Method for preparing low-valence vanadium oxide through self-reduction

Abstract

The invention discloses a method for preparing low-valence vanadium oxide through self-reduction. The method comprises the following steps that S1, ammonium metavanadate of a preset volume is taken and placed in a container; s2, putting the container filled with ammonium metavanadate into a vacuum tube furnace; and S3, sintering under a vacuum condition, sintering at a first reaction temperature to obtain vanadium dioxide powder, or sintering at a second reaction temperature to obtain vanadium trioxide powder. According to the method, ammonium metavanadate is used as a precursor, high-selectivity synthesis of the specific low-valence vanadium oxide is achieved by accurately regulating and controlling the self-reduction reaction in the thermal decomposition process, the reaction temperature can be accurately controlled to generate the low-valence vanadium oxide meeting the required stoichiometric ratio in a targeted mode, the whole preparation process is extremely simple, and the method is suitable for industrial production. The indispensable additional reducing agent and the tedious steps of dissolving, washing, filtering and drying in the traditional process are abandoned.

Description

Technical Field

[0001] The present invention relates to the technical field of vanadium oxide preparation, and particularly to a method for self-reducing the preparation of low-valent vanadium oxides. Background Art

[0002] Low-valent vanadium oxides, especially vanadium dioxide (VO 2 ), and vanadium trioxide (V 2 O 3 ), have attracted much attention due to their extensive application backgrounds. Vanadium dioxide exhibits great market potential in the field of intelligent thermal insulation materials by virtue of its unique phase transition characteristics near room temperature. Through a simple sulfuric acid dissolution process, it can be rapidly converted into vanadyl sulfate, which enables it to occupy an important position in the denitration catalyst and vanadium battery electrolyte markets. Vanadium trioxide, as a key raw material for the production of ferrovanadium and vanadium nitride alloy, can significantly optimize the production process and reduce the consumption of reducing agents compared to the traditional process using vanadium pentoxide as the raw material, thereby reducing production costs. In addition, due to its low resistivity and high current density characteristics at room temperature, vanadium trioxide has become an indispensable material for the preparation of high-end products such as target materials, electronic components, ceramic materials, and battery materials. In the past five to ten years, the demand for low-valent vanadium oxides represented by vanadium dioxide and vanadium trioxide has increased sharply, demonstrating their great potential in accelerating the industrialization process.

[0003] However, the multiple oxidation states of vanadium and its accompanying complexity and diverse stable and metastable structures pose severe challenges to the synthesis of high-purity and precisely chemically stoichiometrically controlled low-valent vanadium oxides, which is also the key to the preparation of high-performance devices. Currently, the production of low-valent vanadium oxides mainly relies on hydrothermal / solvothermal methods, chlorination methods, or sintering of vanadium-containing raw materials with reducing agents (such as carbon powder, sodium formaldehyde sulfoxylate, hydrogen).

[0004] Chinese Patent Application CN202310793159 proposes a low-temperature preparation process for low-valent vanadium oxides, which includes the following steps: (1) dissolving vanadium raw materials in oxalic acid; (2) adding ascorbic acid and reacting at 110°C to 165°C for 30 min to 120 min for hydrothermal reduction. After the reaction is completed, it is cooled to room temperature, and after filtration and washing, a low-valent vanadium oxide intermediate VC 2 O 4 ·2H 2 O is obtained; (3) roasting the intermediate, and after roasting is completed, it is cooled to room temperature to obtain a low-valent vanadium oxide VOy (0.1 ≤ y ≤ 1.3). The valence state of vanadium in the low-valent vanadium oxide prepared by this method is limited between 0.2 and 2.6, and the selective production of low-valent vanadium oxides with a valence higher than 3 cannot be achieved, and the overall preparation process is relatively cumbersome.

[0005] Chinese invention patent CN202410025749 discloses a method for preparing low-valent vanadium oxides by gas-solid combined reduction, which includes the following steps: (1) mixing high-valent vanadium solids with reducing solids and feeding them into a reaction furnace, followed by calcination with an inert gas; (2) introducing a mixed gas of methane and hydrogen and heating up for secondary calcination; (3) cooling to obtain low-valent vanadium oxides. However, in the implementation of this method, it is necessary to rely on the introduction of the mixed gas of methane and hydrogen, which poses certain safety hazards. In addition, it is difficult to precisely control the flow rate and volume ratio of the mixed gas, and the stoichiometric ratio of the prepared low-valent vanadium oxides is difficult to reach a stable and controllable level. Moreover, the secondary heating stage not only increases additional energy consumption but also prolongs the time cost of the overall process flow.

