Method for judging reduction end point during chemical reduction of alkaline vanadium-containing solution

Abstract

The invention relates to the technical field of preparation of an electrolyte for a vanadium redox flow battery, in particular to a method for judging a reduction end point during chemical reduction of an alkaline vanadium-containing solution. The method comprises the following steps: (1) sampling from a chemical reduction production process reactor of an alkaline vanadium-containing solution to obtain a liquid sample, and putting the liquid sample into a sample bottle; (2) adding a sulfuric acid-phosphoric acid mixed solution into the sample bottle, mixing with the liquid sample in the step (1), and acidifying; (3) observing the color of the acidified sample through a visual method, and judging whether the vanadium-containing solution finishes the reduction reaction or not; and (4) returning the sampled liquid sample and the acidified sample to a chemical reduction production process reactor. The method is simple, does not need a professional complete set of instruments and equipment, is convenient to apply in front of a production workshop, and can quickly and accurately obtain a qualitative judgment result of the production process.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of electrolytes for vanadium redox flow batteries, and specifically to a method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution. Background Art

[0002] With the continuous increase in the installed capacity of renewable energy, the demand for energy storage is also growing day by day. As an important energy storage method, the application of all-vanadium redox flow batteries is also increasing.

[0003] Vanadium electrolyte is one of the core materials of all-vanadium redox flow batteries. It is usually prepared by alkali dissolution and reduction using vanadium pentoxide as a raw material, or directly using the vanadium-containing leaching solution after sodium roasting as a raw material, and prepared by extraction after reduction treatment. Both of the above two methods involve the step of reducing pentavalent vanadium in the solution to tetravalent vanadium.

[0004] In principle, the accurate dosage of the reducing agent required to reduce pentavalent vanadium to tetravalent vanadium can be calculated based on basic information such as the volume of the feed liquid, the content of pentavalent vanadium in the feed liquid, including the content of impurity hexavalent chromium, etc. through stoichiometric relationships, and production operations can be completed by means of metering such as belt scales and positive displacement pumps. However, in actual production, due to actual factors such as statistical errors in the volume of the feed liquid, analysis errors in the content of different valence components in the feed liquid, and operation errors of metering equipment and actuators, a simple and fast method is still needed to directly feedback whether the reduction reaction is completed, that is, the problem of judging the reduction end point.

[0005] Specifically for the reduction process of the pentavalent vanadium solution, there are currently various mature analysis methods to detect the content of vanadium in different valence states in the solution. For example, traditional redox titration analysis based on redox indicators (CN104181158A), automatic titration method using redox potential measurement, and ultraviolet-visible spectrophotometry based on absorption spectrum analysis (CN 102621085A) can all achieve quantitative analysis of pentavalent vanadium and tetravalent vanadium in the solution. However, in the actual production process, there are processes such as sampling and sending samples in the workshop, receiving samples, registering, detecting, and reporting data in the analysis room, and it is impossible to achieve instant feedback before work in the production workshop. Therefore, a simple and convenient method is still needed to judge the end point of the reduction of pentavalent vanadium during the production operation. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution to solve the problem of the lack of instant monitoring means in the reduction production process of pentavalent vanadium solution during the preparation of vanadium electrolyte at present. This method is simple, does not require professional complete sets of instrument equipment, is convenient to be applied before work in the production workshop, and can quickly and accurately obtain the qualitative judgment result of the production process.

[0007] In order to achieve the above invention purpose, the specific technical solution of the present invention is as follows:

[0008] A method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, comprising the following steps:

[0009] (1) Sampling from the reactor of the chemical reduction production process of the alkaline vanadium-containing solution to obtain a liquid sample, which is placed in a sample bottle;

[0010] (2) Adding a sulfuric acid-phosphoric acid mixed solution to the sample bottle, and mixing and acidifying it with the liquid sample collected in step (1);

[0011] (3) By visual method, observing the color of the acidified sample to judge whether the vanadium-containing solution has completed the reduction reaction;

[0012] (4) Returning the sampled liquid sample and the acidified sample to the reactor of the chemical reduction production process.

[0013] Further, in step (1) of the method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, the reducing agent used in the chemical reduction production process is one or a mixture of more than one of sodium sulfite, sodium metabisulfite, and sulfur dioxide.

