A method for preparing 3.5-valence vanadyl sulfate electrolyte by gas-based reduction of ammonium polyvanadate

Abstract

The application provides a method for preparing 3.5-valence vanadyl sulfate electrolyte by reducing ammonium polyvanadate with a gas, which comprises the following steps: (1) ammonium polyvanadate is reduced and calcined by a reducing gas to obtain vanadium oxide; the vanadium oxide contains V4O7; the reducing gas comprises a mixed gas of NH3, CO and H2; (2) a mixed sulfuric acid solution and the vanadium oxide are subjected to a dissolution reaction, and vanadium adjustment is performed to obtain 3.5-valence vanadyl sulfate electrolyte. The process is simple and easy to implement, 3.5-valence vanadyl sulfate electrolyte product can be obtained from ammonium polyvanadate as raw material, the vanadium concentration is high, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of vanadium electrolyte preparation technology, and in particular to a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Background Technology

[0002] Vanadium redox flow batteries have advantages such as high safety, strong capacity expansion, long cycle life, and low total life cycle cost, making them the most commercially promising flow batteries currently available. The electrolyte is an important component of vanadium redox flow batteries and plays a decisive role in the overall performance of vanadium batteries. The most mainstream method for preparing vanadium oxysulfate electrolyte is to use vanadium pentoxide as raw material, reduce pentavalent vanadium with a chemical reducing agent to obtain tetravalent vanadium electrolyte, and then use electrolysis to electrolyze tetravalent vanadium to prepare a lower-valent vanadium oxysulfate electrolyte. The problems with this method are: 1) the solubility of high-valent vanadium oxide is low, making it difficult to obtain high-concentration vanadium electrolyte; 2) it is difficult to directly obtain trivalent vanadium solution through a reducing agent; 3) there may be reducing agent residue in the vanadium electrolyte; (4) the process is long and the cost is high. There is an urgent need to develop a new method for preparing vanadium oxysulfate electrolyte with a short process.

[0003] CN114156516A discloses a method for producing ammonium-free vanadium electrolyte. The method involves sodium roasting and leaching to obtain a crude sodium vanadate solution, followed by acidification and reduction to obtain a crude vanadium oxysulfate solution. This is then subjected to extraction and back-extraction to obtain a high-purity vanadium oxysulfate solution, and finally, vanadium electrolyte is obtained by adjusting the valence state. The advantage of this method is that it can directly prepare vanadium oxysulfate solution from vanadium-containing leachate. However, the process is lengthy, acidic wastewater containing organic matter is generated after extraction, and the resulting vanadium oxysulfate electrolyte contains a small amount of organic matter, affecting the electrolyte performance.

[0004] CN114361549A discloses a method for preparing vanadium electrolyte for all-vanadium redox flow batteries. This method involves reducing high-purity vanadium pentoxide under a reducing gas to obtain low-valence vanadium oxide. The low-valence vanadium oxide is then mixed with an activator and activated by heating to obtain a vanadium-containing paste electrolyte. Finally, water is added to dissolve the vanadium paste electrolyte, yielding a vanadium electrolyte with an average vanadium valence state ranging from +3 to +4. This method is rapid and effective, but it still requires vanadium pentoxide as a reactant and cannot precisely obtain a vanadium oxysulfate electrolyte with a valence of 3.5.

[0005] Therefore, it is necessary to develop a production process for vanadium oxysulfate electrolyte with 3.5 valence to simplify production steps, reduce production costs, and achieve efficient and clean production of vanadium electrolyte. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. The method can directly obtain vanadium oxysulfate electrolyte by reducing with reducing gas-sulfuric acid dissolution-vanadium adjustment, avoiding the long process of obtaining high-purity vanadium pentoxide by calcining ammonium vanadate and then preparing vanadium oxysulfate electrolyte by chemical reduction-electrochemical reduction. The method directly obtains the electrolyte in two steps of ammonium vanadate reduction-calcination-dissolution, which greatly simplifies the process and optimizes the production process of vanadium oxysulfate electrolyte.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate, the method comprising the following steps:

[0009] (1) Ammonium polyvanadate is calcined by reducing gas to obtain vanadium oxide; the vanadium oxide contains V4O7; the reducing gas includes a mixture of NH3, CO and H2;

[0010] (2) Mix sulfuric acid solution and vanadium oxide to carry out a dissolution reaction, and adjust the vanadium to obtain vanadium oxysulfate electrolyte with 3.5 valence.

