A nitrogen-doped biomass charcoal / transition metal catalyst, and a preparation method and application thereof

Abstract

This invention discloses a nitrogen-doped biochar / transition metal catalyst, its preparation method, and its application, belonging to the field of catalyst technology. The invention involves calcining waste biomass in an inert atmosphere to obtain biochar; calcining the biochar, melamine, and potassium hydroxide in a CO2 atmosphere to obtain nitrogen-doped biochar; then impregnating the nitrogen-doped biochar in a transition metal salt solution, followed by hydrothermal treatment; finally, reducing the mixture obtained through hydrothermal treatment in a hydrogen atmosphere to obtain the nitrogen-doped carbon / transition metal catalyst. The nitrogen-doped carbon / transition metal catalyst provided by this invention exhibits high selectivity and high conversion rate in the catalytic pyrolysis of coal tar to produce aromatics, with mild reaction conditions, high selectivity for light aromatics, safe operation, and a simple process.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a nitrogen-doped biochar / transition metal catalyst, its preparation method, and its application. Background Technology

[0002] With the rapid development of my country's economy, energy consumption has become an increasingly serious problem. Coal, due to its abundant reserves and wide distribution, is considered one of my country's most important fossil energy sources. However, the pyrolysis or gasification of coal produces a large amount of coal tar, a valuable resource, and the need for large-scale utilization is becoming increasingly urgent as production capacity increases. However, coal tar's poor chemical and thermal stability, high viscosity, corrosiveness, and density severely limit its applications. Therefore, it is necessary to convert coal tar into chemicals or hydrocarbon fuels. Light aromatics, especially benzene, toluene, xylene, trimethylbenzene, and naphthalene, are widely used as raw materials for important chemical products such as synthetic rubber, resins, fibers, pharmaceuticals, dyes, and gasoline additives. However, the C-C bonds in coal tar are very stable, meaning that its conversion usually requires overcoming thermodynamic and kinetic barriers under harsh conditions. Hydrocracking can refine coal tar to obtain high-content aromatics. However, existing research mainly uses hydrogenation and pressurization and external catalysts to convert coal tar into aromatics. The process is complex and consumes a large amount of hydrogen and solvents as co-reactants.

[0003] CN107537477A discloses a Pt / TiO2 catalyst. This catalyst has a complex preparation process, uses the noble metal Pt as the active component and TiO2 containing rare metals as the support, resulting in high preparation costs and making it unsuitable for large-scale applications. CN105536860A discloses a Ni2P / Zr-MCM41 catalyst and its preparation method. This catalyst has a complex preparation process, demanding conditions, releases highly toxic phosphine during preparation, and has a long preparation time; the preparation method requires further improvement.

[0004] In recent years, catalytic pyrolysis technology has been recognized as an effective strategy for activating C-C bonds due to its high tar conversion rate and low cost. However, most catalysts only exhibit excellent single-function catalytic activity and cannot simultaneously achieve the conversion of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons in coal tar to light aromatic hydrocarbons. Ni-based catalysts have become the most promising catalysts for industrial applications due to their low price and catalytic activity similar to that of noble metals. However, Ni-based catalysts suffer from problems such as easy carbon deposition and durability, and are easily oxidized. In recent years, although nanocatalysts based on d-block transition metals (especially Fe, Co, and Ni) anchored on nitrogen-doped carbon matrices have attracted much attention, the high surface energy of Ni metal easily induces catalyst aggregation, making the precise preparation of highly active Ni-based catalytic systems still a significant challenge. In addition, due to the complexity of the composition of real coal tar, current catalysts still face problems such as low aromatic hydrocarbon yield and low selectivity for light aromatic hydrocarbons. To address these issues, this invention uses waste biomass as a template and carbon source to prepare a nitrogen-doped carbon / transition metal catalyst for the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a nitrogen-doped biochar / transition metal catalyst, its preparation method, and its application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a nitrogen-doped biochar / transition metal catalyst includes the following steps:

[0008] (1) Waste biomass is calcined under an inert gas to obtain biochar, then a nitrogen source and a strong alkali are added and mixed evenly and calcined under CO2 gas, and finally washed and dried to obtain nitrogen-doped biochar.

