A biochar-based alkali metal catalyst, and a preparation method and application thereof

Abstract

The application discloses a kind of biochar base alkali metal catalyst and its preparation method and application, belong to agricultural waste processing technical field.The biochar base alkali metal catalyst of the application includes 20-30 parts modified biochar and 18-25 parts alkali metal compound by weight fraction, the nitrogen-rich solution produced after hydrothermal reaction of poultry manure is used as modifier, and the modified biochar is obtained by modifying straw treatment.The preparation method of the biochar base alkali metal catalyst is also disclosed, and the application of the biochar base alkali metal catalyst in the hydrothermal conversion of crop residue.The biochar base alkali metal catalyst prepared by the method of the application can effectively improve the hydrothermal conversion efficiency and reaction rate of agricultural waste, has excellent physical stability and recyclability, and realizes the resource utilization of agricultural waste.

Description

Technical Field

[0001] This invention relates to the field of agricultural waste treatment technology, and more specifically, to a biochar-based alkali metal catalyst, its preparation method, and its application. Background Technology

[0002] Under the dual pressures of the global energy crisis and environmental pollution, the efficient resource utilization of agricultural waste has become a crucial issue for sustainable development. Agricultural waste is produced in massive quantities annually, and traditional treatment methods such as open burning and indiscriminate dumping not only waste resources but also cause environmental problems such as air pollution, eutrophication of water bodies, and the emission of greenhouse gases. Hydrothermal conversion technology, as a key pathway for the thermochemical conversion of biomass, uses high-temperature and high-pressure environments to induce hydrolysis, dehydration, decarboxylation, and aromatization reactions in biomass macromolecules, converting them into high-value-added hydrothermal char, bio-oil, and gaseous products. However, the complex composition of agricultural waste, with its interwoven structure of cellulose, hemicellulose, and lignin, limits the efficiency of hydrothermal conversion, and the products are prone to retaining harmful substances such as heavy metals and persistent organic pollutants. To overcome this bottleneck, the development of biochar-based alkali metal catalysts has become a research hotspot. This type of catalyst uses biochar as a support and loads alkali metals or transition metals. By utilizing the synergistic effect of the abundant oxygen-containing functional groups on its surface and the active sites of the metals, it can significantly improve the depolymerization efficiency of organic matter in hydrothermal reactions, promote carbon skeleton rearrangement and aromatization processes, and simultaneously achieve the fixation of heavy metals and the degradation of harmful substances, providing technical support for the high-value utilization of agricultural waste.

[0003] Patent application CN110801840A discloses a Cu-Ni bimetallic catalyst supported on biochar and its application. The Cu-Ni bimetallic catalyst is prepared by the following steps: (1) Under stirring conditions, α-cellulose is mixed with ionic liquid and heated, and then concentrated H2SO4 is added until the mixture is heated. After reacting for 10-20 hours, the mixture is filtered, washed and dried to obtain a biochar precursor; (2) The biochar precursor is carbonized under a nitrogen atmosphere, and after washing and drying, biochar is obtained; (3) Copper salt and nickel salt are dissolved in water and mixed evenly, and biochar is added and stirred for impregnation. The impregnated sample is dried under vacuum and then calcined under a nitrogen atmosphere. Finally, it is reduced in a hydrogen atmosphere to obtain a bimetallic Cu-Ni catalyst supported on biochar. The Cu-Ni bimetallic catalyst involved in this patent application uses cellulose derived from biomass as a raw material, which is inexpensive and widely available. However, this catalyst is not suitable for application in the hydrothermal conversion process of agricultural waste. This is because agricultural waste has a complex composition, containing a large amount of cellulose, hemicellulose, lignin, and inorganic impurities, which easily form a high-viscosity system under hydrothermal conditions. Furthermore, the catalyst preparation process did not perform structural optimization for such a complex matrix, and its active sites are easily covered or poisoned by impurities. Summary of the Invention

[0004] The purpose of this invention is to provide a biochar-based alkali metal catalyst, its preparation method, and its application, to solve the technical problems of low hydrothermal conversion efficiency and slow reaction rate of agricultural waste (mainly crop residues, such as straw, rice husks, and fruit shells) in the prior art.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a biochar-based alkali metal catalyst, comprising, by weight, 20-30 parts modified biochar and 18-25 parts alkali metal compound;

[0007] The method for preparing the modified biochar includes the following steps:

[0008] S1. The straw and livestock manure are dried separately, ground, and then dried again to obtain straw powder and livestock manure powder.

[0009] S2. After mixing poultry and livestock manure powder with distilled water, a hydrothermal reaction is carried out to obtain solid carbon and a mixture.

[0010] S3. Mix the mixture obtained in step S2 with the straw powder in step S1 and stir it. Then carry out a second hydrothermal reaction (in a hydrothermal reactor). After drying, carbonize it (in a tube furnace) to obtain the final product.

