CN109231204B - Method for preparing porous carbon by biomass step-by-step activation - Google Patents

Method for preparing porous carbon by biomass step-by-step activation Download PDF

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CN109231204B
CN109231204B CN201811147626.XA CN201811147626A CN109231204B CN 109231204 B CN109231204 B CN 109231204B CN 201811147626 A CN201811147626 A CN 201811147626A CN 109231204 B CN109231204 B CN 109231204B
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biomass
biochar
porous carbon
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activating agent
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CN109231204A (en
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陈伟
陈应泉
杨海平
王贤华
邵敬爱
张�雄
杨晴
张世红
陈汉平
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Huazhong University of Science and Technology
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    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/30—Active carbon
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    • C01B32/342—Preparation characterised by non-gaseous activating agents
    • C01B32/348—Metallic compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/30—Active carbon
    • C01B32/312—Preparation
    • C01B32/318—Preparation characterised by the starting materials
    • C01B32/324—Preparation characterised by the starting materials from waste materials, e.g. tyres or spent sulfite pulp liquor
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/30—Active carbon
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    • C01B32/342—Preparation characterised by non-gaseous activating agents

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Abstract

The invention discloses a method for preparing porous carbon by stepwise activating biomass, which comprises the following steps: after biomass is crushed and dried, the biomass is uniformly mixed with an activating agent and then is subjected to activation treatment under inert gas, the activating agent and the biomass generate activation reaction to preliminarily form biochar with certain porosity, the biochar and the activating agent are uniformly impregnated and mixed again, so that the activating agent fully enters pores of the biochar, the effective utilization rate of the activating agent with good dispersibility in a secondary activation process is greatly improved, a carbon framework can be fully etched, a large number of micropores and mesopores are generated, a porous carbon material with a developed pore structure can be formed even if a small amount of activating agent is used, and the porous carbon material has wide application prospects in the fields of catalysis, adsorption, energy storage and the like, so that the green preparation of the porous carbon material by the biomass is realized, and the high-valued biomass utilization process is promoted.

Description

Method for preparing porous carbon by biomass step-by-step activation
Technical Field
The invention relates to the field of biomass utilization, in particular to a method for preparing porous carbon by stepwise activating biomass.
Background
With the gradual depletion of fossil fuels and their resulting increasingly serious environmental problems, the development of renewable resources has become an ongoing and urgent task. Biomass is the only renewable carbon source in nature and has a series of advantages of huge content, environmental friendliness, negative carbon emission and the like, so that the development of biomass energy is a hot research topic at present. The biomass can be subjected to simple heat treatment (such as pyrolysis) to obtain a biochar material, but the biochar obtained by direct pyrolysis has low porosity and is difficult to be utilized at a high value. Therefore, the biochar needs to be activated to form a porous carbon material with a developed pore structure, and the biochar can be widely applied to the fields of electrode materials of ion batteries and supercapacitors, carbon-based materials of catalysts, adsorbents for gas separation and the like, and has a large market space.
At present, KOH, K2CO3、ZnCl2、H3PO4、KHCO3The activating agents are commonly used for preparing porous carbon materials, although the activating agents can etch the biochar to form a developed pore structure, the adding amount of the activating agents is large in the activating process, the adding amount is usually 1-4 times of the mass of the biomass, and the large amount of the activating agents can cause serious corrosion to equipment, so that the activating agents are difficult to be widely applied.
Therefore, a green and environment-friendly method for preparing a porous carbon material with a developed pore structure is urgently needed to meet a large amount of domestic demands.
Disclosure of Invention
Aiming at the defects and the improvement requirements, the invention aims to provide a method for preparing porous carbon by biomass step-by-step activation, wherein the biomass is activated by one step to generate biochar with a partial pore structure, an activating agent can be fully and uniformly dispersed into pores during secondary activation, and then the activating agent and the biochar are subjected to secondary full activation reaction to generate a large number of micropores and mesopores, so that the porous carbon material with developed pores can be obtained by only adding a small amount of the activating agent. The method provided by the invention obviously reduces the dosage of the activating agent, and obtains the porous carbon material with more developed porosity.
