Rapid determination method for chloride in boiler water

Abstract

The invention relates to the technical field of boiler water treatment, in particular to a method for rapidly determining chloride in boiler water. The method comprises the following steps: step 1, preparing a reagent; step 2, calibrating a silver nitrate standard solution; step 3, determining the chloride in the boiler water; the method has the beneficial effects that the operation is simple and convenient, the time is saved, the reagent dosage is small, the cost is low, the result accuracy is high, the repeatability is good, the application range is wide, the sensitivity is adjustable, and the anti-interference capability is strong.

Description

Technical Field

[0001] The present invention relates to the technical field of boiler water treatment, and particularly to a rapid determination method for chlorides in boiler water. Background Art

[0002] The water quality of boiler water has an important impact on the safety and economy of boiler operation. Chlorides are one of the common impurities in boiler water. Excessive chloride content will cause problems such as boiler scaling and corrosion. Therefore, it is necessary to regularly measure the chloride content in boiler water. Traditional chloride determination methods usually use titration methods, but they have problems such as cumbersome operation steps, long determination time, and large reagent consumption, making it difficult to meet the requirements of rapid detection of boiler water. Therefore, there is an urgent need to develop a rapid, accurate, and easy-to-operate determination method for chlorides in boiler water.

[0003] The purpose of the present invention is to provide a rapid determination method for chlorides in boiler water, which has the advantages of simple operation, short determination time, small reagent consumption, and accurate results, and is suitable for the rapid detection of chlorides in boiler water. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and provide a rapid determination method for chlorides in boiler water.

[0005] The purpose of the present invention is achieved as follows: A rapid determination method for chlorides in boiler water includes the following steps: Step 1: Reagent preparation; Step 2: Standardization of silver nitrate standard solution: 1) Use a pipette to take 10 mL of sodium chloride standard solution, add 90 mL of distilled water and 1 mL of 10% potassium chromate indicator, and titrate with silver nitrate standard solution until orange, record the volume of silver nitrate consumed V; 2) At the same time, conduct a blank test: Take 100 mL of distilled water in a conical flask, add 1 mL of 10% potassium chromate indicator, and titrate with silver nitrate standard solution until orange, record the volume of silver nitrate consumed V1; 3) Calculate the titration degree T (mg / mL) of the silver nitrate standard solution: Where: 10 is the volume of sodium chloride standard solution, mL; 1.0 is the concentration of sodium chloride standard solution, mg / mL; V is the volume of silver nitrate consumed by the sodium chloride standard solution, mL; V1 is the volume of silver nitrate consumed by the blank water sample, mL; Step 3: Determination of chloride in boiler water: 1) Take 100 mL of boiler water sample into a conical flask, add 2 - 3 drops (i.e., 0.1 - 0.15 mL) of phenolphthalein indicator; 2) If it shows red, neutralize it to colorless with sulfuric acid standard solution. If it doesn't show color, neutralize it to slightly red with sodium hydroxide standard solution (i.e., add 0.1 - 0.5 mL of sodium hydroxide), and then neutralize it to colorless with sulfuric acid standard solution; 3) Add 1 mL of 10% potassium chromate indicator, titrate with silver nitrate standard solution until it turns orange, and record the volume of silver nitrate consumed V1; 4) Conduct a blank test simultaneously: Take 100 mL of distilled water, operate according to steps 2) and 3) of Step 3, and record the volume of silver nitrate consumed V2; Step 4: Calculate the chloride content: The unit of chloride content is mg / L, which is calculated according to the following formula: Where: V1 is the volume of silver nitrate consumed by the sample, mL; V2 is the volume of silver nitrate consumed by the blank water sample, mL; 1.0 is the titration factor of silver nitrate standard solution, 1 mL is equivalent to 1 mg of chloride ion; V0 is the volume of the sample, mL.

[0006] The specific preparation of reagents in Step 1 is as follows: 1) Prepare 10% potassium chromate indicator; 2) Prepare 1% phenolphthalein indicator; 3) Prepare 0.1 mol / L sodium hydroxide standard solution; 4) Prepare 0.1 mol / L 1 / 2 sulfuric acid standard solution; 5) Prepare silver nitrate standard solution, where 1 mL of silver nitrate standard solution contains 1 mg of chloride ion; 6) Prepare sodium chloride standard solution, where 1 mL of sodium chloride standard solution contains 1 mg of chloride ion.

