Modified nitrogen-doped biochar and preparation method and application thereof

Abstract

This invention discloses a modified nitrogen-doped biochar, its preparation method, and its applications. The preparation process involves drying and mixing high-nitrogen biomass with lignin-based biomass, grinding the mixture, placing it in a quartz cup at the top of a reactor, continuously introducing inert gas, heating, and then sending the mixed sample to the center of the reactor for pyrolysis. Liquid and gaseous products are collected simultaneously. After pyrolysis, the sample is cooled to obtain nitrogen-doped biochar. This biochar is then activated with KOH, K₂CO₃, KHCO₃, KCl, KMnO₄, or KH₂PO₄ to obtain modified nitrogen-doped biochar, which is then used for catalytic reforming to prepare high-value-added phenols. This invention's modified nitrogen-doped biochar method is simple, low-cost, highly active, and exhibits stronger selectivity for target products. It not only overcomes the shortcomings of bio-oil applications in the chemical industry and promotes higher-value utilization of bio-oil, but also demonstrates excellent stability during long-term recycling, making it more suitable for practical industrial applications.

Description

Technical Field

[0001] This invention belongs to the field of biomass high-value application technology, specifically relating to a modified nitrogen-doped biochar, its preparation method, and its application. Background Technology

[0002] Biomass is a carbon-neutral renewable resource and the only renewable carbon source. Biomass pyrolysis is one of the important biomass conversion technologies, converting biomass into gaseous, liquid, and solid products, making it a simple technology for high-value utilization of biomass. Biochar is a carbon-rich solid product produced by the thermochemical conversion of biomass under anaerobic or hypoxic conditions. However, biochar produced by direct biomass pyrolysis has an underdeveloped pore structure, small specific surface area, and poor physicochemical properties, limiting its applications. Heteroatom doping has become a common method for improving carbon materials in recent years. Introducing heteroatoms, such as nitrogen (N), sulfur (S), and phosphorus (P), can not only optimize the physicochemical properties of the material itself but also increase its application prospects in related fields, thus attracting increasing research attention.

[0003] Bio-oil, a product of rapid biomass pyrolysis, not only possesses the advantages of being carbon neutral and renewable, but also effectively addresses problems encountered in biomass utilization such as resource dispersion, low energy density, and high collection and transportation costs. However, current bio-oil produced by pyrolysis mainly suffers from drawbacks including high acidity, low calorific value, high oxygen content, and poor stability. Phenolic compounds are important aromatic organic compounds, serving as crucial intermediate platform chemicals for the preparation of downstream products such as polycarbonates, epoxy resins, phenolic resins, nylon, caprolactam, and pharmaceuticals. Currently, the main method for producing phenol is the cumene process, which not only consumes large amounts of fossil fuels but also causes environmental pollution. Biochar catalysts exhibit excellent activity and high selectivity in the pyrolysis of lignin-based biomass to produce phenol. Furthermore, bio-oil produced through biochar catalysis is rich in aromatics. Therefore, utilizing biochar catalysts for deoxygenation and upgrading of biomass to produce fuels and phenolic chemicals holds significant potential.

[0004] Current research focuses on two types of active groups on the surface of biochar: nitrogen-containing and oxygen-containing sites. Existing studies have shown that the relative content of oxygen-containing active sites changes significantly before and after the reaction, indicating poor stability. Catalysts with oxygen-containing groups as the core active sites are difficult to reuse. Nitrogen-containing sites, on the other hand, are more stable, and their introduction can greatly improve the selectivity of the target product. Therefore, from both the perspective of catalytic site activity and catalyst reuse, increasing the number of nitrogen-containing sites on the biochar surface is expected to improve the yield of phenolic compounds in the pyrolysis products.

