Method for preparing approximately 3.5-valent vanadium electrolyte by reducing ammonium metavanadate through coke oven gas

Abstract

The invention provides a method for preparing a nearly 3.5-valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas, which comprises the following steps: (1) reducing and calcining ammonium metavanadate in coke oven gas to obtain a reduced product; (2) carrying out replacement deamination on the reduced product in the step (1) to obtain a nearly 3.5-valent vanadium oxide, wherein the nearly 3.5-valent vanadium oxide contains V4O7; and (3) a mixed sulfuric acid solution and the approximately 3.5-valent vanadium oxide are subjected to a dissolution reaction, and the approximately 3.5-valent vanadium electrolyte is obtained. The process method disclosed by the invention is simple and easy to implement, the approximately 3.5 valence vanadyl sulfate electrolyte product with high vanadium concentration and low ammonia content can be obtained by taking the ammonium metavanadate and the coke oven gas as raw materials, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of vanadium electrolyte technology, and more particularly to a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Background Technology

[0002] Vanadium redox flow batteries (VRBs) possess advantages such as high safety, strong capacity scalability, long cycle life, and low total lifespan cost, making them the most commercially promising type of flow battery. Vanadium electrolyte, a crucial component of vanadium batteries, determines the battery's energy storage capacity based on the amount of active material it contains. Vanadium electrolytes are classified into trivalent, 3.5valent, and tetravalent electrolytes according to the vanadium ion valence state. Trivalent and tetravalent vanadium electrolytes are used as the negative and positive electrodes, respectively, while 3.5valent electrolytes can be used as both the positive and negative electrodes. Typically, tetravalent vanadium electrolytes are first prepared through chemical reduction, solvent extraction, or ion exchange processes, followed by further electrolysis to obtain 3.5valent vanadium electrolytes. Existing preparation processes suffer from problems such as long flow rates, high costs, difficulty in removing reducing / extracting agent residues, large electrolyte volume, and challenges in long-distance transportation. Therefore, there is an urgent need to develop a new, short-process method for preparing 3.5valent vanadium oxysulfate electrolyte.

[0003] 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.

[0004] CN117819603A discloses a method for preparing low-valent vanadium oxides through gas-solid combined reduction. This method involves mixing pentavalent vanadium raw materials such as vanadium pentoxide and ammonium vanadate with reducing solids such as ammonium oxalate and ammonium carbonate, reacting under nitrogen or inert gas at 200-400℃ for 10-60 min, followed by introducing a mixed gas of methane and hydrogen, and reacting at 500-600℃ for 10-120 min to obtain low-valent vanadium oxides.

[0005] CN116995285A discloses a short-process method for preparing vanadium oxysulfate electrolyte. The method uses ammonium polyvanadate / ammonium metavanadate as raw materials, and performs reduction calcination in a reducing gas mixture including NH3, CO, and H2 to obtain vanadium oxide with V4O7 as the main phase. After dissolving in sulfuric acid solution and adjusting for vanadium, the vanadium oxysulfate electrolyte is obtained.

[0006] Therefore, developing a short-process production technology for vanadium oxysulfate electrolyte to reduce production costs is the future direction of vanadium electrolyte preparation technology. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing near-3.5 vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Using coke oven gas as the reducing gas, this method achieves the utilization of coke oven gas in steel enterprises while simultaneously realizing a short-process preparation of 3.5 vanadium electrolyte with high vanadate concentration and low ammonia content, resulting in lower costs.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas, the method comprising the following steps:

[0010] (1) Ammonium metavanadate is reduced and calcined in coke oven gas to obtain the reduced product;

[0011] (2) The reduction product in step (1) is subjected to displacement deammoniation to obtain near-3.5 valent vanadium oxide, wherein the near-3.5 valent vanadium oxide contains V4O7;

[0012] (3) The mixed sulfuric acid solution and the near-3.5 valent vanadium oxide were reacted to obtain a near-3.5 valent vanadium electrolyte.

