Fire extinguishing gel with wide temperature range, high water retention and CO inhibition and preparation and application thereof

Abstract

The application discloses a wide-temperature-range high-water-retention CO inhibiting fire extinguishing gel as well as a preparation and application thereof, and adopts beta-cyclodextrin to pre-adsorb halloysite nanotubes, then adds sodium carboxymethyl cellulose to perform interface coating, so as to obtain an interface-regulated halloysite nanotube dispersion liquid; soluble silver salt is added to introduce Ag + coordination / adsorption sites; the obtained dispersion liquid is mixed with a chitosan solution, then phytic acid is added, and a three-dimensional network structure is formed through electrostatic cross-linking and hydrogen bond cross-linking. The application solves the problem that the halloysite nanotubes are prone to aggregation through a sequential interface regulation strategy, utilizes the multi-point cross-linking of phytic acid and the phosphorus-based inhibition to construct a gel skeleton, and Ag + coordination / adsorption sites and a multi-scale limited structure are cooperated to achieve the adsorption and release delay of CO. The gel has wide-temperature-range thermal stability, high water-retention capacity and excellent CO inhibition performance, the preparation process is mild, and is suitable for various fire extinguishing scenes of coal mines.

Description

Technical Field

[0001] This invention belongs to the technical field of coal mine fire prevention and extinguishing materials, specifically relating to a wide-temperature-range, high-water-retention, CO-suppressing fire prevention and extinguishing gel, its preparation, and its application. Background Technology

[0002] Coal still occupies an important position in my country's energy structure. In coal mine goafs, coal pillars, high-risk areas in roadways, and coal storage yards, residual coal is exposed to a leaky, oxygen-supplied environment for extended periods. This environment is prone to low-temperature oxidation and continuous heat release, which may eventually induce spontaneous combustion, releasing harmful gases such as CO and CO2, and potentially triggering secondary disasters such as gas explosions. Among these, CO is a crucial indicator gas for assessing the risk of spontaneous combustion in coal.

[0003] Among existing coal mine fire prevention and extinguishing methods, gel fire prevention and extinguishing technology is widely used due to its excellent water retention and cooling properties, oxygen barrier properties, and air leakage prevention performance. Chinese patent CN111214799A discloses a fire prevention and extinguishing gel using sodium carboxymethyl cellulose as a polymer and zirconium citrate as a crosslinking agent; however, its network structure is relatively simple, and its long-term water retention and mechanical strength are insufficient. Chinese patent CN116656009A proposes an Al... 3+ The sodium carboxymethyl cellulose-montmorillonite / polyacrylamide fully physically crosslinked dual-network gel exhibits improved mechanical and leak-stopping properties, but lacks chemical inhibition functional units and does not address CO release inhibition. Chinese patent CN111420337A discloses an in-situ generated composite gel using silicate as a base material and CO2 as a coagulant, but its water retention relies on an inorganic silicate network, making it prone to water loss and cracking at high temperatures, and similarly lacks chemical inhibition functionality.

[0004] Halloysite nanotubes, as natural hollow tubular aluminosilicate minerals, can be used to improve the stability of gel structures and gas migration pathways. However, halloysite nanotubes without interface regulation are prone to agglomeration in aqueous systems, and their compatibility with organic gel networks and interfacial bonding ability are insufficient, making it difficult to fully exert their reinforcing and pore confinement effects.

[0005] Furthermore, phytic acid molecules contain multiple phosphate groups, which can inhibit phosphorus-based oxidation, promote char formation, and complex Fe and Mn metal ions in coal. Chitosan has film-forming adhesion and network construction capabilities, but the single phytic acid / chitosan gel system still has shortcomings in long-term adhesion, structural enhancement, and gas diffusion regulation. Although some existing metal-supported materials can improve CO adsorption capacity, their preparation is complex and costly, and high metal loading sites may pose a risk of catalytic coal oxidation.

[0006] In summary, existing coal mine fire prevention and extinguishing gels suffer from problems such as insufficient synergy between chemical inhibition function and gas diffusion regulation, difficulty in halloysite dispersion, lack of low-content CO-affinity metal sites, and low biomass utilization rate. Summary of the Invention

[0007] In view of the problems mentioned in the background art, such as insufficient synergy between chemical inhibition function and gas diffusion regulation, easy aggregation of halloysite nanotubes, lack of low-content CO-affinity metal sites, and low biomass utilization rate of existing coal mine fire prevention and extinguishing gels, this invention provides a wide-temperature-range, high-water-retention, and CO-inhibiting fire prevention and extinguishing gel, its preparation method, and its application.

[0008] This invention includes the following technical solutions: This invention provides a method for preparing a wide-temperature-range, high-water-retention, CO-inhibiting fire-extinguishing gel, comprising the following steps: S1: Prepare chitosan solution.

