A method for producing vanadium oxysulfate solution

Abstract

This invention provides a method for producing vanadium oxysulfate solution, comprising: (1) mixing vanadium pentoxide, oxalic acid dihydrate, and water uniformly in a reactor to obtain a mixed solution, wherein the mass ratio of vanadium pentoxide, oxalic acid dihydrate, and water in the mixed solution is 1:(0.64-0.66):(3.5-3.6); (2) adding concentrated sulfuric acid to the mixed solution in three stages to prepare the vanadium oxysulfate solution; wherein the total mass m0 of the added concentrated sulfuric acid and the mass m of vanadium pentoxide satisfy m0:m = (2.6-2.8):1. The method of this invention has advantages such as energy saving, mild and controllable operation, and no risk of material spillage.

Description

Technical Field

[0001] This invention belongs to the field of vanadium electrolyte production, and specifically relates to a method for producing vanadium oxysulfate solution. Background Technology

[0002] In the production of vanadium electrolytes, the combination of chemical reduction and electrolytic reduction is a widely used method in industrial production. Specifically, vanadium pentoxide is reacted with reducing agents such as oxalic acid, formic acid, and acetic acid in a sulfuric acid solution under heat to produce a tetravalent vanadium oxysulfate solution, which is then further electrolytically reduced to a 3.5-valent electrolyte. This method is widely used due to its simple reaction process and low equipment cost. Taking oxalic acid as an example, the principle of this method is as follows:

[0003] V2O5+2H + →2VO2 + +H₂O, △H<0 (1)

[0004] 2VO2 + +H₂C₂O₄ + 2H₂ + →2VO 2+ +2CO2↑+2H2O, △H>0 (2)

[0005] This method requires the system to reach and maintain a certain reaction temperature for the reaction to proceed smoothly. It can be inferred that the reaction is mainly affected by the rate of the first step mentioned above, namely the dissolution rate of vanadium pentoxide. Therefore, increasing the temperature is beneficial to promoting the reaction and improving the utilization rate of raw materials. However, in actual production, the reaction rate is difficult to control and generates a large amount of gas, which can easily lead to raw material overflow from the reactor, causing material loss, equipment corrosion, and environmental damage. Technologies and inventions that can save energy and specifically address the aforementioned shortcomings of this method are relatively scarce.

[0006] CN110404498A discloses a method and apparatus for controlling the reaction temperature of vanadium oxysulfate solution. This method controls the reaction rate by adding a reducing agent in stages, and controls the temperature within the range of 70-85℃ by adding sulfuric acid and water in stages. However, in actual production, this method has the following drawbacks: First, after the initial addition of water and sulfuric acid to the reactor, a large amount of acid mist and escaping heat are present in the reactor during the reaction. Using powder conveying equipment under high-temperature acidic conditions can easily cause corrosion to the equipment. Second, the solid reducing agent oxalic acid is hygroscopic and prone to clumping. When adding the reducing agent in stages, it can easily cause the reducing agent to absorb moisture and clump together during transportation, clogging the conveying pipes. Third, controlling the temperature within the range of 70-85℃ is not conducive to the rapid dissolution of vanadium pentoxide, easily leading to incomplete reaction, reduced raw material utilization, and residual oxalic acid. Summary of the Invention

[0007] The purpose of this invention is to provide a method for producing vanadium oxysulfate solution that is energy-saving, gentle and controllable, avoids equipment corrosion and clogging, and leaves no oxalic acid residue.

[0008] The method of this invention first mixes vanadium pentoxide, oxalic acid (a reducing agent), and water, and finally adds concentrated sulfuric acid, which is beneficial for protecting powder conveying equipment in industrial production. The method of this invention adds concentrated sulfuric acid in three stages, selecting appropriate flow rates and amounts at each stage to control the temperature of the reaction system. The sulfuric acid addition strategy ensures full utilization of the dilution heat, eliminating the need for external heating assistance.

