PH-sensitive coal spontaneous combustion inhibition microcapsule as well as preparation method and application thereof

Abstract

The invention provides a pH-sensitive coal spontaneous combustion inhibition microcapsule as well as a preparation method and application thereof, and belongs to the technical field of inhibitors. According to the preparation method, the PLGA-chitosan grafted copolymer is taken as a shell, and the inhibitor is wrapped in the shell, so that the pH-sensitive coal spontaneous combustion inhibition microcapsule is prepared. The inhibition system and CO2 gas are compounded in the pH-sensitive coal spontaneous combustion inhibition microcapsule, so that a chemical-physical-gaseous multi-stage synergistic mechanism is formed; experiments show that the pH-sensitive coal spontaneous combustion inhibition microcapsule can quickly sense the change of chemical environment pH in the coal oxidation process, and can realize targeted release in the key stage of coal oxygen reaction to efficiently inhibit coal spontaneous combustion.

Description

Technical Field

[0001] The present invention relates to the technical field of inhibitors, and particularly to a pH-sensitive coal spontaneous combustion inhibitor microcapsule, a preparation method thereof, and an application thereof. Background Art

[0002] Coal spontaneous combustion is a major safety hazard that has long existed during coal mining and storage processes. Under the action of oxidation heat release of the coal body, the temperature gradually rises and causes spontaneous combustion, releasing a large amount of toxic and harmful gases (such as CO, CH 4 ), seriously threatening the safety of underground operations and causing resource waste.

[0003] At present, the prevention and control technologies for coal spontaneous combustion mainly include grouting, nitrogen injection, inhibitor spraying, etc. Among them, inhibitors (such as magnesium chloride, polymer gels, etc.) achieve good flame retardant effects by inhibiting the coal-oxygen composite reaction or isolating the diffusion of oxygen. Conventional inhibitors act on the surface of the coal body through direct spraying or perfusion, and the initial inhibitor effect is significant. However, affected by factors such as the humid underground environment, seepage of coal body fissures, and the driving force of oxidation reaction heat, the inhibitor is easily washed away or quickly consumed, and it is difficult to continuously play a role during the development process of coal spontaneous combustion, resulting in a short inhibitor aging time. At the same time, significant chemical environment changes accompany the process of coal spontaneous combustion. In particular, the oxidation reaction will gradually change the local pH value. The reaction of organic acids in coal will cause the initial pH of lignite oxidation to drop to 6.5. As the oxidation reaction progresses, the pH in coal drops to 4.5. The oxidation of pyrite, a mineral in coal, will cause the pH of high-sulfur coal to drop to 6 at the initial stage of the reaction. In addition, the dissolution of alkaline minerals participating in oxidation will increase the pH of coal. However, the existing inhibitor release types cannot monitor the chemical environment changes during the reaction process of the coal body, and cannot effectively dynamically regulate the release behavior according to the pH change during the oxidation process of the coal body, resulting in waste of inhibitors or insufficient release at key stages.

[0004] In recent years, microencapsulation technology has been introduced into the field of inhibitor slow release. However, existing carriers (such as paraffin, silicate, etc.) generally have problems such as strong environmental inertness, poor controllability of degradation, and inability to respond to specific environmental signals (such as pH). In addition, the compatibility of some materials with inhibitors is poor, resulting in a low encapsulation rate or uncontrollable release kinetics. In view of the above problems, there is an urgent need to develop a new controlled release system that can intelligently sense environmental changes (such as pH fluctuations) during coal spontaneous combustion and realize the on-demand release of inhibitors.

[0005] The ester bond of PLGA can undergo hydrolysis under acidic or alkaline conditions, and its degradation rate is closely related to the pH of the medium, which provides a theoretical basis for designing a pH-responsive inhibitor carrier. However, combining the pH-responsive characteristics of PLGA with the requirements for coal spontaneous combustion inhibition and constructing an intelligent inhibition device suitable for complex coal mine environments has not been reported in relevant research at present. Summary of the Invention

[0006] The object of the present invention is to provide a pH-sensitive microcapsule for inhibiting coal spontaneous combustion, a preparation method and an application thereof. The pH-sensitive microcapsule for inhibiting coal spontaneous combustion can quickly sense the change of pH in the chemical environment during the coal oxidation process. After hydrolysis of the PLGA-chitosan graft copolymer shell of the microcapsule for inhibiting coal spontaneous combustion, inhibitor and inert gas can be released to form a "chemical-physical-gaseous" multi-stage synergistic inhibition mechanism, and target release is carried out at the key stage of the coal-oxygen reaction to efficiently inhibit coal spontaneous combustion.

[0007] In order to achieve the above object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of a pH-sensitive microcapsule for inhibiting coal spontaneous combustion, comprising the following steps:

[0009] (1) Mix PLGA-chitosan graft copolymer with dichloromethane to obtain an oil phase;

[0010] (2) Dissolve an inhibitor in water to obtain an aqueous phase;

[0011] (3) Mix the oil phase obtained in step (1) with the aqueous phase obtained in step (2), and perform gradient ultrasonic treatment to obtain an emulsion;

[0012] (4) Stir and centrifuge the emulsion obtained in step (3), and perform freezing and freeze-drying treatments on the precipitate obtained by centrifugation to obtain the pH-sensitive microcapsule for inhibiting coal spontaneous combustion.

