A nano-carbon fiber reinforced gel material for preventing and controlling coal spontaneous combustion and its preparation method

Abstract

The present invention provides a nano-carbon fiber reinforced gel material for preventing and controlling coal spontaneous combustion and a preparation method thereof, which relates to the field of coal fire prevention and extinguishing materials in coal mines. The physical inhibitor gel is polymerized from polyacrylamide (PAM) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS), the crosslinking agent is N,N'-methylenebisacrylamide (MBA), the toughening agent is hydroxypropyl methylcellulose (HPMC), the initiator is potassium persulfate (KPS), the chemical inhibitor is tea polyphenol (TP) and the nano material is nano-carbon fiber. Each component is compounded into a nano-carbon fiber high-toughness three-dimensional crosslinked inhibitor gel by means of crosslinking, grafting and in-situ polymerization. The gel has a dense three-dimensional spatial structure, excellent water retention capacity, strong toughness, can wrap on the surface of the coal body, block cracks, isolate oxygen, reduce the surface temperature of the coal and the CO production, can effectively eliminate the surface active groups of the coal, and has an overall inhibition effect on coal spontaneous combustion, and is an efficient, environmentally friendly and stable inhibitor.

Description

Technical Field

[0001] The present invention relates to the field of coal fire prevention and extinguishing materials in coal mines, and particularly relates to a nano-carbon fiber high-toughness three-dimensional cross-linked inhibitor gel for coal mines. Background Technique

[0002] Spontaneous combustion of coal is one of the major disasters threatening the safe production of coal mines. Gas and coal dust explosion accidents induced by spontaneous combustion fires in mine shafts occur from time to time, seriously threatening people's lives and property safety, hindering the sustainable development of the coal industry, and affecting social stability. Most of the existing coal spontaneous combustion prevention and control technology systems have varying degrees of usage restrictions. Therefore, it is urgent to develop new coal spontaneous combustion prevention and extinguishing technologies to meet the increasingly complex prevention and extinguishing requirements. In this context, the high-toughness gel fire prevention and extinguishing technology has begun to receive wide attention.

[0003] The existing technologies have achieved temperature reduction and flame retardancy of coal, but there are still obvious deficiencies in the performance of the current inhibitor materials, and further research is needed. The hydrogel-based composite inhibitor proposed in the patent CN202210461958.5 improves the inhibition performance of the hydrogel and enhances the inhibition effect of the inhibitor on the whole stage of coal spontaneous combustion. However, due to the addition of anthocyanins, the action time of anthocyanins is short and it is easy to decompose. Therefore, new inhibitor materials still need to be further developed in practical applications; a nano-modified antioxidant for inhibiting coal spontaneous combustion proposed in the patent CN202110554648.3, although the modified antioxidant improves the inhibition performance of the material, especially its fluidity is good, but since it cannot play a wrapping role and cannot isolate oxygen well, the inhibition effect is affected; the inhibitor gel production process proposed in CN202110335968.X is complex, and the flame retardancy effect at low temperature is not obvious.

[0004] Therefore, there are still deficiencies in the existing coal spontaneous combustion inhibitor materials. To effectively protect coal resources and ensure the safe exploitation of coal mines, a composite material with both physical and chemical inhibition capabilities, high toughness and environmental friendliness should be prepared. A nano-carbon fiber reinforced gel material for preventing coal spontaneous combustion proposed by the present invention can form an oxygen isolation protective film on the outer surface of coal, reducing the probability of coal-oxygen combination in the gob area. In addition, since the gelling agent and the base material themselves are inhibitors, the gel also plays the role of an inhibitor for fire prevention and extinguishing. Summary of the Invention

[0005] In order to solve the problems of insufficient inhibition ability, easy decomposition, poor wrapping property, and insignificant inhibition effect at low temperature of existing coal spontaneous combustion inhibitor materials, the present invention proposes to use a nano-carbon fiber high-toughness three-dimensional crosslinked inhibition gel to control coal spontaneous combustion, that is, a double-network crosslinked gel with polyacrylamide (PAM) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as the main body. At the same time, N,N'-methylenebisacrylamide (MBA) is used as a three-dimensional crosslinking point to form a three-dimensional skeleton structure with cellulose, and the chemical inhibitor tea polyphenol (TP) is added. Finally, nano-carbon fibers are added to enhance the mechanical properties of the composite material. It can not only inhibit throughout the process, but also isolate oxygen well at low temperature. Through the combined action of physical inhibition gel, chemical inhibitor, and nano-materials, better application effects can be obtained.

