CN107662946B - Preparation method of vanadium trioxide - Google Patents

Abstract

The invention discloses a preparation method of vanadium trioxide applicable to a vanadium battery, which comprises the following steps: and (3) carrying out liquid phase reduction on ammonium vanadate with the vanadium valence of +5 and oxalic acid or a solvate of oxalic acid in a reaction solvent, evaporating the reaction solution to dryness, and calcining to obtain the catalyst. The method takes cheap and easily-obtained + 5-valent ammonium vanadate as a raw material, and vanadium trioxide with the purity of up to 99 percent can be obtained by oxalic acid reduction and calcination. The production process has the advantages of simple operation, low energy consumption, safety and low equipment requirement, is suitable for industrial large-scale production, and can obviously reduce the production cost of vanadium trioxide.

Description

The preparation method of vanadium trioxide

technical field

The invention relates to a preparation method of vanadium trioxide, and belongs to the field of chemical material synthesis.

Background technique

Vanadium trioxide is an important vanadium oxide, which is widely used in the production of high vanadium iron and vanadium nitrogen alloys, sensors, new electronic components and battery production. Among them, vanadium trioxide has good application prospects in the production process of all-vanadium redox flow battery electrolyte, because the method for preparing 3.5-valent vanadium electrolyte by reducing vanadium pentoxide with vanadium The process is simple, the reduction effect is good, and other impurities are not introduced, and it has the advantages of chemical reduction and electrolysis, so that the production cost of vanadium electrolyte can be reduced. However, due to the high preparation cost and low product purity of vanadium trioxide at present, this method of producing vanadium electrolyte is limited.

At present, vanadium trioxide is mainly obtained by reduction of high-valence vanadium compounds. The reduction methods include reduction with external solid reducing agents (eg, sulfur, carbon powder, graphite, etc.), reduction with reducing gases (eg, H ₂ , CO, etc.), decomposition of ammonium vanadate, and reduction by ammonia cracking. Among them, the method of adding reducing agents such as graphite and carbon for reduction has a simple production process, but the required reduction temperature is high, and carbon is easily left in the product or other impurities are easily introduced; _H2 or CO and other reducing gases have good reduction effects and high product purity. But there are dangers such as burning, explosion or toxic gas leakage; ammonium vanadate is decomposed, and the generated ammonia is cracked into H ₂ and N ₂ The method for reducing vanadium trioxide is clean and environmentally friendly, and does not need to add any reducing agent, but due to ammonia gas The cracking is incomplete, the reduction is insufficient, and the equipment requirements are high. In addition to the above several main preparation methods, vanadium-containing hydrazine salts can also be calcined under protective gas conditions, and organic reducing agents can be added to synthesize vanadium trioxide with uniform and fine particle size by hydrothermal synthesis or solvothermal methods. , and achieved good application results in related fields, but these methods have shortcomings such as high equipment requirements and low production efficiency, resulting in high production costs of vanadium trioxide.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a preparation method of vanadium trioxide, to overcome the defects of higher cost and complicated operation of the existing production process.

The present invention provides a method for preparing vanadium trioxide, which comprises the following steps: performing liquid phase reduction of ammonium vanadate whose vanadium valence is +5 and oxalic acid or a solvate of oxalic acid in a reaction solvent, evaporating the reaction solution to dryness, and calcining , that is.

Further, the ammonium vanadate whose vanadium valence state is +5 is ammonium metavanadate or ammonium polyvanadate.

Further, the molar ratio of vanadium in the ammonium vanadate to the molar ratio of oxalic acid is 1:(1.5-3).

Further preferably, the molar ratio of vanadium in the ammonium vanadate to the molar ratio of oxalic acid is 1:(1.5-2.5).

Further, the molar amount of vanadium in the ammonium vanadate: the volume of the reaction solvent is 5-12 mol/L.

Further preferably, the molar amount of vanadium in the ammonium vanadate: the volume of the reaction solvent is 8.5-10 mol/L.

Further, the reaction temperature is 80-100°C.

