A method for determining the content of lignin sulfonate and humic acid in a mixed sample.

Abstract

This invention relates to the field of detection technology for negative electrode additives in lead-acid batteries, and discloses a method for testing the content of lignin sulfonate and humic acid in a mixed sample. The method includes quantitatively taking a mixed sample, dissolving and separating the precipitate, combining the dissolved samples, measuring the absorbance of a portion of the solution, and calculating the absorbance index; dissolving the precipitate in a strong alkaline solution, oxidizing it with potassium dichromate to obtain the total potassium dichromate reduction index n; weighing pure lignin and pure humic acid and repeating the above steps to obtain the corresponding coefficients, and then solving for them. The detection method of this application can detect the content of lignin sulfonate and humic acid in a mixed sample and can be used for quality control of negative electrode expansion agents in lead-acid batteries.

Description

Technical Field

[0001] This invention relates to the field of detection technology for lead-acid battery negative electrode additives, specifically to a method for testing the content of lignin sulfonate and humic acid in a mixed sample. Background Technology

[0002] In the preparation of negative electrode plates for lead-acid batteries, expanding agents are added to the active material to inhibit the formation of a continuous passivation layer on the electrode surface and improve the electrical performance of the negative electrode plate. Commonly used expanding agents include inorganic expanding agents such as barium sulfate and strontium sulfate, as well as organic expanding agents such as humic acid, lignin, and lignin sulfonate (sulfonated lignin). Currently, the negative electrode expanding agents used by various lead-acid battery manufacturers are basically mixtures of multiple expanding agents. These are provided by upstream raw material suppliers after premixing the various expanding agents according to the type and content requirements specified by the main manufacturer, and can be used directly. Since the content ratio of each expanding agent greatly affects the negative electrode performance of the battery, it is necessary to confirm whether the content of each component in the expanding agent provided by the upstream manufacturer meets the predetermined requirements before use and to carry out quality control. At the same time, for expanding agents with unknown component ratios, it is also necessary to determine the composition for ease of use. However, when the expanding agent is a mixture of lignin sulfonate and humic acid, it is currently difficult to quantitatively test the content of the mixed components of lignin sulfonate and humic acid because both lignin sulfonate and humic acid are organic additives with the same functional groups.

[0003] Lu Yuan et al. (Detection and Influencing Factors of Humic Acid Content [J], 2008, 34(6):28-30.) used sodium pyrophosphate alkaline solution to dissolve and extract humic acid from peat, then reduced potassium dichromate under acidic conditions, and then titrated the remaining potassium dichromate with ferrous sulfate to determine the total humic acid content. However, since lignin sulfonate can also be oxidized by potassium dichromate, the above potassium dichromate oxidation method cannot detect the content of both humic acid and lignin sulfonate in a mixed sample. Summary of the Invention

[0004] To address the current lack of methods for detecting the content of lignin sulfonate and humic acid in mixed samples, the present invention aims to provide a testing method for the content of lignin sulfonate and humic acid in mixed samples. This method combines the potassium dichromate oxidation method and the absorbance method, which can simultaneously detect the content of lignin sulfonate and humic acid. It can be used to determine whether the composition of a mixed sample meets the requirements, and it can also be used to test mixed samples with unknown composition ratios. It is suitable for the quality control of lead-acid battery negative electrode expansion agents containing a mixture of lignin sulfonate and humic acid.

[0005] This invention provides the following technical solution:

[0006] A method for testing the content of lignin sulfonate and humic acid in a mixed sample, comprising the following steps:

[0007] (1) Take a quantitative sample of the mixture of lignin sulfonate and humic acid to be tested, dissolve the mixture in water, filter and wash with water, combine the solution and eluent and make up to volume.

[0008] (2) Take a quantitative amount of the solution after volume adjustment in step (1), adjust the dilution factor so that the absorbance is within the range of linear superposition, record the absorbance, and linearly extrapolate to the unit concentration of 1 g / L to obtain the absorbance index t.

[0009] (3) Dissolve and wash the filter residue from step (1) with a strong alkaline solution, filter, and dilute the filtrate to a fixed volume. Take a quantitative amount of the diluted liquid and oxidize it with potassium dichromate. Calculate the amount of potassium dichromate reduced per unit mass of sample, i.e., the total potassium dichromate reduction index n:

[0010] (4) Weigh out pure lignin sulfonate and repeat steps (1) to (3); weigh out pure humic acid and repeat steps (1) to (3).

[0011] (5) Calculate the proportions of lignin sulfonate and humic acid according to the following formula:

[0012] ax + by = t;

[0013] cx + dy = n;

[0014] Where x is the mass percentage of lignin sulfonate in the mixed sample, and y is the mass percentage of humic acid;

[0015] a and b are the linear superposition coefficients of the absorbance indices of lignin sulfonate and humic acid in the water-soluble fraction, respectively.

[0016] c and d are the linear superposition coefficients of the potassium dichromate reduction index of the water-insoluble lignin sulfonate and humic acid.