[0011] Using the nitrogen-rich solution (a mixture rich in nutrients and catalyst) produced by the hydrothermal reaction of poultry and livestock manure in step S2 as a modifier, the straw is subjected to secondary hydrothermal and carbonization treatment in step S3, so that the pore structure and surface chemical properties of the obtained modified biochar are optimized.

[0012] As some specific embodiments of the present invention, in step S1, the poultry and livestock manure is selected from one or more of chicken manure, cow manure and pig manure;

[0013] And / or, the straw is selected from one or more of corn straw, rice straw, wheat straw and soybean straw;

[0014] And / or, the particle size of the straw powder and livestock manure powder is 60-120 μm;

[0015] And / or, the drying temperature is 80-85℃ and the time is 12-20h;

[0016] And / or, the continued drying temperature is 80-85℃, and the time is 20-24h.

[0017] As some specific embodiments of the present invention, in step S2, the ratio of the amount of poultry and livestock manure powder to distilled water is 1-2g:5-10mL;

[0018] And / or, the hydrothermal reaction is carried out at a temperature of 180-200°C for a time of 1-2 hours.

[0019] As some specific embodiments of the present invention, in step S3, the ratio of the mixture to the straw powder is 4-10 mL: 1-2.2 g;

[0020] And / or, the temperature of the secondary hydrothermal reaction is 200-230℃, and the holding time is 1-2 h;

[0021] And / or, the carbonization treatment temperature is 500-700℃.

[0022] As some specific embodiments of the present invention, the alkali metal compound is selected from one or more of potassium carbonate, potassium nitrate, potassium hydroxide, and potassium acetate.

[0023] In a second aspect, the present invention provides a method for preparing a biochar-based alkali metal catalyst as described in any of the preceding claims, comprising the following steps:

[0024] A1. Modified biochar is ground and sieved to obtain modified biochar powder. Alkali metal compound is dissolved in deionized water to obtain alkali metal compound solution.

[0025] A2. The alkali metal compound solution was added dropwise to the modified biochar powder, stirred and mixed, dried and ground, calcined under a nitrogen atmosphere, and cooled to obtain the biochar-based alkali metal catalyst.

[0026] In the above process, the alkali metal active components are loaded onto the modified biochar support by solution impregnation, ultimately forming a biochar-based alkali metal catalyst with highly dispersed active sites.

[0027] As some specific embodiments of the present invention, in step A1, the particle size of the sieved material is 80-100 mesh.

[0028] As some specific embodiments of the present invention, in step A1, the concentration of the alkali metal compound solution is 0.5-2 mol / L, preferably 1 mol / L.

[0029] As some specific embodiments of the present invention, in step A2, an alkali metal compound solution is added dropwise to the modified biochar powder to wet it, forming a uniform mud-like substance without excess free liquid.

[0030] As some specific embodiments of the present invention, in step A2, the drying temperature is 105-120°C and the time is 6-12 hours;

[0031] And / or, the calcination temperature is 400-600℃, the time is 1-2h, and the heating rate is 3-5℃ / min.

[0032] Thirdly, the present invention provides the application of the biochar alkali metal-based catalyst as described in any of the preceding claims in the hydrothermal conversion of crop residues, comprising the following steps:

[0033] D1. After crushing, drying and sieving the crop residues, add them to a container containing ethanol and biochar-based alkali metal catalyst, mix evenly to obtain a slurry.

[0034] D2. Heat the slurry and stir it to react. After the reaction is complete, cool it and separate the products.

[0035] As some specific embodiments of the present invention, in step D1, the crop residue is selected from at least one of straw, rice husk, and fruit shell.

[0036] Preferably, the crop residues include straw, rice husks, and fruit shells, and the ratio of straw, rice husks, fruit shells to ethanol and biochar-based alkali metal catalyst is 10-14 g:9-15 g:12-17 g:2-6 mL:2.8-3.5 g.

[0037] As some specific embodiments of the present invention, in step D2, the heating rate is 5-10℃ / min;

[0038] And / or, the reaction temperature is 200-400 °C, and the stirring rate is 200-500 rpm.

[0039] In step D2, the slurry is added to the reactor, sealed, heated and stirred to carry out the reaction.

