Expandable graphite-based natural polysaccharide hydrogel for preventing and treating spontaneous combustion of coal and preparation method of expandable graphite-based natural polysaccharide hydrogel

Abstract

The invention discloses expandable graphite-based natural polysaccharide hydrogel for preventing and treating spontaneous combustion of coal and a preparation method of the expandable graphite-based natural polysaccharide hydrogel. The hydrogel is prepared by physically blending chitosan, glucomannan, acrylamide and expandable graphite according to the weight ratio of (1-2.5): (1-2.5): 1: (5-12.5). The method comprises the following steps: step 1, completely dissolving weighed chitosan in an ethanol solution to form a turbid solution; step 2, adding weighed glucomannan into the turbid solution in the step 1 to obtain a mixed solution; step 3, adding weighed acrylamide into the mixed solution obtained in the step 2; step 4, adding the weighed expandable graphite into the mixed solution obtained in the step 3; and step 5, fully cooling and swelling at room temperature to obtain the expandable graphite-based natural polysaccharide hydrogel. The hydrogel disclosed by the invention has the advantages of good wrapping performance, permeability and water retention performance, environment friendliness, no pollution and controllable gelling time.

Description

Technical Field

[0001] The invention relates to the field of hydrogels, in particular to an expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion and a preparation method thereof. Background Art

[0002] At present, the methods for preventing and controlling coal spontaneous combustion in coal mines include grouting, spraying inhibitors, pressurizing inert gas, injecting gel and other methods. Among them, injecting gel can not only block air leakage channels, absorb heat and reduce temperature, but also keep the coal body moist and isolate oxygen for a long time, so it has a good anti-spontaneous combustion effect.

[0003] The gels injected to prevent coal spontaneous combustion in the prior art are commonly ammonium salt crosslinking agent gels and inorganic gel materials. The presence of ammonium salt crosslinking agent gels will release NH 3 There are problems with toxic and harmful gases, and inorganic gels have problems such as poor fluidity and easy cracking. Summary of the invention

[0004] The invention provides an expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion and a preparation method thereof, so as to solve the problems of releasing toxic and harmful gases, being easy to crack and not easy to flow existing in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: The expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion is prepared from chitosan, glucomannan, acrylamide and expandable graphite. The weight ratio of chitosan, glucomannan, acrylamide and expandable graphite is (1-2.5):(1-2.5):1:(5-12.5).

[0006] Furthermore, it is prepared by physically blending chitosan, glucomannan, acrylamide and expandable graphite.

[0007] Furthermore, the first network is formed by physical cross-linking of chitosan and glucomannan, and the second network is formed by chemical cross-linking of acrylamide, chitosan and glucomannan.

[0008] A method for preparing the expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion comprises the following steps: Step 1, weighing chitosan, glucomannan, acrylamide, and expandable graphite according to corresponding weight ratios, and completely dissolving the weighed chitosan in an acetic acid solution to form a turbid solution; Step 2, adding the weighed glucomannan to the turbid solution in step 1, and then stirring the mixture in a water bath at 48° C. to 51° C. until the mixture is uniform and stable, to obtain a mixed solution of chitosan and glucomannan, wherein the mixed solution of chitosan and glucomannan is physically cross-linked to form a first network; Step 3, adding weighed acrylamide to the mixed solution obtained in step 2, and then stirring under a water bath condition of 48° C. to 51° C. to obtain a mixed solution of chitosan, glucomannan and acrylamide, wherein the mixed solution of chitosan, glucomannan and acrylamide is chemically cross-linked with acrylamide, chitosan and glucomannan to form a second network; Step 4, adding the weighed expandable graphite to the mixed solution obtained in step 3, and then stirring in a water bath at 48° C. to 51° C. until the expandable graphite is evenly distributed in the mixed solution obtained in step 3; In step 5, after the stirring in step 4 is completed, the mixed solution to which expandable graphite is added is fully cooled and swelled at room temperature to obtain an expandable graphite-based natural polysaccharide hydrogel.

[0009] Furthermore, in steps 2, 3 and 4, the water bath condition is 50°C.

[0010] Furthermore, in steps 2, 3, and 4, the stirring speed used during stirring is 1500 r / min.

