Thermo-sensitive hydrogel composite inhibitor for inhibiting spontaneous combustion of coal and preparation method of thermo-sensitive hydrogel composite inhibitor

Abstract

The invention provides a thermo-sensitive hydrogel composite inhibitor for inhibiting spontaneous combustion of coal. The composite stopping agent mainly comprises the following components: a temperature-sensitive material, an antioxidant and a nano material. The temperature-sensitive material is methyl cellulose, polyethylene glycol and sodium chloride; the antioxidant is DL-malic acid; the nano material is modified nano zinc oxide. The preparation method comprises the following steps: carrying out graft copolymerization on a temperature-sensitive material and an antioxidant, and adding a nano material to prepare the composite stopping agent. Compared with a traditional inhibitor, the composite inhibitor integrates the performance advantages of all inhibition materials into a whole, the physical inhibition effects of cooling, moisturizing and oxygen isolation of hydrogel and the chemical inhibition effects of combining the antioxidant with active sites in coal and interrupting or inhibiting the coal spontaneous combustion reaction process are fully exerted, and the composite inhibitor has the advantages of being high in stability and good in stability. And a composite inhibitor system with physical and chemical synergistic inhibition efficiency is constructed through the enhancement effect of nano materials on improving the stability of the inhibitor, and a new theoretical basis and a new practice direction are provided for the comprehensive prevention and control technology of coal spontaneous combustion.

Description

Technical Field

[0001] The invention relates to the technical field of composite inhibitors, in particular to a temperature-sensitive hydrogel composite inhibitor for inhibiting coal spontaneous combustion. Background Art

[0002] Given the enclosed and complex structure of underground mines, once spontaneous combustion occurs, the fire often spreads rapidly, resulting in large-scale, rapid development, and high difficulty in extinguishing. Implementing reasonable and effective fire prevention and extinguishing measures to address the issue of spontaneous combustion is crucial for ensuring the safe mining of coal resources, reducing economic losses, protecting the lives of underground workers, and maintaining the surrounding environment.

[0003] At present, inhibitors are a commonly used technology for preventing and controlling coal spontaneous combustion. However, a single type of inhibitor can only act on a specific stage of coal spontaneous combustion, and the inhibitory effect is relatively simple. Composite inhibitors are the key research direction of future coal spontaneous combustion prevention and control technologies. Polymer gel is a new type of fire-fighting inhibitor with good water retention and inhibitory effect. It has great development potential in the prevention and control of coal spontaneous combustion. However, the permeability of the gel material is weak and a corresponding gel delivery pipeline is required. Therefore, its application is subject to certain restrictions. In order to improve the shortcomings of existing inhibitors, the present invention uses methyl cellulose and polyethylene glycol as the main materials, and then adds antioxidants DL-malic acid and nano zinc oxide to form a composite inhibitor material.

[0004] Methylcellulose (MC) is non-toxic, odorless, and biocompatible, posing no risk to humans or the environment. The coexistence of its hydrophobic methyl groups and hydrophilic hydroxyl groups gives it unique amphiphilicity, enabling it to exhibit temperature-dependent dissolution-gel transition behavior in water. The temperature sensitivity of methylcellulose enables it to adapt to the complex environment of mines. It is liquid at low temperatures, making it easy to transport, and solid at high temperatures, insulating and plugging leaks. It also exhibits good biocompatibility, effectively reducing pollution caused by the inhibitor itself. However, a single methylcellulose gel is composed of only a single physically cross-linked network, resulting in defects such as low mechanical properties and poor high-temperature resistance.

[0005] Polyethylene glycol (PEG) is chemically stable and resistant to oxygen reaction at room temperature. Its excellent thermal properties make it effective in enhancing the overall high-temperature resistance of composite gel materials. The hydroxyl groups at the ends of its molecular chains react with reactive groups on the coal surface to form chemically more stable ether bonds, thereby inhibiting the coal's oxidation process. Through surface adsorption, molecular entrapment, or chemical grafting, PEG can form stable composite structures with other functional materials.

[0006] DL-malic acid (DL-MA) is a naturally occurring dicarboxylic acid. Incorporating DL-malic acid into a gel system significantly improves its barrier properties. The gel framework provides a physical barrier, effectively isolating oxygen. Simultaneously, the DL-malic acid molecules penetrate the coal's micropores and chemically passivate it.

[0007] Nano-zinc oxide (n-ZnO) is a nanoscale form of zinc oxide (ZnO). Its surface is rich in active sites, making it an effective free radical scavenger. Furthermore, the ultrafine particle size of nano-zinc oxide allows it to adhere evenly to the coal surface without disrupting the coal structure due to overly large particles.

[0008] The present invention prepares a thermosensitive hydrogel composite inhibitor for preventing and controlling coal spontaneous combustion. The composite inhibitor obtained by grafting and copolymerizing thermosensitive hydrogel and antioxidant and adding nanomaterials integrates the physical inhibitory effect of thermosensitive hydrogel, the chemical inhibitory effect of antioxidant and the effect enhancement effect of nanomaterials, so that the composite inhibitor has a physical and chemical synergistic inhibitory effect and can exert an inhibitory effect in the whole process of coal spontaneous combustion. The main technical difficulties that the present invention intends to overcome include: carefully selecting inhibitor raw materials and appropriate methods to meet the requirements of simple preparation conditions and environmental protection; exploring and optimizing the ratio of thermosensitive hydrogel and composite inhibitor; preparing a composite inhibitor that can better exert the inhibitory performance of each component and improve the overall inhibitory efficiency. Summary of the Invention

[0009] The purpose of the present invention is to prepare a thermosensitive hydrogel composite inhibitor for preventing and controlling coal spontaneous combustion, the main components of which include a thermosensitive material, an antioxidant, and a nanomaterial. The thermosensitive material and the antioxidant are grafted and copolymerized, and the nanomaterial is added to form a composite inhibitor. The composite inhibitor has excellent moisture absorption and water retention properties and exhibits significant effects in inhibiting coal spontaneous combustion. The efficient combination and synergistic effect of multiple inhibitory materials are achieved, which has a significant effect in inhibiting coal spontaneous combustion and can exert an inhibitory effect throughout the entire coal spontaneous combustion process. At the same time, the prepared material is economical, environmentally friendly, and can adapt to the complex environment underground.

[0010] A temperature-sensitive hydrogel composite inhibitor for inhibiting coal spontaneous combustion is characterized in that the composite inhibitor mainly comprises a temperature-sensitive hydrogel (hereinafter referred to as MC / PEG), an antioxidant DL-malic acid (hereinafter referred to as DL-MA), and nano-material-modified nano-zinc oxide (hereinafter referred to as modified n-ZnO). The amount of the antioxidant is 0.2%-0.5% by mass relative to the MC / PEG solution, the amount of the nano-zinc oxide material is 0.1%-0.4%, the amount of the initiator is 0.1%-0.3%, the amount of the cross-linking agent is 0.2%-0.6%, and the balance is deionized water. The reaction temperature is 50°C-75°C.

[0011] Furthermore, the thermosensitive hydrogel is prepared by mixing methylcellulose (MC), polyethylene glycol (PEG) and sodium chloride (NaCl) and allowing them to swell. Specifically, based on the mass ratio of methylcellulose to deionized water, the amount of methylcellulose is 1.0%-3.4%, the amount of polyethylene glycol is 3.0%-9.0%, and the amount of sodium chloride is 2.0%-14.0%. The reaction temperature is 50°C-70°C.

