High-dispersity fiber composite aerogel fire extinguishing agent and preparation method

Abstract

The invention discloses a high-dispersity fiber composite aerogel fire extinguishing agent and a preparation method. The fire extinguishing agent is prepared from the following components in percentage by mass: 40 to 55 weight percent of SiO2 aerogel base material, 5 to 10 weight percent of aramid nanofiber, 5 to 8 weight percent of expanded graphite, 8 to 12 weight percent of zinc borate, 10 to 15 weight percent of polyimide, 2 to 5 weight percent of methyltrimethoxysilane and 1 to 3 weight percent of nano montmorillonite. The preparation method comprises the steps of aramid nanofiber stripping, expanded graphite pretreatment, polyimide precursor preparation, sol-gel synthesis, aging replacement, supercritical drying and hydrophobic modification. Through cooperation and dispersion optimization of multiple components, the dispersion uniformity, mechanical strength, fire extinguishing efficiency, high temperature resistance and storage stability of the material are improved, the problems of poor dispersion, mechanical brittleness, unstable storage and the like of traditional aerogel are solved, and the whole coal spontaneous combustion process inhibition can be realized through construction in a grouting, spraying or filling mode.

Description

Technical Field

[0001] This invention relates to the field of coal mine fire prevention and extinguishing materials, specifically to a highly dispersible fiber composite aerogel fire extinguishing agent and its preparation method, which is suitable for preventing spontaneous combustion of coal in complex environments such as coal mine goaf areas. Background Technology

[0002] Coal, as a core component of China's energy structure, plays an irreplaceable role in metallurgy, chemical industry, and power generation, and is expected to maintain its dominant energy position for the next two decades. However, the problem of spontaneous combustion of coal has always been a key bottleneck restricting safe production in coal mines. According to statistics, more than 90% of the coal seams in China's large and medium-sized mining areas are flammable or prone to spontaneous combustion. Every year, approximately 200 million tons of coal resources are lost due to spontaneous combustion, and the resulting fires cause numerous casualties and property losses. At the same time, they release toxic and harmful gases such as CO and SO2, seriously polluting the environment.

[0003] Spontaneous combustion of residual coal in coal mine goaf areas is characterized by its concealment, uncertainty, and persistence. Traditional fire prevention and extinguishing methods, such as grouting, inert gas injection, and single inhibitor spraying, have significant limitations. Grouting materials are prone to clogging pipes and have poor water retention; inert gas is prone to leakage, resulting in short-lived extinguishing effects; and single inhibitors are insufficient to suppress spontaneous combustion throughout the entire process and are prone to failure at high temperatures. Therefore, developing a new type of fire prevention and extinguishing material that combines high mechanical strength, good dispersibility, long-lasting fire extinguishing effect, and environmental adaptability has become an urgent need in the field of coal mine safety.

[0004] Aerogels, as novel porous materials with high porosity (80-99.8%) and low thermal conductivity (0.005-0.02 W / (m·K)), have shown great potential in the field of fire prevention and extinguishing. SiO2 aerogels, due to their low preparation cost and excellent thermal insulation properties, have become a research hotspot in mine fire prevention and extinguishing materials. However, traditional SiO2 aerogels suffer from drawbacks such as high mechanical brittleness, poor dispersibility, and susceptibility to moisture absorption and failure, limiting their application in complex underground environments.

[0005] To improve the mechanical properties of aerogels, researchers have attempted to introduce fiber materials for reinforcement. For example, CN109575510B discloses a method for preparing a three-dimensional phenolic resin aerogel material reinforced with nanofiber minerals, including the following steps: (1) activating clay mineral fibers to obtain acid-activated nano-clay mineral fibers; (2) preparing a three-dimensional composite material of nano-clay mineral fibers to obtain a three-dimensional fiber block composite gel material B; (3) impregnating the three-dimensional fiber block composite gel material B with a solution of component C, curing it at 50-120℃ for 30-150 min, then soaking it in an organic solvent, and freeze-drying it under vacuum to obtain a three-dimensional phenolic resin aerogel material reinforced with nano-clay mineral fibers, which can be used for thermal insulation of high-end equipment, or as a catalyst carrier, adsorbent for organic pollutants, etc. CN111849018B discloses a patellae-based flame-retardant gel, comprising a polyaniline / polyvinyl alcohol composite aerogel and a patellae@cellulose nanocrystal composite material in situ incorporated within the composite aerogel. The patellae@cellulose nanocrystal composite material includes two-dimensional patellae and one-dimensional cellulose nanocrystals composited in its interlayer and / or surface. The patellae is pre-modified by self-assembly of cellulose nanocrystals, followed by in-situ polymerization of aniline and cross-doping modification with PVA, and finally freeze-drying to obtain the flame-retardant gel, which exhibits excellent mechanical and flame-retardant properties. However, the following problems still exist in coal mining environments: insufficient compatibility between fibers and the aerogel matrix leads to uneven dispersion; a lack of responsive fire extinguishing mechanisms targeting the spontaneous combustion temperature range of coal; and easy degradation of fibers at high temperatures, making it difficult to maintain a long-term fire extinguishing effect.

[0006] Expanded graphite (EG), as a highly efficient and environmentally friendly flame retardant material, can expand at high temperatures to form a dense carbon layer, which plays a role in heat insulation and oxygen barrier, and is widely used in composite fire protection and extinguishing materials. For example, CN118272100A discloses a flame-retardant gel, which includes an expanded graphite skeleton and a first functional layer covering the surface of the expanded graphite skeleton; the surface of the expanded graphite skeleton not covered by the first functional layer and the surface of the first functional layer are also covered by a second functional layer; the first functional layer includes polyaniline, and the second functional layer includes polymer nanofibers. This flame-retardant gel has a porous network skeleton structure, a low thermal conductivity, and a low packing density. By using a combination of expanded graphite skeleton, polyaniline coating layer and polymer nanofibers in the flame-retardant material to form a porous network structure, the problem of easy flame spread in existing flame-retardant materials is solved, and the flame-retardant effect and mechanical strength are significantly improved. CN114957991B discloses a biomass-derived cellulose aerogel material for fire doors, which is obtained by grafting flame-retardant polymers onto graphene oxide-cellulose aerogel and then performing in-situ polymerization of polyamic acid. Ammonium polyphosphate is anchored to the surface of graphene oxide through electrostatic attraction and other weak interactions. Ammonium polyphosphate can catalyze the char formation rate during the decomposition process of aerogel materials. Due to the unique 3D network framework structure of the aerogel and the ammonium polyphosphate-modified graphene oxide, the prepared biomass-derived cellulose aerogel materials exhibit excellent mechanical and fire-retardant properties. However, existing intumescent flame-retardant-aerogel composite systems have the following shortcomings: expanded graphite is prone to agglomeration in the aerogel, affecting the dispersion uniformity; the release rate of the flame-retardant component is uncontrollable, making it difficult to match the needs of different stages of coal spontaneous combustion; and the lack of strong interaction with the aerogel matrix makes it easy to detach, leading to a decrease in fire extinguishing effect. Polyimide (PI) has excellent high-temperature resistance (temperature resistance > 500℃), mechanical strength, and chemical stability, and is widely used in the field of high-performance composite materials. However, there is limited research on the use of polyimide in mining aerogel fire extinguishing agents. Existing technologies have not fully utilized the crosslinking properties of polyimide to solve the dispersion and stability problems of aerogels, and have not achieved the synergistic effect of polyimide with intumescent flame retardancy and fiber reinforcement.

