Fire extinguishing powder based on seed crystal induced struvite and preparation method thereof

Abstract

The invention belongs to the technical field of environment-friendly fire extinguishing materials, and particularly relates to fire extinguishing powder based on seed crystal induced struvite and a preparation method of the fire extinguishing powder. The method comprises the following steps: by taking nitrogen and phosphorus-rich supernate in a sewage treatment plant as a raw material, firstly removing heavy metal ions in sewage through a cation selective permeable membrane, then adjusting the pH value of the supernate and the ratio of nitrogen to phosphorus, introducing seed crystal to induce struvite (MAP) to crystallize and precipitate, and filtering and drying to obtain seed crystal induced synthesized MAP particles; a horizontal planetary ball mill is further adopted, MAP and a modifier are evenly mixed and ground, and the MAP fire extinguishing powder with the good fire extinguishing performance is prepared. The layered double hydroxide (LDH) is creatively adopted as a seed crystal inducer, the pyrolysis starting temperature of the layered double hydroxide (LDH) can be remarkably increased, meanwhile, the thermal decomposition dynamic process is optimized, and therefore the thermal stability and the fire extinguishing efficiency of the layered double hydroxide (LDH) serving as the dry powder fire extinguishing agent are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly fire extinguishing materials technology, specifically relating to a fire extinguishing powder based on seed-induced struvite (MgNH4PO4·6H2O, MAP), its preparation method and application, and is particularly suitable for high-efficiency and environmentally friendly dry powder fire extinguishing agents. Background Technology

[0002] The particle size of ordinary dry powder extinguishing agents is typically between 10 and 75 μm. Due to the relatively large mass of individual particles, they suffer from drawbacks such as rapid settling, poor dispersibility, and small specific surface area. Consequently, their ability to capture free radicals and reactive groups during the chemical extinguishing mechanism is relatively weak, resulting in limited extinguishing capacity. Therefore, the key objective in designing high-efficiency dry powder extinguishing agents is to develop extinguishing agents with smaller particle size, better flowability, larger specific surface area, higher activity, stable dispersion, and the ability to remain suspended in the air for extended periods.

[0003] MAP, with the chemical formula MgNH4PO4·6H2O, commonly known as guano, was first discovered in wastewater treatment plants. When Mg in urban wastewater... 2+ NH4 + and PO4 3- At higher concentrations, MAP can crystallize and precipitate under alkaline conditions and suitable temperatures. In wastewater treatment systems, MAP typically forms hard scale in pipes, which can lead to blockages if not treated promptly. Therefore, wastewater treatment plants produce large amounts of MAP annually. Currently, many centralized wastewater treatment plants recycle MAP for use as slow-release fertilizer. However, due to its high heavy metal content, direct application can easily cause soil pollution, thus limiting its application in agriculture. Currently, recycled MAP is mostly used in building materials to improve their flame retardancy. Notably, MAP possesses chemical properties similar to ammonium dihydrogen phosphate (NH4H2PO4), the main chemical component of commercial ABC dry powder fire extinguishing agents. Researchers have found that MAP does indeed have fire extinguishing capabilities and can be considered a potential fire extinguishing material.

[0004] The synthesis of MAP is related to factors such as the nitrogen-phosphorus-magnesium ion ratio, wastewater pH, organic matter in the wastewater, and seed crystal addition. Patent CN202011305662.1 discloses a method for preparing MAP from phosphorus-containing wastewater. It selects crushed and refined or commercially available MAP particles as seed crystals, and controls the particle size of the produced MAP by using a fluidized bed to control the particle size of the added seed crystals, the amount of seed crystals, and the discharge cycle of the target MAP, thus ensuring the continuity of MAP production.

[0005] Patent CN202310713771.4 discloses a method for preparing modified MAP. By adding lignin sulfonate to the supernatant and then performing a MAP precipitation process, the MAP is modified in situ to improve its thermal stability, making it easier to adhere to the surface of various substrates to form a dense fire-retardant coating and improving the flame retardant effect of MAP.

[0006] Patent CN202210882495.X discloses a method for preparing MAP ultrafine dry powder. By using silicone oil, talc, magnesium stearate and DOPO-VST to modify the surface of MAP particles synthesized by amorphous seed induction, the particles can be made to meet the ultrafine standard and enhance their fire extinguishing performance.

[0007] The current methods for synthesizing MAP and preparing it as fire extinguishing powder have the following main problems: (1) Ordinary MAP dry powder has a low pyrolysis temperature and is not easy to store for a long time; (2) Ordinary MAP powder has a long fire extinguishing time and insufficient fire extinguishing efficiency; (3) There are few processes that focus on the fire extinguishing application of MAP to carry out targeted structural design and precipitation process improvement; (4) The modification process of MAP in the field of fire extinguishing is relatively complicated, which limits its industrial production.