Further preferably, the reaction temperature is 80-90°C.

Further, calcination is carried out in a protective atmosphere.

Further, the protective atmosphere is one or a mixture of two or more of nitrogen, helium, argon, ammonia, CO, and gaseous alkanes.

Further preferably, the protective atmosphere is nitrogen.

Further, the calcination temperature is 700-1000°C.

Further preferably, the calcination temperature is 700-900°C.

Further, the calcination time is 1.5-5h.

Further preferably, the calcination time is 2-4h.

Further, the reaction solvent is water.

Further, the solvate of oxalic acid is oxalic acid dihydrate.

Further, drying is performed before calcination; in the drying process, in order to prevent the precursor from agglomerating after drying, the precursor needs to be mechanically stirred every 10-20 minutes.

The invention provides a preparation method of vanadium trioxide. The method uses cheap and readily available +5-valent ammonium vanadate as a raw material, and through oxalic acid reduction and calcination, vanadium trioxide with a purity of up to 99% can be obtained, and the yield is 100% (excluding transfer loss). The production process of the invention has the advantages of simple operation, low energy consumption, safety, low equipment requirements, suitable for industrialized large-scale production, and can significantly reduce the production cost of vanadium trioxide. In addition, the V ₂ O ₃ obtained by this method is suitable for the preparation of electrolytes for all-vanadium redox flow batteries. It was placed in a vanadium battery with an effective area of 100 cm ² for 40 charge-discharge cycles, and the coulombic efficiency of the battery remained at 96%. Above, the energy efficiency is maintained above 80%, and the Coulomb efficiency and the energy efficiency are hardly attenuated. It has broad application prospects in the production process of all-vanadium redox flow battery electrolyte.

Description of drawings

Fig. 1 is vanadium trioxide production process schematic diagram of the present invention;

Fig. 2 is the XRD diffractogram of ammonium metavanadate and oxalic acid molar ratio of 1:0.5 reaction products obtained in Comparative Example 1;

Fig. 3 is the XRD diffractogram of ammonium metavanadate and oxalic acid molar ratio of 1:1 reaction products obtained in Comparative Example 1;

Fig. 4 is the XRD diffraction pattern of the product obtained by calcining at 400°C in Comparative Example 2;

Fig. 5 is the XRD diffractogram of the product obtained by calcining at 450°C in Comparative Example 2;

Fig. 6 is the XRD diffractogram of the product obtained by calcining at 500°C in Comparative Example 2;

Fig. 7 is the XRD diffractogram of the product obtained by calcination at 550°C in Comparative Example 2;

Fig. 8 is the XRD diffraction pattern of the product obtained by calcination at 600°C in Comparative Example 2;

Fig. 9 is the XRD diffraction pattern of the product obtained by calcination at 650°C in Comparative Example 2;

Fig. 10 is the XRD diffraction pattern of the product obtained by calcination at 700°C in Comparative Example 2;

Fig. 11 is a diagram showing the coulombic efficiency and energy efficiency of battery charging and discharging in Test Example 1;

Figure 12 is the XRD diffractogram of the product obtained from the reaction of ammonium metavanadate and oxalic acid in the molar ratio of 1:1.5 in Test Example 2;

Fig. 13 is the XRD diffractogram of ammonium metavanadate and oxalic acid molar ratio of 1:2 reaction products obtained in Test Example 2;

Figure 14 is the XRD diffractogram of the product obtained by the reaction of ammonium metavanadate and oxalic acid in the molar ratio of 1:2.5 in Test Example 2;

Figure 15 is the XRD diffraction pattern of the product obtained by the reaction of ammonium metavanadate and oxalic acid in a molar ratio of 1:3 in Test Example 2.

Detailed ways

The raw materials and equipment used in the specific embodiments of the present invention are all known products, which are obtained by purchasing commercially available products.

