CN110627050B - 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 PDF

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CN110627050B
CN110627050B CN201911088470.7A CN201911088470A CN110627050B CN 110627050 B CN110627050 B CN 110627050B CN 201911088470 A CN201911088470 A CN 201911088470A CN 110627050 B CN110627050 B CN 110627050B
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lignin
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杜奇石
冼学权
唐培朵
龙思宇
黄日波
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Guangxi Academy of Sciences
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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 a lignin raw material; (2) vitrification (softening) of lignin: (3) thermal cracking of lignin; (4) high-temperature carbonization of lignin; (5) microcrystalline graphene addition of lignin carbon; and (6) 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

Method for preparing microcrystalline graphene capacitor carbon by taking lignin as raw material
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 play the roles of 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 sharply increase the demands of the nation and the society on the super capacitor. The capacitance carbon is a medium for storing electric energy of the super capacitor, is high-quality activated carbon, has high conductivity, large specific surface and specific capacitance, and special mechanical properties such as hardness, strength, granularity and the like, 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 continuous increase of the market demand of super capacitors, the demand of capacitor carbon is also continuously increased, and the capacitor carbon has a wide growth 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 research of using lignin to produce activated carbon or capacitance carbon has been carried out in the literature, and for example, the invention patent "a preparation method of biomass porous graphene structure activated carbon" (CN 201810344875.1) is greatly different from the invention. (1) The invention patent (CN 201810344875.1) uses unseparated powdery biomass as a raw material, and the invention uses purified lignin as a raw material; (2) The invention patent (CN 201810344875.1) 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 (CN 201810344875.1) may contain a small amount of powder state nano-scale graphene components, and the capacitance carbon of the invention is a hard block-shaped graphene microcrystal structure.
The "direct activation of lignin for preparing activated carbon for super capacitor" (Yu Baojun, etc.) published in carbon (third stage 2015), which adds KOH directly into lignin, then burns it into activated carbon, and carbonizes and activates them in one step. Our studies found that when lignin was used to prepare graphene microcrystalsMonovalent alkali metal ion (K) + 、Na + ) The extension of a graphene network can be prevented, the formation of a graphene microcrystal structure is seriously disturbed, the conductivity of graphene is reduced, and the structure and the mechanical property of capacitance carbon are influenced. Therefore, the method of Baojun et al cannot generate graphene microcrystals, and the capacitor carbon has no graphene structure.
The Shuoshi paper (Zhang Ziming) "the preparation of porous carbon material by thermal cracking of lignin and its application in super capacitor" (http:// www.docin.com/p-2113348706. Html) reports the preparation of capacitive carbon by catalytic thermal cracking of lignin, and the catalysts used are NaOH and KOH, which are substantially the same as the method of Yu Baojun "direct activation of lignin with KOH", and can not generate graphene structure.
The patent (application number: 201911031406.5) "a method for preparing special-type activated carbon and capacitive carbon by lignin-modified inferior biomass, which has the core content that lignin is used for modifying powdery inferior biomass, the proportion of lignin components is increased, chemical bonds are formed between lignin and cellulose and hemicellulose, the lignin components are converted into a hard biomass raw material to replace coconut shells, and granular activated carbon and capacitive carbon are prepared.
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 120-180min in an environment of inert gas and ammonia gas to enable the lignin to generate a thermal cracking reaction;
(4) Carbonizing lignin: keeping the lignin at 600-800 ℃ for 120-220min in an environment of inert gas and ammonia gas to ensure that the lignin is subjected to 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-H 2 O 2 And (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, in the step (2), vitrification of the lignin raw material is carried out in a programmed 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 measurement of the glass point of the lignin raw material, and the lignin is kept for 2 hours in the temperature range of 150-220 ℃ in an inert gas environment, so that the lignin is sufficiently 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-controlled atmosphere, the temperature is raised to 300-450 ℃ in inert gas and ammonia gas, the temperature is maintained 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: keeping the temperature of the lignin raw material for 120min at 600-800 ℃ in an inert gas and ammonia environment in an electric furnace with a programmed temperature-controlled atmosphere to further carbonize the thermally cracked lignin raw material.
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 step (6) is as follows:
A. crushing blocky microcrystalline graphene capacitance carbon into particles, and placing the particles in a hydrothermal kettle;
B. koh, 5% by mass: 20% of H 2 O 2 =10:1 to 10:3, preparing KOH + H 2 O 2 The mixed solution of (2), said 5% KOH and 20% H 2 O 2 Are all the mass percentage;
C. according to the solid-liquid weight ratio of 1:5 to 1:10, microcrystalline graphene capacitive carbon and KOH + H 2 O 2 Adding the mixed solution into a hydrothermal kettle, carrying out activation reaction for 1 hour at the temperature of 200-220 ℃, etching holes and enlarging the specific surface;
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 microcrystal 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 =10:1 to 10:3, adding ammonia gas into the inert gas flow. Adding ammonia gas into inert gasAnd ammonia gas is decomposed into nitrogen and hydrogen at high temperature, so that oxygen in lignin is reduced into water, and the purity of the microcrystalline graphene capacitance carbon is improved. Using KOH + H 2 O 2 The mixed solution activates microcrystalline graphene capacitance carbon in a hydrothermal kettle, which is beneficial to K 2 CO 3 And (3) etching larger holes.
The research mechanism of the invention is as follows: in the research, the inventor finds that lignin can obtain a material of a graphene microcrystal after carbonization and graphitization, and reports the Chinese invention patent (a graphene microcrystal and a preparation method thereof, application number is 201810223709.6). The graphene crystallite is a crystalline structure consisting of sp 3 Bonding sp of carbon atom of state 2 The formed long-range disorder and short-range order microcrystal structure body is hard in texture, high in conductivity and provided with a large number of nanoscale 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 area and the specific capacitance are improved. The invention is further improved on the basis of the former patent to prepare the microcrystalline graphene capacitor 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 synthesized 2 O 2 ) 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 nanoscale holes, high hardness and strength, reasonable hole distribution, large specific surface area 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 + H 2 O 2 The 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 state diagram 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 2 2 O 2 Scanning 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
The method for preparing the microcrystalline graphene capacitive 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 capacitive 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: 8, dissolving in water, filtering to remove insoluble impurities, sequentially adding 10% by mass of dilute acid, adjusting the pH to be =6.0, separating lignin precipitate, spin-drying by a centrifuge, washing for 3 times by deionized water, and drying in an oven at 120 ℃ for 4 hours 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 cotton-like.
(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 lignin to obtain a vitreous body with uniform texture;
(3) Thermal cracking of the 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 raising rate of 5 ℃/min, and keeping for 1 hour to convert the temperature into graphene microcrystal so as to obtain microcrystalline graphene capacitive carbon;
(6) Activation of microcrystalline graphene capacitor carbon: coarsely crushing blocky microcrystalline graphene capacitor carbon, putting deionized water and microcrystalline graphene capacitor carbon into a high-pressure reaction kettle according to the proportion of 10.
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, which is a Scanning Electron Microscope (SEM) photograph of the microcrystalline graphene capacitive carbon prepared in example 1, the microcrystalline graphene capacitive carbon 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 mountains and the wild, which are mainly used for paper making and plywood production. In the embodiment, lignin of 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 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 nitrogen flow in a quartz tube type atmosphere electric furnace with program temperature control, keeping for 2 hours, expelling water and small molecular substances in the lignin raw material, and fully softening and vitrifying the lignin;
(3) Thermal cracking of the 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. koh, 5% by mass: 20% of H 2 O 2 =10:2, preparing KOH + H 2 O 2 The mixed solution of (1);
C. according to the solid-liquid weight ratio of 1:8 ratio of KOH + H 2 O 2 Adding 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 microcrystal 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 in an environment of 40ml/min argon gas and 4ml/min ammonia gas, so 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 +4ml/min ammonia gas, maintaining the lignin carbon at 1050 ℃ for 300min to convert the lignin carbon into graphene microcrystals, 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. according to the mass ratio5% KOH:20% of H 2 O 2 =10:3, preparing KOH + H 2 O 2 The mixed solution of (1);
C. according to the solid-liquid weight ratio of 1:10 ratio of KOH + H 2 O 2 Adding 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
Figure BDA0002266147950000091
* Activating by high-pressure steam;
**KOH—H 2 O 2 activating 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 (8)