[0012] Furthermore, the antioxidant DL-malic acid is used in a free radical chain reaction initiated by MC using an initiator KPS under high temperature or in the presence of a TEMED catalyst. During the cross-linking polymerization process, DL-MA is grafted onto the MC molecular chain through a graft copolymerization reaction. During the free radical chain reaction, the catalyst dosage is 4-5 drops.

[0013] Furthermore, the modified nano zinc oxide is prepared by modifying nano zinc oxide using a silane coupling agent KH-570. 0.5g-1.5g of nano zinc oxide is dissolved in an 85%-95% ethanol solution and stirred thoroughly. After ultrasonic dispersion, 1ml-3ml of KH-570 is slowly added while continuing to stir.

[0014] Furthermore, the crosslinking agent N,N-methylenebisacrylamide reacts with the hydroxyl groups on the MC molecular chain by initiating a free radical chain reaction through the initiator KPS under high temperature or catalyst TEMED conditions, thereby crosslinking different MC molecular chains together.

[0015] Furthermore, the initiator during the MC / PEG-MA solution graft copolymerization is potassium persulfate (KPS).

[0016] Furthermore, the crosslinking agent during the MC / PEG-MA solution graft copolymerization is N,N-methylenebisacrylamide (MBA).

[0017] Furthermore, the catalyst used in the MC / PEG-MA solution graft copolymerization is tetramethylethylenediamine (TEMED).

[0018] The preparation method of the composite inhibitor as described above is characterized in that: DL-MA is dissolved in deionized water, and an initiator is added to obtain a pretreated DL-MA solution; MC, PEG and NaCl are used to prepare an MC / PEG solution under heating conditions; the pretreated DL-MA solution, a crosslinking agent and a catalyst are sequentially added, and an MC / PEG-MA solution is prepared by graft copolymerization in a constant temperature water bath of 50°C-75°C; modified n-ZnO powder is dissolved in deionized water, and a nano-zinc oxide suspension is formed by ultrasonic treatment. The nano-zinc oxide suspension is slowly added while the MC / PEG-MA solution is stirred to prepare the composite inhibitor, i.e., the MC / PEG-MA-ZnO solution.

[0019] Furthermore, under high temperature or TEMED catalyst conditions, MC triggers a free radical chain reaction through the initiator KPS, and DL-MA is grafted onto the MC molecular chain through graft copolymerization during the cross-linking polymerization process.

[0020] MBA triggers a free radical chain reaction through the initiator KPS, reacts with the hydroxyl groups on the MC molecular chain, and cross-links different MC molecular chains together.

[0021] When the modified n-ZnO is introduced into the MC / PEG-MA solution system, the nanoparticles are evenly dispersed and penetrate into the gaps between the MC molecular chains. When the phase transition temperature is reached, the modified n-ZnO can act as a physical cross-linking point.

[0022] The graft copolymerization method of the present invention is to initiate a free radical chain reaction by the initiator KPS, graft DL-MA in the solution onto the MC molecular chain, and MBA reacts with the hydroxyl groups on the MC molecular chain to cross-link different MC molecular chains together, thereby increasing the network cross-linking density of the system and forming a MC / PEG-MA solution system with a dense three-dimensional network structure.

[0023] The present invention grafts and copolymerizes the thermosensitive hydrogel and the antioxidant, and adds nanomaterials, so that the physical inhibition effect of the thermosensitive hydrogel, the chemical inhibition effect of the antioxidant and the effect enhancement effect of the nanomaterial are integrated, so that the composite inhibitor has a physical and chemical synergistic inhibition effect, has a significant effect in inhibiting the spontaneous combustion of coal, and can exert an inhibitory effect throughout the entire process of coal spontaneous combustion.

[0024] The present invention first prepares a composite inhibitor by graft copolymerization. The raw material ratio of MC / PEG is optimized by a single factor method, and the raw material ratio of MC / PEG-MA-ZnO is optimized by a BBD response surface analysis method to obtain the optimal raw material ratio. Electron microscopy scanning experiments demonstrate that the composite inhibitor has excellent moisture absorption and water retention properties. Infrared spectroscopy experiments demonstrate that cross-linking between polyethylene glycol and methyl cellulose is mainly achieved by hydrogen bonding, and that modified nano zinc oxide can be interconnected with thermosensitive hydrogels by means of hydrogen bonding. X-ray diffraction experiments analyze the interlaminar spacing, peak area, and crystallinity of the crystal structure, respectively demonstrating that the nano zinc oxide modification is successful and that the modified nano zinc oxide is successfully composited with MC / PEG-MA.

[0025] The material of the present invention was used to perform an inhibitory treatment on raw coal samples to obtain inhibitory coal samples. Thermogravimetric analysis experiments proved that MC / PEG-MA-ZnO has both physical inhibitory effects, chemical inhibitory effects and nanomaterial inhibitory effects. Oxidation kinetic analysis proved that DL-MA began to play a chemical inhibitory role in the pyrolysis and combustion stages, and modified n-ZnO can effectively enhance the performance of the inhibitor. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) experiments proved that the composite inhibitor improved the stability of the coal body and inhibited the coal-oxygen reaction process. X-ray photoelectron spectroscopy (XPS) experiments proved that the composite inhibitor can enhance the stability of the chemical structure of the coal sample and effectively weaken the spontaneous combustion tendency of the coal body.

[0026] The beneficial effects of the above technical solution of the present invention are as follows:

[0027] The present invention graft-copolymerizes a thermosensitive hydrogel and an antioxidant, and then consolidates the gel structure by adding nanomaterials to produce a thermosensitive hydrogel composite inhibitor. This material integrates the physical inhibitory effect of the thermosensitive hydrogel, the chemical inhibitory effect of the antioxidant, and the effect-enhancing effect of the nanomaterial, allowing the composite inhibitor to possess a physicochemical synergistic inhibitory effect. This has a significant effect in suppressing the spontaneous combustion of coal, and can exert an inhibitory effect throughout the entire process of coal spontaneous combustion. This material improves the problems of traditional inhibitors, such as single inhibitory properties, inconvenient transportation, and environmental damage. It is more versatile in the complex environment of underground mines and is a highly efficient, long-lasting, stable, environmentally friendly, and easily transportable thermosensitive hydrogel composite inhibitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the preparation process of MC / PEG-MA-ZnO of the present invention;

[0029] Figure 2 Schematic diagram of the phase transition mechanism of MC / PEG of the present invention;

[0030] Figure 3 This is the preparation mechanism of MC / PEG-MA-ZnO of the present invention;

[0031] Figure 4 This is the inhibition mechanism diagram of MC / PEG-MA-ZnO of the present invention;

[0032] Figure 5 This is the microscopic morphology of MC / PEG-MA-ZnO of the present invention;

[0033] Figure 6 is the infrared spectrum of MC, PEG and MC / PEG of the present invention;

[0034] Figure 7 This is the peak fitting result of MC / PEG-MA-ZnO of the present invention;

[0035] Figure 8 XRD patterns of three samples of the present invention;

[0036] Figure 9 TG-DTG curve of MC / PEG-MA-ZnO-impaired coal sample of the present invention;

[0037] Figure 10 The infrared spectrum of the raw coal sample of the present invention at 30°C-300°C;

[0038] Figure 11 This is the infrared spectrum of the retardant coal sample at 30°C-300°C of the present invention;

[0039] Figure 12 is the XPS total spectrum of the raw coal sample of the present invention;

[0040] Figure 13 This is the XPS total spectrum of the inhibitory coal sample of the present invention. DETAILED DESCRIPTION

[0041] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0042] The invention provides a temperature-sensitive hydrogel composite inhibitor for preventing and controlling coal spontaneous combustion.