[0009] A first aspect of the present invention provides a method for producing vanadium oxysulfate solution, the method comprising the steps of:

[0010] (1) Vanadium pentoxide, oxalic acid dihydrate and water are mixed evenly in a reactor to obtain a mixture, wherein the mass ratio of vanadium pentoxide, oxalic acid dihydrate and water in the mixture is 1:(0.64-0.66):(3.5-3.6);

[0011] (2) Add concentrated sulfuric acid to the mixture obtained in step (1) in three stages to prepare the vanadium oxysulfate solution;

[0012] In step (2), the total mass m0 of the added concentrated sulfuric acid and the mass m of vanadium pentoxide satisfy m0:m = (2.6-2.8):1;

[0013] In the first stage of step (2), the flow rate Q1 of the added concentrated sulfuric acid satisfies Q1 = (4.0% - 4.5%)·m0 / min, and the mass m1 of the added concentrated sulfuric acid satisfies m1 = (43% - 47%)·m0;

[0014] In the second stage of step (2), the flow rate Q2 of the added concentrated sulfuric acid satisfies Q2 = (0.8% - 1.0%)·m0 / min, and the mass m2 of the added concentrated sulfuric acid satisfies m2 = (9% - 11%)·m0;

[0015] In the third stage of step (2), the flow rate Q3 of the added concentrated sulfuric acid satisfies Q3 = (4.0% - 4.5%)·m0 / min, and the mass m3 of the added concentrated sulfuric acid satisfies m3 = (43% - 47%)·m0.

[0016] In one or more embodiments, the method further includes the step of:

[0017] (3) Add water and / or sulfuric acid to the vanadium oxysulfate solution prepared in step (2) according to the required concentrations of vanadium ions and sulfate ions in the vanadium oxysulfate solution.

[0018] In one or more embodiments, the method further includes filtering the vanadium oxysulfate solution prepared in step (2) or step (3).

[0019] In one or more embodiments, the filter has a pore size of 0.1 micrometer to 0.2 micrometer.

[0020] In one or more embodiments, in step (1), the volume of water is 30%-35% of the reactor volume.

[0021] In one or more embodiments, in step (1), vanadium pentoxide and oxalic acid dihydrate are first added to the reactor at once, and then water is added to mix them.

[0022] In one or more embodiments, in the first stage of step (2), the mass m1 of concentrated sulfuric acid added satisfies m1 = 45%·m0.

[0023] In one or more embodiments, in the second stage of step (2), the mass m2 of concentrated sulfuric acid added satisfies m2 = 10%·m0.

[0024] In one or more embodiments, in the third stage of step (2), the mass m3 of concentrated sulfuric acid added satisfies m3 = 45%·m0.

[0025] In one or more embodiments, in step (2), after adding all the concentrated sulfuric acid, stirring is continued for 10 min to 30 min.

[0026] In one or more embodiments, during step (2), the temperature of the reaction system rises and is maintained at 90°C-98°C during the addition of concentrated sulfuric acid.

[0027] In one or more embodiments, steps (1) and (2) are carried out in the same reactor.

[0028] In one or more embodiments, the reaction system is not heated in step (2). Detailed Implementation

[0029] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form preferred technical solutions.

[0030] This invention provides a method for producing vanadium oxysulfate solution, comprising the following steps:

[0031] (1) Vanadium pentoxide, oxalic acid dihydrate and water are mixed evenly to obtain a mixture, wherein the mass ratio of vanadium pentoxide, oxalic acid dihydrate and water in the mixture is 1:(0.64-0.66):(3.5-3.6);

[0032] (2) Add concentrated sulfuric acid to the mixture obtained in step (1) in three stages to prepare the vanadium oxysulfate solution;

[0033] In step (2), the total mass m0 of the added concentrated sulfuric acid and the mass m of vanadium pentoxide satisfy m0:m = (2.6-2.8):1;

