Method for the analysis of potassium hydroxide in a hydrazine boronic acid system

Abstract

The application belongs to the field of chemical detection and analysis, and particularly relates to a method for analyzing potassium hydroxide in a hydrazine boronic acid system, comprising the following steps: step 1, adding hydrogen peroxide to a sample for sample pretreatment; step 2, adding bromothymol blue indicator to the pretreated sample, titrating the pretreated sample with hydrochloric acid, and recording the volume of hydrochloric acid consumed by the sample; step 3, performing a blank test, and recording the volume of hydrochloric acid consumed by the blank test; step 4, calculating the concentration of KOH in the sample, denoted as a measured concentration; and step 5, calculating the difference of the measured concentration, and determining the concentration of KOH in the sample. The method can solve the interference of a weak acid and weak base system on the titration of potassium hydroxide, and can quickly and accurately analyze the concentration of potassium hydroxide in a potassium hydrazine boronic acid alkali solution by adding hydrogen peroxide for pretreatment and selecting bromothymol blue as an indicator.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical detection and analysis, and particularly relates to a method for analyzing potassium hydroxide in a hydrazine borate system. BACKGROUND

[0002] The chemical reagent tank of a containment spray system of a nuclear power plant contains a mixed solution of hydrazine, boric acid and potassium hydroxide. The function of the solution is to inject potassium borate solution into the containment under the design basis accident of one-loop coolant leakage of the unit, so as to reduce the radioactivity level in the containment and long-term inhibit the radioisotope of iodine in the containment pit. Accurate measurement of the concentration of KOH in the reagent tank is a prerequisite for guiding the system to add chemicals and controlling the chemical indicators of the system. Therefore, it is particularly necessary to establish an analysis method for KOH in the system.

[0003] According to the current domestic analysis method of KOH, GB / T 1919-2014 Industrial Potassium Hydroxide has two analysis methods. One is that under weak acid conditions, potassium ions react with sodium tetraphenylborate to generate tetraphenyl potassium borate precipitate, and then filtering, drying and weighing are performed. The other is that the acid-base titration method is used for analysis. For the mixed solution of hydrazine, boric acid and potassium base used in the nuclear power plant (the components are shown in Table 1), because the sample contains radioactivity, the tedious precipitation method is not suitable for analysis.

[0004] Table 1 Chemical reagent components and concentrations in the containment spray system

[0005] Analysis project name Diagnosis value Boric acid (g / L) 39.5-44.5 Potassium (g / L) 100-150 Hydrazine (g / L) 10-15

[0006] The analysis steps of the acid-base titration analysis method are simple and clear, but because hydrazine and boric acid are weak alkali and weak acid, a buffer system is formed, and the acid-base titration of potassium hydroxide in the system is easily affected. It is proved through tests that the ordinary acid-base titration method will cause two problems: 1) the titration result is more than 6% higher, and the relative error is large; 2) there is no obvious breakthrough point in the titration end point, and the color change is not obvious. The pH-volume V and ERC (first derivative of pH)-volume V curves of the titration using the potential titration auxiliary titration are shown in Figure 1 .

[0007] Therefore, it is urgent to seek an acid-base titration method suitable for KOH in the weak acid-base system of the nuclear power plant. SUMMARY

[0008] The purpose of the present application is to provide a method for analyzing potassium hydroxide in a hydrazine borate system, which can solve the interference of the weak acid-weak base system on the titration of potassium hydroxide, and can quickly and accurately analyze the concentration of potassium hydroxide in the hydrazine boric acid potassium base solution by adding hydrogen peroxide for pretreatment and selecting bromothymol blue as an indicator.