[0006] Although these methods have achieved the preparation of low-valent vanadium oxides to a certain extent, they all have problems such as cumbersome processes, high vanadium loss, uncontrollable stoichiometric ratios of vanadium oxides, and increased costs.

[0007] Therefore, developing an efficient and general preparation technology for low-valent vanadium oxides to meet the urgent market demand for high-purity, precisely stoichiometrically controlled low-valent vanadium oxides has important strategic significance and development value.

[0008] In view of this, improvements should be made to the existing technology. Summary of the Invention

[0009] The main object of the present invention is to provide a method for self-reducing preparation of low-valent vanadium oxides. Using ammonium metavanadate as a precursor, by precisely controlling the self-reduction reaction during its thermal decomposition, high-selectivity synthesis of specific low-valent vanadium oxides is achieved. This application can not only precisely control the reaction temperature to target the generation of low-valent vanadium oxides that meet the required stoichiometric ratio, but also the entire preparation process is extremely streamlined, abandoning the indispensable external reducing agent and the cumbersome steps of dissolution, washing, filtration, and drying in the traditional process.

[0010] According to one aspect of the present invention, a method for self-reducing preparation of low-valent vanadium oxides is proposed, which includes the following steps: S1. Take a predetermined volume of ammonium metavanadate and place it in a container; S2. Place the container containing ammonium metavanadate in a vacuum tube furnace; S3. Sinter under vacuum conditions, where sintering at the first reaction temperature to obtain vanadium dioxide powder, or sintering at the second reaction temperature to obtain vanadium sesquioxide powder.

[0011] According to an embodiment of the present invention, the first reaction temperature is 225 - 275 °C, and the second reaction temperature is 450 - 600 °C.

[0012] According to an embodiment of the present invention, during sintering, the heating rate is 5-10 °C / min and the reaction time is 10-90 min.

[0013] According to an embodiment of the present invention, the volume ratio of ammonium metavanadate to the container is ≤0.8.

[0014] According to an embodiment of the present invention, before starting sintering, an inert gas is introduced to evacuate the air in the furnace, and then vacuum is pumped to obtain a vacuum condition.

[0015] According to an embodiment of the present invention, the gas flow rate of the inert gas is ≤10 L / min.

[0016] According to an embodiment of the present invention, the vacuum condition includes that the vacuum degree in the furnace is ≤ -0.09 MPa.

[0017] According to an embodiment of the present invention, the inert gas includes one or more of nitrogen and argon.

[0018] According to an embodiment of the present invention, the method further includes pre-grinding ammonium metavanadate into nano-scale or micro-scale powder.

[0019] According to an embodiment of the present invention, a high-purity alumina layer is provided at the bottom of the container to isolate ammonium metavanadate from the container.

[0020] In a method for self-reducing preparation of low-valent vanadium oxides according to an embodiment of the present invention, ammonium metavanadate is used as a precursor, and by precisely controlling the self-reduction reaction during its thermal decomposition, high-selectivity synthesis of specific low-valent vanadium oxides is achieved. This application can not only precisely control the reaction temperature to target the generation of low-valent vanadium oxides that meet the required stoichiometric ratio, but also the entire preparation process is extremely streamlined, eliminating the indispensable external reducing agent and the cumbersome steps of dissolution, washing, filtration, and drying in the traditional process. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0022] Figure 1 Shows a process flow chart of a method for self-reducing preparation of low-valent vanadium oxides according to an exemplary embodiment of the present invention; Figure 2 Shows VO 2 and V 2 O 3 XRD patterns of. Detailed implementation manners

[0023] The following detailed description of the embodiments is used to exemplarily illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention. The present invention can be implemented in many different forms, not limited to the specific embodiments disclosed in the text, but including all technical solutions falling within the scope of the claims.

[0024] These embodiments of the present invention are provided to make the present disclosure thorough and complete, and to fully convey the scope of the present invention to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions and values set forth in these embodiments should be construed as merely exemplary, rather than as limitations.