[0009] Chitosan, as a gel backbone component, contains a large number of amino groups in its molecular chain, providing cross-linking sites for subsequent electrostatic cross-linking with phytic acid. The amount of chitosan added is 1% to 5% based on the total mass of the final gel.

[0010] Preferably, the chitosan is water-soluble chitosan with an average molecular weight of 100,000 to 300,000 Da and a degree of deacetylation of 80.0% to 95.0%. When water-soluble chitosan is used, it is dissolved directly in deionized water; when ordinary chitosan is used, it is dissolved in a weakly acidic aqueous solution of acetic acid, citric acid, or lactic acid with a mass fraction of 0.5% to 3%.

[0011] S2: Halloysite nanotubes are dispersed in an aqueous medium, and β-cyclodextrin is added for pre-adsorption, so that β-cyclodextrin is adsorbed on the surface and orifice of halloysite nanotubes through hydrogen bonding. Then, sodium carboxymethyl cellulose is added for interfacial coating to obtain a sodium carboxymethyl cellulose-β-cyclodextrin interface-regulated halloysite nanotube dispersion.

[0012] β-Cyclodextrin first forms hydrogen bonds with the hydroxyl groups on the surface of halloysite nanotubes through its outer hydroxyl groups, preferentially adsorbing onto the surface and orifice region of the halloysite nanotubes. Subsequently, sodium carboxymethyl cellulose is added, forming hydrogen bond entanglements and interfacial coatings with the halloysite nanotubes and β-cyclodextrin through its carboxyl and hydroxyl groups. This sequential interfacial regulation effectively reduces the aggregation of halloysite nanotubes and improves their dispersion stability and interfacial bonding strength in the phytic acid / chitosan gel network.

[0013] The mass ratio of halloysite nanotubes, β-cyclodextrin, and sodium carboxymethyl cellulose is 0.5~5 : 0.2~3 : 0.2~3; the mass ratio of β-cyclodextrin to sodium carboxymethyl cellulose is 1:5~5:1; the reaction temperature is 20~60℃, and the reaction time is 0.5~4h.

[0014] Preferably, the halloysite nanotubes have an inner diameter of 15–100 nm and a length of 500–1000 nm. Within this size range, the hollow lumen of the halloysite nanotubes can, together with the cavities of β-cyclodextrin molecules and the pores of the gel network, form a multi-scale confined structure, which is beneficial for extending the gas migration path.

[0015] S3: Add a soluble silver salt aqueous solution to the dispersion obtained in S2, and stir the reaction under light-protected conditions to allow Ag to react. + Ag-containing compounds undergo coordination or adsorption with sodium carboxymethyl cellulose, β-cyclodextrin, and halloysite nanotube surface groups to obtain Ag-containing compounds. + Interfacial regulation of halloysite nanotube dispersions by coordination / adsorption sites.

[0016] Ag + Immobilized on the surface of interface-controlled halloysite nanotube composite units and within the gel network, it exhibits coordination affinity for CO, enhancing CO adsorption and retention. Simultaneously, the subsequently added polyphosphate groups of phytic acid enhance the adsorption and retention of free or excess Ag. + It has a complexing and immobilizing effect, which helps reduce the risk of metal ion migration.

[0017] Preferably, the soluble silver salt is at least one selected from silver nitrate, silver acetate, silver lactate, or silver sulfate. The mass percentage of Ag element is 0.005% to 0.06% based on the total mass of the final gel.

[0018] S4: Mix the dispersion obtained in S3 with the chitosan solution obtained in S1 to obtain a composite dispersion system.

[0019] S5: Add phytic acid to the composite dispersion system obtained in S4, so that the amino groups in the chitosan molecular chain and the phosphate groups in the phytic acid molecules undergo electrostatic cross-linking and hydrogen bonding cross-linking to form a three-dimensional network structure, thus obtaining the fire extinguishing gel.

[0020] Phytic acid molecules contain multiple phosphate groups, while chitosan molecular chains contain a large number of amino groups. The two undergo multi-point cross-linking through electrostatic interactions and hydrogen bonding, forming a gel with a three-dimensional network structure. The amount of phytic acid added, based on the total mass of the final gel, is 0.5%–3%.

[0021] Preferably, the phytic acid is added dropwise at a rate of 0.1-2 mL / min and at a reaction temperature of 20-50°C to ensure uniform cross-linking.

[0022] Preferably, the phytic acid is derived from an aqueous extract of one or more agricultural processing byproducts, such as rice bran, wheat bran, corn soaking solution, soybean meal, or rapeseed cake. Specifically, the above-mentioned agricultural processing byproducts are dried and pulverized, then extracted with a 0.5%–3% (w / w) aqueous solution of acetic acid, citric acid, or lactic acid at 30–70°C for 0.5–4 hours. Solid-liquid separation yields the phytic acid-containing extract. This method enables the resource utilization of agricultural processing byproducts and reduces raw material costs.