[0005] Due to the low nitrogen content of lignin-based biomass, the yield and quality of nitrogen-containing products are limited. Studies have found that co-pyrolysis of biomass can alter pyrolysis behavior and affect pyrolysis products. Research on the co-pyrolysis of bamboo waste and green algae revealed a higher biochar content and a significant increase in nitrogen content. Introducing exogenous nitrogen into algal biomass co-pyrolysis can achieve nitrogen-rich pyrolysis of low-nitrogen biomass, increasing the number of active nitrogen sites. Furthermore, co-pyrolyzed biochar exhibits a lower H / C ratio, increased aromaticity, larger specific surface area and total pore volume, smaller average pore size, and more developed pores compared to biochar pyrolyzed biochar alone, which facilitates prolonged catalytic reaction time and promotes macromolecular decomposition. In addition, studies have found that the presence of alkali metals / alkaline earth metals in the biomass pyrolysis system can lower the pyrolysis reaction temperature and activation energy, while simultaneously promoting the depolymerization of biomass macromolecules, thus facilitating the formation of small molecules (such as furanones, furfural, and phenols). Currently, there are few reports on the alkali modification of nitrogen-doped biochar for the catalytic reforming of biomass to prepare high-value-added products. Summary of the Invention

[0006] To address the above problems, the present invention aims to provide a modified nitrogen-doped biochar, its preparation method, and its application.

[0007] The specific technical solution is as follows:

[0008] A method for preparing modified nitrogen-doped biochar includes the following steps: drying high-nitrogen biomass and lignin-based biomass, mixing and grinding them, placing them in a quartz cup at the top of a reactor, continuously introducing inert gas, heating, sending the mixed sample to the center of the reactor for pyrolysis, and simultaneously collecting liquid and gaseous products. After pyrolysis, cooling is performed to obtain nitrogen-doped biochar. KOH, K2CO3, KHCO3, KCl, KMnO4 or KH2PO4 are mixed with the nitrogen-doped biochar, activated, acid-washed, and washed with deionized water until the waste liquid pH=7, to obtain activated modified nitrogen-doped biochar.

[0009] Furthermore, the high-nitrogen biomass is spirulina (SP) with a nitrogen content of 10.58 wt.%, and the lignin-containing biomass is soybean straw. The mass ratio of the mixture is 1:3-3:1, preferably 3:1.

[0010] Furthermore, the drying temperature is 100-110℃ for 24 hours, and the material is ground to a particle size of less than 0.25mm. By controlling the particle size, the biomass is heated more evenly inside and out during pyrolysis, thus obtaining biochar of uniform quality.

[0011] Furthermore, the inert gas is argon, the flow rate is 50 mL / min, the temperature is raised to 600℃ for pyrolysis, and the pyrolysis time is 10-60 min, preferably 30 min.

[0012] Furthermore, the condensable portion generated by pyrolysis is cooled in an ice-water bath to obtain bio-oil. The non-condensable gases are first absorbed by nitrogen-containing gases HCN and NH3 through NaOH and H2SO4 solutions, respectively. The other pyrolysis gases are dried and collected by a gas bag.

[0013] Furthermore, the mass ratio of potassium salt to nitrogen-doped biochar was 1:1, the activation temperature was 800℃, the activation time was 1 h, and the biochar was acid-washed with 1 mol / L HCl for 12 h.

[0014] A modified nitrogen-doped biochar prepared by the above preparation method.

[0015] An application of modified nitrogen-doped biochar includes the following steps: pyrolyzing activated modified nitrogen-doped biochar with lignin-based biomass pine wood, absorbing the resulting pyrolysis oil with dichloromethane, and then detecting it by GC-MS.

[0016] Furthermore, the mass ratio of nitrogen-doped biochar to lignin-based biomass pine wood is 1:2.

[0017] The beneficial effects of this invention are as follows:

[0018] 1) In an inert atmosphere, a one-step process for preparing high-nitrogen biochar using high-nitrogen raw materials is achieved, overcoming the traditional two-step process of carbonization followed by activation in biochar preparation, or the process that requires pyrolysis in an NH3 atmosphere.