[0013] Preferably, the preparation method of the PLGA-chitosan graft copolymer in step (1) is: mix poly(lactic-co-glycolic acid) with dichloromethane to obtain solution 1, mix chitosan with acetic acid solution to obtain solution 2, mix solution 1 and solution 2, and perform freeze-drying to obtain the PLGA-chitosan graft copolymer; the mass-volume ratio of poly(lactic-co-glycolic acid) to dichloromethane and chitosan is 1 g: 45-55 ml: 1 g; the mass percentage content of the acetic acid solution is 0.8-1.2%, and the mass-volume ratio of poly(lactic-co-glycolic acid) to the acetic acid solution is 1 g: 45-55 ml.

[0014] Preferably, the mass-volume ratio of the PLGA-chitosan graft copolymer to dichloromethane in step (1) is 1 g: 15-25 ml.

[0015] Preferably, the inhibitor in step (2) comprises one or more of magnesium chloride, sodium sulfate, and tetrabutylphosphonium bromide; the mass-volume ratio of magnesium chloride to water is 1 g: 45-55 ml; the mass-volume ratio of sodium sulfate to water is 1 g: 15-25 ml; the mass-volume ratio of tetrabutylphosphonium bromide to water is 1 g: 45-55 ml.

[0016] Preferably, before mixing in step (3), sulfonated montmorillonite nanosheets are added to the oil phase, and the addition amount of the sulfonated montmorillonite nanosheets is 1-5% of the mass of the oil phase; the mass ratio of the oil phase to the water phase is 3-5:1; the gradient ultrasonic treatment is carried out under ice bath conditions.

[0017] Preferably, the gradient ultrasonic treatment in step (3) includes three stages: the ultrasonic frequency in the first stage is 15-25 Hz and the power is 90-100 W, the ultrasonic frequency in the second stage is 35-45 Hz and the power is 190-200 W, and the ultrasonic power in the third stage is 75-85 Hz and the power is 45-55 W; the ultrasonic time in each stage of the gradient ultrasonic treatment is 25-35 s; the interval between each stage of the gradient ultrasonic treatment is 55-65 s; the number of times of the gradient ultrasonic treatment is 5-6 times.

[0018] Preferably, the rotation speed of the stirring in step (4) is 200-500 rpm, and the stirring time is 5.5-6.5 h; the centrifugal force of the centrifugation is 4000-6000 x g; the centrifugation time is 8-12 min; the number of times of centrifugation is 2-3 times; the freezing temperature is -75 to -85 °C, and the freezing time is 2-4 h; the freeze-drying temperature is -30 to -50 °C; the freeze-drying time is 24-48 h.

[0019] The present invention also provides a pH-sensitive coal spontaneous combustion inhibitor microcapsule prepared by the preparation method described above.

[0020] The present invention also provides the application of the pH-sensitive coal spontaneous combustion inhibitor microcapsule in the preparation of fire prevention and extinguishing products.

[0021] The present invention also provides the application of the pH-sensitive coal spontaneous combustion inhibitor microcapsule in coal mine fire prevention and extinguishing.

[0022] The beneficial effects of the present invention compared with the prior art are as follows:

[0023] The pH-sensitive coal spontaneous combustion inhibitor microcapsule provided by the present invention incorporates an inhibitor system (magnesium chloride + sodium sulfate + tetrabutylphosphonium bromide) and CO 2 gas to form a "chemical-physical-gaseous" multi-level synergistic mechanism; the tetrabutylphosphonium bromide (TBPB) can interrupt the chain reaction by scavenging free radicals, sodium sulfate can inhibit the oxidation of functional groups, and magnesium chloride can absorb moisture and reduce the coal temperature; the CO 2 gas released after the degradation of PLGA can quickly diffuse into the coal pores to form an inert gas layer to isolate oxygen; CO 2 dissolves in the coal body moisture to generate a weak acidic environment (H 2 CO 3) It reversely promotes the further degradation of the PLGA shell, forming an intelligent cycle of "release - feedback - re - release", strengthening the targeted release of the inhibitor at key stages, and efficiently inhibiting coal spontaneous combustion.

[0024] Experiments show that at different stages of coal spontaneous combustion, the PLGA - chitosan graft copolymer shell exhibits controllable pH - sensitive characteristics. When acidic substances are generated in the initial stage of coal oxidation (such as the production of acid due to the oxidation of pyrite leading to a decrease in pH, and the reaction of phytic acid and organic acid structures in coal) or when alkaline minerals dissolve in the later stage (pH increases), the ester bonds of PLGA undergo specific hydrolysis, and the degradation rate of the shell dynamically matches the local pH environment, triggering the release of the inhibitor on demand. The release of the inhibitor is highly coordinated with the process of coal spontaneous combustion, breaking through the limitations of traditional single - release modes, and significantly reducing the injection frequency and cost.