[0040] In step D2, during the product separation process, the gaseous product is separated into condensable and non-condensable gases by a condenser. The non-condensable gas is treated with desulfurization and decarbonization and then used as fuel or chemical raw material. The condensable gas is condensed and converted into liquid, which is then incorporated into the liquid product. The liquid product is centrifuged or filtered to remove solid residues and then upgraded by fractionation, extraction or catalytic hydrogenation to prepare biofuels or fine chemicals. The solid product is washed and dried and then used as a soil conditioner, adsorbent or re-carbonized to prepare activated carbon. The unreacted biochar-based alkali metal catalyst is regenerated by acid washing, and the alkali metal is recovered and recycled.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. This invention first prepares modified biochar, and then uses the modified biochar as a carrier to prepare a biochar-based alkali metal catalyst. When applied to the hydrothermal conversion of agricultural waste, it can realize the resource utilization of waste and simultaneously obtain biofuel bio-oil. Moreover, the renewability and recycling of this catalyst significantly reduces process costs and environmental risks, forming a comprehensive advantage of high-efficiency catalysis and product diversification.

[0043] 2. This invention applies the prepared modified biochar to the preparation process of biochar-based alkali metal catalysts, and simultaneously uses it as a catalyst in the hydrothermal conversion process of agricultural waste. It can accelerate the hydrolysis reaction and improve the hydrothermal conversion efficiency. The abundant minerals and metal ions in chicken manure can act as natural catalysts in the hydrothermal reaction, promoting the decomposition of cellulose in agricultural waste, accelerating hydrolysis and other reactions, and improving the hydrothermal conversion rate. The modified biochar with more active sites is formed by mixing corn stalks and chicken manure through two hydrothermal reactions. It can effectively catalyze the conversion of waste, increase the yield of solid hydrothermal char and liquid bio-oil, enhance catalytic activity, and improve conversion efficiency. The combination of hydrothermal reaction and carbonization process gives the modified biochar a more developed mesoporous structure, increases the specific surface area, and enhances the adsorption capacity for harmful substances. In addition, the organic matter and nitrogen-containing compounds contained in chicken manure introduce oxygen-containing and nitrogen-containing surface functional groups during modification, which improves surface reactivity, pore structure, and adsorption performance.

[0044] 3. The present invention applies the prepared biochar-based alkali metal catalyst to the hydrothermal conversion process of agricultural waste, which can significantly improve the conversion efficiency and rate. The obtained catalyst reduces the hydrolysis activation energy by destroying the biomass crystal structure, shortens the reaction time, reduces the reaction energy consumption, and increases the product yield. Compared with homogeneous alkali catalysts, the prepared catalyst is easy to recover and reuse. It can be separated by simple operation and can be recycled multiple times after regeneration treatment, avoiding secondary pollution and realizing green catalysis. Detailed Implementation

[0045] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0046] Example 1

[0047] 1. This embodiment provides a method for preparing modified biochar, including the following steps:

[0048] (1) The corn stalks and chicken manure were dried at 80℃ for 18h, ground to a particle size of 80μm, and then dried at 85℃ for 24h to obtain corn stalk powder and chicken manure powder.

[0049] (2) Mix 1.5g of chicken manure powder with 7.5mL of distilled water, place it in a hydrothermal reactor, heat it to 180℃ and keep it at that temperature for 2h to obtain solid carbon and a mixture;

[0050] (3) Mix 7 mL of the mixture with 1.6 g of corn stalk powder and stir. Then add the mixture to a hydrothermal reactor, heat it to 220 °C and keep it at that temperature for 2 h. After drying, place it in a tube furnace for carbonization at a carbonization temperature of 600 °C to obtain modified biochar.

[0051] 2. This embodiment provides a biochar-based alkali metal catalyst, comprising 25 parts of modified biochar prepared in the above steps and 21.5 parts of potassium carbonate. The preparation method includes the following steps:

[0052] (1) Grind the modified biochar and sieve it to obtain modified biochar powder with a particle size of 100 mesh; dissolve potassium carbonate in deionized water to obtain a 1 mol / L potassium carbonate solution.

[0053] (2) Add the modified biochar powder to the container, and add potassium carbonate solution dropwise to the powder until the modified biochar powder becomes wet and forms a uniform mud without excess free liquid. After stirring and mixing, dry at 110℃ for 8 hours, grind, calcine under nitrogen atmosphere, heat to 500℃ at a heating rate of 5℃ / min, hold at the temperature for 2 hours, and cool to obtain the biochar-based alkali metal catalyst.

[0054] 3. This embodiment provides an application of a biochar-based alkali metal catalyst in the hydrothermal conversion of agricultural waste, including the following steps:

[0055] (1) After crushing, drying and sieving 12g of corn stalks, 12g of rice husks and 14.5g of walnut shells, add them to a container containing 4mL of ethanol and 3.2g of biochar-based alkali metal catalyst, mix evenly to obtain a slurry;

[0056] (2) Add the slurry to the reactor, seal it, and heat it to 200°C at a rate of 5°C / min while stirring. The stirring speed is 500 rpm. After the reaction is completed, cool it and separate the products. During the product separation process, the gaseous products are separated into condensable and non-condensable gases by a condenser. The non-condensable gases are treated by desulfurization and decarbonization and used as fuel or chemical raw materials. The condensable gases are condensed and converted into liquids, which are then incorporated into the liquid products. The liquid products are centrifuged or filtered to remove solid residues and then upgraded by fractionation, extraction or catalytic hydrogenation to prepare biofuels or fine chemicals. The solid products are washed and dried and used as soil conditioners, adsorbents or re-carbonized to prepare activated carbon. The unreacted biochar-based alkali metal catalyst is regenerated by acid washing, and the alkali metals are recovered and recycled.