[0034] In the first stage of step (2), the flow rate Q1 of the added concentrated sulfuric acid satisfies Q1 = (4.0% - 4.5%)·m0 / min, and the mass m1 of the added concentrated sulfuric acid satisfies m1 = (43% - 47%)·m0;

[0035] In the second stage of step (2), the flow rate Q2 of the added concentrated sulfuric acid satisfies Q2 = (0.8% - 1.0%)·m0 / min, and the mass m2 of the added concentrated sulfuric acid satisfies m2 = (9% - 11%)·m0;

[0036] In the third stage of step (2), the flow rate Q3 of the added concentrated sulfuric acid satisfies Q3 = (4.0% - 4.5%)·m0 / min, and the mass m3 of the added concentrated sulfuric acid satisfies m3 = (43% - 47%)·m0.

[0037] In step (1), oxalic acid dihydrate is used as a reducing agent. The preferred mass ratio of vanadium pentoxide, oxalic acid dihydrate, and water is 1:(0.64-0.66):(3.5-3.6). The volume of water is preferably 30%-35% of the reactor volume, for example, 34%-35%. Controlling the water volume to 30%-35% of the reactor volume helps to ensure that the material volume during the reaction process remains within a safe range, preventing material overflow from the reactor and causing pollution and danger. In this invention, the reactor can be a reaction vessel. The water used in this invention is preferably ultrapure water.

[0038] In some implementations, in step (1), the required vanadium pentoxide and oxalic acid dihydrate are added to the reactor at one time according to the mass ratio m(vanadium pentoxide):m(oxalic acid dihydrate):m(water) = 1:(0.64-0.66):(3.5-3.6); then water is added, the volume of which accounts for 30%-35% of the reactor volume, and stirring is started.

[0039] In step (2), concentrated sulfuric acid is added continuously in three stages. In this invention, concentrated sulfuric acid refers to an aqueous solution of sulfuric acid with a concentration of 98wt%-99wt%, for example, 98.3wt%. The ratio of the total mass of concentrated sulfuric acid added to the mass of vanadium pentoxide is (2.6-2.8):1, for example, (2.7-2.8):1. After all the concentrated sulfuric acid has been added, stirring can continue for 10-30 minutes, for example, 15-25 minutes, or 20 minutes. In this document, the total mass of concentrated sulfuric acid added in step (2) is denoted as m0. A peristaltic pump, such as a micro peristaltic pump, can be used to add the concentrated sulfuric acid.

[0040] In the first stage, the flow rate Q1 of the added concentrated sulfuric acid satisfies Q1 = (4.0% - 4.5%)·m0 / min, and the mass m1 of the added concentrated sulfuric acid satisfies m1 = (43% - 47%)·m0; in the second stage, the flow rate Q2 of the added concentrated sulfuric acid satisfies Q2 = (0.8% - 1.0%)·m0 / min, and the mass m2 of the added concentrated sulfuric acid satisfies m2 = (9% - 11%)·m0; in the third stage, the flow rate Q3 of the added concentrated sulfuric acid satisfies Q3 = (4.0% - 4.5%)·m0 / min, and the mass m3 of the added concentrated sulfuric acid satisfies m3 = (43% - 47%)·m0.

[0041] Preferably, in the first stage, the flow rate of concentrated sulfuric acid added is (4.0%-4.5%)·m0 / min, and the amount added is 45%·m0; in the second stage, the flow rate of concentrated sulfuric acid added is (0.8%-1.0%)·m0 / min, and the amount added is 10%·m0; in the third stage, the flow rate of concentrated sulfuric acid added is (4.0%-4.5%)·m0 / min, and the amount added is 45%·m0.