[0009] The technical scheme for achieving the object of the present application is as follows:

[0010] A method for analyzing potassium hydroxide in a hydrazine boronic acid system, the method comprising the following steps:

[0011] Step 1, adding hydrogen peroxide to the sample for sample pretreatment;

[0012] Step 2, adding bromothymol blue indicator to the pretreated sample, titrating the treated sample with hydrochloric acid, and recording the volume of hydrochloric acid consumed by the sample;

[0013] Step 3, performing a blank test, and recording the volume of hydrochloric acid consumed by the blank test;

[0014] Step 4, calculating the concentration of KOH in the sample, denoted as the measured concentration;

[0015] Step 5, calculating the difference of the measured concentration result, and determining the concentration of KOH in the sample.

[0016] The step 1 is specifically as follows: transferring the sample into a conical flask with a stopper, diluting the sample with water; then adding hydrogen peroxide solution, adding copper sulfate solution dropwise, covering the stopper, shaking uniformly, and standing for 5-10 minutes.

[0017] The step 2 is specifically as follows: adding 2 drops of bromothymol blue in the conical flask, adding hydrochloric acid solution in the acid burette, using hydrochloric acid titration, and recording the volume of hydrochloric acid consumed for titrating the solution in the conical flask from blue to yellow.

[0018] The step 3 is specifically as follows: adding water with the same volume as step 1, hydrogen peroxide solution with the same concentration and volume as step 1, and copper sulfate solution into a conical flask with a stopper, covering the stopper, shaking uniformly, and standing for 5-10 minutes;

[0019] adding 2 drops of bromothymol blue in the conical flask, adding hydrochloric acid solution with the same concentration as step 2 in the acid burette, using hydrochloric acid titration, and recording the volume of hydrochloric acid consumed for titrating the blank test solution from blue to yellow.

[0020] The calculation formula of the concentration of KOH in the sample in the step 4 is as follows:

[0021] ρ=C1*(V1-V0)*M KOH / V KOH

[0022] In the formula:

[0023] ρ-KOH concentration, unit: g / L;

[0024] C1: hydrochloric acid concentration, mol / L;

[0025] V1: volume of hydrochloric acid consumed, mL;

[0026] V0: volume of hydrochloric acid consumed in the blank test, mL;

[0027] M KOH : molar mass of KOH, taking 56.1 g / mol;

[0028] V KOH : volume of the sample for titration, mL.

[0029] The step 5 is specifically: taking the arithmetic mean of the concentration of the step 4 parallel determination as the determination result, and the absolute difference of the two parallel determination results of the sample should not be greater than 3 g / L; if the difference requirement is not met, start step 1 again.

[0030] The concentration of the hydrogen peroxide solution in the step 1 and step 3 is 26 g / L, and the concentration of the copper sulfate solution is 5 g / L.

[0031] The concentration of the hydrochloric acid solution in the step 1 and step 3 is 0.5 mol / L.

[0032] The volume ratio of water to sample in the step 1 is: water: sample = 30:1-100:1.

[0033] The volume ratio of the hydrogen peroxide solution to the sample in the step 1 is: hydrogen peroxide solution: sample = 1:1-2:1.

[0034] The beneficial technical effect of the present application is that:

[0035] 1. The analysis method of potassium hydroxide in a hydrazine boric acid system provided by the present application fully analyzes the interference reasons of potassium hydroxide measurement in a hydrazine, boric acid and potassium base solution, and for the first time finds that the key influencing factor affecting the measurement of KOH concentration in the hydrazine boric acid system is the concentration of hydrazine, and finds a method to eliminate the interference: by adding hydrogen peroxide to react with hydrazine for pretreatment to remove the influence of hydrazine, and then performing acid-base titration, so as to achieve the purpose of quickly and accurately measuring the concentration of KOH.

[0036] 2. The analysis method of potassium hydroxide in a hydrazine boric acid system provided by the present application uses a potential titrator titration curve to assist manual titration for determination.

