Preparation method of biomass fuel oil based on straw

Abstract

The invention discloses a preparation method of biomass fuel oil based on straw, and relates to the technical field of biomass fuel oil. The straw-based biomass fuel oil is prepared from alkali-pretreated straw, aspergillus niger, a manganese ferrite, titanium dioxide and aluminum doped mesoporous silica composite catalyst, molybdenum disulfide and cobalt powder. The method comprises the following steps: performing biological fermentation on alkali-pretreated straws and an aspergillus niger spore suspension, and performing catalytic pyrolysis under the action of a manganese ferrite, titanium dioxide and aluminum doped mesoporous silica composite catalyst, so that a biological and chemical synergistic multi-stage catalytic system not only realizes precise striking and efficient catalysis, but also effectively improves the liquefaction yield, and the process is simple and convenient. The oxygen content and the acid value of the biomass fuel oil are greatly reduced and the quality of the fuel oil is remarkably improved in a manner of deep deoxidation and organic acid degradation.

Description

Technical Field

[0001] This invention belongs to the field of biomass fuel technology, specifically referring to a method for preparing biomass fuel based on straw. Background Technology

[0002] With the rapid economic growth of the 21st century, the demand for energy has continued to rise. However, the current energy structure cannot effectively meet the needs of sustainable social development. It faces the urgent challenges of exploring strategies to optimize the energy structure, discovering ways to improve energy efficiency, and promoting the development of renewable energy. Against this backdrop, the solution to the energy crisis is imminent, and biomass fuels, represented by straw, have thus been put on the agenda. As an alternative to traditional petroleum energy, biomass fuels have attracted widespread attention due to their non-toxicity, biodegradability, renewable characteristics, and positive environmental impact, especially their potential to improve air quality and mitigate global warming.

[0003] The existing technology currently has the following main problems:

[0004] Liquid fuel obtained by cracking using traditional catalysts suffers from low yield and mediocre quality, which is not conducive to improving catalytic efficiency and product quality. Summary of the Invention

[0005] In view of the above situation and to overcome the defects of the prior art, the present invention proposes a method for preparing straw-based biomass fuel. The straw-based biomass fuel is made from the following components in parts by weight: 20-30 parts of alkali-pretreated straw, 10-20 parts of Aspergillus niger, 8-10 parts of manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst, 10-15 parts of molybdenum disulfide, and 3-5 parts of cobalt powder.

[0006] The manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst is made from the following components in parts by weight: 30-50 parts of ferric chloride hexahydrate, 20-40 parts of manganese chloride tetrahydrate, 5-10 parts of tetrabutyl titanate, 75-112 parts of tetraethyl orthosilicate, 10-18 parts of aluminum chloride, 20-24 parts of hexadecyltrimethylammonium bromide, 30-40 parts of sodium acetate, and 8-10 parts of trisodium citrate.

[0007] The preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst specifically includes the following steps:

[0008] (1) Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved in 80 mL of ethylene glycol, and 3.0-4.0 g of sodium acetate and 0.8-1.0 g of trisodium citrate were added. After magnetic stirring for 30-50 min, the mixture was placed in an autoclave and kept at 180-200 °C for 6-8 h. After cooling, the mixture was centrifuged and washed 3-5 times alternately with anhydrous ethanol and deionized water. The mixture was then vacuum dried at 60-80 °C. Manganese ferrite nanoparticles were synthesized from ferric chloride hexahydrate and manganese chloride tetrahydrate. The Fe on the manganese ferrite nanoparticles... 3+ Mn 2+ Acidic sites and redox active sites can synergistically catalyze the breaking of C-C bonds and CO bonds in the macromolecules produced by straw pyrolysis, decomposing them into small molecules within the range of gasoline or diesel fuel. Furthermore, manganese ferrite nanoparticles undergo deoxygenation treatment through catalytic dehydrogenation reaction, directly increasing the calorific value of the fuel. They also catalyze the ketylation reaction of short-chain carboxylic acids such as acetic acid and formic acid or the esterification reaction with alcohols in the system, reducing the acid value, reducing corrosiveness and improving the stability of the oil. At the same time, the superparamagnetism of manganese ferrite nanoparticles solves the defects of traditional catalysts such as difficult filtration, low recovery rate and inability to be reused, thus obtaining manganese ferrite nanoparticles.

[0009] (2) Disperse the manganese ferrite nanoparticles described in step (1) in 80 mL of anhydrous ethanol, sonicate for 20-30 min to form a suspension for later use, then dissolve tetrabutyl titanate in 20 mL of anhydrous ethanol, stir magnetically for 10-20 min to form a tetrabutyl titanate alcohol solution for later use, then add the tetrabutyl titanate alcohol solution to the suspension at a rate of 1-2 drops / second while stirring at 1000-2000 rpm. After the addition is complete, continue stirring at room temperature for 2-4 h at a stirring speed of 600-800 rpm, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene, seal it and place it in an oven, react at 160-180℃ for 8-12 h, cool to room temperature, centrifuge, and wash with anhydrous ethanol and deionized water alternately 3-5 times. Vacuum drying at 0-80℃ physically isolates the sensitive magnetic manganese ferrite from the harsh reaction environment through a titanium dioxide shell, improving the chemical stability of the manganese ferrite and helping to maintain high activity and long-lasting catalytic effect. The core manganese ferrite performs catalytic cracking and dehydration reactions, while the titanium dioxide shell provides photocatalytic activity. The multifunctional catalytic active sites enhance catalytic efficiency. The combined effect of titanium dioxide and manganese ferrite forms a multi-pathway deoxygenation network, which helps to remove oxygen atoms in the form of H2O, CO2, and CO, greatly reducing the oxygen content of fuel and increasing the calorific value. Furthermore, titanium dioxide can also directly oxidize and decompose unstable carboxylic acids and other active molecules using photogenerated holes and hydroxyl radicals, significantly reducing the acid value of fuel and improving the stability of oil products, resulting in manganese ferrite@titanium dioxide nanoparticles.

[0010] (3) Disperse the manganese ferrite@titanium dioxide nanoparticles described in step (2) in 150 mL of deionized water, add 2.0-2.4 g of hexadecyltrimethylammonium bromide and 7-9 mL of ammonia water, stir for 20-30 min, then add aluminum chloride, stir for 10-20 min, then add 8-12 mL of tetraethyl orthosilicate, stir for 20-24 h, centrifuge, wash the precipitate, dry at 60-80 °C, calcine at 500-550 °C for 5-6 h, using hexadecyltrimethylammonium bromide as a template agent, and coat the surface of the manganese ferrite@titanium dioxide nanoparticles with an aluminum-doped silica shell through the sol-gel method, forming a mesoporous structure with high specific surface area and ordered nanopores. The structure provides numerous attachment and reaction sites for reactants, as well as a pore confinement effect, thus improving catalytic efficiency. Among them, aluminum atoms doped in the silica framework network provide acidic sites, which work synergistically with the photocatalysis of the inner titanium dioxide and the redox catalysis of manganese ferrite. The powerful catalytic sites provide core support for the high efficiency of the catalytic reaction. By constructing a three-dimensional, multi-pathway deep deoxygenation and acid reduction network, oxygen atoms can be removed more thoroughly, greatly increasing the proportion of hydrocarbon products and thus significantly improving the calorific value of fuel. It can also effectively degrade carboxylic acid molecules, eliminate corrosion molecules, and comprehensively improve the quality and stability of fuel, resulting in a manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst.

[0011] Preferably, in step (1), the amount of ferric chloride hexahydrate and manganese chloride tetrahydrate added is 3.0-5.0g and 2.0-4.0g, respectively. Ferric chloride hexahydrate and manganese chloride tetrahydrate are precursors of manganese ferrite, which constitute the magnetic core material of the catalyst. They can form the bulk structure of the catalyst and provide the active site for catalysis.

[0012] Preferably, in step (2), the amount of tetrabutyl titanate added is 0.5-1.0 mL. The addition of tetrabutyl titanate can coat a uniform layer of titanium dioxide nanoparticles on the surface of manganese ferrite. The huge specific surface area provides a rich contact interface for the reactants. The constructed core-shell nanoparticles can concentrate the reaction on the particle surface and its vicinity, optimize the mass transfer path, and improve the reaction rate.

[0013] Preferably, in step (3), the amount of aluminum chloride added is 1.0-1.8g. As an aluminum source, aluminum chloride can be doped into the silica framework network at the atomic level under alkaline conditions, creating a large number of Lewis acid sites, providing a powerful chemical reaction active center for the entire catalytic process, and can strongly catalyze dehydration, decarboxylation, decarbonylation and other reactions.