[0043] The composite inhibitor includes thermosensitive hydrogel (MC / PEG), antioxidant DL-malic acid (DL-MA), and nanomaterial-modified nano zinc oxide (modified n-ZnO). The preparation of the composite inhibitor can be divided into three steps. The first is the preparation of thermosensitive hydrogel, which is made of methyl cellulose (MC), polyethylene glycol (PEG) and sodium chloride (NaCl); the second is the preparation of nanomaterials, which is made by modifying nano zinc oxide; and the last is the preparation of composite inhibitor, which is made of MC / PEG solution, antioxidant, nanomaterial, initiator, crosslinker and deionized water. Among them, according to the mass ratio of MC / PEG solution, the amount of antioxidant is 0.2%-0.5%, the amount of nanomaterial is 0.1%-0.4%, the amount of initiator is 0.1%-0.3%, the amount of crosslinker is 0.2%-0.6%, and the balance is deionized water. The reaction temperature is 50℃-75℃. The overall preparation process of modified antioxidant is as follows: Figure 1 shown.

[0044] Preparation process of thermosensitive hydrogel composite inhibitor (MC / PEG-MA-ZnO):

[0045] 1) Preparation of modified n-ZnO

[0046] Accurately weigh 1g of nano-zinc oxide using an electronic balance and place it in a 200ml beaker. Then, measure 100ml of a 90% by volume ethanol solution and inject it into the beaker. Stir thoroughly with a glass rod to evenly disperse the nano-zinc oxide in the ethanol solution. Transfer the beaker to a KQ-50E ultrasonic cleaner and sonicate for 10 minutes. After ultrasonic dispersion is complete, add a clean magnetic rotor to the solution and secure the beaker in a magnetic stirring water bath for continuous stirring. While stirring, slowly add 2ml of the silane coupling agent KH-570. Continue stirring for 2 hours to prepare the modified nano-zinc oxide solution.

[0047] The solution was placed in a 2-16R desktop high-speed centrifuge at a speed of 2000 rpm for 15 minutes, allowing the modified nano-zinc oxide to settle at the bottom of the centrifuge tube to achieve solid-liquid separation. The supernatant in the centrifuge tube was then filtered out, and the remaining nano-zinc oxide precipitate was placed in a DH-101 electric constant temperature blast drying oven for drying at 100°C for 6 hours to obtain modified nano-zinc oxide powder.

[0048] 2) Preparation of MC / PEG with the optimal ratio

[0049] First, pour 50ml of deionized water into a beaker and heat it to 60°C in a constant-temperature magnetic stirrer. Then, add a magnetic stir bar and start stirring. While stirring, add 2.2g of methylcellulose and 5g of polyethylene glycol, continuing to stir until both are completely dissolved. Once dissolved, add 50ml of room-temperature deionized water to the solution, accelerate cooling, and continue stirring for a period of time to form a clear, viscous solution.

[0050] The viscous solution was allowed to stand at room temperature for 3 hours. Afterward, 8g of sodium chloride was added and stirred continuously using a constant-temperature magnetic stirrer until the sodium chloride was completely dissolved. The stirring temperature was set to room temperature. Finally, the solution was allowed to stand at room temperature to allow the solution to fully swell, yielding a thermosensitive hydrogel solution, MC / PEG.

[0051] 3) Graft copolymerization

[0052] An appropriate amount of DL-MA was dissolved in deionized water, and 0.231 g of initiator KPS was added to initiate a free radical reaction, yielding a pretreated DL-MA solution. Next, 100 g of MC / PEG solution was prepared according to the optimal ratio and stirred in a magnetic stirrer. The pretreated DL-MA solution was slowly added while stirring. 0.344 g of initiator MBA and an appropriate amount of catalyst TEMED were then added and stirred for a further 3 hours. The solution was then sealed and allowed to react for a further 12 hours to complete the graft copolymerization, forming the MC / PEG-MA solution.

[0053] 4) Preparation of nanosuspension

[0054] 0.25 g of modified nano zinc oxide powder was dissolved in deionized water and ultrasonically treated for 20 min using a KQ-50E ultrasonic cleaner to form a stable nano suspension.

[0055] 5) Preparation of MC / PEG-MA-ZnO

[0056] The MC / PEG-MA solution was placed in a beaker and stirred using a magnetic stirrer. During this stirring process, a stable nano-zinc oxide suspension was slowly added. Stirring was continued for 3 hours to uniformly disperse the solution, thereby obtaining an MC / PEG-MA-ZnO solution. The uniformly mixed solution was then freeze-dried in a vacuum freeze dryer for 12 hours to obtain MC / PEG-MA-ZnO solid particles.

[0057] Phase transition mechanism of MC / PEG:

[0058] The MC molecular chain contains both hydrophilic hydroxyl groups and hydrophobic methyl groups. When the system temperature is lower than the phase transition temperature, the hydrophilic groups on the molecular chain form a stable hydration layer with water molecules through hydrogen bonds, and the system is in a solution state. When the system temperature is higher than the phase transition temperature, the molecular thermal motion intensifies, resulting in the breaking of hydrogen bonds. The hydrophobic effect between the MC molecular chains dominates, and the mutual cross-linking between the molecular chains forms a three-dimensional network system with a certain spatial structure, presenting a gelation state. The introduction of PEG and NaCl can regulate the phase transition behavior of the system: the flexible long chain of PEG can be interspersed in the three-dimensional structure formed by MC to form an interpenetrating network structure, thereby improving the mechanical strength of the gel; at the same time, the hydrophilic groups contained in the PEG molecular chain can compete with MC for water molecules, thereby reducing the gelation time and phase transition temperature of the system. NaCl can destroy the hydration layer of MC molecules through the ion shielding effect, promote the exposure of hydrophobic groups, and further reduce the gelation time and phase transition temperature of the system. Figure 2 shown.

[0059] Preparation mechanism of MC / PEG-MA-ZnO:

[0060] 1) Formation of MC / PEG-MA solution system

[0061] KPS will form persulfate ion S2O8 when dissolved in water 2- , under high temperature or TEMED catalyst conditions, it will further decompose to generate highly active sulfate radicals (SO4 -·), which can trigger a free radical chain reaction. MC molecular chains contain numerous hydroxyl structures, which serve as potential free radical reaction sites. They are easily attacked by free radicals, losing hydrogen atoms and forming active centers. These active centers can react with the hydroxyl groups on DL-MA to form ether bonds (COC), thereby grafting DL-MA onto the MC molecular chain. Simultaneously, the carbon-carbon double bonds (C═C) in MBA are also easy targets for free radical attack, forming active sites that react with the hydroxyl groups on the MC molecular chain, thereby cross-linking different MC molecular chains together, increasing the system's network cross-linking density and ultimately forming a MC / PEG-MA solution system with a dense three-dimensional network structure.

[0062] 2) Introducing modified nano zinc oxide

[0063] The surface energy of the modified nano zinc oxide n-ZnO is reduced, the hydrophilicity is enhanced, the dispersion stability in the solution is improved, and the particle agglomeration effect is effectively improved. When the modified n-ZnO is introduced into the MC / PEG-MA solution system, the nanoparticles can be evenly dispersed and penetrate into the gaps between the MC molecular chains. When the phase transition temperature is reached, the modified n-ZnO can act as a physical cross-linking point, interact with the gel network, consolidate the gel structure, and ultimately form a composite inhibitor MC / PEG-MA-ZnO with both temperature responsiveness and a certain mechanical strength. Figure 3 shown.

[0064] The flame retardant mechanism of the composite inhibitor is analyzed below.