[0037] 3. The analysis method of potassium hydroxide in a hydrazine boric acid system provided by the present application uses bromothymol blue as an indicator, the titration color change is obvious, and the operation convenience is improved. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a pH-ERC / V graph of direct acid-base titration in the prior art;

[0039] Figure 2The pH-ERC / V graph of the pre-treatment acid-base titration for the analysis method of potassium hydroxide in a hydrazine boronic acid system according to the present application. DETAILED DESCRIPTION

[0040] The present application is further described in detail below with reference to the accompanying drawings and examples.

[0041] The analysis method of potassium hydroxide in a hydrazine boronic acid system according to the present application is to add hydrogen peroxide solution to the sample to be measured, use copper sulfate solution as catalyst for pre-treatment, and use bromothymol blue as indicator to titrate the sample from blue to yellow with hydrochloric acid. The working principle involved in the analysis method is specifically as follows:

[0042] 1. Influence of hydrazine and boric acid on potassium hydroxide titration

[0043] Hydrazine reacts with hydrochloric acid to generate monohydrazine dihydrochloride and dihydrazine dihydrochloride, which increases the consumption of hydrochloric acid during the titration of KOH; boric acid is weakly acidic and hydrolyzes to generate B(OH)4 - +H + , which may reduce the consumption of hydrochloric acid. Therefore, the influence of the mixed solution of hydrazine and boric acid on acid-base titration is a complex process.

[0044] In order to determine the influencing factors, a single variable control method is needed for testing.

[0045] The following tests are carried out with boric acid and hydrazine as single variables, respectively:

[0046] 1) In the absence of boric acid, prepare pure hydrazine solution and hydrazine + KOH solution, and titrate with hydrochloric acid using phenolphthalein as indicator.

[0047] 2) In the absence of hydrazine, prepare pure boric acid solution and boric acid + KOH solution, and titrate with hydrochloric acid using phenolphthalein as indicator.

[0048] 1.1. Influence of hydrazine

[0049] Prepare the drug concentrations shown in Table 2, and then perform titration.

[0050] Table 2 Titration analysis of hydrazine + KOH simulated samples

[0051]

[0052] From the test results, it can be seen that the result of using hydrochloric acid to titrate and measure KOH in the hydrazine + KOH simulated sample is about 6%-7% higher, indicating that hydrazine causes the result of KOH titration to be higher.

[0053] 1.2. Influence of boric acid

[0054] Three samples without hydrazine in Table 3 were prepared, and titrated with hydrochloric acid using phenolphthalein as indicator. The titration results are as follows:

[0055] Table 3 Preparation and titration of borate + KOH simulation samples (without hydrazine)

[0056]

[0057] The manual titration of borate + KOH simulation samples had the problem of unclear end point color change when using phenolphthalein as indicator, and the titration results were about 1% lower than the theoretical value.

[0058] The test results show that borate has little effect on the titration results of KOH, and the main effect is on the pH of the titration end point. Since the pH jump point is not consistent with the color change range of the indicator in theory, the selection of the indicator can be optimized.

[0059] 2. Remove the influencing factors

[0060] Based on the analysis of the above influencing factors, hydrazine affects the titration results, and borate affects the color change of the titration end point, so the new scheme optimizes these two aspects.

[0061] 2.1 Eliminate the influence of hydrazine

[0062] Based on the reaction principle of hydrazine and hydrogen peroxide, hydrazine is removed.

[0063] N2H4 + 2H2O2 → N2↑ + 4H2O

[0064] The reaction uses copper sulfate solution as catalyst, and the amount of hydrogen peroxide added is twice the amount of hydrazine. The reaction time and the concentration of hydrazine are shown in Table 4:

[0065] Table 4 Reaction time of hydrazine with copper sulfate

[0066]

[0067] Considering the actual production analysis, the reaction time of 5-10 minutes is finally selected.

[0068] 2.2 Eliminate the effect of borate

[0069] According to the pH value of the diluted sample of pure borate with a specific concentration (for example, 1 mL of 42 g / L borate sample is diluted to 100 mL, and the end point pH is 5.8), bromothymol blue is selected, and its color change range is 6.0 (yellow) - 7.6 (blue).