[0042] In this invention, it is preferable not to heat the reaction system in step (2). During the addition of concentrated sulfuric acid, the temperature of the reaction system can be raised from room temperature to 90℃-98℃ (e.g., 92℃, 94℃, 96℃, 97℃) and maintained within the aforementioned temperature range. By controlling the mass and flow rate of concentrated sulfuric acid added in the three stages, this invention achieves the goal of maintaining the reaction system temperature within a relatively high range (e.g., 90℃-98℃), which is beneficial for a complete and thorough reaction, avoids the impact of oxalic acid residue on electrolyte performance, and results in high production efficiency and raw material utilization. In this invention, steps (1) and (2) can be carried out in the same reactor.

[0043] Optionally, the method of the present invention may further include step (3): adding water and / or sulfuric acid to the vanadium oxysulfate solution prepared in step (2) according to the desired concentrations of vanadium ions and sulfate ions in the vanadium oxysulfate solution. The sulfuric acid added in step (3) may be concentrated sulfuric acid.

[0044] In some implementations, in step (3), a sample is taken from the reaction solution after the reaction in step (2) to detect the concentration of vanadium ions and sulfate ions. If necessary, water and / or sulfuric acid are added to prepare a vanadium oxysulfate solution of the required concentration.

[0045] In some implementations, in step (3), under stirring conditions, water and a small amount of concentrated sulfuric acid are added according to the required vanadium ion concentration of the vanadium oxysulfate solution to complete the concentration adjustment of the solution.

[0046] In this invention, the vanadium oxysulfate solution prepared in step (2) or step (3) can be filtered. Filtration is preferably precision filtration. The filter pore size is preferably 0.1 μm-0.2 μm.

[0047] The present invention has the following advantages: The present invention makes full use of the heat of sulfuric acid dilution, without the need for additional heating, thus saving energy; the reaction is mild and controllable, avoiding the risk of material spillage; when the reducing agent powder is added at once, the powder addition process is separated from the reaction process, eliminating the risk of corrosion and blockage of conveying equipment; it has a high reaction temperature (e.g., 90℃-98℃) within the safe range of material liquid level, which is conducive to a full and thorough reaction, avoiding the impact of oxalic acid residue on electrolyte performance, and resulting in high production efficiency and raw material utilization.

[0048] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, percentages and parts are by weight.

[0049] The following tests were conducted in accordance with NB / T 42006-2013 "Test Methods for Electrolytes for Vanadium Redox Flow Batteries":

[0050] Vanadium content (vanadium ion concentration, total vanadium concentration) determination: using a sulfur-phosphoric acid buffer solution as the medium, titration is performed with potassium permanganate standard solution until a potential jump occurs. The corresponding vanadium ion concentration is calculated based on the electrolyte volume corresponding to the potential jump.

[0051] Determination of sulfate content: In the electrolyte, sulfate reacts with added barium chloride to form barium sulfate precipitate. The precipitate is washed with dilute hydrochloric acid until the residual amount of vanadium ions is below 0.1%, and then washed with deionized water until no chloride ions are present (detected by silver nitrate method). The precipitate is dried, ignited to constant weight, and the mass of barium sulfate is weighed. The sulfate content is calculated based on the mass of barium sulfate.

[0052] Conductivity was measured using a conductivity meter.

[0053] Viscosity was measured using a glass capillary viscometer.

[0054] Example 1

[0055] The method of this invention was used to prepare a tetravalent electrolyte in a 500 mL three-necked flask:

[0056] S1: Add 50g of vanadium pentoxide and 33g of oxalic acid dihydrate to a three-necked flask, then add 176mL of ultrapure water, close the water addition valve, and turn on the stirrer;

[0057] S2: Open the acid addition valve and calculate the total amount of concentrated sulfuric acid to be added as 74.5 mL (136.4 g). Use a micro peristaltic pump for continuous feeding, setting the peristaltic pump acid addition parameters as follows, and simultaneously monitor the system temperature during the feeding process:

[0058] 1) First stage: 33.5 mL of concentrated sulfuric acid was added at a flow rate of 3.0 mL / min, and the temperature was measured to rise rapidly from room temperature to about 95℃;

[0059] 2) Second stage: Add 7.5 mL of concentrated sulfuric acid at a flow rate of 0.6 mL / min, and maintain the temperature at 95 ± 1 °C;

[0060] 3) Third stage: Add 33.5 mL of concentrated sulfuric acid at a flow rate of 3.0 mL / min, and keep the temperature at 95 ± 1℃.