[0065] (1) Physical inhibition mechanism of thermosensitive hydrogel PEG-MC

[0066] Its physical inhibition mechanism is mainly reflected in the following three aspects:

[0067] 1) Moisturizing

[0068] PEG-MC contains a large number of hydrophilic groups that can bind to water molecules through hydrogen bonds, thereby retaining a large amount of water within the hydrogel's grid structure. When the temperature is below the phase transition temperature of PEG-MC, PEG-MC becomes liquid, which gives PEG-MC great fluidity and allows it to penetrate into the gaps in the coal seam, thereby bringing the absorbed large amounts of water deep into the coal seam, wetting the coal seam and reducing the coal's tendency to spontaneous combustion.

[0069] 2) Evaporation absorbs heat

[0070] When the temperature of the coal body rises, the hydrogen bonds formed between PEG-MC and water molecules begin to break, and the water gradually evaporates, taking away a large amount of heat in the coal body, delaying the temperature rise trend of the coal body and inhibiting the development of coal spontaneous combustion.

[0071] 3) Isolation of oxygen

[0072] When the temperature reaches the phase transition temperature of PEG-MC, PEG-MC gradually gels to form a solid gel covering the surface of the coal seam and the gaps in the coal seam, thereby sealing and covering the coal body, isolating the contact between the coal and oxygen, hindering the coal-oxygen complex reaction, and effectively inhibiting the spontaneous combustion process of the coal.

[0073] (2) Chemical inhibition of antioxidant DL-MA

[0074] Its chemical inhibition mechanism focuses on the following two core pathways:

[0075] 1) Eliminate free radicals in the system

[0076] DL-MA contains carboxylic acid and hydroxyl groups. The synergistic effect of these two groups gives it unique chemical activity, effectively scavenging reactive free radicals in coal. The hydroxyl groups in DL-MA can donate hydrogen ions during coal spontaneous combustion, converting highly reactive oxygen species into less reactive oxygen species, thereby effectively reducing the generation of oxygen free radicals. Furthermore, the hydroxyl groups in DL-MA can participate in the coal-oxygen chain reaction, replacing the free hydroxyl groups in the coal to react with the oxygen atoms in the peroxide radicals, effectively suppressing the generation of alkoxy free radicals and thus interrupting the chain reaction of the oxidation reaction. Furthermore, during the coal spontaneous combustion process, DL-MA preferentially binds to the reactive groups in the coal, competing with the free hydroxyl groups for reaction sites, reducing the number of free radicals in the coal, effectively deactivating the reactive groups and interrupting the chain reaction, thereby inhibiting the coal spontaneous combustion process.

[0077] 2) Promote the formation of stable compounds

[0078] The hydroxyl groups in DL-MA can act as hydrogen donors during coal spontaneous combustion and generate hydroperoxides. This substance decomposes upon heating to produce alcohol and water. Other hydroxyl groups in DL-MA further react with the generated alcohol to form more stable ether bonds, thereby improving the stability of the coal. Furthermore, due to their high activity, the hydroxyl groups in DL-MA can absorb free hydroxyl groups in the coal and associate them through hydrogen bonds, effectively reducing the activity of the free hydroxyl groups in the coal molecules and thus inhibiting the chain reaction.

[0079] (3) Nano-inhibition effect of n-ZnO modified by nanomaterials

[0080] Its nano-inhibition mechanism mainly includes the following three aspects:

[0081] 1) Reduce free radicals

[0082] The modified n-ZnO contains a large number of hydroxyl structures, which can react with active free radicals in coal to generate ether bonds through etherification reaction, thereby reducing the concentration of free hydroxyl groups in coal, improving the stability of coal samples, and inhibiting the spontaneous combustion process of coal.

[0083] 2) Decomposition absorbs heat

[0084] Modified n-ZnO exhibits extremely small particle size and a very high specific surface area. When dispersed within the composite inhibitor and penetrating into the interstices of the coal seam, the large specific surface area enables the modified n-ZnO to rapidly absorb large amounts of heat, decomposing and gasifying, dispersing throughout the reaction system. Because the modified n-ZnO absorbs a significant amount of heat during the gasification process, it slows the rise in coal temperature, thereby reducing the coal sample's reaction rate and inhibiting the spontaneous combustion process.

[0085] 3) Homogeneous inhibition

[0086] The modified n-ZnO reacts more thoroughly with the free radicals in coal during the gasification process, which can significantly reduce the concentration of free radicals, thereby cutting off the chain reaction path of coal spontaneous combustion and fully exerting its inhibitory effect.

[0087] (4) Synergistic inhibition mechanism of composite inhibitor MC / PEG-MA-ZnO

[0088] The inhibition mechanism of composite inhibitor MC / PEG-MA-ZnO is as follows Figure 4 shown.

[0089] Below the phase transition temperature of the composite inhibitor, MC / PEG-MA-ZnO is primarily liquid, exhibiting exceptional fluidity. It can easily penetrate deep into the coal seam's interstices and wet the surrounding coal by carrying significant amounts of water, thereby exerting a physical inhibitory effect. As the coal temperature gradually rises, the MC / PEG-MA-ZnO and the water in the coal seam begin to evaporate, dissipating significant heat and slowing the rise in coal seam temperature. As the coal temperature rises further, reaching the phase transition temperature of the composite inhibitor, the MC / PEG-MA-ZnO gradually transforms from a liquid to a solid state. At this point, the MC / PEG-MA-ZnO that has penetrated the coal seam interstices transforms into a thin film, covering the coal seam surface or filling cracks in the coal seam. This provides a covering and plugging effect, effectively preventing contact between the coal and oxygen, isolating the coal-oxygen reaction and interrupting the coal's spontaneous combustion process. At high temperatures, the physical inhibitory effect of the composite inhibitor gradually diminishes, and the antioxidant DL-MA, which binds to the MC molecules through a grafting reaction, begins to exert a chemical inhibitory effect. DL-MA has strong antioxidant activity and can effectively reduce the concentration of active free radicals in coal. It also competes with active groups in coal for reaction sites, inhibiting their reactivity and generating more stable ether bonds. This improves the stability of coal molecules, interrupts the coal-oxygen chain reaction, and inhibits the spontaneous combustion process. During the spontaneous combustion process, the modified n-ZnO enhances the composite inhibitor's catalytic performance. Through homogeneous inhibition and decomposition heat absorption, it effectively slows the temperature rise of the coal, reduces the concentration of free hydroxyl groups in the coal, and enhances the composite inhibitor's physicochemical synergistic catalytic effect.

[0090] In specific applications,

[0091] Scanning electron microscopy revealed that the thermosensitive hydrogel formed by methylcellulose and polyethylene glycol exhibits a large number of pores. The introduction of DL-malic acid further exacerbates the surface roughness and significantly increases the number of pores. The addition of modified nano-zinc oxide creates a fibrous, wrinkled structure on the surface, significantly increasing the specific surface area and providing more sites for water absorption. Experiments have shown that this composite inhibitor exhibits excellent moisture absorption and water retention properties, effectively enhancing the inhibitory effect.

[0092] Infrared spectroscopy analysis revealed the consistent presence of characteristic peaks for polyethylene glycol, indicating that its chemical structure remained stable during the preparation process. The addition of DL-malic acid introduced a carboxyl stretching vibration peak, while the modified nano-zinc oxide weakened the hydroxyl stretching vibration peak. These results suggest that polyethylene glycol cross-links with methylcellulose via hydrogen bonds, while the modified nano-zinc oxide binds to the hydrogel via hydrogen bonds, without any chemical reaction occurring.

[0093] X-ray diffraction results showed that the interplanar spacing of the modified nano-zinc oxide increased and its crystallinity decreased, indicating enhanced reactivity. After complexing with MC / PEG-MA, the interplanar spacing remained unchanged, but the crystallinity further decreased, and the disorder increased, demonstrating that the complexation process did not destroy the modified nano-zinc oxide structure while enhancing the material's activity. The experiments verified the successful modification and complexation of nano-zinc oxide.