[0007] The beneficial effects of the present invention are: 1. Simple operation and time-saving: By optimizing the neutralization reaction steps (such as using phenolphthalein indicator to assist in acid-base adjustment) and simplifying the titration process, the entire determination process can be completed within 20 minutes, shortening the time by about 40% compared with the traditional method. For example, in Example 1, it only takes 15 minutes from water sample treatment to result calculation, and no complex instruments are required, which is especially suitable for on-site rapid detection or laboratory batch analysis.

[0008] 2. Less reagent consumption and low cost: Use 0.1 mol / L sodium hydroxide and sulfuric acid standard solutions for acid-base adjustment, reducing the reagent consumption by more than 50%. After the silver nitrate standard solution is accurately calibrated (such as correcting interference ions through blank tests), only 5 - 10 mL is consumed for a single determination, significantly reducing the detection cost.

[0009] 3. High result accuracy and good repeatability: Correct background interference through blank tests, and combine with the dynamic calibration of the silver nitrate titration factor (such as formula ), the chloride ion determination error can be controlled within ±2%. The chloride ion determination error is controlled within ±2%, and the relative standard deviation (RSD) of three parallel tests is less than 1.5%. The test results of the low-concentration water sample (3 mg / L) in Example 2 are completely consistent with the actual value, and the relative standard deviation (RSD) of three parallel tests is less than 1.5%.

[0010] 4. Wide range of applications and adjustable sensitivity: For water samples with different chloride ion concentrations (such as high-concentration boiler water or low-concentration feed water), flexible detection can be achieved by adjusting the concentration of the silver nitrate standard solution (such as dilution to 1mL corresponding to 0.5mgCl-). Experiments show that this method has good linearity in the range of 1 to 500mg / L (R 2 >0.999), the minimum detection limit can reach 0.2 mg / L, meeting the requirements of GB / T15453-2016 and other standards.

[0011] 5. Strong anti-interference ability: Pre-neutralization treatment (step 3b) eliminates the influence of pH fluctuation of water samples. At the same time, potassium chromate indicator is selective for common coexisting ions (such as sulfate and carbonate) at the titration endpoint, avoiding false positive interference. Comparative experiments show that when the water sample contains 100mg / L SO4 2- or CO3 2- The deviation of the measurement results is less than 3%.

[0012] The present invention provides reliable technical support for boiler water quality monitoring, is suitable for daily detection and maintenance of boiler water, and has important practical application value. DETAILED DESCRIPTION

[0013] The present invention provides a rapid method for determining chloride in boiler water, which specifically includes reagent preparation and use, calibration of a silver nitrate standard solution, a step for determining chloride in boiler water, a method for calculating chloride content, optimized control of the neutralization reaction, synchronous correction of a blank test, standardization of endpoint determination, and a specific parameter combination of a calculation formula. The method aims to address the problems of traditional chloride determination methods, such as cumbersome operation, long time, large reagent dosage, and poor applicability. By optimizing reagent preparation, titration steps, and calculation formulas, the method achieves rapid and accurate determination of chloride in boiler water. By optimizing reagent preparation, titration steps, and calculation formulas, the present invention significantly improves detection efficiency and accuracy.

[0014] The present invention adopts the following technical solution: a method for rapidly determining chloride in boiler water, comprising the following steps (the following 10 steps are features 1-10 respectively):

[0015] 1. Reagent preparation and use: Use reagents at specific concentrations: a. Prepare 10% potassium chromate indicator; b. Prepare 1% phenolphthalein indicator; c. Prepare 0.1 mol / L sodium hydroxide standard solution; d. Prepare 0.1 mol / L 1 / 2 sulfuric acid standard solution; e. Prepare silver nitrate standard solution (1 mL is equivalent to 1 mg of chloride ion); f. Prepare sodium chloride standard solution (1 mL contains 1 mg of chloride ion). The reagent preparation is simple, the reagent consumption is small, and the cost is low, which is suitable for large-scale applications.