The invention provides a preparation method of vanadium trioxide, comprising the following steps (see Fig. 1 for a schematic diagram of the production process):

1) Mix ammonium metavanadate or ammonium polyvanadate with oxalic acid (the mixing ratio is, the molar amount of vanadium: the molar amount of oxalic acid=1: 1.5～1: 2.5), add to the deionization temperature that the temperature is 80～90 ℃ In water (molar amount of vanadium: the volume of water is 8.5～10mol/L), carry out liquid phase reduction;

2) after ammonium metavanadate or ammonium polyvanadate is completely dissolved, heated to boiling, the solution is concentrated and evaporated to dryness to obtain a precursor;

3) calcining the obtained precursor under the protection of nitrogen and the temperature of 700-900 DEG C for 2-4 hours, and cooling to room temperature under the protection of nitrogen to obtain vanadium trioxide.

In this production process, a precursor whose main components are (NH ₄ ) ₂ (VO) ₂ (C ₂ O ₄ ) ₃ and oxalic acid mixture is obtained. Due to the high carbon content, the reduction effect during calcination and decomposition is good; Ammonia gas is produced, and the ammonia gas itself has reducibility and plays a protective role, which can better reduce the intermediate product. Based on the above reasons, the preparation process of the present invention has obvious advantages: 1. vanadium trioxide can be obtained with high purity and high yield, and the process stability is strong, and the quality of the obtained product is stable; 2. the obtained vanadium trioxide is very suitable for preparing vanadium Electrolyte, the battery has good charge and discharge efficiency, which proves that its application effect is good.

In addition, the present invention further investigates various parameters and conditions in the preparation process, and it is found that the interaction between the amount of oxalic acid and the calcination temperature has a significant impact on the product. When the molar ratio of vanadium and oxalic acid is lower than 1:1.5, it is difficult to obtain vanadium trioxide; correspondingly, under the condition that the calcination temperature is lower than 700 ℃, even if the amount of oxalic acid is repeatedly adjusted, the purity of vanadium trioxide is It is also difficult to meet the requirements. Under the specific combination of the two, the product purity is finally increased to more than 99%, and the yield of vanadium has no other losses except the transfer loss during the production process.

At present, there is no report on the preparation of vanadium trioxide by the reaction of +5-valent ammonium vanadate with oxalic acid. Compared with the existing preparation process by adding a solid reducing agent (eg, sulfur, carbon powder, graphite, etc.) or reducing gas (eg, H ₂ , CO, etc.) and other reduction methods, the present invention has the advantages of low production cost, simple operation, and safety. and other significant advantages.

Embodiment 1 adopts the technology of the present invention to prepare vanadium trioxide

1) Mix analytically pure ammonium metavanadate with analytically pure dihydrate oxalic acid (the mixing ratio is, the molar amount of vanadium: the molar amount of oxalic acid=1:1.5), and adding it in batches into deionized water (vanadium) at a temperature of 80° C. The molar amount of: the volume of water=10mol/L), carry out liquid phase reduction;

2) after the ammonium metavanadate is completely dissolved, heated to boiling, the solution is concentrated and evaporated to dryness to obtain a precursor;

3) After drying the obtained precursor at 160° C., calcining for 2.5 h under nitrogen protection and at a temperature of 700° C., and cooling to room temperature under nitrogen protection. The purity of vanadium trioxide finally obtained is 98.8%.

Embodiment 2 adopts the technology of the present invention to prepare vanadium trioxide

1) Mix analytically pure ammonium metavanadate with analytically pure dihydrate oxalic acid (the mixing ratio is, the molar amount of vanadium: the molar amount of oxalic acid=1:2), and adding it in batches into deionized water (vanadium) at a temperature of 95° C. The molar weight: the volume of water=9mol/L), carry out liquid phase reduction;

2) after the ammonium metavanadate is completely dissolved, heated to boiling, the solution is concentrated and evaporated to dryness to obtain a precursor;

3) The obtained precursor was dried at 100°C, calcined for 3 hours under nitrogen protection and at a temperature of 750°C, and cooled to room temperature under nitrogen protection. The purity of vanadium trioxide finally obtained is 99.2%.