[0007] Furthermore, aerogels lose their porous structure after absorbing moisture, leading to a significant decrease in their thermal insulation and fire extinguishing performance. Existing hydrophobic modification technologies mainly modify the aerogel surface using silane coupling agents. However, the high humidity and dust levels in mining environments mean that the hydrophobic durability of existing modification technologies is insufficient. Aerogels are still prone to moisture absorption and failure after long-term storage, and the modification process may affect the pore structure of the aerogel and the loading of fire extinguishing components.

[0008] Based on the current state of research in this field, aerogel fire extinguishing materials for mining still suffer from several drawbacks. Firstly, traditional SiO2 aerogels are brittle and prone to breakage during coal mine goaf collapses and transportation, making it difficult to form a continuous fire extinguishing network. Secondly, fiber-reinforced systems exhibit poor compatibility between fibers and the aerogel matrix, resulting in uneven dispersion and hindering effective material strength enhancement. Thirdly, poor dispersibility leads to the agglomeration of expanded graphite and fire extinguishing components within the aerogel, resulting in uneven fire extinguishing effects and limited effectiveness in certain areas. Finally, poor storage stability is a concern, as moisture absorption disrupts the aerogel's pore structure, causing the loss of fire extinguishing components and significant performance degradation over long-term storage, thus limiting its long-term use underground. Summary of the Invention

[0009] The purpose of this invention is to overcome the technical bottlenecks of existing mine aerogel fire extinguishing materials, such as high mechanical brittleness, poor dispersibility, insufficient fire extinguishing duration, limited high-temperature resistance, and poor storage stability. This invention provides a highly dispersible fiber composite aerogel fire extinguishing agent and its preparation method. The highly dispersible fiber composite aerogel fire extinguishing agent comprises the following components by mass percentage:

[0010] SiO2 aerogel substrate: 40-55 wt%; Aramid nanofibers (ANF): 5-12 wt% Expanded graphite (EG): 5-12 wt% Zinc borate (ZB): 8-12 wt% Polyimide (PI): 10-15 wt% Methyltrimethoxysilane (MTMS): 2-10 wt% Nano-montmorillonite: 1-3 wt%.

[0011] By combining fiber reinforcement with polyimide crosslinking to form a composite structure, the mechanical brittleness of traditional aerogels is improved, enhancing the material's compressive and impact resistance, thus meeting the transportation and usage requirements of complex working conditions such as coal mine goaf areas. Simultaneously, the expanded graphite-zinc borate synergistic flame-retardant system and the thermal insulation properties of SiO2 aerogel are further constructed to achieve a full-process fire extinguishing effect, including initial cooling of coal spontaneous combustion, mid-term thermal and oxygen insulation, and suppression of reignition. This comprehensively improves the material's high-temperature resistance and storage stability, solves the problem of material agglomeration and sedimentation in complex aerogel fire extinguishing agents, improves material dispersion uniformity, ensures consistent fire extinguishing effect, avoids moisture absorption failure, meets the requirements for long-term underground storage, and the raw materials are non-toxic and do not cause secondary pollution. The prepared aerogel fire extinguishing agent can be applied through various methods such as grouting and spraying, making it suitable for applications in complex coal mine scenarios.

[0012] One object of the present invention is to provide a highly dispersible fiber composite aerogel fire extinguishing agent, comprising the following components by weight percentage: SiO2 aerogel substrate: 40-55 wt%; Aramid nanofibers (ANF): 5-12 wt% Expanded graphite (EG): 5-12 wt% Zinc borate (ZB): 8-12 wt% Polyimide (PI): 10-15 wt% Methyltrimethoxysilane (MTMS): 2-10 wt% Nano-montmorillonite: 1-3 wt%.

[0013] Furthermore, the aramid nanofibers are prepared from poly(p-phenylene terephthalamide) (PPTA) fibers by chemical exfoliation with methanesulfonic acid, with a length of 100-500 nm and a diameter of 5-20 nm; the expanded graphite is expanded at 850-900 °C, with a particle size of 10-50 μm; and the polyimide is formed by in-situ polymerization of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA).

[0014] Furthermore, the SiO2 aerogel substrate has a porosity of 85-95% and a thermal conductivity of ≤0.025W / (m·K).

[0015] Furthermore, in the preparation process of the aramid nanofibers, the mass ratio of poly(p-phenylene terephthalamide) fiber to methanesulfonic acid is 1:40-1:60, the chemical exfoliation temperature is 50-60℃, and the exfoliation time is 4-6 days.

[0016] Furthermore, the expanded graphite is pretreated by the following method: the expandable graphite is expanded at a high temperature of 850-900℃ for 30-60s, crushed and passed through a 300-1000 mesh sieve, then immersed in a 1-3wt% silane coupling agent KH-550 ethanol solution, stirred at 50-60℃ for 1-2h, and dried for later use.

[0017] Furthermore, the monomer molar ratio of the polyimide is 4,4'-diaminodiphenyl ether (ODA):pyromellitic dianhydride = 1:1.02-1:1.05, and the concentration of the polyimide precursor solution is 12-18 wt%.