[0017] This application utilizes the linear additive nature of the absorbance of the water-soluble fractions of lignin sulfonate and humic acid at the characteristic absorption peak wavelength of lignin sulfonate, and the linear additive nature of the molar amounts of potassium dichromate reduced by water from the insoluble fractions of lignin sulfonate and humic acid. By combining the absorbance method and the potassium dichromate reduction method, the content of lignin sulfonate and humic acid in a mixed sample can be determined.

[0018] Specifically, assuming the mass percentage of lignin sulfonate in the mixed sample is x and humic acid is y, then x + y = 1. Since the absorbance is linearly superimposed, the following equation holds: ax + by = t; simultaneously, the potassium dichromate reduction indices of the insoluble portions of both have a linearly superimposed characteristic, and the following equation holds: cx + dy = n; thus, we obtain a system of equations consisting of the above two formulas, where a, b, c, and d are the corresponding linear superposition coefficients. Solving the above system of equations allows us to determine the content ratio of lignin sulfonate and humic acid in the expanding agent.

[0019] The key to solving the above system of equations is to obtain the values ​​of a, b, c, and d. As shown in step (4), pure lignin sulfonate is taken, at which point x = 1 and y = 0. Steps (1), (2), and (3) are repeated, including the same dilution factor as in step (2). The corresponding absorbance and potassium dichromate reduction index are measured to obtain the values ​​of a and c, i.e.:

[0020] When x = 1 and y = 0

[0021] a = t = A * V * dilution factor / m / 1000;

[0022] t (unit L / g) is the absorbance linearly extrapolated to a unit concentration of 1 g / L, where A is the absorbance, V is the volume of the pure lignin sulfonate dissolved and brought to a fixed volume, and m is the weight of the lignin sulfonate.

[0023] c = n = (blank sample titration volume - sample titration volume) / 6;

[0024] n (unit: mmol / g) is the potassium dichromate reduction index, which is the amount of potassium dichromate reduced per unit mass sample.

[0025] When lignin sulfonates are completely soluble, such as sodium lignin sulfonate, c = 0.

[0026] Correspondingly, take pure humic acid, at which point x = 0 and y = 1. Repeat the above operation to obtain the values ​​of b and d.

[0027] As a preferred embodiment of the method of the present invention,

[0028] The lignin sulfonate is sodium lignin sulfonate or potassium lignin sulfonate.

[0029] As a preferred embodiment of the method of the present invention,

[0030] This also includes strengthening the mixing of the alkaline solution before dilution to enhance absorbance.

[0031] As a preferred embodiment of the method of the present invention, the time from dilution to completion of absorbance measurement in step (2) is ≤20 min. The absorbance test time must be short; a longer time will cause the absorbance to drop too quickly, affecting the detection results.

[0032] As a preferred embodiment of the method of the present invention,

[0033] The absorbance in step (2) can be linearly superimposed in the range of 0.2 to 0.8.

[0034] As a preferred embodiment of the method of the present invention,

[0035] The absorbance in step (2) can be linearly superimposed in the range of 0.2 to 0.7.

[0036] As a preferred embodiment of the method of the present invention,

[0037] The strong alkaline solution used in step (2) is a sodium hydroxide or potassium hydroxide solution with a mass concentration of 0.3 to 1 wt%.

[0038] As a preferred embodiment of the method of the present invention,

[0039] Lignosulfonate is sodium lignosulfonate, with a characteristic absorption peak wavelength of 350 nm.

[0040] As a preferred embodiment of the method of the present invention,

[0041] The potassium dichromate oxidation method in step (3) is as follows:

[0042] Potassium dichromate and concentrated sulfuric acid are added to the solution to remove insoluble substances, and then Fe is added dropwise. 2+ The remaining potassium dichromate was titrated with the solution.

[0043] The beneficial effects of this invention are as follows:

[0044] The test method provided in this application combines the potassium dichromate oxidation method and the absorbance method, which can simultaneously detect the content of lignin sulfonate and humic acid. It can be used to determine whether the composition of the mixed sample meets the requirements, and it can also be used to detect mixed samples with unknown composition ratios. It can be used for quality control of the negative electrode expansion agent of lead paste batteries. Detailed Implementation

[0045] The specific embodiments of the present invention will be further described below.

[0046] Unless otherwise specified, all raw materials used in this invention are commercially available or commonly used in the field; unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0047] Examples 1-3

[0048] (1) Weigh about 0.1 to 0.2 g of dried lignin sulfonate and about 0.2 to 0.3 g of humic acid (accurate to 0.0001 g), place them in a 100 ml beaker, add 60 ml of water, stir thoroughly, filter, wash the precipitate with water, and do not let the precipitate disperse too much. Collect the filtrate and washing liquid in a 250 ml volumetric flask, and add water to make up to volume.