In order to realize the aim, the invention provides a method for preparing porous carbon by biomass step-by-step activation, which comprises the following steps:
s1: crushing the biomass solid waste into particles smaller than 60 meshes, and then drying;
s2: fully mixing the biomass solid waste and the activating agent in the step S1 in a dipping mode according to the mass ratio of 50: 1-5: 1, evaporating water in the mixture, and drying to obtain a uniformly mixed sample;
s3: performing an activation reaction on the sample in the step S2 in a nitrogen or argon atmosphere, and performing an activation reaction on an activating agent and active components in the biomass solid waste to form biochar with a certain pore structure
S4: acid washing the biochar obtained in the step S3, then filtering and washing the biochar with excessive deionized water until filtrate is neutral, and drying to obtain primary activated biochar;
s5: and (3) fully mixing the biochar obtained in the step S4 with the activating agent used in the step S2 again in an impregnation mode, evaporating water to dryness, and drying a sample, wherein the amount of the activating agent is the same as the quality of the activating agent in the step S2, fully activating in the nitrogen or argon atmosphere again, and fully entering pores of the biochar formed after primary activation in the impregnation process, so that the uniformly dispersed activating agent fully etches the carbon skeleton, and a large number of micropores and mesopores are generated, thereby forming the biochar with a developed pore structure.
S6: and (5) carrying out the operation of the step S4 on the biochar obtained in the step S5 to finally obtain the porous carbon material.
The principle of the above inventive concept of the present invention is: in the primary activation process of biomass, an activator reacts with active substances in biomass waste to preliminarily form biochar with certain porosity, in the secondary impregnation process of the biochar, the activator can fully enter pores formed by the primary activation of the biomass, so that the activator has fully uniform dispersity, the utilization rate of the activator is greatly improved, a carbon framework can be fully etched to generate a large number of micropores and mesopores, a porous carbon material with a developed pore structure can be formed even if a small amount of the activator is used, the porous carbon material has wide application prospects in the fields of catalysis, adsorption, energy storage and the like, and high-value utilization of the biomass is realized.
When the porous activated carbon is prepared by taking an activating agent and biomass as raw materials, a large amount of activating agent is usually added, the purpose of full hole expansion can be achieved by the adding amount of the activating agent, and the more the amount of the activating agent is, the better the porosity of the prepared porous activated carbon is. However, an excess of activator can seriously damage equipment. The invention only seems to increase the activation times, but breaks through the cognition of the prior art, the activation dosage is more and better, but the invention needs a 'eating less and eating more' type, the preliminarily formed pores after the first activation are fully utilized, the carbon skeleton is further, more fully, more effectively and more comprehensively etched in the second and later activations, and finally the porous carbon material with more developed porosity is obtained. According to the method, the same or higher porosity porous carbon material can be obtained by only using 2-10% of activating agent in the prior art.
Further, the biomass in the step S1 is one or more of bamboo chips, peanut shells, rice hulls and wheat straws, the drying temperature is 100-150 ℃, and the drying time is 10-30 hours.
Further, the activating agent in the step S2 is selected from KOH and K2CO3、ZnCl2、H3PO4、KHCO3The temperature for evaporating water is 50-80 ℃, the temperature for drying the mixed sample is 100-150 ℃, and the drying time is 10-30 h.
Further, the flow rate of argon or nitrogen in the step S3 is 50m L/min-500 m L/min, the activation temperature is 700 ℃ to 900 ℃, and the reaction time is 30min to 90 min.
Further, the acid solution in the step S4 is hydrochloric acid solution, the concentration is 0.05-2 mol/L, the temperature for drying the biochar is 100-150 ℃, and the drying time is 10-30 h.
Further, the temperature of the evaporated moisture and the temperature of the dried sample in the step S5 are the same as those in the step S2.
Further, the flow rate, the activation temperature, and the reaction time of the argon gas or the nitrogen gas in the step S5 are the same as those in the step S3.
Further, the concentration of the hydrochloric acid solution and the drying temperature in the step S6 are the same as those in the step S4.
