A highly soluble vanadium sulfate, its preparation method and application

Abstract

The present invention provides a highly soluble vanadium sulfate, a preparation method thereof and an application, comprising the following steps: mixing V2O4, sulfuric acid and a solvent, and reacting at 60-100 °C for 1-8 h to prepare a high-concentration vanadyl sulfate solution; electrolytically reducing the high-concentration vanadyl sulfate solution until the high-concentration vanadyl sulfate solution is completely converted into a trivalent vanadium sulfate solution; adding sulfuric acid to the trivalent vanadium sulfate solution and then crystallizing, wherein the addition amount of sulfuric acid satisfies V:SO4 2‑ = 1:0.5-1.5, and filtering to obtain V2(SO4)3 crystals; adjusting the valence state by adding vanadium pentoxide according to the molar ratio of V 3+ :V 5+ = 1:0.9-1.0, and using the obtained low-concentration vanadyl sulfate solution to prepare a high-concentration vanadyl sulfate solution. The preparation method of the highly soluble vanadium sulfate of the present invention is environmentally friendly and pollution-free, the raw materials are recycled without waste, and the prepared vanadium sulfate has high purity, good solubility, and can be used to prepare the electrolyte crystals of a vanadium redox flow battery.

Description

Technical Field

[0001] The present invention relates to vanadium sulfate technology, and particularly to a highly soluble vanadium sulfate, a preparation method thereof, and an application thereof. Background Art

[0002] Vanadium batteries have many advantages. Their energy depends on the electrolyte. By increasing the amount of the electrolyte, the battery capacity can be increased, and by replacing the electrolyte, instant charging can be achieved. Therefore, the electrolyte plays a very important role in the research of vanadium batteries. Thus, a suitable electrolyte for vanadium batteries needs to be found. Currently, using a vanadium sulfate [V2(SO4)3] solution in the electrolyte of vanadium batteries has become a research hotspot.

[0003] V2(SO4)3 is mainly used in the preparation of the electrolyte of all-vanadium redox flow batteries and plays an important role therein; at the same time, it can also be used as a vanadium source to participate in the preparation of other materials; since vanadium-based products can be used as catalysts, V2(SO4)3 can be used as a catalyst for some reactions.

[0004] Currently, the preparation method of V2(SO4)3 is as described in Patent CN 103199293: (1) Activate vanadium pentoxide with sulfuric acid and add zinc powder as a reducing agent, and a mixture of low-valent vanadium is obtained after the reaction; (2) Add an excessive amount of zinc powder to the mixture in step (1) until the solution turns purple, and filter to remove the zinc powder; (3) Add excessive ammonia water to the solution obtained in step (2), filter to remove divalent zinc ions, and at the same time generate vanadium dihydroxide; (4) Oxidize vanadium dihydroxide in the air to generate vanadium trihydroxide, and filter the vanadium trihydroxide precipitate; (5) Wash the vanadium trihydroxide precipitate multiple times, heat and concentrate vanadium trihydroxide, and then dissolve vanadium trihydroxide with sulfuric acid to obtain a vanadium sulfate solution containing trivalent vanadium.

[0005] Currently, the preparation technology of V2(SO4)3 requires the addition of a reducing agent and the addition of an alkali such as ammonium for precipitation, resulting in poor product quality. The treatment of a large amount of ammonium salt wastewater in the later stage is also a very serious problem.

[0006] In addition, the vanadium content in the electrolyte of the all-vanadium redox flow battery is relatively low, and more than half of its weight is composed of water. If the electrolyte is transported to the project site for filling, the freight of the electrolyte will become extremely high and cannot be ignored. A rough calculation shows that the freight per 1000 Km will be as high as 7000 yuan (converted to per ton of V2O5). In order to reduce the freight of the vanadium electrolyte, it can be converted into crystals with content ratios meeting the requirements of the electrolyte, transported to the project site, then dissolved and adjusted to the required concentration, and filled into the battery system, which can reduce the transportation cost by at least more than 50%. When producing electrolyte crystals, vanadium sulfate is required. However, general vanadium sulfate has problems such as high impurity content, poor solubility, and difficulty in solidifying with vanadyl sulfate and sulfuric acid, which restricts the industrialization of electrolyte crystals. Summary of the Invention