[0011] The method for preparing 3.5-valent vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate provided by this invention controls the reduction and calcination process to reduce and calcine ammonium polyvanadate to generate vanadium oxide, which is V4O7. The valence state of this vanadium oxide is 3.5. Dissolving it in sulfuric acid solution yields a crude vanadium oxysulfate solution. Subsequent vanadium adjustment is then performed to obtain the 3.5-valent vanadium oxysulfate electrolyte. Vanadium oxide is readily soluble in sulfuric acid, and the valence state of the solution obtained after dissolving vanadium oxide with a high V4O7 content is almost identical to the required valence state of the electrolyte, making the subsequent dissolution in sulfuric acid relatively simple to prepare the 3.5-valent vanadium oxysulfate electrolyte. However, since the V4O7 obtained after reduction and calcination contains a small amount of VO2 and / or V2O3 solids, a vanadium adjustment solution needs to be added to fine-tune the valence state to accurately obtain the 3.5-valent vanadium electrolyte.

[0012] The preparation process of this invention is shorter. Compared with the calcination-chemical reduction-electrochemical reduction process, the process is shorter and the production cost is lower, which significantly optimizes the production process of vanadium oxysulfate electrolyte.

[0013] Furthermore, it is worth noting that this invention uses a mixture of NH3, CO, and H2 as the reducing gas. Compared to other reducing gases, this mixture can better integrate with the upstream and downstream gases of vanadium products, eliminating the need for the additional introduction of gases such as hydrogen sulfide. By adjusting the ratio of these gases, coal gas can be directly used as the reducing gas, without the need for the separate introduction of high-purity hydrogen or CO, thus offering greater potential for industrial application. Moreover, this invention unexpectedly discovered that the vanadium oxide reduced by this reducing gas has a higher V4O7 content, resulting in a higher V concentration in the final 3.5-valent vanadium oxysulfate electrolyte.

[0014] It is worth noting that the ammonium polyvanadate provided by this invention has a purity of 99.5% to 99.9%.

[0015] Preferably, the reduction calcination in step (1) includes: introducing a reducing gas, heating to the reaction temperature, carrying out the reaction in a reducing gas atmosphere, and cooling down in a reducing gas atmosphere after the reaction is completed.

[0016] Preferably, the volume ratio of NH3, CO, and H2 in the reducing gas is NH3:CO:H2 = (60-80):(10-30):(5-30), for example, NH3:CO:H2 = 80:10:10, 75:15:15, 70:20:10, 60:20:20, or 60:30:10, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Preferably, the total flow rate of the reducing gas in step (1) is 20 to 100 ml / min, for example, it can be 20 ml / min, 30 ml / min, 40 ml / min, 50 ml / min, 60 ml / min, 70 ml / min, 80 ml / min, 90 ml / min or 100 ml / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the reaction temperature in step (1) is 450 to 600°C, for example, it can be 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the reaction time in step (1) is 0.5 to 3 hours, for example, it can be 0.5 hours, 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.5 hours, 1.8 hours, 1.9 hours, 2 hours, 2.2 hours, 2.5 hours or 3 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the mass fraction of the sulfuric acid solution in step (2) is 10% to 30%, for example, it can be 10%, 11%, 12%, 14%, 15%, 18%, 20%, 21%, 22%, 24%, 26% or 30%, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the liquid-to-solid ratio of the sulfuric acid solution and vanadium oxide is 6 to 9 ml / g, for example, it can be 6 ml / g, 6.5 ml / g, 7 ml / g, 7.4 ml / g, 7.7 ml / g, 8 ml / g, 8.2 ml / g, 8.5 ml / g, 8.8 ml / g or 9 ml / g, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the temperature of the dissolution reaction in step (2) is 60 to 95°C, for example, it can be 60°C, 62°C, 65°C, 67°C, 68°C, 70°C, 71°C, 72°C, 76°C, 80°C, 83°C, 84°C, 87°C, 90°C, 93°C or 95°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the dissolution reaction time is 8 to 24 hours, for example, it can be 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 15 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours or 24 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the concentration of V in the solution obtained after the dissolution reaction is ≥1.5 mol / L, for example, it can be 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2.0 mol / L, etc. Other values ​​not listed within this range are also applicable.