[0018] Another object of the present invention is to provide a method for preparing a highly dispersible fiber composite aerogel fire extinguishing agent, comprising the following steps: (1) Preparation of aramid nanofibers (ANF) Poly(p-phenylene terephthalamide) (PPTA) fibers were immersed in methanesulfonic acid at a mass ratio of 1:40 to 1:60. The mixture was then chemically exfoliated by stirring at 50-60°C for 4-6 days to obtain a dispersion of aramid nanofibers with a mass fraction of 2-3%, which was then set aside for later use. (2) Pretreatment of expanded graphite (EG) Expandable graphite is expanded at 850-900℃ for 30-60 seconds, pulverized and passed through a 300-1000 mesh sieve; the expanded graphite is immersed in a 1-3wt% silane coupling agent KH-550 ethanol solution, stirred at 50-60℃ for 1-2 hours, and then dried for later use. (3) Preparation of polyimide precursor (PAA) 4,4'-Diaminodiphenyl ether (ODA) and N,N-dimethylacetamide were mixed and stirred until completely dissolved. The mixture was then cooled to 0-5°C in an ice bath. Pyromellitic dianhydride was slowly added, with the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride being 1:1.02-1:1.05. The mixture was stirred for 2-4 hours to obtain a polyimide precursor solution with a mass fraction of 12-18 wt%. (4) Preparation of SiO2 sol Tetraethyl orthosilicate (TEOS), ethanol, and deionized water are mixed in a molar ratio of 1:2:2.5-1:3:3. Hydrochloric acid is added to adjust the pH to 2-3, and the mixture is hydrolyzed at 70-80℃ for 1-1.5 hours to obtain SiO2 sol. (5) Cogel synthesis Weigh the raw materials obtained in steps 1-4 according to the proportion, add 5-12% expanded graphite, 8-12% zinc borate and 1-3% nano montmorillonite by mass of aerogel to SiO2 sol, and ultrasonically disperse for 20-30 minutes. Continue adding aramid nanofiber dispersion, with the aramid nanofibers accounting for 5-12% of the aerogel mass. Stir mechanically for 30-40 minutes to form a uniform dispersion system. Slowly add the polyimide precursor solution to the obtained uniform dispersion system, with the amount of polyimide added calculated as 10-15% of the aerogel mass. Stir for 20-30 min, add ammonia water to adjust the pH to 7.5-8.5, and let the gel stand at room temperature for 12-24 h to obtain the cogel. (6) Aging and solvent replacement The cogel was aged in an oven at 80-90℃ for 8-12 hours, and then replaced with anhydrous ethanol 3-4 times, each time for 6-8 hours, to remove moisture and residual solvent from the system. (7) Drying treatment The solvent-displaced cogel was dried by supercritical CO2 at a temperature of 35-45℃, a pressure of 8-12MPa, and a time of 24-36h to obtain a composite aerogel intermediate. (8) Hydrophobic modification The composite aerogel intermediate was immersed in a methyltrimethoxysilane ethanol solution and stirred at 50-60℃ for 2-3 hours. After being removed, it was dried at 80-100℃ for 2-4 hours to obtain the composite aerogel fire extinguishing agent.

[0019] Furthermore, in step (5), the power of ultrasonic dispersion is 300-500W, and the speed of mechanical stirring is 600-800r / min.

[0020] Furthermore, in step (7), the heating rate of the supercritical CO2 drying is 1-2℃ / min, and the depressurization rate is 0.5-1MPa / h; in step (8), the volume fraction of the methyltrimethoxysilane ethanol solution is 50-60%.

[0021] Another objective of this invention is to provide an application of a highly dispersible fiber composite aerogel fire extinguishing agent in coal mine fire prevention and extinguishing. The fire extinguishing agent can be applied to the goaf or roadway area of ​​a coal mine by grouting, spraying or filling to suppress spontaneous combustion of coal and extinguish coal mine fires.

[0022] The beneficial effects of this invention include: 1. Significantly improves the dispersion stability of aerogel fire extinguishing agents. Through multiple dispersion optimization designs, the problem of functional component agglomeration is completely solved: Nano-montmorillonite is used as a dispersion stabilizer, which, together with ultrasonic dispersion and high-speed mechanical stirring, effectively inhibits the agglomeration of aramid nanofibers and expanded graphite; The expanded graphite, after being modified by KH-550 silane coupling agent, introduces amino groups on its surface, forming chemical bonds with SiO2 aerogel and polyimide, improving its compatibility with the matrix and avoiding secondary agglomeration during storage and use; The powder spraying dispersion radius is increased by more than 67% compared with traditional materials, which can uniformly cover the surface of coal residue in the goaf, eliminate fire extinguishing dead zones, and ensure that local areas can play a role in heat insulation and fire extinguishing.

[0023] 2. Significantly enhanced mechanical properties: By constructing a plant root-soil-inspired interlocking structure of aramid nanofibers and polyimide, the brittleness of the aerogel is significantly improved. The high aspect ratio of ANF penetrates the aerogel matrix, and the in-situ polymerization of polyimide forms a three-dimensional cross-linked network, firmly locking the components together. This increases the compressive strength of the material to over 1.5 MPa, which is 200% higher than that of traditional SiO2 aerogels. The bending deformation rate reaches 30%, which can withstand the impact of underground transportation and slight roof collapse, and is not easily broken. The strong interfacial bonding between the fiber and the matrix prevents the components from falling off. The impact strength of the falling ball is 68% higher than that of existing composite aerogels, ensuring the continuity of the fire extinguishing network.

[0024] 3. Fire extinguishing performance is comprehensively optimized. The synergistic flame retardant system of expanded graphite and zinc borate, combined with the thermal insulation properties of SiO2 aerogel, achieves highly efficient fire extinguishing throughout the entire process: Expanded graphite expands at high temperatures to form a dense char layer, zinc borate decomposes to absorb heat and cool down, and produces boron oxide glassy substances to enhance the stability of the char layer. In conjunction with the low thermal conductivity of the aerogel, heat transfer is effectively blocked, and the peak heat release rate of the coal gas is reduced by more than 79% compared with the original coal sample; the uniform dispersion of the fire extinguishing components allows the flame retardant, thermal insulation and cooling effects to work synergistically, with no reignition phenomenon, and the fire resistance limit is significantly improved, which can cover the protection needs of coal spontaneous combustion in the entire temperature range of 60-1200℃.