[0025] Through the innovative design of the PLGA microcapsule structure, the present invention realizes the pH - triggered release of the inhibitor during the oxidation process of coal. The pH - sensitive coal spontaneous combustion inhibitor microcapsules can dynamically adjust the release behavior according to the actual environmental pH of the target area for coal spontaneous combustion prevention and control, significantly improving the inhibition efficiency and resource utilization rate, and providing technical support for the green and safe mining of coal mines. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is a schematic plan view of the pH - sensitive coal spontaneous combustion inhibitor microcapsules prepared in Example 2 of the present invention; among them, Figure 1 (1) in it is the PLGA - chitosan graft copolymer shell, Figure 1 (2) in it is magnesium chloride, Figure 1 (3) in it is sodium sulfate, Figure 1 (4) in it is tetrabutylphosphonium bromide (TBPB), Figure 1 (5) in it is CO 2 gas;

[0028] Figure 2 It is the inhibition effect of the trigger time change of the inhibitor microcapsules on the oxidation process of lignite under different pH environments. Among them, Figure 2 (a) in it is the CO inhibition diagram of the inhibitor microcapsule structure when the pH of the coal sample environment is 5, Figure 2 (b) in it is the CO inhibition diagram of the inhibitor microcapsule structure when the pH of the coal sample environment is 6, Figure 2Among them, (c) is the CO inhibition diagram of the structure of the inhibitor microcapsule when the pH of the coal sample environment is 8. Figure 2 Among them, (d) is the CO inhibition diagram of the structure of the inhibitor microcapsule when the pH of the coal sample environment is 9.

[0029] Figure 2 The microcapsule among them is the abbreviation of the pH-sensitive coal spontaneous combustion inhibitor microcapsule. Detailed implementation manners

[0030] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0031] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0032] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0033] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0034] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0035] The present invention provides a preparation method of a pH-sensitive coal spontaneous combustion inhibitor microcapsule, including the following steps:

[0036] (1) Mix the PLGA-chitosan graft copolymer with dichloromethane to obtain an oil phase;

[0037] (2) Dissolve the inhibitor in water to obtain an aqueous phase.

[0038] (3) Mix the oil phase obtained in step (1) with the water phase obtained in step (2), and perform gradient ultrasonic treatment to obtain an emulsion;

[0039] (4) Stir and centrifuge the emulsion obtained in step (3), and freeze and freeze-dry the precipitate obtained by centrifugation to obtain the pH-sensitive coal spontaneous combustion inhibitor microcapsules.

[0040] In the present invention, the preparation method of the PLGA-chitosan graft copolymer in step (1) is preferably: mix the poly(lactic-co-glycolic acid) copolymer with dichloromethane to obtain solution 1, mix chitosan with an acetic acid solution to obtain solution 2, mix solution 1 and solution 2, and perform freeze-drying to obtain the PLGA-chitosan graft copolymer; the mass-volume ratio of the poly(lactic-co-glycolic acid) copolymer to dichloromethane is preferably 1 g: 45-55 ml, more preferably 1 g: 48-52 ml, and even more preferably 1 g: 50 ml; the mass-volume ratio of chitosan to the acetic acid solution is preferably 1 g: 45-55 ml, more preferably 1 g: 48-52 ml, and even more preferably 1 g: 50 ml; the mass percentage content of the acetic acid solution is preferably 0.8-1.2%, more preferably 1.0%; after mixing solution 1 and solution 2, stirring is preferably performed, and the temperature of the stirring is preferably 20-30 °C, more preferably 22-28 °C, even more preferably 24-26 °C, and still more preferably 25 °C; the stirring time is preferably 20-25 h, more preferably 22-24 h, and even more preferably 23 h; the purpose of the stirring is to promote the reaction between the PLGA active ester and the amino group of chitosan to form an amide bond to form a copolymer; after the stirring, filtration is preferably performed; the freeze-drying method is preferably pre-freezing at -78 to 82 °C for 3-5 h, primary drying at -38 to 42 °C for 22-25 h, and secondary drying at 24-26 °C for 22-25 h, more preferably pre-freezing at -80 °C for 4 h, primary drying at -40 °C for 24 h, and secondary drying at 25 °C for 24 h; the mass percentage of PLGA and chitosan contained in the PLGA-chitosan graft copolymer is preferably 80-90:10-20, more preferably 82-88:12-18, even more preferably 84-86:14-16, and still more preferably 85:15; the mass-volume ratio of the PLGA-chitosan graft copolymer to dichloromethane is preferably 1 g: 15-25 ml, more preferably 1 g: 16-24 ml, even more preferably 1 g: 18-22 ml, and still more preferably 1 g: 20 ml.

[0041] In the present invention, the inhibitor described in step (2) preferably includes one or more of magnesium chloride, sodium sulfate, and tetrabutylphosphonium bromide; the mass-volume ratio of the magnesium chloride to water is preferably 1 g: 45 to 55 ml, more preferably 1 g: 46 to 54 ml, still more preferably 1 g: 48 to 52 ml, and even more preferably 1 g: 50 ml; the mass-volume ratio of the sodium sulfate to water is preferably 1 g: 15 to 25 ml, more preferably 1 g: 16 to 24 ml, still more preferably 1 g: 18 to 22 ml, and even more preferably 1 g: 20 ml; the mass-volume ratio of the tetrabutylphosphonium bromide to water is preferably 1 g: 45 to 55 ml, more preferably 1 g: 46 to 54 ml, still more preferably 1 g: 48 to 52 ml, and even more preferably 1 g: 50 ml.