[0013] The method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas provided by this invention controls the reduction and calcination process, so that ammonium metavanadate, under the conditions of coke oven gas and its own ammonia-assisted reduction, generates V₈O₃ electrolyte at a relatively low temperature. 15 V6O 11 A mixed near-3.5 valence vanadium oxide with V4O7 and V2O3 as the main phases, with V4O7 being the predominant phase. The vanadium valence in these mixed near-3.5 valence vanadium oxides ranges from 3 to 4, but the average valence is near 3.5. The near-3.5 valence vanadium oxides have a multi-layered, porous structure. Ammonia from ammonium metavanadate is easily adsorbed within the near-3.5 valence vanadium oxides, and it is difficult to completely remove them simply by increasing the calcination temperature and time. A method is adopted to replace the ammonia with argon gas as a protective gas after reduction calcination. Increasing the argon gas flow rate at the end of the high-temperature calcination period reduces the ammonia content in the near-3.5 valence vanadium oxides to 0.006-0.012%, meeting the requirements of vanadium electrolyte. Vanadium oxides with near-3.5 valence have the characteristic of being easily soluble in sulfuric acid. Moreover, the valence state of the solution obtained after dissolving near-3.5 valence vanadium oxides with high V4O7 content is almost the same as the valence state required by the electrolyte. The near-3.5 valence vanadium oxide obtained by reduction can be easily prepared by dissolving it in sulfuric acid.

[0014] Preferably, the reduction calcination temperature in step (1) is 450~500℃, for example, it can be 450℃, 456℃, 462℃, 467℃, 473℃, 478℃, 484℃, 489℃, 495℃ or 500℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the reduction calcination time is 0.5~1.5h, for example, it can be 0.5h, 0.7h, 0.8h, 0.9h, 1h, 1.1h, 1.2h, 1.3h, 1.4h or 1.5h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the flow rate of the coke oven gas in step (1) is 40~100 ml / min, for example, it can be 40 ml / min, 47 ml / min, 54 ml / min, 60 ml / min, 67 ml / min, 74 ml / min, 80 ml / min, 87 ml / min, 94 ml / min or 100 ml / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] The present invention preferably controls the flow rate of coke oven gas within the above-mentioned range, which enables the average valence state of vanadium in the electrolyte to approach 3.5.

[0018] Preferably, the coke oven gas in step (1) comprises 5-8% CO, 55-60% H2, and 23-27% CH4. The CO content in the coke oven gas can be, for example, 5%, 5.4%, 5.7%, 6%, 6.4%, 6.7%, 7%, 7.4%, 7.7%, or 8%, but is not limited to the listed values; other unlisted values ​​within this range also apply. The H2 content can be, for example, 55%, 55.6%, 56.2%, 56.7%, 57.3%, 57.8%, 58.4%, 58.9%, 59.5%, or 60%, but is not limited to the listed values; other unlisted values ​​within this range also apply. The CH4 content can be, for example, 23%, 23.5%, 23.9%, 24.4%, 24.8%, 25.3%, 25.7%, 26.2%, 26.6%, or 27%, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0019] CO, H2, or CH4 are commonly used reducing gases. However, from an industrial application perspective, the high production cost, complex storage and transportation conditions, and explosion / toxicity risks of CO or H2 alone limit their application in large-scale basic industries. Considering cost, safety, source stability, and process compatibility, using coke oven gas as a reducing gas is cost-effective, scalable, and fully meets the requirements for large-scale process applications. Moreover, for ammonium metavanadate, the product morphology obtained after reduction with a mixed gas is more porous, which is beneficial for subsequent displacement deammoniation and the acquisition of vanadium electrolytes with lower ammonia content.

[0020] Preferably, the reduction product includes V8O. 15 V6O 11 V4O7 and V2O3.

[0021] Preferably, the reduced product contains V 3+ With V 4+ The molar ratio is (0.9~1.1):1, for example, it can be 0.9:1, 0.92:1, 0.95:1, 0.96:1, 0.98:1, 1:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.08:1 or 1.1:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the replacement gas for ammonia removal in step (2) is a protective gas.

[0023] Preferably, the protective gas includes argon.

[0024] Preferably, the flow rate of the protective gas is 150~200 ml / min, for example, it can be 150 ml / min, 156 ml / min, 162 ml / min, 167 ml / min, 173 ml / min, 178 ml / min, 184 ml / min, 189 ml / min, 195 ml / min or 200 ml / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] The present invention preferably controls the flow rate of the protective gas within the above-mentioned range, which can significantly reduce the ammonia content in the electrolyte.

[0026] Preferably, the displacement deammoniation includes: cooling the self-reducing calcination temperature to a first temperature under protective gas conditions.