Further, the steps S5 and S6 may be repeated for a plurality of cycles to obtain a porous carbon material with higher porosity.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) according to the method, the biomass waste is used for preparing the porous carbon material through step-by-step activation, and in the primary activation process of the biomass, an activating agent reacts with active substances in the biomass waste to initially form biochar with a certain porosity; in the secondary impregnation process of the biochar, the activating agent is fully dispersed into pores of the biochar, so that the activating agent can fully etch the carbon skeleton in the secondary activation process of the biochar to generate a large number of micropores and mesopores, and thus, the porous carbon material with a developed pore structure is formed.
(2) In the method, the utilization rate of the activating agent is improved by a step-by-step activation mode, so that compared with a one-step activation mode, the addition amount of the activating agent can be greatly reduced under the condition of obtaining similar porosity, the corrosion of the activating agent to equipment in the activation process is reduced, and the large-scale production of the porous carbon material is facilitated. According to the prior art, the addition amount of the activating agent is 1-4 times of the mass of the biomass, and according to the method, the addition amount of the activating agent is 1/50-1/5 of the mass of the biomass.
(3) In the method, the pore structure of the porous carbon, the addition amount of the activating agent and the like can be regulated and controlled by regulating the activation times of step-by-step activation and the like, so that the quality of the porous carbon with a developed pore structure is ensured, meanwhile, the corrosive harm in the activation process is solved, and the method is an environment-friendly porous carbon preparation method.
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FIG. 1 is a schematic flow chart of a method according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a method for preparing porous carbon by biomass step-by-step activation, which specifically comprises the following steps:
(1) crushing the biomass solid waste into particles smaller than 60 meshes, and then drying;
(2) fully mixing the biomass solid waste and the activating agent in the step (1) in a dipping mode according to the mass ratio of 50: 1-5: 1, evaporating water in the mixture, and drying to obtain a uniformly mixed sample;
(3) performing an activation reaction on the sample in the step (2) in a nitrogen or argon atmosphere, and performing an activation reaction on an activating agent and active components in the biomass solid waste to form biochar with a certain pore structure
(4) Acid washing the biochar obtained in the step (3), then filtering and washing the biochar with excessive deionized water until filtrate is neutral, and drying to obtain primary activated biochar;
(5) and (3) fully mixing the biochar obtained in the step (4) with the activating agent used in the step (2) again in an impregnation mode, evaporating water to dryness, and drying a sample, wherein the amount of the activating agent is the same as the quality of the activating agent in the step (2), fully activating in the nitrogen or argon atmosphere again, and fully entering pores of the biochar formed after primary activation in the impregnation process, so that the uniformly dispersed activating agent fully etches the carbon skeleton, and a large number of micropores and mesopores are generated, thereby forming the biochar with a developed pore structure.
(6) And (4) carrying out the operation of the step (4) on the biochar obtained in the step (5) to finally obtain the porous carbon material.
Wherein the biomass in the step (1) is one or more of bamboo scraps, peanut shells, rice hulls and wheat straws, the drying temperature is 100-150 ℃, and the drying time is 10-30 h.
The activating agent in the step (2) is selected from KOH and K2CO3、ZnCl2、H3PO4、KHCO3The temperature for evaporating water is 50-80 ℃, the temperature for drying the mixed sample is 100-150 ℃, and the drying time is 10-30 h.
The flow rate of argon or nitrogen in the step (3) is 50m L/min-500 m L/min, the activation temperature is 700-900 ℃, and the reaction time is 30-90 min.
The acid solution in the step (4) is hydrochloric acid solution, the concentration is 0.05-2 mol/L, the temperature for drying the biochar is 100-150 ℃, and the drying time is 10-30 h.
The temperature for evaporating moisture and the temperature for drying the sample in the step (5) are the same as those in the step S2; the flow rate, activation temperature and reaction time of argon or nitrogen are the same as those in step S3.
The concentration of the hydrochloric acid solution and the drying temperature in the step (6) are the same as those in the step S4.