[0011] Furthermore, the stirring time in step 2 is 10 to 20 min, the stirring time in step 3 is 5 to 10 min, and the stirring time in step 4 is 4 to 6 min.

[0012] Furthermore, in step 5, the mixed solution to which expandable graphite is added is cooled and swelled at room temperature for 5 to 10 minutes, so that the mixed solution is fully cooled and swelled.

[0013] The expandable graphite-based natural polysaccharide hydrogel of the present invention has the advantages of good wrapping performance, permeability and water retention performance, is green and environmentally friendly, pollution-free, and has controllable gelation time, and can effectively achieve a continuous and efficient inhibition of coal spontaneous combustion. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a SEM image of the hydrogel of the present invention, wherein: (a) is at 66 SEM image at magnification, (b) at 220 SEM image at magnification, (c) at 440 SEM images at magnification.

[0015] Figure 2 It is the FTIR graph of the hydrogel of the embodiment of the present invention.

[0016] Figure 3 1 and 1 are SEM images of a mixture of hydrogel and coal according to an embodiment of the present invention, wherein: (a) is a SEM image of the raw coal sample, and (b) is a SEM image of the raw coal sample after being treated with gel.

[0017] Figure 4This is a comparison of the CO production of raw coal and coal treated with hydrogel in the embodiment of the present invention. Figure 5 It is a comparison chart of oxygen consumption rate of raw coal and coal treated with hydrogel according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0019] This embodiment discloses an expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion, which is prepared by physical blending of chitosan, glucomannan, acrylamide, and expandable graphite. The weight ratio of chitosan, glucomannan, acrylamide, and expandable graphite is (1-2.5): (1-2.5): 1: (5-12.5), wherein acrylamide is used as a cross-linking agent and expandable graphite is used as a filler.

[0020] In the expandable graphite-based natural polysaccharide hydrogel of this embodiment, the first network is formed by physical cross-linking of chitosan and glucomannan, and the second network is formed by chemical cross-linking of acrylamide, chitosan and glucomannan.

[0021] This embodiment also discloses a method for preparing the expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion, comprising the following steps: Step 1. Weigh chitosan, glucomannan, acrylamide and expandable graphite in a weight ratio of (1-2.5): (1-2.5): 1: (5-12.5), wherein the mesh size of the expandable graphite is 100 mesh.

[0022] The weighed chitosan was fully mixed with the acetic acid solution at a weight ratio of 1: (60-70), and then stirred at 1500 r / min in a water bath at 48-51°C for 10-15 min until the chitosan was completely dissolved in the acetic acid solution to form a turbid solution. The optimal temperature of the water bath was 50°C, and the optimal stirring time was 12 min.

[0023] Step 2: add the weighed glucomannan to the turbid solution in step 1, and then stir the mixture at 1500 r / min for 10 to 20 min in a water bath at 48°C to 51°C using a stirrer to make the mixed solution of chitosan and glucomannan uniform and stable, thereby obtaining a mixed solution of chitosan and glucomannan, wherein the first network is formed by physical cross-linking of chitosan and glucomannan in the mixed solution of chitosan and glucomannan. The optimal temperature of the water bath condition is 50°C, and the optimal stirring time is 15 min.

[0024] Step 3, adding acrylamide weighed as a crosslinking agent to the mixed solution obtained in step 2, and then stirring at a speed of 1500 r / min for 5 to 10 min using a stirrer under a water bath condition of 48°C to 51°C to obtain a mixed solution of chitosan, glucomannan, and acrylamide, wherein the mixed solution of chitosan, glucomannan, and acrylamide is chemically crosslinked with acrylamide, chitosan, and glucomannan to form a second network. Among them, the optimal temperature of the water bath condition is 50°C, and the optimal stirring time is 7 minutes.

[0025] Step 4: add the 100-mesh expandable graphite weighed as a filler to the mixed solution obtained in step 3, and then stir the mixture at a speed of 1500 r / min for 5 to 10 minutes using a stirrer under a water bath condition of 48°C to 51°C to uniformly distribute the expandable graphite in the mixed solution obtained in step 3. The optimal temperature of the water bath condition is 50°C, and the optimal stirring time is 7 minutes.