[0057] Example 2

[0058] 1. This embodiment provides a method for preparing modified biochar, including the following steps:

[0059] (1) The corn stalks and chicken manure were dried at 85℃ for 16h, ground to a particle size of 80μm, and then dried at 85℃ for 24h to obtain corn stalk powder and chicken manure powder.

[0060] (2) Mix 1g of chicken manure powder with 10mL of distilled water, put it into a hydrothermal reactor, heat it to 180℃ and keep it at that temperature for 2h to obtain solid carbon and a mixture;

[0061] (3) After mixing 4 mL of the mixture with 2.2 g of corn stalk powder, add it to a hydrothermal reactor, heat it to 220 °C and keep it at that temperature for 2 h, then dry it and place it in a tube furnace for carbonization at a temperature of 600 °C to obtain modified biochar.

[0062] 2. This embodiment discloses a biochar-based alkali metal catalyst, comprising 20 parts of modified biochar prepared in the above steps and 25 parts of potassium nitrate. The preparation method includes the following steps:

[0063] (1) Grind the modified biochar and sieve it with a particle size of 100 mesh to obtain modified biochar powder. Dissolve potassium nitrate in deionized water to obtain a 1 mol / L potassium nitrate solution.

[0064] (2) Add the modified biochar powder to the container, and add potassium nitrate solution dropwise to the powder until the modified biochar powder becomes wet, forming a uniform mud-like substance without excess free liquid. After stirring and mixing, dry at 110℃ for 8 hours, grind, calcine under nitrogen atmosphere, heat to 500℃ at a heating rate of 5℃ / min, hold at the temperature for 2 hours, and cool to obtain the biochar-based alkali metal catalyst.

[0065] 3. This embodiment discloses the application of a biochar-based alkali metal catalyst in the hydrothermal conversion of agricultural waste, including the following steps:

[0066] (1) After crushing, drying and sieving 10g of wheat straw, 9g of rice husk and 12g of peanut shell, add them to a container containing 6mL of ethanol and 2.8g of biochar-based alkali metal catalyst, mix evenly to obtain slurry;

[0067] (2) Add the slurry to the reactor, seal it, and heat it to 200°C at a rate of 5°C / min while stirring. The stirring speed is 500 rpm. After the reaction is completed, cool it and separate the products. During the product separation process, the gaseous products are separated into condensable and non-condensable gases by a condenser. The non-condensable gases are desulfurized and decarbonized and then used as fuel or chemical raw materials. The condensable gases are condensed and converted into liquids, which are then incorporated into the liquid products. The liquid products are centrifuged or filtered to remove solid residues and then upgraded by fractionation, extraction or catalytic hydrogenation to prepare biofuels or fine chemicals. The solid products are washed and dried and then used as soil conditioners, adsorbents or re-carbonized to prepare activated carbon. The unreacted biochar-based alkali metal catalyst is regenerated by acid washing, and the alkali metals are recovered and recycled.

[0068] Example 3

[0069] 1. This embodiment discloses a method for preparing modified biochar, including the following steps:

[0070] (1) The rice straw and pig manure were dried at 80℃ for 18h, ground to a particle size of 80μm, and then dried at 85℃ for 24h to obtain rice straw powder and pig manure powder.

[0071] (2) Mix 2g of pig manure powder with 5mL of distilled water, put it into a hydrothermal reactor, heat it to 180℃ and keep it at that temperature for 2h to obtain solid carbon and a mixture;

[0072] (3) Mix 10 mL of the mixture with 1 g of rice straw powder, add it to a hydrothermal reactor, heat it to 220 °C and keep it at that temperature for 2 h, then dry it and place it in a tube furnace for carbonization at a temperature of 600 °C to obtain modified biochar.

[0073] 2. This embodiment discloses a biochar-based alkali metal catalyst, comprising 30 parts of modified biochar prepared in the above steps and 18 parts of potassium nitrate. The preparation method includes the following steps:

[0074] (1) Grind the modified biochar and sieve it with a particle size of 100 mesh to obtain modified biochar powder. Dissolve potassium nitrate in deionized water to obtain a 1 mol / L potassium nitrate solution.