And (3) the step (5) and the step (6) can be circulated for multiple times to obtain the porous carbon material with higher porosity.
The principle of the above inventive concept of the present invention is: in the primary activation process of biomass, an activating agent reacts with active substances in biomass waste to preliminarily form biochar with certain porosity, in the secondary impregnation process of the biochar, the activating agent can fully enter pores formed by primary activation of the biomass, so that the activating agent has good dispersibility, the utilization rate of the activating agent is greatly improved, a carbon framework can be fully etched to generate a large number of micropores and mesopores, a porous carbon material with a developed pore structure can be formed even if a small amount of the activating agent is used, and the porous carbon material has wide application prospects in the fields of catalysis, adsorption, energy storage and the like, so that high-value utilization of the biomass is realized.
In order to illustrate the process of the invention in more detail, the following examples are given to further illustrate the process
Example 1
The embodiment of the invention discloses a method for preparing porous carbon by step-by-step activation of biomass, which specifically comprises the following steps:
s1: crushing and screening the bamboo scraps to be smaller than 60 meshes, and drying the bamboo scraps in a 105 ℃ oven for 24 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and a KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 20:1, steaming off water at the temperature of 60 ℃, and then drying in an oven at the temperature of 105 ℃ for 24 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with the activator, and the argon flow is 200m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is about 0.1g, evaporating water at the temperature of 60 ℃, drying the biochar in a 105 ℃ oven for 24 hours, then carrying out an activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activating agent with the argon flow of 200m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain the porous carbon material.
The obtained porous carbon material has developed pore structure and specific surface area up to 1260m2/g。
Example 2
This example is the same as example 1, the activator being K2CO3。
The obtained porous carbon material has a developed pore structure and a specific surface area of 1050m2/g。
Example 3
This example is the same as example 1 except that the activator is ZnCl2。
The obtained porous carbon material has developed pore structure and specific surface area up to 1190m2/g。
Example 4
This example is the same as example 1 except that the activator is H3PO4。
The obtained porous carbon material has a developed pore structure and a specific surface area of 920m2/g。
Example 5
This example is the same as example 1 except that the activator is KHCO3。
The obtained porous carbon material has developed pore structure and specific surface area up to 950m2/g。
Example 6
S1: crushing and screening the bamboo scraps to be smaller than 60 meshes, and drying the bamboo scraps in a 105 ℃ oven for 24 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and the KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 50:1, steaming off water at the temperature of 60 ℃, and then drying in an oven at the temperature of 105 ℃ for 24 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with the activator, and the argon flow is 200m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is 0.04g, evaporating water at the temperature of 60 ℃, drying the biochar in a 105 ℃ oven for 24 hours, then performing activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activating agent with the argon flow of 200m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain the porous carbon material.
The obtained porous carbon material has a developed pore structure and a specific surface area of 760m2/g。
Example 7
S1: crushing and screening the bamboo scraps to be smaller than 60 meshes, and drying the bamboo scraps in a 105 ℃ oven for 24 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and a KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 5:1, steaming off water at the temperature of 60 ℃, and then drying in an oven at the temperature of 105 ℃ for 24 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with the activator, and the argon flow is 200m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is 0.3g, evaporating water at the temperature of 60 ℃, drying the biochar in a 105 ℃ oven for 24 hours, then performing activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activating agent with the argon flow of 200m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain the porous carbon material.
The obtained porous carbon material has developed pore structure and specific surface area of 3060m2/g。
Example 8
S1: crushing and screening peanut shell, placing the crushed peanut shell into a 105 ℃ oven, and drying the peanut shell for 24 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and a KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 10:1, steaming off water at the temperature of 60 ℃, and then drying in an oven at the temperature of 105 ℃ for 24 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with the activator, and the argon flow is 200m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is 0.2g, evaporating water at the temperature of 60 ℃, drying the biochar in a 105 ℃ oven for 24 hours, then performing activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activating agent with the argon flow of 200m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain the porous carbon material.
The obtained porous carbon material has a developed pore structure and a specific surface area of 1690m2/g。
Example 9
This example is identical to example 8, except that the activation temperature is 700 ℃ and the activation time is 90 min.