[0023] Further, following step S5, the following steps are performed: Acrylamide, N,N′-methylenebisacrylamide, and ammonium persulfate are added to the gel system obtained in S5, and the mixture is allowed to react statically at 55-65°C. This allows the acrylamide to polymerize in situ under the action of the N,N′-methylenebisacrylamide crosslinking agent and the ammonium persulfate initiator, forming a crosslinked polyacrylamide-assisted network. This polyacrylamide-assisted network interpenetrates with the phytic acid / chitosan three-dimensional network, forming a dual-network structure. Based on the final total gel mass, the amount of acrylamide added is 0.5%-5%; the amount of N,N′-methylenebisacrylamide added is 0.02%-0.5% of the acrylamide mass; and the amount of ammonium persulfate added is 0.5%-5% of the acrylamide mass. This dual-network structure is beneficial for improving the overall supporting strength, water retention stability, and adhesion and coverage stability of the gel.

[0024] The present invention also provides a fire extinguishing gel with a wide temperature range, high water retention and CO inhibition, prepared by the above preparation method.

[0025] Preferably, the water retention rate of the fire extinguishing gel after being placed at 50°C and 60% relative humidity for 300 min is not less than 60%; and the average inhibition rate of CO release during the low-temperature oxidation of coal is not less than 60%.

[0026] This invention also provides the application of the above-mentioned fire-prevention and extinguishing gel in the prevention and control of spontaneous combustion of coal in coal mine goaf areas, coal body fissures, coal pillars, high-risk areas in roadways, or coal storage yards. The fire-prevention and extinguishing gel is applied to the surface of the coal body or coal body fissures by spraying, coating, grouting, or filling.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a sequential interface regulation strategy of “β-cyclodextrin pre-adsorption-sodium carboxymethyl cellulose interface coating” to treat halloysite nanotubes, which effectively improves the dispersion stability and interfacial bonding strength of halloysite nanotubes in aqueous gel system, so that the confinement effect of hollow tubes can be fully exerted.

[0028] (2) The present invention constructs a three-dimensional gel network through electrostatic crosslinking and hydrogen bonding crosslinking between phytic acid and chitosan. Phytic acid provides chemical inhibition functions such as phosphorus inhibition, promoting carbonization and complexing of metal ions such as Fe and Mn in coal, while chitosan provides film-forming adhesion. The synergy of the two is beneficial to reducing the low-temperature oxidation rate of coal.

[0029] (3) This invention introduces a low content of immobilized Ag + Coordination / adsorption sites, Ag + In conjunction with sodium carboxymethyl cellulose, β-cyclodextrin, halloysite nanotubes, and phytic acid, it is immobilized in a composite gel network, enhancing the coordination adsorption and retention capacity of CO; simultaneously, phytic acid inhibits the free or excess Ag... + It has a complexing and immobilizing effect, which helps reduce the risk of metal ion migration.

[0030] (4) In this invention, the β-cyclodextrin molecule cavity, the halloysite nanotube hollow cavity and the gel network pores together constitute a multi-scale confined structure, which is beneficial to prolong the gas migration path and reduce the CO release rate.

[0031] (5) This invention can utilize agricultural processing byproducts such as rice bran, wheat bran, and corn soaking solution to extract phytic acid, thereby realizing the utilization of biomass resources and reducing preparation costs.

[0032] (6) The preparation process of this invention is an all-aqueous system, without the use of strong acids, strong bases, organic solvents and high-temperature calcination. The process conditions are mild, which is convenient for scale-up preparation and field application.

[0033] (7) The present invention can form an interpenetrating double network structure by using polyacrylamide-assisted reinforcing network and phytic acid / chitosan network to improve the overall support strength, water retention stability and adhesion coverage stability of gel, and enhance its continuous coverage and inhibition ability in complex coal mine environment.

[0034] (8) The gel of the present invention can be applied to various coal spontaneous combustion prone areas such as coal mine goaf, coal body fissures, coal pillars, roadway high-risk areas and coal storage yards by spraying, coating, grouting or filling, and has strong engineering applicability. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the preparation and performance characterization of the fire-extinguishing gel of the present invention.

[0036] Figure 2 This is a graph showing the change in water retention rate of the fire-retardant gel of the present invention at different times under conditions of 50°C and 60% relative humidity.

[0037] Figure 3 The images shown are scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses of the fire-retardant gel of this invention. Figure 3 Image (a) is a SEM image of the fire-resistant gel from Example 1. Figure 3 (b) is the SEM image of the gel without sequential interface regulation in Comparative Example 2. Figure 3 (c) in the image is a SEM image of the residual char of the fire extinguishing gel. Figure 3 (d) in the figure is the surface scan distribution of Ag element in the char residue of the fire extinguishing gel. Figure 3 (e) in the figure is the EDS spectrum of the fire extinguishing gel residue;

[0038] Figure 4 The Fourier transform infrared spectra of the fire-extinguishing gel, raw anthracite, and inhibited anthracite samples of this invention are shown.