[0027] Preferably, the first temperature is ≤100℃, for example, it can be 100℃, 98℃, 97℃, 95℃, 90℃, 89℃, 85℃, 82℃, 80℃, 78℃, 75℃, 70℃, 65℃, 60℃, 55℃ or 50℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] Preferably, the cooling rate is 2~3℃ / min, for example, it can be 2℃ / min, 2.2℃ / min, 2.3℃ / min, 2.4℃ / min, 2.5℃ / min, 2.6℃ / min, 2.7℃ / min, 2.8℃ / min, 2.9℃ / min or 3℃ / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] The present invention preferably controls the cooling rate within the above-mentioned range, which has a better deammoniation effect. When the cooling rate is too fast, there is a problem of incomplete deammoniation; when the cooling rate is too slow, there is a problem of excessive reaction time and low efficiency.

[0030] Preferably, the sulfuric acid concentration of the sulfuric acid solution in step (3) is 25~35wt%, for example, it can be 25wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt% or 35wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the liquid-solid ratio of the sulfuric acid solution to the near-3.5 valence vanadium oxide in step (3) is 6~9 ml / g, for example, it can be 6 ml / g, 6.4 ml / g, 6.7 ml / g, 7 ml / g, 7.4 ml / g, 7.7 ml / g, 8 ml / g, 8.4 ml / g, 8.7 ml / g or 9 ml / g, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the temperature of the dissolution reaction in step (3) is 85~99℃, for example, it can be 85℃, 87℃, 89℃, 90℃, 92℃, 93℃, 95℃, 96℃, 98℃ or 99℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the dissolution reaction time is 18 to 30 hours, for example, 18 hours, 20 hours, 21 hours, 22 hours, 24 hours, 25 hours, 26 hours, 28 hours, 29 hours or 30 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the molar concentration of vanadium in the near-trivalent vanadium electrolyte is ≥1.7 mol / L, for example, it can be 1.7 mol / L, 1.75 mol / L, 1.8 mol / L, 1.85 mol / L, 1.9 mol / L, 1.95 mol / L, 2.0 mol / L, 2.05 mol / L or 2.1 mol / L, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0035] Preferably, the average valence state of vanadium in the near-3.5 valence vanadium electrolyte is 3.3 to 3.8, for example, it can be 3.3, 3.4, 3.5, 3.6, 3.7 or 3.8, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] As a preferred technical solution of the present invention, the method includes the following steps:

[0037] (1) Ammonium metavanadate is reduced and calcined in coke oven gas at 450~500℃ for 0.5~1.5h, and the flow rate of coke oven gas is 40~100ml / min to obtain the reduced product; wherein, the coke oven gas includes 5~8% CO, 55~60% H2, and 23~27% CH4;

[0038] (2) The reduced product described in step (1) is subjected to argon gas at a flow rate of 150~200 ml / min, and the temperature of the self-reduction calcination is reduced to ≤100℃ at a rate of 2~3℃ / min to undergo displacement deammoniation to obtain near-3.5 valent vanadium oxide. In the near-3.5 valent vanadium oxide, V 3+ With V 4+ The molar ratio is (0.9~1.1):1, and the near-3.5 valence vanadium oxide contains V4O7;

[0039] (3) The near-3.5 vanadium oxide is mixed with a sulfuric acid solution of 25-35 wt% and the liquid-solid ratio of 6-9 ml / g at 85-99℃ for 18-30 h to obtain a near-3.5 vanadium electrolyte with a vanadium molar concentration ≥1.7 mol / L and an average valence state of 3.3-3.8.

[0040] 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.

[0041] 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 metavanadate as raw material, eliminating not only the need for calcining ammonium vanadate to vanadium pentoxide but also the subsequent energy-intensive electrolysis step, thereby significantly reducing process costs and equipment investment.

[0042] Compared with the prior art, the present invention has at least the following beneficial effects:

[0043] (1) The method for preparing near-3.5 valence vanadium electrolyte by reducing ammonium metavanadate with coke oven gas provided by the present invention can obtain 3.5 valence vanadium oxysulfate electrolyte with vanadium concentration ≥1.7mol / L, and the ammonia content in the electrolyte is low, with the ammonia content below 20ppm;

[0044] (2) The method for preparing near-3.5 valence vanadium electrolyte by reducing ammonium metavanadate with coke oven gas provided by the present invention can directly obtain 3.5 valence vanadium oxysulfate electrolyte through chemical adjustment. Moreover, it uses coke oven gas and does not require the storage and transportation of reducing gas, which can significantly reduce production costs. Compared with traditional electrochemical processes, the equipment and process flow are greatly simplified and have broad application prospects. Detailed Implementation