[0014] Further, in step (1) of the method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, sampling can be carried out by manual sampling or peristaltic pump sampling, and peristaltic pump sampling is preferred.

[0015] Further, in step (1) of the method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, the sampling volume is 5-10 mL.

[0016] Further, in step (2) of the method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, for the added sulfuric acid-phosphoric acid mixed solution, the volume ratio of analytical pure reagent sulfuric acid in the mixed solution is 10%-30% (more preferably 20%), the volume ratio of analytical pure reagent phosphoric acid is 10%-30% (more preferably 10%), the balance is deionized water, and the total volume percentage is 100%.

[0017] Further, in step (2) of the method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, the volume ratio of the added sulfuric acid-phosphoric acid mixed solution to the liquid sample is 1-5.

[0018] Further, in step (3) of the method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, the basis for visual observation is that when the acidified sample is sky blue, the reduction reaction is completed and the reduction reaction end point is reached; when the acidified sample is bright green, it is close to the reduction reaction end point; the more obvious the yellow component of the acidified sample, the farther it is from the reduction reaction end point.

[0019] Further, in step (1) of the method for judging the reduction end point during the chemical reduction of an alkaline vanadium-containing solution, in the said alkaline vanadium-containing solution, vanadium is pentavalent vanadium, chromium is hexavalent chromium, and iron is trivalent iron.

[0020] Further, in the method for judging the reduction end point during the chemical reduction of an alkaline vanadium-containing solution, both the sodium sulfite and sodium metabisulfite used are analytical pure solid powder reagents, and the sulfur dioxide used is a commercially available standard gas encapsulated in a steel cylinder with a purity of 99.999%.

[0021] Further, in the method for judging the reduction end point during the chemical reduction of an alkaline vanadium-containing solution, both the sulfuric acid and phosphoric acid are analytical pure reagents.

[0022] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0023] The method in the present invention is simple, does not require professional complete sets of instruments and equipment, is convenient for pre-job application in the production workshop, and can quickly and accurately obtain the qualitative judgment results of the production process.

[0024] The method of the present invention is applicable to the judgment of the reduction production process using high-purity vanadium pentoxide as the raw material, and is also applicable to the judgment of the reduction production process using complex alkaline vanadium-containing solutions containing impurities such as chromium, iron, silicon, and phosphorus as the raw materials.

[0025] For the method of the present invention, all the collected liquid samples and the samples after dilution-acidification treatment are returned to the production process, and no additional impurity ions will be introduced into the production process, which is beneficial to reducing the waste liquid output during the production monitoring process. For example, if the reduction production process uses high-purity vanadium pentoxide as the raw material, and since the flow batteries using vanadyl sulfate electrolytes all add phosphoric acid or phosphates to stabilize the electrolyte, the method of the present invention will not have an adverse effect on the quality of the subsequent products when the acidified samples are returned to the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of a method for judging the reduction end point during the chemical reduction of an alkaline vanadium-containing solution recorded in the present invention;

[0027] In the figure, from left to right, the containers are successively an alkaline vanadium-containing solution, acidified sample 1 (yellow), acidified sample 2 (bright green 1), acidified sample 3 (bright green 2), and acidified sample 4 (sky blue), that is, acidified sample 4 reaches the reduction reaction end point. DETAILED DESCRIPTION OF THE INVENTION

[0028] All the features disclosed in this specification, or all the steps in the disclosed methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

[0029] Any feature disclosed in this specification (including claims and abstract), unless specifically stated, can be replaced by other equivalent or similar-purpose alternative features. That is, unless specifically stated, each feature is just an example in a series of equivalent or similar features.

[0030] The features and properties of the present invention will be further described in detail below in conjunction with embodiments.

[0031] In the following embodiments, the main components of the alkaline vanadium-containing solution are: vanadium 29.83 g / L, chromium 2.734 g / L, calcium 17.4 mg / L, iron 10.5 mg / L, silicon 804.1 mg / L, phosphorus 174.2 mg / L, where vanadium is pentavalent, chromium is hexavalent, and iron is trivalent.

[0032] The sodium sulfite and sodium metabisulfite used in the reduction operation are both commercially available solid powder analytical pure reagents, the sulfuric acid used is analytical pure reagent sulfuric acid, and the sulfur dioxide used is a commercially available standard gas encapsulated in a steel cylinder with a purity of 99.999%.