[0039] Figure 5 This is an infrared thermal imaging test image of the fire-resistant and extinguishing gel coating layer of the present invention, wherein... Figure 5 (a) in the diagram is a diagram of the flame impact experimental setup. Figure 5 (b) in the image shows the infrared thermal imaging temperature distribution after heating for 120 seconds. Figure 5 (c) in the image shows the infrared thermal imaging temperature distribution after heating for 240 seconds. Figure 5 (d) in the image is the infrared thermal imaging temperature distribution after heating for 360 seconds. Figure 5 (e) in the image is the infrared thermal imaging temperature distribution after heating for 480 s. Figure 5 (f) in the figure is the infrared thermal imaging temperature distribution map after heating for 600s.

[0040] Figure 6 The graph shows the gas concentration changes of raw anthracite and inhibited anthracite samples during the programmed temperature rise process. Figure 6 (a) in the figure is a curve showing the change in CO concentration. Figure 6 (b) in the figure is a curve showing the change in CO2 concentration.

[0041] Figure 7 This is a graph showing the change in the inhibition rate of the fire-extinguishing gel of the present invention during the low-temperature oxidation process of coal. Detailed Implementation

[0042] like Figure 1 As shown, the present invention proposes a wide-temperature-range, high-water-retention, CO-inhibiting fire-extinguishing gel. The overall preparation and characterization process, from raw material weighing, water bath heating and stirring polymerization, to gel mixing with coal samples and vacuum drying, and then to various performance tests (water retention rate, infrared spectroscopy, scanning electron microscopy, infrared thermal imaging, and programmed temperature oxidation test), is as follows. The invention will be further described below with reference to specific embodiments and test examples. However, the scope of protection of the present invention is not limited thereto.

[0043] Unless otherwise stated, all raw materials used in the embodiments of this invention are commercially available analytical grade products. Specifically, water-soluble chitosan was purchased from Beijing Mairuida Technology Co., Ltd., product number M02899, CAS number 9012-76-4, with an average molecular weight of 100,000~300,000 Da and a degree of deacetylation of 80.0%~95.0%; halloysite nanotubes were purchased from Xi'an Mingchuangda Biotechnology Co., Ltd., with a purity of ≥99%, an inner diameter of 15~100 nm, and a length of 500~1000 nm. Phytic acid extract was prepared from rice bran through aqueous phase extraction. The specific method is as follows: rice bran was dried and pulverized, then extracted with a 1.5% (w / w) acetic acid aqueous solution at 50℃ for 2 hours. After centrifugation to remove insoluble residues, an extract containing phytic acid was obtained. The effective phytic acid content was determined by the phosphomolybdic blue colorimetric method before use.

[0044] In this invention, the water retention rate is determined as follows: a certain mass of fire-retardant gel is placed in a weighing container, and the mass of the empty container is recorded. and the total mass of the container and gel at the initial moment The samples were placed in a constant temperature and humidity chamber (temperature 50±1℃, relative humidity 60±5%), and weighed at different time points, and the results were recorded. Time container and total mass of gel Calculate the water retention rate using the following formula: .

[0045] Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were performed using a ZEISS Sigma 360 field emission scanning electron microscope (FE-SEM) with a test voltage of 5–20 kV. Samples were freeze-dried and then sputter-coated with gold. Fourier transform infrared (FTIR) spectroscopy was performed using a Nicolet iS50FT-IR spectrometer with a test range of 4000–500 cm⁻¹. -1 The resolution is 4 cm. -1 The number of scans was 64. Infrared thermal imaging was performed using a FLUKE RSE 60H / CN-L25 infrared thermal imager, with a flame impact heating time of 600 s. The programmed temperature rise experiment was conducted using a ZRD-I coal spontaneous combustion characteristic tester. The coal sample mass was 45.00 g, the reaction gas was dry air (oxygen volume fraction approximately 20.96%), the heating rate was 0.8℃ / min, and the test temperature range was 35.9~215.2℃. The concentrations of CO and CO2 in the outlet gas were detected using a gas chromatography system. The inhibition rate was calculated using the following formula: .

[0046] In the formula, This refers to the CO concentration released by raw anthracite coal at the same temperature. To inhibit the CO concentration released by anthracite samples at the same temperature.

[0047] Example 1: This embodiment provides a wide-temperature-range, high-water-retention, CO-inhibiting fire extinguishing gel, the formulation of which is shown in Table 1.

[0048] Table 1: Formulation of Example 1 (based on 100 parts of the final gel total mass).