[0045] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0046] As a specific embodiment of the present invention, a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas is provided, the method comprising the following steps:

[0047] (1) Ammonium metavanadate is reduced and calcined in coke oven gas at 450~500℃ for 0.5~1.5h, and the flow rate of coke oven gas is 40~100ml / min to obtain the reduced product; wherein, the coke oven gas includes 5~8% CO, 55~60% H2, and 23~27% CH4;

[0048] (2) The reduced product described in step (1) is subjected to argon gas at a flow rate of 150~200 ml / min, and the temperature of the self-reduction calcination is reduced to ≤100℃ at a rate of 2~3℃ / min to undergo displacement deammoniation to obtain near-3.5 valent vanadium oxide. In the near-3.5 valent vanadium oxide, V 3+ With V 4+ The molar ratio is (0.9~1.1):1, and the near-3.5 valence vanadium oxide contains V4O7;

[0049] (3) The near-3.5 vanadium oxide is mixed with a sulfuric acid solution of 25-35 wt% and the liquid-solid ratio of 6-9 ml / g at 85-99℃ for 18-30 h to obtain a near-3.5 vanadium electrolyte with a vanadium molar concentration ≥1.7 mol / L and an average valence state of 3.3-3.8.

[0050] Example 1

[0051] This embodiment provides a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas, comprising the following steps:

[0052] (1) Ammonium metavanadate is placed in a calcination device, and coke oven gas with a flow rate of 60 ml / min is introduced. The coke oven gas is reduced and calcined at 500°C for 0.5 h to obtain the reduced product. The coke oven gas includes 6% CO, 58% H2 and 24% CH4.

[0053] (2) The reduced product in step (1) is subjected to argon gas at a flow rate of 200 ml / min, and the temperature of the reduction calcination is reduced to 100℃ at a rate of 2.5℃ / min to undergo displacement deammoniation to obtain near-3.5 valence vanadium oxide. The reduced product contains V 3+ With V 4+ The molar ratio is 1:1, and the near-3.5 valence vanadium oxide contains V4O7;

[0054] (3) A vanadium oxide near 3.5 valence was dissolved in a 30 wt% sulfuric acid solution at 9 ml / g liquid-to-solid ratio for 24 h at 90 °C to obtain a vanadium near 3.5 valence electrolyte.

[0055] Example 2

[0056] This embodiment provides a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas, comprising the following steps:

[0057] (1) Ammonium metavanadate is placed in a calcination apparatus and coke oven gas with a flow rate of 100 ml / min is introduced. The mixture is reduced and calcined in the coke oven gas at 450°C for 1.5 h to obtain the reduced product. The coke oven gas contains 5% CO, 60% H2 and 27% CH4.

[0058] (2) The reduced product in step (1) is subjected to argon gas at a flow rate of 180 ml / min, and the temperature of the self-reduction calcination is reduced to 90℃ at a rate of 2℃ / min to undergo displacement deammoniation to obtain near-3.5 valence vanadium oxide. The reduced product contains V 3+ With V 4 + The molar ratio is 0.95:1, and the near-3.5 valence vanadium oxide contains V4O7;

[0059] (3) A near-3.5 vanadium oxide was dissolved in a 25 wt% sulfuric acid solution at a liquid-to-solid ratio of 8 ml / g for 18 h at 99 °C to obtain a near-3.5 vanadium electrolyte.

[0060] Example 3

[0061] This embodiment provides a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas, comprising the following steps:

[0062] (1) Ammonium metavanadate is placed in a calcination device, and coke oven gas with a flow rate of 80 ml / min is introduced. The product is reduced and calcined in coke oven gas at 470°C for 1 h to obtain the reduced product. The coke oven gas includes 8% CO, 55% H2 and 27% CH4.

[0063] (2) The reduced product in step (1) is subjected to argon gas at a flow rate of 150 ml / min, and the temperature of the self-reduction calcination is reduced to 95℃ at a rate of 3℃ / min to undergo displacement deammoniation to obtain near-3.5 valence vanadium oxide. The reduced product contains V 3+ With V 4 + The molar ratio is 1.05:1, and the near-3.5 valence vanadium oxide contains V4O7;

[0064] (3) A vanadium oxide near 3.5 valence was dissolved in a 35 wt% sulfuric acid solution at 85 °C for 30 h at a liquid-to-solid ratio of 6 ml / g to obtain a vanadium near 3.5 valence electrolyte.