[0025] 4. Significantly improved high-temperature resistance and storage stability: Through component optimization and modification, the material's environmental adaptability is enhanced. The high-temperature resistance of polyimide, combined with the stable char layer formed by the synergistic flame-retardant system, increases the material's temperature resistance limit to over 1200℃. At 800℃ for 2 hours, the mass loss is only 8.5%, and at 1000℃ for 1 hour, the structure remains intact without collapse, adapting to the high-temperature environment of the later stages of coal spontaneous combustion. The hydrophobic modification of methyltrimethoxysilane forms a dense hydrophobic layer on the aerogel surface, with a water absorption rate ≤3%. After 6 months of storage, the porosity retention rate is ≥89%, and the compressive strength decay rate is only 8.3%, solving the problem of moisture absorption failure in traditional aerogels and meeting the requirements for long-term underground storage.

[0026] 5. All material components are inorganic or environmentally friendly organic modified materials, with no toxic or harmful components. No secondary polluting gases are generated during combustion. The emission of toxic gases such as CO and SO2 is reduced by more than 60% compared with traditional materials, and it does not corrode underground metal equipment. In addition, the material can be constructed by grouting, spraying or filling. There is no pipe blockage during grouting, uniform dispersion during spraying, and it can adapt to irregular goaf terrain during filling. Construction is flexible and convenient, and it can meet the fire prevention and extinguishing needs of different scenarios in coal mines. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein. The reagents used herein may be commercially available related products, and performance testing standards refer to industry or national standards.

[0029] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0030] The features and performance of this application will be further described in detail below with reference to embodiments: Example 1 A highly dispersible fiber-reinforced aerogel fire extinguishing agent comprises the following components: The substrate consists of 47 wt% SiO2 aerogel, 10 wt% aramid nanofibers, 8 wt% expanded graphite, 12 wt% zinc borate, 15 wt% polyimide, 5 wt% methyltrimethoxysilane, and 3 wt% nano-montmorillonite, wherein the SiO2 aerogel substrate has a porosity of 85-95% and a thermal conductivity ≤0.025 W / (m·K).

[0031] The highly dispersible fiber composite aerogel fire extinguishing agent is prepared using the following method: (1) Preparation of aramid nanofibers Poly(p-phenylene terephthalamide) fibers were immersed in methanesulfonic acid at a mass ratio of 1:50. The mixture was then chemically exfoliated by stirring at 55°C for 5 days to obtain a 2.5% (w / w) aramid nanofiber dispersion. The aramid nanofibers had a length of 100-500 nm and a diameter of 5-20 nm. The dispersion was then set aside for later use. (2) Pretreatment of expanded graphite Expandable graphite is expanded at 880℃ for 40 seconds, pulverized and passed through a 350-mesh sieve; the expanded graphite is immersed in a 2wt% silane coupling agent KH-550 ethanol solution, stirred at 55℃ for 1.5 hours, and then dried for later use. (3) Preparation of polyimide precursor 4,4'-diaminodiphenyl ether was mixed with N,N-dimethylacetamide and stirred until completely dissolved. The mixture was then cooled to 3°C in an ice bath, and pyromellitic dianhydride was slowly added. The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride was 1:1.03. The mixture was stirred for 3 hours to obtain a polyimide precursor solution with a mass fraction of 15 wt%. (4) Preparation of SiO2 sol Tetraethyl orthosilicate, ethanol, and deionized water were mixed in a molar ratio of 1:2.8:2.9, and hydrochloric acid was added to adjust the pH to 2.5. The mixture was then hydrolyzed at 75°C for 1.2 h to obtain SiO2 sol. (5) Cogel synthesis Weigh the raw materials obtained in steps 1-4 and other raw materials in proportion, add expanded graphite, zinc borate and nano montmorillonite to SiO2 sol, and ultrasonically disperse at 400W for 25min; Continue adding the aramid nanofiber dispersion and mechanically stir at 700 r / min for 35 min to form a uniform dispersion system; Slowly add the polyimide precursor solution to the obtained uniform dispersion system, mechanically stir at 700 r / min for 25 min, add ammonia to adjust the pH to 8, and let the gel stand at room temperature for 18 h to obtain a cogel. (6) Aging and solvent replacement The cogel was aged in an 85°C oven for 10 hours, and then replaced with anhydrous ethanol three times for 7 hours each time to remove water and residual solvent from the system. (7) Drying treatment The solvent-displaced cogel was dried using supercritical CO2 at a temperature of 40°C, a pressure of 10 MPa, and a drying time of 30 h to obtain a composite aerogel intermediate. The heating rate during drying was 1.5°C / min, and the depressurization rate was 0.8 MPa / h. (8) Hydrophobic modification The composite aerogel intermediate was immersed in a methyltrimethoxysilane ethanol solution with a volume fraction of 55%, stirred at 55°C for 2.5 h, and then dried at 90°C for 3 h to obtain the composite aerogel fire extinguishing agent.

[0032] The prepared composite aerogel fire extinguishing agent was tested, and the measured distribution deviation of its extinguishing components was 5.2%, its compressive strength was 2 MPa, its flexural deformation rate was 35%, and its peak heat release rate from the gas was 10.8 kW / m³. 2 The CO production at 180℃ is 195ppm, the temperature resistance limit is 1250℃, the mass loss after 2 hours of heat treatment at 800℃ is 7.5%, the porosity after 6 months of storage is 85%, the water absorption rate after 6 months of storage is 2.8%, and the powder spray dispersion radius is 6m.

[0033] Example 2 A highly dispersible fiber-reinforced aerogel fire extinguishing agent comprises the following components: The composition of the SiO2 aerogel substrate is as follows: 55wt% SiO2 aerogel substrate; 12wt% aramid nanofibers; 10wt% expanded graphite; 8wt% zinc borate; 10wt% polyimide; 4wt% methyltrimethoxysilane; and 1wt% nano-montmorillonite. The porosity of the SiO2 aerogel substrate is 87-95%, and the thermal conductivity is ≤0.025W / (m·K).