[0014] This invention also provides a method for preparing biomass fuel based on straw, specifically including the following steps:

[0015] S1. Activate Aspergillus niger by inoculating it onto PDB slant agar and incubating it in a constant temperature incubator at 28-30℃ for 5-7 days. In a clean bench, add 10-20 mL of sterilized 0.05% Tween 80 aqueous solution to the PDB slant agar filled with spores. Gently and repeatedly blow and aspirate the surface of the agar with a sterile pipette to thoroughly wash off the spores. Transfer the spore eluent to a sterile Erlenmeyer flask containing glass beads. Then, vortex the flask for 5-10 minutes. Filter the flask using four layers of sterile gauze and collect the filtrate. When Aspergillus niger metabolizes sugars, it can consume some oxygen atoms in the substrate through respiration and release them as CO2, thereby reducing the oxygen content and increasing the calorific value of fuel through biological deoxygenation. Aspergillus niger can also directly consume short-chain organic acids as carbon and energy sources for its metabolism, thereby directly removing acidic substances from the reaction system, effectively reducing the acid value, and improving fuel stability, thus obtaining an Aspergillus niger spore suspension.

[0016] S2. Add 2.0-3.0g of crushed straw material through a 40-60 mesh sieve to 100mL of 2% sodium hydroxide solution and place it in a 70-80℃ water bath shaker for 1-2 hours at a shaking speed of 130-150rpm. Use a funnel to separate the solid and liquid, collect the solid material and wash it alternately with anhydrous ethanol and deionized water 3-5 times. Vacuum dry at 60-80℃. Under the action of heated alkali solution, the hydrogen bond network of cellulose is destroyed, the crystallinity decreases and the structure becomes loose, making it easier for the C-C bonds and CO bonds of cellulose to break in subsequent catalytic cracking, reducing the activation energy required for the reaction, making the catalytic reaction more thorough and faster, and obtaining alkali pretreated straw.

[0017] S3. Place the alkali-pretreated straw from step S2 into an Erlenmeyer flask, add PDB liquid culture medium to ensure the medium evenly wets all the alkali-pretreated straw, achieving a slightly moist but not liquid-stagnant state. Autoclave at 121℃ for 15-20 minutes. After cooling to room temperature, on a sterile operating table, use a sterile pipette to transfer the Aspergillus niger spore suspension from step S1 into the Erlenmeyer flask, then place it in a shaker and ferment at 28-30℃ and 130-150 rpm for 5-7 days. After fermentation, filter the fermentation mixture to obtain a solid residue. Then add a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst to the solid residue and catalytically pyrolyze at 300-400℃ for 50-60 minutes under nitrogen protection. After pyrolysis, introduce hydrogen gas into the generated pyrolysis oil and pressurize... The pressure is maintained at 3-7 MPa. Molybdenum disulfide and cobalt powder are added and stirred at 200-300℃ for 1-2 hours. The reaction product is filtered, and the liquid is collected as crude fuel. Finally, it is refined by distillation. First, the light fraction with a boiling point of 60-200℃ is collected, and then the heavy fraction with a boiling point of 200-350℃ is collected. The light and heavy fractions are mixed. In this process, through bio-enzymatic hydrolysis and catalytic cracking, the stubborn natural structure and complex macromolecules of straw are completely destroyed, and the material with a simpler structure and more optimized composition is efficiently converted into high-quality fuel. Molybdenum disulfide and cobalt powder form a Co-Mo-S active phase under high pressure hydrogen, and undergo deep hydrodeoxygenation treatment to convert carboxylic acids into corresponding aldehydes or alcohols, and further into alkanes, thereby completely eliminating the source of acidity from the molecular structure and obtaining straw-based biomass fuel.

[0018] Preferably, in step S1, the inoculum amount of Aspergillus niger is 1.0-2.0g. Aspergillus niger can secrete a variety of powerful hydrolytic enzymes such as cellulase and hemicellulase, which can cut large molecular biomass into small molecular soluble sugars through biocatalysis, providing a more readily reacting substrate for subsequent catalytic cleavage, thereby greatly improving the overall conversion rate and efficiency.

[0019] The beneficial effects achieved by this invention are as follows:

[0020] This invention involves the bio-fermentation of alkali-pretreated straw with Aspergillus niger spore suspension, followed by catalytic pyrolysis under the action of a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst. This multi-stage catalytic system, combining biological and chemical processes, not only achieves precise targeting and efficient catalysis, effectively improving liquefaction yield, but also significantly reduces the oxygen content and acid value of biomass fuel through deep deoxygenation and degradation of organic acids, thus significantly improving fuel quality. In the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst, manganese ferrite forms the core, sequentially encapsulated by titanium dioxide and aluminum-doped silica shells, forming a mesoporous structure with high specific surface area and ordered nanopores. This provides numerous attachment and reaction sites for reactants, as well as a pore confinement effect, which is beneficial for improving catalytic efficiency. The aluminum atoms doped in the silica framework network provide acidic sites, synergistically working with the photocatalysis of the inner titanium dioxide layer and the redox catalysis of the manganese ferrite. These powerful catalytic sites ensure the high efficiency of the catalytic reaction. Simultaneously, a three-dimensional, multi-pathway catalytic system is constructed. The deep deoxygenation and acid reduction network can not only remove oxygen atoms more thoroughly, greatly increasing the proportion of hydrocarbon products and thus improving the calorific value of fuel, but also effectively degrade organic acid molecules such as carboxylic acids, eliminate corrosive factors, and comprehensively improve the quality and stability of fuel. In the fermentation mixture, alkali-pretreated straw is bio-fermented with Aspergillus niger spore suspension. The cellulase and hemicellulase secreted by Aspergillus niger can precisely degrade lignin and hemicellulose wrapped around cellulose, increasing the contact area between the catalyst and cellulose. The enzymes cut large polymer molecules into smaller ones. The soluble sugars and oligosaccharides in the molecules enable a faster reaction rate and lower energy consumption in catalytic pyrolysis. Furthermore, Aspergillus niger can reduce oxygen content through biological deoxygenation, thereby increasing the calorific value of fuel. It also directly consumes short-chain organic acids as carbon and energy sources for its metabolism, thus directly removing acidic substances from the reaction system, effectively reducing acid value, and improving fuel stability. The fuel prepared by the straw-based biomass fuel preparation method of this invention not only has a high yield but also effectively increases calorific value and reduces acid value, thereby significantly improving the quality and stability of the fuel. Attached Figure Description

[0021] Figure 1 The graph shows the liquefaction yield results of Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0022] Figure 2 The graphs show the calorific value results of Examples 1-4 and Comparative Examples 1-3 of the present invention.

[0023] Figure 3 The diagram shows the acid value results of Examples 1-4 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0026] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0027] Example 1

[0028] This embodiment proposes a method for preparing straw-based biomass fuel. The straw-based biomass fuel is made from the following components in parts by weight: 30 parts of alkali-pretreated straw, 20 parts of Aspergillus niger, 10 parts of manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst, 15 parts of molybdenum disulfide, and 5 parts of cobalt powder.

[0029] The manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst is made from the following components in parts by weight: 50 parts of ferric chloride hexahydrate, 40 parts of manganese chloride tetrahydrate, 10 parts of tetrabutyl titanate, 112 parts of tetraethyl orthosilicate, 18 parts of aluminum chloride, 24 parts of hexadecyltrimethylammonium bromide, 40 parts of sodium acetate, and 10 parts of trisodium citrate.

[0030] The preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst specifically includes the following steps:

[0031] (1) Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved in 80 mL of ethylene glycol. The amounts of ferric chloride hexahydrate and manganese chloride tetrahydrate added were 5.0 g and 4.0 g, respectively. Ferric chloride hexahydrate and manganese chloride tetrahydrate are precursors of manganese ferrite, which constitute the magnetic core material of the catalyst. They can form the bulk structure of the catalyst and provide active sites for catalysis. 4.0 g of sodium acetate and 1.0 g of trisodium citrate were added. After magnetic stirring for 50 min, the mixture was placed in an autoclave and kept at 200 °C for 8 h. After cooling, the mixture was centrifuged and washed 5 times alternately with anhydrous ethanol and deionized water. The mixture was then vacuum dried at 80 °C. Manganese ferrite nanoparticles were synthesized from ferric chloride hexahydrate and manganese chloride tetrahydrate. The Fe on the manganese ferrite nanoparticles... 3+ Mn2+ Acidic sites and redox active sites can synergistically catalyze the breaking of C-C bonds and CO bonds in the macromolecules produced by straw pyrolysis, decomposing them into small molecules within the range of gasoline or diesel fuel. Furthermore, manganese ferrite nanoparticles undergo deoxygenation treatment through catalytic dehydrogenation reaction, directly increasing the calorific value of the fuel. They also catalyze the ketylation reaction of short-chain carboxylic acids such as acetic acid and formic acid or the esterification reaction with alcohols in the system, reducing the acid value, reducing corrosiveness and improving the stability of the oil. At the same time, the superparamagnetism of manganese ferrite nanoparticles solves the defects of traditional catalysts such as difficult filtration, low recovery rate and inability to be reused, thus obtaining manganese ferrite nanoparticles.