[0075] (2) Add the modified biochar powder to the container, and add potassium nitrate solution dropwise to the powder until the modified biochar powder becomes wet, forming a uniform mud-like substance without excess free liquid. After stirring and mixing, dry at 110℃ for 8 hours, grind, calcine under nitrogen atmosphere, heat to 500℃ at a heating rate of 5℃ / min, hold at the temperature for 2 hours, and cool to obtain the biochar-based alkali metal catalyst.

[0076] 3. This embodiment discloses the application of a biochar-based alkali metal catalyst in the hydrothermal conversion of agricultural waste, including the following steps:

[0077] (1) After crushing, drying and sieving 14g of corn stalks, 15g of rice husks and 17g of coconut shells, add them to a container containing 2mL of ethanol and 3.5g of biochar-based alkali metal catalyst, mix evenly to obtain a slurry;

[0078] (2) Add the slurry to the reactor, seal it, and heat it to 200°C at a rate of 5°C / min. Stir the reaction at a stirring rate of 500 rpm. After the reaction is completed, cool it and separate the products. During the product separation process, the gaseous products are separated into condensable and non-condensable gases by a condenser. The non-condensable gases are desulfurized and decarbonized and then used as fuel or chemical raw materials. The condensable gases are condensed and converted into liquids, which are then incorporated into the liquid products. The liquid products are centrifuged or filtered to remove solid residues. They are then upgraded by fractionation, extraction or catalytic hydrogenation to prepare biofuels or fine chemicals. The solid products are washed and dried and then used as soil conditioners, adsorbents or re-carbonized to prepare activated carbon. The unreacted biochar-based alkali metal catalyst is regenerated by acid washing, and the alkali metals are recovered and recycled.

[0079] Example 4

[0080] 1. This embodiment discloses a method for preparing modified biochar, including the following steps:

[0081] (1) Soybean straw and cow dung were dried at 80°C for 20 hours, ground to 80 μm, and then dried at 85°C for 24 hours to obtain soybean straw powder and cow dung powder.

[0082] (2) Mix 1.2g of cow dung powder with 6mL of distilled water, put it into a hydrothermal reactor, heat it to 180℃ and keep it at that temperature for 2h to obtain solid carbon and a mixture;

[0083] (3) Mix 5 mL of the mixture with 1.3 g of soybean straw powder, add it to a hydrothermal reactor, heat it to 220 °C and keep it at that temperature for 2 h, then dry it and place it in a tube furnace for carbonization at a temperature of 600 °C to obtain modified biochar.

[0084] 2. This embodiment discloses a biochar-based alkali metal catalyst, comprising 28 parts of modified biochar prepared in the above steps and 22 parts of potassium hydroxide. The preparation method includes the following steps:

[0085] (1) Grind the modified biochar and sieve it with a particle size of 100 mesh to obtain modified biochar powder. Dissolve potassium hydroxide in deionized water to obtain a 1 mol / L potassium hydroxide solution.

[0086] (2) Add the modified biochar powder to the container, and add potassium hydroxide solution dropwise to the powder until the modified biochar powder becomes wet, forming a uniform mud-like substance without excess free liquid. After stirring and mixing, dry at 110℃ for 8 hours, grind, calcine under nitrogen atmosphere, heat to 500℃ at a heating rate of 5℃ / min, hold at the temperature for 2 hours, and cool to obtain the biochar-based alkali metal catalyst.

[0087] 3. This embodiment discloses the application of a biochar-based alkali metal catalyst in the hydrothermal conversion of agricultural waste, including the following steps:

[0088] (1) After crushing, drying and sieving 11g of rice straw, 10g of rice husk and 13g of walnut shell, add them to a container containing 3mL of ethanol and 2.9g of biochar-based alkali metal catalyst, mix evenly to obtain slurry;

[0089] (2) Add the slurry to the reactor, seal it, and heat it to 200°C at a rate of 5°C / min. Stir the reaction at a stirring rate of 500 rpm. After the reaction is completed, cool it and separate the products. During the product separation process, the gaseous products are separated into condensable and non-condensable gases by a condenser. The non-condensable gases are desulfurized and decarbonized and then used as fuel or chemical raw materials. The condensable gases are condensed and converted into liquids, which are then incorporated into the liquid products. The liquid products are centrifuged or filtered to remove solid residues. They are then upgraded by fractionation, extraction or catalytic hydrogenation to prepare biofuels or fine chemicals. The solid products are washed and dried and then used as soil conditioners, adsorbents or re-carbonized to prepare activated carbon. The unreacted biochar-based alkali metal catalyst is regenerated by acid washing, and the alkali metals are recovered and recycled.

[0090] Example 5

[0091] 1. This embodiment discloses a method for preparing modified biochar, including the following steps:

[0092] (1) Wheat straw and cow dung were dried at 82℃ for 20h, ground to 80μm, and then dried at 85℃ for 24h to obtain wheat straw powder and cow dung powder.