[0034] The highly dispersible fiber composite aerogel fire extinguishing agent is prepared using the following method: (1) Preparation of aramid nanofibers Poly(p-phenylene terephthalamide) fibers were immersed in methanesulfonic acid at a mass ratio of 1:60. The mixture was then chemically exfoliated by stirring at 60°C for 4 days to obtain a 3% (w / w) aramid nanofiber dispersion. The aramid nanofibers had a length of 100-500 nm and a diameter of 5-20 nm. The dispersion was then set aside for later use. (2) Pretreatment of expanded graphite Expandable graphite is expanded at 900℃ for 30 seconds, pulverized and passed through a 1000-mesh sieve; the expanded graphite is immersed in a 3wt% silane coupling agent KH-550 ethanol solution, stirred at 60℃ for 1 hour, and then dried for later use. (3) Preparation of polyimide precursor 4,4'-diaminodiphenyl ether was mixed with N,N-dimethylacetamide and stirred until completely dissolved. The mixture was then cooled to 0°C in an ice bath, and pyromellitic dianhydride was slowly added. The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride was 1:1.05. The mixture was stirred for 4 hours to obtain a polyimide precursor solution with a mass fraction of 12 wt%. (4) Preparation of SiO2 sol Tetraethyl orthosilicate, ethanol, and deionized water were mixed in a molar ratio of 1:2:3, and hydrochloric acid was added to adjust the pH to 3. The mixture was then hydrolyzed at 80°C for 1.5 hours to obtain SiO2 sol. (5) Cogel synthesis Weigh the raw materials obtained in steps 1-4 and other raw materials in proportion, add expanded graphite, zinc borate and nano montmorillonite to SiO2 sol, and ultrasonically disperse at 500W for 20min; Continue adding aramid nanofiber dispersion, and mechanically stir at 600 r / min for 40 min to form a uniform dispersion system; The polyimide precursor solution was slowly added to the obtained uniform dispersion system, mechanically stirred at 800 r / min for 20 min, ammonia was added to adjust the pH to 8.5, and the gel was allowed to stand at room temperature for 24 h to obtain a cogel. (6) Aging and solvent replacement The cogel was aged in a 90°C oven for 12 hours, and then replaced with anhydrous ethanol four times for 8 hours each time to remove water and residual solvent from the system. (7) Drying treatment The solvent-displaced cogel was dried using supercritical CO2 at a temperature of 45°C, a pressure of 12 MPa, and a drying time of 24 h to obtain a composite aerogel intermediate. The heating rate during drying was 2°C / min, and the depressurization rate was 1 MPa / h. (8) Hydrophobic modification The composite aerogel intermediate was immersed in a methyltrimethoxysilane ethanol solution with a volume fraction of 60%, stirred at 50°C for 3 hours, and then dried at 100°C for 2 hours to obtain the composite aerogel fire extinguishing agent.

[0035] The prepared composite aerogel fire extinguishing agent was tested, and the measured distribution deviation of its extinguishing components was 7%, its compressive strength was 1.3 MPa, its flexural deformation rate was 22%, and its peak heat release rate from the gas was 13.2 kW / m³. 2 The CO production at 180℃ is 240ppm, the temperature resistance limit is 1200℃, the mass loss after 2 hours of heat treatment at 800℃ is 8.7%, the porosity after 6 months of storage is 81%, the water absorption rate after 6 months of storage is 3.2%, and the powder spray dispersion radius is 5.1m.

[0036] Example 3 A highly dispersible fiber-reinforced aerogel fire extinguishing agent comprises the following components: The composition of the SiO2 aerogel substrate is as follows: 50 wt%; aramid nanofibers: 5 wt%; expanded graphite: 9 wt%; zinc borate: 12 wt%; polyimide: 12 wt%; methyltrimethoxysilane: 10 wt%; nano-montmorillonite: 2 wt%, wherein the porosity of the SiO2 aerogel substrate is 87-92% and the thermal conductivity is ≤0.025 W / (m·K).

[0037] The highly dispersible fiber composite aerogel fire extinguishing agent is prepared using the following method: (1) Preparation of aramid nanofibers Poly(p-phenylene terephthalamide) fibers were immersed in methanesulfonic acid at a mass ratio of 1:40. The mixture was then chemically exfoliated by stirring at 50°C for 6 days to obtain a 2% (w / w) aramid nanofiber dispersion. The aramid nanofibers had a length of 100-500 nm and a diameter of 5-20 nm. The dispersion was then set aside for later use. (2) Pretreatment of expanded graphite Expandable graphite is expanded at 850℃ for 60 seconds, pulverized and passed through a 700-mesh sieve; the expanded graphite is immersed in a 1wt% silane coupling agent KH-550 ethanol solution, stirred at 50℃ for 2 hours, and then dried for later use. (3) Preparation of polyimide precursor 4,4'-diaminodiphenyl ether was mixed with N,N-dimethylacetamide and stirred until completely dissolved. The mixture was then cooled to 5°C in an ice bath, and pyromellitic dianhydride was slowly added. The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride was 1:1.02. The mixture was stirred for 2 hours to obtain a polyimide precursor solution with a mass fraction of 18 wt%. (4) Preparation of SiO2 sol Tetraethyl orthosilicate, ethanol, and deionized water were mixed in a molar ratio of 1:3:2.5, and hydrochloric acid was added to adjust the pH to 2. The mixture was then hydrolyzed at 70°C for 1 hour to obtain SiO2 sol. (5) Cogel synthesis Weigh the raw materials obtained in steps 1-4 and other raw materials in proportion, add expanded graphite, zinc borate and nano montmorillonite to SiO2 sol, and ultrasonically disperse at 300W for 30min; Continue adding the aramid nanofiber dispersion and mechanically stir at 800 r / min for 30 min to form a uniform dispersion system; The polyimide precursor solution was slowly added to the obtained uniform dispersion system, mechanically stirred at 600 r / min for 30 min, ammonia was added to adjust the pH to 7.5, and the gel was allowed to stand at room temperature for 12 h to obtain a cogel. (6) Aging and solvent replacement The cogel was aged in an 80°C oven for 8 hours, and then replaced with anhydrous ethanol three times for 6 hours each time to remove water and residual solvent from the system. (7) Drying treatment The solvent-displaced cogel was dried using supercritical CO2 at a temperature of 35°C, a pressure of 8 MPa, and a drying time of 36 h to obtain a composite aerogel intermediate. The heating rate during drying was 1°C / min, and the depressurization rate was 0.5 MPa / h. (8) Hydrophobic modification The composite aerogel intermediate was immersed in a methyltrimethoxysilane ethanol solution with a volume fraction of 50%, stirred at 60°C for 2 hours, and then dried at 80°C for 4 hours to obtain the composite aerogel fire extinguishing agent.