[0049] (2) Use a pipette to transfer 10 mL of the diluted solution, and dilute it to a 100 mL volumetric flask with 0.5 wt% sodium hydroxide diluent. Use water as a reference solution and measure the absorbance at 350 nm. Linearly extrapolate to a unit concentration of 1 g / L to obtain the absorbance index t. If the absorbance is not between 0.2 and 0.8, adjust the dilution factor and repeat the measurement. The process should be completed within 20 minutes from dilution to absorbance measurement. (3) Dissolve the precipitate from step (1) with 1 wt% sodium hydroxide eluent. Collect the eluent in a 250 mL volumetric flask and dilute it to a volumetric flask to obtain an alkaline solution. Quantitatively pipette the alkaline solution into a 250 mL Erlenmeyer flask, add 10.00 mL of 0.05 mol / L potassium dichromate standard solution and 15 mL of concentrated sulfuric acid, boil in a water bath for 30 min, cool, add 50 mL of water and 3 drops of o-phenanthroline-ferrous indicator, and use Fe 2+ Titrate with the standard solution; simultaneously perform a blank test, replacing the alkaline solution with an equal volume of water, with all other operations remaining the same. Calculate the amount of potassium dichromate reduced per unit mass sample, i.e., the potassium dichromate reduction index n, which is the reduction index of potassium dichromate to Cr₂O₇ under acidic conditions. 2- The restoration index;

[0050] (4) Weigh out equal amounts of approximately 0.1g of pure sodium lignosulfonate (accurate to 0.0001g) and approximately 0.2g of pure humic acid, and repeat steps 1 to 3, including diluting to the same multiple in step (2);

[0051] (5) Set the proportion of lignin sulfonate to the total mass as x and humic acid as y, x+y=1, and calculate x and y according to the following set of equations: ax+by=t;

[0052] cx + dy = n;

[0053] a and b are the linear superposition coefficients of the absorbance indices of the water-soluble lignin sulfonate and humic acid, and their values ​​are the same as those of the absorbance indices of the pure lignin sulfonate and humic acid in step (4).

[0054] c and d are the linear superposition coefficients of the potassium dichromate reduction index of the insoluble lignin sulfonate and humic acid, respectively, and their values ​​are the same as the potassium dichromate reduction index of the pure lignin sulfonate and humic acid in step (4).

[0055] Taking sodium lignosulfonate as an example, the test results are shown in Table 1 below.

[0056] Table 1 Test Results

[0057]

[0058] As can be seen from the table above, the test method of this application can detect the proportion of sodium lignosulfonate and humic acid in the mixed sample, and the result is very close to the theoretical value with small error. At the same time, the test results show good stability.

Claims

1. A method for testing the content of lignin sulfonate and humic acid in a mixed sample, characterized in that, Includes the following steps: (1) Take a quantitative sample of the mixture of lignin sulfonate and humic acid to be tested, dissolve the mixture in water, filter and wash with water, combine the solution and eluent and make up to volume. (2) Take a quantitative amount of the solution after volume adjustment in step (1), adjust the dilution factor so that the absorbance is within the range of linear superposition, record the absorbance, and linearly extrapolate to the unit concentration of 1 g / L to obtain the absorbance index t. (3) Dissolve and wash the filter residue from step (1) with a strong alkaline solution, filter, and dilute the filtrate to a fixed volume. Take a quantitative amount of the diluted liquid and oxidize it under acidic conditions with potassium dichromate. Calculate the amount of potassium dichromate reduced per unit mass of sample, i.e., the total potassium dichromate reduction index n: (4) Weigh out pure lignin sulfonate and repeat steps (1) to (3); weigh out pure humic acid and repeat steps (1) to (3). (5) Calculate the proportions of lignin sulfonate and humic acid according to the following formula: ax + by = t; cx + dy = n; Where x is the mass percentage of lignin sulfonate and y is the mass percentage of humic acid; a and b are the linear superposition coefficients of the absorbance indices of lignin sulfonate and humic acid in the water-soluble fraction, respectively. c and d are the linear superposition coefficients of the potassium dichromate reduction index of the water-insoluble lignin sulfonate and humic acid.

2. The test method according to claim 1, characterized in that, The lignin sulfonate is sodium lignin sulfonate or potassium lignin sulfonate.

3. The test method according to claim 1, characterized in that, This also includes strengthening the mixing of the alkaline solution before dilution.

4. The test method according to claim 1, characterized in that, The time from dilution to completion of absorbance measurement in step (2) is ≤20 min.

5. The test method according to claim 1, characterized in that, The absorbance in step (2) can be linearly superimposed in the range of 0.2 to 0.

8.

6. The test method according to claim 1 or 5, characterized in that, The absorbance in step (2) can be linearly superimposed in the range of 0.2 to 0.

7.

7. The test method according to claim 1 or 3, characterized in that, The strong alkaline solution used is a sodium hydroxide or potassium hydroxide solution with a mass concentration of 0.3 to 1 wt%.

8. The test method according to claim 2, characterized in that, Lignosulfonate is sodium lignosulfonate, with a characteristic absorption peak wavelength of 350 nm.

9. The test method according to claim 1, characterized in that, The potassium dichromate oxidation method in step (3) is as follows: Potassium dichromate and concentrated sulfuric acid are added to the solution to remove insoluble substances, and then Fe is added dropwise. 2+ The remaining potassium dichromate was titrated with the solution.

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