[0019] 2) The modified nitrogen-doped biochar method of this invention is simple, low-cost, highly active, and more selective for target products. Among them, the nitrogen-doped biochar activated by KOH has the largest specific surface area and outstanding ability to prepare phenols, with phenolic substances reaching 70%. Compared with pine wood pyrolysis oil without biochar catalysis, the yield is increased by about 22%.

[0020] 3) Compared with previous patents, the modified nitrogen-doped biochar of the present invention not only overcomes the defects of bio-oil in the chemical field and promotes the higher value utilization of bio-oil, but also shows excellent stability in long-term recycling, which is more in line with the actual industrial application. Attached Figure Description

[0021] Figure 1 This is a graph showing the nitrogen content ratio of nitrogen-doped biochar prepared in Examples 1-5 of this invention, as determined by XPS.

[0022] Figure 2 Distribution diagrams of biooil products from the mixed pyrolysis of nitrogen-doped biochar and biomass in Examples 1.1-1.5 of this invention;

[0023] Figure 3 Distribution diagrams of phenolic substances in biooil from nitrogen-doped biochar and biomass mixed pyrolysis, as shown in Examples 1.1-1.5 of this invention;

[0024] Figure 4 This is a distribution diagram of bio-oil products from the mixed pyrolysis of potassium-activated nitrogen-doped biochar and biomass, as shown in Examples 2.1-2.6 of this invention.

[0025] Figure 5 This is a distribution diagram of phenolic substances in biooil from potassium-activated nitrogen-doped biochar and biomass mixed pyrolysis, as shown in Examples 2.1-2.6 of this invention.

[0026] Figure 6 The results of FTIR testing are for the activated nitrogen-doped biochar used in Examples 2.1-2.6 of this invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Example 1

[0029] A method for preparing nitrogen-doped biochar material, comprising the following steps:

[0030] (1) Dry the original Spirulina and soybean straw samples at 105℃ for 24h. After drying, pass them through a 60-mesh sieve. Weigh the Spirulina and soybean straw samples (in a ratio of 3:1), grind them in a mortar until the particle size is less than 0.25mm, mix them evenly to form a mixed sample, pack them in a self-sealing bag and place them in a desiccator for later use.

[0031] (2) Weigh approximately 2g of the mixed sample and place it in a quartz basket, suspending it at the top of the reactor. Introduce Ar into the reactor at 50mL / min, then begin the heating program. When the furnace temperature reaches 600℃, directly transfer the sample to the center of the reactor for pyrolysis, simultaneously collecting the liquid and gaseous products. Maintain the pyrolysis process for 30min. The condensable portion is cooled in an ice-water bath to obtain bio-oil. The non-condensable gases are first absorbed by NaOH and H2SO4 solutions to remove nitrogen-containing gases HCN and NH3, respectively. Other pyrolysis gases are dried and collected in a gas bag. After pyrolysis, move the quartz basket back to the top of the reactor. Cool the solid products in the Ar atmosphere to ambient temperature to obtain nitrogen-doped biochar, denoted as CharN. 31 .

[0032] Example 2

[0033] A method for preparing nitrogen-doped biochar material, comprising the following steps:

[0034] (1) Dry the original Spirulina and soybean straw samples at 105℃ for 24h. After drying, pass them through a 60-mesh sieve. Weigh the Spirulina and soybean straw samples (ratio 2:1), grind them in a mortar until the particle size is less than 0.25mm, mix them evenly to form a mixed sample, pack them in a self-sealing bag and place them in a desiccator for later use.

[0035] (2) Weigh approximately 2g of the mixed sample and place it in a quartz basket, suspending it at the top of the reactor. Introduce Ar into the reactor at 50mL / min, then begin the heating program. When the furnace temperature reaches 600℃, directly transfer the sample to the center of the reactor for pyrolysis, simultaneously collecting the liquid and gaseous products. Maintain the pyrolysis process for 30min. The condensable portion is cooled in an ice-water bath to obtain bio-oil. The non-condensable gases are first absorbed by NaOH and H2SO4 solutions to remove nitrogen-containing gases HCN and NH3, respectively. Other pyrolysis gases are dried and collected in a gas bag. After pyrolysis, move the quartz basket back to the top of the reactor. Cool the solid products in the Ar atmosphere to ambient temperature to obtain nitrogen-doped biochar, denoted as CharN. 21 .