The obtained porous carbon material has developedPore structure with specific surface area up to 1550m2/g。
Example 10
This example is identical to example 8, except that the activation temperature is 900 ℃ and the activation time is 30 min.
The obtained porous carbon material has developed pore structure and specific surface area of 1730m2/g。
Example 11
S1: crushing and screening the rice hulls to be smaller than 60 meshes, and drying the rice hulls in a 100 ℃ oven for 30 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and a KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 10:1, then steaming off water at the temperature of 60 ℃, and then drying in an oven at the temperature of 100 ℃ for 30 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with the activator, and the argon flow is 200m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 100 ℃ for 30 hours to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is 0.2g, evaporating water at the temperature of 60 ℃, drying the biochar in a drying oven at the temperature of 100 ℃ for 30 hours, then performing activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activating agent at the argon flow rate of 200m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 100 ℃ for 30 hours to obtain the porous carbon material.
The obtained porous carbon material has a developed pore structure and a specific surface area of 1660m2/g。
Example 12
S1: crushing and screening wheat straws to be smaller than 60 meshes, and drying the wheat straws in a 150 ℃ oven for 10 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and a KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 10:1, steaming off water at the temperature of 60 ℃, and then drying in an oven at the temperature of 150 ℃ for 10 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with the activator, and the argon flow is 200m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the obtained product by using excessive deionized water until the filtrate is neutral, and drying the filtrate for 10 hours at 150 ℃ to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is 0.2g, evaporating water at the temperature of 60 ℃, drying the biochar in a drying oven at the temperature of 150 ℃ for 10 hours, then performing activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activating agent at the argon flow rate of 200m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 1 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 150 ℃ for 10 hours to obtain the porous carbon material.
The obtained porous carbon material has a developed pore structure and a specific surface area of 1630m2/g。
Example 13
S1: crushing and screening the bamboo scraps to be smaller than 60 meshes, and drying the bamboo scraps in a 105 ℃ oven for 24 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and a KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 10:1, steaming off water at the temperature of 80 ℃, and then drying in an oven at the temperature of 105 ℃ for 24 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with an activating agent, and the nitrogen flow is 500m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 2 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is-0.2 g, evaporating water at the temperature of 80 ℃, drying the biochar in a 105 ℃ oven for 24 hours, then performing activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activating agent at the nitrogen flow rate of 500m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 2 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain the porous carbon material.
The obtained porous carbon material has developed pore structure and specific surface area up to 1450m2/g。
Example 14
S1: crushing and screening the bamboo scraps to be smaller than 60 meshes, and drying the bamboo scraps in a 105 ℃ oven for 24 hours to obtain an activated raw material;
s2: fully mixing the bamboo sawdust and a KOH activating agent in the step S1 for 24 hours in a dipping mode according to the mass ratio of 10:1, steaming off water at the temperature of 50 ℃, and then drying in an oven at the temperature of 105 ℃ for 24 hours to obtain a uniformly mixed biomass sample;
s3, activating by using a fixed bed reactor with the diameter of 45mm and the length of 60mm, heating the reactor to the activation temperature of 800 ℃, and quickly feeding 2g of the uniformly mixed biomass sample obtained in the step S2 to the middle of the reactor, wherein the activation time is 60min, so that the biomass reacts with an activator, and the nitrogen flow is 50m L/min;
s4, acid-washing the biochar obtained in the step S3, wherein the concentration of a hydrochloric acid solution is 0.5 mol/L, then filtering and washing the filtrate by using excessive deionized water until the filtrate is neutral, and drying the filtrate for 24 hours at 105 ℃ to obtain primary activated biochar;
s5, mixing the biochar obtained in the step S4 with KOH again in a KOH dipping mode for 24 hours, wherein the mass of KOH is 0.2g, evaporating water at the temperature of 50 ℃, drying the biochar in a 105 ℃ oven for 24 hours, then performing activation reaction at the temperature of 800 ℃ for 60 minutes, and fully reacting the biochar with an activator at the nitrogen flow rate of 50m L/min;
and S6, acid-washing the biochar obtained in the step S5, wherein the concentration of a hydrochloric acid solution is 0.5 mol/L, then filtering and washing the biochar with excessive deionized water until the filtrate is neutral, and drying the biochar at 105 ℃ for 24 hours to obtain the porous carbon material.