[0061] The reaction was continued with stirring for 20 minutes. The reaction was gentle and no material overflowed. After the reaction was completed, 247.5 mL of vanadium electrolyte was obtained. A sample was taken and tested. The concentration of tetravalent vanadium ions was 2.129 mol / L, the concentration of pentavalent vanadium ions was 0.091 mol / L, and the concentration of sulfate ions was 5.467 mol / L.

[0062] S3: Add water to a final volume of 333 mL, and the total vanadium concentration was measured to be 1.648 mol / L and the sulfate concentration to be 4.106 mol / L.

[0063] S4: The electrolyte was filtered using a 0.1μm microporous filter. No visible solid powder residue was observed after filtration. The electrolyte conductivity was measured to be 252 mS / cm and the viscosity was 4.95 mP·s. High performance liquid chromatography (HPLC) analysis showed that the product contained no oxalic acid, which meets the qualified standard for vanadium electrolyte.

[0064] Example 2

[0065] The method of this invention was used to conduct scale-up pilot production in a 200L carbon steel PTFE-lined reactor:

[0066] S1: Add 13kg of oxalic acid and 20kg of vanadium pentoxide to a 200L reactor, close the feed valve, open the water valve to inject 70L of ultrapure water, close the water valve, and turn on the stirrer.

[0067] S2: Open the acid addition valve and calculate the total amount of concentrated sulfuric acid to be added as 30L (55.2kg). Use a peristaltic pump for feeding, and set the acid addition strategy as follows, while simultaneously monitoring the system temperature during the feeding process:

[0068] 1) First stage: 13.5L of concentrated sulfuric acid was added at a flow rate of 1.3L / min, and the temperature was measured to rise rapidly from room temperature to about 95.5℃;

[0069] 2) Second stage: Add 3L of concentrated sulfuric acid at a flow rate of 0.3L / min, and maintain the temperature at 95.5±1℃;

[0070] 3) Third stage: Add 13.5L of concentrated sulfuric acid at a flow rate of 1.3L / min, and keep the temperature at 96.0±1℃.

[0071] The reaction was continued with stirring for 20 minutes. The reaction was gentle, with no material overflow. The exhaust gas was purified by a circulating spray acid mist absorber before being discharged into the atmosphere. After the reaction was completed, 98.5 L of vanadium electrolyte was obtained. Sampling and testing showed that the concentration of tetravalent vanadium ions was 2.141 mol / L, the concentration of pentavalent vanadium ions was 0.091 mol / L, and the concentration of sulfate ions was 5.602 mol / L.

[0072] S3: Add water to a final volume of 130L, and the total vanadium concentration was measured to be 1.622 mol / L and the sulfate concentration to be 4.245 mol / L.

[0073] S4: The electrolyte was filtered using a 0.1μm precision filter. No visible solid powder residue was observed after filtration. The electrolyte conductivity was measured to be 248 mS / cm and the viscosity to be 5.02 mP·s. HPLC analysis showed that the product contained no oxalic acid and met the qualified standards for vanadium electrolyte.

[0074] Comparative Example 1

[0075] Vanadium electrolyte was prepared using the following steps:

[0076] S1: Add 50g of vanadium pentoxide and 33g of oxalic acid dihydrate to a 500mL three-necked flask, then add 176mL of ultrapure water, close the water addition valve, and turn on the stirrer;

[0077] S2: Open the acid addition valve and measure 74.5 mL of concentrated sulfuric acid. Add the sulfuric acid at a constant flow rate of 0.6 mL / min using a micro peristaltic pump, and monitor the system temperature during the addition process. The results show that the reaction system temperature does not exceed 75℃ during the acid addition process. After the acid addition is complete, stirring is maintained for 1 hour, and the vanadium pentoxide powder is not completely dissolved.