[0032] (2) Disperse the manganese ferrite nanoparticles described in step (1) in 80 mL of anhydrous ethanol, sonicate for 30 min to form a suspension for later use, then dissolve tetrabutyl titanate in 20 mL of anhydrous ethanol. The amount of tetrabutyl titanate added is 1.0 mL. The addition of tetrabutyl titanate can coat the surface of the manganese ferrite with a uniform layer of titanium dioxide nanoparticles. The huge specific surface area provides a rich contact interface for the reactants. The constructed core-shell nanoparticles can concentrate the reaction on the particle surface and its vicinity, optimize the mass transfer path, and improve the reaction rate. Stir magnetically for 20 min to form a tetrabutyl titanate alcohol solution for later use. Then, under stirring at 2000 rpm, add the tetrabutyl titanate alcohol solution to the suspension at a rate of 1 drop / second. After the addition is completed, continue stirring at room temperature for 4 h at a stirring speed of 800 rpm. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in a container. In an oven, the reaction was carried out at 180℃ for 12 hours, cooled to room temperature, centrifuged, and washed five times alternately with anhydrous ethanol and deionized water. The mixture was then vacuum dried at 80℃. The titanium dioxide shell physically isolates the sensitive magnetic manganese ferrite from the harsh reaction environment, improving the chemical stability of the manganese ferrite and helping to maintain high activity and long-lasting catalytic effect. The core manganese ferrite undergoes catalytic cracking and dehydration reactions, while the titanium dioxide shell provides photocatalytic activity. The multifunctional catalytic active sites enhance catalytic efficiency. The combined action of titanium dioxide and manganese ferrite forms a multi-pathway deoxygenation network, which helps remove oxygen atoms in the form of H2O, CO2, and CO, significantly reducing the oxygen content of fuel and increasing its calorific value. Furthermore, titanium dioxide can utilize photogenerated holes and hydroxyl radicals to directly oxidize and decompose unstable carboxylic acids and other active molecules, significantly reducing the acid value of fuel and improving the stability of the oil, resulting in manganese ferrite@titanium dioxide nanoparticles.

[0033] (3) Disperse the manganese ferrite@titanium dioxide nanoparticles described in step (2) in 150 mL of deionized water, add 2.4 g of hexadecyltrimethylammonium bromide and 9 mL of ammonia water, stir for 30 min, then add aluminum chloride, the amount of aluminum chloride added is 1.8 g. Aluminum chloride, as an aluminum source, can be atomically doped into the silica framework network under alkaline conditions, creating a large number of Lewis acid sites, providing a strong chemical reaction active center for the entire catalytic process, and can strongly catalyze dehydration, decarboxylation, decarbonylation and other reactions. Stir for 20 min, then add 12 mL of tetraethyl orthosilicate, stir for 24 h, centrifuge, wash the precipitate, dry at 80 °C, calcine at 550 °C for 6 h, using hexadecyltrimethylammonium bromide as a template agent, and through the sol-gel method, on the surface of manganese ferrite@titanium dioxide nanoparticles A layer of aluminum-doped silica is then coated onto the surface, forming a mesoporous structure with a high specific surface area and ordered nanopores. This provides numerous adhesion and reaction sites for reactants, as well as a confinement effect within the pores, thus improving catalytic efficiency. The aluminum atoms doped within the silica framework provide acidic sites, working synergistically with the photocatalysis of the inner titanium dioxide layer and the redox catalysis of the manganese ferrite. These powerful catalytic sites provide core support for the high efficiency of the catalytic reaction. By constructing a three-dimensional, multi-pathway deep deoxygenation and acid reduction network, oxygen atoms can be removed more thoroughly, significantly increasing the proportion of hydrocarbon products and thus significantly improving the calorific value of fuel. Simultaneously, it effectively degrades carboxylic acid molecules, eliminates corrosion molecules, and comprehensively improves the quality and stability of fuel, resulting in a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst.

[0034] This embodiment provides a method for preparing biomass fuel based on straw, specifically including the following steps:

[0035] S1. *Aspergillus niger* was inoculated onto PDB slant agar for activation. The inoculation amount was 2.0 g. *Aspergillus niger* can secrete various powerful hydrolytic enzymes such as cellulase and hemicellulase, which can biocatalyze the breakdown of large biomolecules into small soluble sugars, providing a more readily reactant substrate for subsequent catalytic cleavage, thereby significantly improving the overall conversion rate and efficiency. The culture was placed in a 30℃ incubator for 7 days. In a clean bench, 20 mL of sterilized 0.05% Tween 80 aqueous solution was added to the PDB slant agar that had been contaminated with spores. The surface of the agar was gently aspirated repeatedly using a sterile pipette. The spores were thoroughly washed off, and the spore eluent was transferred to a sterile Erlenmeyer flask containing glass beads. The flask was then vortexed for 10 minutes. The mixture was filtered through four layers of sterile gauze, and the filtrate was collected. When Aspergillus niger metabolizes sugars, it can consume some of the oxygen atoms in the substrate through respiration and release them as CO2, thereby reducing the oxygen content and increasing the calorific value of fuel through biological deoxygenation. Aspergillus niger can also directly consume short-chain organic acids as carbon and energy sources for its metabolism, thereby directly removing acidic substances from the reaction system, effectively reducing the acid value, improving fuel stability, and obtaining an Aspergillus niger spore suspension.

[0036] S2. Add 3.0g of crushed straw material through a 60-mesh sieve to 100mL of 2% sodium hydroxide solution and place it in an 80℃ water bath shaker for 2h at a shaking speed of 150rpm. Use a funnel to separate the solid and liquid, collect the solid material and wash it 5 times alternately with anhydrous ethanol and deionized water, and dry it under vacuum at 80℃. Under the action of heated alkaline solution, the hydrogen bond network of cellulose is destroyed, the crystallinity decreases and the structure becomes loose, making it easier for the C-C bonds and CO bonds of cellulose to break in subsequent catalytic cracking, reducing the activation energy required for the reaction, making the catalytic reaction more thorough and faster, and obtaining alkali pretreated straw.

[0037] S3. Place the alkali-pretreated straw from step S2 into an Erlenmeyer flask, add PDB liquid culture medium to ensure the medium evenly wets all the alkali-pretreated straw, achieving a slightly moist but not liquid-stagnant state. Autoclave at 121°C for 20 minutes. After cooling to room temperature, use a sterile pipette to transfer the Aspergillus niger spore suspension from step S1 into the Erlenmeyer flask on a sterile operating table. Then place the flask in a shaker and ferment at 30°C and 150 rpm for 7 days. After fermentation, filter the fermentation mixture to obtain a solid residue. Add a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst to the solid residue and perform catalytic pyrolysis at 400°C for 60 minutes under nitrogen protection. After pyrolysis, introduce hydrogen into the generated pyrolysis oil, maintaining pressure. At a pressure of 7 MPa, molybdenum disulfide and cobalt powder are added and stirred at 300°C for 2 hours. The resulting reaction product is filtered, and the liquid is collected as crude fuel. Finally, it is refined by distillation. First, the light fraction with a boiling point of 200°C is collected, and then the heavy fraction with a boiling point of 350°C is collected. The light and heavy fractions are mixed. In this process, through bio-enzymatic hydrolysis and catalytic cracking, the stubborn natural structure and complex macromolecules of straw are completely destroyed, and the material with a simpler structure and more optimized composition is efficiently converted into high-quality fuel. Molybdenum disulfide and cobalt powder form a Co-Mo-S active phase under high-pressure hydrogen, and undergo deep hydrodeoxygenation treatment to convert carboxylic acids into corresponding aldehydes or alcohols, and further into alkanes, thereby completely eliminating the source of acidity from the molecular structure and obtaining straw-based biomass fuel.