[0009] (2) Nitrogen-doped biochar was immersed in a transition metal salt solution and stirred and sonicated. Then, hydrothermal reaction, drying and calcination under hydrogen were carried out in sequence to obtain nitrogen-doped biochar / transition metal catalyst.

[0010] In a preferred embodiment of the present invention, the waste biomass is one of wheat straw, tobacco stalks, pine needles, and corn stalks.

[0011] As a preferred embodiment of the present invention, in step (1), the waste biomass is calcined under inert gas at a temperature of 550-900℃ for 1-2 hours, a heating rate of 10-40℃ / min, and an inert gas flow rate of 20-150ml / min.

[0012] The inert gas is one of nitrogen, argon, or helium.

[0013] As a preferred embodiment of the present invention, in step (1), the calcination temperature under CO2 gas is 600-900℃, the time is 1-3h, the concentration of CO2 is 5%-100%, and the flow rate is 20-150mL / min.

[0014] Compared to inert gases, the calcination in CO2 in step (2) of this invention is beneficial to the activation of biochar. The prepared biochar has more developed pore size, larger specific surface area, and richer defect structure. Most importantly, it is beneficial to the loading and dispersion of transition metal active components, so that the catalyst has higher activity.

[0015] In a preferred embodiment of the present invention, the nitrogen source is at least one of melamine, urea, and polyethylene glycol; the strong alkali is one of sodium hydroxide, potassium hydroxide, and calcium hydroxide; and the mass ratio of the biochar, nitrogen source, and strong alkali is 2-5:0.2-0.8:1-5.

[0016] This invention prepares nitrogen-doped biochar by a two-step calcination method using waste wheat straw, melamine, and potassium hydroxide. This overcomes the disadvantage that nitrogen-doped biochar prepared by one-step calcination of waste wheat straw, melamine, and potassium hydroxide is not conducive to the loading and dispersion of the transition metal active phase, resulting in lower catalyst activity.

[0017] In a preferred embodiment of the present invention, the transition metal salt is at least one of nickel nitrate, cobalt nitrate, iron nitrate, and copper nitrate, and the mass of the transition metal salt is 1-10% of the mass of nitrogen-doped biochar.

[0018] As a preferred embodiment of the present invention, in step (2), the stirring time is 10-30 min, the ultrasonic time is 20-40 min, the hydrothermal reaction temperature is 150-300℃, and the time is 12-24 h.

[0019] This invention utilizes a hydrothermal reaction, which makes the prepared catalyst more conducive to the adsorption and activation of coal tar components, and also improves the catalyst's activity and stability. Without the hydrothermal reaction, the yield of aromatics and the selectivity of light aromatics in the prepared material are significantly reduced, and the performance stability of the material is also significantly reduced.

[0020] As a preferred embodiment of the present invention, in step (2), the calcination temperature under hydrogen is 700-900℃, the time is 30-120min, the concentration of hydrogen is 3%-100%, and the flow rate is 50-100mL / min.

[0021] The present invention also claims protection for nitrogen-doped carbon / transition metal catalysts prepared by the method described above.

[0022] This invention also claims protection for the application of the nitrogen-doped carbon / transition metal catalyst in the catalytic pyrolysis of coal tar to produce aromatics.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: the preparation method of the nitrogen-doped biochar / transition metal catalyst of the present invention is simple and suitable for large-scale production. The nitrogen-doped carbon / transition metal catalyst prepared has a large specific surface area. Nitrogen doping and transition metal improve the defect structure of the catalyst, promote electron transfer, optimize the charge distribution of the catalyst, and the transition metal particles are small in size and uniformly distributed. It can realize the catalytic pyrolysis of coal tar to produce light aromatics under hydrogen-free and solvent-free conditions, demonstrating high tar conversion rate and high light aromatic selectivity. Attached Figure Description

[0024] Figure 1 This is a component distribution diagram of coal tar.