Embodiment 3 adopts the technology of the present invention to prepare vanadium trioxide

1) Mix analytically pure ammonium metavanadate with analytically pure dihydrate oxalic acid (the mixing ratio is, the molar amount of vanadium: the molar amount of oxalic acid=1:2.5), and adding in batches is that the temperature is 85 ℃ of deionized water (vanadium Molar weight: volume of water=10mol/L), carry out liquid phase reduction;

2) after the ammonium metavanadate is completely dissolved, heated to boiling, the solution is concentrated and evaporated to dryness to obtain a precursor;

3) The obtained precursor was dried at 200°C, calcined for 2 h under nitrogen protection and at a temperature of 800°C, and cooled to room temperature under nitrogen protection. The purity of vanadium trioxide finally obtained is 99.4%.

Embodiment 4 adopts the technology of the present invention to prepare vanadium trioxide

1) Mix analytically pure ammonium metavanadate with analytically pure dihydrate oxalic acid (the mixing ratio is, the molar amount of vanadium: the molar amount of oxalic acid=1:3), and adding it in batches into deionized water (vanadium) at a temperature of 90° C. The molar amount of : the volume of water=8.5mol/L), carry out liquid phase reduction;

2) after the ammonium metavanadate is completely dissolved, heated to boiling, the solution is concentrated and evaporated to dryness to obtain the precursor;

3) The obtained precursor was dried at 180 °C, calcined for 3 h under nitrogen protection and at a temperature of 900 °C, and cooled to room temperature under nitrogen protection. The purity of vanadium trioxide finally obtained is 99.0%.

Influence of the amount of oxalic acid on the product in the preparation process of Comparative Example 1

In this experiment, ammonium metavanadate and oxalic acid were reacted in molar ratios of 1:0.5 and 1:1 respectively, and the prepared precursor was calcined at 700°C under nitrogen protection to obtain a product. The specific process conditions were the same as those in Example 1. The obtained product was subjected to XRD diffraction analysis, and the analysis results are shown in Figures 2 and 3.

The analysis of the XRD patterns of Figures 2 and 3 shows that when the molar ratio of ammonium metavanadate and oxalic acid is 1:0.5 and 1:1, the main components of the obtained product are VO ₂ and V ₃ O ₅ , rather than the target substance. V ₂ O ₃ .

In addition, the comparative test also further increased the amount of oxalic acid on the basis of ammonium metavanadate: the oxalic acid molar ratio of 1:3, and the result did not increase the calcination temperature. With the increase of , the stray peaks of amorphous carbon diffraction peaks appear more and more obvious in XRD diffraction, indicating that the purity of the obtained product is significantly reduced.

The above test results show that the amount of oxalic acid will have a significant impact on the final product. Within the dosage range determined by the preparation process of the present invention, that is, when the molar ratio of vanadium in the ammonium vanadate to the molar ratio of oxalic acid is 1: (1.5～3) , high-purity target product V ₂ O ₃ can be prepared in high yield.

Influence of calcination temperature on product in preparation process of comparative example 2

The precursor was prepared according to Example 1. The precursor was placed in a tube furnace, protected by nitrogen, and calcined at 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, and 700 °C for 4 hours. , continue to pass nitrogen until the furnace temperature drops to room temperature. The obtained product was subjected to XRD diffraction analysis, and the analysis results are shown in Figures 4-10.

It can be seen from Figures 4 to 10 that with the continuous increase of the calcination temperature, the diffraction peaks of V ₂ O ₃ become more and more obvious, and the impurity peaks become weaker and weaker. It shows that when the calcination temperature is lower than 700℃, the decomposition of the precursor is incomplete, the content of amorphous carbon in the product is large, and the purity of the product is not high; The reducing ability is strong, and high-purity V ₂ O ₃ can be obtained.

The beneficial effects of the present invention are demonstrated below through test examples.