[0008] Layered bimetallic hydroxides (LDHs), as inorganic nanolayered materials, can attract PO4 through mechanisms such as hydrogen bonding, electrostatic attraction between hydroxide and oxygen ions, and ion exchange. 3- Highly selective adsorption is achieved to promote the formation of MAP, and LDH is often used as a flame retardant material due to its green and environmentally friendly characteristics and high flame retardant efficiency.

[0009] Patent 202310086527.X discloses a method for preparing porous bimetallic hydroxides. Under inert gas protection, sodium hydroxide solution and magnesium nitrate and aluminum nitrate mixed solution are added simultaneously to sodium nitrate solution with pH=10-11, and the pH of the mixed solution is maintained at 10.5-11.5. After precipitation for 8 hours, bimetallic hydroxide precipitate is obtained.

[0010] Patent 202411166598.1 discloses a method for preparing layered bimetallic hydroxides, which uses a divalent metal base to simultaneously adjust the pH of the solution and provide metal ions, dissolves it and a trivalent metal salt in CO2-free water, and adjusts the reaction temperature to 140-180℃ and reacts for 10-15 hours to obtain bimetallic hydroxides.

[0011] The main problems in LDH preparation are as follows: (1) Common LDH preparation methods involve complex reaction conditions and require high-quality equipment; (2) Common LDH preparation methods involve high reaction temperatures and high energy consumption; (3) Common LDH preparation processes are complex and difficult to scale up.

[0012] Therefore, this invention proposes a simpler method for preparing LDH and uses LDH as a seed crystal to induce the precipitation of MAP. This simplifies the preparation process and conditions of LDH in the prior art and simultaneously solves the problems of thermal stability, fire extinguishing efficiency and process simplification of MAP fire extinguishing powder prepared by the prior art. Summary of the Invention

[0013] To address the shortcomings of existing technologies, this invention provides a method for preparing seed-induced MAP fire extinguishing powder. It innovatively introduces LDH as a seed crystal, achieving PO4 precipitate formation through hydrogen bonding, electrostatic adsorption, and other interactions. 3- The high efficiency of adsorption enhances the crystallization and precipitation efficiency and pyrolysis temperature of MAP, and facilitates the subsequent pulverization and refinement process to obtain extinguishing powder with better dispersibility, larger specific surface area and higher extinguishing efficiency, thus solving the problems of low pyrolysis temperature and insufficient extinguishing efficiency of ordinary MAP extinguishing powder.

[0014] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0015] The first aspect of this invention provides a method for preparing layered bimetallic hydroxide (LDH), comprising the following steps:

[0016] Soluble divalent metal ions and soluble trivalent metal ions are mixed in deionized water; the pH of the mixed solution is adjusted to alkaline using NaOH; the mixed solution is placed in a hydrothermal reactor and reacted for a certain period of time; the precipitate is centrifuged and dried to obtain LDH with the corresponding metal composition.

[0017] Furthermore, soluble divalent metal ions include Mg 2+ Zn 2+ Ni 2+ Co 2+ Mn 2+ Cu 2+ Cd 2+ Sn 2+ At least one of the following; soluble trivalent metal ions include Al 3 +, Fe 3+ Cr 3+ Bi 3+ La 3+ Ce 3+ At least one of them; the molar ratio of soluble divalent metal ions to soluble trivalent metal ions is (1-3):(1-3).

[0018] Furthermore, the LDH preparation reaction requires an environmental pH of 7.5-14 and a reaction temperature of 80-170℃.

[0019] Furthermore, the LDH preparation reaction is carried out by a programmed temperature increase of 5-10℃ / min for a duration of 8-15 hours.

[0020] Furthermore, the centrifugation speed required for recovering the product obtained from the LDH preparation reaction is 6000-8000 rpm, and the centrifugation time is 5-10 minutes; the drying temperature of the obtained product is 30-35℃, and the drying time is 25-30 hours.