[0025] Preferably, the valence state of V in the solution obtained after the dissolution reaction is in the range of 3.1 to 4.1, for example, it can be 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0 or 4.1, etc. Other values ​​not listed in this range are also applicable, preferably 3.3 to 3.7.

[0026] Preferably, the vanadium adjustment in step (2) includes the solution obtained after the mixed dissolution reaction and the vanadium adjustment solution to obtain a vanadium oxysulfate electrolyte with a valence of 3.5.

[0027] The present invention selects a vanadium adjusting solution to adjust the oxidation state. On the one hand, the solubility of vanadium-containing solids such as V2O3 and V2O5 in solution is limited. On the other hand, it is necessary to ensure the ratio of sulfate to vanadium in the final vanadium oxysulfate electrolyte. Therefore, a vanadium adjusting solution is selected for adjustment, thereby adjusting the oxidation state of the vanadium oxysulfate electrolyte to 3.5.

[0028] It is worth noting that the fundamental purpose of this invention is to reduce the production cost of vanadium oxysulfate electrolyte. Therefore, the less vanadium conditioning solution is added, the better for cost reduction. Thus, it is desirable to control the valence state of vanadium in the reduced calcined vanadium oxide to be as close to 3.5 as possible.

[0029] Preferably, the vanadium conditioning solution in step (2) comprises a sulfuric acid solution containing trivalent vanadium and / or tetravalent vanadium.

[0030] Preferably, the mass fraction of sulfuric acid in the vanadium conditioning solution is 10-30%, for example, it can be 10%, 11%, 12%, 14%, 15%, 16%, 17%, 20%, 22%, 23%, 25%, 28% or 30%, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] Preferably, the concentration of V in the vanadium conditioning solution is ≥1.5 mol / L, for example, it can be 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.85 mol / L, 1.9 mol / L or 2.0 mol / L, etc. Other values ​​not listed within this range are also applicable.

[0032] Preferably, the volume ratio of the solution obtained after the dissolution reaction to the vanadium adjustment solution is 50:1 to 1:1, for example, it can be 50:1, 48:1, 45:1, 40:1, 35:1, 30:1, 25:1, 20:1, 15:1, 10:1, 5:1 or 1:1, etc. Other values ​​not listed within this range are also applicable.

[0033] It is worth noting that the content of tetravalent and trivalent vanadium in the vanadium adjustment is related to the valence state and amount of vanadium in crude vanadium oxysulfate as follows: xV 4+ +yV 3+ +zV n+ = (x+y+z)V 3.5+And 0.5x - 0.5y + (n - 3.5)z = 0. In actual operation, fine adjustments are made according to this formula, where n is the valence state of vanadium in the solution after the dissolution reaction, z is the amount of vanadium in the solution after the dissolution reaction, and x and y are the vanadium content in the vanadium adjustment solution, respectively. 4+ and V 3+ The amount of substance.

[0034] As a preferred technical solution of the present invention, the method includes the following steps:

[0035] (1) Ammonium polyvanadate is placed in a calcination apparatus and a reducing gas with a flow rate of 20-100 ml / min is introduced. The volume ratio of NH3, CO, and H2 in the reducing gas is NH3:CO:H2 = (60-80):(10-30):(5-30). After heating to the reaction temperature of 450-600℃, the reaction is carried out in the atmosphere of reducing gas for 0.5-3 hours. Then the reducing gas is turned off to obtain vanadium oxide containing V4O7.

[0036] (2) Mix sulfuric acid solution with a mass fraction of 10-30% and vanadium oxide at a liquid-to-solid ratio of 6-9 ml / g and carry out a dissolution reaction at 60-95℃ for 8-24 hours. Mix the solution obtained after the dissolution reaction with a vanadium adjustment solution and adjust the vanadium content. The mass fraction of sulfuric acid in the vanadium adjustment solution is 10-30% and the concentration of V element is ≥1.5 mol / L to obtain a 3.5 valence sulfuric acid vanadium oxychloride electrolyte.

[0037] The present invention does not limit the calcination device, and any calcination device known to those skilled in the art that can be used for calcination can be used, and adjustments can also be made according to the actual situation.

