A pilot scale-up method for preparing manganese dioxide by acidic hydrothermal continuous method

Abstract

The present application relates to the field of inorganic chemical synthesis, in particular to a pilot scale-up method for continuously preparing manganese dioxide by acid hydrothermal method, which comprises the following steps: dissolving divalent manganese salt and persulfate in water according to a certain molar ratio, carrying out oxidation reaction under specific temperature conditions, and obtaining high-purity manganese dioxide powder after filtration, washing and drying. The present application can guide the directional growth of manganese-based low-temperature nanoscale enzyme by accurately controlling the proportion of reactants and temperature, and has the advantages of simple process, easy control of reaction conditions, by-product of sulfate, environmental friendliness, regular crystal form of the obtained product, and suitability for low-temperature degradation of biomass or catalyst field.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical synthesis, specifically to a pilot-scale method for the continuous hydrothermal preparation of manganese dioxide using acidic methods. Background Technology

[0002] Manganese-based nanozymes are important inorganic materials with wide applications in catalysts, water treatment, and low-temperature biomass degradation. Traditional preparation processes, such as electrolysis, suffer from high energy consumption, while chemical oxidation often results in products with numerous impurities and poor crystal form control. Although persulfate is a strong oxidant capable of efficiently oxidizing manganese ions at relatively low temperatures, optimizing processes to obtain large quantities of products with specific morphologies (such as nanorods and prismatic structures) remains a research hotspot. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and propose a pilot-scale method for the continuous preparation of manganese dioxide using acidic hydrothermal processes. The process is simple, the reaction conditions are easy to control, and the resulting product has a regular crystal structure and excellent electrochemical performance. It is suitable for the field of low-temperature degradation of biomass or catalysts.

[0004] To achieve the above objectives, the technical solution specifically adopted by the present invention is as follows: A pilot-scale method for the continuous hydrothermal preparation of manganese dioxide in acidic conditions includes the following steps: (a) Dissolve divalent manganese salt in water to prepare a manganese salt solution; (b) Add ammonium persulfate to the manganese salt solution and stir until homogeneous to obtain the reaction precursor solution; (c) After strictly controlling the pH of the reaction precursor solution to the range of 1-3 using dilute acid, heat it at 90℃-180℃ for 12-24h. (d) After the reaction is complete, the precipitate is collected, washed and dried to obtain manganese dioxide.

[0005] Further, in step (a), the divalent manganese salt is selected from at least one of manganese sulfate, manganese chloride, manganese acetate, or manganese nitrate.

[0006] Further, in step (b), the persulfate is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, barium persulfate, magnesium persulfate, calcium persulfate, and potassium peroxymonosulfate.

[0007] Furthermore, the molar ratio of the divalent manganese salt to the persulfate is 1:1 to 1:1.5.

[0008] Furthermore, the pH adjuster used in step (c) is selected from at least one of dilute sulfuric acid, dilute nitric acid, dilute hydrochloric acid, acetic acid, and citric acid.

[0009] Furthermore, the heating reaction in step (c) is heating by stirring, and the stirring method is one of anchor stirring, propeller stirring, disc stirring, vortex stirring, or paddle stirring.

[0010] Furthermore, the reaction in step (c) is carried out in a sealed high-pressure reactor, and the volume of the precursor liquid is 60-80L.

[0011] This invention has the following characteristics and beneficial effects: The directional growth of manganese-based low-temperature nanozymes can be guided by precisely controlling the reactant ratio and temperature. The process is simple, the reaction conditions are easy to control, the byproduct is sulfate, which is environmentally friendly, and the obtained product has a regular crystal form and excellent enzyme-like activity at low temperature. It is suitable for the field of low-temperature degradation of biomass or catalysts. Attached Figure Description

[0012] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a process flow diagram of the pilot-scale amplification method for preparing manganese dioxide according to the present invention.

[0013] Figure 2 The image shows a transmission electron microscope (TEM) image of α-MnO2 obtained in Example 1, along with its mapping pattern.

[0014] Figure 3 The image shows a transmission electron microscope (TEM) image of β-MnO2 obtained in Example 2, along with its mapping pattern.

[0015] Figure 4 The image shows a transmission electron microscope (TEM) image of γ-MnO2 obtained in Example 3, along with its mapping pattern.