[0042] In the present invention, preferably, sulfonated montmorillonite nanosheets are added to the oil phase before mixing. The addition amount of the sulfonated montmorillonite nanosheets is preferably 1-5% of the mass of the oil phase, more preferably 2-4%, and even more preferably 3%. The particle size of the sulfonated montmorillonite nanosheets is preferably 50-100 nm, more preferably 60-90 nm, even more preferably 70-80 nm, and still more preferably 75 nm. The ion exchange capacity of the sulfonated montmorillonite nanosheets is preferably 1.2-1.8 meq / g, more preferably 1.4-1.6 meq / g, and even more preferably 1.5 meq / g; preferably, ultrasonic dispersion treatment is carried out after adding the sulfonated montmorillonite nanosheets. The frequency of the ultrasonic dispersion is preferably 35 - 45 kHz, more preferably 36 - 44 kHz, still more preferably 38 - 42 kHz, and even more preferably 40 kHz; the power of the ultrasonic dispersion is preferably 150 - 250 W, more preferably 160 - 240 W, still more preferably 180 - 220 W, and even more preferably 200 W; the time of the ultrasonic dispersion is preferably 8 - 12 min, more preferably 9 - 11 min, still more preferably 10 min; the mass ratio of the oil phase to the water phase is preferably 3 - 5:1, more preferably 4:1; the gradient ultrasonic treatment is preferably carried out under ice bath conditions; the ice bath conditions are preferably maintained by adding dry ice; the stages of the gradient ultrasonic treatment preferably include three stages: the ultrasonic frequency in the first stage is 15 - 25 Hz and the power is 90 - 100 W, the ultrasonic frequency in the second stage is 35 - 45 Hz and the power is 190 - 200 W, and the ultrasonic power in the third stage is 75 - 85 Hz and the power is 45 - 55 W; more preferably, the ultrasonic frequency in the first stage is 16 - 24 Hz and the power is 92 - 98 W, the ultrasonic frequency in the second stage is 36 - 44 Hz and the power is 192 - 198 W, and the ultrasonic power in the third stage is 76 - 84 Hz and the power is 46 - 54 W; still more preferably, the ultrasonic frequency in the first stage is 18 - 22 Hz and the power is 94 - 96 W, the ultrasonic frequency in the second stage is 38 - 42 Hz and the power is 194 - 196 W, and the ultrasonic power in the third stage is 78 - 82 Hz and the power is 48 - 52 W; even more preferably, the ultrasonic frequency in the first stage is 20 Hz and the power is 95 W, the ultrasonic frequency in the second stage is 40 Hz and the power is 195 W, and the ultrasonic power in the third stage is 80 Hz and the power is 50 W; the ultrasonic time in each stage during the gradient ultrasonic treatment is preferably 25 - 35 s, more preferably 26 - 34 s, still more preferably 28 - 32 s, and even more preferably 30 s; the interval between each stage during the gradient ultrasonic treatment is preferably 55 - 65 s, more preferably 56 - 64 s, still more preferably 58 - 62 s, and even more preferably 60 s; the number of times of the gradient ultrasonic treatment is preferably 5 - 6 times.

[0043] In the present invention, the stirring method in step (4) is preferably magnetic stirring; the purpose of the magnetic stirring is to volatilize the organic solvent; the stirring speed is preferably 200 - 500 rpm, more preferably 300 - 400 rpm, and even more preferably 350 rpm; the stirring time is preferably 5.5 - 6.5 h, more preferably 5.7 - 6.4 h, even more preferably 5.8 - 6.2 h, and still more preferably 6.0 h; the stirring temperature is preferably 20 - 30 °C, more preferably 22 - 28 °C, even more preferably 24 - 26 °C, and still more preferably 25 °C; the centrifugal force for centrifugation is preferably 4000 - 6000 xg, more preferably 5000 xg; the centrifugation time is preferably 8 - 12 min, more preferably 10 min; the number of centrifugation times is preferably 2 - 3 times; after centrifugation, the precipitate is preferably washed with deionized water to remove impurities; the freezing temperature is preferably -75 to -85 °C, more preferably -76 to -84 °C, even more preferably -78 to -82 °C, and still more preferably -80 °C; the freezing time is preferably 2 - 4 h, more preferably 2.5 - 3.5 h, even more preferably 3 h; the temperature for freeze-drying is preferably -30 to -50 °C, more preferably -45 to -45 °C, even more preferably -50 °C; the freeze-drying time is preferably 24 - 48 h, more preferably 28 - 45 h, even more preferably 30 - 40 h, and still more preferably 35 h.

[0044] The present invention also provides a pH-sensitive coal spontaneous combustion inhibitor microcapsule prepared by the preparation method described above.

[0045] In the present invention, the particle size of the microcapsule is preferably 10 - 50 μm, and the encapsulation efficiency of tetrabutylphosphonium bromide in the microcapsule > 85%, the encapsulation efficiency of sodium sulfate > 78%, and the encapsulation efficiency of magnesium chloride > 82%.