[0038] It is worth noting that the traditional process for preparing vanadium oxysulfate electrolyte generally uses high-purity vanadium pentoxide as raw material, which is obtained through solution chemical reduction followed by electrolytic reduction. This invention uses ammonium polyvanadate as raw material, directly transforming the ammonium vanadate calcination process and eliminating the subsequent energy-intensive electrolysis step, thereby significantly reducing process costs and equipment investment.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] (1) The method for preparing 3.5 valence vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate provided by the present invention has simple process steps and can preferably prepare 3.5 valence vanadium oxysulfate electrolyte with vanadium concentration ≥1.97mol / L. Moreover, the utilization rate of vanadium in ammonium polyvanadate is preferably above 99.7%, that is, the amount of vanadium to be added for additional adjustment is low.

[0041] (2) The method for preparing 3.5-valent vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate provided by the present invention directly obtains 3.5-valent vanadium oxysulfate electrolyte through chemical adjustment. Compared with traditional electrochemical processes, the equipment and process flow are greatly simplified. Attached Figure Description

[0042] Figure 1 This is a schematic flowchart of the method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate provided by the present invention. Detailed Implementation

[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0044] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0045] As a specific embodiment of the present invention, a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate is provided, such as... Figure 1 As shown, the method includes the following steps:

[0046] (1) Ammonium polyvanadate is placed in a calcination apparatus and a reducing gas is introduced. The volume ratio of NH3, CO and H2 in the reducing gas is NH3:CO:H2 = (60-80):(10-30):(5-30). After heating to the reaction temperature, the reaction is carried out in the atmosphere of the reducing gas. Then the reducing gas is turned off to obtain vanadium oxide containing V4O7.

[0047] (2) Mix sulfuric acid solution and vanadium oxide to carry out a dissolution reaction, and mix the solution obtained after the dissolution reaction with vanadium adjustment solution to adjust vanadium, so as to obtain vanadium oxysulfate electrolyte with valence 3.5.

[0048] Figure 1 This is a process flow diagram for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Ammonium polyvanadate is calcined in a reducing gas atmosphere to obtain vanadium oxide intermediates, which are then dissolved in acid to obtain a crude vanadium oxysulfate solution. Finally, the solution is adjusted with a vanadium conditioning solution to obtain the vanadium oxysulfate electrolyte. This process greatly simplifies the production of vanadium oxysulfate electrolyte, completely converting raw materials into products with no wastewater generation.

[0049] It should be clarified that any use of the process provided in the embodiments of the present invention or any substitution or change of conventional data falls within the protection and disclosure scope of the present invention.

[0050] Example 1

[0051] This embodiment provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate, the method comprising the following steps:

[0052] (1) Ammonium polyvanadate was placed in a calcining furnace and a reducing gas with a flow rate of 40 ml / min was introduced. The reducing gas was a mixture of NH3, CO and H2, and the mixing ratio of the three gases was NH3:CO:H2 = 80:10:10. After heating to the reaction temperature of 480℃, the reaction was carried out for 2.5 h in the atmosphere of reducing gas. Then the reducing gas was turned off to obtain vanadium oxide.

[0053] (2) Mix sulfuric acid solution with a mass fraction of 28% and vanadium oxide at a liquid-to-solid ratio of 7 ml / g and carry out a dissolution reaction at 90°C for 8 h to obtain crude vanadium oxysulfate solution;

[0054] And according to xV 4+ +yV 3+ +zV n+ = (x+y+z)V 3.5+ And 0.5x-0.5y+(n-3.5)z=0, mix crude sulfuric acid oxyvanadium solution and vanadium adjustment solution to adjust vanadium. The mass fraction of sulfuric acid in the vanadium adjustment solution is 28% and the concentration of V element is 1.7mol / L, to obtain 3.5 valence sulfuric acid oxyvanadium electrolyte.

[0055] Example 2

[0056] This embodiment provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate, the method comprising the following steps:

[0057] (1) Ammonium polyvanadate was placed in a calcining furnace and a reducing gas with a flow rate of 100 ml / min was introduced. The reducing gas was a mixture of NH3, CO and H2, and the mixing ratio of the three gases was NH3:CO:H2 = 60:30:10. After heating to the reaction temperature of 600℃, the reaction was carried out for 0.5 h in the atmosphere of reducing gas, and then the reducing gas was turned off to obtain vanadium oxide.