[0094] Through thermogravimetric analysis experiments, the changes in the characteristic temperature points of coal samples before and after the inhibition treatment were measured, indicating that MC / PEG-MA-ZnO has the best inhibition effect due to its physical inhibition, chemical inhibition and nanomaterial inhibition. It can effectively inhibit the spontaneous combustion process of coal, thereby significantly increasing the characteristic temperature point of the coal sample.

[0095] Diffuse reflectance Fourier transform infrared spectroscopy experiments revealed that the inhibitor treatment significantly altered the functional group evolution of the coal sample during heating. The inhibitor competitively occupied the active sites of free hydroxyl groups, increasing their content and slowing their decomposition rate. It also inhibited the oxidative consumption of aliphatic groups and reduced the formation of intermediates. Furthermore, the ether bond content increased rapidly, indicating that the inhibitor promoted the formation of stable chemical bonds. These effects collectively enhanced the thermal stability of the coal and effectively slowed the coal-oxygen reaction.

[0096] X-ray photoelectron spectroscopy experiments revealed significant changes in the elemental composition of the coal sample surface after the treatment: a decrease in the carbon content and an increase in the oxygen content. These results confirm that the composite inhibitor significantly increases the proportion of stable functional groups, such as ether bonds, in the coal, enhancing the chemical stability of the coal sample. This inhibitor effectively reduces the coal's tendency to spontaneously combust, thereby suppressing the risk of spontaneous combustion.

[0097] The following describes this with reference to specific embodiments.

[0098] Example 1: Scanning electron microscopy (SEM) experiment

[0099] This example was tested using a Czech TESCAN MIRA LMS scanning electron microscope. First, a certain amount of methylcellulose, polyethylene glycol, thermosensitive hydrogel, antioxidant thermosensitive hydrogel, and composite inhibitor were weighed and ground to prepare five solid powder samples. The samples were then cut and fixed with conductive adhesive, and the surfaces were uniformly loaded with the sample by gluing and purging. The samples were vacuumed using a MCIOOO gold spraying apparatus and then gold-sprayed to form a conductive film. Finally, the samples were placed in a scanning electron microscope, and clear microscopic images were obtained through low-power positioning, focus adjustment, and parameter optimization. Microscopic images of the five samples at 2kx and 5kx magnification were obtained, respectively.

[0100] Observing the microscopic morphology of methylcellulose, the methylcellulose particles are long and narrow, which is related to the molecular structure and the arrangement of molecules; the surface grooves increase the specific surface area and give it water absorption properties.

[0101] Observing the microscopic morphology of polyethylene glycol, the surface of polyethylene glycol particles is flat and smooth without obvious groove structure, and the water absorption performance mainly depends on the molecular structure rather than the physical adsorption sites.

[0102] Observation of the MC / PEG micromorphology shows that the surface is rough and porous after compounding, and the specific surface area is significantly increased, which improves the water absorption performance; the small particles on the surface may be sodium chloride precipitated during the freeze-drying process.

[0103] Observation of the microscopic morphology of MC / PEG-MA shows that the surface becomes rougher after grafting with DL-MA, with more pores, further enlarged specific surface area, and enhanced water absorption and water retention capacity.

[0104] Figure 5 This is the microscopic morphology of MC / PEG-MA-ZnO. After adding modified nano-zinc oxide, wrinkles and pores are densely distributed on the surface, and sodium chloride is wrapped in them; nanoparticles promote the formation of wrinkles, significantly improving the specific surface area and water absorption efficiency.

[0105] In summary, among the five materials analyzed, MC / PEG-MA-ZnO exhibits the roughest surface micromorphology. Its surface is covered with a large number of pores and wrinkled structures. These microscopic features significantly increase the specific surface area of ​​MC / PEG-MA-ZnO. The rich specific surface area provides ample space and numerous action sites for the adsorption of water molecules, giving MC / PEG-MA-ZnO extremely strong water absorption properties. Based on this characteristic, in the low-temperature stage of coal spontaneous combustion, MC / PEG-MA-ZnO can rely on its excellent water absorption capacity to more effectively inhibit the contact between coal and oxygen, delay the increase in coal body temperature, and thus exert a more outstanding inhibitory effect, effectively delaying the process of coal spontaneous combustion.

[0106] Example 2: Fourier transform infrared spectroscopy (FTIR) experiment

[0107] This example uses a Nicolet iS50 Fourier transform infrared spectrometer for testing. Using the potassium bromide tableting method, methylcellulose, polyethylene glycol, thermosensitive hydrogel, antioxidant thermosensitive hydrogel, and composite inhibitor were ground into solid powders with a particle size of less than 100 μm. After mixing and grinding with dry potassium bromide at a ratio of 1:100, the mixture was pressed at a pressure of 2 MPa for 5 minutes to form a thin slice to be tested. The infrared spectrometer was set at 400-4000 cm -1 Scanning range, 4cm -1The resolution and number of scans were 32, and the atmospheric background was automatically subtracted by OMNIC software. Finally, each sample was scanned in turn to obtain infrared spectrum data, and the chemical structure characteristics were analyzed based on the characteristic peak assignment table.

[0108] Figure 6 The infrared spectra of MC, PEG and MC / PEG are shown in Figure 2. -1 The stretching vibration peak of hydroxyl group (-OH) appears at 2885cm, but the peak intensity of PEG is weaker and narrower due to the lower hydroxyl content. -1 The methylene (-CH2) stretching vibration peak at 1470cm is more significant in PEG and MC / PEG, reflecting the high content of methylene in their molecular chains. -1 (methylene bending vibration absorption peak) and 1421cm -1 The difference in the (methyl bending vibration absorption peak) indicates that the methyl / methylene ratios of MC and PEG are different. -1 The characteristic peak of ether bond (COC) is shown at 958cm -1 and 841cm -1 The fingerprint peaks were retained in MC / PEG, indicating that its structure was unchanged. In summary, the MC / PEG complex formed a physical complex through hydrogen bonding without chemical reaction.

[0109] For the infrared spectra of the three inhibitors MC / PEG, MC / PEG-MA and MC / PEG-MA-ZnO, since the functional groups in each inhibitor are relatively complex, the spectra need to be peak separated and fitted.

[0110] In the peak fitting results of MC / PEG, the peaks at 2750-3750 cm -1 Area, 3517.9cm -1 The stretching vibration peak of free hydroxyl group is 3363.8cm -1 The peaks at 2892.3 cm are the intermolecular hydrogen bond hydroxyl peaks, which are derived from the PEG terminal hydroxyl group and the MC interchain hydrogen bond; -1 The presence of the methylene stretching vibration peak at 750-1750cm confirms that the ether bond-methylene chain of PEG and the hydroxyl structure of MC remain stable after gelation. -1 Within the range, 1464.0cm -1 (Methyl / methylene bending vibration absorption peak), 1352.9 cm -1 (methyl symmetric bending absorption peak) and PEG characteristic peak (950.5cm -1 、842.6cm -1) are consistent with the characteristics of the original components, indicating that the two form a physical cross-linked network through weak interactions between hydroxyl groups, without destroying the chemical structure of their respective molecular chains. In summary, it is confirmed that methylcellulose and polyethylene glycol form a thermosensitive hydrogel through physical cross-linking without undergoing chemical changes.