[0007] The object of the present invention is to propose a preparation method of highly soluble vanadium sulfate aiming at the problems of high impurity content, poor solubility, and difficulty in solidifying with vanadyl sulfate and sulfuric acid existing in vanadium sulfate prepared by traditional methods. The preparation method is environmentally friendly and pollution-free, the raw materials are recycled without waste, and the prepared highly soluble vanadium sulfate has high purity, good solubility, and can be used to prepare all-vanadium redox flow battery electrolyte crystals.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a preparation method of highly soluble vanadium sulfate, comprising the following steps:

[0009] Step 1: Mix V2O4 (vanadium tetraoxide), sulfuric acid and a solvent, and react at 60 - 100 °C for 1 - 8 h to prepare a high-concentration vanadyl sulfate solution, where the solvent is water and / or a low-concentration vanadyl sulfate solution;

[0010] Step 2: Electrolytically reduce the high-concentration vanadyl sulfate solution to completely convert the high-concentration vanadyl sulfate solution into a trivalent vanadium sulfate solution;

[0011] Step 3: Add sulfuric acid to the trivalent vanadium sulfate solution for crystallization, and the added amount of sulfuric acid satisfies V:SO4 2- (molar ratio) = 1:0.5 - 1.5, filter to obtain vanadium sulfate V2(SO4)3 crystals, namely highly soluble vanadium sulfate, and the highly soluble vanadium sulfate contains crystal water;

[0012] Step 4: In the filtrate obtained by filtering in Step 3, add vanadium pentoxide according to V 3+ :V 5+ molar ratio = 1:0.9 - 1.0 to adjust the valence state (because in the presence of trivalent vanadium, the dissolution of tetravalent vanadium is inhibited and the concentration of the tetravalent vanadium solution is reduced), to obtain a low-concentration vanadyl sulfate solution; return the low-concentration vanadyl sulfate solution to Step 1 (as a solvent) for preparing a high-concentration vanadyl sulfate solution.

[0013] Further, the concentration of the high-concentration vanadyl sulfate solution is 3 - 5.5 mol / L, preferably 4 - 5 mol / L, and the concentration of the low-concentration vanadyl sulfate solution is 1 - 1.8 mol / L, preferably 1.3 - 1.5 mol / L. Within this concentration range, the solubility of the solution is the highest, and the crystallization rate of the final electrolysis is also high.

[0014] Further, in step 1, the dosages of V2O4 and sulfuric acid are V:SO4 2- (molar ratio) = 1:1.0 - 1.7, preferably 1:1.3 - 1.5.

[0015] Further, in step 1, the addition amount of the solvent ensures that the vanadium concentration in the system is 2 - 5.5 mol / L, preferably 3 - 5 mol / L.

[0016] Further, in step 1, V2O4, sulfuric acid and the solvent are mixed and reacted at 80 - 95 °C for 3 - 5 h to prepare a high-concentration vanadyl sulfate solution.

[0017] Further, the sulfuric acid concentration in step 1 is 92 - 98% wt.

[0018] Further, in step 2, the electrolysis voltage is 0.6 - 2.0 V, preferably 0.8 - 1.5 V; the electrolysis current is 2000 - 4000 mA, preferably 3000 - 3500 mA; the electrolysis time is 5 - 20 h, preferably 8 - 12 h.

[0019] Further, the sulfuric acid concentration in step 3 is 92 - 98% wt, and it is supplemented according to V:SO4 2- (molar ratio) = 1:0.5 - 1.0. Supplementing sulfuric acid can improve the crystallization rate and crystallization time.

[0020] Further, the crystallization temperature in step 3 is 20 - 55 °C, and the crystallization time is 5 - 10 h.

[0021] Reaction principle: Utilize the fact that vanadium tetraoxide is extremely soluble in sulfuric acid (compared with vanadium trioxide), and the high solubility of vanadyl sulfate to prepare a high-concentration vanadyl sulfate solution. Then, prepare a vanadium sulfate solution through electrolysis, and further obtain crystals. Moreover, trivalent vanadium and pentavalent vanadium in the mother liquor can react to form tetravalent vanadium, so that sulfate ions and trivalent vanadium in the solution can be reused, enabling the entire reaction system to cycle.

[0022] Another object of the present invention also discloses a highly soluble vanadium sulfate prepared by the above method.