The obtained porous carbon material has a developed pore structure and a specific surface area of 1980m2/g。
The porous carbon material prepared by the method can be used as a catalyst, an adsorbent or/and an electrode material for application. For example, for the preparation of carbon-based catalysts for the adsorption of CO2、SOx、NOxAnd the like, and is used for preparing electrodes of supercapacitors or batteries and the like.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. A method for preparing porous carbon by biomass step-by-step activation is characterized by comprising the following steps:
s1: crushing the biomass solid waste into particles smaller than 60 meshes, and then drying;
s2: fully mixing the biomass solid waste and the activating agent in the step S1 in a dipping mode according to the mass ratio of 50: 1-5: 1, evaporating water, and drying to obtain a uniformly mixed sample;
s3: performing an activation reaction on the sample in the step S2 in a nitrogen or argon atmosphere, and performing an activation reaction on an activating agent and active components in the biomass solid waste to form biochar with a certain pore structure;
s4: acid washing the biochar obtained in the step S3, then filtering and washing the biochar with excessive deionized water until filtrate is neutral, and drying to obtain primary activated biochar;
s5: fully mixing the primary activated biochar obtained in the step S4 with the activating agent used in the step S2 again in an impregnation mode, evaporating water to dryness, and drying a sample, wherein the amount of the activating agent is the same as the mass of the activating agent in the step S2, and performing full activation reaction again in the nitrogen or argon atmosphere, so that the activating agent which is uniformly dispersed can fully enter the pores of the biochar formed after primary activation in the impregnation process, and the carbon skeleton can be further fully etched by the uniformly dispersed activating agent to generate a large number of micropores and mesopores, so that the biochar with a developed pore structure is formed;
s6: and (5) carrying out the operation of the step S4 on the biochar obtained in the step S5 to finally obtain the porous carbon material with more developed pores.
2. The method for preparing porous carbon through stepwise activation of biomass according to claim 1, wherein the biomass in step S1 is one or more of bamboo sawdust, peanut shells, rice hulls and wheat straws, the drying temperature is 100-150 ℃, and the drying time is 10-30 h.
3. The method for preparing porous carbon by biomass step activation according to claim 2, wherein the activating agent in the step S2 is KOH or K2CO3、ZnCl2、H3PO4、KHCO3The temperature for evaporating water is 50-80 ℃, the temperature for drying the mixed sample is 100-150 ℃, and the drying time is 10-30 h.
4. The method for preparing porous carbon through stepwise biomass activation according to claim 3, wherein the flow rate of argon or nitrogen in the step S3 is 50m L/min-500 m L/min, the activation temperature is 700 ℃ to 900 ℃, and the reaction time is 30min to 90 min.
5. The method for preparing porous carbon through stepwise biomass activation according to claim 4, wherein hydrochloric acid solution is adopted for acid washing in the step S4, the concentration of the hydrochloric acid solution is 0.05-2 mol/L, the temperature for drying the biochar is 100-150 ℃, and the drying time is 10-30 h.
6. The method for preparing porous carbon through biomass step activation according to claim 5, wherein the temperature of the evaporated moisture and the temperature of the dried sample in the step S5 are the same as those in the step S2.
7. The method for preparing porous carbon through biomass step-by-step activation according to claim 6, wherein the flow rate, the activation temperature and the reaction time of the argon or nitrogen in the step S5 are the same as those in the step S3.
8. The method for preparing porous carbon through biomass step activation according to claim 7, wherein the concentration of the hydrochloric acid solution and the drying temperature in the step S6 are the same as those in the step S4.
9. The method for preparing porous carbon by biomass step activation according to claim 8, wherein the steps S5 and S6 are repeated for a plurality of times to obtain porous carbon material with higher porosity.
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