[0046] The present invention also provides the application of the pH-sensitive coal spontaneous combustion inhibitor microcapsule in the preparation of fire prevention and extinguishing products.

[0047] The present invention also provides the application of the pH-sensitive coal spontaneous combustion inhibitor microcapsule in coal mine fire prevention and extinguishing.

[0048] In the present invention, when the microcapsule is transported to the target area for coal spontaneous combustion prevention and control, during the oxidation process of the coal body, the pH value changes, and the microcapsule will hydrolyze to release the inhibitor and CO 2 gas, inhibiting the spontaneous combustion of the coal body; the pH response range for the hydrolysis of the microcapsule is pH > 8 and pH < 6.

[0049] Example 1

[0050] Dissolve 1 g of poly(lactic-co-glycolic acid) (PLGA) in 50 ml of dichloromethane to obtain Solution 1, dissolve 1 g of chitosan in 50 ml of acetic acid solution with a mass percentage of 1.0% to obtain Solution 2, mix Solution 1 and Solution 2, stir at 25 °C for 24 h, filter, pre-freeze at -80 °C for 4 h, conduct primary drying at -40 °C for 24 h, and conduct secondary drying at 25 °C for 24 h to obtain the PLGA-chitosan graft copolymer. The PLGA-chitosan graft copolymer contains 85% by mass of PLGA and 15% by mass of chitosan.

[0051] Example 2

[0052] A preparation method of pH-sensitive microcapsules for inhibiting coal spontaneous combustion is as follows:

[0053] (1) Mix 1 g of the PLGA-chitosan graft copolymer prepared in Example 1 with 20 ml of dichloromethane to obtain the oil phase;

[0054] (2) Dissolve 1 g of magnesium chloride in 50 ml of water to obtain the aqueous phase;

[0055] (3) Add 3% by mass of sulfonated montmorillonite nanosheets (particle size of 80 nm and ion exchange capacity of 1.5 meq / g) based on the mass of the oil phase obtained in step (1), disperse by ultrasonic wave at 40 kHz and 200 W for 10 min, mix with the aqueous phase obtained in step (2), add dry ice in small amounts and multiple times to maintain an ice bath environment, and set the ultrasonic conditions for three stages respectively, i.e., the first stage: 20 Hz, 100 W, the second stage: 40 Hz, 200 W, the third stage: 80 Hz, 50 W, conduct gradient ultrasonic treatment, the ultrasonic time for each stage is 30 s, and the interval between each stage is 60 s to obtain an emulsion;

[0056] (4) Stir the emulsion obtained in step (3) magnetically at 25 °C and 300 r / min for 6.0 h, conduct centrifugation at 5000 xg for 10 min, centrifuge twice in total, wash the precipitate with deionized water after each centrifugation, freeze the precipitate obtained by centrifugation at -80 °C for 3 h, and conduct freeze-drying treatment at -40 °C for 48 h to obtain the pH-sensitive microcapsules for inhibiting coal spontaneous combustion.

[0057] Example 3

[0058] A preparation method of pH-sensitive microcapsules for inhibiting coal spontaneous combustion is as follows:

[0059] (1) Mix 1 g of the PLGA-chitosan graft copolymer (prepared according to the method in Example 1, containing 80% by mass of PLGA and 20% by mass of chitosan) with 15 ml of dichloromethane to obtain the oil phase;

[0060] (2) Dissolve 1 g of sodium sulfate in 15 ml of water to obtain an aqueous phase;

[0061] (3) Add 1% by mass of sulfonated montmorillonite nanosheets (particle size of 50 nm and ion exchange capacity of 1.2 meq / g) based on the mass of the oil phase obtained in step (1), ultrasonically disperse for 12 min at 35 kHz and 150 W, mix with the aqueous phase obtained in step (2), add dry ice in small amounts multiple times to maintain an ice bath environment, and set the ultrasonic conditions for three stages respectively, that is, the first stage: 15 Hz, 90 W, the second stage: 35 Hz, 190 W, the third stage: 75 Hz, 45 W, perform gradient ultrasonic treatment, the ultrasonic time for each stage is 35 s, and the interval between each stage is 65 s to obtain an emulsion;

[0062] (4) Magnetically stir the emulsion obtained in step (3) at 30 °C at 200 r / min, stir for 6.5 h, centrifuge at 4000 xg for 12 min, centrifuge 3 times in total, wash the precipitate with deionized water after each centrifugation, freeze the precipitate obtained by centrifugation at -75 °C for 4 h, and perform freeze-drying treatment at -50 °C for 24 h to obtain the pH-sensitive coal spontaneous combustion inhibitor microcapsules.