[0065] Example 4

[0066] This embodiment provides a method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the reduction and calcination temperature of 550°C, the method is the same as in Example 1 and will not be repeated here.

[0067] Example 5

[0068] This embodiment provides a method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the reduction and calcination temperature of 400°C, the method is the same as that in Example 1, and will not be repeated here.

[0069] Example 6

[0070] This embodiment provides a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the coke oven gas flow rate of 30 ml / min, the method is the same as in Example 1 and will not be repeated here.

[0071] Example 7

[0072] This embodiment provides a method for preparing near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the coke oven gas flow rate of 130 ml / min, the method is the same as in Example 1 and will not be repeated here.

[0073] Example 8

[0074] This embodiment provides a method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the argon flow rate of 100 ml / min in step (2), the method is the same as in Example 1, and will not be repeated here.

[0075] Example 9

[0076] This embodiment provides a method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the argon flow rate of 250 ml / min in step (2), the method is the same as in Example 1, and will not be repeated here.

[0077] Example 10

[0078] This embodiment provides a method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the self-reduction calcination temperature being lowered to 100°C at a rate of 1°C / min to perform displacement deammoniation and obtain near-3.5 valent vanadium oxide, the method is the same as in Example 1 and will not be repeated here.

[0079] Example 11

[0080] This embodiment provides a method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for the self-reduction calcination temperature being lowered to 100°C at 4°C / min to perform displacement deammoniation to obtain near-3.5 valent vanadium oxide, the method is the same as in Example 1 and will not be repeated here.

[0081] Comparative Example 1

[0082] This comparative example provides a method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for step (1), in which coke oven gas is not introduced so that V2O5 is obtained in step (1), the method is the same as in Example 1, and will not be repeated here.

[0083] Comparative Example 2

[0084] This comparative example provides a method for preparing near-3.5 valence vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. Except for step (2) where argon gas is not introduced, the method is the same as in Example 1, and will not be repeated here.

[0085] Comparative Example 3

[0086] This comparative example provides a method for preparing near-3.5 valence vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. The method is the same as in Example 1 except that the coke oven gas is replaced with pure CO, and will not be described again here.

[0087] Comparative Example 4

[0088] This comparative example provides a method for preparing near-3.5 valence vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. The method is the same as in Example 1 except that the coke oven gas is replaced with pure H2, and will not be described again here.

[0089] 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 metavanadate was recorded as the ratio of the amount of vanadium initially added to the amount of vanadium in the final electrolyte.

[0090] 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 1-4 are shown in Table 1.

[0091] Table 1

[0092]

[0093] As can be seen from Table 1:

[0094] (1) As can be seen from Examples 1-3, the method for preparing near-3.5 valent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas provided by the present invention obtains near-3.5 valent vanadium oxide by reducing ammonium metavanadate with coke oven gas. After the near-3.5 valent vanadium oxide is dissolved in sulfuric acid solution, a vanadium concentration ≥1.78 mol / L and NH4+ can be obtained. + The presence of vanadium oxysulfate electrolyte with a concentration below 20 ppm (3.5 ± 0.1 valence) indicates that a high-vanadium-concentration, low-ammonia-content vanadium oxysulfate electrolyte can be obtained by using ammonium metavanadate as raw material and a process of reduction calcination followed by sulfuric acid dissolution, thus achieving full utilization of raw materials and products.

[0095] (2) As can be seen from Examples 1 and 4-5, both excessively high and low reaction temperatures affect the valence state and vanadium content of the obtained electrolyte. Example 4 shows that when the reaction temperature increases from 500℃ to 550℃, the valence state of the vanadium electrolyte decreases from 3.45 to 3.28. Due to the low solubility of trivalent vanadium, the vanadium concentration in the electrolyte decreases from 1.97 mol / L to 1.32 mol / L. Example 5 shows that when the reaction temperature decreases from 500℃ to 400℃, the valence state of the vanadium electrolyte increases from 3.45 to 3.84. Due to the limited solubility of the obtained near-3.5 valence vanadium oxide, the vanadium concentration in the electrolyte decreases from 1.97 mol / L to 1.28 mol / L. This indicates that when the reduction calcination temperature is too high, over-reduction occurs, increasing the proportion of trivalent near-3.5 valence vanadium oxide in the obtained near-3.5 valence vanadium oxide. Consequently, the valence state of the vanadium electrolyte is below the required range, and the overall vanadium concentration of the obtained electrolyte is low. When the reduction calcination temperature is too low, insufficient reduction will occur, resulting in an increased proportion of tetravalent near-3.5 vanadium oxides in the obtained near-3.5 vanadium oxides, and even the inclusion of some unreduced pentavalent vanadium. Consequently, the valence state of the vanadium electrolyte is higher than the required range, and the overall vanadium concentration of the obtained electrolyte is low.