[0111] In the peak fitting results of MC / PEG-MA, compared with MC / PEG, MC / PEG-MA has a peak of 2750-3750cm after grafting DL-malic acid. -1 The number of absorption peaks in the range increased from 3 to 5, with the addition of 3230.6 cm -1 The intramolecular hydrogen bond -OH stretching vibration peak at 1729.8cm is derived from the introduction of hydroxyl groups in DL-malic acid, bringing the total number of hydroxyl peaks to 5; -1 A new peak of carboxyl stretching vibration appeared at 1099.5 cm, confirming the successful grafting of DL-malic acid carboxyl groups; -1 The ether bond peak is larger than that of the original MC / PEG (1107.8 cm -1 ) shifted, indicating that the ether bond structure changed due to the formation of new ether bonds. At the same time, the characteristic peak of polyethylene glycol (946.6 cm -1 、841.4cm -1 ) position remained unchanged, proving that its chemical structure remained stable. In summary, this indicates that DL-malic acid was successfully grafted onto MC / PEG, and the chemical structure of polyethylene glycol was not destroyed, indicating that the DL-malic acid grafting position was on methylcellulose.

[0112] The peak fitting results of MC / PEG-MA-ZnO are as follows Figure 7 Compared with MC / PEG-MA, the -1 In the range of 750-1750cm, the three -OH bond stretching vibration peaks of MC / PEG-MA-ZnO all move toward higher wavenumbers. This is due to the interaction between the modified nano-zinc oxide and the matrix hydroxyl groups. At the same time, the intensity of the hydroxyl absorption peak decreases, indicating that a chemical reaction occurs between the two. -1 In the region, the ether bond stretching vibration peak of MC / PEG-MA-ZnO is from 1099.5 cm -1 Move to 1106.5cm -1 The shift is due to the overlap of Si-O-Si bond stretching vibration peak and ether bond peak in modified nano-zinc oxide. -1 ) showed that the modified nano-zinc oxide had been successfully polymerized into MC / PEG-MA, and the composite inhibitor was successfully prepared.

[0113] Example 3: X-ray diffraction (XRD) experiment

[0114] This example uses a Rigaku SmartLab SE X-ray diffractometer for testing. First, prepare the sample by grinding nano-zinc oxide, modified nano-zinc oxide, and composite inhibitor particles into a uniform powder that can pass through a 200-mesh sieve. Next, set the instrument parameters. After preheating the X-ray diffractometer, select a copper target, set the scanning range to 10-80°, and the speed to 2° / min. Finally, place the sample on the sample stage for diffraction scanning, and record the diffraction intensity data at different angles.

[0115] The XRD patterns of the three experimental sample crystal particles of nano zinc oxide, modified nano zinc oxide and MC / PEG-MA-ZnO are as follows: Figure 8 As shown, the XRD patterns of the three experimental samples were analyzed by Jade 6.5 software.

[0116] Nano zinc oxide has three significant diffraction peaks in the range of 30°-40°: the interlayer spacing at 31.859° is 2.8066 angstroms (peak height 30297, diffraction peak integral width 0.160, diffraction peak area 285845); the interlayer spacing at 34.502° is 2.5974 angstroms (peak height 23224, diffraction peak integral width 0.149, diffraction peak area 203540); and the interlayer spacing at 36.340° is 2.4702 angstroms (peak height 51763, diffraction peak integral width 0.164, diffraction peak area 499757). Although other diffraction peaks exist in the region above 40°, the peak heights are significantly reduced. All main diffraction peak positions are consistent with the standard zinc oxide crystal form, indicating that the material is of high purity and has a low impurity content. Analysis using Jade 6.5 software shows that the crystallinity of nano zinc oxide is 44.58%.

[0117] The modified nano zinc oxide exhibits different characteristics from that before modification: the centroid positions of the three main diffraction peaks in the range of 30°-40° are shifted to the left (the diffraction angle is reduced) compared with those before modification, and the corresponding crystal plane interlayer spacing is expanded by 0.07%-0.12%, respectively, indicating that the spacing of the crystal structure is increased. At the same time, the peak area of ​​each diffraction peak is significantly reduced, and the areas of the three characteristic peaks at 31.820°, 34.478°, and 36.301° are reduced by 23.5%, 28.4%, and 22.4%, respectively. Using Jade 6.5 software analysis, the crystallinity of nano zinc oxide is 42.55%, which is lower than that before modification, indicating that the proportion of crystalline area of ​​the modified nano zinc oxide is reduced, indicating that the modification of nano zinc oxide is successful.

[0118] Compared with nano-zinc oxide and modified nano-zinc oxide, the diffraction peaks of MC / PEG-MA-ZnO in the 30°-40° range merged from three to one, and three weak peaks were added in the 10°-30° range, indicating that the modified nano-zinc oxide and MC / PEG-MA were successfully composited. The main peak at 31.820° corresponds to the overlap of the characteristic peaks of nano-zinc oxide (31.859°) before composite and modified zinc oxide (31.820°). The interlayer spacing remained unchanged at 2.8099 angstroms, but the peak height intensity decreased by 72.8% to 5994, the peak area decreased by 52.7% to 103332, and the crystallinity dropped from the higher value before composite to 37.04%. This indicates that the composite process has little effect on the crystal structure of ZnO itself. The further reduction in crystallinity indicates that the composite material is more disordered, and the composite degree and chemical reactivity are stronger.

[0119] In summary, the modification of nano-zinc oxide was successful, and the modified nano-zinc oxide was successfully composited with MC / PEG-MA, and the composite inhibitor was successfully prepared.

[0120] Example 4: Thermogravimetric analysis (TGA) experiment

[0121] Before the experiment, according to the "Preparation Method of Coal Samples" (GB / T 474-2008), the original coal samples were pre-crushed by using a hammer to a particle size of <12 mm; then a roller crusher and screening machine were used to crush them for a second time to 1-4 mm, with a processing capacity of about 500 g each time; then a top-impact vibrating screen was used with 150-mesh and 80-mesh sieves for 180 seconds, and the coal samples were divided into three grades according to the particle size: >80 mesh, 80-150 mesh, and <150 mesh, with a processing capacity of about 300 g per grade; finally, the graded coal samples were sealed and bagged, labeled with numbers, and stored in a cool, dark place to prevent oxidation and deterioration.

[0122] This example uses a STA7200 thermogravimetric analyzer for testing. First, turn on the instrument and software for zeroing. Place a clean crucible on the sample stage and stabilize it, then return to zero. Then, accurately weigh 5-10mg of coal sample into the right crucible and record the initial mass. Next, set the coal sample temperature to a 30°C-800°C temperature range (at a rate of 10°C / min), turn on the air cylinder switch, select air atmosphere (gas flow rate of 100ml / min), start the experiment, and the system automatically records the TG-TGA curve. After the temperature reaches the endpoint, the instrument automatically cools to room temperature. Remove the crucible to clean any residue and reset the instrument. Finally, turn off the power to complete the experiment.

[0123] According to the trend of the curve in the figure, the characteristic values ​​and stages of the coal oxidation process are divided as follows. Critical temperature T1: the starting point of the first self-acceleration stage of coal spontaneous combustion, corresponding to the first mass loss rate peak on the TG-DTG curve, marking the weight loss acceleration period dominated by water and gas desorption; Drying temperature T2: the first lowest mass point of the TG curve, the dynamic equilibrium of chemical adsorption and desorption, indicating that a violent oxidation reaction is about to start, the higher the temperature, the stronger the oxidation stability; Active temperature T3: the turning point of the TG curve from falling to rising, oxygen adsorption inhibits mass loss, the higher the temperature, the weaker the adsorption effect, and the spontaneous combustion rate slows down; Acceleration temperature T4: the maximum point of DTG, the oxygen absorption weight gain turns to violent oxidation weight loss, the higher the temperature The larger the activation energy threshold, the slower the spontaneous combustion process; thermal decomposition temperature T5: the peak point of the TG curve where oxygen absorption and weight gain end, marking the start of pyrolysis combustion, and the higher the temperature, the stronger the low-temperature oxidation stability; ignition temperature T6: the combustion trigger point calculated by extrapolation of the decomposition temperature, which triggers the breakage of the aromatic ring and the explosion of free radicals. The higher the temperature, the more difficult it is to spontaneously combust; maximum weight loss rate temperature T7: the point where the absolute value of the slope of the DTG curve is the largest, corresponding to the full combustion stage. The higher the peak, the more intense the reaction; burnout temperature T8: the end point where the TG curve tends to flatten, marking the exhaustion of volatile components. The higher the temperature, the longer the combustion process lasts.