[0063] Example 4

[0064] A preparation method of pH-sensitive coal spontaneous combustion inhibitor microcapsules is as follows:

[0065] (1) Mix 1 g of PLGA-chitosan graft copolymer (prepared according to the method in Example 1, containing 90% by mass of PLGA and 10% of chitosan) with 25 ml of dichloromethane to obtain an oil phase;

[0066] (2) Dissolve 1 g of tetrabutylphosphonium bromide in 45 ml of water to obtain an aqueous phase;

[0067] (3) Add 5% by mass of sulfonated montmorillonite nanosheets (particle size of 100 nm and ion exchange capacity of 1.8 meq / g) based on the mass of the oil phase obtained in step (1), ultrasonically disperse for 8 min at 45 kHz and 250 W, mix with the aqueous phase obtained in step (2), add dry ice in small amounts multiple times to maintain an ice bath environment, and set the ultrasonic conditions for three stages respectively, that is, the first stage: 25 Hz, 100 W, the second stage: 45 Hz, 200 W, the third stage: 85 Hz, 55 W, perform gradient ultrasonic treatment, the ultrasonic time for each stage is 25 s, and the interval between each stage is 55 s to obtain an emulsion;

[0068] (4) At 20 °C, the emulsion obtained in step (3) was magnetically stirred at 500 r / min for 5.5 h, centrifuged at 6000 xg for 8 min, and centrifuged twice in total. After each centrifugation, the precipitate was washed with deionized water, frozen at -85 °C for 2 h, and freeze-dried at -30 °C for 35 h to obtain the pH-sensitive coal spontaneous combustion inhibitor microcapsules.

[0069] Experimental Example 1 Inhibiting Experiment on Oxidative Spontaneous Combustion of High-Sulfur Coal

[0070] According to the method in Example 2, pH-sensitive coal spontaneous combustion inhibitor microcapsules containing magnesium chloride, pH-sensitive coal spontaneous combustion inhibitor microcapsules containing sodium sulfate, and pH-sensitive coal spontaneous combustion inhibitor microcapsules containing tetrabutylphosphonium bromide were prepared respectively.

[0071] High-sulfur coal (sulfur content 4.5%) with a particle size of 0.18 - 0.25 mm was selected as the experimental coal sample. The above-obtained pH-sensitive coal spontaneous combustion inhibitor microcapsules were mixed with the experimental coal sample at a mass ratio of 1:10 respectively. After mixing evenly, they were placed in the coal sample tank of the programmed temperature experiment device and used as experimental group samples for the experiment; and the coal sample without the inhibitor was used as the control group sample for the same experiment. The specific operations are as follows:

[0072] Put 100 g of the sample into the sample tank of the ZRD-II type coal spontaneous combustion characteristic tester, ensure that the inlet, outlet, and temperature sensor of the instrument are connected normally and sealed, and externally connect a GC-7008 gas chromatograph to collect the oxygen concentration. The gas atmosphere is dry air, and the flow rate is set at 50 ml / min. The initial temperature is 30 °C, the heating rate is 1 °C / min, and the gas is collected every 20 °C until 200 °C. Each group of experiments was repeated 3 times, and the gas change laws of CO, CO 2 and CH 4 were monitored through the gas chromatograph. The gas release concentration during the heating process was statistically analyzed, and the inhibition rate of the inhibitor microcapsules was calculated according to Formula I. The results are shown in Table 1 and Table 2.

[0073]

[0074] Table 1 Comparison of CO Generation Amounts before and after Inhibition

[0075]

[0076]

[0077] Table 2 Comparison of CO 2 Generation Amounts before and after Inhibition

[0078] Temperature (°C) <![CDATA[CO 2 (Experimental group, ppm)]]> <![CDATA[CO 2 (Control group, ppm)]]> Inhibition rate (%) 50 174±9.5 428±17 59.3 70 205±15 580±32 64.7 90 305±20 923±46 66.4 110 474±28 1350±75 64.9 130 653±33 1815±93 64.0 150 854±45 2235±120 61.8 170 1087±52 2995±157 63.7 190 1320±68 3680±185 64.1

[0079] The results showed that CH 4The generation amount was always lower than the detection limit (<5 ppm), while CH appeared in the control group after 150 °C, 4 and its concentration was 25 ppm. During the coal spontaneous combustion stage, the inhibition rates of the microcapsules for CO and CO 2 both exceeded 60%, and the inhibition effect remained stable within the range of coal temperature rising to 190 °C, indicating that the microcapsules provided by the present invention have strong inhibition ability and long-term effectiveness during the coal spontaneous combustion process.

[0080] During the coal spontaneous combustion and oxidation process, the oxidation formula of pyrite in high-sulfur coal is: 2FeS 2 +2H 2 O + 7O 2 →2FeSO 4 +2H 2 SO 4 +Q 1 ; FeS 2 +Fe 2 (SO 4 ) 3 +3O 2 +2H 2 O → 3FeSO 4 +2H 2 SO 4 +Q 2 . The oxidation of pyrite will release heat (Q), triggering the temperature rise of the coal body. After spraying the inhibitory microcapsules, in the acidic environment after the oxidation of pyrite, PLGA undergoes hydrolysis to release the inhibitor magnesium chloride, forming a liquid film on the surface of the coal body and can penetrate into the internal coal fissures, blocking oxygen and reducing temperature by filling and wrapping coal particles. The inhibitor tetrabutylphosphonium bromide (TBPB) is used to scavenge the free radical structure during the coal oxidation reaction process. Sodium sulfate reacts with active groups such as carboxylic acid and methylene in the coal to form stable substances such as ethers and alkyls, reducing the oxidation activity and inhibiting the generation of CO; and the CO 2 gas released by the inhibitory microcapsules can block the adsorption of coal and oxygen, reduce the coal-oxygen reaction, and inhibit the generation of gas.