[0033] The sulfuric acid-phosphoric acid mixed solution is prepared by mixing analytical pure reagent sulfuric acid, analytical pure reagent phosphoric acid with deionized water. Its composition is expressed in volume ratio, and the balance is deionized water.

[0034] Example 1

[0035] Take 200 mL of the alkaline vanadium-containing solution and place it in a plastic bottle with a sealed cap. Add 1.1 times the theoretical amount of sodium sulfite. After complete dissolution, quickly add 0.9 times the theoretical amount of sulfuric acid and quickly seal the cap for reduction. After reacting for 1 min, take 5 mL of the solution after the reduction reaction and place it in a sample bottle. Add 25 mL of a mixed solution composed of 10% sulfuric acid - 30% phosphoric acid, and mix for 1 min for acidification. The acidified sample is yellowish-green, and it is visually judged that there is still residual pentavalent vanadium in the sample that has not been reduced, and the reduction reaction has not reached the end point. Take another 1 mL of the solution after the reduction reaction and analyze it using a ZDJ-5B automatic titrator. The reduction rate of pentavalent vanadium is 89%. The visually qualitative judgment result is correct.

[0036] Return the acidified sample to the reactor of the chemical reduction production process to reduce the amount of waste liquid produced during the production monitoring process.

[0037] Example 2

[0038] Take 200 mL of alkaline vanadium-containing solution and place it in a plastic bottle with a sealed cap. Add 1.1 times the theoretical amount of sodium sulfite. After complete dissolution, quickly add 1.1 times the theoretical amount of sulfuric acid and immediately seal the cap for reduction. After reacting for 1 minute, take a 10-mL sample of the reduced solution and place it in a sample bottle. Add 10 mL of a mixed solution composed of 20% sulfuric acid - 20% phosphoric acid, mix for 1 minute for acidification. The acidified sample is sky blue. Visually judge that there is no residual pentavalent vanadium in the sample, and the reduction reaction reaches the end point. Take another 1-mL sample of the reduced solution and analyze it using a ZDJ-5B automatic titrator. Pentavalent vanadium is not detected, and the reduction rate of pentavalent vanadium is 100%. The visually qualitative judgment result is correct.

[0039] Return the acidified sample to the reactor of the chemical reduction production process to reduce the amount of waste liquid generated during the production monitoring process.

[0040] Example 3

[0041] Take 200 mL of alkaline vanadium-containing solution and place it in a plastic bottle with a sealed cap. Add 0.9 times the theoretical amount of sodium metabisulfite. After complete dissolution, quickly add 0.9 times the theoretical amount of sulfuric acid and immediately seal the cap for reduction. After reacting for 1 minute, take a 5-mL sample of the reduced solution and place it in a sample bottle. Add 30 mL of a mixed solution composed of 20% sulfuric acid - 30% phosphoric acid, mix for 1 minute for acidification. The acidified sample is yellowish green. Visually judge that there is still residual pentavalent vanadium in the sample that has not been completely reduced, and the reduction reaction does not reach the end point. Take another 1-mL sample of the reduced solution and analyze it using a ZDJ-5B automatic titrator. The reduction rate of pentavalent vanadium is 84%. The visually qualitative judgment result is correct.

[0042] Return the acidified sample to the reactor of the chemical reduction production process to reduce the amount of waste liquid generated during the production monitoring process.

[0043] Example 4

[0044] Take 200 mL of alkaline vanadium-containing solution and place it in a plastic bottle with a sealed cap. Add 1.05 times the theoretical amount of sodium metabisulfite. After complete dissolution, quickly add 1.05 times the theoretical amount of sulfuric acid and immediately seal the cap for reduction. After reacting for 1 minute, take a 5-mL sample of the reduced solution and place it in a sample bottle. Add 20 mL of a mixed solution composed of 10% sulfuric acid - 20% phosphoric acid, mix for 1 minute for acidification. The acidified sample is bright green. Visually judge that there is still residual pentavalent vanadium in the sample that has not been reduced, and the reduction reaction does not reach the end point. Take another 1-mL sample of the reduced solution and analyze it using a ZDJ-5B automatic titrator. The reduction rate of pentavalent vanadium is 95.5%. The visually qualitative judgment result is correct.