[0006] The technical solution of the present invention is as follows:

[0007] A nano-carbon fiber reinforced gel material for preventing and controlling coal spontaneous combustion, its composition by weight percentage, water is 85-90%, physical inhibition gel is 2.4-3.6%, crosslinking agent is 0.1%-0.18%, toughening agent is 0.5-0.8%, initiator is 0.18-0.36%, chemical inhibitor is 0.2-0.4%, and nano-material is 0.1-0.3%.

[0008] Preferably, the physical inhibition gel is composed of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and polyacrylamide (PAM), wherein the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid to polyacrylamide is 1:2.6-3.4.

[0009] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide (MBA), the toughening agent is hydroxypropyl methylcellulose (HPMC), the initiator is potassium persulfate (KPS), the chemical inhibitor is tea polyphenol (TP), and the nano-material is nano-carbon fiber (CNFs).

[0010] The preparation method of the nano-carbon fiber reinforced gel includes the following steps:

[0011] S1: Pour the crosslinking agent into the physical inhibition gel, then dissolve the toughening agent in deionized water, slowly drop it into the solution, and stir in a constant temperature water bath for 20-30 minutes to obtain a three-dimensional crosslinked gel.

[0012] S2: Dissolve the initiator in deionized water, add the chemical inhibitor to the three-dimensional crosslinked gel, continuously stir for 2-3 hours, and carry out graft copolymerization reaction in a sealed environment at 65-75°C.

[0013] S3: Drop the nano-material solution into the three-dimensional crosslinked gel after graft copolymerization reaction, and stir in a constant temperature water bath for 2-3 hours to obtain a mixed gel solution.

[0014] S4: Place the mixed gel solution prepared in S3 in a vacuum drying oven at 80 - 90 °C and dry it for 6 - 10 h to obtain nano - carbon fiber high - toughness three - dimensional cross - linked inhibitor gel powder.

[0015] Furthermore, the physical inhibitor gel described in S1 is prepared by dissolving 2 - acrylamido - 2 - methylpropane sulfonic acid (AMPS) in deionized water, adjusting its pH with 10% NaOH solution, and slowly adding polyacrylamide (PAM), and stirring in a constant - temperature water bath for 20 - 30 minutes to obtain the physical inhibitor gel.

[0016] Furthermore, the nano - material described in S3 is prepared by dissolving nano - carbon fiber in an aqueous solution of sodium dodecyl sulfate and ultrasonic dispersing for 1 - 2 hours to make a nano - material solution.

[0017] Furthermore, the temperature of the constant - temperature water bath is 65 °C - 75 °C.

[0018] Furthermore, the mass ratio of the cross - linker to the toughening agent in S1 is 1:3 - 5.

[0019] Furthermore, the mass ratio of the initiator to the chemical inhibitor in S2 is 1:0.9 - 1.2.

[0020] Furthermore, the pH value in the preparation of the physical inhibitor gel is 6.8 - 7.3.

[0021] Furthermore, the mass ratio of the nano - material to the sodium dodecyl sulfate is 1:6 - 7.

[0022] In the above - mentioned technical solution, the nano - carbon fiber high - toughness three - dimensional cross - linked inhibitor gel has high water - retention property, strong mechanical properties, and the ability of full - process inhibition, avoiding the traditional gel from cracking due to excessive water loss at high temperature and then losing the inhibition ability, and having the ability of full - process inhibition.

[0023] The beneficial effects of the present invention are:

[0024] The nano-carbon fiber high-toughness three-dimensional cross-linked inhibitor gel of the present invention has a dense three-dimensional network structure, and at the same time has physical and chemical inhibition properties and mechanical properties, playing an overall inhibition role. At the low-temperature stage, a large amount of water is absorbed by the hydrophilic groups in the physical inhibitor gel, covering the coal surface in the form of a gel, plugging the gaps in the coal, and isolating oxygen. At the same time, the gel transports the chemical inhibitor to the active groups on the coal surface, inhibiting the chain reaction on the coal surface. With the addition of the three-dimensional network cross-linked structure and toughening agent, the mechanical properties are greatly improved. As the temperature rises, a large amount of water in the gel evaporates, generating steam to reduce the temperature of the coal surface and destroying the heat accumulation on the coal surface. At the same time, the gel transports the chemical inhibitor to the active groups on the coal surface, inhibiting the chain reaction on the coal surface. The chemical inhibitor continues to play a role, blocking the formation of intermediate products in coal molecules and reducing the generation amount of CO. Adding nano-carbon fibers to the composite inhibitor material can effectively improve the three-dimensional mechanical properties of the material, play the role of heat insulation and temperature resistance, and avoid the rise of coal temperature. Therefore, the nano-carbon fiber high-toughness three-dimensional cross-linked inhibitor gel proposed by the present invention effectively exerts the inhibition effect through the combined action of physical inhibitor gel, chemical inhibitor and nano-materials. At the same time, it reduces environmental pollution, improves the toughness of the material, and enhances the covering performance. The prepared gel material is an environmentally friendly and efficient fire prevention and extinguishing material, providing new methods and ideas for the prevention and control of coal mine shaft fires. Description of the Drawings