[0081] Test Example 2 Inhibitory Experiment on the Oxidation and Spontaneous Combustion of Low-Rank Lignite

[0082] According to the method in Example 2, pH-sensitive coal spontaneous combustion inhibitory microcapsules containing magnesium chloride, pH-sensitive coal spontaneous combustion inhibitory microcapsules containing sodium sulfate, and pH-sensitive coal spontaneous combustion inhibitory microcapsules containing tetrabutylphosphonium bromide were respectively prepared.

[0083] Low-rank lignite with a particle size of 0.18 - 0.25 mm (volatile matter > 40%, sulfur content < 1%) was selected as the experimental coal sample. The coal sample was pre-soaked in different pH buffer solutions (pH = 5.0, 6.0, 8.0, 9.0) for 24 h to simulate the local chemical environment at different stages of spontaneous combustion, and then dried for 48 h after soaking.

[0084] The obtained pH-sensitive coal spontaneous combustion inhibitor microcapsules and experimental coal samples with different pH values were mixed at a mass ratio of 1:10 respectively. After being evenly mixed, they were placed in the coal sample tank of the programmed temperature rise experimental device and used as experimental group samples for experiments; coal samples without inhibitor were used as control group samples for the same experiments. The specific operations are as follows:

[0085] Put 100 g of the sample into the sample tank of the ZRD-II type coal spontaneous combustion property tester, ensure that the inlet, outlet and temperature sensor of the instrument are connected normally and sealed, and externally connect a GC-7008 gas chromatograph to collect the oxygen concentration. The gas atmosphere is dry air, and the flow rate is set at 50 ml / min. The initial temperature is 30 °C, the heating rate is 1 °C / min, and the gas is collected every 20 °C until 200 °C. Each group of experiments is repeated 3 times, and the changes in CO and CO 2 gas are monitored by the gas chromatograph, and the CO and CO 2 gas release concentrations during the heating process are statistically analyzed, and the inhibition rates of the inhibitor microcapsules on coal samples with different pH values at 190 °C are calculated and compared. The calculation formula is shown in Formula Ⅰ. The results are shown in Table 3.

[0086] Table 3 Inhibition rates of coal samples with different pH values

[0087] pH trigger point CO generation inhibition rate (%) <![CDATA[CO 2 Inhibition rate generated (%)]]> pH 5.0 69.3±4.1 61.5±3.8 pH 6.0 58.1±4.2 52.2±4.2 pH 8.0 52.2±3.5 43.6±3.2 pH 9.0 41.5±2.9 38.7±3.1

[0088] The results show that in an acidic environment, the inhibition effect of the pH-sensitive coal spontaneous combustion inhibitor microcapsules provided by the present invention is the best, which is highly compatible with the early oxidation acid production characteristics of low-rank lignite; the pH value corresponding to low-rank coal near the critical temperature is 5-6, and the release of the inhibitor exerts the multi-stage synergistic inhibition ability of the microcapsules. Below this threshold, the hydrolysis of the inhibitor microcapsules and the release of the inhibitor, CO 2 inert gas can maximize the inhibition efficiency, and the slow-release characteristics of the inhibitor microcapsules in an alkaline environment can reduce the waste of the inhibitor and continuously inhibit the oxidation process of coal.

[0089] Test Example 3 Experimental study on the response effect of inhibitor microcapsules in different pH environments

[0090] Prepare pH-sensitive coal spontaneous combustion inhibitor microcapsules containing magnesium chloride, pH-sensitive coal spontaneous combustion inhibitor microcapsules containing sodium sulfate, and pH-sensitive coal spontaneous combustion inhibitor microcapsules containing tetrabutylphosphonium bromide respectively according to the method in Example 2.

[0091] Select low-rank lignite with a particle size of 0.18 - 0.25 mm (volatile matter > 40%, sulfur content < 1%) as the experimental coal sample. The coal sample is pre-soaked in different pH buffer solutions (pH = 5.0, 6.0, 8.0, 9.0) for 24 h to simulate the local chemical environment at different stages of spontaneous combustion, and then dried for 48 h after soaking.

[0092] The pH-sensitive microcapsules for inhibiting coal spontaneous combustion obtained above were respectively mixed with experimental coal samples with different pH values at a mass ratio of 1:10. After being mixed evenly, they were placed in a coal sample tank (as the experimental group), and the constant-temperature oxidation process was carried out through a programmed temperature rise box with a flow rate set at 50 ml / min. The constant temperature was 50 °C, and gas was collected in the experimental airbag once every minute. The change law of CO gas at different triggering times was monitored by a gas chromatograph. The mixing and assembly process time of each sample was kept consistent. And the same experiment was carried out with the coal sample without inhibitor as the control group. Analyze the change law of gas concentration during the constant-temperature experiment. The results are as Figure 2 shown.