[0016] Figure 5 The X-ray diffraction (XRD) patterns of the products obtained in Examples 1, 2 and 3 are shown.

[0017] Figure 6 The low-temperature catalytic performance of the products (a) α-MnO2, (b) β-MnO2 and (c) γ-MnO2 obtained in Examples 1, 2 and 3 is shown in the graph. Detailed Implementation

[0018] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0019] This invention provides a pilot-scale method for the continuous preparation of manganese dioxide using acidic hydrothermal processes. The method involves dissolving divalent manganese salt and persulfate in water at a specific molar ratio, conducting an oxidation reaction under specific temperature conditions, and obtaining high-purity manganese dioxide powder after filtration, washing, and drying. This manganese dioxide powder has a tetragonal crystal structure, a specific surface area of ​​approximately 50–80 m² / g, and exhibits excellent catalytic performance, making it suitable for applications such as nanozymes and pollutant degradation. Its morphology (e.g., nanorods, prismatic shapes, and hollow sea urchin-like structures) can be controlled by pH, temperature, and other conditions, achieving high-purity product preparation without the need for template agents. The main chemical reaction equations are as follows: Mn 2+ +XS₂O₈ + 2H₂O → MnO₂ + 2SO₄ 2- +4H + Specifically, the following steps are included: (a) Dissolve divalent manganese salt in water to prepare a manganese salt solution; (b) Add persulfate to the manganese salt solution and stir until homogeneous to obtain a reaction precursor solution; wherein the molar ratio of the divalent manganese salt to the persulfate is 1:1 to 1:1.5; (c) After the pH of the reaction precursor solution is strictly controlled within the range of 1-3 using a pH adjuster, it is heated at 90℃-180℃ for 12 to 24 hours. (d) After the reaction is complete, the precipitate is collected, washed and dried to obtain manganese dioxide.

[0020] This method can guide the directional growth of manganese-based low-temperature nanozymes by precisely controlling the reactant ratio and temperature. Its core mechanism is as follows: Strongly acidic conditions (pH 1-3) promote the growth of manganese ions (Mn). 2+ MnO6 is oxidized by persulfate at a specific rate to form octahedral structural units. These units tend to align preferentially along a one-dimensional direction at low pH, laying the foundation for the nanorod / linear morphology.

[0021] Mild hydrothermal conditions drive self-assembly: 90–180℃ falls within the low-temperature hydrothermal reaction range, avoiding rapid, disordered aggregation caused by high temperatures and allowing for slow, directional crystal growth; 12–24 hours provides a sufficient self-assembly window, enabling primary nanoparticles to gradually stack into specific morphologies (such as nanorods formed through oriented attachment) via Ostwald ripening. Specifically: I. Nanorod / Line Morphology Generation Path Formation conditions: pH≈2, temperature 100-110℃.

[0022] Regulation principle: In a strongly acidic environment, the octahedral structural units of MnO6 are linked together along the c-axis of the crystal, driving one-dimensional directional growth and eventually forming a uniform nanorod or nanowire α-MnO2 structure.

[0023] II. Generation path of coarse rod-shaped or prismatic morphology Formation conditions: pH≈1.5, temperature 120-180℃.

[0024] Regulation principle: Due to the increased amount of sulfuric acid produced by the reaction, the system is in a strongly acidic state, at which point the thermodynamically most stable β-MnO2 becomes the main product. The β phase has a narrow tunnel structure (1... 1) Crystal growth tends to form large, coarse rod-shaped or prismatic micron-sized blocks.

[0025] III. Generation Path of Hollow Sea Urchin-like Morphology Formation conditions: pH close to 3, temperature 90℃.

[0026] Regulation principle: Under hydrothermal pressure, primary microparticles tend to grow along the

[001] crystal orientation to form one-dimensional nanorods or nanoneedles. These nanorods grow radially outward from the micronucleus formed in the early stage. If accompanied by acid corrosion (H2SO4 produced by the reaction), a "self-templating" mechanism will be triggered to dissolve the center, eventually forming a hollow sea urchin-like γ-MnO2. Example 1

[0027] S1. Dissolve 2.265 kg of manganese sulfate (15 mol) in 60 L of water.

[0028] S2. Add 3.423 kg of ammonium persulfate (15 mol) and stir continuously for 30 min until transparent.