[0025] Figure 2 This is a flowchart illustrating the preparation process of nitrogen-doped biochar / transition metal catalysts.

[0026] Figure 3 Figure 1 shows TEM images of the catalysts prepared in Example 2 and Comparative Example 3. Figure 2(a) is a TEM image of the biochar / transition metal catalyst prepared in Comparative Example 3, Figure 2(b) is a TEM image of the nitrogen-doped biochar / transition metal catalyst prepared in Example 2, and Figure 2(c) is an HRTEM image of the nitrogen-doped biochar / transition metal catalyst prepared in Example 2.

[0027] Figure 4 The XRD patterns are of the catalysts prepared in Example 2 and Comparative Examples 1-3.

[0028] Figure 5 The above are Raman diagrams of the catalysts prepared in Example 2 and Comparative Examples 1-3. Detailed Implementation

[0029] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] A method for preparing a nitrogen-doped biochar / transition metal catalyst includes the following steps:

[0032] (1) The waste wheat straw was crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 12 hours, dried in a 105℃ forced-air drying oven for 12 hours, and calcined at 750℃ for 1 hour under nitrogen gas with a nitrogen flow rate of 50 mL / min (heating rate: 10℃ / min) to obtain biochar.

[0033] (2) Add 0.2g of melamine and 4.0g of potassium hydroxide to 2g of biochar and grind them evenly. Then calcine them under 10% CO2 gas for 1h (heating rate: 10℃ / min) and CO2 flow rate of 50mL / min. After cooling, filter and wash several times with deionized water and dry in a 105℃ forced-air drying oven for 12h to obtain nitrogen-doped biochar.

[0034] (3) Add nitrogen-doped biochar to a pre-prepared nickel nitrate solution (nickel is 2% by mass relative to nitrogen-doped biochar) and stir for 15 min. Then, ultrasonically impregnate the mixture for 15 min. Transfer the impregnated mixture to an autoclave and heat treat it at 250°C for 12 h. After cooling, dry the mixture in a 105°C forced-air drying oven for 24 h.

[0035] (4) The solid obtained in step (3) is calcined and reduced in a tube furnace (heating rate: 10℃ / min) in a 15% hydrogen atmosphere (hydrogen flow rate: 50mL / min) for 1h to obtain nitrogen-doped biochar / transition metal catalyst.

[0036] Example 2

[0037] The only difference between this embodiment and the method for preparing a nitrogen-doped biochar / transition metal catalyst in embodiment 1 is that in step (3), nitrogen-doped biochar is added to a pre-prepared nickel nitrate solution, and the mass fraction of nickel relative to nitrogen-doped biochar is 5%.

[0038] according to Figure 3 It can be seen that, compared with the biochar / nickel catalyst of Comparative Example 3, the nitrogen-doped carbon-nickel catalyst prepared in Example 2 has better nickel dispersion, and the nickel exists in the form of elemental nickel. According to Figure 4 It is known that zero-valent nickel metal exists in nitrogen-doped carbon / nickel catalysts. The intensity of the nickel diffraction peak in nitrogen-doped carbon-nickel catalysts is lower than that in biomass carbon-nickel catalysts, indicating that nitrogen doping improves the defects of the catalyst, which is beneficial to the formation of nickel nanoparticles. Figure 5 Raman's work shows that nitrogen-doped carbon-nickel catalysts have I D / I G The strength ratio of (0.99) is higher than that of biomass carbon nickel catalyst (0.95), indicating that it has more defects, which is beneficial to increasing the active sites in the tar conversion process.

[0039] Example 3

[0040] The only difference between this embodiment and the method for preparing a nitrogen-doped biochar / transition metal catalyst in embodiment 1 is that in step (3), nitrogen-doped biochar is added to a pre-prepared ferric nitrate solution, and the mass fraction of iron relative to nitrogen-doped biochar is 5%.