[0096] (3) As can be seen from Examples 1 and 6-7, when the coke oven gas flow rate is insufficient, insufficient reduction will occur, the proportion of tetravalent near-3.5 vanadium oxides in the obtained near-3.5 vanadium oxides will increase, the valence state of the corresponding vanadium electrolyte will be higher than the required range, and the overall vanadium concentration of the obtained electrolyte will be low; when the coke oven gas flow rate is too large, the V in the obtained near-3.5 vanadium oxides will be reduced. 3+ :V 4+ The ratio and the corresponding valence state of the vanadium electrolyte have little impact, but excessive gas consumption will increase the preparation cost of the electrolyte and affect the economic efficiency of the process.

[0097] (4) As can be seen from Examples 1 and 8-9, the flow rate of argon in Example 8 was too low, which affected the ammonia content in the obtained 3.5-valent near-3.5-valent vanadium oxide, resulting in the ammonia content in the final vanadium electrolyte exceeding the standard. In Example 9, when the flow rate of ammonia gas used for replacement was too high, it did not have much effect on the ammonia content in the obtained 3.5-valent near-3.5-valent vanadium oxide, but it would lead to a large consumption of argon gas, affecting the economic efficiency of the process. In addition, since the obtained near-3.5-valent vanadium oxide was in powder form, an excessive flow rate of argon gas might cause some of the near-3.5-valent vanadium oxide to be carried away by the gas, affecting the overall recovery rate of vanadium.

[0098] (5) As can be seen from Examples 1 and 10-11, a better deammoniation effect can be obtained when the cooling rate is controlled within the preferred range. When the cooling rate is too slow, it will lead to high process energy consumption and low efficiency, but it will not affect the ammonia content in the near-3.5 vanadium electrolyte. When the cooling rate is too fast, there is a problem of incomplete deammoniation, resulting in a higher ammonia content in the obtained near-3.5 vanadium electrolyte.

[0099] (6) As can be seen from Comparative Example 1, when no reducing gas is introduced, only ammonium metavanadate 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 only reduction is carried out without displacement deammoniation, the adsorbed ammonia cannot be fully replaced, resulting in a serious over-limit of ammonium content in the subsequent electrolyte.

[0100] (7) Based on the combined results of Example 1 and Comparative Examples 3-4, it can be seen that in Comparative Example 3, when pure CO was used as the reducing gas and all other conditions were the same as in Example 1, the proportion of trivalent near-3.5 vanadium oxides in the obtained near-3.5 vanadium oxides increased, and the valence state of the vanadium electrolyte was lower than the required range. In addition, the overall vanadium concentration of the obtained electrolyte was lower, and because the density of the reduction product obtained by CO reduction was relatively high, the ammonia removal effect during deammoniation was not as good as in Example 1. In Comparative Example 4, when pure H2 was used as the reducing gas and all other conditions were the same as in Example 1, the proportion of trivalent near-3.5 vanadium oxides in the obtained near-3.5 vanadium oxides increased, and the valence state of the vanadium electrolyte was lower than the required range, and the overall vanadium concentration was lower. In addition, because the product of H2 reduction is H2O, it affects the physical properties of the material such as porosity, which affects the subsequent displacement deammoniation, and the ammonia content in the obtained electrolyte is higher.