[0038] Example 2

[0039] This embodiment proposes a method for preparing straw-based biomass fuel. The straw-based biomass fuel is made from the following components in parts by weight: 20 parts of alkali-pretreated straw, 10 parts of Aspergillus niger, 8 parts of manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst, 10 parts of molybdenum disulfide, and 3 parts of cobalt powder.

[0040] The manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst is made from the following components in parts by weight: 30 parts ferric chloride hexahydrate, 20 parts manganese chloride tetrahydrate, 5 parts tetrabutyl titanate, 75 parts tetraethyl orthosilicate, 10 parts aluminum chloride, 20 parts hexadecyltrimethylammonium bromide, 30 parts sodium acetate, and 8 parts trisodium citrate.

[0041] The preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst specifically includes the following steps:

[0042] (1) Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved in 80 mL of ethylene glycol. The amounts of ferric chloride hexahydrate and manganese chloride tetrahydrate added were 3.0 g and 2.0 g, respectively. Ferric chloride hexahydrate and manganese chloride tetrahydrate are precursors of manganese ferrite, which constitute the magnetic core material of the catalyst. They can form the bulk structure of the catalyst and provide active sites for catalysis. 3.0 g of sodium acetate and 0.8 g of trisodium citrate were added, and the mixture was magnetically stirred for 30 min and then placed in an autoclave. It was kept at 180 °C for 6 h. After cooling, it was centrifuged and washed three times alternately with anhydrous ethanol and deionized water. It was then vacuum dried at 60 °C. The ferric chloride hexahydrate and manganese chloride tetrahydrate were used to synthesize manganese ferrite nanoparticles. The Fe on the manganese ferrite nanoparticles... 3+ Mn 2+ Acidic sites and redox active sites can synergistically catalyze the breaking of C-C bonds and CO bonds in the macromolecules produced by straw pyrolysis, decomposing them into small molecules within the range of gasoline or diesel fuel. Furthermore, manganese ferrite nanoparticles undergo deoxygenation treatment through catalytic dehydrogenation reaction, directly increasing the calorific value of the fuel. They also catalyze the ketylation reaction of short-chain carboxylic acids such as acetic acid and formic acid or the esterification reaction with alcohols in the system, reducing the acid value, reducing corrosiveness and improving the stability of the oil. At the same time, the superparamagnetism of manganese ferrite nanoparticles solves the defects of traditional catalysts such as difficult filtration, low recovery rate and inability to be reused, thus obtaining manganese ferrite nanoparticles.

[0043] (2) Disperse the manganese ferrite nanoparticles described in step (1) in 80 mL of anhydrous ethanol, sonicate for 20 min to form a suspension for later use, then dissolve tetrabutyl titanate in 20 mL of anhydrous ethanol. The amount of tetrabutyl titanate added is 0.5 mL. The addition of tetrabutyl titanate can coat a uniform layer of titanium dioxide nanoparticles on the surface of manganese ferrite. The huge specific surface area provides a rich contact interface for the reactants. The constructed core-shell nanoparticles can concentrate the reaction on the particle surface and its vicinity, optimize the mass transfer path, and improve the reaction rate. Stir magnetically for 10 min to form a tetrabutyl titanate alcohol solution for later use. Then, under stirring at 1000 rpm, add the tetrabutyl titanate alcohol solution to the suspension at a rate of 2 drops / second. After the addition is completed, continue stirring at room temperature for 2 h at a stirring speed of 600 rpm. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in a container. In an oven, the reaction was carried out at 160℃ for 8 hours, cooled to room temperature, centrifuged, and washed three times alternately with anhydrous ethanol and deionized water. The mixture was then vacuum dried at 60℃. The titanium dioxide shell physically isolates the sensitive magnetic manganese ferrite from the harsh reaction environment, improving the chemical stability of the manganese ferrite and helping to maintain high activity and long-lasting catalytic effect. The core manganese ferrite undergoes catalytic cracking and dehydration reactions, while the titanium dioxide shell provides photocatalytic activity. The multifunctional catalytic active sites enhance catalytic efficiency. The combined action of titanium dioxide and manganese ferrite forms a multi-pathway deoxygenation network, which helps remove oxygen atoms in the form of H2O, CO2, and CO, significantly reducing the oxygen content of fuel and increasing its calorific value. Furthermore, titanium dioxide can utilize photogenerated holes and hydroxyl radicals to directly oxidize and decompose unstable carboxylic acids and other active molecules, significantly reducing the acid value of fuel and improving the stability of the oil, resulting in manganese ferrite@titanium dioxide nanoparticles.

[0044] (3) Disperse the manganese ferrite@titanium dioxide nanoparticles described in step (2) in 150 mL of deionized water, add 2.0 g of hexadecyltrimethylammonium bromide and 7 mL of ammonia water, stir for 20 min, then add aluminum chloride, the amount of aluminum chloride added is 1.0 g. Aluminum chloride, as an aluminum source, can be atomically doped into the silica framework network under alkaline conditions, creating a large number of Lewis acid sites, providing a strong chemical reaction active center for the entire catalytic process, and can strongly catalyze dehydration, decarboxylation, decarbonylation and other reactions. Stir for 10 min, then add 8 mL of tetraethyl orthosilicate, stir for 20 h, centrifuge, wash the precipitate, dry at 60 °C, calcine at 500 °C for 5 h, using hexadecyltrimethylammonium bromide as a template agent, and through the sol-gel method, on the surface of manganese ferrite@titanium dioxide nanoparticles A layer of aluminum-doped silica is then coated onto the surface, forming a mesoporous structure with a high specific surface area and ordered nanopores. This provides numerous adhesion and reaction sites for reactants, as well as a confinement effect within the pores, thus improving catalytic efficiency. The aluminum atoms doped within the silica framework provide acidic sites, working synergistically with the photocatalysis of the inner titanium dioxide layer and the redox catalysis of the manganese ferrite. These powerful catalytic sites provide core support for the high efficiency of the catalytic reaction. By constructing a three-dimensional, multi-pathway deep deoxygenation and acid reduction network, oxygen atoms can be removed more thoroughly, significantly increasing the proportion of hydrocarbon products and thus significantly improving the calorific value of fuel. Simultaneously, it effectively degrades carboxylic acid molecules, eliminates corrosion molecules, and comprehensively improves the quality and stability of fuel, resulting in a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst.

[0045] This embodiment provides a method for preparing biomass fuel based on straw, specifically including the following steps:

[0046] S1. *Aspergillus niger* was inoculated onto PDB slant agar for activation. The inoculation amount was 1.0 g. *Aspergillus niger* can secrete various powerful hydrolytic enzymes such as cellulase and hemicellulase, which can biocatalyze the breakdown of large biomolecules into small soluble sugars, providing a more readily reactant substrate for subsequent catalytic cleavage, thereby significantly improving the overall conversion rate and efficiency. The culture was placed in a 28℃ incubator for 5 days. In a clean bench, 10 mL of sterilized 0.05% Tween 80 aqueous solution was added to the PDB slant agar that had been contaminated with spores. The surface of the agar was gently aspirated repeatedly using a sterile pipette. The spores were thoroughly washed off, and the spore eluent was transferred to a sterile Erlenmeyer flask containing glass beads. The flask was then vortexed for 5 minutes. The mixture was filtered using four layers of sterile gauze, and the filtrate was collected. When Aspergillus niger metabolizes sugars, it can consume some oxygen atoms in the substrate through respiration and release them as CO2, thereby reducing the oxygen content and increasing the calorific value of fuel through biological deoxygenation. Aspergillus niger can also directly consume short-chain organic acids as carbon and energy sources for its metabolism, thereby directly removing acidic substances from the reaction system, effectively reducing the acid value, improving fuel stability, and obtaining an Aspergillus niger spore suspension.

[0047] S2. Add 2.0g of crushed straw material through a 40-mesh sieve to 100mL of 2% sodium hydroxide solution and place it in a 70℃ water bath shaker for 1h at a shaking speed of 130rpm. Use a funnel to separate the solid and liquid, collect the solid material and wash it three times alternately with anhydrous ethanol and deionized water, and dry it under vacuum at 60℃. Under the action of heated alkaline solution, the hydrogen bond network of cellulose is destroyed, the crystallinity decreases and the structure becomes loose, making it easier for the C-C bonds and CO bonds of cellulose to break in subsequent catalytic cracking, reducing the activation energy required for the reaction, making the catalytic reaction more thorough and faster, and obtaining alkali pretreated straw.