[0093] (2) Mix 1.8g of cow dung powder with 8mL of distilled water, put it into a hydrothermal reactor, heat it to 180℃ and keep it at that temperature for 2h to obtain solid carbon and a mixture;

[0094] (3) Mix 8 mL of the mixture with 1.9 g of wheat straw powder and stir. Then add the mixture to a hydrothermal reactor, heat it to 220 °C and keep it at that temperature for 2 h. After drying, place it in a tube furnace for carbonization at a temperature of 600 °C to obtain modified biochar.

[0095] 2. This embodiment discloses a biochar-based alkali metal catalyst, comprising 22 parts of modified biochar prepared in the above steps and 19 parts of potassium acetate. The preparation method includes the following steps:

[0096] (1) Grind the modified biochar and sieve it with a particle size of 100 mesh to obtain modified biochar powder. Dissolve potassium acetate in deionized water to obtain a 1 mol / L potassium acetate solution.

[0097] (2) Add the modified biochar powder to the container, and add potassium acetate solution dropwise to the powder until the modified biochar powder becomes wet, forming a uniform mud-like substance without excess free liquid. After stirring and mixing, dry at 110℃ for 8 hours, grind, calcine under nitrogen atmosphere, heat to 500℃ at a heating rate of 3℃ / min, hold at the temperature for 2 hours, and cool to obtain the biochar-based alkali metal catalyst.

[0098] 3. This embodiment discloses the application of a biochar-based alkali metal catalyst in the hydrothermal conversion of agricultural waste, including the following steps:

[0099] (1) After crushing, drying and sieving 13g of wheat straw, 13g of rice husk and 16g of coconut shell, add them to a container containing 5mL of ethanol and 3.3g of biochar-based alkali metal catalyst, mix evenly to obtain slurry;

[0100] (2) Add the slurry to the reactor, seal it, and heat it to 200°C at a rate of 5°C / min while stirring. The stirring speed is 500 rpm. After the reaction is completed, cool it and separate the products. During the product separation process, the gaseous products are separated into condensable and non-condensable gases by a condenser. The non-condensable gases are desulfurized and decarbonized and then used as fuel or chemical raw materials. The condensable gases are condensed and converted into liquids, which are then incorporated into the liquid products. The liquid products are centrifuged or filtered to remove solid residues and then upgraded by fractionation, extraction or catalytic hydrogenation to prepare biofuels or fine chemicals. The solid products are washed and dried and then used as soil conditioners, adsorbents or re-carbonized to prepare activated carbon. The unreacted biochar-based alkali metal catalyst is regenerated by acid washing, and the alkali metals are recovered and recycled.

[0101] Comparative Example 1

[0102] 1. This comparative example provides a common biochar prepared from corn stalks, and the preparation method is as follows:

[0103] (1) The corn stalks were dried at 80℃ for 18 hours, ground to a particle size of 80μm, and then dried at 85℃ for 24 hours to obtain corn stalk powder.

[0104] (2) Mix 7 mL of distilled water with 1.6 g of corn stalk powder and stir. Add the mixture to a hydrothermal reactor, heat to 220 °C and keep it at that temperature for 2 h. Then dry the mixture and place it in a tube furnace for carbonization at a temperature of 600 °C to obtain modified biochar.

[0105] 2. Referring to Example 1, the ordinary biochar was used to replace the modified biochar to prepare the biochar-based alkali metal catalyst, and the remaining steps were carried out in accordance with Example 1.

[0106] 3. Referring to Example 1, the biochar-based alkali metal catalyst prepared from the ordinary biochar was used for the hydrothermal conversion of agricultural waste, and the remaining steps were carried out in accordance with Example 1.

[0107] Comparative Example 2

[0108] This comparative example does not involve the preparation of biochar, modified biochar, or biochar-based alkali metal catalysts. In the hydrothermal conversion of agricultural waste, potassium acetate is directly used to replace the biochar-based alkali metal catalyst in Example 5, and the remaining steps are carried out in accordance with Example 5.

[0109] Effect Example

[0110] I. Specific surface area, total pore volume, and pore size distribution

[0111] The modified biochar and ordinary biochar (prepared according to Comparative Example 1) prepared according to Examples 1-5 were tested using GB / T 7702.20-2025. The test results are shown in Table 1.