[0029] S3. Transfer the solution to a 100L high-temperature reactor, heat it to 100℃, and maintain the temperature for 24 hours.

[0030] S4. After natural cooling, centrifuge, wash with deionized water, and vacuum dry at 60℃ for 12 hours.

[0031] Results: XRD analysis showed that the product was highly crystalline α-MnO2, and as... Figure 6 As shown, this α-MnO2 has oxidase activity, and its catalytic performance is basically consistent within the range of 4-37℃. Example 2

[0032] S1. Dissolve 2.265 kg of manganese sulfate (15 mol) in 60 L of water.

[0033] S2. Add 3.423 kg of ammonium persulfate (15 mol) and stir continuously for 30 min until transparent.

[0034] S3. Transfer the solution to a 100L high-temperature reactor, heat it to 120℃, and maintain the temperature for 12 hours.

[0035] S4. After natural cooling, centrifuge, wash with deionized water, and vacuum dry at 60℃ for 12 hours.

[0036] Results: XRD analysis showed that the product was a highly crystalline β-MnO2 nanozyme, and as... Figure 6 As shown, the β-MnO2 nanozyme exhibits oxidase activity, and its catalytic performance remains essentially consistent across the temperature range of 4-37℃. Example 3

[0037] S1. Dissolve 2.265 kg of manganese sulfate (15 mol) in 60 L of water.

[0038] S2. Add 3.423 kg of ammonium persulfate (15 mol) and stir continuously for 30 min until transparent.

[0039] S3. Transfer the solution to a 100L high-temperature reactor, heat it to 90℃, and maintain the temperature for 24 hours.

[0040] S4. After natural cooling, centrifuge, wash with deionized water, and vacuum dry at 60℃ for 12 hours.

[0041] Results: XRD analysis showed that the product was a highly crystalline γ-MnO2 nanozyme, and as... Figure 6 As shown, the γ-MnO2 nanozyme exhibits oxidase activity, and its catalytic performance remains essentially consistent across the temperature range of 4-37℃.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A pilot-scale method for the continuous hydrothermal preparation of manganese dioxide in acidic conditions, characterized in that, Includes the following steps: (a) Dissolve divalent manganese salt in water to prepare a manganese salt solution; (b) Add persulfate to the manganese salt solution and stir until homogeneous to obtain the reaction precursor solution; (c) After using a pH adjuster to strictly control the pH of the reaction precursor solution within the range of 1-3, heat the reaction solution at 90℃-180℃ for 12-24h. (d) After the reaction is complete, the precipitate is collected, washed and dried to obtain manganese dioxide.

2. The pilot-scale amplification method for the continuous acidic hydrothermal preparation of manganese dioxide as described in claim 1, characterized in that, In step (a), the divalent manganese salt is selected from at least one of manganese sulfate, manganese chloride, manganese acetate, or manganese nitrate.

3. The pilot-scale amplification method for the continuous hydrothermal preparation of manganese dioxide in acidic conditions as described in claim 1, characterized in that, In step (b), the persulfate is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, barium persulfate, magnesium persulfate, calcium persulfate, and potassium peroxymonosulfate.

4. The pilot-scale amplification method for the continuous hydrothermal preparation of manganese dioxide according to claim 1, characterized in that, The molar ratio of the divalent manganese salt to the persulfate is 1:1 to 1:1.

5.

5. The pilot-scale amplification method for the continuous hydrothermal preparation of manganese dioxide according to claim 1, characterized in that, The reaction in step (c) is carried out in a sealed high-pressure reactor.

6. The pilot-scale amplification method for the continuous acidic hydrothermal preparation of manganese dioxide as described in claim 1, characterized in that, The pH adjuster used in step (c) is selected from at least one of dilute sulfuric acid, dilute nitric acid, dilute hydrochloric acid, acetic acid, and citric acid.

7. The pilot-scale amplification method for the continuous acidic hydrothermal preparation of manganese dioxide as described in claim 1, characterized in that, The heating reaction in step (c) is heating by stirring, and the stirring method is one of anchor stirring, propeller stirring, disc stirring, vortex stirring, or paddle stirring.

8. The pilot-scale amplification method for the continuous hydrothermal preparation of manganese dioxide in acidic conditions as described in claim 1, characterized in that, The volume of the reaction precursor liquid in step (c) is 60-80L.

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