[0049] The preparation method in this embodiment is carried out according to the following steps: S1: Dissolve 3 parts of water-soluble chitosan directly in an appropriate amount of deionized water and stir until completely dissolved to obtain a chitosan solution.

[0050] S2: Add 2 parts halloysite nanotubes to an appropriate amount of deionized water and ultrasonically disperse for 30 min. Add 1 part β-cyclodextrin and stir to allow β-cyclodextrin to adsorb onto the surface and orifice of halloysite nanotubes through hydrogen bonding. Then add 1 part sodium carboxymethyl cellulose and stir at 40℃ for 2 h to obtain a sodium carboxymethyl cellulose-β-cyclodextrin interface-regulated halloysite nanotube dispersion.

[0051] S3: Add 0.08 parts of silver nitrate aqueous solution to the dispersion obtained in S2, and stir for 45 minutes under light-protected conditions to allow Ag to react. + Ag-containing compounds undergo coordination or adsorption with sodium carboxymethyl cellulose, β-cyclodextrin, and halloysite nanotube surface groups to obtain Ag-containing compounds. + Interfacial regulation of halloysite nanotube dispersions by coordination / adsorption sites.

[0052] S4: Mix the dispersion obtained in S3 with the chitosan solution obtained in S1 and stir until homogeneous to obtain a composite dispersion system.

[0053] S5: Add phytic acid extract (equivalent to 1.5 parts of effective phytic acid) dropwise to the composite dispersion system obtained in S4 at a dropping rate of 0.5 mL / min. Stir the reaction at 35°C to allow the amino groups in the chitosan molecular chain to undergo electrostatic cross-linking and hydrogen bonding cross-linking with the phosphate groups in the phytic acid molecules, forming a three-dimensional network structure.

[0054] S6: Add 2 parts of acrylamide and 0.002 parts of N,N′-methylenebisacrylamide mixed solution to the gel system obtained in S5, stir at low speed to mix evenly, then add 0.04 parts of ammonium persulfate aqueous solution, stir gently for 1~2 min and then stop stirring, let stand at 60℃ for 40 min to allow acrylamide to polymerize in situ to form a cross-linked polyacrylamide auxiliary network, thus obtaining the fire extinguishing gel.

[0055] Example 2: This embodiment provides a wide-temperature-range, high-water-retention, CO-inhibiting fire extinguishing gel, the formulation of which is shown in Table 2.

[0056] Table 2: Formulation of Example 2 (based on 100 parts of the final total gel mass);

[0057] The preparation method of this embodiment is the same as that of Example 1. The difference is that the amount of each component is as shown in Table 2. In S5, the phytic acid dropping rate is 0.1 mL / min and the reaction temperature is 20℃. In S6, the static reaction temperature is 55℃ and the reaction time is 60 min.

[0058] Example 3: This embodiment provides a wide-temperature-range, high-water-retention, CO-inhibiting fire extinguishing gel, the formulation of which is shown in Table 3.

[0059] Table 3: Formulation of Example 3 (based on 100 parts of the final gel total mass)

[0060] The preparation method of this embodiment is the same as that of Example 1. The difference is that the amount of each component is as shown in Table 3. In S5, the phytic acid dropping rate is 2 mL / min and the reaction temperature is 50℃. In S6, the static reaction temperature is 65℃ and the reaction time is 20 min.

[0061] Comparative Example 1: This comparative example provides an Ag-free solution. + The fire extinguishing gel with coordination / adsorption sites differs from that of Example 1 in that silver nitrate is not added, while the remaining components and amounts are exactly the same as in Example 1. The preparation method differs from that of Example 1 in that step S3 is omitted, and the dispersion obtained in S2 is directly mixed with the chitosan solution before subsequent steps.

[0062] Comparative Example 2: This comparative example provides a fire extinguishing gel without sequential interface regulation, and its formulation is exactly the same as that of Example 1. The difference in preparation method from Example 1 is that in S2, halloysite nanotubes, β-cyclodextrin, and sodium carboxymethyl cellulose are directly mixed and added to water in the same proportion, without the sequential treatment steps of "pre-adsorption of β-cyclodextrin followed by interfacial coating of sodium carboxymethyl cellulose".

[0063] Comparative Example 3: This comparative example provides a fire extinguishing gel without halloysite nanotubes. The formula differs from Example 1 in that halloysite nanotubes are not added, while the remaining components and amounts are identical. The preparation method differs from Example 1 in that halloysite nanotubes are not added in step S2; β-cyclodextrin and sodium carboxymethyl cellulose are directly added to water, while the remaining steps are the same.

[0064] Comparative Example 4: This comparative example provides a fire-retardant gel without a polyacrylamide-assisted reinforcing network. The formulation differs from Example 1 in that acrylamide, N,N′-methylenebisacrylamide, and ammonium persulfate are not added; the remaining components and their amounts are identical to those in Example 1. The preparation method differs from Example 1 in that step S6 is omitted, and the gel system obtained in S5 is the final product.