[0023] Another object of the present invention also discloses the application of a highly soluble vanadium sulfate in the field of vanadium battery electrolytes.

[0024] Another object of the present invention also discloses an application of highly soluble vanadium sulfate in the production process of vanadium battery electrolyte crystals. The highly soluble vanadium sulfate can be used to produce vanadium electrolyte crystals with a valence of 3.5, achieving the effect of rapid solidification.

[0025] Furthermore, the highly soluble vanadium sulfate, vanadyl sulfate are mixed and solidified with sulfuric acid to prepare vanadium electrolyte crystals with a valence of 3.5.

[0026] Furthermore, the dosage ratio of the highly soluble vanadium sulfate and vanadyl sulfate satisfies V 3+ / V 4+ molar ratio = 1:0.95 - 1.05, and the dosage of concentrated sulfuric acid satisfies V 4+ / H2SO4 molar ratio = 1:2.6 - 3.0.

[0027] The vanadium electrolyte crystals with a valence of 3.5 are a kind of vanadium energy storage medium crystals. The vanadium electrolyte can be prepared by dissolving the vanadium electrolyte crystals with a valence of 3.5 at the vanadium battery project site.

[0028] The highly soluble vanadium sulfate, its preparation method and application of the present invention have the following advantages compared with the prior art:

[0029] 1) The vanadium sulfate obtained in the present invention is a kind of highly soluble vanadium sulfate crystal, and further it can be used to quickly solidify and synthesize electrolyte crystals for all-vanadium redox flow batteries with vanadyl sulfate and sulfuric acid;

[0030] 2) Only sulfuric acid, vanadium oxide and water are used in the preparation process of the highly soluble vanadium sulfate of the present invention, without introducing impurities, ensuring the purity of the quality, and the purity is as high as more than 99.5%;

[0031] 3) The process of the present invention is simple, and the reaction is carried out below 100 °C without high-temperature and high-pressure reactions, and the safety is good.

[0032] 4) During the preparation of the highly soluble vanadium sulfate of the present invention, the vanadium and sulfate radicals in the filtrate (low-concentration vanadyl sulfate solution) will not be wasted. By adjusting the content of vanadyl sulfate in the low-concentration vanadyl sulfate solution, it can be restored to the initial state before crystallization without generating waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of the preparation method of the highly soluble vanadium sulfate of the present invention;

[0034] Figure 2 is an XRD diagram of the highly soluble vanadium sulfate crystal. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be further described below with reference to the embodiments:

[0036] Example 1

[0037] This embodiment discloses a preparation method of highly soluble vanadium sulfate. As Figure 1 shown, it includes the following steps:

[0038] 1. Weigh vanadium pentoxide, concentrated sulfuric acid and pure water respectively. The usage amounts of vanadium pentoxide and concentrated sulfuric acid are V:

[0039] SO4 2- (molar ratio) = 1:1.5, and the added amount of pure water ensures that the vanadium concentration in the system is 5 mol / L;

[0040] 2. Slowly pour the concentrated sulfuric acid into the pure water, and then gradually add vanadium pentoxide;

[0041] 3. Put the mixture into a water bath and carry out a stirring constant temperature reaction at 95 °C for 3 h;

[0042] 4. After the reaction is completed, electrolyze the solution with a current of 3800 mA. When the electrolysis voltage reaches 1.5 V, stop electrolysis;

[0043] 5. Add sulfuric acid to the electrolyzed solution, and add it according to V:SO4 2- (molar ratio) = 1:0.6. After the solution crystallizes, filter it to obtain highly soluble vanadium sulfate crystals. The XRD test results are as Figure 2 shown, and the filtrate is reserved;

[0044] 6. Add vanadium pentoxide to the filtrate, and add it according to V 3+ :V 5+ = 1:0.9;

[0045] 7. After the solution turns blue, add vanadium pentoxide, sulfuric acid and pure water, and the solution returns to the state before electrolysis and goes back to step 4.

[0046] The solubility of the highly soluble vanadium sulfate prepared in this embodiment is 2.2 mol / L.

[0047] Using the highly soluble vanadium sulfate in this embodiment for the preparation of 3.5-valent vanadium electrolyte crystals includes the following steps:

[0048] s1. Mix the highly soluble vanadium sulfate crystals, vanadyl sulfate crystals and concentrated sulfuric acid. Among them, the highly soluble vanadium sulfate crystals and vanadyl sulfate crystals are added according to V 3+ / V 4+ (molar ratio) = 1:1, and the usage amount of concentrated sulfuric acid is added according to V 4+ / H2SO4 molar ratio = 2.7.