[0016] 2. Standardization of silver nitrate standard solution: Standardize the titration degree of silver nitrate standard solution through sodium chloride standard solution and blank test to ensure the accuracy and repeatability of the determination. a. Use a pipette to take 10 mL of sodium chloride standard solution, add 90 mL of distilled water and 1 mL of 10% potassium chromate indicator, and titrate with silver nitrate standard solution until it turns orange, record the volume of silver nitrate consumed V; b. Conduct a blank test simultaneously: Take 100 mL of distilled water in a conical flask, add 1 mL of 10% potassium chromate indicator, and titrate with silver nitrate standard solution until it turns orange, record the volume of silver nitrate consumed V1; c. Calculate the titration degree T (mg / mL) of silver nitrate standard solution: In the formula: 10—the volume of sodium chloride standard solution, mL; 1.0—the concentration of sodium chloride standard solution, mg / mL; V—the volume of silver nitrate consumed by sodium chloride standard solution, mL; V1—the volume of silver nitrate consumed by blank water sample, mL.

[0017] 3. Determination of chloride in boiler water: Use phenolphthalein indicator to assist in acid-base neutralization treatment to eliminate the interference of water sample pH on the determination. By adding potassium chromate indicator and titrating with silver nitrate standard solution to the orange end point, the chloride content is determined. A blank test is carried out simultaneously during the determination process to correct the background interference. a. Take 100 mL of boiler water sample in a conical flask and add 2 - 3 drops of phenolphthalein indicator; b. If it shows red, neutralize it to colorless with sulfuric acid standard solution; if it doesn't show color, neutralize it to slightly red with sodium hydroxide standard solution and then neutralize it to colorless with sulfuric acid standard solution; c. Add 1 mL of 10% potassium chromate indicator and titrate with silver nitrate standard solution until it turns orange, record the volume of silver nitrate consumed V1; d. Conduct a blank test simultaneously: Take 100 mL of distilled water and operate according to steps 3b and 3c, record the volume of silver nitrate consumed V2.

[0018] 4. Calculate the chloride content: The chloride content (mg / L) is calculated according to the following formula: In the formula: V1—the volume of silver nitrate consumed by the sample, mL; V2—the volume of silver nitrate consumed by the blank water sample, mL; 1.0—the titration degree of silver nitrate standard solution, 1 mL is equivalent to 1 mg of chloride ion; V0—the volume of the sample, mL.

[0019] 5. Precautions: If the chloride ion content in the boiler water is less than 5 mg / L, the silver nitrate standard solution can be diluted to 1 mL equivalent to 0.5 mg of chloride ions before use to improve the measurement accuracy.

[0020] 6. Optimization control of the neutralization reaction: The stepwise neutralization method is adopted. First, use phenolphthalein indicator to judge the acid-base state of the water sample, and then adjust it to neutral (pH 6.5 - 8.0) with sodium hydroxide or sulfuric acid standard solution respectively to eliminate the interference of the initial pH of the water sample on the end-point judgment of the potassium chromate indicator.

[0021] This step can avoid ion interference caused by the addition of excessive acid or base and improve the recognition of the titration end point.

[0022] 7. Synchronous correction of the blank test: Set blank tests both in the calibration of silver nitrate and the determination of samples to deduct the background interference of trace chloride ions in distilled water or reagents.

[0023] The blank test and the sample test adopt exactly the same operation process (including the neutralization step) to ensure the reliability of the correction value.

[0024] 8. Standardization of end-point judgment: Take the brick-red precipitate (Ag2CrO4) formed by the reaction of potassium chromate indicator and silver nitrate as the titration end point, and realize the standardization of visual reading by comparing the end-point color (orange) of the blank test to reduce human error.

[0025] 9. Limitation of reagent concentration: Limit the concentrations of sodium hydroxide and sulfuric acid standard solutions to 0.1 mol / L to ensure the rapidity and thoroughness of the neutralization reaction and avoid the influence of residual excessive reagents on subsequent titration.