[0065] Test Example 1: Water retention test.

[0066] The fire-retardant gel sample prepared in Example 1 was tested according to the water retention rate determination method described above, and the water retention rate at different time points was recorded. The test results are as follows: Figure 2 As shown.

[0067] Depend on Figure 2 It can be seen that, under conditions of 50℃ and 60% relative humidity, the water retention rate of the fire-retardant gel gradually decreases with prolonged placement time, but the rate of decrease is relatively slow. The water retention rate decreases rapidly within the first 0-50 minutes (the rapid evaporation phase), but the rate of decrease slows significantly after 50 minutes, and a high water retention rate is maintained even after 300 minutes. These results indicate that the network structure of the fire-retardant gel of this invention has a strong ability to bind water, which is beneficial for extending the wet coverage time on the coal surface and improving the sustained inhibition effect through heat absorption during water evaporation and oxygen barrier properties.

[0068] Test Example 2: Scanning electron microscopy and energy dispersive spectroscopy (EDS) tests.

[0069] The fire-retardant gel and its char residue prepared in Example 1 were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The gel sample was freeze-dried, and its cross-section was observed and then sputtered with gold. Typical areas of the char residue sample were observed after natural cooling. The test results are as follows: Figure 3 As shown, where Figure 3 Microstructure and elemental distribution of fire-retardant gel, comparative gel, and char residue: Figure 3 Image (a) is a SEM image of the fire-resistant gel from Example 1; Figure 3 (b) is a SEM image of the gel without sequential interface regulation in Comparative Example 2; Figure 3 (c) is a SEM image of the residual char of the fire extinguishing gel; Figure 3 (d) in the figure is a surface scan distribution diagram of Ag element in the char residue of fire extinguishing gel; Figure 3 (e) in the figure is the EDS spectrum of the fire extinguishing gel residue.

[0070] Depend on Figure 3It can be seen that the fire-extinguishing gel exhibits a porous network or skeletal structure with relatively continuous pore walls, indicating that the chitosan / phytic acid three-dimensional cross-linked network and the in-situ formed cross-linked polyacrylamide-assisted reinforcing network jointly construct a relatively complete gel skeleton. Compared with the sample without sequential interface regulation, the gel structure in the example sample is more uniform, while obvious sheet-like or rod-like particle accumulation can be observed in the sample without sequential interface regulation, indicating that halloysite nanotubes are prone to local aggregation without the "pre-adsorption of β-cyclodextrin followed by interfacial coating with sodium carboxymethyl cellulose". The above results indicate that sequential interface regulation is beneficial to improving the dispersion state and interfacial binding effect of halloysite nanotubes in the gel system.

[0071] Meanwhile, pore wall coating, pore blockage, or continuous char layer structures can still be observed on the surface of the fire-extinguishing gel residue, indicating that the gel helps form a protective coating layer during heating, thereby reducing the transfer of oxygen and heat into the coal body. Energy dispersive spectroscopy (EDS) results detected elements such as C, O, N, P, Si, Al, and Ag, indicating the presence of phytic acid, halloysite nanotubes, and Ag. + Coordination / adsorption sites have been introduced into the composite gel system; Ag elemental surface scan results show that Ag element is distributed in a certain way in the residual carbon region, indicating that Ag + The coordination / adsorption sites can still be retained in the char structure after the gel is heated.

[0072] Test Example 3: Fourier transform infrared spectroscopy test.

[0073] Fourier transform infrared spectroscopy was performed on the fire-retardant gel, raw anthracite, and inhibited anthracite samples prepared in Example 1. The samples were freeze-dried and ground into powder before testing. The test results are as follows: Figure 4 As shown.

[0074] Depend on Figure 4 It can be seen that the fire extinguishing gel is effective at ~OH / ~NH (3200~3500 cm⁻¹). -1 CH (approximately 2920 cm) -1 C=O / C=C (approximately 1650 cm) -1 ), ~COO - / PO (approximately 1400~1600 cm) -1 ), PO / CO / Si-O (approximately 1000~1100 cm⁻¹) -1 ) and Si-O-Al / Al-O (approximately 500~600 cm⁻¹) -1 The presence of characteristic absorption peaks in regions such as phytic acid, chitosan, sodium carboxymethyl cellulose, β-cyclodextrin, halloysite nanotubes, and polyacrylamide-assisted network indicates that phytic acid, chitosan, sodium carboxymethyl cellulose, β-cyclodextrin, halloysite nanotubes, and polyacrylamide-assisted network jointly participate in the construction of the gel structure. Compared with raw anthracite, the inhibited anthracite sample exhibits higher absorption peaks in the 1000–1100 cm⁻¹ region.-1 1400~1650 cm -1 and 3200~3500 cm -1 The changes in peak shape or intensity in certain regions indicate that there are hydrogen bonds, complexations, covering, or interfacial binding between the fire extinguishing gel and the oxygen-containing functional groups or mineral components on the coal surface, which helps to reduce coal-oxygen contact and lower the low-temperature oxidation activity of coal.