[0078] In this comparative example, the concentrated sulfuric acid was added slowly, and its heat of dilution diffused into the environment without being effectively utilized, making it impossible to raise the system temperature above 85°C. The dissolution rate of vanadium pentoxide was low, and the reaction was incomplete.

[0079] Comparative Example 2

[0080] Vanadium electrolyte was prepared using the following steps:

[0081] S1: Add 50g of vanadium pentoxide and 33g of oxalic acid dihydrate to a 500mL three-necked flask, then add 176mL of ultrapure water, close the water addition valve, and turn on the stirrer;

[0082] S2: Open the acid addition valve and measure 74.5 mL of concentrated sulfuric acid. Add the sulfuric acid using a micro peristaltic pump at a constant flow rate of 3.0 mL / min, and monitor the system temperature during the addition process. The results show that the reaction intensity increases continuously with the increase of the amount of concentrated sulfuric acid added. When the cumulative amount of concentrated sulfuric acid added reaches 33 mL, the system temperature rises to 95℃, and a large number of bubbles begin to be generated. The liquid level rises to the 400 mL mark on the flask. After continuing to add concentrated sulfuric acid at a constant flow rate, the reaction intensifies, causing the material to overflow from the reaction vessel.

[0083] In this comparative example, a higher flow rate of concentrated sulfuric acid can rapidly raise the system temperature to 95°C, promoting the dissolution of vanadium pentoxide. When the system volume fraction (the ratio of reactants to reactor volume) reaches 80%, continuing to add acid while maintaining a constant flow rate intensifies the reaction, causing the bubble formation rate to exceed the bursting rate, resulting in a rapid rise in the liquid level and material overflowing from the reaction vessel. To maintain the reaction rate while ensuring reaction safety, the rate of addition of concentrated sulfuric acid should be reduced after the temperature reaches approximately 95°C, allowing the reaction temperature to be maintained while preventing the system liquid level from continuing to rise rapidly.

[0084] Comparative Example 3

[0085] Vanadium electrolyte was prepared using the following steps:

[0086] S1: Add 50g of vanadium pentoxide and 33g of oxalic acid dihydrate to a 500mL three-necked flask, then add 176mL of ultrapure water, close the water addition valve, and turn on the stirrer;

[0087] S2: Open the acid addition valve and add 74.5 mL of concentrated sulfuric acid in two stages using a micro peristaltic pump:

[0088] First stage: 33.5 mL of concentrated sulfuric acid was added at a flow rate of 3.0 mL / min, and the temperature was measured to reach 95.5℃;

[0089] Second stage: The remaining concentrated sulfuric acid was added at a flow rate of 0.6 mL / min, and the system temperature was monitored during the addition process. The results showed that when the amount of concentrated sulfuric acid added accumulated to 7.5 mL in this stage, the reaction maintained equilibrium, the liquid level remained basically unchanged, and the measured temperature was 95.6℃. As the flow rate was maintained and acid was added further, the intensity of the reaction decreased, a large amount of solid powder dissolved, the gas production rate decreased, and the liquid level change was mainly affected by the volume of concentrated sulfuric acid. After the acid addition was completed, the measured temperature was 76.3℃.

[0090] The reaction was stirred for another 20 minutes. After the reaction was completed, the vanadium electrolyte contained some undissolved vanadium pentoxide powder. The concentration of tetravalent vanadium ions was measured to be 1.786 mol / L, the concentration of pentavalent vanadium ions was 0.321 mol / L, and the concentration of sulfate ions was 5.587 mol / L.