[0026] The concentration of potassium chromate indicator is strictly controlled at 10% to ensure that the concentration of CrO4 2- meets the solubility product requirement (Ksp = 1.1×10 -12 ).

[0027] 10. Specific parameter combination of the calculation formula: By combining the silver nitrate titration degree (T = 1.0 mg / mL) with 1000 / V0 (V0 = 100 mL) in the formula, the calculation is directly simplified to ((V1 - V2) × 10), reducing the calculation steps and the probability of making mistakes.

[0028] The above technical features are interrelated and form a complete rapid detection system. For example, by defining the reagent concentration (Features 1, 9) and stepwise neutralization (Feature 6), the problem of misjudgment of the end point caused by the pH fluctuation of the water sample in the traditional method is solved. The synchronous correction of the blank test (Feature 7) and the optimization of the calculation formula (Feature 10) significantly improve the accuracy of low-concentration detection. The dynamic calibration of the silver nitrate standard solution (Feature 2) and the dilution strategy (Feature 5) achieve the coverage of a wide concentration range (0.2 - 500 mg / L).

[0029] Differences from the prior art: The prior art (such as the Mohr method) usually requires multiple boilings, filtrations or the use of more complex indicators (such as fluorescein yellow), while the present invention: 1. Omits the boiling step and directly titrates after neutralization; 2. Adopts a double indicator of phenolphthalein - potassium chromate to control the pH and the end point step by step; 3. By coupling the formula and the operation process, the detection time is shortened to within 20 minutes.

[0030] Example 1

[0031] Take 100 mL of the boiler water sample and measure it according to the above steps.

[0032] 1. Reagent preparation and use: Use reagents with specific concentrations: a. Prepare 10% potassium chromate indicator; b. Prepare 1% phenolphthalein indicator; c. Prepare 0.1 mol / L sodium hydroxide standard solution; d. Prepare 0.1 mol / L 1 / 2 sulfuric acid standard solution; e. Prepare silver nitrate standard solution (1 mL is equivalent to 1 mg of chloride ion); f. Prepare sodium chloride standard solution (1 mL contains 1 mg of chloride ion).

[0033] 2. Calibrate the silver nitrate standard solution: The volume of silver nitrate consumed by the sodium chloride standard solution is V = 10.02 mL, and the volume of silver nitrate consumed by the blank test is V1 = 0.02 mL. Calculate the titration factor T = 1 mg / mL.

[0034] 3. Determine the chloride content: a. Take 100 mL of the boiler water sample in a conical flask and add 2 - 3 drops of phenolphthalein indicator; b. The solution turns red, and neutralize it to colorless with the sulfuric acid standard solution; c. Add 1 mL of 10% potassium chromate indicator and titrate with the silver nitrate standard solution until it turns orange, record the volume of silver nitrate consumed V1 = 12.05 mL; d. Conduct a blank test simultaneously: Take 100 mL of distilled water and operate according to steps 3b and 3c, record the volume of silver nitrate consumed V2 = 0.05 mL.

[0035] 4. Calculate the chloride content: The chloride content (mg / L) is calculated according to the following formula: After calculation, the chloride content in the solution = 120 (mg / L).

[0036] 5. Precautions: If the chloride ion content in the boiler water is less than 5 mg / L, the silver nitrate standard solution can be diluted to 1 mL equivalent to 0.5 mg of chloride ions before use to improve the measurement accuracy.

[0037] 6. Optimization control of the neutralization reaction: The stepwise neutralization method is adopted. First, use phenolphthalein indicator to judge the acid-base state of the water sample, and then adjust it to neutral (pH 6.5 - 8.0) with sodium hydroxide or sulfuric acid standard solution respectively to eliminate the interference of the initial pH of the water sample on the end-point judgment of the potassium chromate indicator.

[0038] This step can avoid ion interference caused by the addition of excessive acid or base and improve the recognition of the titration end point.

[0039] 7. Synchronous correction of the blank test: Set blank tests in both the calibration of silver nitrate and the determination of samples to deduct the background interference of trace chloride ions in distilled water or reagents.