[0058] (2) Mix sulfuric acid solution with a mass fraction of 18% and vanadium oxide at a liquid-to-solid ratio of 8.5 ml / g and carry out a dissolution reaction at 60°C for 24 h to obtain crude vanadium oxysulfate solution;

[0059] And according to xV 4+ +yV 3+ +zV n+ = (x+y+z)V 3.5+And 0.5x-0.5y+(n-3.5)z=0, mix crude sulfuric acid oxyvanadium solution and vanadium adjustment solution to adjust vanadium. The mass fraction of sulfuric acid in the vanadium adjustment solution is 18% and the concentration of V element is 1.6mol / L, to obtain 3.5 valence sulfuric acid oxyvanadium electrolyte.

[0060] Example 3

[0061] This embodiment provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate, the method comprising the following steps:

[0062] (1) Ammonium polyvanadate was placed in a calcining furnace and a reducing gas with a flow rate of 60 ml / min was introduced. The reducing gas was a mixture of NH3, CO and H2, and the mixing ratio of the three gases was NH3:CO:H2 = 80:15:5. After heating to the reaction temperature of 450℃, the reaction was carried out for 3 hours in the atmosphere of reducing gas. Then the reducing gas was turned off to obtain vanadium oxide.

[0063] (2) Mix sulfuric acid solution with a mass fraction of 25% and vanadium oxide at a liquid-to-solid ratio of 7 ml / g and carry out a dissolution reaction at 95°C for 8 h to obtain crude vanadium oxysulfate solution;

[0064] And according to xV 4+ +yV 3+ +zV n+ = (x+y+z)V 3.5+ And 0.5x-0.5y+(n-3.5)z=0, mix crude sulfuric acid oxyvanadium solution and vanadium adjustment solution to adjust vanadium. The mass fraction of sulfuric acid in the vanadium adjustment solution is 18% and the concentration of V element is 1.6mol / L, to obtain 3.5 valence sulfuric acid oxyvanadium electrolyte.

[0065] Example 4

[0066] This embodiment provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate, the method comprising the following steps:

[0067] (1) Ammonium polyvanadate was placed in a calcining furnace and a reducing gas with a flow rate of 60 ml / min was introduced. The reducing gas was a mixture of NH3, CO and H2, and the mixing ratio of the three gases was NH3:CO:H2 = 70:20:10. After heating to the reaction temperature of 550℃, the reaction was carried out for 2 hours in the atmosphere of reducing gas. Then the reducing gas was turned off to obtain vanadium oxide.

[0068] (2) Mix sulfuric acid solution with a mass fraction of 30% and vanadium oxide at a liquid-to-solid ratio of 9 ml / g and carry out a dissolution reaction at 90°C for 24 h to obtain crude vanadium oxysulfate solution;

[0069] And according to xV 4+ +yV3+ +zV n+ = (x+y+z)V 3.5+ And 0.5x-0.5y+(n-3.5)z=0, mix crude sulfuric acid oxyvanadium solution and vanadium adjustment solution to adjust vanadium. The mass fraction of sulfuric acid in the vanadium adjustment solution is 30% and the concentration of V element is 1.5mol / L, to obtain 3.5 valence sulfuric acid oxyvanadium electrolyte.

[0070] Example 5

[0071] This embodiment provides a method for preparing 3.5-valent vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except for adjusting the reaction temperature to 400°C in step (1) and adjusting the amount of vanadium conditioning solution accordingly to finally obtain 3.5-valent vanadium oxysulfate electrolyte, the rest of the method is the same as in Example 1, and will not be repeated here.

[0072] Example 6

[0073] This embodiment provides a method for preparing 3.5-valent vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except for step (1) where the reaction temperature is adjusted to 700°C and the amount of vanadium conditioning solution is adjusted accordingly to finally obtain 3.5-valent vanadium oxysulfate electrolyte, the rest of the method is the same as in Example 1, and will not be repeated here.