[0026] After the stirring in step 5 and step 4 is completed, the mixed solution with expandable graphite is cooled and swelled at room temperature for 5 to 10 minutes to allow the mixed solution to be fully cooled and swelled, thereby obtaining an expandable graphite-based natural polysaccharide hydrogel. The optimal cooling and swelling time is 8 minutes.

[0027] The following is a description of the properties of the expandable graphite-based natural polysaccharide hydrogel described in this example.

[0028] (1) The gelation time of expandable graphite-based natural polysaccharide hydrogels at different weight ratios is shown in Table 1: Table 1 Gelation timetable under different weight ratios

[0029] In Table 1, CS is chitosan, KGM is glucomannan, and EG is expandable graphite. Acrylamide is used as the crosslinking agent. Since the amount of acrylamide used in the preparation process is relatively small (less than 0.1%), the acrylamide content is not discussed in Table 1.

[0030] The gelling time refers to the time required for various base materials to be added to form a training system, and then transform from a flowing liquid state to a solid gel with certain stability and strength. The hydrogel is mainly used to prevent and control the spontaneous combustion of coal in coal mine goafs, and the gelling time should be controlled according to actual factors such as fire prevention and extinguishing technology and mine conditions. If the gelling time is too short, it may lead to pipeline blockage and equipment damage; if the gelling time is too long, the gel will remain in a free-flowing state in the coal mine, resulting in small gel coverage area and poor fire prevention and extinguishing effect. The expandable graphite-based natural polysaccharide hydrogel of this embodiment is mainly used to prevent fire accidents caused by spontaneous combustion of coal in coal mines, and the gelling time should be controlled at 5-10 min. Therefore, it can be seen from Table 1 that the expandable graphite-based natural polysaccharide hydrogel of this embodiment has a gelation time of 5.4 min when the ratio is 1.2% CS + 1.4% KGM + 4.0% EG, a gelation time of 8.5 min when the ratio is 2.0% CS + 0.8% KGM + 4.0% EG, a gelation time of 7.5 min when the ratio is 1.6% CS + 1.2% KGM + 8.0% EG, and a gelation time of 5.8 min when the ratio is 2.0% CS + 1.2% KGM + 8.0% EG. Therefore, the above ratio is selected to form the expandable graphite-based natural polysaccharide hydrogel of this embodiment, and the gelation time can meet the requirements for preventing and controlling coal spontaneous combustion.

[0031] (2) The SEM image of the expandable graphite-based natural polysaccharide hydrogel described in this embodiment is as follows: Figure 1 As shown, Figure 1 The ratio is 2.0% CS + 1.2% KGM + 8.0% EG.

[0032] It can be seen from the SEM image of the hydrogel that the expandable graphite-based natural polysaccharide hydrogel described in this embodiment has a loose and porous three-dimensional network structure as a whole, and has a large specific surface area, which is conducive to the formation of hydrogen bonds between a large number of hydroxyl groups on the KGM molecular chain and water molecules. At the same time, there are also abundant wrinkles on the surface of the expandable graphite-based natural polysaccharide hydrogel described in this embodiment, which enhances its water absorption and water retention properties. In addition, when the expandable graphite-based natural polysaccharide hydrogel described in this embodiment is subjected to external force, the three-dimensional network structure of the hydrogel can also play a supporting and protective role, thereby improving the mechanical strength of the hydrogel.

[0033] (3) The FTIR image of the expandable graphite-based natural polysaccharide hydrogel described in this example is as follows: Figure 2 As shown, Figure 2 The ratio is 2.0% CS + 1.2% KGM + 8.0% EG.

[0034] from Figure 2 It can be seen that at 3348cm-1 There is a broad absorption band at 2883 cm, which is mainly related to OH stretching and NH vibration, indicating that the expandable graphite-based natural polysaccharide hydrogel described in this example contains a large number of hydroxyl and amino groups; -1 The absorption peak at 1630cm is related to CH stretching vibration; -1 The absorption peak at 621 cm is related to the overlap of the amide groups in chitosan; -1 and 1038cm -1 The absorption peak at is related to the stretching vibration of the CH bond and the mannose group in glucomannan. Through the FTIR spectrum analysis of the hydrogel, it can be seen that there are multiple important functional groups in the expandable graphite-based natural polysaccharide hydrogel described in this embodiment, and the interaction of these functional groups has an important influence on the mechanical properties, hydrophilicity and water retention of the hydrogel.