[0112] Table 1

[0113]

[0114] As shown in Table 1, compared with ordinary biochar, the modified biochar prepared according to Examples 1-5 has a higher specific surface area and a larger average pore volume. The high specific surface area provides more opportunities for contact and adsorption of reactant molecules. The average pore size is in the mesopore range (2-10 nm), which is conducive to the smooth diffusion of larger biomass-derived molecules into the interior of the catalyst and contact with the active sites loaded inside. At the same time, it can also allow product molecules to be discharged smoothly and prevent pore blockage. The high average pore volume provides storage space for intermediates and products in the reaction process, which helps to alleviate the carbon deposition problem. In contrast, the ordinary biochar prepared according to Comparative Example 1 has a smaller specific surface area and pore volume, and the pores are not smooth, which affects the loading, active sites and catalytic efficiency.

[0115] II. Catalyst Support

[0116] 0.1 g of the biochar-based alkali metal catalyst prepared according to Examples 1-5 and Comparative Example 1 was added to a clean polytetrafluoroethylene digestion vessel liner. Then, 8 mL of concentrated nitric acid and 2 mL of hydrogen peroxide were added. The digestion vessel was sealed and placed in a microwave digester. The temperature was raised to 120°C and held for 5 min, then raised to 180°C and held for 20 min. After digestion, the mixture was cooled to room temperature. The digestion vessel was opened, and the digestate was transferred to a volumetric flask and brought to volume. A series of potassium standard curve solutions of known concentrations were then prepared. The wavelength was measured at 776 nm, and the potassium concentration in the solution was calculated. The potassium loading in the catalyst was calculated using the formula: Potassium loading (wt%) = (C × V × D) / (m × 10⁻⁶) 4 ), where C is the potassium concentration in the sample solution (mg / L), V is the final volume of the sample (L), D is the dilution factor before measurement (1 if no dilution is performed), m is the mass of the catalyst sample weighed (g), 10 4 This is the unit conversion factor, and the test results are shown in Table 2:

[0117] Table 2

[0118]

[0119] As shown in Table 2, the modified biochar prepared according to Examples 1-5 has a better potassium loading capacity than the ordinary biochar of Comparative Example 1.

[0120] III. Yield of hydrothermal conversion products

[0121] Agricultural waste was subjected to hydrothermal treatment according to the methods of Examples 1-5 and Comparative Examples 1-2. Gas, liquid, and solid products were collected. The liquid phase included an aqueous phase and an oil phase. The oil phase was extracted with dichloromethane, followed by dehydration and concentration. The yield of bio-oil in the liquid phase was calculated as (mass of bio-oil / total mass of agricultural waste raw material) × 100%. The gaseous products were collected using a gas bag and analyzed by gas chromatography. The gas yield was calculated as (moles of gas / total moles of agricultural waste raw material, usually carbon-based) × 100%. The solid product consisted of the solid residue after reaction, which was filtered, washed, dried, and weighed. The solid residue yield was calculated as (mass of dried solid residue / mass of agricultural waste raw material) × 100%. The results are shown in Table 3.

[0122] Table 3

[0123]

[0124] As shown in Table 3, the catalysts prepared according to Examples 1-5 can effectively improve the bio-oil yield when applied to the hydrothermal conversion of agricultural waste. By optimizing the dispersion of active sites, biomass is converted into a liquid fuel precursor. In terms of gas yield, Comparative Example 2, due to the direct use of potassium acetate as a catalyst and the lack of support control, resulted in an overly vigorous and non-selective catalytic reaction, leading to excessive cracking and decarboxylation of biomass and the generation of more small molecule gases. In Examples 1-5, under the regulation of the support, the reaction pathway is more selective, and the generation of gas is effectively controlled. Comparative Example 1, due to insufficient catalyst activity, resulted in incomplete biomass conversion and a large amount of residual solids, resulting in a higher solid residue yield. Comparative Example 2, due to its uniform catalytic characteristics, is prone to condensation and coking, resulting in a higher solid residue yield than Examples 1-5. The addition of the catalysts prepared according to Examples 1-5 resulted in a lower solid residue yield, indicating that the addition of biochar-based alkali metal catalysts can effectively inhibit coke formation and direct more carbon to the target product, bio-oil.

[0125] IV. Catalyst Recyclability

[0126] After the hydrothermal conversion experiment of agricultural waste was completed, the solid products were separated by centrifugation and filtration. The catalyst mass was weighed, and the recovery rate was calculated. The recovered catalyst was then washed with 0.1 mol / L nitric acid solution, dried at 110℃, and calcined at a rate of 5℃ / min for 2 hours under a nitrogen atmosphere to restore the pore structure and activity. The catalyst was then put into use again for 3-5 cycles. The bio-oil yield was recorded and compared with the bio-oil yield during the first use to calculate the reduction rate. The test results are shown in Table 4.