[0048] S3. Place the alkali-pretreated straw from step S2 into an Erlenmeyer flask, add PDB liquid culture medium to ensure the medium evenly wets all the alkali-pretreated straw, achieving a slightly moist but not liquid-stagnant state. Autoclave at 121°C for 15 minutes. After cooling to room temperature, use a sterile pipette to transfer the Aspergillus niger spore suspension from step S1 into the Erlenmeyer flask on a sterile operating table. Then place the flask in a shaker and ferment at 28°C and 130 rpm for 5 days. After fermentation, filter the fermentation mixture to obtain a solid residue. Add a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst to the solid residue and perform catalytic pyrolysis at 300°C for 50 minutes under nitrogen protection. After pyrolysis, introduce hydrogen into the generated pyrolysis oil, maintaining pressure. Molybdenum disulfide and cobalt powder are added at 3 MPa and stirred at 200℃ for 1 hour. The resulting reaction product is filtered, and the liquid is collected as crude fuel. Finally, it is refined by distillation. First, the light fraction with a boiling point of 60℃ is collected, and then the heavy fraction with a boiling point of 200℃ is collected. The light and heavy fractions are mixed. In this process, through bio-enzymatic hydrolysis and catalytic cracking, the stubborn natural structure and complex macromolecules of straw are completely destroyed, and the material with a simpler structure and more optimized composition is efficiently converted into high-quality fuel. Molybdenum disulfide and cobalt powder form a Co-Mo-S active phase under high-pressure hydrogen, and undergo deep hydrodeoxygenation treatment to convert carboxylic acids into corresponding aldehydes or alcohols, and further into alkanes, thereby completely eliminating the source of acidity from the molecular structure and obtaining straw-based biomass fuel.

[0049] Example 3

[0050] This embodiment proposes a method for preparing straw-based biomass fuel. The straw-based biomass fuel is made from the following components in parts by weight: 25 parts of alkali-pretreated straw, 15 parts of Aspergillus niger, 9 parts of manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst, 12.5 parts of molybdenum disulfide, and 4 parts of cobalt powder.

[0051] The manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst is made from the following components in parts by weight: 40 parts ferric chloride hexahydrate, 30 parts manganese chloride tetrahydrate, 7.5 parts tetrabutyl titanate, 93.5 parts tetraethyl orthosilicate, 14 parts aluminum chloride, 22 parts hexadecyltrimethylammonium bromide, 35 parts sodium acetate, and 9 parts trisodium citrate.

[0052] The preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst specifically includes the following steps:

[0053] (1) Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved in 80 mL of ethylene glycol. The amounts of ferric chloride hexahydrate and manganese chloride tetrahydrate added were 4.0 g and 3.0 g, respectively. Ferric chloride hexahydrate and manganese chloride tetrahydrate are precursors of manganese ferrite, which constitute the magnetic core material of the catalyst. They can form the bulk structure of the catalyst and provide active sites for catalysis. 3.5 g of sodium acetate and 0.9 g of trisodium citrate were added, and the mixture was magnetically stirred for 40 min and then placed in an autoclave. It was kept at 190 °C for 7 h. After cooling, it was centrifuged and washed 4 times alternately with anhydrous ethanol and deionized water. It was then vacuum dried at 70 °C. The ferric chloride hexahydrate and manganese chloride tetrahydrate were used to synthesize manganese ferrite nanoparticles. The Fe on the manganese ferrite nanoparticles... 3+ Mn 2+ Acidic sites and redox active sites can synergistically catalyze the breaking of C-C bonds and CO bonds in the macromolecules produced by straw pyrolysis, decomposing them into small molecules within the range of gasoline or diesel fuel. Furthermore, manganese ferrite nanoparticles undergo deoxygenation treatment through catalytic dehydrogenation reaction, directly increasing the calorific value of the fuel. They also catalyze the ketylation reaction of short-chain carboxylic acids such as acetic acid and formic acid or the esterification reaction with alcohols in the system, reducing the acid value, reducing corrosiveness and improving the stability of the oil. At the same time, the superparamagnetism of manganese ferrite nanoparticles solves the defects of traditional catalysts such as difficult filtration, low recovery rate and inability to be reused, thus obtaining manganese ferrite nanoparticles.

[0054] (2) Disperse the manganese ferrite nanoparticles described in step (1) in 80 mL of anhydrous ethanol, sonicate for 25 min to form a suspension for later use, then dissolve tetrabutyl titanate in 20 mL of anhydrous ethanol. The amount of tetrabutyl titanate added is 0.75 mL. The addition of tetrabutyl titanate can coat a uniform layer of titanium dioxide nanoparticles on the surface of manganese ferrite. The huge specific surface area provides a rich contact interface for the reactants. The constructed core-shell nanoparticles can concentrate the reaction on the particle surface and its vicinity, optimize the mass transfer path, and improve the reaction rate. Stir magnetically for 15 min to form a tetrabutyl titanate alcohol solution for later use. Then, under stirring at 1500 rpm, add the tetrabutyl titanate alcohol solution to the suspension at a rate of 2 drops / second. After the addition is completed, continue stirring at room temperature for 3 h at a stirring speed of 700 rpm. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in a container. In an oven, the reaction was carried out at 170℃ for 10 hours, cooled to room temperature, centrifuged, and washed four times alternately with anhydrous ethanol and deionized water. The mixture was then vacuum dried at 70℃. The titanium dioxide shell physically isolates the sensitive magnetic manganese ferrite from the harsh reaction environment, improving the chemical stability of the manganese ferrite and helping to maintain high activity and long-lasting catalytic effect. The core manganese ferrite undergoes catalytic cracking and dehydration reactions, while the titanium dioxide shell provides photocatalytic activity. The multifunctional catalytic active sites enhance catalytic efficiency. The combined action of titanium dioxide and manganese ferrite forms a multi-pathway deoxygenation network, which helps remove oxygen atoms in the form of H2O, CO2, and CO, significantly reducing the oxygen content of fuel and increasing its calorific value. Furthermore, titanium dioxide can utilize photogenerated holes and hydroxyl radicals to directly oxidize and decompose unstable carboxylic acids and other active molecules, significantly reducing the acid value of fuel and improving the stability of the oil, resulting in manganese ferrite@titanium dioxide nanoparticles.

[0055] (3) Disperse the manganese ferrite@titanium dioxide nanoparticles described in step (2) in 150 mL of deionized water, add 2.2 g of hexadecyltrimethylammonium bromide and 8 mL of ammonia water, stir for 25 min, then add aluminum chloride, the amount of aluminum chloride added is 1.4 g. Aluminum chloride, as an aluminum source, can be atomically doped into the silica framework network under alkaline conditions, creating a large number of Lewis acid sites, providing a strong chemical reaction active center for the entire catalytic process, and can strongly catalyze dehydration, decarboxylation, decarbonylation and other reactions. Stir for 15 min, then add 10 mL of tetraethyl orthosilicate, stir for 22 h, centrifuge, wash the precipitate, dry at 70 °C, calcine at 525 °C for 5.5 h, using hexadecyltrimethylammonium bromide as a template agent, and through the sol-gel method, on the surface of manganese ferrite@titanium dioxide nanoparticles A layer of aluminum-doped silica is then wrapped around the surface, forming a mesoporous structure with high specific surface area and ordered nanopores. This provides numerous adhesion and reaction sites for reactants, as well as a pore confinement effect, improving catalytic efficiency. Aluminum atoms doped into the silica framework network provide acidic sites, which work synergistically with the photocatalysis of the inner titanium dioxide layer and the redox catalysis of manganese ferrite. These powerful catalytic sites provide core support for the high efficiency of the catalytic reaction. By constructing a three-dimensional, multi-pathway deep deoxygenation and acid reduction network, oxygen atoms can be removed more thoroughly, greatly increasing the proportion of hydrocarbon products and thus significantly improving the calorific value of fuel. It can also effectively degrade carboxylic acid molecules, eliminate corrosion molecules, and comprehensively improve the quality and stability of fuel, resulting in a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst.