[0025] Figure 1 are the infrared spectra of four gels;

[0026] Figure 2 are the microscopic SEM images of four gel samples (a. SEM image of g(PAM / AMPS); b. SEM image of g(PAM / AMPS / HPMC); c. SEM image of g(PAM / AMPS / HPMC)-TP; d. SEM image of g(PAM / AMPS / HPMC)-TP / CNFs);

[0027] Figure 3 are the X-ray energy spectrum and EDS stratification diagram of g(PAM / AMPS / HPMC)-TP / CNFs gel;

[0028] Figure 4 are the thermogravimetric curves of four gel samples inhibiting coal samples and raw coal;

[0029] Figure 5 are the change curves of CO concentration of raw coal and four inhibited coal samples during programmed temperature rise;

[0030] Figure 6 are the bar charts of the inhibition rates of four inhibited gels;

[0031] Figure 7It is a three-dimensional infrared spectrogram (a. raw coal spectrogram; b. g(PAM / AMPS / HPMC)-TP / CNFs inhibited sample spectrogram);

[0032] Figure 8 It is a diagram showing the variation of hydroxyl groups and carbonyl groups with temperature (a. raw coal diagram; b. g(PAM / AMPS / HPMC)-TP / CNFs). Detailed implementation manners

[0033] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be specifically described in conjunction with specific embodiments and accompanying drawings:

[0034] Example 1

[0035] First, weigh 0.6 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) powder, stir and completely dissolve it in 100 ml of deionized water, and then place it in a water bath heating environment at 70 °C. Add 10% NaOH solution and adjust the neutralization degree to 7. Then, weigh 2 g of polyacrylamide (PAM) and add it to the solution and stir. After stirring for 20 minutes, a physical inhibitor gel, namely g(PAM / AMPS) double-network cross-linked gel, is obtained.

[0036] Weigh 0.16 g of cross-linking agent and add it to the stirred g(PAM / AMPS) double-network cross-linked gel. Then, dissolve 0.7 g of toughening agent and slowly drip it into the solution. After stirring for 20 minutes, g(PAM / AMPS / HPMC) three-dimensional cross-linked gel is obtained.

[0037] Dissolve 0.3 g of chemical inhibitor and 0.26 KPS in 10 ml of deionized water, and then drip it into the g(PAM / AMPS / HPMC) gel solution. After continuously stirring at 70 °C for 2.5 hours, seal it and carry out a graft copolymerization reaction for 2.5 hours to obtain g(PAM / AMPS / HPMC)-TP gel.

[0038] Use sodium dodecyl sulfate (SDS) as the nanofiber carbon dispersant. First, dissolve nanofiber carbon (CNFs) in an aqueous solution of sodium dodecyl sulfate (SDS). Then, ultrasonically disperse for 1 hour, where m(CNFs):m(SDS)=1:6.5. Use a glass dropper to drip 0.1 g of nanofiber carbon solution into the g(PAM / AMPS / HPMC)-TP gel solution. Stir at 70 °C in a water bath for 2 h to obtain g(PAM / AMPS / HPMC)-TP / CNFs. Place the gel in an oven, dry at 80 °C for 10 h, and grind to obtain g(PAM / AMPS / HPMC)-TP / CNFs powder.

[0039] Example 2

[0040] First, weigh 0.8 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) powder, stir and completely dissolve it in 100 ml of deionized water, and then place it in a water bath heating environment at 65 °C. Add 10% NaOH solution and adjust the neutralization degree to 6.8. Then, weigh 2.5 g of polyacrylamide (PAM) and add it to the solution and stir. After stirring for 30 minutes, a physical inhibitor, namely g(PAM / AMPS) double-network crosslinked gel, is obtained.