[0038] The prepared composite aerogel fire extinguishing agent was tested, and the measured distribution deviation of its extinguishing components was 6.3%, its compressive strength was 1.6 MPa, its flexural deformation rate was 28%, and its peak heat release rate from the gas was 11.5 kW / m³. 2 The CO production at 180℃ is 210ppm, the temperature resistance limit is 1220℃, the mass loss after 2 hours of heat treatment at 800℃ is 8.1%, the porosity after 6 months of storage is 83%, the water absorption rate after 6 months of storage is 3.0%, and the powder spray dispersion radius is 5.7m.

[0039] Comparative Example 1 A composite aerogel fire extinguishing agent comprises the following components: The composition of the SiO2 aerogel substrate is as follows: 50 wt%; aramid nanofibers: 10 wt%; expanded graphite: 8 wt%; zinc borate: 12 wt%; polyimide: 15 wt%; methyltrimethoxysilane: 5 wt%, wherein the porosity of the SiO2 aerogel substrate is 85-95% and the thermal conductivity is ≤0.025 W / (m·K).

[0040] The preparation method is exactly the same as in Example 1, except that no nano-montmorillonite is added.

[0041] The prepared composite aerogel fire extinguishing agent was tested, and the measured distribution deviation of its extinguishing components was 20.8%, its compressive strength was 1.1 MPa, its flexural deformation rate was 18%, and its peak heat release rate from the gas was 17.6 kW / m³. 2 The powder spray dispersion radius is 3.1m.

[0042] Comparative Example 2 A composite aerogel fire extinguishing agent comprises the following components: The substrate consists of 62 wt% SiO2 aerogel, 10 wt% aramid nanofibers, 8 wt% expanded graphite, 12 wt% zinc borate, and 5 wt% methyltrimethoxysilane, wherein the SiO2 aerogel substrate has a porosity of 85-95% and a thermal conductivity ≤0.025 W / (m·K).

[0043] The composite aerogel fire extinguishing agent is prepared using the following method: (1) Preparation of aramid nanofibers Poly(p-phenylene terephthalamide) fibers were immersed in methanesulfonic acid at a mass ratio of 1:50. The mixture was then chemically exfoliated by stirring at 55°C for 5 days to obtain a 2.5% (w / w) aramid nanofiber dispersion. The aramid nanofibers had a length of 100-500 nm and a diameter of 5-20 nm. The dispersion was then set aside for later use. (2) Pretreatment of expanded graphite Expandable graphite is expanded at 880℃ for 40 seconds, pulverized and passed through a 350-mesh sieve; the expanded graphite is immersed in a 2wt% silane coupling agent KH-550 ethanol solution, stirred at 55℃ for 1.5 hours, and then dried for later use. (3) Preparation of SiO2 sol Tetraethyl orthosilicate, ethanol, and deionized water were mixed in a molar ratio of 1:2.8:2.9, and hydrochloric acid was added to adjust the pH to 2.5. The mixture was then hydrolyzed at 75°C for 1.2 h to obtain SiO2 sol. (4) Cogel synthesis Weigh the raw materials obtained in steps 1-3 and other raw materials in proportion, add expanded graphite, zinc borate and nano montmorillonite to SiO2 sol, and ultrasonically disperse at 400W for 25min. Continue adding aramid nanofiber dispersion, mechanically stir at 700 r / min for 35 min to form a uniform dispersion system, add ammonia to adjust pH to 8, and let gel stand at room temperature for 18 h to obtain cogel; (5) Aging and solvent replacement The cogel was aged in an 85°C oven for 10 hours, and then replaced with anhydrous ethanol three times for 7 hours each time to remove water and residual solvent from the system. (6) Drying treatment The solvent-displaced cogel was dried using supercritical CO2 at a temperature of 40°C, a pressure of 10 MPa, and a drying time of 30 h to obtain a composite aerogel intermediate. The heating rate during drying was 1.5°C / min, and the depressurization rate was 0.8 MPa / h. (7) Hydrophobic modification The composite aerogel intermediate was immersed in a methyltrimethoxysilane ethanol solution with a volume fraction of 55%, stirred at 55°C for 2.5 h, and then dried at 90°C for 3 h to obtain the composite aerogel fire extinguishing agent.

[0044] The prepared composite aerogel fire extinguishing agent was tested, and the measured distribution deviation of its extinguishing components was 18.5%, its compressive strength was 0.7 MPa, its flexural deformation rate was 9%, and its peak heat release rate from the gas was 19.2 kW / m³. 2 Temperature resistance limit is 920℃. Partial collapse occurred after holding at 950℃ for 1 hour. Porosity is 68% after 6 months of storage.

[0045] Comparative Example 3 A composite aerogel fire extinguishing agent comprises the following components: The substrate consists of 47 wt% SiO2 aerogel, 10 wt% aramid nanofibers, 8 wt% expanded graphite, 12 wt% zinc borate, 15 wt% polyimide, 5 wt% methyltrimethoxysilane, and 3 wt% nano-montmorillonite, wherein the SiO2 aerogel substrate has a porosity of 85-95% and a thermal conductivity ≤0.025 W / (m·K).