[0025] It should be noted that in the description of the present invention, unless otherwise specified, the meaning of "a plurality" is greater than or equal to two; the orientation or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0026] It should also be noted that in the description of the present invention, unless otherwise clearly defined and limited, the terms "mounted", "connected", and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0027] All terms used in the present invention have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in, for example, a general dictionary should be construed as having meanings consistent with their meanings in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless clearly defined as such here.

[0028] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, these technologies, methods, and devices should be regarded as part of the specification.

[0029] Such as Figure 1As shown in the figure, the present invention provides a method for self-reducing the preparation of vanadium oxides with low valence, which comprises the following steps: S1. Take a predetermined volume of ammonium metavanadate and place it in a container; S2. Place the container containing ammonium metavanadate in a vacuum tube furnace; S3. Sinter under vacuum conditions, wherein sintering at the first reaction temperature to obtain vanadium dioxide powder, or sintering at the second reaction temperature to obtain vanadium trioxide powder.

[0030] In the prior art, the process of reducing high-valence vanadium solids to low-valence vanadium solids requires the intervention of an external reducing agent. In contrast, the present application proposes an innovative method that utilizes the characteristic products - vanadium pentoxide solid and reducing gas ammonia - naturally generated after the thermal decomposition of ammonium metavanadate (NH 4 VO 3 ). By precisely regulating the ratio of these two products, the present application can skillfully achieve the conversion of high-valence vanadium to vanadium oxide with a valence of four (i.e., vanadium dioxide) or directly to the reduction end product vanadium trioxide without the need to additionally add a reducing agent, thereby optimizing the reaction path and potentially improving the reaction efficiency.

[0031] In the method for self-reducing the preparation of vanadium oxides with low valence according to an embodiment of the present invention, ammonium metavanadate is used as a precursor, and by precisely regulating the self-reduction reaction during its thermal decomposition, the highly selective synthesis of specific vanadium oxides with low valence is achieved. It can not only precisely control the reaction temperature to target the generation of vanadium oxides with low valence that meet the required stoichiometric ratio, but also the entire preparation process is extremely streamlined, eliminating the indispensable external reducing agent and the cumbersome steps of dissolution, washing, filtration, and drying in the traditional process. In some specific embodiments, the first reaction temperature is 225 - 275 °C, and the second reaction temperature is 450 - 600 °C. Vanadium dioxide powder is more easily obtained at the first reaction temperature. Since higher-temperature conditions tend to form oxides that are more thermodynamically stable, vanadium trioxide powder can be obtained under the condition of the second reaction temperature.

[0032] On the basis of the above embodiments, when sintering, the heating rate is 5 - 10 °C / min, and the reaction time is 10 - 90 min.

[0033] In some specific embodiments, the volume ratio of ammonium metavanadate to the container ≤ 0.8. There will be relatively more space in the container that is not occupied by ammonium metavanadate, which is conducive to the uniform transfer of heat in the container during sintering and ensures that ammonium metavanadate can be uniformly heated.

[0034] Based on the above embodiments, before starting sintering, an inert gas is introduced to evacuate the air in the furnace, and then vacuum is pumped to obtain a vacuum condition. By introducing an inert gas and pumping vacuum multiple times, the residual air in the furnace can be minimized, ensuring that ammonium metavanadate is not interfered by external gases during the reduction process, thereby maintaining the purity of the product.

[0035] In some specific embodiments, the gas flow rate of the inert gas ≤ 10 L / min, which is beneficial to precisely control reaction conditions such as temperature, pressure, and gas composition, and can also make the distribution in the reaction system more uniform, reducing local concentration fluctuations caused by gas flow, thereby improving the stability of the reaction.

[0036] Based on the above embodiments, the vacuum condition also includes that the vacuum degree in the furnace ≤ -0.09 MPa. When the negative pressure is pumped to -0.09 MPa or lower by a vacuum pump, the number of oxygen molecules in the furnace significantly decreases, effectively avoiding the contact between ammonium metavanadate and oxygen during heating. Avoiding oxidation can not only prevent the degradation of material properties but also reduce the formation of oxide residues in the furnace, which is beneficial to improving the purity and quality of the final product.

[0037] As Figure 2 shown, it is the XRD pattern of low-valent vanadium oxides prepared under different process parameters, where (a) VO 2 , (b) V 2 O 3 .