[0021] A second aspect of this invention provides a method for seed-induced synthesis of struvite (MAP) fire extinguishing powder, comprising the following steps:

[0022] Wastewater treatment plant supernatant was selected as raw material. Solid porous media was added and stirred thoroughly. The mixture was allowed to settle and then filtered to remove heavy metal ions. A certain amount of ammonium salt and phosphate were added to the supernatant to adjust the nitrogen-phosphorus ion ratio. Then, LDH obtained by the method provided in the first aspect was added as seed crystals and stirred to mix thoroughly with the supernatant. The pH of the supernatant was adjusted using NaOH solution and magnesium salt was added to adjust the nitrogen-phosphorus-magnesium ion ratio. After stirring at room temperature, the mixture was allowed to settle for a certain period of time and centrifuged to obtain the bottom precipitate. The precipitate was then dried to obtain seed-induced MAP particles. The obtained MAP particles were mixed with a modifier in a certain proportion and pulverized and refined using a horizontal planetary ball mill to obtain MAP fire extinguishing powder with an average particle size of 20-35 μm that meets the requirements of fire extinguishing powder.

[0023] Furthermore, the solid porous medium used for heavy metal ion adsorption is one or a combination of at least two of activated carbon, chitosan resin, montmorillonite, and acidified sepiolite.

[0024] Furthermore, the ammonium salt required for the MAP precipitation reaction is one or a combination of at least two of (NH4)3PO4·3H2O, NH4Cl, NH4NO3, and (NH4)2CO3.

[0025] Furthermore, the phosphate required for the MAP precipitation reaction is one or a combination of at least two of the following: Na3PO4·12H2O, (NH4)3PO4·3H2O, NaH2PO4, Na2HPO4·12H2O, NaH2PO4·12H2O, NH4H2PO4, and (NH4)2HPO4.

[0026] Furthermore, the magnesium salt required for the MAP precipitation reaction is one or a combination of at least two of MgCl2·6H2O, Mg(NO3)2, and MgSO4.

[0027] Furthermore, the molar ratio of nitrogen, phosphorus, and magnesium ions in the MAP precipitation reaction is N:P:Mg = (0.8-1.5):(0.8-1.8):(1-1.8).

[0028] Furthermore, the LDH required for the MAP precipitation reaction is one or a combination of at least two of MgAl-LDH, MgFe-LDH, NiCr-LDH, ZnAl-LDH, and CoCr-LDH synthesized by the method provided in the first aspect.

[0029] Furthermore, the pH range for the MAP precipitation reaction is 8-13;

[0030] Furthermore, the reaction temperature for the MAP precipitation reaction is 25-35℃;

[0031] Furthermore, the precipitation time for the MAP precipitation reaction is 3-5 hours;

[0032] Furthermore, the MAP precipitation product is centrifuged at 6000-8000 rpm for 8-10 minutes; and dried at 30-35℃.

[0033] Furthermore, the modifier for the MAP particles obtained by the MAP precipitation reaction is one or a combination of at least two of the following: talc powder, hydrophobic silica, magnesium stearate, activated carbon, acidified sepiolite, and aluminum zirconium-pillared montmorillonite.

[0034] Furthermore, the mass ratio of MAP particles obtained from the MAP precipitation reaction to the modifier is (75-95):(5-25);

[0035] Furthermore, the ball milling parameters for the solid particles obtained from the MAP precipitation reaction and the modifier mixed and crushed are 300-400 rpm and the ball milling time is 30-60 minutes.

[0036] Furthermore, the extinguishing powder has a D50 of 10-15 μm, a D90 of 20-35 μm, and a specific surface area of ​​25-90 m². 2 / g.

[0037] It should be noted that this invention uses nitrogen- and phosphorus-rich supernatant from a wastewater treatment plant as raw material. First, heavy metal ions in the wastewater are removed using a cation-selective permeation membrane. Then, the pH and nitrogen-to-phosphorus ratio of the supernatant are adjusted, and seed crystals are introduced to induce MAP crystallization and precipitation. After filtration and drying, MAP particles synthesized by seed crystal induction are obtained. Further, a horizontal planetary ball mill is used to uniformly mix and grind the MAP with hydrophobic nano-silica, talc, and magnesium stearate modifiers to obtain MAP fire extinguishing powder with good fire extinguishing performance. This invention innovatively introduces a dimetallic hydroxide (LDH) as a seed crystal during the MAP recovery process, utilizing hydrogen bonding and electrostatic attraction to efficiently adsorb PO4 in the supernatant. 3-This process not only significantly improves the crystallization rate of MAP but also greatly increases the yield of MAP recovered from wastewater. In addition, LDH itself has flame-retardant properties, and its introduction can significantly increase the pyrolysis temperature of MAP extinguishing powder, allowing it to penetrate deep into the root of the flame before pyrolysis in fire extinguishing scenarios, thereby enhancing fire extinguishing performance. By mixing and refining the seed-induced MAP with the modifier through ball milling, the contact area between the extinguishing powder and the flame can be effectively increased, giving full play to its synergistic effect of fire extinguishing and smoke suppression, and finally obtaining MAP extinguishing powder with excellent comprehensive performance.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) This invention proposes a seed-induced precipitation method for MAP in wastewater. By adding LDH as a seed, the nucleation time of MAP is shortened, the nucleation rate is accelerated, and the yield of MAP is improved, which is more conducive to the recovery of MAP.