[0074] Example 7

[0075] This embodiment provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except for step (1) where the volume ratio of NH3, CO, and H2 in the reducing gas is NH3:CO:H2 = 90:5:5, and the amount of vanadium conditioning solution is adjusted accordingly to finally obtain vanadium oxysulfate electrolyte, the rest of the method is the same as in Example 1, and will not be repeated here.

[0076] Example 8

[0077] This embodiment provides a method for preparing 3.5 valence vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except for step (1) where the volume ratio of NH3, CO, and H2 in the reducing gas is NH3:CO:H2 = 50:25:25, and step (2) where the valence state of the crude vanadium oxysulfate solution is not adjusted, the method is the same as in Example 1 and will not be repeated here.

[0078] Example 9

[0079] This embodiment provides a method for preparing 3.5 valence vanadium oxysulfate electrolyte by reducing ammonium polyvanadate with gas. Except for step (1) where the volume ratio of NH3, CO, and H2 in the reducing gas is NH3:CO:H2 = 40:5:55, and step (2) where the valence state of the crude vanadium oxysulfate solution is not adjusted, the method is the same as in Example 1 and will not be repeated here.

[0080] Example 10

[0081] This embodiment provides a method for preparing 3.5-valent vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except for step (2), in which the mass fraction of sulfuric acid in the sulfuric acid solution is 8%, and the amount of vanadium conditioning solution is adjusted accordingly to finally obtain 3.5-valent vanadium oxysulfate electrolyte, the rest of the method is the same as in Example 1, and will not be repeated here.

[0082] Example 11

[0083] This embodiment provides a method for preparing 3.5-valent vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except for step (2) where the dissolution reaction temperature is adjusted to 55°C and the amount of vanadium conditioning solution is adjusted accordingly to finally obtain 3.5-valent vanadium oxysulfate electrolyte, the rest of the method is the same as in Example 1, and will not be repeated here.

[0084] Comparative Example 1

[0085] This comparative example provides a method for preparing 3.5 valence vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except that no reducing gas is introduced, so that the result in step (1) is V2O5, and the valence state of the crude vanadium oxysulfate solution obtained in step (2) is not adjusted, the method is the same as in Example 1, and will not be repeated here.

[0086] Because the vanadium oxysulfate solution that can be used as an electrolyte has requirements for the valence state and concentration of vanadium, namely, the valence state of vanadium is required to be 3.5 and the concentration of vanadium is required to be ≥1.5mol / L, while vanadium oxides such as V2O5 have low solubility in solution, it is difficult to obtain the final vanadium electrolyte even if the original ratio is adjusted by vanadium in the subsequent process.

[0087] Comparative Example 2

[0088] This comparative example provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. Except that the reducing gas is a mixture of CO and H2 in a ratio of CO:H2 = 50:50, so that the mixture obtained in step (1) is a mixture of V2O5 and VO2, and the amount of vanadium conditioning solution is adjusted accordingly to finally obtain vanadium oxysulfate electrolyte, the rest of the method is the same as in Example 1, and will not be repeated here.

[0089] Because the vanadium oxysulfate solution that can be used as an electrolyte has requirements for the valence state and concentration of vanadium, namely, the valence state of vanadium is required to be 3.5 and the concentration of vanadium is required to be ≥1.5mol / L, while vanadium oxides such as V2O5 have low solubility in solution, it is difficult to obtain the final vanadium electrolyte even if the original ratio is adjusted by vanadium in the subsequent process.

[0090] Comparative Example 3

[0091] This comparative example provides a method for preparing 3.5 valence vanadium oxysulfate electrolyte by reducing ammonium polyvanadate with gas. Except that the reducing gas is a mixture of CO and NH3 in a mixing ratio of CO:NH3 = 50:50, and the crude vanadium oxysulfate solution obtained in step (2) is not adjusted in valence state, the method is the same as in Example 1 and will not be repeated here.

[0092] Comparative Example 4

[0093] This comparative example provides a method for preparing 3.5 valence vanadium oxysulfate electrolyte by reducing ammonium polyvanadate with gas. Except that the reducing gas is a mixture of H2 and NH3 in a mixing ratio of H2:NH3 = 50:50, and the valence state of the crude vanadium oxysulfate solution obtained in step (2) is not adjusted, the method is the same as in Example 1, and will not be repeated here.