[0075] Test Example 4: Infrared thermal imaging heat insulation test.

[0076] The gel prepared in Example 1 was applied to the heated surface of a glass slide substrate. The gel-covered surface was heated using a flame torch, and the temperature of the back side of the sample was recorded using an infrared thermal imager for 600 seconds. The infrared thermal imaging results are as follows: Figure 5 As shown, where Figure 5 (a) in the diagram is a diagram of the flame impact test setup. Figure 5 In the images (b) to (f), the infrared thermal images were obtained after heating for 120s, 240s, 360s, 480s, and 600s, respectively.

[0077] Depend on Figure 5 It can be seen that the temperature on the back of the sample gradually increased with the extension of the flame heating time: approximately 39.3℃ at 120s, 68.1℃ at 240s, 78.8℃ at 360s, 80.5℃ at 480s, and 83.1℃ at 600s. The rate of temperature increase slowed significantly after 360s, indicating that the fire-resistant gel coating layer can delay heat transfer to the back of the sample. The results show that the fire-resistant gel has certain heat insulation and water retention / cooling effects. This is mainly due to the heat absorption of water evaporation in the gel, the continuous gel layer covering and blocking oxygen and delaying heat transfer, while phytic acid promotes char formation, and halloysite nanotubes and polyacrylamide networks provide skeletal support.

[0078] Test Example 5: Temperature programmable rise experiment and resistance calculation.

[0079] A programmed temperature rise experiment was conducted on raw anthracite coal samples and anthracite coal samples treated with the fire-retardant gel of Example 1. The inhibited anthracite coal was prepared by uniformly mixing the fire-retardant gel with anthracite coal in a predetermined ratio and then drying it at a low temperature to a predetermined state. The experiment started at approximately 40°C and proceeded with a programmed temperature rise to approximately 215°C, and the concentrations of CO and CO2 in the outlet gas were measured.

[0080] Test results are as follows Figure 6 and Figure 7 As shown. Figure 6 In Figure (a), the CO concentration change curves of raw anthracite and inhibited anthracite during the programmed temperature rise process are shown. Figure 6In Figure (b), the curve shows the change in CO2 concentration. (From...) Figure 6 It can be seen that as the temperature increases, the release of CO and CO2 from the raw anthracite coal sample increases significantly; in contrast, the release of CO from inhibited anthracite coal at the same temperature decreases significantly, and the release of CO2 decreases overall or the growth rate slows down, indicating that the fire-extinguishing gel can effectively inhibit the low-temperature oxidation process of anthracite coal.

[0081] Figure 7 The inhibition rate of the fire extinguishing gel on the low-temperature oxidation process of coal is shown in the curve (calculated with CO concentration). The results show that the inhibited anthracite samples maintain a high inhibition rate within the test temperature range, especially in the low-temperature stage (50~100℃), where the inhibition effect is more significant, with an average inhibition rate of approximately 66.51%. The above results indicate that the fire extinguishing gel described in this invention can effectively inhibit the generation and release of CO during the low-temperature oxidation process of anthracite.

[0082] Summary of comparative test results: To more intuitively compare the performance differences between the various embodiments and the comparative examples, the test results of water retention rate (300 min) and average inhibition rate are summarized in Table 4. The water retention rate was determined according to the method of Test Example 1, and the average inhibition rate was determined according to the method of Test Example 5.

[0083] Table 4: Summary of performance test results for each embodiment and comparative example;

[0084] As shown in Table 4, the water retention rate and inhibition rate of Examples 1-3 are superior to those of the comparative examples. The inhibition rate of Comparative Example 1 is significantly lower than that of Example 1, indicating that Ag... + Coordination / adsorption sites significantly contribute to the retardation of CO adsorption and release. Comparative Example 2 exhibited the lowest water retention and inhibition rates, indicating that halloysite nanotubes without sequential interface regulation have poor dispersibility and cannot effectively exert their reinforcing and confinement effects. Comparative Example 3 showed a significantly lower inhibition rate than Example 1, demonstrating that the hollow cavity confinement effect of the halloysite nanotubes significantly contributes to the retardation of CO release. Comparative Example 4 showed a significantly lower water retention rate than Example 1, indicating that the polyacrylamide-assisted network significantly enhances the water binding capacity of the gel. These results demonstrate that sequential interface regulation of halloysite nanotubes and Ag... + The synergistic effect of coordination / adsorption sites and polyacrylamide-assisted reinforcement network is key to achieving high water retention and high inhibition rate.