[0070] 3. Measurement of KOH concentration in hydrazine borate system

[0071] The main content of the measurement technology is: adding hydrogen peroxide solution in the sample to be measured, using copper sulfate solution as catalyst, reacting for 5-10 minutes; using bromothymol blue as indicator, using hydrochloric acid to titrate the sample from blue to yellow.

[0072] The application provides a method for analyzing potassium hydroxide in a hydrazine boronic acid system, and specifically comprises the following steps:

[0073] Step 1, adding hydrogen peroxide to the sample for sample pretreatment

[0074] The sample is taken into a conical flask with a plug, diluted with water, and the volume ratio of water to sample is 30:1-100:1; hydrogen peroxide solution with a concentration of 26 g / L is added, and the volume ratio of hydrogen peroxide solution to sample is 1:1-2:1; 1-2 drops of copper sulfate solution with a concentration of 5 g / L are added dropwise, the plug is covered, and after shaking, the sample is left to stand for 5-10 minutes.

[0075] Step 2, adding bromothymol blue indicator to the pretreated sample, using hydrochloric acid to titrate the pretreated sample, and recording the volume of hydrochloric acid consumed by the sample

[0076] 2 drops of bromothymol blue are added to the conical flask, 0.5 mol / L hydrochloric acid solution is added to the acid burette, hydrochloric acid is used for titration, and the volume of hydrochloric acid consumed for titrating the solution in the conical flask from blue to yellow is recorded.

[0077] Step 3, performing a blank test, and recording the volume of hydrochloric acid consumed by the blank test

[0078] The same volume of water, hydrogen peroxide solution with a concentration of 26 g / L and copper sulfate solution with a concentration of 5 g / L as in step 1 are added to the conical flask with a plug, the plug is covered, and after shaking, the sample is left to stand for 5-10 minutes.

[0079] 2 drops of bromothymol blue indicator are added to the conical flask with a plug, 0.5 mol / L hydrochloric acid solution is added to the acid burette, hydrochloric acid is used for titration, and the volume of hydrochloric acid consumed for titrating the blank test solution from blue to yellow is recorded.

[0080] Step 4, calculating the concentration of KOH in the sample, denoted as the measured concentration

[0081] The concentration of KOH in the sample is denoted as ρ, and the value is expressed in grams per liter (g / L), and is calculated according to formula (1):

[0082] ρ=C1*(V1-V0)*M KOH / V KOH (1)

[0083] In the formula:

[0084] ρ-KOH concentration, unit: g / L;

[0085] C1: hydrochloric acid concentration, mol / L;

[0086] V1: volume of consumed hydrochloric acid, mL;

[0087] V0: volume of consumed hydrochloric acid in blank test, mL;

[0088] M KOH : molar mass of KOH, taking 56.1 g / mol;

[0089] V KOH : volume of titrated sample, mL.

[0090] Step 5, calculate the difference of the results of the concentration determination, determine the concentration of KOH in the sample

[0091] Take the arithmetic mean of the parallel determination of the concentration in step 4 as the determination result, the absolute difference of the two parallel determination results of the sample should not be greater than 3 g / L; if it does not meet the difference requirement, start step 1 again.

[0092] Example 1

[0093] Reagents and materials: The reagents used in this method, unless otherwise specified, only use analytical pure reagents.

[0094] Water, GB / T 6682, level 3.

[0095] Hydrogen peroxide solution: 26 g / L. Weigh 80 mL of 30% hydrogen peroxide solution into a 1 L volumetric flask, and dilute to the calibration line with water. This solution contains 26 mg of hydrogen peroxide per mL.

[0096] Copper sulfate solution: 5 g / L. Weigh 1 g of copper sulfate, dissolve in water, transfer to a 200 mL volumetric flask, and dilute to the calibration line with water. This solution contains 5 mg of copper sulfate per mL.