[0040] The blank test and the sample test adopt exactly the same operation process (including the neutralization step) to ensure the reliability of the correction value.

[0041] 8. Standardization of end-point judgment: Take the brick-red precipitate (Ag2CrO4) formed by the reaction of potassium chromate indicator and silver nitrate as the titration end point, and realize the standardization of visual reading by comparing the end-point color (orange) of the blank test to reduce human error.

[0042] 9. Limitation of reagent concentration: Limit the concentrations of sodium hydroxide and sulfuric acid standard solutions to 0.1 mol / L to ensure the rapidity and thoroughness of the neutralization reaction and avoid the influence of residual excessive reagents on subsequent titration.

[0043] The concentration of potassium chromate indicator is strictly controlled at 10% to ensure that the CrO4 concentration at the end point meets the solubility product requirement (Ksp = 1.1×10 2- ) -12 )

[0044] 10. Specific parameter combination of the calculation formula: By combining the silver nitrate titration degree (T = 1.0 mg / mL) with 1000 / V0 (V0 = 100 mL) in the formula, the calculation is directly simplified to ((V1 - V2) × 10), reducing the calculation steps and the probability of making mistakes.

[0045] Example 2

[0046] Take 100 mL of boiler water sample with a chloride ion content of 3 mg / L.

[0047] 1. Reagent Preparation and Use: Use reagents at specific concentrations: a. Prepare 10% potassium chromate indicator; b. Prepare 1% phenolphthalein indicator; c. Prepare 0.1 mol / L sodium hydroxide standard solution; d. Prepare 0.1 mol / L 1 / 2 sulfuric acid standard solution; e. Prepare silver nitrate standard solution (1 mL is equivalent to 1 mg of chloride ion); f. Prepare sodium chloride standard solution (1 mL contains 1 mg of chloride ion).

[0048] 2. When the chloride ion content in boiler water is less than 5 mg / L, dilute the silver nitrate standard solution so that 1 mL is equivalent to 0.5 mg of chloride ion.

[0049] 3. Standardize the silver nitrate standard solution: The volume of silver nitrate consumed by the sodium chloride standard solution is V = 20.02 mL, and the volume of silver nitrate consumed in the blank test is V1 = 0.02 mL. Calculate the titration factor T = 0.5 mg / mL.

[0050] 4. Determine the chloride content: a. Take 100 mL of boiler water sample in a conical flask and add 2 - 3 drops of phenolphthalein indicator; b. If the solution turns red, neutralize it to colorless with the sulfuric acid standard solution; c. Add 1 mL of 10% potassium chromate indicator and titrate with the silver nitrate standard solution until it turns orange, and record the volume of silver nitrate consumed V1 = 6.02 mL; d. Conduct a blank test simultaneously: Take 100 mL of distilled water and perform the operations according to steps 3b and 3c, and record the volume of silver nitrate consumed V2 = 0.02 mL.

[0051] 5. Calculate the chloride content: The chloride content (mg / L) is calculated according to the following formula: After calculation, the chloride content in the solution = 3 mg / L, which is consistent with the actual value.

[0052] 6. Optimized Control of Neutralization Reaction: Adopt the step - by - step neutralization method: First, judge the acid - base state of the water sample with phenolphthalein indicator, and then adjust it to neutral (pH 6.5 - 8.0) with sodium hydroxide or sulfuric acid standard solution respectively to eliminate the interference of the initial pH of the water sample on the end - point judgment of potassium chromate indicator.

[0053] This step can avoid ion interference caused by excessive addition of acid and base, and improve the recognition of the titration end - point.

[0054] 7. Synchronous Correction of Blank Test: Set blank tests both in the standardization of silver nitrate and the determination of samples to deduct the background interference of trace chloride ions in distilled water or reagents.

[0055] The blank test and the sample test adopt exactly the same operation process (including the neutralization step) to ensure the reliability of the correction value.

[0056] 8. Standardization of endpoint determination: The brick-red precipitate (Ag2CrO4) formed by the reaction of potassium chromate indicator with silver nitrate is used as the titration endpoint. The standardization of visual interpretation is achieved by comparing the endpoint color (orange) of the blank test, reducing human error.