[0041] Weigh 0.12 g of crosslinking agent and add it to the stirred gel. Then, dissolve 0.6 g of toughening agent and slowly drip it into the solution. After stirring for 30 minutes, g(PAM / AMPS / HPMC) three-dimensional crosslinked gel is obtained.

[0042] Dissolve 0.4 g of chemical inhibitor and 0.32 KPS in 10 ml of deionized water, and then drip it into the g(PAM / AMPS / HPMC) gel solution. After continuously stirring at 65 °C for 3 hours, seal it and carry out a graft copolymerization reaction for 2 hours to obtain g(PAM / AMPS / HPMC)-TP gel.

[0043] Sodium dodecyl sulfate (SDS) is used as the nanofiber carbon dispersant. First, dissolve nanofiber carbon (CNFs) in an aqueous solution of sodium dodecyl sulfate (SDS). Then, ultrasonically disperse for 1.5 hours, where m(CNFs):m(SDS)=1:7. Use a glass dropper to drip 0.15 nanofiber carbon solution into the g(PAM / AMPS / HPMC)-TP gel solution. Stir at 65 °C in a water bath for 2 h to obtain g(PAM / AMPS / HPMC)-TP / CNFs. Place the gel in an oven, dry at 85 °C for 8 h, and grind to obtain g(PAM / AMPS / HPMC)-TP / CNFs powder.

[0044] Test Comparative Example 1

[0045] Perform infrared spectroscopy test experiments on four samples of g(PAM / AMPS), g(PAM / AMPS / HPMC), g(PAM / AMPS / HPMC)-TP, and g(PAM / AMPS / HPMC)-TP / CNFs obtained in Example 1.

[0046] The samples were tested by infrared spectroscopy using a Nicolet iS50 Fourier transform infrared spectrometer. The scanning wavenumber was 400 - 4000 cm -1 . The resolution was 4 cm -1 , and the number of scans was 64 times.

[0047] The infrared test results of the four samples are as Figure 1As shown. The peak height of the infrared spectrum increases successively from g(PAM / AMPS) to g(PAM / AMPS / HPMC)-TP / CNFs, and the peak area gradually increases. It can be seen from this that with the deepening of crosslinking polymerization and graft copolymerization, the number and types of free radicals increase greatly, and the toughness and inhibition performance of the gel are enhanced accordingly.

[0048] The g(PAM / AMPS) and g(PAM / AMPS / HPMC) gels are mainly composed of PAM and AMPS. After adding the MBA crosslinking agent and through crosslinking polymerization with HPMC, the gel mainly contains groups such as -OH, -COOH, N-H, C=O, C=C, etc. It can be clearly seen from the infrared spectrum that there is a stretching vibration of free -OH bonds at 3430 cm -1 , as shown by the vibration of the hydroxyl group in AMPS. There is a stretching vibration of N-H single bonds in the range of 3200 cm -1 , and there are multiple bending vibrations of N-H single bonds in the range of 1670 cm -1 . These vibrations are all caused by amide groups. The asymmetric stretching and bending vibrations of C-N in the region of 1375 - 1340 cm -1 indicate the presence of the AMPS chain. In addition, the asymmetric vibrations of the S-O group and the C=N band at 1050 - 1029 cm -1 also confirm the formation of these chains. Therefore, the existence of the network crosslinking structure is verified from the perspective of chemical groups.

[0049] g(PAM / AMPS / HPMC)-TP and g(PAM / AMPS / HPMC)-TP / CNFs are composite gels formed by graft copolymerization of chemical inhibitors with three-dimensional network crosslinked gels. The results show that the aromatic hydrocarbon groups and hydroxyl groups of the gel increase significantly. The wavenumber band of 3697 - 3684 cm -1 is for highly active free hydroxyl groups, and the content of intermolecular associated hydrogen bonds (wavenumber band of 3500 - 3200 cm -1 ) is the highest. The peak bands of the stretching vibrations of aliphatic groups (wavenumber range of 1770 - 1720 cm -1 ) and C=C groups (wavenumber range of 1604 - 1599 cm -1 ) are brought by the benzene ring skeleton of the chemical inhibitor.

[0050] Tea polyphenols are grafted on the gel to form ether C-O-C. Due to the addition of the chemical inhibitor, the absorption peaks of the C-H stretching vibrations of aliphatic methyl and methylene groups are weakened, and the absorption peak of the ether group C-O-C (1320 - 1050 cm -1 ) is enhanced, proving that tea polyphenols have undergone graft copolymerization reactions. The increase in peak intensity within this range proves the smooth fusion of the materials in g(PAM / AMPS / HPMC)-TP / CNFs.