[0094] Comparative Example 5

[0095] This comparative example provides a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. The method is the same as that in Example 1 except that vanadium adjustment is not performed, and will not be described again here.

[0096] The roasting temperature and time were controlled by an atmosphere furnace, the gas flow was controlled by a flow meter, and the content of each element in the solution was quantitatively analyzed by ICP-OES. The vanadium valence was determined by potentiometric titration. The utilization rate of vanadium in ammonium polyvanadate was recorded as the ratio of the amount of vanadium initially added to the amount of vanadium in the final electrolyte.

[0097] The purity and yield were obtained according to the above test methods and calculation formulas. The vanadium concentration and vanadium valence in the vanadium oxysulfate solutions prepared in Examples 1-11 and Comparative Examples 1-5 are shown in Table 1.

[0098] Table 1

[0099]

[0100] In Table 1, " / " indicates that there is no relevant data.

[0101] From the data in Table 1, we can see the following points:

[0102] (1) As can be seen from Examples 1 to 4, the method for preparing 3.5-valent vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate provided by the present invention can obtain a high-purity 3.5-valent vanadium oxysulfate electrolyte with a vanadium concentration ≥1.90mol / L by using a special gas combination for reduction. This indicates that by using ammonium polyvanadate as raw material, a high-purity vanadium oxysulfate electrolyte can be obtained through the process of reduction calcination-sulfuric acid dissolution-valence adjustment. No wastewater is generated in the whole process, and the full utilization of raw materials to products is realized.

[0103] (2) As can be seen from Examples 1 and 5-6, when the reaction temperature is insufficient, vanadium in vanadium oxide cannot be fully reduced, making it difficult to obtain vanadium oxide with high V4O7 content. In Example 5, the utilization rate of vanadium in ammonium polyvanadate was only 77.1%, and the cost was higher than that in Example 1. When the reaction temperature is too high, vanadium is over-reduced, resulting in low-valent vanadium oxide with poor solubility. In Example 6, the utilization rate of vanadium in ammonium polyvanadate was as low as 68.1%. Therefore, it can be seen that too low or too high reaction temperature will cause insufficient or excessive reduction of vanadium, leading to a significant increase in the amount of adjusting solution added, thereby increasing production costs.

[0104] (3) As can be seen from Examples 1 and 7-9, when the volume ratio of NH3, CO and H2 in the reducing gas is adjusted to a value outside the preferred range, vanadium cannot be fully reduced in Examples 8-9, and vanadium is over-reduced in Example 7. Both will increase the amount of adjusting liquid used, resulting in increased process costs. When the vanadium valence in the product is too low, the vanadium trioxide content increases. Since vanadium trioxide has poor solubility in acid solution, a certain amount of insoluble matter is generated during dissolution, which leads to a decrease in vanadium utilization. In Examples 8-9, the vanadium valence in the product is too high, making it difficult to adjust and obtain vanadium oxysulfate product with a valence of 3.5.

[0105] (4) As can be seen from Examples 10-11, when the mass fraction of sulfuric acid in step (4) is too low or the dissolution temperature is insufficient, vanadium cannot be fully dissolved, resulting in a low vanadium concentration in the electrolyte. It is difficult to obtain a vanadium oxysulfate electrolyte with a vanadium concentration ≥1.9mol / L. This shows that by controlling the mass fraction of sulfuric acid and the temperature during the dissolution process, the present invention can better ensure both the valence state and concentration of vanadium.

[0106] (5) As can be seen from Comparative Example 1, when no reducing gas is introduced, only ammonium vanadate decomposes to generate a small amount of ammonia gas to participate in the reaction, resulting in only a small amount of pentavalent vanadium being reduced. Since pentavalent vanadium has low solubility in acid, it is impossible to obtain a product with a concentration that meets the requirements of the electrolyte. As can be seen from Comparative Example 2, when the reducing gas composition is changed to the absence of ammonia gas, the reduction amount of pentavalent vanadium is still very low at the same temperature, and it is impossible to obtain a product with a concentration that meets the requirements of the electrolyte. As can be seen from Comparative Examples 3-4, when the reducing gas composition is changed to the presence of CO or hydrogen gas, the reduction amount of pentavalent vanadium is still very low at the same temperature, and it is impossible to obtain a product with a concentration that meets the requirements of the electrolyte.