[0036] Example 3

[0037] A method for preparing nitrogen-doped biochar, comprising the following steps:

[0038] (1) Dry the original Spirulina and soybean straw samples at 105℃ for 24h. After drying, pass them through a 60-mesh sieve. Weigh the Spirulina and soybean straw samples (ratio 1:1), grind them in a mortar until the particle size is less than 0.25mm, mix them evenly to form a mixed sample, pack them in a self-sealing bag and place them in a desiccator for later use.

[0039] (2) Weigh approximately 2g of the mixed sample and place it in a quartz basket, suspending it at the top of the reactor. Introduce Ar into the reactor at 50mL / min, then begin the heating program. When the furnace temperature reaches 600℃, directly transfer the sample to the center of the reactor for pyrolysis, simultaneously collecting the liquid and gaseous products. Maintain the pyrolysis process for 30min. The condensable portion is cooled in an ice-water bath to obtain bio-oil. The non-condensable gases are first absorbed by NaOH and H2SO4 solutions to remove nitrogen-containing gases HCN and NH3, respectively. Other pyrolysis gases are dried and collected in a gas bag. After pyrolysis, move the quartz basket back to the top of the reactor. Cool the solid products in the Ar atmosphere to ambient temperature to obtain nitrogen-doped biochar, denoted as CharN. 11 .

[0040] Example 4

[0041] A method for preparing nitrogen-doped biochar, comprising the following steps:

[0042] (1) Dry the original Spirulina and soybean straw samples at 105℃ for 24h. After drying, pass them through a 60-mesh sieve. Weigh the Spirulina and soybean straw samples (ratio 1:2), grind them in a mortar until the particle size is less than 0.25mm, mix them evenly to form a mixed sample, pack them in a self-sealing bag and place them in a desiccator for later use.

[0043] (2) Weigh approximately 2g of the mixed sample and place it in a quartz basket, suspending it at the top of the reactor. Introduce Ar into the reactor at 50mL / min, then begin the heating program. When the furnace temperature reaches 600℃, directly transfer the sample to the center of the reactor for pyrolysis, simultaneously collecting the liquid and gaseous products. Maintain the pyrolysis process for 30min. The condensable portion is cooled in an ice-water bath to obtain bio-oil. The non-condensable gases are first absorbed by NaOH and H2SO4 solutions to remove nitrogen-containing gases HCN and NH3, respectively. Other pyrolysis gases are dried and collected in a gas bag. After pyrolysis, move the quartz basket back to the top of the reactor. Cool the solid products in the Ar atmosphere to ambient temperature to obtain nitrogen-doped biochar, denoted as CharN. 12 .

[0044] Example 5

[0045] A method for preparing nitrogen-doped biochar, comprising the following steps:

[0046] (1) Dry the original Spirulina and soybean straw samples at 105℃ for 24h. After drying, pass them through a 60-mesh sieve. Weigh the Spirulina and soybean straw samples (ratio 1:3), grind them in a mortar until the particle size is less than 0.25mm, mix them evenly to form a mixed sample, pack them in a self-sealing bag and place them in a desiccator for later use.

[0047] (2) Weigh approximately 2g of the mixed sample and place it in a quartz basket, suspending it at the top of the reactor. Introduce Ar into the reactor at 50mL / min, then begin the heating program. When the furnace temperature reaches 600℃, directly transfer the sample to the center of the reactor for pyrolysis, simultaneously collecting the liquid and gaseous products. Maintain the pyrolysis process for 30min. The condensable portion is cooled in an ice-water bath to obtain bio-oil. The non-condensable gases are first absorbed by NaOH and H2SO4 solutions to remove nitrogen-containing gases HCN and NH3, respectively. Other pyrolysis gases are dried and collected in a gas bag. After pyrolysis, move the quartz basket back to the top of the reactor. Cool the solid products in the Ar atmosphere to ambient temperature to obtain nitrogen-doped biochar, denoted as CharN. 13 .