Test Example 1 Preparation of vanadium battery with vanadium trioxide of the present invention as raw material

Vanadium pentoxide was mixed with vanadium trioxide prepared according to Example 1 of the present invention in a molar ratio of 4.2:1, 6 mol/L sulfuric acid was added, the reaction was carried out at 90 ° C for 120 min, after cooling to room temperature, filtered, Measure the content of trivalent vanadium and pentavalent vanadium in the filtrate (V ⁺³ :V ⁺⁵ =1.04:1), add deionized water to adjust the H ₂ SO ₄ concentration in the solution to be 3mol/L, and the total vanadium concentration to be 2mol/L . Get an equal amount of this electrolyte and place it in the positive and negative electrode storage tanks of the vanadium battery respectively (the effective area of the vanadium battery is 100cm ² ), with a current density of 40mA/cm , carry out constant current charge ^- discharge cycle 40 times, the energy of the battery Efficiency and Coulombic efficiency are shown in Figure 11.

It can be seen from Figure 11 that the coulombic efficiency of the battery is maintained above 96%, the energy efficiency is maintained above 80%, and the coulombic efficiency and energy efficiency are almost not attenuated, indicating that the electrolyte has good performance.

The above test results show that the V ₂ O ₃ prepared by the method of the present invention is suitable for preparing the electrolyte of all-vanadium redox flow batteries, and its purity can meet the requirements for preparing vanadium batteries. The method of preparing 3.5-valent vanadium electrolyte by reducing vanadium pentoxide with vanadium as reducing agent has been further popularized and applied.

Test Example 2 Verification test of the preparation process of the present invention

Ammonium metavanadate and oxalic acid were reacted in molar ratios of 1:1.5, 1:2, 1:2.5, and 1:3, respectively, and the prepared precursor was calcined at 700 °C under nitrogen protection to obtain a reduced product. The process conditions Same as Example 1. The obtained product was subjected to XRD diffraction analysis, and the analysis results are shown in Figures 12-15.

The analysis of the XRD patterns in Figs. 12-15 shows that the main components of these products are all V ₂ O ₃ .

The above test results show that the preparation process of the present invention is stable and reliable, and the quality of the obtained product is stable.

Claims (12)

1. the preparation method of vanadium trioxide, it is characterized in that: comprise the steps: the solvate of ammonium vanadate and oxalic acid or oxalic acid that vanadium valence state is +5 valence carries out liquid phase reduction in reaction solvent, evaporated to dryness reaction solution , calcining to obtain; the molar ratio of vanadium in the ammonium vanadate to the molar ratio of oxalic acid is 1: (1.5～3); the temperature of liquid-phase reduction is 80～100 ℃; the calcination temperature is 700～1000 ℃; The solvate of oxalic acid is oxalic acid dihydrate; calcination is carried out in a protective atmosphere. 2. preparation method as claimed in claim 1 is characterized in that: the ammonium vanadate that described vanadium valence state is +5 valence is ammonium metavanadate or ammonium polyvanadate. 3 . The preparation method according to claim 1 , wherein the molar ratio of vanadium in the ammonium vanadate to the molar ratio of oxalic acid is 1:(1.5～2.5). 4 . 4. The preparation method according to any one of claims 1 to 3, wherein the molar amount of vanadium in the ammonium vanadate: the volume of the reaction solvent is 5 to 12 mol/L. 5. The preparation method according to any one of claims 1 to 3, wherein the molar amount of vanadium in the ammonium vanadate: the volume of the reaction solvent is 8.5 to 10 mol/L. 6 . The preparation method according to claim 1 , wherein the temperature of the liquid phase reduction is 80-90° C. 7 . 7. The preparation method of claim 1, wherein the protective atmosphere is a mixture of one or more of nitrogen, helium, argon, ammonia, CO, and gaseous alkanes. 8. The preparation method of claim 1, wherein the protective atmosphere is nitrogen. 9. The preparation method of claim 1, wherein the calcination temperature is 700-900°C. 10. The preparation method according to any one of claims 1, 7 to 9, wherein the calcination time is 1.5 to 5 hours. 11. The preparation method according to any one of claims 1, 7 to 9, wherein the calcination time is 2 to 4 hours. 12. The preparation method of claim 1, wherein the reaction solvent is water.

Images