[0040] (2) The present invention innovatively uses LDH as a seed crystal inducer, which can significantly increase its pyrolysis initiation temperature and optimize the thermal decomposition kinetics process, thereby greatly enhancing its thermal stability and extinguishing efficiency as a dry powder fire extinguishing agent;

[0041] (3) The MAP synthesized in this invention is a byproduct of wastewater treatment, which reduces the cost of solid waste disposal, opens up the "pollutant-resource" pathway, gives MAP new functional application value, and provides new application scenarios for MAP. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0043] Figure 1 The flowchart illustrates the preparation method of LDH-MAP fire extinguishing powder provided by this invention.

[0044] Figure 2 The 1m used in the experiment of this invention 3 Schematic diagram of a small fire extinguishing platform.

[0045] Figure 3 The images show a comparison of the SEM morphological features of different types of LDH in the embodiments. Figure 3 (a) is MgAl-LDH. Figure 3 (b) is MgFe-LDH. Figure 3 (c) is ZnAl-LDH. Figure 3 (d) is NiCr-LDH, Figure 3 (e) is CoCr-LDH. Figure 3 (f) is LDH-MAP.

[0046] Figure 4 The XRD composition comparison analysis of different fire extinguishing powders in the examples is shown.

[0047] Figure 5 a and b are the adsorption-desorption curves and pore size distribution curves of commercial ABC dry powder, blank MAP fire extinguishing powder, and MAP fire extinguishing powder in the examples.

[0048] Figure 6 This study compares the thermogravimetric data of commercial ABC dry powder, blank MAP fire extinguishing powder, and the MAP fire extinguishing powder in the examples. Figure 6 a represents the thermogravimetric (TG) curve. Figure 6 b is the differential scanning calorimetry (DSC) curve. Figure 6 c represents the derivative thermogravimetric (DTG) curve.

[0049] Figure 7 Screenshots from fire extinguishing videos of commercial ABC dry powder, blank MAP fire extinguishing powder, and MAP fire extinguishing powder in Example 4. Figure 7 (a) Figure 7 (b) Figure 7 (c) is a Class B fire. Figure 7 (d) Figure 7 (e) Figure 7 (f) is a Class A fire.

[0050] Figure 8 This is a comparison chart showing the smoke suppression effect (CO concentration) of commercial ABC dry powder, blank MAP fire extinguishing powder, and MAP fire extinguishing powder in the examples in a fire scene.

[0051] Figure 9 The particle size distributions of commercial ABC dry powder, blank MAP fire extinguishing powder, and MAP fire extinguishing powder in the examples are shown. Figure 9 (a) is for commercial ABC dry powder, Figure 9 (b) is blank MAP extinguishing powder, Figure 9 (c) is MgAl-MAP, Figure 9 (d) is MgFe-MAP, Figure 9 (e) is ZnAl-MAP, Figure 9 (f) is NiCr-MAP, Figure 9 (g) represents CoCr-MAP. Detailed Implementation

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0053] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0054] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0055] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0056] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0057] This invention discloses a method for seed-induced synthesis of MAP fire extinguishing dry powder.

[0058] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0059] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0060] Example 1

[0061] This embodiment provides a method for seed-induced synthesis of MAP fire extinguishing dry powder, the method comprising the following steps:

[0062] Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water, controlling the molar ratio of metal ions to Mg.2+ :Al 3+ =3:2, the pH of the solution was adjusted to 9 with 5 mol / L NaOH solution, and then placed in a hydrothermal reactor and reacted at 120℃ for 8 hours. The resulting product was centrifuged and dried in a forced-air drying oven at 35℃ to obtain MgAl-LDH.

[0063] After pretreatment, the supernatant from the wastewater treatment plant is adjusted to N:P = 1:1 by adding orthophosphate and ammonium salt. The aforementioned MgAl-LDH is then added to the supernatant, and the pH is adjusted to 11 using 5 mol / L NaOH solution. The mixture is then stirred thoroughly using a magnetic stirrer. A certain amount of MgCl2·6H2O is dissolved in deionized water according to the molar ratio of N:P:Mg = 1:1:1.5. The solution is stirred thoroughly and then added to the supernatant for 8-10 hours. The resulting precipitate is centrifuged at 8000 rpm for 10 minutes and then dried in a forced-air drying oven at 35°C to obtain MgAl-MAP.