[0048] Test Implementation Examples

[0049] 1. XPS Test. The nitrogen-doped biochar from Examples 1-5 were subjected to XPS tests, and the test results are as follows: Figure 1 As shown, SP represents Spirulina. Nitrogen-doped biochar mainly contains four types of nitrogen: pyridine-N (N-5), quaternary-N, pyrrole-N (N-6), and protein-N. When the mixing ratio of Spirulina (SP) and soybean straw is 3:1, pyridine-N reaches its maximum value, resulting in the highest total nitrogen content.

[0050] Application Examples

[0051] 1. First application example. Nitrogen-doped biochar CharN... 31 The pyrolysis was carried out in the reactor with lignin-based biomass pine (1:2). The resulting pyrolysis oil was absorbed by dichloromethane and detected by GC-MS, as detailed below.

[0052] Application Example 1.1 Pine - CharN 31

[0053] 2g of nitrogen-doped biochar and pine wood were mixed in a mass ratio of 1:2 and placed in a quartz basket, which was then suspended at the top of the reactor. Ar was introduced into the reactor at a rate of 50mL / min, and the heating program was started. When the furnace temperature reached 600℃, the sample was directly sent to the center of the reactor for pyrolysis. Liquid and gaseous products were collected at the same time. The pyrolysis process was maintained for 30min. The condensable part generated was cooled in an ice-water bath to obtain pyrolysis oil.

[0054] Application Example 1.2 Pine - CharN 21

[0055] The difference between this application example and application example 1.1 is that the nitrogen-doped biochar is different; the nitrogen-doped biochar is CharN. 21 .

[0056] Application Example 1.3 Pine - CharN 11

[0057] The difference between this application example and application example 1.1 is that the nitrogen-doped biochar is different; the nitrogen-doped biochar is CharN. 11 .

[0058] Application Example 1.4 Pine - CharN 12

[0059] The difference between this application example and application example 1.1 is that the nitrogen-doped biochar is different; the nitrogen-doped biochar is CharN. 12 .

[0060] Application Example 1.5 Pine - CharN13

[0061] The difference between this application example and application example 1.1 is that the nitrogen-doped biochar is different; the nitrogen-doped biochar is CharN. 13 .

[0062] 2. Second group of application examples. This application example differs from the first group of examples in that nitrogen-doped biochar CharN is used. 31 Activation with different potassium salts was performed, as detailed below.

[0063] Application Example 2.1C KOH

[11] +pine

[0064] (1) KOH activator and nitrogen-doped biochar CharN 31 Mix at a mass ratio of 1:1, activate at 800℃ for 1 hour, acid wash with 1 mol / L HCl for 12 hours, and wash with deionized water until the waste liquid pH=7 to obtain activated modified nitrogen-doped biochar C. KOH

[11]

[0065] (2) Activated nitrogen-doped biochar C KOH

[11] Pyrolyze the lignin-based biomass pine wood at a mass ratio of 1:2 (reaction conditions and process are the same as in application example 1.1). The resulting pyrolysis oil is absorbed by dichloromethane and detected by GC-MS.

[0066] Application Example 2.2C K2CO3

[11] +pine

[0067] The activator is K2CO3, and other conditions are the same as in application example 2.1.

[0068] Application Example 2.3C KHCO3

[11] +pine

[0069] The activator is KHCO3, and other conditions are the same as in application example 2.1.

[0070] Application Example 2.4C KCl

[11] +pine

[0071] The activator is KCl, and other conditions are the same as in application example 2.1.

[0072] Application Example 2.5C KH2PO4

[11] +pine

[0073] The activator is KH2PO4, and other conditions are the same as in application example 2.1.

[0074] Application Example 2.6C KMnO4

[11] +pine

[0075] The activator was KMnO4, and other conditions were the same as in application example 2.1.