[0101] In summary, this invention provides a method for preparing near-3.5 vanadium electrolyte by reducing ammonium metavanadate with coke oven gas. This method controls the reduction and calcination process to generate V8O from ammonium metavanadate under relatively low-temperature conditions with the assistance of coke oven gas and its own ammonia. 15 V6O 11 A mixed near-3.5 valence vanadium oxide with V4O7 and V2O3 as the main phases was used. The vanadium valence state of these mixed near-3.5 vanadium oxides ranged from 3 to 4, but the average valence state was 3.5. A novel method was employed to remove ammonia by replacing the vanadium with argon gas as a protective gas after reduction calcination. By increasing the argon gas flow rate at the end of the high-temperature calcination, the ammonia content in the near-3.5 valence vanadium oxides could be reduced to 0.006~0.012%, meeting the requirements of vanadium electrolyte. The resulting electrolyte contained NH4+. +The concentration is below 20 ppm. Compared with the calcination-chemical reduction-electrochemical reduction process for preparing 3.5 valent electrolyte, this invention has a shorter process, lower production cost, and significantly optimizes the production process of 3.5 valent vanadium oxysulfate electrolyte.

[0102] The present invention has been illustrated with the above embodiments to illustrate its detailed features, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected technical features, additions of auxiliary technical features, 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 near-trivalent vanadium electrolyte by reducing ammonium metavanadate with coke oven gas, characterized in that, The method includes the following steps: (1) Ammonium metavanadate is reduced and calcined in coke oven gas to obtain the reduced product; (2) The reduction product in step (1) is subjected to displacement deammoniation to obtain near-3.5 valent vanadium oxide, wherein the near-3.5 valent vanadium oxide contains V4O7; (3) The mixed sulfuric acid solution and the near-3.5 valent vanadium oxide were reacted to obtain a near-3.5 valent vanadium electrolyte.

2. The method according to claim 1, characterized in that, The reduction calcination temperature in step (1) is 450~500℃; Preferably, the reduction calcination time is 0.5~1.5h.

3. The method according to claim 1 or 2, characterized in that, The flow rate of coke oven gas in step (1) is 40~100 ml / min.

4. The method according to any one of claims 1 to 3, characterized in that, The coke oven gas mentioned in step (1) includes 5-8% CO, 55-60% H2, and 23-27% CH4; Preferably, the reduction product includes V8O. 15 V6O 11 V4O7 and V2O3; Preferably, the reduced product contains V 3+ With V 4+ The molar ratio is (0.9~1.1):

1.

5. The method according to any one of claims 1 to 4, characterized in that, The replacement gas used in step (2) for ammonia removal is a protective gas; Preferably, the protective gas includes argon; Preferably, the flow rate of the protective gas is 150~200 ml / min; Preferably, the displacement deammoniation includes: cooling the self-reducing calcination temperature to a first temperature under protective gas conditions; Preferably, the first temperature is ≤100℃; Preferably, the cooling rate is 2~3℃ / min.

6. The method according to any one of claims 1 to 5, characterized in that, The sulfuric acid concentration of the sulfuric acid solution in step (3) is 25~35wt%.

7. The method according to any one of claims 1 to 6, characterized in that, The liquid-solid ratio of the sulfuric acid solution to the near-3.5 valence vanadium oxide in step (3) is 6~9 ml / g.

8. The method according to any one of claims 1 to 7, characterized in that, The temperature of the dissolution reaction in step (3) is 85~99℃; Preferably, the dissolution reaction takes 18 to 30 hours.

9. The method according to any one of claims 1 to 8, characterized in that, The molar concentration of vanadium in the near-trivalent vanadium electrolyte is ≥1.7 mol / L; Preferably, the average valence state of vanadium in the near-3.5 vanadium electrolyte is 3.3 to 3.

8.

10. The method according to any one of claims 1 to 9, characterized in that, The method includes the following steps: (1) Ammonium metavanadate is reduced and calcined in coke oven gas at 450-500℃ for 0.5-1.5h, with a coke oven gas flow rate of 40-100ml / min, to obtain the reduced product; wherein, in the reduced product, V 3+ With V 4+ The molar ratio is (0.9~1.1):1, and the coke oven gas includes 5~8% CO, 55~60% H2, and 23~27% CH4; (2) The reduced product in step (1) is subjected to argon gas with a flow rate of 150~200 ml / min, and the temperature of the reduction calcination is reduced to ≤100℃ at a rate of 2~3℃ / min to undergo displacement deammoniation to obtain near-3.5 valent vanadium oxide, wherein the near-3.5 valent vanadium oxide contains V4O7; (3) The near-3.5 vanadium oxide is mixed with a sulfuric acid solution of 25-35 wt% and the liquid-solid ratio of 6-9 ml / g at 85-99℃ for 18-30 h to obtain a near-3.5 vanadium electrolyte with a vanadium molar concentration ≥1.7 mol / L and an average valence state of 3.3-3.8.

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