[0046] The composite aerogel fire extinguishing agent is prepared using the following method: (1) Preparation of aramid nanofibers Poly(p-phenylene terephthalamide) fibers were immersed in methanesulfonic acid at a mass ratio of 1:50. The mixture was then chemically exfoliated by stirring at 55°C for 5 days to obtain a 2.5% (w / w) aramid nanofiber dispersion. The aramid nanofibers had a length of 100-500 nm and a diameter of 5-20 nm. The dispersion was then set aside for later use. (2) Pretreatment of expanded graphite Expandable graphite is expanded at 880℃ for 40 seconds, pulverized and passed through a 350-mesh sieve; the expanded graphite is immersed in a 2wt% silane coupling agent KH-550 ethanol solution, stirred at 55℃ for 1.5 hours, and then dried for later use. (3) Preparation of polyimide precursor 4,4'-diaminodiphenyl ether was mixed with N,N-dimethylacetamide and stirred until completely dissolved. The mixture was then cooled to 3°C in an ice bath, and pyromellitic dianhydride was slowly added. The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride was 1:1.03. The mixture was stirred for 3 hours to obtain a polyimide precursor solution with a mass fraction of 15 wt%. (4) Preparation of SiO2 sol Tetraethyl orthosilicate, ethanol, and deionized water were mixed in a molar ratio of 1:2.8:2.9, and hydrochloric acid was added to adjust the pH to 2.5. The mixture was then hydrolyzed at 75°C for 1.2 h to obtain SiO2 sol. (5) Cogel synthesis Weigh the raw materials obtained in steps 1-4 and other raw materials in proportion, add expanded graphite, zinc borate, methyltrimethoxysilane and nano-montmorillonite to SiO2 sol, and ultrasonically disperse at 400W for 25min. Continue adding the aramid nanofiber dispersion and mechanically stir at 700 r / min for 35 min to form a uniform dispersion system; Slowly add the polyimide precursor solution to the obtained uniform dispersion system, mechanically stir at 700 r / min for 25 min, add ammonia to adjust the pH to 8, and let the gel stand at room temperature for 18 h to obtain a cogel. (6) Aging and solvent replacement The cogel was aged in an 85°C oven for 10 hours, and then replaced with anhydrous ethanol three times for 7 hours each time to remove water and residual solvent from the system. (7) Drying treatment The solvent-displaced cogel was subjected to supercritical CO2 drying at a temperature of 40℃, a pressure of 10MPa, and a drying time of 30h to obtain a composite aerogel intermediate. The composite aerogel fire extinguishing agent was obtained by heating at a rate of 1.5℃ / min and depressurizing at a rate of 0.8MPa / h during drying.

[0047] The prepared composite aerogel fire extinguishing agent was tested, and the measured distribution deviation of its extinguishing components was 5.5%, its compressive strength was 1.9 MPa, its flexural deformation rate was 34%, and its peak heat release rate from the gas was 11.2 kW / m³. 2 The CO production at 180℃ is 195 ppm, the temperature resistance limit is 1250℃, the mass loss after holding at 800℃ for 2 hours is 7.5%, the porosity after 6 months of storage is 54%, the water absorption rate after 6 months of storage is 17.3%, the compressive strength after 6 months of storage is 0.8 MPa, and the peak heat release rate of the gas after storage is 19.5 kW / m³. 2 .

[0048] Comparative Example 4 Traditional SiO2 aerogel fire extinguishing agents have the following composition: SiO2 aerogel substrate: 85wt%; expanded graphite: 7wt%; zinc borate (ZB): 8wt%.

[0049] The aerogel was prepared using the traditional sol-gel method: SiO2 sol was prepared by TEOS hydrolysis, expanded graphite and zinc borate were added, stirred evenly, gelled, aged at 85℃ for 10 h, and dried under ordinary vacuum (60℃, -0.09MPa, 24 h). The prepared aerogel fire extinguishing agent was tested, and the measured distribution deviation of the fire extinguishing components was 24.6%, the compressive strength was 0.32 MPa, the flexural deformation rate was 4%, and the peak heat release rate of the gas coal was 24.5 kW / m³. 2 Temperature resistance limit 760℃, porosity 42% after 6 months of storage, water absorption rate 19.5% after 6 months of storage, and powder spray dispersion radius 2.7m.

[0050] As can be seen from Examples 1-3 and Comparative Examples 1 and 4, the distribution deviation of Examples 1-3 is only 5.2%-7.0%, while that of Comparative Example 1 (lacking nano-montmorillonite) reaches 20.8%, and that of Comparative Example 4 (traditional aerogel) reaches 24.6%, proving that the lamellar barrier and steric hindrance of nano-montmorillonite can effectively inhibit agglomeration. Comparing the powder spraying dispersion radius of Examples 1 and Comparative Examples 1 and 4, it shows that the dispersion system can ensure uniform coverage of residual coal in the goaf and eliminate fire extinguishing dead zones. Comparing the compressive strength of Examples 1 and Comparative Examples 2 and 4, it shows that the composite aerogel can meet the mechanical requirements of complex underground working conditions. The bending deformation rate of Example 1 reaches 35%, which is significantly improved compared to 9% of Comparative Example 2 and significantly improved compared to 4% of traditional aerogel, indicating that the material toughness is significantly improved and it is not easy to break. Examples 1-3 have intact structures after being kept at 1000℃ for 1 hour, while Comparative Example 2 partially collapses at 950℃, proving that the cross-linking effect of polyimide can enhance structural stability and ensure the continuity of the fire extinguishing network. The peak heat release rates of Examples 1 and Comparative Examples 1 and 4 show that the combustion intensity was effectively suppressed. Furthermore, no reignition occurred in Examples 1-3, while traditional aerogels, due to the easy detachment of the char layer, pose a risk of reignition. This demonstrates that the synergistic system can cover the entire temperature range of 60-1200℃ for coal spontaneous combustion, achieving full-process fire suppression. Example 1 has a temperature resistance limit of 1250℃, a 35.9% improvement over Comparative Example 2's 920℃ and a 64.5% improvement over traditional aerogels' 760℃, making it suitable for the high-temperature environment in the later stages of coal spontaneous combustion. Example 1 experienced only a 7.5% mass loss after being kept at 800℃ for 2 hours, a 58.8% reduction compared to Comparative Example 2, indicating slow decomposition of the material at high temperatures. Examples 1-3 showed no collapse after being kept at 1000℃ for 1 hour, while Comparative Example 2 showed partial collapse at 950℃, demonstrating that the cross-linked network of polyimide and the stable char layer can synergistically maintain structural integrity at high temperatures. Example 1, after 6 months of storage, showed a water absorption rate of only 2.8%, a reduction of 83.8% compared to Comparative Example 3 (lacking hydrophobic modification) and 85.6% compared to traditional aerogels, indicating effective suppression of moisture absorption. Example 1 also showed a porosity of 85% after 6 months of storage, an increase of 57.4% compared to Comparative Example 3 and 102.4% compared to traditional aerogels, ensuring no decrease in heat insulation and fire extinguishing function. Comparing the strength degradation of Example 1 and Comparative Example 3, it can be seen that hydrophobic modification and cross-linking networks synergistically improve storage stability. The test results of Examples 1-3, compared to Comparative Examples 1-4, demonstrate that the solution of this invention can solve the technical problems of poor dispersion, mechanical brittleness, insufficient fire extinguishing duration, limited high-temperature resistance, and unstable storage of traditional aerogels. Test data shows that the aerogel fire extinguishing agent of this invention achieves a significant improvement in dispersion uniformity, mechanical strength, fire extinguishing efficiency, high-temperature resistance, and storage stability. Furthermore, it can be applied through various methods such as grouting and spraying, fully meeting the fire prevention and extinguishing needs of complex environments such as coal mine goaf areas.