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 120-180min 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 lignin at 600-800 ℃ for 120-220min in an environment of inert gas and ammonia gas to ensure that the lignin is subjected to 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-H 2 O 2 Carrying out activation treatment on microcrystalline graphene capacitive carbon by a hydrothermal method;
the KOH-H 2 O 2 The 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. koh at a mass ratio of 5%: 20% of H 2 O 2 =10:1 to 10:3, preparing KOH + H 2 O 2 The mixed solution of (1);
C. according to the solid-liquid weight ratio of 1:5~1:10, microcrystalline graphene capacitive carbon and KOH + H 2 O 2 The 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.
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 paper mill black liquor; depending on the pulping process in the paper mill, different methods for 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 from lignin serving 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 electric furnace with a program temperature-controlled inert atmosphere, determining the vitrification temperature according to the measurement of the glass point of the used lignin raw material, and keeping the vitrification temperature within the temperature range of 150-220 ℃ for 2 hours in an inert gas environment to fully soften and vitrify the lignin.
4. The method for preparing microcrystalline graphene capacitive carbon from lignin serving 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-controlled atmosphere, the temperature is increased 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: keeping the temperature of the lignin raw material at 600-800 ℃ for 120min in a programmed temperature controlled atmosphere electric furnace in an inert gas and ammonia environment, and further carbonizing the thermally cracked lignin raw material.
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 microcrystalline graphene of the lignin carbon in the step (5) 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 capacitive carbon from lignin as a raw material according to any one of claims 1 to 6, wherein: the inert gas is one of nitrogen, argon and helium or any combination thereof.
8. The method for preparing microcrystalline graphene capacitive carbon from lignin as a raw material according to any one of claims 1 to 6, 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 =10:1 to 10:3, ammonia gas is added to the inert gas stream.
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