[0064] MgAl-MAP and nano-hydrophobic silica were mixed at a mass ratio of 95:5 and then pulverized and refined using a horizontal planetary ball mill at 300 r / min for 40 minutes to obtain MAP powder with certain fire extinguishing properties.

[0065] Example 2

[0066] This embodiment provides a method for seed-induced synthesis of MAP fire extinguishing dry powder, the method comprising the following steps:

[0067] Dissolve MgCl2·6H2O and FeCl3·6H2O in deionized water, controlling the molar ratio of metal ions to Mg. 2+ :Fe 3+ =1:1, the pH of the solution was adjusted to 10 with 5 mol / L NaOH solution, and then placed in a hydrothermal reactor and reacted at 135℃ for 10 hours. The resulting product was centrifuged and dried in a forced-air drying oven at 35℃ to obtain MgFe-LDH.

[0068] After pretreatment, the supernatant from the wastewater treatment plant is adjusted to N:P = 1:1 by adding orthophosphate and ammonium salt. The aforementioned MgFe-LDH is then added to the supernatant, and the pH is adjusted to 9.5 using 5 mol / L NaOH solution. The mixture is then stirred thoroughly with a magnetic stirrer. A certain amount of MgCl2·6H2O is dissolved in deionized water according to the molar ratio of N:P:Mg = 1:1:1.5. The solution is stirred thoroughly and then added to the supernatant. The reaction is carried out for 8-10 hours. The resulting precipitate is centrifuged at 8000 rpm for 8 minutes and then dried in a forced-air drying oven at 35°C to obtain MgFe-MAP.

[0069] MgFe-MAP and magnesium stearate were mixed at a mass ratio of 90:10 and then pulverized and refined using a horizontal planetary ball mill at 320 r / min for 45 minutes to obtain MAP powder with certain fire extinguishing properties.

[0070] Example 3

[0071] This embodiment provides a method for seed-induced synthesis of MAP fire extinguishing dry powder, the method comprising the following steps:

[0072] ZnCl2·6H2O and AlCl3·6H2O were dissolved in deionized water, and the molar ratio of metal ions was controlled to be Zn 2+ :Al 3+ = 2:3, the pH of the solution was adjusted to 11 with 5 mol / L NaOH solution, and then placed in a hydrothermal reactor and reacted at 115℃ for 9 hours. The resulting product was centrifuged and dried in a forced-air drying oven at 35℃ to obtain ZnAl-LDH.

[0073] After pretreatment, the supernatant from the wastewater treatment plant is adjusted to N:P = 1:1 by adding orthophosphate and ammonium salt. The aforementioned ZnAl-LDH is then added to the supernatant, and the pH is adjusted to 12 using 5 mol / L NaOH solution. The mixture is then stirred thoroughly using a magnetic stirrer. A certain amount of MgCl2·6H2O is dissolved in deionized water according to the molar ratio of N:P:Mg = 1:1:1.4. The solution is stirred thoroughly and then added to the supernatant. The reaction is carried out for 8-10 hours. The resulting precipitate is centrifuged at 8000 rpm for 8 minutes and then dried in a forced-air drying oven at 35°C to obtain ZnAl-MAP.

[0074] ZnAl-MAP and talc powder were mixed at a mass ratio of 88:12 and then pulverized and refined using a horizontal planetary ball mill at 350 r / min for 35 minutes to obtain MAP powder with certain fire extinguishing properties.

[0075] Example 4

[0076] This embodiment provides a method for seed-induced synthesis of MAP fire extinguishing dry powder, the method comprising the following steps:

[0077] NiCl2·6H2O and CrCl3·6H2O were dissolved in deionized water, and the molar ratio of metal ions was controlled to be Ni 2+ :Cr 3+ =2.5:3, the pH of the solution was adjusted to 11 with 5 mol / L NaOH solution, and then placed in a hydrothermal reactor and reacted at 145℃ for 10 hours. The resulting product was centrifuged and dried in a forced-air drying oven at 35℃ to obtain NiCr-LDH.

[0078] After pretreatment, the supernatant from the wastewater treatment plant is adjusted to N:P = 1:1 by adding orthophosphate and ammonium salt. The aforementioned NiCr-LDH is then added to the supernatant, and the pH is adjusted to 10 using 5 mol / L NaOH solution. The mixture is then stirred thoroughly with a magnetic stirrer. A certain amount of MgCl2·6H2O is dissolved in deionized water according to the molar ratio of N:P:Mg = 1:1:1.3. The solution is stirred thoroughly and then added to the supernatant. The reaction is carried out for 8-10 hours. The resulting precipitate is centrifuged at 8000 rpm for 10 minutes and then dried in a forced-air drying oven at 35°C to obtain NiCr-MAP.