[0045] Return the acidified sample to the reactor of the chemical reduction production process to reduce the amount of waste liquid produced during production monitoring.

[0046] Example 5

[0047] For the remaining solution of Example 4, sulfur dioxide gas was introduced through a conduit at a flow rate of 100 mL / min. After reacting for 3 minutes, 5 mL of the sample was taken and placed in a sample bottle. 5 mL of a mixed solution composed of 10% sulfuric acid - 10% phosphoric acid was added, and the mixture was acidified for 1 minute. The acidified sample was sky blue, and it was visually judged that there was no residual pentavalent vanadium in the sample, indicating that the reduction reaction reached the end point. Another 1 mL of the solution after the reduction reaction was taken and analyzed using a ZDJ-5B automatic titrator. Pentavalent vanadium was not detected, and the reduction rate of pentavalent vanadium was 100%. The visually qualitative judgment result was correct.

[0048] Return the acidified sample to the reactor of the chemical reduction production process to reduce the amount of waste liquid produced during production monitoring.

[0049] It can be seen from the present invention that for the method of the present invention, the collected liquid samples and the samples after dilution-acidification treatment are all returned to the production process, without introducing additional impurity ions into the production process, which is beneficial to reducing the amount of waste liquid produced during production monitoring.

[0050] If high-purity vanadium pentoxide is used as the raw material in the reduction production process, since liquid flow batteries using vanadyl sulfate electrolyte all add phosphoric acid or phosphate to stabilize the electrolyte, the method of the present invention, returning the acidified sample to the production process, will not have an adverse impact on the quality of subsequent products.

[0051] The above-described embodiments only represent the specific implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the technical solution of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application.

[0052] This background art section is provided to generally present the context of the present invention. The work of the currently named inventors, to the extent described in this background art section, and aspects that are not prior art at the time of filing this application, are neither expressly nor impliedly admitted to be prior art of the present invention.

Claims

1. A method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution, characterized in that It includes the following steps: (1) Sampling from the reactor of the chemical reduction production process of the alkaline vanadium-containing solution to obtain a liquid sample, which is placed in a sample bottle; (2) Adding a sulfuric acid-phosphoric acid mixed solution to the sample bottle, mixing and acidifying it with the liquid sample in step (1); (3) By visual method, observing the color of the acidified sample to judge whether the reduction reaction of the vanadium-containing solution is completed; (4) Returning the sampled liquid sample and the acidified sample to the reactor of the chemical reduction production process.

2. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 1, characterized in that: The reducing agent used in the chemical reduction production process described in step (1) is one or a mixture of more of sodium sulfite, sodium metabisulfite, and sulfur dioxide.

3. The method for judging the reduction end point during the chemical reduction of an alkaline vanadium-containing solution according to claim 1, wherein: The sampling method in step (1) is manual sampling or peristaltic pump sampling.

4. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 1, wherein: The volume of the liquid sample collected in step (1) is 5 - 10 mL.

5. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 1, characterized in that: For the sulfuric acid-phosphoric acid mixed solution added in step (2), in the mixed solution, the volume ratio of analytical pure reagent sulfuric acid is 10% - 30%, the volume ratio of analytical pure reagent phosphoric acid is 10% - 30%, the balance is deionized water, and the total volume is 100%.

6. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 1, characterized in that: In step (2), the volume ratio of the added sulfuric acid-phosphoric acid mixed solution to the liquid sample is 1 - 5.

7. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 1, wherein The basis for visual observation in step (3) is: when the acidified sample is sky blue, the reduction reaction is completed and the reduction reaction end point is reached; when the acidified sample is bright green, it is close to the reduction reaction end point; the more obvious the yellow component of the acidified sample, the farther it is from the reduction reaction end point.

8. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 1, characterized in that, In the described alkaline vanadium-containing solution, vanadium is pentavalent vanadium, chromium is hexavalent chromium, and iron is trivalent iron.

9. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 2, characterized in that, Both the sodium sulfite and sodium metabisulfite are solid powder analytical pure reagents, and the sulfur dioxide used is a commercially available standard gas encapsulated in a steel cylinder with a purity of 99.999%.

10. The method for judging the reduction end point when chemically reducing an alkaline vanadium-containing solution according to claim 5, characterized in that, Both the sulfuric acid and phosphoric acid are analytical pure reagents.

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