[0097] Bromothymol blue indicator: weigh 0.1 g of bromothymol blue, add to 100 mL of 20% alcohol solution, and dissolve to prepare.

[0098] Hydrochloric acid solution: 0.5 mol / L.

[0099] Instrument equipment: general laboratory instruments and the following instruments.

[0100] Titration table.

[0101] Pipette: 1-5 mL.

[0102] Volumetric flask: 200 mL, 1000 mL.

[0103] Balance: accuracy: ±0.0001 g.

[0104] Acid burette: 25 mL.

[0105] Erlenmeyer flask: 500 mL

[0106] The analysis method specifically comprises the following steps:

[0107] Step 1, adding hydrogen peroxide to the sample for sample pretreatment

[0108] Transfer 2 mL of the sample into a 250 mL stoppered Erlenmeyer flask, add 100 mL of water; then add 2 mL of hydrogen peroxide solution, drop 1-2 drops of copper sulfate solution, cover the stopper, shake well and stand for 5 minutes.

[0109] Step 2, adding bromothymol blue indicator to the pretreated sample, using hydrochloric acid to titrate the treated sample, and recording the volume of hydrochloric acid consumed by the sample

[0110] Prepare the hydrochloric acid solution in the acid burette. Add 2 drops of bromothymol blue in the Erlenmeyer flask. Titrate with hydrochloric acid and record the volume of hydrochloric acid consumed to titrate the solution in the Erlenmeyer flask from blue to yellow.

[0111] Step 3, perform a blank test and record the volume of hydrochloric acid consumed by the blank test

[0112] In a 250 mL stoppered Erlenmeyer flask, add 100 mL of water; then add 2 mL of hydrogen peroxide solution, drop 1-2 drops of copper sulfate solution, cover the stopper, shake well and stand for 5 minutes.

[0113] Prepare the hydrochloric acid solution in the acid burette. Add 2 drops of bromothymol blue in the Erlenmeyer flask. Titrate with hydrochloric acid and record the volume of hydrochloric acid consumed to titrate the solution in the Erlenmeyer flask from blue to yellow.

[0114] Step 4, calculate the concentration of KOH in the sample

[0115] The concentration of KOH in the sample is denoted by p, and the value is expressed in grams per liter (g / L), calculated according to formula (1):

[0116] p = C1 * (V1 - V0) * M KOH / V KOH (1)

[0117] In the formula:

[0118] p - KOH concentration, unit: g / L;

[0119] C1: concentration of hydrochloric acid, mol / L;

[0120] V1: volume of hydrochloric acid consumed, mL;

[0121] V0: volume of hydrochloric acid consumed in blank test, mL;

[0122] M KOH : molar mass of KOH, 56.1 g / mol;

[0123] V KOH : volume of sample titrated, mL.

[0124] Step 5, calculate the difference of the results of the determination of the concentration, and determine the concentration of KOH in the sample

[0125] Take the arithmetic mean of the parallel determination of the concentration in step 4 as the determination result, and the absolute difference of the two parallel determination results of the sample should not be greater than 3 g / L; if the difference requirement is not met, start step 1 again.

[0126] According to the specific operation steps of Example 1, the following three samples in Table 5 are pretreated and titrated, and the results are as follows:

[0127] Table 5 Titration results of KOH after pretreatment

[0128]

[0129] From the above experimental results, it can be seen that after using hydrogen peroxide for pretreatment to remove hydrazine and using bromothymol blue as an indicator, the accuracy of the titration of KOH in the ammonia borate system is significantly improved, and the absolute value of the relative error is reduced from 6%-7% before pretreatment to less than 1%; using bromothymol blue as an indicator has a clear breakthrough point, and has more obvious advantages in operation than using phenolphthalein as an indicator. The titration curve of sample 7 using a potentiometric titrator is shown in Figure 2 , and compared with Figure 1 , the pH breakthrough point is more obvious.