[0038] Based on the above embodiments, the inert gas includes one or more of nitrogen and argon. During the preparation process, introducing an inert gas can effectively exclude oxygen (O 2 ), preventing ammonium metavanadate and other reactants from being oxidized, thereby ensuring the chemical stability and purity of the product. Nitrogen (N 2 ) and argon (Ar) are both typical inert gases with stable chemical properties and are not easily reactive with other substances.

[0039] In some specific embodiments, the method further includes pre-grinding ammonium metavanadate into nano-scale or micro-scale powder. After powdering, ammonium metavanadate has a larger specific surface area, so that in a chemical reaction, the contact area between reactants increases, thereby improving the reaction rate and efficiency.

[0040] Based on the above embodiments, a high-purity alumina layer is provided at the bottom of the container to isolate ammonium metavanadate from the container, prevent the sample from sticking to the container, and can also protect the container from corrosion and extend the service life of the container.

[0041] In some specific embodiments, the container is a crucible, and ammonium metavanadate is evenly spread on the bottom of the flat-bottom crucible. Subsequently, the crucible containing the sample is placed in a vacuum condition for sintering.

[0042] Low-valent vanadium oxides have a wide range of applications in the fields of energy, steel, and new material devices. The increasing demand for high-performance materials in these fields provides a broad market space for the wide application of low-valent vanadium oxides. The present invention precisely controls the reaction temperature to target the generation of low-valent vanadium oxides that meet the required stoichiometric ratio. The preparation process is streamlined, eliminating the indispensable external reducing agent and the cumbersome steps of dissolution, washing, filtration, and drying in traditional processes, showing significant potential for promotion and application prospects in both small-scale laboratory preparation and large-scale industrial production.

[0043] The following describes the present application with specific examples.

[0044] Example 1: (1) Preparation of vanadium dioxide Ammonium metavanadate was loosely spread in a flat-bottomed crucible at a volume ratio of 0.5 and placed in a vacuum tube furnace. Argon was introduced to exhaust the air in the tube furnace, and the gas flow rate was 2 L / min. Subsequently, a vacuum pump was used to draw a negative pressure to -0.09 Pa, and this was repeated three times. When the final negative pressure reached -0.09 MPa, the tube furnace was sealed and heated at a rate of 5 °C / min to 225 °C and held for 60 min to obtain vanadium dioxide powder. The equivalent valence state of vanadium was 4, and the direct recovery rate of vanadium was 100%.

[0045] (2) Preparation of vanadium trioxide Ammonium metavanadate was loosely spread in a flat-bottomed crucible at a volume ratio of 0.5 and placed in a vacuum tube furnace. Argon was introduced to exhaust the air in the tube furnace, and the gas flow rate was 2 L / min. Subsequently, a vacuum pump was used to draw a negative pressure to -0.09 Pa, and this was repeated three times. When the final negative pressure reached -0.09 MPa, the tube furnace was sealed and heated at a rate of 5 °C / min to 450 °C and held for 60 min to obtain vanadium trioxide powder. The equivalent valence state of vanadium was 3, and the direct recovery rate of vanadium was 100%.

[0046] Example 2: (1) Preparation of vanadium dioxide Ammonium metavanadate was loosely spread in a flat-bottomed crucible at a volume ratio of 0.2 and placed in a vacuum tube furnace. Argon was introduced to exhaust the air in the tube furnace, and the gas flow rate was 5 L / min. Subsequently, a vacuum pump was used to draw a negative pressure to -0.10 Pa, and this was repeated three times. When the final negative pressure reached -0.10 MPa, the tube furnace was sealed and heated at a rate of 8 °C / min to 250 °C and held for 10 min to obtain vanadium dioxide powder. The equivalent valence state of vanadium was 4, and the direct recovery rate of vanadium was 100%.

[0047] (2) Preparation of vanadium trioxide Ammonium metavanadate was loosely spread out in a flat-bottomed crucible at a volume ratio of 0.2 and placed in a vacuum tube furnace. Argon was introduced to exhaust the air in the tube furnace, and the gas flow rate was 5 L / min. Subsequently, a vacuum pump was used to pump to a negative pressure of -0.10 Pa, and this was repeated three times. When the final negative pressure reached -0.10 MPa, the sealed tube furnace was heated at a rate of 8 °C / min to 500 °C and held for 10 min to obtain vanadium trioxide powder. The equivalent valence state of vanadium was 3, and the direct recovery rate of vanadium was 100%.