[0076] The liquid phase products from application examples 1.1-1.5 were tested, and the GC-MS test results are as follows: Figure 2 , Figure 3 As shown, the levels of phenolic compounds and aromatics increased significantly with the addition of nitrogen-doped biochar. Under the catalysis of biochar at a mixing ratio of 3:1, phenolic compounds increased by approximately 13%. Oxygen-containing substances and acidic substances decreased, and the pH value of the bio-oil increased. This is mainly because the basic nitrogen-containing groups in the nitrogen-doped biochar adsorbed acidic intermediates and promoted the decarboxylation, dehydration, and removal of alkyl branches from the pyrolysis intermediates. The compounds in the bio-oil are mainly phenols and furans. After the addition of nitrogen-doped biochar, the relative content of bisphenol compounds such as catechol and 4-methyl-1,2-benzenediol increased significantly, while the relative content of guaiacol compounds decreased. This indicates that nitrogen-doped biochar facilitates the demethylation reaction of bio-oil to form bisphenol compounds. This may be due to: (1) the active oxygen and nitrogen functional groups in nitrogen-doped biochar promote the breaking of β-O-4 bonds in pine wood, forming more phenolic intermediates; (2) nitrogen-doped biochar promotes the reaction of hydrogen donors (water, acetaldehyde, and ethanol, etc.) produced by the cracking of hemicellulose and cellulose with phenolic intermediates (hydrogen acceptors) to form more phenolic substances; (3) nitrogen-doped biochar promotes the breaking of -O-CH3 bonds in phenolic intermediates to form phenols; (4) nitrogen-doped biochar promotes the decomposition of lignin while inhibiting the decomposition of hemicellulose and cellulose, thus leading to an increase in the content of phenolic substances. In addition, nitrogen-doped biochar has a deoxygenation effect, which reduces the content of oxygen-containing substances in bio-oil. For example, oxygen-containing intermediates undergo deoxygenation reactions in the process of providing hydrogen for the formation of phenolic substances. Therefore, there are almost no acidic compounds, and it contains fewer aldehydes and furans, which promotes the decarboxylation reaction in bio-oil and is conducive to the conversion of pyrolysis oil phase products of cellulose and hemicellulose into small molecules such as esters. Nitrogen-doped biochar can also promote the dehydration and condensation of ketones to form aromatics, and can also convert furfural into aromatics through multiple steps, increasing the aromatic hydrocarbon content. Therefore, nitrogen-doped biochar, as a catalyst, can improve the quality of bio-oil, reduce its acidity, improve its stability, and reduce problems associated with its subsequent use.

[0077] Application examples 2.1-2.6 were tested using liquid phase products, and the GC-MS test results are as follows: Figure 4 , Figure 5As shown, C

[11] indicates that no activator potassium salt was added. The specific surface area of ​​the biochar catalyst activated by potassium salt increases, which increases the residence time of volatiles, allowing for further dehydration and cyclization reactions of acids and oxygen-containing compounds in the volatiles, followed by decarbonylation and aromatization reactions. The large specific surface area makes it easier for oxygen-containing compounds and acid compounds to interact with the active sites, further decomposing them into small molecule gaseous products. The larger the specific surface area of ​​the activated biochar, the more developed the porosity, and the easier it is for small molecule volatiles to pass through the catalyst layer. The volatile substances are less likely to undergo condensation and aromatization, resulting in a reduction of aromatic substances. At the same time, the increase of phenolic substances is more obvious. Compared with coke, the catalytic effect of potassium salt is manifested in accelerating the accumulation and conversion of dehydrated sugars, as well as the demethylation reaction of guaiacol. Under the activation of KOH, it increased by about 22%, and the phenol content reached 70.88%. This process promotes the breaking of the -O-CH3 bond on methoxyphenols, and the reaction of heavy phenolic compounds with side chains with the active sites (oxygen- and nitrogen-containing functional groups) on activated biochar, leading to side chain breakage and the generation of more simple phenolic compounds, while simultaneously producing CH4. This conclusion is consistent with the increase in CH4 content in the gas. Phenyl and naphthyl substances form on the surface of biochar, which then react with water in the volatile matter to generate phenol and naphthol, resulting in an increase in phenolic substances and a decrease in aromatic hydrocarbons.