[0041] Example 4

[0042] The only difference between this embodiment and the method for preparing a nitrogen-doped biochar / transition metal catalyst in Embodiment 1 is that in step (3), nitrogen-doped biochar is added to a pre-prepared cobalt nitrate solution, and the mass fraction of cobalt relative to nitrogen-doped biochar is 5%.

[0043] Example 5

[0044] The only difference between this embodiment and the method for preparing a nitrogen-doped biochar / transition metal catalyst in embodiment 1 is that in step (3), nitrogen-doped biochar is added to a pre-prepared copper nitrate solution, and the mass fraction of copper relative to nitrogen-doped biochar is 5%.

[0045] Example 6

[0046] A method for preparing a nitrogen-doped biochar / transition metal catalyst includes the following steps:

[0047] (1) The tobacco stalks were crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 6 hours, dried in an 80℃ forced-air drying oven for 24 hours, and calcined at 900℃ for 2 hours under nitrogen gas with a nitrogen flow rate of 150 mL / min (heating rate: 40℃ / min) to obtain biochar.

[0048] (2) Add 0.8g of polyethylene glycol and 1.0g of sodium hydroxide to 5g of biochar and grind them evenly. Then calcine them under 5% CO2 gas for 3h (heating rate: 40℃ / min) and CO2 flow rate of 20mL / min. After cooling, filter and wash several times with deionized water and dry in an 80℃ forced-air drying oven for 24h to obtain nitrogen-doped biochar.

[0049] (3) Add nitrogen-doped biochar to a pre-prepared nickel nitrate solution (nickel is 10% of the mass of nitrogen-doped biochar) and stir for 30 min. Then, ultrasonically impregnate the mixture for 20 min. Transfer the impregnated mixture to an autoclave and heat treat it at 150°C for 24 h. After cooling, dry the mixture in an 80°C forced-air drying oven for 12 h.

[0050] (4) The solid obtained in step (3) is calcined and reduced in a tube furnace (heating rate: 40℃ / min) in a 3% hydrogen atmosphere (hydrogen flow rate: 100mL / min) for 1h to obtain nitrogen-doped biochar / transition metal catalyst.

[0051] Example 7

[0052] A method for preparing a nitrogen-doped biochar / transition metal catalyst includes the following steps:

[0053] (1) Pine needles were crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 6 hours, dried in a 90℃ forced-air drying oven for 20 hours, and calcined at 550℃ for 1.5 hours under nitrogen gas with a nitrogen flow rate of 20 mL / min (heating rate: 20℃ / min) to obtain biochar.

[0054] (2) Add 0.5g of urea and 5.0g of calcium hydroxide to 3g of biochar and grind them evenly. Then calcine them under 100% CO2 gas for 3h (heating rate: 20℃ / min) and CO2 flow rate of 150mL / min. After cooling, filter and wash several times with deionized water and dry in a 90℃ forced-air drying oven for 18h to obtain nitrogen-doped biochar.

[0055] (3) Add nitrogen-doped biochar to a pre-prepared nickel nitrate solution (nickel is 6% by mass relative to nitrogen-doped biochar) and stir for 10 min. Then, ultrasonically impregnate the mixture for 40 min. Transfer the impregnated mixture to an autoclave and heat treat it at 300℃ for 12 h. After cooling, dry the mixture in a 90℃ forced-air drying oven for 18 h.

[0056] (4) The solid obtained in step (3) is calcined and reduced in a tube furnace (heating rate: 20℃ / min) in a 100% hydrogen atmosphere (hydrogen flow rate: 50mL / min) for 1h to obtain nitrogen-doped biochar / transition metal catalyst.