[0124] Based on the eight characteristic temperature points that appear in the coal during the heating process, the coal spontaneous combustion process can be divided into four consecutive stages: water evaporation and adsorption stage (room temperature-T2), oxygen absorption and weight gain stage (T2-T5), pyrolysis and combustion stage (T5-T8) and burnout stage (>T8).

[0125] In the TG-DTG curve of the raw coal sample, in the water evaporation and adsorption stage (room temperature-103.7℃), T1=53.0℃ is the critical temperature, T2=103.7℃ is the cracking temperature, and physical reaction is dominant. Water evaporation absorbs heat, resulting in a decrease in mass. In the oxygen absorption and weight gain stage (103.7℃-249.2℃), T3=153.1℃ is the active temperature, T4=225.9℃ is the acceleration temperature, and the amount of chemically adsorbed oxygen exceeds the amount of desorbed gas, causing the mass to recover. In the pyrolysis and combustion stage (249.2℃-474.0℃), T5=249.2℃ is the decomposition temperature, T6=364.8℃ is the ignition temperature, and T7=372.4℃ reaches the maximum weight loss rate. Violent oxidation produces CO2 / CO, causing a sudden drop in mass. In the burnout stage (>474.0℃), T8=474.0℃ is the burnout temperature, and the stable ash residue makes the mass tend to equilibrium.

[0126] In the TG-DTG curve of the MC / PEG-retarded coal sample, in the stage of moisture evaporation and adsorption from room temperature to 115.2℃, the critical temperature T1 (52.4℃) is similar to that of the original coal, and the cracking temperature T2 (115.2℃) is 11.5℃ (+9.98%) higher than that of the original coal, because MC / PEG absorbs moisture and retains water, evaporates to cool down and covers the surface to reduce oxygen contact; in the stage of oxygen absorption and weight increase from 115.2 to 241.8℃, the active temperature T3 (158.9℃) increases by 6.7℃ (+4.38%), but T4 (205.3℃) and T5 (241.8℃) decrease, because high temperature causes MC / PEG to lose water and fail, and gel decomposition promotes spontaneous combustion; in the stage of pyrolysis and combustion from 241.8 to 481.9℃ and burnout above 481.9℃, the characteristic temperature is similar to that of the original coal, indicating that MC / PEG has no inhibitory effect in the high temperature stage. Its inhibitory effect is mainly reflected in physical moisture absorption and covering at low temperature, and it loses effectiveness after high temperature decomposition.

[0127] In the TG-DTG curve of MC / PEG-MA-retarded coal sample, the critical temperature T1 (63.4℃) and the cracking temperature T2 (122.5℃) in the water evaporation and adsorption stage (room temperature-122.5℃) were 10.4℃ and 18.8℃ higher than those of the original coal, respectively. This was mainly attributed to the fact that the hydrophilic groups such as hydroxyl and carboxyl introduced by DL-MA grafting enhanced the water absorption of the gel; the active temperature T3 (159.8℃) in the oxygen absorption and weight gain stage (122.5℃-259.9℃) was ) and thermal decomposition temperature T5 (259.9°C) increased by 6.7°C and 10.7°C, respectively, compared to the raw coal. The antioxidant DL-MA exerted a chemical inhibition effect by inhibiting functional group activity and eliminating free radicals. During the pyrolysis and combustion phase (259.9°C-481.6°C), the ignition temperature T6 (378.8°C) and the temperature of maximum weight loss rate T7 (387.1°C) increased by 14.0°C and 14.7°C, respectively, compared to the raw coal. Enhanced physical water absorption and chemical inhibition formed a synergistic effect. DL-MA effectively inhibited coal oxidation reactions from low to high temperatures through hydrophilic group regulation, free radical scavenging, and gel structure optimization.

[0128] Figure 9The TG-DTG curve of the MC / PEG-MA-ZnO-retarded coal sample is shown below. During the water evaporation and adsorption stage (room temperature - 123.6°C), its desiccation temperature T2 (123.6°C) increased by 19.9°C compared to the raw coal and by 1.1°C compared to the MC / PEG-MA-retarded coal. During the oxygen absorption and weight gain stage (123.6°C-273.9°C), its activity temperature T3 (164.1°C), ignition temperature T6 (390.1°C), and thermal decomposition temperature T5 (273.9°C) increased by 11.0°C, 18.0°C, and 24.7°C, respectively, compared to the raw coal. During the pyrolysis and combustion stage (273.9°C-517.0°C), its ignition temperature increased by 25.3°C compared to the raw coal, and its maximum weight loss rate temperature T7 (397.1°C) increased by 24.7°C compared to the raw coal. The addition of modified n-ZnO further improves the inhibitory effect of the gel system during the entire process of coal spontaneous combustion by enhancing moisture absorption and water retention, the melting endothermic effect of nanomaterials, and strengthening the gel system.

[0129] In summary, MC / PEG can only exert a physical inhibition effect in the low-temperature stage of coal spontaneous combustion, delaying the coal spontaneous combustion process to a certain extent; DL-MA shows significant chemical inhibition efficiency in the high-temperature stage of coal spontaneous combustion, and the synergistic physical and chemical inhibition effect makes the MC / PEG-MA inhibited coal sample have a higher characteristic temperature point; the addition of n-ZnO further improves the inhibition effect of the gel system in the entire process of coal spontaneous combustion, so that MC / PEG-MA-ZnO has both physical inhibition, chemical inhibition and nanomaterial inhibition, and has the best inhibition effect, which can effectively inhibit the coal spontaneous combustion process, thereby greatly increasing the characteristic temperature point of the coal sample.

[0130] Example 5: Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) Experiment

[0131] This example uses a Nicolet iS50 Fourier transform infrared spectrometer and an ATK-024-4 temperature programmable experimental instrument. Before the experiment, turn on the instrument, connect the OMNIC software, pre-cool the liquid nitrogen, complete the gas circulation and cold water circulation preheating; set the 4000-650cm -1 Scanning range, 4cm -1 The potassium bromide powder was tested with the following parameters: resolution and 32 scans, background data was obtained, and the instrument was set to automatically deduct atmospheric background interference; after changing the sample to be tested, a 30°C-300°C temperature program was set (3°C / min, 40ml / min gas flow rate), and the OMNIC software was configured for a 100-minute acquisition time; the basis vector acquisition and temperature program were executed step by step, and the sample test was started at 30°C. The spectrum was saved and the type and content of functional groups in the coal sample were analyzed through the characteristic peak attribution table.