[0051] Test Comparative Example 2

[0052] Scanning electron microscopy tests were carried out on the four samples of g(PAM / AMPS), g(PAM / AMPS / HPMC), g(PAM / AMPS / HPMC)-TP, and g(PAM / AMPS / HPMC)-TP / CNFs obtained in Example 1.

[0053] The Zeiss Gemini SEM 500 scanning electron microscope was used in the experiment. The four gel samples were ground into particles with a particle size less than 100 microns, and gold was sprayed on the samples. At an acceleration voltage of 20 kV, the morphology of each specimen was observed. The EDS test of the samples was carried out with an X-ray energy spectrometer (Ultim Max 170, Oxford Instruments).

[0054] Through scanning electron microscopy tests, the changes in the microscopic morphologies of the four powder materials of g(PAM / AMPS), g(PAM / AMPS / HPMC), g(PAM / AMPS / HPMC)-TP, and g(PAM / AMPS / HPMC)-TP / CNFs were comprehensively compared, providing a scientific basis for further analyzing the water absorption performance of the composite materials. The gel SEM images are as Figure 1 shown.

[0055] Figure 2 As shown in (a), the surface of the g(PAM / AMPS) double-crosslinked gel is rough and disordered, the structure is loose, showing granular protrusions, and the voids are large, which is consistent with its characteristics of being easily broken and having poor water retention. As Figure 2 shown in (b), after crosslinking copolymerization with the crosslinking agent and toughening agent, the gel surface is relatively rough and dense, without obvious large pores, proving that a spatial structure is formed after the crosslinking of HPMC and g(PAM / AMPS), enhancing the toughness of the gel. And the rough surface increases its contact area with water molecules, improving the water absorption and covering ability. As Figure 2 shown in (c), after graft copolymerization of g(PAM / AMPS / HPMC) with the chemical inhibitor TP, its surface becomes well-proportioned, holes appear, the number of folds increases, and at the same time, small granular protrusions are intertwined on the gel surface, proving that the chemical inhibitor TP is evenly graft copolymerized in the three-dimensional spatial structure. As Figure 2 shown in (d), the gel surface becomes smooth, the three-dimensional structure is more three-dimensional, the spatial structure becomes more dense, more holes appear, increasing the specific surface area of the gel. At the same time, the filling of CNFs makes the particle-flake structure on the gel surface evenly distributed, improving the skeleton hardness of the gel, proving that the gel toughness is improved.

[0056] Figure 3X-ray energy spectrum and EDS stratification map of g(PAM / AMPS / HPMC)-TP / CNFs gel. As Figure 3 (b) shows, it mainly contains elements such as C, N, O, Na, Si, S, etc. The distribution of elements in the selected area indicates that Figure 3 (d) matches the bright areas in Figure 3 (e) and Figure 3 (g). The corresponding substances may come from AMPS and MBA, which reflects the polymerization process and reaction mechanism of the gel. Molecules polymerize to form a macromolecular backbone chain, connecting the main body of the gel in series. During this process, HPMC, as a cross-linking polymerization raw material, enhances the toughness of the gel. As Figure 3 (f) shows, S is evenly distributed on the entire gel surface, and S mainly comes from AMPS and SDS. During the gelation process, AMPS serves as the cross-linking main chain, forming a three-dimensional structure, and the gel framework becomes three-dimensional. Therefore, this proves that the three-dimensional structure of the gel is completely cross-linked. And SDS is a dispersant for CNFs. With the help of the dispersant, CNFs are dispersed into the center and chain ends of the three-dimensional skeleton, improving the tensile strength of the gel and enhancing the mechanical properties of the gel.

[0057] Test Comparative Example 3

[0058] Thermogravimetric analysis was carried out on four samples of g(PAM / AMPS), g(PAM / AMPS / HPMC), g(PAM / AMPS / HPMC)-TP, and g(PAM / AMPS / HPMC)-TP / CNFs obtained in Example 1.

[0059] Thermogravimetric analysis was carried out on the raw coal sample and the coal samples treated with the four gel samples. The ratio of raw coal to gel sample was 1:1.5. After the coal sample and the gel reacted fully for 24 h, they were naturally dried for 48 h and then put into a sealed bag. Then, 10 mg of the experimental sample was loaded into a thermogravimetric analyzer. The heating rate was set at 10 °C / min. The temperature range was 20 °C to 700 °C, and the air flow rate was 100 ml / min.