[0056] This embodiment provides a method for preparing biomass fuel based on straw, specifically including the following steps:

[0057] S1. *Aspergillus niger* was inoculated onto PDB slant agar for activation. The inoculation amount was 1.5g. *Aspergillus niger* can secrete various powerful hydrolytic enzymes such as cellulase and hemicellulase, which can biocatalyze the breakdown of large biomolecules into small soluble sugars, providing a more readily reactant substrate for subsequent catalytic cleavage, thereby significantly improving the overall conversion rate and efficiency. The culture was placed in a 29℃ incubator for 6 days. In a clean bench, 15mL of sterilized 0.05% Tween 80 aqueous solution was added to the PDB slant agar that had been contaminated with spores. The surface of the agar was gently aspirated repeatedly using a sterile pipette. The spores were thoroughly washed off, and the spore eluent was transferred to a sterile Erlenmeyer flask containing glass beads. The flask was then vortexed for 7.5 minutes. The mixture was filtered through four layers of sterile gauze, and the filtrate was collected. When Aspergillus niger metabolizes sugars, it can consume some of the oxygen atoms in the substrate through respiration and release them as CO2, thereby reducing the oxygen content and increasing the calorific value of the fuel through biological deoxygenation. Aspergillus niger can also directly consume short-chain organic acids as carbon and energy sources for its metabolism, thereby directly removing acidic substances from the reaction system, effectively reducing the acid value, improving fuel stability, and obtaining an Aspergillus niger spore suspension.

[0058] S2. Add 2.5g of crushed straw material through a 50-mesh sieve to 100mL of 2% sodium hydroxide solution and place it in a 75℃ water bath shaker for 1.5h at a shaking speed of 140rpm. Use a funnel to separate the solid and liquid, collect the solid material and wash it four times alternately with anhydrous ethanol and deionized water, and dry it under vacuum at 70℃. Under the action of heated alkaline solution, the hydrogen bond network of cellulose is destroyed, the crystallinity decreases and the structure becomes loose, making it easier for the C-C bonds and CO bonds of cellulose to break in subsequent catalytic cracking, reducing the activation energy required for the reaction, making the catalytic reaction more thorough and faster, and obtaining alkali pretreated straw.

[0059] S3. Place the alkali-pretreated straw from step S2 into an Erlenmeyer flask, add PDB liquid culture medium to ensure the medium evenly wets all the alkali-pretreated straw, achieving a slightly moist but not liquid-stagnant state. Autoclave at 121°C for 17.5 min. After cooling to room temperature, use a sterile pipette to transfer the Aspergillus niger spore suspension from step S1 into the Erlenmeyer flask on a sterile operating table. Then place the flask in a shaker and ferment at 29°C and 140 rpm for 6 days. After fermentation, filter the fermentation mixture to obtain a solid residue. Add a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst to the solid residue. Catalytically pyrolyze at 350°C for 55 min under nitrogen protection. After pyrolysis, introduce hydrogen into the generated pyrolysis oil, maintaining pressure. Molybdenum disulfide and cobalt powder are added at 5 MPa and stirred at 250℃ for 1.5 h. The resulting reaction product is filtered, and the liquid is collected as crude fuel. Finally, it is refined by distillation. First, the light fraction with a boiling point of 130℃ is collected, and then the heavy fraction with a boiling point of 275℃ is collected. The light and heavy fractions are mixed. In this process, through bio-enzymatic hydrolysis and catalytic cracking, the stubborn natural structure and complex macromolecules of straw are completely destroyed, and the material with a simpler structure and more optimized composition is efficiently converted into high-quality fuel. Molybdenum disulfide and cobalt powder form a Co-Mo-S active phase under high-pressure hydrogen, and undergo deep hydrodeoxygenation treatment to convert carboxylic acids into corresponding aldehydes or alcohols, and further into alkanes, thereby completely eliminating the source of acidity from the molecular structure and obtaining straw-based biomass fuel.

[0060] Example 4

[0061] This embodiment proposes a method for preparing straw-based biomass fuel. The straw-based biomass fuel is made from the following components in parts by weight: 30 parts of alkali-pretreated straw, 10 parts of Aspergillus niger, 10 parts of manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst, 15 parts of molybdenum disulfide, and 5 parts of cobalt powder.

[0062] The manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst is made from the following components in parts by weight: 50 parts ferric chloride hexahydrate, 40 parts manganese chloride tetrahydrate, 5 parts tetrabutyl titanate, 112 parts tetraethyl orthosilicate, 10 parts aluminum chloride, 24 parts hexadecyltrimethylammonium bromide, 40 parts sodium acetate, and 10 parts trisodium citrate.

[0063] The preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst specifically includes the following steps:

[0064] (1) Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved in 80 mL of ethylene glycol. The amounts of ferric chloride hexahydrate and manganese chloride tetrahydrate added were 5.0 g and 4.0 g, respectively. Ferric chloride hexahydrate and manganese chloride tetrahydrate are precursors of manganese ferrite, which constitute the magnetic core material of the catalyst. They can form the bulk structure of the catalyst and provide active sites for catalysis. 4.0 g of sodium acetate and 1.0 g of trisodium citrate were added. After stirring magnetically for 30 min, the mixture was placed in an autoclave and kept at 200 °C for 6 h. After cooling, the mixture was centrifuged and washed 5 times alternately with anhydrous ethanol and deionized water. The mixture was then vacuum dried at 80 °C. Manganese ferrite nanoparticles were synthesized from ferric chloride hexahydrate and manganese chloride tetrahydrate. The Fe on the manganese ferrite nanoparticles... 3+ Mn 2+ Acidic sites and redox active sites can synergistically catalyze the breaking of C-C bonds and CO bonds in the macromolecules produced by straw pyrolysis, decomposing them into small molecules within the range of gasoline or diesel fuel. Furthermore, manganese ferrite nanoparticles undergo deoxygenation treatment through catalytic dehydrogenation reaction, directly increasing the calorific value of the fuel. They also catalyze the ketylation reaction of short-chain carboxylic acids such as acetic acid and formic acid or the esterification reaction with alcohols in the system, reducing the acid value, reducing corrosiveness and improving the stability of the oil. At the same time, the superparamagnetism of manganese ferrite nanoparticles solves the defects of traditional catalysts such as difficult filtration, low recovery rate and inability to be reused, thus obtaining manganese ferrite nanoparticles.

[0065] (2) Disperse the manganese ferrite nanoparticles described in step (1) in 80 mL of anhydrous ethanol, sonicate for 20 min to form a suspension for later use, then dissolve tetrabutyl titanate in 20 mL of anhydrous ethanol. The amount of tetrabutyl titanate added is 0.5 mL. The addition of tetrabutyl titanate can coat a uniform layer of titanium dioxide nanoparticles on the surface of manganese ferrite. The huge specific surface area provides a rich contact interface for the reactants. The constructed core-shell nanoparticles can concentrate the reaction on the particle surface and its vicinity, optimize the mass transfer path, and improve the reaction rate. Stir magnetically for 10 min to form a tetrabutyl titanate alcohol solution for later use. Then, under stirring at 2000 rpm, add the tetrabutyl titanate alcohol solution to the suspension at a rate of 1 drop / second. After the addition is completed, continue stirring at room temperature for 2 h at a stirring speed of 800 rpm. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in a container. In an oven, the reaction was carried out at 180℃ for 8 hours, cooled to room temperature, centrifuged, and washed five times alternately with anhydrous ethanol and deionized water. The mixture was then vacuum dried at 80℃. The titanium dioxide shell physically isolates the sensitive magnetic manganese ferrite from the harsh reaction environment, improving the chemical stability of the manganese ferrite and helping to maintain high activity and long-lasting catalytic effect. The core manganese ferrite undergoes catalytic cracking and dehydration reactions, while the titanium dioxide shell provides photocatalytic activity. The multifunctional catalytic active sites enhance catalytic efficiency. The combined action of titanium dioxide and manganese ferrite forms a multi-pathway deoxygenation network, which helps remove oxygen atoms in the form of H2O, CO2, and CO, significantly reducing the oxygen content of fuel and increasing its calorific value. Furthermore, titanium dioxide can utilize photogenerated holes and hydroxyl radicals to directly oxidize and decompose unstable carboxylic acids and other active molecules, significantly reducing the acid value of fuel and improving the stability of the oil, resulting in manganese ferrite@titanium dioxide nanoparticles.