[0132] According to the diffuse reflectance three-dimensional infrared spectra of the raw coal sample and the retardant coal sample, 10 infrared spectra of the raw coal sample and the retardant coal sample were intercepted at intervals of 30°C in the range of 30°C-300°C, such as Figure 10 and Figure 11 The experimental results show that, by comparing the raw coal samples, the hydroxyl peak area of ​​the inhibitory coal sample slows down after 180℃. Due to moisture absorption and water lock and competitive reaction of active groups, the hydroxyl consumption of inhibitory coal is lower than that of raw coal. The aliphatic group peak area shows a trend of first increasing and then decreasing. The inhibitory coal has higher methyl and methylene content, and its consumption rate is slowed down. The peak area of ​​oxygen-containing functional groups increases more slowly and the value is smaller, reflecting that the inhibitor inhibits the coal-oxygen reaction and the formation of intermediate products. The ether bond content in inhibitory coal increases significantly and at a faster rate, forming a stable structure through etherification reaction and cutting off the oxidation chain reaction.

[0133] In summary, the composite inhibitor MC / PEG-MA-ZnO can compete with hydroxyl groups for reaction sites, effectively reduce the consumption rate of hydroxyl groups in coal, inhibit the consumption rate of methyl and methylene groups in coal, thereby reducing the generation rate of intermediate products of coal-oxygen reaction, and increase the ether bond content through etherification reaction, thereby improving the stability of coal samples and effectively inhibiting the spontaneous combustion process of coal.

[0134] Example 6: X-ray Photoelectron Spectroscopy (XPS) Experiment

[0135] This example uses an ESCALAB 250Xi X-ray photoelectron spectrometer. First, a certain amount of raw coal and catalytic coal samples are ground into uniform powder and then pressed into tablets to ensure that the sample surface is flat; then the sample is placed in a vacuum chamber with a vacuum degree set to 1.0×10 -7 mbar. After vacuum extraction, the sample was placed in the analysis chamber, and spectra were acquired using a monochromatic Al Kα (1486.6eV) X-ray source with a 160eV pass energy scan over the 0-1200eV range. During data processing, the contaminated carbon peak (C1s, 284.8eV) was used as the benchmark for energy offset calibration. After sample testing, Avantage software was used for peak fitting, and the elemental composition and content of the sample were analyzed and calculated.

[0136] Figure 12 and Figure 13Figure 3 is the XPS total spectrum of the raw coal sample and the inhibitory coal sample. It can be seen that the surface elements of the raw coal sample and the inhibitory coal sample are mainly C, O, N, and Si. After the inhibitory treatment, the C content in the coal sample decreases, the O content increases, the N content is close to the original, and the Si content decreases. Avantage software was then used to fit and separate the XPS spectra. It was found that after the inhibition treatment, in terms of the C element, the proportion of aliphatic side chains (CH / CC) decreased from 63.73% to 16.27%, while the stable ether bond (COC) increased from 9.83% to 43.97%, indicating that the inhibition effect effectively reduced the active functional groups and promoted the transformation of alkyl groups to stable structures; in terms of the O element, the proportion of stable C=O increased from 17.81% to 31.15%, and the proportion of newly generated -O- reached 1.56%, further inhibiting the coal-oxygen reaction; in terms of the N element, the proportion of stable pyridinic nitrogen (N-5) increased from 0.89% to 1.30%, and the highly active pyrrolic nitrogen (N-6) decreased from 0.60% to 0.21%; in terms of the Si element, the content of SiO2, which is prone to embrittlement, decreased from 1.30% to 0.99%, indicating that the inhibition treatment optimized the coal structure. Experimental results confirm that the composite inhibitor can significantly increase the proportion of stable functional groups such as ether bonds in the coal body. By enhancing the stability of the chemical structure of the coal sample, the inhibitor effectively weakens the spontaneous combustion tendency of the coal body and suppresses the risk of spontaneous combustion.

[0137] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A temperature-sensitive hydrogel composite inhibitor for inhibiting coal spontaneous combustion, characterized in that: The composite inhibitor mainly includes thermosensitive hydrogel MC / PEG, antioxidant DL-malic acid DL-MA), nano-material modified nano zinc oxide n-ZnO, wherein, based on the mass ratio of the MC / PEG solution, the amount of antioxidant is 0.2%-0.5%, the amount of nano-material is 0.1%-0.4%, the amount of initiator is 0.1%-0.3%, the amount of cross-linking agent is 0.2%-0.6%, and the balance is deionized water. The reaction temperature is 50°C-75°C.

2. The composite inhibitor according to claim 1, characterized in that: The thermosensitive hydrogel is prepared by mixing methylcellulose MC, polyethylene glycol PEG and sodium chloride NaCl, and then standing to swell. Specifically, based on the mass ratio of methylcellulose to deionized water, the amount of methylcellulose is 1.0%-3.4%, the amount of polyethylene glycol is 3.0%-9.0%, and the amount of sodium chloride is 2.0%-14.0%. The reaction temperature is 50°C-70°C.

3. The composite inhibitor according to claim 1, characterized in that: The antioxidant DL-malic acid is used under high temperature or TEMED catalyst conditions. MC is used to initiate a free radical chain reaction through the initiator KPS. During the cross-linking polymerization process, DL-MA is grafted onto the MC molecular chain through a graft copolymerization reaction. Nano zinc oxide is modified using a silane coupling agent KH-570. During the free radical chain reaction, the amount of catalyst used is 4-5 drops.

4. The composite inhibitor according to claim 1, characterized in that: The modified nano zinc oxide is prepared by modifying nano zinc oxide using silane coupling agent KH-570. 0.5g-1.5g nano zinc oxide is dissolved in 85%-95% ethanol solution and stirred thoroughly. After ultrasonic dispersion, 1ml-3ml KH-570 is slowly added while stirring continuously.

5. The composite inhibitor according to claim 1, characterized in that: The crosslinking agent N,N-methylenebisacrylamide is a crosslinking agent that reacts with hydroxyl groups on MC molecular chains by initiating a free radical chain reaction with the initiator KPS under high temperature or TEMED catalyst conditions, thereby crosslinking different MC molecular chains.

6. The composite inhibitor according to claim 1, characterized in that: The initiator for the MC / PEG-MA solution graft copolymerization is potassium persulfate KPS.

7. The composite inhibitor according to claim 1, characterized in that: The crosslinking agent during the MC / PEG-MA solution graft copolymerization is N,N-methylenebisacrylamide MBA.

8. The composite inhibitor according to claim 3 or 5, characterized in that: The catalyst for the MC / PEG-MA solution graft copolymerization is tetramethylethylenediamine (TEMED).

9. The method for preparing the composite inhibitor according to claim 1, wherein: Dissolving DL-MA in deionized water and adding an initiator to obtain a pretreated DL-MA solution; using MC, PEG and NaCl under heating conditions to prepare an MC / PEG solution; A pretreated DL-MA solution, a cross-linking agent, and a catalyst are sequentially added, and a MC / PEG-MA solution is prepared by graft copolymerization in a constant temperature water bath of 50°C-75°C. Modified n-ZnO powder is dissolved in deionized water and subjected to ultrasonic treatment to form a nano-zinc oxide suspension. The nano-zinc oxide suspension is slowly added while the MC / PEG-MA solution is stirred to prepare a composite inhibitor, namely, a MC / PEG-MA-ZnO solution.

10. The method for preparing the composite inhibitor according to claim 9, characterized in that: Under high temperature or catalyst TEMED conditions, MC triggers a free radical chain reaction through the initiator KPS, and DL-MA is grafted onto the MC molecular chain through grafting copolymerization during the cross-linking polymerization process; MBA triggers a free radical chain reaction through the initiator KPS, reacting with the hydroxyl groups on the MC molecular chain to cross-link different MC molecular chains together; when the modified n-ZnO is introduced into the MC / PEG-MA solution system, the nanoparticles are evenly dispersed and penetrate into the gaps between the MC molecular chains. When the phase transition temperature is reached, the modified n-ZnO can act as a physical cross-linking point.

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