[0060] Coal molecules can participate in the physical adsorption, chemical adsorption, and heat generated by chemical reactions between coal and oxygen at a certain specific temperature, thus triggering coal spontaneous combustion. Temperature is the macroscopic concentration manifestation of the kinetic energy of coal molecules. The lower the temperature, the smaller the kinetic energy of coal molecules, the lower the activity, and the less likely it is to react. The characteristic temperature points reflect the process of coal molecule oxidation and spontaneous combustion, providing a basis for judging the macroscopic thermal effect of the gel inhibiting coal oxidation.

[0061] The thermogravimetric curves of different gel samples inhibiting coal samples are as Figure 4As shown in the figure. According to the TG curves of each group of coal samples obtained from the experiment, it can be analyzed that there are four stages in the process of programmed temperature rise of raw coal and inhibited coal samples: evaporation and adsorption, oxygen absorption and weight gain, thermal decomposition and combustion, and burnout stage. By analyzing the changes in the four stages and the characteristic interval temperature points of the coal samples before and after inhibition treatment, each stage of the spontaneous combustion process of the coal samples can be comprehensively and quantitatively evaluated, providing an experimental basis for comprehensively evaluating the pros and cons of the inhibition performance of inhibitors.

[0062] As Figure 4 shown, in Stage1 (evaporation and adsorption), the mass of the raw coal and the four inhibited coal samples begins to decrease slowly, the moisture in the coal and the inhibited samples begins to evaporate, and the adsorbed gas is gradually desorbed. At the same time, the coal begins to adsorb oxygen, but the content of adsorbed oxygen is less than the content of lost moisture and desorbed gas, so the weight of the coal sample shows a decreasing state. Starting from Stage2 (oxygen absorption and weight gain), the change trend of the sample mass changes. The adsorption rate of the raw coal molecules to molecules such as oxygen accelerates, and the mass of the raw coal increases significantly. In this stage, the activity of the coal molecules decreases and the reaction slows down. After adding the inhibited gel, due to the good water absorption and moisture retention performance of the gel, as the temperature rises, the moisture stored in the gel evaporates and absorbs heat. Therefore, in this stage, physical inhibition mainly plays a role in reducing the temperature of the coal surface and inhibiting the rise of the coal body temperature.

[0063] In Stage3 (thermal decomposition and combustion), the raw coal burns rapidly and the mass decreases rapidly. g(PAM / AMPS) has insufficient high-temperature resistance, cracks under heat, and the inhibition ability disappears, resulting in a rapid decrease in the mass of the inhibited sample. In this stage, the curves of g(PAM / AMPS / HPMC)-TP and g(PAM / AMPS / HPMC)-TP / CNFs decrease steadily. This is because the chemical inhibitor TP plays a major inhibitory role in this stage. TP eliminates the surface active groups of the coal molecules, and the intermediate products after the reaction are not easily decomposed, cutting off the chain reaction. Due to the addition of CNFs, the structure of g(PAM / AMPS / HPMC)-TP / CNFs is stable and not easily decomposed, so the mass curve is relatively flat, showing the advantage of stable inhibition of nanomaterials.

[0064] In summary, g(PAM / AMPS / HPMC)-TP / CNFs can adsorb more moisture due to the existence of a stable three-dimensional structure, and has excellent physical inhibition performance. After compounding with the chemical inhibitor TP and the nanomaterial CNFs, the skeleton stability and mechanical properties are improved, it can better wrap the surface of the coal seam, and the inhibition ability is enhanced.

[0065] Test Comparative Example 4

[0066] The inhibition performance experiments of coal samples and inhibited samples were carried out on four samples of g(PAM / AMPS), g(PAM / AMPS / HPMC), g(PAM / AMPS / HPMC)-TP, and g(PAM / AMPS / HPMC)-TP / CNFs obtained in Example 1 using a programmed temperature system.

[0067] The samples were analyzed using an SG2-6-12TP programmable box-type atmosphere furnace and a GASERA ONE gas analyzer. The gel and coal were completely mixed at a mass ratio of 1:1.5. The temperature range was 25 - 200 °C, the heating rate was 1 °C / min, the air flow rate was 100 ml / min, and the released gas (CO) was measured every 10 °C. Finally, the inhibition rate of the inhibited gel was analyzed. The calculation formula for the inhibition rate is shown in Formula 1.