[0079] NiCr-MAP and activated carbon were mixed at a mass ratio of 98:2 and then pulverized and refined using a horizontal planetary ball mill at 320 r / min for 45 minutes to obtain MAP powder with certain fire extinguishing properties.

[0080] Example 5

[0081] This embodiment provides a method for seed-induced synthesis of MAP fire extinguishing dry powder, the method comprising the following steps:

[0082] CoCl2·6H2O and CrCl3·6H2O were dissolved in deionized water, and the molar ratio of metal ions was controlled to be Co 2+ :Cr 3+ =3:2, the pH of the solution was adjusted to 11 with 5 mol / L NaOH solution, and then placed in a hydrothermal reactor and reacted at 150℃ for 12 hours. The resulting product was centrifuged and dried in a forced-air drying oven at 35℃ to obtain CoCr-LDH.

[0083] After pretreatment, the supernatant from the wastewater treatment plant is adjusted to N:P = 1:1 by adding orthophosphate and ammonium salt. The aforementioned CoCr-LDH is then added to the supernatant, and the pH is adjusted to 9.5 using 5 mol / L NaOH solution. The mixture is then stirred thoroughly with a magnetic stirrer. A certain amount of MgCl2·6H2O is dissolved in deionized water according to the molar ratio of N:P:Mg = 1:1:1.6. The solution is stirred thoroughly and then added to the supernatant. The reaction is carried out for 8-10 hours. The resulting precipitate is centrifuged at 8000 rpm for 10 minutes and then dried in a forced-air drying oven at 35°C to obtain CoCr-MAP.

[0084] CoCr-MAP and acidified sepiolite were mixed at a mass ratio of 85:15 and then pulverized and refined using a horizontal planetary ball mill at 300 r / min for 50 min to obtain MAP powder with certain fire extinguishing properties.

[0085] The dry powder performance test is divided into Class A fire test and Class B fire test, and the specific steps are as follows:

[0086] (1) Class A fire test

[0087] 1) Weigh 50g of commercial ABC dry powder, MgAl-MAP powder, MgFe-MAP powder, ZnAl-MAP powder, NiCr-MAP powder and CoCr-MAP powder for fire extinguishing experiment. Weigh the remaining weight after the fire extinguishing experiment, record the dry powder consumption and fire extinguishing time. Repeat each group at least three times and take the average value.

[0088] 2) Using 0.4MPa nitrogen as the driving force, dry powder is released into the fire scene through a nozzle located directly above the fire source;

[0089] 3) Take 30ml of n-heptane and put it into a 200×200×20mm oil pan as a uniform ignition source. Place a 4×4 small wooden stack consisting of 16 small wooden strips of 15×15×150mm directly above the oil pan. Ignite the oil pan with a lighter and release the extinguishing agent after the oil pan has burned out, time 30 seconds.

[0090] 4) The entire experimental process is as follows: Figure 2 The 1m shown 3 The fire was carried out on a small fire-fighting platform.

[0091] (2) Class B fire test

[0092] 1) Weigh 50g of commercial ABC dry powder, MgAl-MAP powder, MgFe-MAP powder, ZnAl-MAP powder, NiCr-MAP powder and CoCr-MAP powder for fire extinguishing experiment. Weigh the remaining weight after the fire extinguishing experiment, record the dry powder consumption and fire extinguishing time. Repeat each group at least three times and take the average value.

[0093] 2) Using 0.4MPa nitrogen as the driving force, dry powder is released into the fire scene through a nozzle located directly above the fire source;

[0094] 3) Take 70ml of n-heptane and 80ml of deionized water and put them into a 200×200×20mm oil pan. Use a lighter to ignite the oil pan and pre-ignite for 25 seconds to allow the flame to stabilize.

[0095] 4) The entire experimental process is as follows: Figure 2 The 1m shown 3 The fire was carried out on a small fire-fighting platform.

[0096] The relevant performance characteristics and parameters of fire extinguishing dry powder are as follows:

[0097] (1) Sample morphology observation: The morphology of different LDHs was observed using a scanning electron microscope (Czech TESCAN MIRA LMS), such as Figure 3As shown, the LDH in the five sets of examples exhibits a typical bimetallic hydroxide morphology. In Examples 1, 2, and 3, a large number of LDH nanosheets are stacked in a "cardboard" layered arrangement; in Example 4, the LDH is formed by a large number of nanosheets stacked in an interlaced manner to form a flower-like structure, with clearly visible interlayer gaps, indicating that the material has an ordered layered structure; in Example 5, the LDH is formed by a large number of ultrathin nanosheets stacked in a "petal-like" arrangement, with uniform mesopores between the layers, all of which are conducive to MAP growth on its surface. Figure 3 (f) shows the morphology of LDH-MAP, which partially exhibits a lamellar structure and partially shows blocky crystals, indicating that during the crystallization process, MAP crystallizes and coats the surface of LDH with LDH as the nucleus.