[0127] Table 4

[0128]

[0129] As shown in Table 4, the prepared biochar-based alkali metal catalyst exhibits excellent cycling performance. The high recovery rate and slow decline of the biochar-based alkali metal catalyst indicate its excellent physical stability and recyclability. Compared with Examples 1-5, Comparative Example 1 shows that the catalyst recovery rate is lower and declines faster, indicating that ordinary biochar has poor structural stability under harsh reaction and regeneration conditions. The potassium acetate used in Comparative Example 2 is soluble in the aqueous phase, and most of it cannot be recovered by filtration after the first reaction, resulting in an extremely low yield and making it impossible to conduct effective multiple cycle tests. Meanwhile, the bio-oil yield reduction rate of Examples 1-5 is low, and the catalytic activity of the surface catalyst is stable. The reduction rate of Comparative Example 1 is significantly higher than that of Examples 1-5, indicating that the catalytic activity of the catalyst prepared using ordinary biochar is reduced. This may be due to poor support fixation capacity and pore blockage or structural collapse.

[0130] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0131] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A biochar-based alkali metal catalyst, characterized in that, By weight, it includes 20-30 parts modified biochar and 18-25 parts alkali metal compounds; The preparation method of the biochar-based alkali metal catalyst includes the following steps: A1. Modified biochar is ground and sieved to obtain modified biochar powder. Alkali metal compound is dissolved in deionized water to obtain alkali metal compound solution. A2. An alkali metal compound solution is added dropwise to modified biochar powder, stirred and mixed, dried and ground, calcined under a nitrogen atmosphere, and cooled to obtain a biochar-based alkali metal catalyst; the alkali metal compound is selected from one or more of potassium carbonate, potassium nitrate, potassium hydroxide and potassium acetate; The method for preparing the modified biochar includes the following steps: S1. The straw and poultry manure are dried separately, ground, and then dried again to obtain straw powder and poultry manure powder; the poultry manure is selected from one or more of chicken manure, cow manure, and pig manure. S2. Poultry and livestock manure powder is mixed with distilled water and then subjected to a hydrothermal reaction to obtain solid char and a mixture; the hydrothermal reaction temperature is 180-200℃ and the time is 1-2 h. S3. The mixture obtained in step S2 is mixed and stirred with the straw powder in step S1, and a second hydrothermal reaction is carried out. After drying, it is carbonized to obtain the final product. The temperature of the second hydrothermal reaction is 200-230℃, and the holding time is 1-2 h. The temperature of the carbonization treatment is 500-700℃.

2. The biochar-based alkali metal catalyst according to claim 1, characterized in that, In step S1, the straw is selected from one or more of corn straw, rice straw, wheat straw, and soybean straw; And / or, the particle size of the straw powder and poultry and livestock manure powder is 60-120 μm; And / or, the drying temperature is 80-85℃ and the time is 12-20h; And / or, the continued drying temperature is 80-85℃, and the time is 20-24h.

3. The biochar-based alkali metal catalyst according to claim 1, characterized in that, In step S2, the ratio of poultry and livestock manure powder to distilled water is 1-2g:5-10mL.

4. The biochar-based alkali metal catalyst according to claim 1, characterized in that, In step S3, the ratio of the mixture to the straw powder is 4-10 mL: 1-2.2 g.

5. The biochar-based alkali metal catalyst according to claim 1, characterized in that, In step A1, the particle size of the sieved material is 80-100 mesh; And / or, the concentration of the alkali metal compound solution is 0.5-2 mol / L; In step A2, the drying temperature is 105-120℃ and the time is 6-12 hours; And / or, the calcination temperature is 400-600℃, the time is 1-2h, and the heating rate is 3-5℃ / min.

6. The application of a biochar-based alkali metal catalyst as described in any one of claims 1-5 in the hydrothermal conversion of crop residues, characterized in that, Includes the following steps: D1. After crushing, drying and sieving the crop residues, add them to a container containing ethanol and biochar-based alkali metal catalyst, mix evenly to obtain a slurry. D2. Heat the slurry to 200-400 ℃ and stir to react. After the reaction is complete, cool and separate the products. The unreacted biochar-based alkali metal catalyst is regenerated by acid washing, and the alkali metal is recovered and recycled.

7. The application according to claim 6, characterized in that, In step D1, the crop residue is selected from at least one of straw, rice husk, and fruit shell; And / or, in step D2, the heating rate is 5-10℃ / min; the stirring rate is 200-500 rpm.

8. The application according to claim 6, characterized in that, In step D2, during the separation of products, the gaseous products are separated into condensable and non-condensable gases by a condenser. The non-condensable gases are desulfurized and decarbonized and then used as fuel or chemical raw materials. The condensable gases are condensed and converted into liquids, which are then incorporated into the liquid products. The liquid products are centrifuged or filtered to remove solid residues and then upgraded by fractionation, extraction, or catalytic hydrogenation to produce biofuels or fine chemicals. The solid products are washed and dried and then used as soil conditioners, adsorbents, or re-carbonized to prepare activated carbon.

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