[0068]

[0069] In the formula:

[0070] W is the inhibition rate of the inhibitor on coal spontaneous combustion (%);

[0071] Q 1 is the CO release amount (ppm) in the raw coal sample;

[0072] Q 2 is the CO amount (ppm) released from the inhibited coal sample.

[0073] The changes in CO concentration and inhibition rate of raw coal and four inhibited coal samples during the programmed temperature increase are as Figure 5 and Figure 6 shown. It can be obtained from Figure 5 that as the temperature increases, the CO concentration of the coal sample and the four inhibited coal samples increases slowly before 60 °C and rises rapidly after 80 °C. However, with the change in the type of added gel, the oxidation products of coal also change significantly. The inhibition rates of g(PAM / AMPS), g(PAM / AMPS / HPMC), g(PAM / AMPS / HPMC)-TP, and g(PAM / AMPS / HPMC)-TP / CNFs gradually increase, and g(PAM / AMPS / HPMC)-TP / CNFs has the best inhibition effect. The inhibition rate of g(PAM / AMPS) is relatively low, only 18.1%, because the strength of the two-dimensional cross-linked structure is poor and the wrapping degree is limited. When the temperature rises, the gel quickly loses water and becomes brittle, and finally loses its inhibitory effect.

[0074] As the degree of three-dimensional network crosslinking deepens and the chemical inhibitor graft copolymerization is successful, the denser network structure covering the coal sample surface acts as a better oxygen barrier and heat insulation layer. At the same time, the chemical inhibitor consumes the active groups on the coal sample surface, blocking the coal-oxygen complex reaction on the coal sample surface. The chain reaction is blocked from the source, thereby increasing the inhibition rate. With the addition of CNFs, the gel skeleton structure becomes more meticulous and the covering and filling ability is further enhanced. Therefore, the initial CO generation rate of this inhibited sample is lower than that of other inhibited samples. When the temperature rises to 200 °C, the inhibition property of g(PAM / AMPS / HPMC)-TP / CNFs does not decrease, proving its strong thermal stability and that it will not lose its inhibition ability due to high-temperature pyrolysis. And finally, its average inhibition rate reaches 74.2%, which is about 56% higher than that of g(PAM / AMPS), indicating its good inhibition performance

[0075] Test Comparative Example 5

[0076] In-situ diffuse reflectance infrared spectroscopy experiments were carried out on four samples of g(PAM / AMPS), g(PAM / AMPS / HPMC), g(PAM / AMPS / HPMC)-TP, and g(PAM / AMPS / HPMC)-TP / CNFs obtained in Example 1

[0077] A Nicolet iS50 Fourier transform infrared spectrometer and an ATK-024-4 programmable temperature controller were used. The sample was 10 mg, and the scanning range was set to 650 - 4000 cm -1 , the temperature rise range of the diffuse reflectance reaction cell was 15 - 300 °C, the temperature rise rate was 3 °C / min, and the air flow rate was 50 ml / min. The diffuse reflectance infrared spectra of the raw coal and the coal sample treated with g(PAM / AMPS / HPMC)-TP / CNF were analyzed from the perspective of functional group changes

[0078] By simulating the heat storage processes of the raw coal and the inhibited coal samples, the trends of the distribution and content changes of functional groups under programmed temperature conditions were studied, providing a solid basis for the microscopic changes in the spontaneous combustion inhibition performance of the inhibited gel for coal samples Figure 7 are the three-dimensional infrared spectra of the raw coal and the g(PAM / AMPS / HPMC)-TP / CNFs inhibited sample Figure 8 are the diagrams of the changes of hydroxyl groups and carbonyl groups of the raw coal and g(PAM / AMPS / HPMC)-TP / CNFs with temperature

[0079] As can be seen from Figure 8 (a), the hydroxyl group content shows an obvious downward trend. As the temperature rises, the hydroxyl group content in the raw coal and the inhibited coal samples becomes lower and lower. Hydroxyl groups mainly exist in the range of 3700 - 3200 cm -1The wavenumber range includes free hydroxyl groups, intermolecular associated hydrogen bonds, etc. In the first two wavenumber bands, the peak shapes are relatively sharp. In the wavenumber band belonging to intermolecular associated hydrogen bonds, the peak shape is wider and flatter. The peak value of each spectral peak band of raw coal is the highest. As the temperature increases, the absorbance of hydroxyl groups generally shows a downward trend. Free hydroxyl groups have higher activity. It can be seen from the figure that after being inhibited by g(PAM / AMPS / HPMC)-TP / CNFs, the hydroxyl content decreases rapidly. The overall absorbance of hydroxyl groups shows a downward trend, indicating that the chemical structure of the inhibitor consumes the hydroxyl groups in coal molecules, the hydroxyl groups associated in the molecules decrease, the active sites are destroyed, and the coal-oxygen reaction is inhibited.