[0098] (2) XRD testing: The samples were tested using an X-ray diffractometer (Rigaku SmartLab SE, Japan). Figure 4 It can be seen that the characteristic peaks of the samples in different embodiments are consistent with the characteristic peaks of the LDH standard card (PDF14-0191) and the MAP standard card (PDF15-0762), confirming that the seed-induced synthesis of MAP did not cause MAP to react chemically with LDH to generate a new chemical phase.

[0099] (3) BET Test: Adsorption-desorption curves of commercial ABC dry powder, seedless induced MAP, MgAl-MAP powder, MgFe-MAP powder, ZnAl-MAP powder, NiCr-MAP powder, and CoCr-MAP powder were tested using an adsorption-desorption instrument (Micromeritics ASAP 2460), and the specific surface area, pore size, and pore volume were obtained. Figure 5 As shown in Table 1.

[0100] Table 1 BET data for different samples

[0101]

[0102] As shown in the table and figure above, the specific surface area of ​​the MAP dry powder synthesized by different LDH-induced synthesis is greater than that of the commercial ABC dry powder. This means that the contact area between the powder particles and the flame is larger, the effective extinguishing components can be released quickly, and the pyrolysis is more complete. Among them, the specific surface area of ​​the powders in Examples 1 and 4 is larger than that of the seedless induced MAP, which further confirms that its pyrolysis is more complete and its flame suppression effect is better.

[0103] (4) TG-DSC Explanation of its Fire Extinguishing Mechanism: TG-DSC curves were obtained by testing commercial ABC dry powder, seedless induced MAP, MgAl-MAP powder, MgFe-MAP powder, ZnAl-MAP, NiCr-MAP, and CoCr-MAP powders using a PerkinElmer STA 6000 simultaneous thermal analyzer. The fire extinguishing mechanism was explained based on the thermogravimetric data, such as... Figure 6 As shown.

[0104] As shown in the figure, the heat absorption of commercial ABC dry powder is 558.79 J / g, while the heat absorption of blank struvite and Examples 1, 2, 3, 4, and 5 are 572.97 J / g, 815.83 J / g, 605.93 J / g, 653.35 J / g, 927.30 J / g, and 523.15 J / g, respectively. Their heat absorption is comparable to that of commercial ABC, and the heat absorption of Examples 1, 2, 3, and 4 is slightly higher than that of ABC dry powder. Furthermore, the thermal stability of the MAP powder synthesized by LDH is improved, increasing from the initial 80℃ to 95-105℃. This is beneficial for storage and also allows the extinguishing powder to reach the root of the flame before pyrolysis, thus maximizing its fire extinguishing effect.

[0105] (5) Screenshots of fire extinguishing videos for Class A and B fires (using 0.4MPa driving air pressure as an example) Figure 7 The NiCr-MAP powder showed the shortest extinguishing time, followed by the MgAl-MAP powder, while the commercial ABC dry powder showed the worst performance.

[0106] (6) Using a Testo 350 smoke analyzer, the changes in CO concentration in the fire scene during different fire extinguishing experiments were tested, such as... Figure 8 As shown, the highest CO concentrations in the fire scene for commercial ABC dry powder, seedless MAP powder, and different samples in Examples 1, 2, 3, 4, and 5 were 163 ppm, 138 ppm, 130 ppm, 126 ppm, 141 ppm, 122 ppm, and 145 ppm, respectively. This confirms that introducing LDH as a seed crystal during the MAP synthesis process can effectively improve the smoke suppression effect of the samples.

[0107] The performance of MAP and commercial ABC dry powder in the above five embodiments is shown in Table 2 and... Figure 9 As shown, D50 (μm) is the particle size corresponding to a cumulative particle size distribution percentage of 50%; D90 (μm) is the particle size corresponding to a cumulative particle size distribution percentage of 90%.

[0108] Table 2. Test results of Class B flammability of commercial ABC dry powder and various embodiments (taking 0.4 MPa driving gas pressure as an example).

[0109]

[0110] Data comparison shows that the relevant performance parameters of the seed-induced synthesis MAP prepared by this invention have reached the level of commercial ABC dry powder, but its extinguishing time and the amount of dry powder used during extinguishing are significantly better than commercial ABC dry powder, with significant effect and obvious improvement in overall extinguishing performance.

