combination thereof.
9. The method for preparing microcrystalline graphene capacitive carbon from lignin as a raw material according to any one of claims 1 to 7, wherein: in the steps (3) to (5), the inert gas + ammonia environment is that in a programmed temperature control atmosphere electric furnace, the volume ratio of inert gas: ammonia gas 10: 1-10: 3, adding ammonia gas into the inert gas flow.
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