[0093] As Figure 2 can be seen, under different pH triggering thresholds, the change law of CO concentration in the coal samples added with inhibitor microcapsules is more obvious than that of the control group. And in an acidic environment, the inhibition effect of the inhibitor microcapsules is more obvious. By comparing the change law of CO before and after adding the inhibitor microcapsules, it is found that after adding the inhibitor microcapsules, CO shows a downward trend at different triggering times and undergoes a mutation, which is due to the hydrolysis of the inhibitor microcapsules in response to the change of environmental pH. Analyzing the CO change curves of coal samples with different pH values, it is found that the delayed release times of the inhibitor microcapsules in the environments of pH 5, pH 6, pH 8, and pH 9 are 5 min, 8 min, 12 min, and 15 min respectively. During the coal oxidation process, the inhibitor microcapsules can be released efficiently and quickly to block the coal-oxygen reaction process and inhibit the spontaneous combustion of coal due to temperature rise.

[0094] Therefore, in practical applications, the dosage of the pH-sensitive microcapsules for inhibiting coal spontaneous combustion should be determined according to the actual situation on site.

[0095] As can be seen from the above embodiments, the present invention provides a pH-sensitive microcapsule for inhibiting coal spontaneous combustion, its preparation method and application. The pH-sensitive microcapsule for inhibiting coal spontaneous combustion can quickly sense the change of pH in the chemical environment during the coal oxidation process, can achieve targeted release at the key stage of the coal-oxygen reaction, and efficiently inhibit coal spontaneous combustion.

[0096] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing pH-sensitive coal spontaneous combustion retardant microcapsules, characterized in that: The steps include: (1) mixing the PLGA-chitosan graft copolymer with dichloromethane to obtain an oil phase; (2) dissolving the inhibitor in water to obtain an aqueous phase; (3) mixing the oil phase obtained in step (1) with the water phase obtained in step (2), and subjecting the mixture to gradient ultrasonic treatment to obtain an emulsion; (4) stirring and centrifuging the emulsion obtained in step (3), freezing and freeze-drying the precipitate obtained by centrifugation, and obtaining the pH-sensitive coal self-ignition retardant microcapsules.

2. The preparation method according to claim 1, characterized in that: The preparation method of the PLGA-chitosan graft copolymer in step (1) is as follows: a polylactic acid-glycolic acid copolymer is mixed with dichloromethane to obtain a solution 1, chitosan is mixed with an acetic acid solution to obtain a solution 2, solution 1 and solution 2 are mixed, and freeze-dried to obtain the PLGA-chitosan graft copolymer; the mass volume ratio of the polylactic acid-glycolic acid copolymer to dichloromethane and chitosan is 1g:45-55ml:1g; the mass percentage content of the acetic acid solution is 0.8-1.2%, and the mass volume ratio of the polylactic acid-glycolic acid copolymer to the acetic acid solution is 1g:45-55ml.

3. The preparation method according to claim 1, characterized in that: The mass volume ratio of the PLGA-chitosan graft copolymer to dichloromethane in step (1) is 1 g: 15-25 ml.

4. The preparation method according to claim 1, characterized in that: The inhibitor in step (2) includes one or more of magnesium chloride, sodium sulfate, and tetrabutylphosphine bromide; the mass volume ratio of the magnesium chloride to water is 1g:45-55ml; the mass volume ratio of the sodium sulfate to water is 1g:15-25ml; the mass volume ratio of the tetrabutylphosphine bromide to water is 1g:45-55ml.

5. The preparation method according to claim 1, characterized in that: In step (3), sulfonated montmorillonite nanosheets are added to the oil phase before mixing, and the amount of the sulfonated montmorillonite nanosheets added is 1-5% of the mass of the oil phase; the mass ratio of the oil phase to the water phase is 3-5:1; and the gradient ultrasonic treatment is carried out in an ice bath.

6. The preparation method according to claim 1 or 5, characterized in that: The gradient ultrasonic treatment in step (3) includes three stages: the ultrasonic frequency of the first stage is 15-25 Hz and the power is 90-100 W, the ultrasonic frequency of the second stage is 35-45 Hz and the power is 190-200 W, and the ultrasonic power of the third stage is 75-85 Hz and the power is 45-55 W; the ultrasonic time of each stage during the gradient ultrasonic treatment is 25-35 s; the interval between each stage during the gradient ultrasonic treatment is 55-65 s; the number of times of the gradient ultrasonic treatment is 5-6 times.

7. The preparation method according to claim 1, characterized in that: In step (4), the stirring speed is 200 to 500 rpm, and the stirring time is 5.5 to 6.5 hours; the centrifugal force of the centrifugation is 4000 to 6000 x g; the centrifugation time is 8 to 12 min; the number of centrifugation is 2 to 3 times; the freezing temperature is -75 to -85°C, and the freezing time is 2 to 4 hours; the freeze-drying temperature is -30 to -50°C; and the freeze-drying time is 24 to 48 hours.

8. pH sensitive coal self-ignition retardant microcapsules prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the pH-sensitive coal spontaneous combustion retardant microcapsules as claimed in claim 8 in the preparation of fire prevention and extinguishing products.

10. Use of the pH sensitive coal spontaneous combustion retardant microcapsules as claimed in claim 8 in coal mine fire prevention and extinguishing.

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