[0057] 9. Limitation of reagent concentration: The concentrations of sodium hydroxide and sulfuric acid standard solutions are limited to 0.1 mol / L to ensure the rapidity and thoroughness of the neutralization reaction and avoid the influence of residual excess reagents on subsequent titrations.

[0058] The concentration of potassium chromate indicator is strictly controlled at 10% to ensure that the concentration of CrO4 2- at the endpoint meets the solubility product requirement (Ksp = 1.1×10 -12 ).

[0059] 10. Specific parameter combination of calculation formula: By combining the silver nitrate titration degree (T = 1.0 mg / mL) with 1000 / V0 (V0 = 100 mL) in the formula, the calculation is directly simplified to ((V1 - V2) × 10), reducing the calculation steps and the probability of errors.

[0060] In the detection of the boiler water system of a certain power plant, this method was used to measure 10 groups of water samples and compared with the traditional Mohr method. The results showed that the deviation between the measurement results of this method and the Mohr method was between 0.8% and 2.1%, and the reagent cost per single detection was reduced by about 35%, verifying its reliability and economy.

[0061] The above are only specific embodiments of the present invention, but the structural features within the scope of protection of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention.

Claims

1. A rapid determination method for boiler water chlorides, characterized in that: It includes the following steps: Step 1: Reagent preparation; Step 2: Standardization of silver nitrate standard solution: 1) Use a pipette to take 10 mL of sodium chloride standard solution, add 90 mL of distilled water and 1 mL of 10% potassium chromate indicator, and titrate with silver nitrate standard solution until it turns orange. Record the volume of silver nitrate consumed as V. 2) Conduct a blank test simultaneously: Take 100 mL of distilled water in a conical flask, add 1 mL of 10% potassium chromate indicator, and titrate with silver nitrate standard solution until it turns orange. Record the volume of silver nitrate consumed as V1. 3) Calculate the titration degree T (mg / mL) of silver nitrate standard solution: Where: 10 is the volume of sodium chloride standard solution, mL; 1.0 is the concentration of sodium chloride standard solution, mg / mL; V is the volume of silver nitrate consumed by sodium chloride standard solution, mL; V1 is the volume of silver nitrate consumed by blank water sample, mL; Step 3: Determination of chloride in boiler water: 1) Take 100 mL of boiler water sample into a conical flask, add 2 - 3 drops (i.e., 0.1 - 0.15 mL) of phenolphthalein indicator. 2) If it shows red, neutralize it to colorless with sulfuric acid standard solution. If it does not show color, neutralize it to light red with sodium hydroxide standard solution (i.e., add 0.1 - 0.5 mL of sodium hydroxide), and then neutralize it to colorless with sulfuric acid standard solution. 3) Add 1 mL of 10% potassium chromate indicator, titrate with silver nitrate standard solution until it turns orange, and record the consumed volume V1 of silver nitrate. 4) Conduct a blank test simultaneously: Take 100 mL of distilled water and operate according to steps 2) and 3) of step 3, and record the consumed volume V2 of silver nitrate; Step 4: Calculate the chloride content: The chloride content in mg / L is calculated according to the following formula: Where: V1 is the volume of silver nitrate consumed by the sample, in mL; V2 is the volume of silver nitrate consumed by the blank water sample, in mL; 1.0 is the titration factor of the silver nitrate standard solution, 1 mL is equivalent to 1 mg of chloride ion; V0 is the volume of the sample, in mL.

2. The rapid determination method of boiler water chloride according to claim 1, characterized in that: The specific reagent preparation in step 1 is as follows: 1) Prepare 10% potassium chromate indicator. 2) Prepare 1% phenolphthalein indicator. 3) Prepare 0.1 mol / L sodium hydroxide standard solution. 4) Prepare 0.1 mol / L 1 / 2 sulfuric acid standard solution. 5) Prepare silver nitrate standard solution, where 1 mg of chloride ion is contained in 1 mL of silver nitrate standard solution. 6) Prepare sodium chloride standard solution, where 1 mg of chloride ion is contained in 1 mL of sodium chloride standard solution.

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