[0130] The analysis method of the present application has been popularized in Tianwan Nuclear Power Unit 1-4, effectively guiding the preparation and measurement of chemical agents in the containment spray system, and contributing to the effective operation of the safety system of the nuclear power plant.

[0131] The above has made a detailed description of the present application in combination with the drawings and examples, but the present application is not limited to the above examples, and various changes can be made within the knowledge possessed by those skilled in the art without departing from the purpose of the present application. The contents not described in detail in the present application can adopt the existing technology.

Claims

1. A method for the analysis of potassium hydroxide in a hydrazine boronic acid system, characterized in that, The method comprises the following steps: Step 1, adding hydrogen peroxide to the sample for sample pretreatment; Step 2, adding bromothymol blue indicator to the pretreated sample, titrating the treated sample with hydrochloric acid, and recording the volume of hydrochloric acid consumed by the sample; Step 3, performing a blank test, and recording the volume of hydrochloric acid consumed by the blank test; Step 4, calculating the concentration of KOH in the sample, denoted as the measured concentration; Step 5, calculating the difference of the measured concentration, and determining the concentration of KOH in the sample; The step 1 is specifically: taking the sample into a conical flask with a stopper, diluting the sample with water; then adding hydrogen peroxide solution, adding copper sulfate solution dropwise, covering the stopper, shaking uniformly, and standing for 5-10 minutes; The step 2 is specifically: adding 2 drops of bromothymol blue in the conical flask, adding hydrochloric acid solution in the acid burette, titrating with hydrochloric acid, and recording the volume of hydrochloric acid consumed for titrating the solution in the conical flask from blue to yellow; The step 3 is specifically: adding water with the same volume as step 1, hydrogen peroxide solution with the same concentration and volume as step 1, and copper sulfate solution into a conical flask with a stopper, covering the stopper, shaking uniformly, and standing for 5-10 minutes; 2 drops of bromothymol blue are added in the conical flask, and hydrochloric acid solution with the same concentration as step 2 is added in the acid burette, and hydrochloric acid is titrated, and the volume of hydrochloric acid consumed for titrating the blank test solution from blue to yellow is recorded.

2. The method for the analysis of potassium hydroxide in a hydrazine boronic acid system according to claim 1, characterized in that, The calculation formula of the concentration of KOH in the sample in step 4 is: p = C1 * (V1 - V0) * M KOH / V KOH In the formula: ρ-KOH concentration, unit: g / L; C1: hydrochloric acid concentration, mol / L; V1: volume of hydrochloric acid consumed, mL; V0: volume of hydrochloric acid consumed by the blank test, mL; M KOH : molar mass of KOH, taken as 56.1 g / mol; V KOH : Volume of sample titrated, mL.

3. A method for the analysis of potassium hydroxide in a hydrazine boronic acid system according to claim 2, characterized in that, The step 5 is specifically: taking the arithmetic mean of the parallel measured concentrations in step 4 as the measured result, and the absolute difference of the two parallel measured results of the sample should not be greater than 3 g / L; if the difference requirement is not met, step 1 is restarted.

4. The method of claim 1, wherein the potassium hydroxide is analyzed in a hydrazine boronic acid system. The concentration of hydrogen peroxide solution in steps 1 and 3 is 26 g / L, and the concentration of copper sulfate solution is 5 g / L.

5. The method of claim 1, wherein the method is for analyzing potassium hydroxide in a hydrazine boronic acid system. The concentration of hydrochloric acid solution in steps 1 and 3 is 0.5 mol / L.

6. The method of claim 1, wherein the potassium hydroxide is analyzed in a hydrazine boronic acid system. The volume ratio of water to sample in step 1 is: water: sample = 30:1-100:

1.

7. The method of claim 4, wherein the potassium hydroxide is analyzed in a hydrazine boronic acid system. The volume ratio of hydrogen peroxide solution to sample in step 1 is: hydrogen peroxide solution: sample = 1:1-2:1.

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