[0048] Example 3: (1) Preparation of vanadium dioxide Ammonium metavanadate was loosely spread out in a flat-bottomed crucible at a volume ratio of 0.8 and placed in a vacuum tube furnace. Nitrogen was introduced to exhaust the air in the tube furnace, and the gas flow rate was 10 L / min. Subsequently, a vacuum pump was used to pump to a negative pressure of -0.09 Pa, and this was repeated three times. When the final negative pressure reached -0.09 MPa, the sealed tube furnace was heated at a rate of 10 °C / min to 275 °C and held for 90 min to obtain vanadium dioxide powder. The equivalent valence state of vanadium was 4, and the direct recovery rate of vanadium was 100%.

[0049] (2) Preparation of vanadium trioxide Ammonium metavanadate was loosely spread out in a flat-bottomed crucible at a volume ratio of 0.8 and placed in a vacuum tube furnace. Nitrogen was introduced to exhaust the air in the tube furnace, and the gas flow rate was 10 L / min. Subsequently, a vacuum pump was used to pump to a negative pressure of -0.09 Pa, and this was repeated three times. When the final negative pressure reached -0.09 MPa, the sealed tube furnace was heated at a rate of 10 °C / min to 600 °C and held for 90 min to obtain vanadium trioxide powder. The equivalent valence state of vanadium was 3, and the direct recovery rate of vanadium was 100%.

[0050] The above are the exemplary embodiments disclosed by the present invention. The order of disclosure of the above embodiments of the present invention is only for description and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of disclosure of the embodiments of the present invention (including the claims) is limited to these examples. Without departing from the scope defined by the claims, various changes and modifications can be made. The functions, steps, and / or actions of the method claims according to the disclosed embodiments here do not need to be executed in any specific order. In addition, although the elements disclosed in the embodiments of the present invention can be described or claimed in individual form, they can also be understood as plural unless explicitly limited to the singular.

[0051] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope (including the claims) disclosed by the embodiments of the present invention is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the embodiments of the present invention shall be included within the protection scope of the embodiments of the present invention.

Claims

1. A method for preparing low-valent vanadium oxide by self-reduction, characterized in that: The following steps are involved: S1. Take a predetermined volume of ammonium metavanadate and place it in a container; S2, placing the container containing ammonium metavanadate in a vacuum tube furnace; S3. Sintering under vacuum conditions, wherein sintering is performed at a first reaction temperature to obtain vanadium dioxide powder, or sintering is performed at a second reaction temperature to obtain vanadium trioxide powder.

2. The method for preparing low-valent vanadium oxide by self-reduction according to claim 1, characterized in that: The first reaction temperature is 225-275°C, and the second reaction temperature is 450-600°C.

3. The method for preparing low-valent vanadium oxide by self-reduction according to claim 1, characterized in that: During the sintering, the heating rate is 5-10°C / min and the reaction time is 10-90min.

4. The method for preparing low-valent vanadium oxide by self-reduction according to claim 1, characterized in that: The volume ratio of the ammonium metavanadate to the container is ≤0.

8.

5. The method for preparing low-valent vanadium oxide by self-reduction according to claim 1, characterized in that: Before starting sintering, the air in the furnace is evacuated by introducing an inert gas, and then the furnace is evacuated to obtain the vacuum condition.

6. The method for preparing low-valent vanadium oxide by self-reduction according to claim 5, characterized in that: The gas flow rate of the inert gas is ≤10 L / min.

7. The method for preparing low-valent vanadium oxide by self-reduction according to claim 1, characterized in that: The vacuum condition includes a furnace vacuum degree ≤-0.09MPa.

8. The method for preparing low-valent vanadium oxide by self-reduction according to claim 5, characterized in that: The inert gas includes one or more of nitrogen and argon.

9. The method for preparing low-valent vanadium oxide by self-reduction according to claim 1, characterized in that: The method further comprises pre-grinding the ammonium metavanadate into nano-scale or micro-scale powder.

10. The method for preparing low-valent vanadium oxide by self-reduction according to claim 1, characterized in that: A high-purity aluminum oxide layer is provided at the bottom of the container to isolate the ammonium metavanadate from the container.

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