[0035] (4) The SEM image of the expandable graphite-based natural polysaccharide hydrogel mixed with coal described in this embodiment is as follows: Figure 3 As shown, Figure 3 The ratio is 2.0% CS + 1.2% KGM + 8.0% EG.

[0036] from Figure 3 It can be seen that the surface of the original coal sample is full of pores and cracks, and fine coal dust is scattered on it, which increases the contact area between coal and oxygen, accelerates the oxidation reaction, and may generate heat in the process, thereby increasing the risk of spontaneous combustion. This microstructure is particularly dangerous during storage and transportation, and it is easy to cause coal to spontaneously combust in a high temperature environment and cause a fire. Relatively speaking, the surface of the coal sample treated with the expandable graphite-based natural polysaccharide hydrogel described in this embodiment is more dense and smooth, significantly reducing pores and cracks, and coal dust is also greatly reduced. This shows that the expandable graphite-based natural polysaccharide hydrogel described in this embodiment effectively wraps the coal sample, forms a protective film, isolates oxygen contact, reduces the oxidation rate, and reduces the heat generated during the oxidation process. Therefore, the expandable graphite-based natural polysaccharide hydrogel treatment described in this embodiment provides an effective technical means for the safe storage and use of coal, which can significantly reduce mine fire accidents and improve the safety and stability of coal. The promotion of this method is of great significance to the safety management and fire prevention and control of the coal industry, and promotes the sustainable utilization and safe production of coal.

[0037] (5) The comparison diagrams of CO generation and oxygen consumption rate of the coal sample treated by the expandable graphite-based natural polysaccharide hydrogel described in this embodiment are as follows: Figure 4 , Figure 5 As shown, Figure 4 and Figure 5 The ratio is 2.0% CS + 1.2% KGM + 8.0% EG.

[0038] Depend on Figure 4 It can be seen that the amount of CO generated by the original coal sample and the coal sample treated with the expandable graphite-based natural polysaccharide hydrogel described in this embodiment during the programmed temperature increase continues. In the initial stage, CO is mainly desorbed from coal, and the amount generated is small. As the temperature increases, the oxidation rate of coal and oxygen accelerates, and the amount of CO generated increases rapidly. When the temperature exceeds 100 ° C, the amount of CO generated by the original coal sample increases exponentially. The coal sample treated with the expandable graphite-based natural polysaccharide hydrogel described in this embodiment only starts to grow rapidly at 140 ° C. When the temperature reaches 200 ° C, the volume fraction of CO produced by oxidation of the coal sample treated with the expandable graphite-based natural polysaccharide hydrogel described in this embodiment is reduced by 54.44%. This means that the expandable graphite-based natural polysaccharide hydrogel described in this embodiment can better delay the oxidation process of coal.

[0039] Coal consumes oxygen during the oxidation and spontaneous combustion process. The oxygen consumption of different coal samples is measured according to the programmed temperature rise. The oxygen consumption rate of different coal samples is calculated using the following formula. The inhibition effect of the hydrogel material on the coal samples is reflected by comparing the oxygen consumption rates. Based on the oxygen concentration at the outlet of the coal sample tank, the oxygen consumption rate of different coal samples at different temperatures can be calculated, as shown in formula (1): (1) In formula (1): —Consumption rate at standard oxygen concentration, mol / (m 3 ·s) —Dry air flow, m 3 / s; S —Bottom area of ​​coal sample tank, m 2 ; L —Height of coal sample tank, m; —Oxygen concentration at the entrance of the coal sample tank, mol / m 3 ; —Oxygen concentration at the outlet of the coal sample tank, mol / m 3 .