[0107] (6) As can be seen from Comparative Example 5, when the valence state is not adjusted, the valence state of vanadium in the solution remains unchanged, and it is impossible to accurately obtain vanadium electrolyte with valence state 3.5.

[0108] In summary, this invention proposes a method for preparing vanadium oxysulfate electrolyte by gas-based reduction of ammonium polyvanadate. The method involves calcining ammonium polyvanadate under a reducing atmosphere to obtain vanadium oxide, then dissolving the vanadium oxide in a sulfuric acid solution to obtain a crude vanadium oxysulfate solution, and finally adding a vanadium conditioning solution to obtain a vanadium oxysulfate solution. This invention eliminates the need for high-purity vanadium pentoxide as a raw material and eliminates the need for an electrochemical conditioning step, thereby simplifying the production process, reducing production costs, and optimizing the production process of vanadium oxysulfate electrolyte.

[0109] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing 3.5-valence vanadyl sulfate electrolyte from ammonium polyvanadate by gas-based reduction, characterized in that, The method includes the following steps: (1) Ammonium polyvanadate is calcined by reduction with a reducing gas to obtain vanadium oxide; the vanadium oxide contains V4O7; the reducing gas includes a mixture of NH3, CO and H2; the volume ratio of NH3, CO and H2 in the reducing gas is NH3:CO:H2=(60~80):(10~30):(5~10); the reaction temperature in the reduction calcination is 450~600℃; (2) Mix sulfuric acid solution and vanadium oxide to carry out a dissolution reaction, and adjust the vanadium to obtain vanadium oxysulfate electrolyte with 3.5 valence.

2. The method of claim 1, wherein, The reduction calcination in step (1) includes: introducing a reducing gas, heating to the reaction temperature, and then reacting in a reducing gas atmosphere. After the reaction is completed, the temperature is lowered in a reducing gas atmosphere.

3. The method according to claim 1 or 2, characterized in that, The total flow rate of the reducing gas in step (1) is 20~100 ml / min.

4. The method according to claim 1 or 2, characterized in that, The reaction time during the reduction calcination is 0.5 to 3 hours.

5. The method according to claim 1 or 2, characterized in that, The mass fraction of the sulfuric acid solution mentioned in step (2) is 10-30%; The liquid-to-solid ratio of the sulfuric acid solution and vanadium oxide is 6-9 ml / g.

6. The method according to claim 1 or 2, characterized in that, The temperature of the dissolution reaction in step (2) is 60~95℃; The dissolution reaction takes 8-24 hours; The concentration of V in the solution obtained after the dissolution reaction is ≥1.5 mol / L.

7. The method according to claim 1 or 2, characterized in that, The vanadium adjustment in step (2) includes the solution obtained after the mixed dissolution reaction and the vanadium adjustment solution, to obtain a vanadium oxysulfate electrolyte with a valence of 3.

5.

8. The method according to claim 7, characterized in that, The vanadium conditioning solution mentioned in step (2) includes a sulfuric acid solution containing trivalent vanadium and / or tetravalent vanadium; The mass fraction of sulfuric acid in the vanadium conditioning solution is 10-30%. The concentration of V in the vanadium conditioning solution is ≥1.5 mol / L.

9. The method according to claim 1 or 2, characterized in that, The method includes the following steps: (1) Ammonium polyvanadate is placed in a calcination apparatus and a reducing gas with a flow rate of 20~100 ml / min is introduced. The volume ratio of NH3, CO and H2 in the reducing gas is NH3:CO:H2=(60~80):(10~30):(5~10). After heating to the reaction temperature of 450~600℃, the reaction is carried out in the atmosphere of reducing gas for 0.5~3h. Then the reducing gas is turned off to obtain vanadium oxide containing V4O7. (2) Mix sulfuric acid solution with a mass fraction of 10-30% and vanadium oxide at a liquid-to-solid ratio of 6-9 ml / g and carry out a dissolution reaction at 60-95℃ for 8-24 hours. Mix the solution obtained after the dissolution reaction with a vanadium adjustment solution and adjust the vanadium content. The mass fraction of sulfuric acid in the vanadium adjustment solution is 10-30% and the concentration of V element is ≥1.5 mol / L to obtain a vanadium oxysulfate electrolyte with a valence of 3.5.

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