[0080] The oxygen-containing functional groups mainly select the carbonyl group (C=O) for analysis. As can be seen from Figure 8 (b), as the temperature of the coal sample increases, the carbonyl content decreases, and the existing carbonyl groups are rapidly oxidized into aldehydes or ketones. However, at 150 °C and 200 °C, the carbonyl content shows a slightly rising trend. This is because the carbonyl group is an intermediate product of aliphatic hydrocarbon oxidation, and at this time, the aliphatic hydrocarbon is rapidly oxidized, resulting in a short-term dynamic equilibrium. After being inhibited by g(PAM / AMPS / HPMC)-TP / CNFs, the short-term dynamic equilibrium is quickly broken, the carbonyl group is oxidized into a stable product, interrupting the chain reaction in the coal molecules, and the inhibition effect is obvious.

[0081] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Preparation method of nano-carbon fiber reinforced gel material for preventing and controlling coal spontaneous combustion, characterized in that, by weight percentage, the gel material composition is as follows: water is 85 - 90%, physical inhibitor gel is 2.4 - 3.6%, cross-linking agent is 0.1% - 0.18%, toughening agent is 0.5 - 0.8%, initiator is 0.18 - 0.36%, chemical inhibitor is 0.2 - 0.4%, and nano-material is 0.1 - 0.3%; The preparation steps are as follows: S1: Pour the cross-linking agent into the physical inhibitor gel, then dissolve the toughening agent in deionized water, slowly drop it into the physical inhibitor gel solution added with the cross-linking agent, and stir in a constant temperature water bath for 20 - 30 minutes to obtain a three-dimensional cross-linked gel; S2: Dissolve the initiator and chemical inhibitor in deionized water, then drop it into the three-dimensional cross-linked gel, continuously stir for 2 - 3 hours, and carry out graft copolymerization reaction in a sealed environment at 65 - 75 °C; S3: Drop the nano-material solution into the three-dimensional cross-linked gel after the graft copolymerization reaction, and stir in a constant temperature water bath for 2 - 3 hours to obtain a mixed gel solution; S4: Place the mixed gel solution prepared in S3 in a vacuum drying oven at 80 - 90 °C and dry it for 6 - 10 h to obtain nano-carbon fiber high-toughness three-dimensional cross-linked inhibitor gel powder; The physical inhibitor gel is composed of 2-acrylamido-2-methylpropanesulfonic acid and polyacrylamide, the cross-linking agent is N,N'-methylenebisacrylamide, the toughening agent is hydroxypropyl methylcellulose, the initiator is potassium persulfate, the chemical inhibitor is tea polyphenol, and the nano-material is nano-carbon fiber.

2. The preparation method according to claim 1, characterized in that, the physical inhibitor gel described in S1 is to dissolve 2-acrylamido-2-methylpropanesulfonic acid in deionized water, adjust its pH with 10% NaOH solution, slowly add polyacrylamide, and the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid to polyacrylamide is 1: 2.6 - 3.4, and stir in a constant temperature water bath for 20 - 30 minutes to obtain the physical inhibitor gel.

3. The preparation method according to claim 1, characterized in that, the nano-material solution described in S3 is to dissolve nano-carbon fiber in sodium dodecyl sulfate aqueous solution, and ultrasonically disperse it for 1 - 2 hours to make the nano-material solution; the mass ratio of nano-material to sodium dodecyl sulfate is 1:6 - 7.

4. The preparation method according to claim 1 or 2, characterized in that, the temperature of the constant temperature water bath is 65 °C - 75 °C.

5. The preparation method according to claim 1, characterized in that, the mass ratio of the cross-linking agent to the toughening agent in S1 is 1:3 - 5.

6. The preparation method according to claim 1, characterized in that, the mass ratio of the initiator to the chemical inhibitor in S2 is 1:0.9 - 1.

2.

7. The preparation method according to claim 2, characterized in that, the pH value is 6.8 - 7.

3.

8. A nano-carbon fiber reinforced gel material for preventing and controlling coal spontaneous combustion, characterized in that, the nano-carbon fiber reinforced gel material for preventing and controlling coal spontaneous combustion is prepared by the method according to any one of claims 1 - 7.

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