[0078] The activated nitrogen-doped biochar from application examples 2.1-2.6 was subjected to FTIR testing, and the test results are as follows: Figure 6 As shown. 435cm -1 There is a broad peak nearby, formed by the vibration of the -OH / -NH functional groups, at 1629 and 1047 cm⁻¹. -1 The nearby peaks are attributed to vibrations of C=O and COC, respectively, at 1396 cm⁻¹. -1 The nearby peak is caused by the out-of-plane bending vibration of CH, 1500 cm⁻¹ -1 The nearby peaks are mainly caused by CN vibrations. The activated catalysts have the same spectral peaks, but their transmittance intensities differ. Among them, the peaks of C=O, COC, and -OH / -NH of KOH-activated catalysts are stronger than those of other catalysts, indicating that their surface has abundant oxygen- and nitrogen-containing functional groups, and heteroatoms O and N can be fixed in the structure of activated carbon.

[0079] The activated nitrogen-doped biochar from Application Examples 2.1-2.6 were subjected to BET testing, and the results are shown in Table 1. With the addition of potassium salt activators, the specific surface area increases, providing more surface reaction sites and channels. The degree of influence of activators with different properties on the specific surface area varies. KOH activator showed the most significant increase. The addition of KCl can generate additional pores and increase the specific surface area, but this effect is limited.

[0080] Table 1 Specific surface area of ​​nitrogen-doped biochar under the action of different potassium salts

[0081]

[0082] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An application of modified nitrogen-doped biochar, characterized in that, The process includes the following steps: pyrolyzing activated modified nitrogen-doped biochar with lignin-based biomass pine wood, absorbing the resulting pyrolysis oil with dichloromethane, and then detecting it by GC-MS. The preparation method of activated modified nitrogen-doped biochar includes the following steps: drying high-nitrogen biomass and lignin-based biomass, mixing and grinding them, placing them in a quartz cup at the top of a reactor, continuously introducing inert gas, heating, sending the mixed sample to the center of the reactor for pyrolysis, and collecting liquid and gaseous products at the same time. After pyrolysis, cooling is performed to obtain nitrogen-doped biochar. An activator is mixed with the nitrogen-doped biochar, activated, acid-washed, and washed with deionized water until the waste liquid pH=7, to obtain activated modified nitrogen-doped biochar. The biomass with high nitrogen content is spirulina, and the lignin-rich biomass is soybean straw. The mass ratio of spirulina to soybean straw is 3:

1. The mass ratio of activator to nitrogen-doped biochar is 1:1; The activator is KOH, K2CO3, KHCO3, KCl, KMnO4 or KH2PO4. 4。 2. The application as described in claim 1, characterized in that, The drying temperature is 100-110℃, the time is 24 hours, and the particles are ground until the particle size is less than 0.25mm.

3. The application as described in claim 1, characterized in that, Argon was used as the inert gas at a flow rate of 50 mL / min. The temperature was raised to 600℃ for pyrolysis, and the pyrolysis time was 10-60 min.

4. The application as described in claim 1, characterized in that, The condensable fraction generated by pyrolysis is cooled in an ice-water bath to obtain bio-oil. The non-condensable gases are first absorbed by nitrogen-containing gases HCN and NH3 in NaOH and H2SO4 solutions, respectively. The other pyrolysis gases are dried and collected in a gas bag.

5. The application as described in claim 1, characterized in that, The activation temperature was 800℃, and the activation time was 1 h. The solution was then acid-washed with 1 mol / L HCl for 12 h.

6. The application as described in claim 1, characterized in that, The mass ratio of activated modified nitrogen-doped biochar to lignin-based biomass pine was 1:2.

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