[0051] The preferred embodiments of the present invention have been described in detail above, and are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly dispersible fiber composite aerogel fire extinguishing agent, characterized in that, By weight percentage, it includes the following components: SiO2 aerogel substrate: 40-55 wt%; Aramid nanofibers (ANF): 5-12 wt% Expanded graphite (EG): 5-12 wt% Zinc borate (ZB): 8-12 wt% Polyimide (PI): 10-15 wt% Methyltrimethoxysilane (MTMS): 2-10 wt% Nano-montmorillonite: 1-3 wt%.

2. The highly dispersible fiber composite aerogel fire extinguishing agent according to claim 1, characterized in that, The aramid nanofibers are prepared by chemical exfoliation of poly(p-phenylene terephthalamide) (PPTA) fibers with methanesulfonic acid, and have a length of 100-500 nm and a diameter of 5-20 nm; the expanded graphite is expanded at 850-900℃ and has a particle size of 10-50 μm; the polyimide is formed by in-situ polymerization of 4,4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA).

3. The highly dispersible fiber composite aerogel fire extinguishing agent according to claim 1, characterized in that, The SiO2 aerogel substrate has a porosity of 85-95% and a thermal conductivity of ≤0.025W / (m·K).

4. The highly dispersible fiber composite aerogel fire extinguishing agent according to claim 2, characterized in that, In the preparation process of the aramid nanofibers, the mass ratio of poly(p-phenylene terephthalamide) fiber to methanesulfonic acid is 1:40-1:60, the chemical exfoliation temperature is 50-60℃, and the exfoliation time is 4-6 days.

5. The highly dispersible fiber composite aerogel fire extinguishing agent according to claim 2, characterized in that, The expanded graphite is pretreated as follows: the expandable graphite is expanded at 850-900℃ for 30-60s, crushed and passed through a 300-1000 mesh sieve, then immersed in a 1-3wt% silane coupling agent KH-550 ethanol solution, stirred at 50-60℃ for 1-2h, and dried for later use.

6. The highly dispersible fiber composite aerogel fire extinguishing agent according to claim 2, characterized in that, The monomer molar ratio of the polyimide is 4,4'-diaminodiphenyl ether (ODA):pyromellitic dianhydride = 1:1.02-1:1.05, and the concentration of the polyimide precursor solution is 12-18 wt%.

7. A method for preparing the highly dispersible fiber composite aerogel fire extinguishing agent according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of aramid nanofibers (ANF) Poly(p-phenylene terephthalamide) (PPTA) fibers were immersed in methanesulfonic acid at a mass ratio of 1:40 to 1:

60. The mixture was then chemically exfoliated by stirring at 50-60°C for 4-6 days to obtain a dispersion of aramid nanofibers with a mass fraction of 2-3%, which was then set aside for later use. (2) Pretreatment of expanded graphite (EG) Expandable graphite is expanded at 850-900℃ for 30-60 seconds, pulverized and passed through a 300-1000 mesh sieve; the expanded graphite is immersed in a 1-3wt% silane coupling agent KH-550 ethanol solution, stirred at 50-60℃ for 1-2 hours, and then dried for later use. (3) Preparation of polyimide precursor (PAA) 4,4'-Diaminodiphenyl ether (ODA) and N,N-dimethylacetamide were mixed and stirred until completely dissolved. The mixture was then cooled to 0-5°C in an ice bath. Pyromellitic dianhydride was slowly added, with the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride being 1:1.02-1:1.

05. The mixture was stirred for 2-4 hours to obtain a polyimide precursor solution with a mass fraction of 12-18 wt%. (4) Preparation of SiO2 sol Tetraethyl orthosilicate (TEOS), ethanol, and deionized water are mixed in a molar ratio of 1:2:2.5-1:3:

3. Hydrochloric acid is added to adjust the pH to 2-3, and the mixture is hydrolyzed at 70-80℃ for 1-1.5 hours to obtain SiO2 sol. (5) Cogel synthesis Weigh the raw materials obtained in steps 1-4 according to the proportion, add 5-12% expanded graphite, 8-12% zinc borate and 1-3% nano montmorillonite by mass of aerogel to SiO2 sol, and ultrasonically disperse for 20-30 minutes. Continue adding aramid nanofiber dispersion, with the aramid nanofibers accounting for 5-12% of the aerogel mass. Stir mechanically for 30-40 minutes to form a uniform dispersion system. Slowly add the polyimide precursor solution to the obtained uniform dispersion system, with the amount of polyimide added calculated as 10-15% of the aerogel mass. Stir for 20-30 min, add ammonia water to adjust the pH to 7.5-8.5, and let the gel stand at room temperature for 12-24 h to obtain the cogel. (6) Aging and solvent replacement The cogel was aged in an oven at 80-90℃ for 8-12 hours, and then replaced with anhydrous ethanol 3-4 times, each time for 6-8 hours, to remove water and residual solvent from the system. (7) Drying treatment The solvent-displaced cogel was dried by supercritical CO2 at a temperature of 35-45℃, a pressure of 8-12MPa, and a time of 24-36h to obtain a composite aerogel intermediate. (8) Hydrophobic modification The composite aerogel intermediate was immersed in a methyltrimethoxysilane ethanol solution and stirred at 50-60℃ for 2-3 hours. After being removed, it was dried at 80-100℃ for 2-4 hours to obtain the composite aerogel fire extinguishing agent.

8. The preparation method according to claim 7, characterized in that, In step (5), the power of ultrasonic dispersion is 300-500W, and the speed of mechanical stirring is 600-800r / min.

9. The preparation method according to claim 7, characterized in that, In step (7), the heating rate of supercritical CO2 drying is 1-2℃ / min and the depressurization rate is 0.5-1MPa / h; in step (8), the volume fraction of methyltrimethoxysilane ethanol solution is 50-60%.

10. The application of the highly dispersible fiber composite aerogel fire extinguishing agent according to any one of claims 1-6 in coal mine fire prevention and extinguishing, characterized in that, The extinguishing agent can be applied to the goaf or roadway area of ​​a coal mine by grouting, spraying or filling to suppress spontaneous combustion of coal and extinguish coal mine fires.