[0049] s2. After mixing evenly, put it into a container and let it stand in an airtight environment. It will solidify within a certain time to be 3.5-valent vanadium electrolyte crystals.

[0050] Example 2

[0051] This embodiment discloses a preparation method of highly soluble vanadium sulfate. As Figure 1 shown, it includes the following steps:

[0052] 1. Weigh vanadium pentoxide, concentrated sulfuric acid, and pure water respectively. The usage amounts of vanadium pentoxide and concentrated sulfuric acid are V:

[0053] SO4 2- (molar ratio) = 1:1.3, and the added amount of pure water ensures that the vanadium concentration in the system is 4.5 mol / L;

[0054] 2. Slowly pour the concentrated sulfuric acid into the pure water, and then gradually add vanadium pentoxide;

[0055] 3. Put the mixture into a water bath and carry out stirring and constant-temperature reaction at 90 °C for 4 h;

[0056] 4. After the reaction is completed, electrolyze the solution with a current of 3500 mA. Stop electrolyzing when the voltage reaches 1.3 V;

[0057] 5. Add sulfuric acid to the electrolyzed solution. Add it according to V:SO4 2- (molar ratio) = 1:0.8. After the solution crystallizes, filter it to obtain highly soluble vanadium sulfate crystals, and reserve the filtrate;

[0058] 6. Add vanadium pentoxide to the filtrate. Add it according to V 3+ :V 5+ = 1:0.95;

[0059] 7. After the solution turns blue, add vanadium pentoxide, sulfuric acid, and pure water, and the solution returns to the state before electrolysis.

[0060] The solubility of the highly soluble vanadium sulfate prepared in this embodiment is 2.0 mol / L.

[0061] Example 3

[0062] This embodiment discloses a preparation method of highly soluble vanadium sulfate. As Figure 1 shown, it includes the following steps:

[0063] 1. Weigh vanadium pentoxide, concentrated sulfuric acid, and pure water respectively. The usage amounts of vanadium pentoxide and concentrated sulfuric acid are V:

[0064] SO4 2- (molar ratio) = 1:1.4, and the added amount of pure water ensures that the vanadium concentration in the system is 4 mol / L;

[0065] 2. Slowly pour the concentrated sulfuric acid into the pure water, and then gradually add vanadium pentoxide;

[0066] 3. Put the mixture into a water bath and carry out a stirring constant-temperature reaction at 85 °C for 4 h;

[0067] 4. After the reaction is completed, electrolyze the solution with a current of 3600 mA. Stop electrolysis when the voltage reaches 1.4 V;

[0068] 5. Add sulfuric acid to the electrolyzed solution and add it according to V:SO4 2- (molar ratio) = 1:0.5. After the solution crystallizes, filter it to obtain highly soluble vanadium sulfate crystals, and reserve the filtrate;

[0069] 6. Add vanadium pentoxide to the filtrate and add it according to V 3+ :V 5+ = 1.0:1.0;

[0070] 7. After the solution turns blue, add vanadium tetraoxide, sulfuric acid and pure water, and the solution returns to the state before electrolysis.

[0071] The solubility of the highly soluble vanadium sulfate prepared in this example is 2.1 mol / L.

[0072] Comparative Example 1

[0073] This Comparative Example 1 discloses a method for preparing vanadium sulfate, which includes the following steps:

[0074] 1. Weigh vanadium tetraoxide, concentrated sulfuric acid and pure water respectively. The amounts of vanadium tetraoxide and concentrated sulfuric acid are V:

[0075] H2SO4 (molar ratio) = 1:1.5, and the addition amount of pure water ensures that the vanadium concentration in the system is 5 mol / L;

[0076] 2. Slowly pour concentrated sulfuric acid into pure water, and then gradually add vanadium tetraoxide;

[0077] 3. Put the mixture into a water bath and carry out a stirring constant-temperature reaction at 95 °C for 3 h;

[0078] 4. After the reaction is completed, electrolyze the solution with a current of 3800 mA. Stop electrolysis when the voltage reaches 1.5 V;

[0079] 5. Add sulfuric acid to the electrolyzed solution and add it according to V:H2SO4 (molar ratio) = 1:2. After the solution crystallizes, filter it, collect the vanadium sulfate crystals, and reserve the filtrate;

[0080] 6. Add vanadium pentoxide to the filtrate and add it according to V 3+ :V 5+ = 1:0.9;

[0081] After the solution turns blue, add vanadium tetraoxide, sulfuric acid and pure water, and the solution returns to the state before electrolysis and go back to step 4.