[0057] Comparative Example 1

[0058] A method for preparing nitrogen-doped biochar includes the following steps:

[0059] (1) The waste wheat straw was crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 12 hours, dried in a 105℃ forced-air drying oven for 12 hours, and calcined at 750℃ for 1 hour under nitrogen gas with a nitrogen flow rate of 50 mL / min (heating rate: 10℃ / min) to obtain biochar.

[0060] (2) Add 0.2g of melamine and 4.0g of potassium hydroxide to 2g of biochar and grind them evenly. Then calcine them under 10% CO2 gas for 1h (heating rate: 10℃ / min) and CO2 flow rate of 50mL / min. After cooling, filter and wash several times with deionized water and dry in a 105℃ forced-air drying oven for 12h to obtain nitrogen-doped biochar.

[0061] Comparative Example 2

[0062] A method for preparing biochar includes the following steps:

[0063] Waste wheat straw was crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 12 hours, dried in a 105℃ forced-air drying oven for 12 hours, and calcined at 750℃ for 1 hour under nitrogen gas with a nitrogen flow rate of 50 mL / min (heating rate: 10℃ / min) to obtain biochar.

[0064] Comparative Example 3

[0065] A method for preparing a biochar / transition metal catalyst includes the following steps:

[0066] (1) The waste wheat straw was crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 12 hours, dried in a 105℃ forced-air drying oven for 12 hours, and calcined at 750℃ for 1 hour under nitrogen gas with a nitrogen flow rate of 50 mL / min (heating rate: 10℃ / min) to obtain biochar.

[0067] (2) Add 2g of biochar to a pre-prepared nickel nitrate solution (the mass fraction of nickel relative to nitrogen-doped biochar is 5%) and stir for 15min. Then, ultrasonically impregnate the mixture for 15min. Transfer the impregnated mixture to an autoclave and heat treat it at 250℃ for 12h. After cooling, dry the mixture in a 105℃ forced-air drying oven for 24h.

[0068] (3) The solid obtained in step (3) is calcined and reduced in a tube furnace (heating rate: 10℃ / min) in a 15% hydrogen atmosphere (hydrogen flow rate: 50mL / min) for 1h to obtain biochar / transition metal catalyst.

[0069] Comparative Example 4

[0070] A method for preparing a nitrogen-doped biochar / transition metal catalyst includes the following steps:

[0071] (1) The waste wheat straw was crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 12 hours, dried in a 105℃ forced-air drying oven for 12 hours, and calcined at 750℃ for 1 hour under nitrogen gas with a nitrogen flow rate of 50 mL / min (heating rate: 10℃ / min) to obtain biochar.

[0072] (2) Add 0.2g of melamine and 4.0g of potassium hydroxide to 2g of biochar and grind them evenly. Then calcine them under 10% CO2 gas for 1h (heating rate: 10℃ / min) and CO2 flow rate of 50mL / min. After cooling, filter and wash several times with deionized water and dry in a 105℃ forced-air drying oven for 12h to obtain nitrogen-doped biochar.

[0073] (3) Add nitrogen-doped biochar to a pre-prepared nickel nitrate solution (nickel is 5% by mass relative to nitrogen-doped biochar) and stir for 15 min. Then, ultrasonically impregnate the mixture for 12 h and dry it in a 105℃ forced-air drying oven for 24 h.

[0074] (4) The solid obtained in step (3) is calcined and reduced in a tube furnace (heating rate: 10℃ / min) in a 15% hydrogen atmosphere (hydrogen flow rate: 50mL / min) for 1h to obtain nitrogen-doped biochar / transition metal catalyst.

[0075] Comparative Example 5

[0076] A method for preparing a nitrogen-doped biochar / transition metal catalyst includes the following steps:

[0077] (1) The waste wheat straw was crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 12 hours, dried in a 105℃ forced-air drying oven for 12 hours, and calcined at 750℃ for 1 hour under nitrogen gas with a nitrogen flow rate of 50 mL / min (heating rate: 10℃ / min) to obtain biochar.