[0091] In this comparative example, the first stage is the reaction rate rise phase. After the temperature reaches 95℃, the reaction rate is relatively fast, at which point the second stage begins. By adjusting the flow rate to control the heat of dilution, heat of reaction absorption, and heat of diffusion, the reaction is kept in a state of high rate and liquid level equilibrium. In the second stage, after the amount of concentrated sulfuric acid reaches 7.5 mL, the reaction rate passes the plateau phase and enters the decline phase. At the same time, due to the decrease in the concentration difference between concentrated sulfuric acid and sulfuric acid in the system, the heat of dilution release decreases. At this point, continuing to add acid at a low flow rate results in heat loss exceeding heat generation, and the temperature continues to drop. Simultaneously, due to the large consumption of oxalic acid, the residual vanadium pentoxide powder in the system cannot be completely dissolved. Therefore, increasing the rate of addition of concentrated sulfuric acid when the reaction rate is about to enter the decline phase helps to prolong the equilibrium period of high reaction rate, promotes the dissolution of residual vanadium pentoxide powder in the system, and ensures that the dissolved pentavalent vanadium and residual oxalic acid react completely.

Claims

1. A method of producing a vanadyl sulfate solution, characterized by, The method includes the following steps: (1) Vanadium pentoxide, oxalic acid dihydrate and water are mixed evenly in a reactor to obtain a mixture, wherein the mass ratio of vanadium pentoxide, oxalic acid dihydrate and water in the mixture is 1:(0.64-0.66):(3.5-3.6); (2) Add concentrated sulfuric acid to the mixture obtained in step (1) in three stages to prepare the vanadium oxysulfate solution; In step (2), the total mass m0 of the added concentrated sulfuric acid and the mass m of vanadium pentoxide satisfy m0:m = (2.6-2.8):1; In the first stage of step (2), the flow rate Q1 of the added concentrated sulfuric acid satisfies Q1 = (4.0% - 4.5%)·m0 / min, and the mass m1 of the added concentrated sulfuric acid satisfies m1 = (43% - 47%)·m0; In the second stage of step (2), the flow rate Q2 of the added concentrated sulfuric acid satisfies Q2=(0.8%-1.0%)·m0 / min, and the mass m2 of the added concentrated sulfuric acid satisfies m2=(9%-11%)·m0; In the third stage of step (2), the flow rate Q3 of the added concentrated sulfuric acid satisfies Q3 = (4.0% - 4.5%)·m0 / min, and the mass m3 of the added concentrated sulfuric acid satisfies m3 = (43% - 47%)·m0; In step (2), the temperature of the reaction system rises and is maintained at 90°C-98°C during the addition of concentrated sulfuric acid, and the reaction system is not heated in step (2); Concentrated sulfuric acid refers to sulfuric acid with a concentration of 98wt%-99wt%.

2. The method of claim 1, wherein, The method further includes the following steps: (3) Add water and / or sulfuric acid to the vanadium oxysulfate solution prepared in step (2) according to the required concentration of vanadium ions and sulfate ions in the vanadium oxysulfate solution.

3. The method of claim 1 or 2, wherein, The method further includes filtering the vanadium oxysulfate solution prepared in step (2) or step (3).

4. The method of claim 3, wherein, The filter has a pore size of 0.1 micrometers to 0.2 micrometers.

5. The method of claim 1, wherein, In step (1), the volume of water is 30%-35% of the reactor volume.

6. The method as described in claim 1, characterized in that, In step (1), vanadium pentoxide and oxalic acid dihydrate are first added to the reactor at once, and then water is added to mix them.

7. The method as described in claim 1, characterized in that, In the first stage of step (2), the mass of concentrated sulfuric acid added, m1, satisfies m1 = 45%·m0; In the second stage of step (2), the mass of concentrated sulfuric acid added, m2, satisfies m2 = 10%·m0; In the third stage of step (2), the mass of concentrated sulfuric acid added, m3, satisfies m3 = 45%·m0.

8. The method as described in claim 1, characterized in that, In step (2), after adding all the concentrated sulfuric acid, continue stirring for 10 min to 30 min.

9. The method as described in claim 1, characterized in that, Steps (1) and (2) are carried out in the same reactor.