[0082] The solubility of the vanadium sulfate prepared in this comparative example is 1.0 mol / L.

[0083] Table 1 Performance tests of vanadium sulfate in Example 1 and Comparative Example 1

[0084] <![CDATA[V / H2SO4 (molar ratio)]]> Dissolution time Color Crystal solidification time Example 1 1:0.6 5min Dark green 2h Control Example 1 1:2 60min Yellowish green 12h

[0085] For the highly soluble vanadium sulfate in Example 1 and the vanadium sulfate in Comparative Example 1, only the amount of sulfuric acid added at the end is different, and the other steps and dosages are the same. The dissolution time, color, and solidification time of the crystals formed into a 3.5-valent vanadium electrolyte were investigated for the two vanadium sulfate crystals. The vanadium sulfates of Example 1 and Comparative Example 1 were respectively prepared into 1 mol / L solutions, and the dissolution time was observed. Using the vanadium sulfate in Comparative Example 1 as the raw material, the vanadium electrolyte crystals were prepared by the method for preparing 3.5-valent vanadium electrolyte crystals in Example 1, and the crystal solidification time was observed. As can be seen from Table 1, the highly soluble vanadium sulfate crystals prepared in Example 1 not only have a short dissolution time but also a short solidification time; however, the vanadium sulfate crystals in Comparative Example 1 have a long dissolution time and a long solidification time.

[0086] Obviously, the effect of Example 1 is significant compared to that of Comparative Example 1.

[0087] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of highly soluble vanadium sulfate, characterized in that, It includes the following steps: Step 1: Mix V2O4, sulfuric acid and a solvent, and react at 60 - 100 °C for 1 - 8 h to prepare a high-concentration vanadyl sulfate solution, where the solvent is water and / or a low-concentration vanadyl sulfate solution; Step 2: Electrochemically reduce the high-concentration vanadyl sulfate solution to convert the high-concentration vanadyl sulfate solution into a trivalent vanadium sulfate solution; Step 3: Add sulfuric acid to the vanadium(III) sulfate solution and then crystallize. The addition amount of the sulfuric acid satisfies V:SO4 2- = 1:0.5 - 1.5, and filter to obtain vanadium sulfate crystals; Step 4: In the filtrate obtained by filtering in Step 3, add vanadium pentoxide according to V 3+ :V 5+ molar ratio = 1:0.9 - 1.0 to adjust the valence state, obtaining a low-concentration vanadyl sulfate solution; return the low-concentration vanadyl sulfate solution to Step 1 for preparing a high-concentration vanadyl sulfate solution; The concentration of the high-concentration vanadyl sulfate solution is 3 - 5.5 mol / L, and the concentration of the low-concentration vanadyl sulfate solution is 1 - 1.8 mol / L.

2. The preparation method of highly soluble vanadium sulfate according to claim 1, characterized in that, In Step 1, the amounts of V2O4 and sulfuric acid used are V:SO4 2- Molar ratio = 1:1.0 - 1.

7.

3. The preparation method of highly soluble vanadium sulfate according to claim 1, characterized in that, In Step 1, the addition amount of the solvent ensures that the vanadium concentration in the system is 2 - 5.5 mol / L.

4. The preparation method of highly soluble vanadium sulfate according to claim 1, characterized in that, In Step 1, mix V2O4, sulfuric acid and the solvent, and react at 80 - 90 °C for 3 - 5 h to prepare a high-concentration vanadyl sulfate solution.

5. The preparation method of highly soluble vanadium sulfate according to claim 1, wherein The sulfuric acid concentration in Step 1 is 90 - 100% wt.

6. The preparation method of highly soluble vanadium sulfate according to claim 1, characterized in that, In Step 2, the electrolysis voltage is 0.6 - 2.0 V; the electrolysis current is 2000 - 4000 mA; the electrolysis time is 5 - 20 h.

Images