[0078] (2) Add 0.2g of melamine and 4.0g of potassium hydroxide to 2g of biochar and grind them evenly. Then calcine them under nitrogen gas for 1h (heating rate: 10℃ / min) with a nitrogen flow rate of 50mL / min. After cooling, filter and wash several times with deionized water and dry in a 105℃ forced-air drying oven for 12h to obtain nitrogen-doped biochar.

[0079] (3) Add nitrogen-doped biochar to a pre-prepared nickel nitrate solution (nickel is 5% by mass relative to nitrogen-doped biochar) and stir for 15 min. Then, ultrasonically impregnate the mixture for 15 min. Transfer the impregnated mixture to an autoclave and heat treat it at 250°C for 12 h. After cooling, dry the mixture in a 105°C forced-air drying oven for 24 h.

[0080] (4) The solid obtained in step (3) is calcined and reduced in a tube furnace (heating rate: 10℃ / min) in a 15% hydrogen atmosphere (hydrogen flow rate: 50mL / min) for 1h to obtain nitrogen-doped biochar / transition metal catalyst.

[0081] Comparative Example 6

[0082] A method for preparing a nitrogen-doped biochar / transition metal catalyst includes the following steps:

[0083] (1) The waste wheat straw was crushed and sieved to 60-80 mesh, added to deionized water and stirred and washed for 12 hours, dried in a 105℃ forced-air drying oven for 12 hours, added 0.2g melamine and 4.0g potassium hydroxide and ground evenly, and then calcined at 750℃ for 2 hours under nitrogen gas with a nitrogen flow rate of 50mL / min (heating rate: 10℃ / min) to obtain nitrogen-doped biochar.

[0084] (2) Add nitrogen-doped biochar to a pre-prepared nickel nitrate solution (nickel is 5% by mass relative to nitrogen-doped biochar) and stir for 15 min. Then, ultrasonically impregnate the mixture for 15 min. Transfer the impregnated mixture to an autoclave and heat treat it at 250°C for 12 h. After cooling, dry the mixture in a 105°C forced-air drying oven for 24 h.

[0085] (3) The solid obtained in step (2) was calcined and reduced in a tube furnace (heating rate: 10℃ / min) in a 15% hydrogen atmosphere (hydrogen flow rate: 50mL / min) for 1h to obtain nitrogen-doped biochar / transition metal catalyst.

[0086] Example of effect

[0087] The materials prepared in Examples 1-7 and Comparative Examples 1-6 were subjected to catalytic pyrolysis of coal tar to prepare aromatics in a rapidly heated fixed-bed reactor. Specifically, this included: adding 1.0 mg of coal tar (the composition of coal tar is shown in the figure below) to the reactor. Figure 1 The catalyst was added to a quartz tube and a small amount of quartz wool was filled on both sides of the coal tar. 1.5 mg of catalyst was placed on each side of the coal tar. The pyrolysis temperature was set to 500℃ and the time was 1 min. After pyrolysis, the components of the coal tar were catalytically pyrolyzed through the catalyst bed. The pyrolysis products were analyzed by gas chromatography-mass spectrometry. The relative yield of aromatics and the selectivity of light aromatics are shown in Table 1.

[0088] The relative yield R of organic compounds in the pyrolysis products yield Determined by a semi-quantitative method using the percentage of chromatographic peak area:

[0089]

[0090] Where P is the peak area of ​​a specific type of organic compound, P total It represents the total peak area of ​​all organic compounds.

[0091] Light aromatic hydrocarbons (C6-C4) among aromatic products 10 The selective determination is as follows:

[0092]

[0093] Where S L It is a light aromatic hydrocarbon (C6-C) 10The selectivity of R L It is a light aromatic hydrocarbon (C6-C) 10 The relative yield of R) a It represents the relative yield of aromatics.