[0066] (3) Disperse the manganese ferrite@titanium dioxide nanoparticles described in step (2) in 150 mL of deionized water, add 2.4 g of hexadecyltrimethylammonium bromide and 9 mL of ammonia water, stir for 20 min, then add aluminum chloride, the amount of aluminum chloride added is 1.0 g. Aluminum chloride, as an aluminum source, can be atomically doped into the silica framework network under alkaline conditions, creating a large number of Lewis acid sites, providing a strong chemical reaction active center for the entire catalytic process, and can strongly catalyze dehydration, decarboxylation, decarbonylation and other reactions. Stir for 10 min, then add 12 mL of tetraethyl orthosilicate, stir for 20 h, centrifuge, wash the precipitate, dry at 80 °C, calcine at 550 °C for 5 h, using hexadecyltrimethylammonium bromide as a template agent, and through the sol-gel method, on the surface of manganese ferrite@titanium dioxide nanoparticles A layer of aluminum-doped silica is then coated onto the surface, forming a mesoporous structure with a high specific surface area and ordered nanopores. This provides numerous adhesion and reaction sites for reactants, as well as a confinement effect within the pores, thus improving catalytic efficiency. The aluminum atoms doped within the silica framework provide acidic sites, working synergistically with the photocatalysis of the inner titanium dioxide layer and the redox catalysis of the manganese ferrite. These powerful catalytic sites provide core support for the high efficiency of the catalytic reaction. By constructing a three-dimensional, multi-pathway deep deoxygenation and acid reduction network, oxygen atoms can be removed more thoroughly, significantly increasing the proportion of hydrocarbon products and thus significantly improving the calorific value of fuel. Simultaneously, it effectively degrades carboxylic acid molecules, eliminates corrosion molecules, and comprehensively improves the quality and stability of fuel, resulting in a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst.

[0067] This embodiment provides a method for preparing biomass fuel based on straw, specifically including the following steps:

[0068] S1. *Aspergillus niger* was inoculated onto PDB slant agar for activation. The inoculation amount was 1.0 g. *Aspergillus niger* can secrete various powerful hydrolytic enzymes such as cellulase and hemicellulase, which can biocatalyze the breakdown of large biomolecules into small soluble sugars, providing a more readily reactant substrate for subsequent catalytic cleavage, thereby significantly improving the overall conversion rate and efficiency. The culture was placed in a 30℃ incubator for 5 days. In a clean bench, 20 mL of sterilized 0.05% Tween 80 aqueous solution was added to the PDB slant agar that had been contaminated with spores. The surface of the agar was gently aspirated repeatedly using a sterile pipette. The spores were thoroughly washed off, and the spore eluent was transferred to a sterile Erlenmeyer flask containing glass beads. The flask was then vortexed for 5 minutes. The mixture was filtered using four layers of sterile gauze, and the filtrate was collected. When Aspergillus niger metabolizes sugars, it can consume some oxygen atoms in the substrate through respiration and release them as CO2, thereby reducing the oxygen content and increasing the calorific value of fuel through biological deoxygenation. Aspergillus niger can also directly consume short-chain organic acids as carbon and energy sources for its metabolism, thereby directly removing acidic substances from the reaction system, effectively reducing the acid value, improving fuel stability, and obtaining an Aspergillus niger spore suspension.

[0069] S2. Add 3.0g of crushed straw material through a 60-mesh sieve to 100mL of 2% sodium hydroxide solution and place it in an 80℃ water bath shaker for 1h at a shaking speed of 150rpm. Use a funnel to separate the solid and liquid, collect the solid material and wash it 5 times alternately with anhydrous ethanol and deionized water, and dry it under vacuum at 80℃. Under the action of heated alkali solution, the hydrogen bond network of cellulose is destroyed, the crystallinity decreases and the structure becomes loose, making it easier for the C-C bonds and CO bonds of cellulose to break in subsequent catalytic cracking, reducing the activation energy required for the reaction, making the catalytic reaction more thorough and faster, and obtaining alkali pretreated straw.

[0070] S3. Place the alkali-pretreated straw from step S2 into an Erlenmeyer flask, add PDB liquid culture medium to ensure the medium evenly wets all the alkali-pretreated straw, achieving a slightly moist but not liquid-stagnant state. Autoclave at 121°C for 15 minutes. After cooling to room temperature, use a sterile pipette to transfer the Aspergillus niger spore suspension from step S1 into the Erlenmeyer flask on a sterile operating table. Then place the flask in a shaker and ferment at 30°C and 150 rpm for 5 days. After fermentation, filter the fermentation mixture to obtain a solid residue. Add a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst to the solid residue and perform catalytic pyrolysis at 400°C for 50 minutes under nitrogen protection. After pyrolysis, introduce hydrogen into the generated pyrolysis oil, maintaining pressure. At 7 MPa, molybdenum disulfide and cobalt powder are added and stirred at 300℃ for 1 hour. The resulting reaction product is filtered, and the liquid is collected as crude fuel. Finally, it is refined by distillation. First, the light fraction with a boiling point of 200℃ is collected, and then the heavy fraction with a boiling point of 350℃ is collected. The light and heavy fractions are mixed. In this process, through bio-enzymatic hydrolysis and catalytic cracking, the stubborn natural structure and complex macromolecules of straw are completely destroyed, and the material with a simpler structure and more optimized composition is efficiently converted into high-quality fuel. Molybdenum disulfide and cobalt powder form a Co-Mo-S active phase under high-pressure hydrogen, and undergo deep hydrodeoxygenation treatment to convert carboxylic acids into corresponding aldehydes or alcohols, and further into alkanes, thereby completely eliminating the source of acidity from the molecular structure and obtaining straw-based biomass fuel.

[0071] Comparative Example 1

[0072] This comparative example provides a method for preparing biomass fuel based on straw. The difference between this method and Example 1 is that the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst does not contain tetrabutyl titanate; the preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst does not include step (2); the preparation method of biomass fuel based on straw is the same as that of Example 1.

[0073] Comparative Example 2

[0074] This comparative example provides a method for preparing biomass fuel based on straw. The difference between this method and Example 1 is that the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst does not contain aluminum chloride; aluminum chloride is not added in step (3) of the preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst; and the preparation method of biomass fuel based on straw is the same as that in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a method for preparing straw-based biomass fuel, which differs from Example 1 in that the straw-based biomass fuel does not contain Aspergillus niger; the preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst is the same as in Example 1; the preparation method of straw-based biomass fuel does not include step S1, and in step S2, the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst is directly added to the alkali pretreated straw for catalytic pyrolysis.

[0077] Experimental Example 1

[0078] Yield Experiment

[0079] Test samples: Straw-based biomass fuels prepared in Examples 1-4 and Comparative Examples 1-3.

[0080] Test method: The liquefaction yield of the test sample is calculated according to the formula Y (%) = (M0-M1) / M0×100%, where M0 is the mass of straw used in the liquefaction process (g) and M1 is the mass of residue in the liquefaction product (g).

[0081] Figure 1 The figures show the liquefaction yield results for Examples 1-4 and Comparative Examples 1-3. As shown, the liquefaction yield for Examples 1-4 was 85-90%, indicating a high liquefaction yield; the liquefaction yield for Comparative Examples 1-3 was 59-75%, indicating a low liquefaction yield. The manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst in Comparative Example 1 did not contain tetrabutyl titanate, thus failing to form a titanium dioxide shell, which was detrimental to protecting the activity of the internal manganese ferrite and also prevented the photocatalytic effect of titanium dioxide from being fully utilized, resulting in a low liquefaction yield. The manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst in Comparative Example 2 did not contain aluminum chloride, thus failing to form acidic catalytic sites in the silica framework and failing to produce a synergistic and efficient catalytic effect with titanium dioxide and manganese ferrite, resulting in a low liquefaction yield. The straw-based biomass fuel in Comparative Example 3 did not contain Aspergillus niger, preventing the fermentation process from cutting large polymer molecules into easily catalytically cleaved small molecule soluble sugars and oligosaccharides, resulting in a low liquefaction yield.

[0082] Experiment Example 2

[0083] Quality and stability tests

[0084] Test samples: Straw-based biomass fuels prepared in Examples 1-4 and Comparative Examples 1-3.

[0085] Test method: (1) Use benzoic acid to calibrate the heat capacity of the instrument, inject the test sample into the combustion vessel with a syringe, put the combustion vessel into the oxygen bomb, connect the ignition wire, fill it with 2-3 MPa oxygen and then put it into the inner cylinder of the calorimeter, add a certain amount of water, start the calorimeter to record the water temperature, ignite and burn, and record the temperature change after the water temperature stabilizes. Calculate the calorific value (MJ / kg) based on the heat capacity and temperature change, and take the average value of 5 experiments;

[0086] (2) Take 0.2g of test sample and dissolve it in 25mL of dioxane aqueous solution (the volume ratio of dioxane to water is 4:1). Titrate it to the equilibrium point using a standardized 0.09mol / L sodium hydroxide solution and measure the acid value (mgKOH / g).