[0111] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a layered bimetallic hydroxide, characterized in that, Includes the following steps: Soluble divalent metal ion salts and soluble trivalent metal ion salts are mixed in deionized water; The pH of the mixed solution was adjusted to be alkaline using NaOH. The mixed solution is placed in a hydrothermal reactor and reacted for a certain period of time. The precipitate was centrifuged and dried to obtain layered bimetallic hydroxides with the corresponding metal composition.

2. The method for preparing layered bimetallic hydroxide according to claim 1, characterized in that, Soluble divalent metal ions include Mg 2+ Zn 2+ Ni 2+ Co 2+ Mn 2+ Cu 2+ Cd 2+ Sn 2+ At least one of the following; soluble trivalent metal ions include Al 3 +, Fe 3+ Cr 3+ Bi 3+ La 3+ Ce 3+ At least one of the following; and the molar ratio of soluble divalent metal ions to soluble trivalent metal ions is (1-3):(1-3).

3. The method for preparing layered bimetallic hydroxide according to claim 1, characterized in that, The reaction for preparing the layered bimetallic hydroxide requires an ambient pH of 7.5-14 and a temperature of 80-170℃; the heating method is a programmed temperature rise of 5-10℃ / min, and the temperature holding time is 8-15 hours.

4. The method for preparing layered bimetallic hydroxide according to claim 1, characterized in that, The centrifugation speed required for product recovery is 6000-8000 rpm, and the centrifugation time is 5-10 minutes; the drying temperature of the product is 30-35℃, and the drying time is 25-30 hours.

5. A method for preparing struvite fire extinguishing powder by seed-induced synthesis, characterized in that, Includes the following steps: Wastewater treatment plant supernatant was selected as raw material, solid porous media was added and stirred thoroughly, allowed to settle and then filtered to remove heavy metal ions. A certain amount of ammonium salt and phosphate is added to the supernatant to adjust the nitrogen-phosphorus ion ratio; then the layered bimetallic hydroxide obtained by the method described in claim 1 is added as a seed crystal and stirred to make it fully and evenly mixed with the supernatant. The pH of the supernatant was adjusted to alkaline using NaOH solution. Then, magnesium salt was added to adjust the nitrogen-phosphorus-magnesium ion ratio in the supernatant and stirred at room temperature. After standing and settling for a certain period of time, the sediment was centrifuged to obtain the bottom precipitate and dried to obtain seed-induced struvite particles. The obtained struvite particles were mixed with a modifier in a certain proportion and then pulverized and refined using a horizontal planetary ball mill to obtain struvite fire extinguishing powder that meets the requirements of fire extinguishing powder and has an average particle size of 20-35μm.

6. The preparation method according to claim 5, characterized in that, The solid porous medium is one or a combination of at least two of activated carbon, chitosan resin, montmorillonite, and acidified sepiolite; the ammonium salt is one or a combination of at least two of (NH4)3PO4·3H2O, NH4Cl, and (NH4)2CO3; the phosphate is one or a combination of at least two of Na3PO4·12H2O, (NH4)3PO4·3H2O, NaH2PO4, Na2HPO4·12H2O, NaH2PO4·12H2O, NH4H2PO4, and (NH4)2HPO4; the magnesium salt is one or a combination of at least two of MgCl2·6H2O, Mg(NO3)2, and MgSO4; the molar ratio of nitrogen, phosphorus, and magnesium ions is N:P:Mg = (0.8-1.5):(0.8-1.8):(1-1.8).

7. The preparation method according to claim 5, characterized in that, The precipitation reaction requires an environment with a pH of 8-13, a temperature of 25-35℃, and a duration of 3-5 hours.

8. The preparation method according to claim 5, characterized in that, The centrifugation speed of the precipitated product is 6000-8000 rpm, and the centrifugation time is 8-10 minutes; the drying temperature is 30-35℃; the ball milling speed of the precipitated product and the modifier is 300-400 rpm, and the ball milling time is 30-60 minutes.

9. The preparation method according to claim 5, characterized in that, The modifier is one or a combination of at least two of the following: talc powder, hydrophobic silica, magnesium stearate, activated carbon, acidified sepiolite, and aluminum zircon-pillared montmorillonite; the mass ratio of struvite particles to modifier is (75-95):(5-25).

10. A seed-induced struvite fire extinguishing powder prepared by the method according to any one of claims 5-9, characterized in that, The extinguishing powder has a D50 of 10-15 μm, a D90 of 20-35 μm, and a specific surface area of ​​25-90 m². 2 / g.

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