[0040] like Figure 5 It can be seen that at low temperature, the oxygen consumption rate of the raw coal sample and the coal sample treated with the expandable graphite-based natural polysaccharide hydrogel described in this embodiment has a similar change range. On the whole, the oxygen consumption rate increases with the increase of temperature. When the temperature reaches 100 °C, the oxygen consumption rate of the raw coal sample is 149.19×10 -5 (mol / m 3·s), the temperature corresponding to the oxygen consumption rate of the coal sample treated with the expandable graphite-based natural polysaccharide hydrogel described in this embodiment is 140 °C; when the temperature is 200 °C, the coal sample treated with the expandable graphite-based natural polysaccharide hydrogel described in this embodiment is reduced by 55.31%. It can be seen that the expandable graphite-based natural polysaccharide hydrogel described in this embodiment can effectively slow down the oxidation process of coal, proving that the expandable graphite-based natural polysaccharide hydrogel described in this embodiment has good resistance to oxidation.

[0041] From the perspective of CO generation and oxygen consumption rate, the expandable graphite-based natural polysaccharide hydrogel described in this embodiment exhibits excellent oxidation resistance. On the one hand, this is because the expandable graphite-based natural polysaccharide hydrogel described in this embodiment can wrap the coal sample after mixing with the coal sample, playing a certain oxygen isolation role; on the other hand, the expandable graphite-based natural polysaccharide hydrogel described in this embodiment has excellent water retention properties. During the oxidation and heating process, the expandable graphite-based natural polysaccharide hydrogel described in this embodiment absorbs a large amount of oxidation heat, effectively delaying the oxidation rate of the coal body.

[0042] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and such combinations should also be regarded as the contents disclosed in the present disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0043] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by technical personnel in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. An expandable graphite-based natural polysaccharide hydrogel for preventing and controlling spontaneous combustion of coal, characterized in that: The invention is prepared from chitosan, glucomannan, acrylamide and expandable graphite, wherein the weight ratio of chitosan, glucomannan, acrylamide and expandable graphite is (1-2.5): (1-2.5): 1: (5-12.5).

2. The expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion according to claim 1, characterized in that: The invention is prepared by physically blending chitosan, glucomannan, acrylamide and expandable graphite.

3. The expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion according to claim 2, characterized in that: The first network is formed by physical cross-linking of chitosan and glucomannan, and the second network is formed by chemical cross-linking of acrylamide, chitosan and glucomannan.

4. A method for preparing an expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1, weighing chitosan, glucomannan, acrylamide, and expandable graphite according to corresponding weight ratios, and completely dissolving the weighed chitosan in an acetic acid solution to form a turbid solution; Step 2, adding the weighed glucomannan to the turbid solution in step 1, and then stirring the mixture in a water bath at 48° C. to 51° C. until the mixture is uniform and stable, to obtain a mixed solution of chitosan and glucomannan, wherein the mixed solution of chitosan and glucomannan is physically cross-linked to form a first network; Step 3, adding weighed acrylamide to the mixed solution obtained in step 2, and then stirring under a water bath condition of 48° C. to 51° C. to obtain a mixed solution of chitosan, glucomannan and acrylamide, wherein the mixed solution of chitosan, glucomannan and acrylamide is chemically cross-linked with acrylamide, chitosan and glucomannan to form a second network; Step 4, adding the weighed expandable graphite to the mixed solution obtained in step 3, and then stirring in a water bath at 48° C. to 51° C. until the expandable graphite is evenly distributed in the mixed solution obtained in step 3; In step 5, after the stirring in step 4 is completed, the mixed solution to which expandable graphite is added is fully cooled and swelled at room temperature to obtain an expandable graphite-based natural polysaccharide hydrogel.

5. The method for preparing expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion according to claim 4, characterized in that: In steps 2, 3 and 4, the water bath condition is 50°C.

6. The method for preparing expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion according to claim 4, characterized in that: In steps 2, 3 and 4, the stirring speed used during stirring is 1500 r / min.

7. The method for preparing expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion according to claim 6, characterized in that: The stirring time in step 2 is 10 to 20 min, the stirring time in step 3 is 5 to 10 min, and the stirring time in step 4 is 4 to 6 min.

8. The method for preparing expandable graphite-based natural polysaccharide hydrogel for preventing and controlling coal spontaneous combustion according to claim 4, characterized in that: In step 5, the mixed solution to which expandable graphite is added is cooled and swelled at room temperature for 5 to 10 minutes, so that the mixed solution is fully cooled and swelled.

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