[0094] Table 1

[0095] Aromatics yield (%) Selectivity of light aromatics (%) Example 1 80.30 91.03 Example 2 83.14 95.06 Example 3 80.12 94.65 Example 4 79.19 95.34 Example 5 81.76 94.83 Example 6 80.82 91.65 Example 7 79.27 89.01 Comparative Example 1 67.27 79.89 Comparative Example 2 47.39 44.04 Comparative Example 3 41.83 41.17 Catalyst-free 42.27 29.62

[0096] Depend on Figure 1 It can be seen that, compared with Comparative Examples 1-3, the catalysts prepared in Examples 1-7 have higher aromatic hydrocarbon yields and selectivity for light aromatic hydrocarbons. In the nitrogen-doped biochar / transition metal catalyst prepared in this invention, nitrogen doping improves the defect structure of the catalyst, promotes electron transfer, optimizes the charge distribution of the catalyst, and results in smaller and more uniformly dispersed transition metal particles, thus exhibiting excellent catalytic activity. Furthermore, the reaction conditions are mild, the selectivity for light aromatic hydrocarbons is high, the process is simple, and it is suitable for large-scale applications.

[0097] In the direct pyrolysis of tar without a catalyst (non-catalytic pyrolysis), the yield of aromatics was only 42.27%, with light aromatics (C6-C4) being the most abundant. 10 The selectivity rate was 29.62%.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. Use of a nitrogen-doped biochar / transition metal catalyst in the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons, characterized in that, The preparation method of the nitrogen-doped biomass charcoal / transition metal catalyst specifically comprises the following steps: (1) calcining the waste biomass under inert gas to obtain biomass charcoal, then adding a nitrogen source and a strong base, mixing uniformly, and calcining under CO2 gas, and finally washing and drying to obtain nitrogen-doped biomass charcoal; (2) immersing the nitrogen-doped biomass charcoal in a transition metal salt solution, stirring and ultrasonicating, then sequentially performing hydrothermal reaction, drying, and calcining under hydrogen to obtain the nitrogen-doped carbon / transition metal catalyst; The nitrogen source is at least one of melamine, urea, and polyethylene diamine; the strong base is one of sodium hydroxide, potassium hydroxide, and calcium hydroxide; and the mass ratio of the biomass charcoal, the nitrogen source, and the strong base is 2-5:0.2-0.8:1-5.

2. Use of the nitrogen-doped biomass char / transition metal catalyst according to claim 1 for the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons, characterized in that, The waste biomass is one of wheat straw, tobacco stems, pine needles, and corn stalks.

3. Use of the nitrogen-doped biomass char / transition metal catalyst according to claim 1 for the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons, characterized in that, In step (1), the waste biomass is calcined under inert gas at a temperature of 550-900℃ for 1-2h, with a temperature rising rate of 10-40℃ / min, and the inert gas has a flow rate of 20-150mL / min.

4. Use of the nitrogen-doped biomass char / transition metal catalyst according to claim 1 for the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons, characterized in that, In step (1), the calcining under CO2 gas is performed at a temperature of 600-900℃ for 1-3h, with a CO2 concentration of 5%-100% and a flow rate of 20-150mL / min.

5. Use of the nitrogen-doped biomass char / transition metal catalyst according to claim 1 for the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons, characterized in that, The transition metal salt is at least one of nickel nitrate, cobalt nitrate, iron nitrate, and copper nitrate, and the mass of the transition metal salt is 1-10% of the mass of the nitrogen-doped biomass charcoal.

6. Use of the nitrogen-doped biomass char / transition metal catalyst according to claim 1 for the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons, characterized in that, In step (2), the stirring time is 10-30min, and the ultrasonicating time is 20-40min; the hydrothermal reaction is performed at a temperature of 150-300℃ for 12-24h.

7. Use of the nitrogen-doped biomass char / transition metal catalyst according to claim 1 for the catalytic pyrolysis of coal tar to produce aromatic hydrocarbons, characterized in that, In step (2), the calcining under hydrogen is performed at a temperature of 700-900℃ for 30-120min, with a hydrogen concentration of 3%-100% and a flow rate of 50-100mL / min.

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