[0087] Figure 2 The graphs show the calorific value results for Examples 1-4 and Comparative Examples 1-3; Figure 3 The graph shows the acid value results for Examples 1-4 and Comparative Examples 1-3; as shown. Figure 2 The calorific values ​​of Examples 1-4 are 36-39 MJ / kg, indicating good quality; the calorific values ​​of Comparative Examples 1-3 are 23-31 MJ / kg, indicating poor quality; Figure 3 The acid values ​​of Examples 1-4 were 8.2-8.9 mgKOH / g, indicating good stability; the acid values ​​of Comparative Examples 1-3 were 15.3-30.5 mgKOH / g, indicating poor stability. The manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst in Comparative Example 1 did not contain tetrabutyl titanate, thus it could not promote deacidification and decarbonylation reactions through the photocatalytic effect of titanium dioxide, which was detrimental to increasing the calorific value. It also could not directly oxidize and decompose unstable carboxylic acids and other active molecules through photogenerated holes and hydroxyl radicals, which was detrimental to reducing the acid value, resulting in poor quality and stability. The manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst in Comparative Example 2... The bulk@titanium dioxide@aluminum-doped mesoporous silica composite catalyst does not contain aluminum chloride, so it cannot strongly catalyze dehydration, decarboxylation, and decarbonylation reactions through acidic sites. This is not conducive to directly stripping oxygen atoms from molecules, nor to removing easily corrosive active molecules such as carboxylic acids, resulting in poor quality and stability. The straw-based biomass fuel in Comparative Example 3 does not contain Aspergillus niger, so it cannot reduce oxygen content through biological deoxygenation, nor can it directly consume short-chain organic acids as carbon and energy sources for its metabolism. This is not conducive to increasing calorific value, nor to removing acidic substances from the reaction system, resulting in poor quality and stability.

[0088] The above experimental results show that the liquefaction yield, quality, and stability of Examples 1-4 of the present invention are significantly better than those of Comparative Examples 1-3. Among them, Example 1, which uses a manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst and Aspergillus niger, has a higher liquefaction yield, better quality, and better stability. The alkali-pretreated straw is first bio-fermented with Aspergillus niger spore suspension, and then catalytically pyrolyzed under the action of manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst. This multi-stage catalytic system of biological and chemical synergy not only achieves precise targeting and efficient catalysis, effectively improving the liquefaction yield, but also significantly reduces the oxygen content and acid value of biomass fuel through deep deoxygenation and degradation of organic acids, thus significantly improving the quality and stability of the fuel.

[0089] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

[0090] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing biomass fuel based on straw, characterized in that: The straw-based biomass fuel is made from the following components in parts by weight: 20-30 parts of alkali-pretreated straw, 10-20 parts of Aspergillus niger, 8-10 parts of manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst, 10-15 parts of molybdenum disulfide, and 3-5 parts of cobalt powder. The method for preparing biomass fuel based on straw specifically includes the following steps: S1. Inoculate Aspergillus niger onto PDB slant medium for activation and incubate at 28-30℃ for 5-7 days. In a clean bench, add 10-20 mL of sterilized 0.05% Tween 80 aqueous solution to the PDB slant medium covered with spores. Gently and repeatedly blow and aspirate the surface of the medium with a sterile pipette to thoroughly wash off the spores. Transfer the spore eluent to a sterile Erlenmeyer flask containing glass beads. Then, vortex the flask for 5-10 minutes. Filter the solution using four layers of sterile gauze and collect the filtrate to obtain an Aspergillus niger spore suspension. S2. Add 2.0-3.0g of crushed straw material through a 40-60 mesh sieve to 100mL of 2% sodium hydroxide solution, place it in a 70-80℃ water bath shaker for 1-2h at a shaking speed of 130-150rpm, use a funnel to separate the solid and liquid, collect the solid material and wash it alternately with anhydrous ethanol and deionized water 3-5 times, and vacuum dry it at 60-80℃ to obtain alkali pretreated straw; S3. Place the alkali-pretreated straw from step S2 into an Erlenmeyer flask, add PDB liquid culture medium to ensure the medium evenly wets all the alkali-pretreated straw, achieving a slightly moist but not liquid-stagnant state. Autoclave at 121°C for 15-20 minutes. After cooling to room temperature, on a sterile operating table, use a sterile pipette to transfer the Aspergillus niger spore suspension from step S1 into the Erlenmeyer flask. Then place it on a shaker and ferment at 28-30°C and 130-150 rpm for 5-7 days. After fermentation, filter the fermentation mixture to obtain a solid residue. Then add manganese ferrite@2 Titanium oxide@aluminum-doped mesoporous silica composite catalyst was subjected to catalytic pyrolysis at 300-400℃ for 50-60 min under nitrogen protection. After pyrolysis, hydrogen was introduced into the resulting pyrolysis oil at a pressure maintained at 3-7 MPa. Molybdenum disulfide and cobalt powder were added, and the mixture was stirred at 200-300℃ for 1-2 h. The resulting reaction product was filtered, and the liquid was collected as crude fuel oil. Finally, it was purified by distillation. First, the light fraction with a boiling point of 60-200℃ was collected, and then the heavy fraction with a boiling point of 200-350℃ was collected. The light and heavy fractions were mixed to obtain straw-based biomass fuel oil.

2. The method for preparing biomass fuel based on straw according to claim 1, characterized in that: In step S1, the inoculum amount of Aspergillus niger is 1.0-2.0g.

3. The method for preparing biomass fuel based on straw according to claim 1, characterized in that: The manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst is made from the following components in parts by weight: 30-50 parts of ferric chloride hexahydrate, 20-40 parts of manganese chloride tetrahydrate, 5-10 parts of tetrabutyl titanate, 75-112 parts of tetraethyl orthosilicate, 10-18 parts of aluminum chloride, 20-24 parts of hexadecyltrimethylammonium bromide, 30-40 parts of sodium acetate, and 8-10 parts of trisodium citrate. The preparation method of the manganese ferrite@titanium dioxide@aluminum-doped mesoporous silica composite catalyst specifically includes the following steps: (1) Dissolve ferric chloride hexahydrate and manganese chloride tetrahydrate in 80 mL of ethylene glycol, add 3.0-4.0 g sodium acetate and 0.8-1.0 g trisodium citrate, stir magnetically for 30-50 min, place in an autoclave, keep at 180-200℃ for 6-8 h, cool and centrifuge, wash with anhydrous ethanol and deionized water alternately 3-5 times, and vacuum dry at 60-80℃ to obtain manganese ferrite nanoparticles; (2) Disperse the manganese ferrite nanoparticles described in step (1) in 80 mL of anhydrous ethanol, sonicate for 20-30 min to form a suspension for later use, then dissolve tetrabutyl titanate in 20 mL of anhydrous ethanol, stir magnetically for 10-20 min to form a tetrabutyl titanate alcohol solution for later use, then add the tetrabutyl titanate alcohol solution to the suspension at a rate of 1-2 drops / second while stirring at 1000-2000 rpm. After the addition is complete, continue stirring at room temperature for 2-4 h at a stirring speed of 600-800 rpm. Transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene, seal it and place it in an oven, react at 160-180℃ for 8-12 h, cool to room temperature, centrifuge, wash with anhydrous ethanol and deionized water alternately 3-5 times, and vacuum dry at 60-80℃ to obtain manganese ferrite@titanium dioxide nanoparticles; (3) Disperse the manganese ferrite@titanium dioxide nanoparticles described in step (2) in 150 mL of deionized water, add 2.0-2.4 g of cetyltrimethylammonium bromide and 7-9 mL of ammonia water, stir for 20-30 min, then add aluminum chloride, stir for 10-20 min, then add 8-12 mL of tetraethyl orthosilicate, stir for 20-24 h, centrifuge, wash the precipitate, dry at 60-80 °C, and calcine at 500-550 °C for 5-6 h to obtain the manganese ferrite@titanium dioxide@aluminum doped mesoporous silica composite catalyst.

4. The method for preparing biomass fuel based on straw according to claim 3, characterized in that: In step (1), the amounts of ferric chloride hexahydrate and manganese chloride tetrahydrate added are 3.0-5.0g and 2.0-4.0g, respectively.

5. The method for preparing biomass fuel based on straw according to claim 3, characterized in that: In step (2), the amount of tetrabutyl titanate added is 0.5-1.0 mL.

6. The method for preparing biomass fuel based on straw according to claim 3, characterized in that: In step (3), the amount of aluminum chloride added is 1.0-1.8g.

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