[0085] It should be noted that the above embodiments are merely preferred embodiments of the present invention, used to explain the technical principles and application effects of the present invention, and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions, modifications, or improvements made based on the technical concept of the present invention within the spirit and principles of the present invention should be included within the scope of protection of the present invention. In practical applications, those skilled in the art can make adaptive adjustments to the relevant parameters according to the specific test materials, working conditions, and accuracy requirements, all of which fall within the scope of protection of the present invention.

Claims

1. A method for preparing a wide-temperature-range, high-water-retention, CO-inhibiting fire-retardant gel, characterized in that, Includes the following steps: S1: Preparation of chitosan solution; S2: Halloysite nanotubes are dispersed in an aqueous medium, and β-cyclodextrin is added for pre-adsorption, allowing β-cyclodextrin to adsorb onto the surface and orifice region of the halloysite nanotubes through hydrogen bonding. Then, sodium carboxymethyl cellulose is added for interfacial coating, resulting in a sodium carboxymethyl cellulose-β-cyclodextrin interface-regulated halloysite nanotube dispersion. The mass ratio of halloysite nanotubes, β-cyclodextrin, and sodium carboxymethyl cellulose is 0.5~5 : 0.2~3 : 0.2~3, and the mass ratio of β-cyclodextrin to sodium carboxymethyl cellulose is 1:5~5:

1. The reaction temperature is 20~60℃, and the reaction time is 0.5~4h. S3: Add a soluble silver salt aqueous solution to the dispersion obtained in S2, and stir the reaction under light-protected conditions to allow Ag to react. + Ag-containing compounds undergo coordination or adsorption with sodium carboxymethyl cellulose, β-cyclodextrin, and halloysite nanotube surface groups to obtain Ag-containing compounds. + Interfacial regulation of halloysite nanotube dispersions at coordination / adsorption sites; S4: Mix the dispersion obtained in S3 with the chitosan solution obtained in S1 to obtain a composite dispersion system; S5: Add phytic acid to the composite dispersion system obtained in S4, so that the amino groups in the chitosan molecular chain and the phosphate groups in the phytic acid molecules undergo electrostatic cross-linking and hydrogen bonding cross-linking to form a three-dimensional network structure, thus obtaining the fire extinguishing gel.

2. The preparation method according to claim 1, characterized in that, The chitosan in S1 is water-soluble chitosan with an average molecular weight of 100,000~300,000 Da and a degree of deacetylation of 80.0%~95.0%.

3. The preparation method according to claim 1, characterized in that, The halloysite nanotubes in S2 have an inner diameter of 15~100 nm and a length of 500~1000 nm.

4. The preparation method according to claim 1, characterized in that, Based on the total mass of the final gel, the amount of chitosan added in S1 is 1%~5%, and the amount of phytic acid added in S5 is 0.5%~3%.

5. The preparation method according to claim 1, characterized in that, The soluble silver salt in S3 is at least one of silver nitrate, silver acetate, silver lactate, or silver sulfate; the mass percentage of Ag element is 0.005% to 0.06% based on the total mass of the final gel.

6. The preparation method according to claim 1, characterized in that, Phytic acid in S5 is derived from an aqueous extract of one or more agricultural processing byproducts, such as rice bran, wheat bran, corn soaking solution, soybean meal, or rapeseed cake. The extract is obtained by solid-liquid separation after extraction with an aqueous solution of acetic acid, citric acid, or lactic acid at a mass fraction of 0.5% to 3% at 30 to 70°C for 0.5 to 4 hours.

7. The preparation method according to claim 1, characterized in that, Phytic acid in S5 is added dropwise at a rate of 0.1-2 mL / min, and the reaction temperature is 20-50℃.

8. The preparation method according to claim 1, characterized in that, After S5, the following steps were performed: acrylamide, N,N′-methylenebisacrylamide and ammonium persulfate were added to the gel system obtained in S5, and the system was allowed to stand at 55~65℃ for reaction. Based on the total mass of the final gel, the amount of acrylamide added is 0.5%~5%; the amount of N,N′-methylenebisacrylamide added is 0.02%~0.5% of the mass of acrylamide; and the amount of ammonium persulfate added is 0.5%~5% of the mass of acrylamide.

9. A wide-temperature-range, high-water-retention, CO-inhibiting fire-retardant gel, characterized in that, Prepared by the preparation method according to any one of claims 1-8; The fire-retardant gel has a water retention rate of no less than 60% after being placed at 50°C and 60% relative humidity for 300 minutes. The average inhibition rate of CO release during the low-temperature oxidation of coal is not less than 60%.

10. The application of the fire-prevention gel according to claim 9 in the prevention and control of spontaneous combustion of coal in coal mine goaf areas, coal body fissures, coal pillars, high-risk areas in roadways, or coal storage yards, characterized in that, The fire-extinguishing gel is applied to the surface of the coal body or into the fissures of the coal body by spraying, coating, grouting or filling.

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