Method for detecting content of chloride ion in urea hydrolysis effluent

Abstract

This invention belongs to the field of urea hydrolysis technology, specifically relating to a method for detecting chloride ion content in urea hydrolyzer wastewater. This invention employs a dual method of removing organic matter from the water sample through organic filter paper filtration combined with digestion. It uses neutralization to remove hydroxide ions and heating and boiling to thoroughly remove ammonium ions. Furthermore, it uses sodium bicarbonate, a strong base and weak acid salt, to adjust the pH of the system, avoiding the introduction of large amounts of hydroxide ions during pH adjustment, reducing side reactions with the titration standard solution, and minimizing interference with indicator color development and titration endpoint determination. This invention effectively avoids multiple interfering factors such as mechanical impurities, ammonium ions, hydroxide ions, and organic matter, significantly improving the accuracy and reliability of chloride ion content determination results in urea hydrolyzer wastewater.

Description

Technical Field

[0001] This invention belongs to the field of urea hydrolysis, and in particular relates to a method for detecting the chloride ion content in the sludge discharged from a urea hydrolyzer. Background Technology

[0002] Currently, most large and medium-sized thermal power units in China have completed denitrification and ultra-low emission retrofitting, and denitrification reducing agents are widely used, mainly in three forms: liquid ammonia, ammonia water, and urea. With the increasing safety awareness of the public and enterprises in China, coupled with frequent accidents involving the transportation, storage, and use of hazardous chemicals, urea hydrolysis to ammonia production technology has gradually become the mainstream technology for power plants choosing denitrification reducing agent preparation systems due to its advantages: no need for loading, unloading, transportation, or storage of hazardous chemicals; small footprint; and safe, stable, and reliable operation.

[0003] However, in actual operation, sodium chloride crystals will appear on the surface of the urea hydrolysis unit. This not only affects the heat exchange efficiency of the hydrolyzer and the normal operation of the denitrification system, but more seriously, a large amount of chloride ions will cause intergranular corrosion, stress corrosion cracking, and uniform corrosion of the stainless steel hydrolyzer, which may even lead to the shutdown of the denitrification system. Therefore, it is essential to monitor and test the conductivity and chloride ion content of the hydrolyzer unit's wastewater. When the conductivity and chloride ion content are high, wastewater discharge should be carried out.

[0004] Currently, there are two main methods for determining chloride ion content in power plants: ion chromatography and titration. When using ion chromatography to detect chloride ion content in urea hydrolysate, organic matter in the solution can contaminate the chromatographic column, and excessive dilution of the solution before entering the ion exchange column can lead to significant measurement errors. In contrast, titration is used when NH4+ is present in the solution. + OH - Large quantities of these exist, and they will all be associated with Ag. + The reaction produces a silver-ammonium complex, which requires more silver nitrate standard titration solution, resulting in an overestimation of the measurement result and introducing a certain degree of error.

[0005] A Chinese patent, CN115684466A, published on February 3, 2023, discloses an invention patent for "a method for detecting chloride ion content in wastewater from a urea hydrolyzer". The invention discloses a method for detecting the chloride ion content in the wastewater from a urea hydrolyzer, comprising the following steps: (1) Take a certain amount of wastewater sample from the urea hydrolyzer, filter it with medium-speed qualitative filter paper to remove impurities, and collect the filtrate as the filtrate; (2) After the color-changing cation exchange resin is treated with sulfuric acid, put it into a funnel with filter paper, take a certain amount of the filtrate, remove the cations after the color-changing cation exchange and rinsing, collect the filtrate and dilute it in a volumetric flask as solution B for later use; (3) Take a certain volume of the neutralized filtrate in a conical flask, add phenolphthalein indicator to the conical flask, place it under a white background and adjust the pH value of the solution until the solution becomes colorless; (4) Add potassium chromate indicator to the neutralized filtrate, titrate it with silver nitrate standard solution under a white background until a brick red color just appears, and perform a blank test at the same time; (5) Calculate the chloride ion content in the wastewater from the urea hydrolyzer. However, this patent only utilizes resin to remove ammonium ions, without effectively removing the influence of organic matter. This method has significant shortcomings: First, the lack of a dedicated process for removing organic matter means that residual organic matter can interfere with subsequent titration processes, reducing detection accuracy. Second, relying solely on conventional acid-base neutralization to adjust the system's pH easily introduces hydroxide ions, which can react with silver nitrate standard solution, interfering with indicator color development and accurate determination of the titration endpoint. Third, the limited removal of ammonium ions through cation exchange resin results in limited removal effectiveness, and residual ammonium ions further exacerbate interference with titration color development, leading to weak anti-interference capabilities and poor accuracy. Therefore, developing a novel, highly accurate, and interference-resistant method for detecting chloride ion content in urea hydrolyzer wastewater is of essential practical significance. Summary of the Invention

[0006] This invention provides a method for detecting the chloride ion content in the sludge discharged from a urea hydrolyzer. The method employs a dual approach of organic filter paper and digestion to remove organic matter, a neutralization method to remove hydroxide ions, and a heating and boiling method to remove ammonium ions. Finally, the pH value is adjusted with a strong base-weak acid salt to reduce the introduction of hydroxide ions and their reaction with the titration standard solution, further reducing the influence of the indicator color development.

[0007] On one hand, the present invention provides a method for detecting the chloride ion content in the sludge discharged from a urea hydrolyzer, the detection method comprising: Step 1: Remove mechanical impurities and organic matter from the urea hydrolyzer effluent by filtration to obtain filtrate; Step 2: Add nitric acid to the filtrate to neutralize the OH- in the filtrate. - The neutralized filtrate was obtained. Step 3: Remove NH3 from the neutralized filtrate by heating to obtain a heated filtrate; Step 4: Add H2O2 to the filtrate after heat treatment to remove residual organic matter, thus obtaining a filtrate with organic matter removed; Step 5: First, add an acid-base indicator to the filtrate after removing organic matter, then add a strong base-weak acid salt to adjust the pH value of the filtrate after removing organic matter. Finally, add nitric acid to the filtrate after removing organic matter to obtain the test solution. Step 6: Detect the chloride ion content in the test solution using the silver nitrate molar method.

[0008] Furthermore, in step 1, the filtration is performed using organic filter paper.

[0009] Furthermore, the organic filter paper has a filtration accuracy of 0.45 μm.

[0010] Furthermore, in step 2, the addition of nitric acid is stopped when the pH of the filtrate is 1-2.

[0011] Furthermore, in step 3, the heating is to heat the neutralized filtrate to boiling.

[0012] Furthermore, in step 3, the heating involves heating the neutralized filtrate to boiling and maintaining it for 10-12 minutes.

[0013] Furthermore, in step 4, the amount of H2O2 added to the heat-treated filtrate is 30% of the total mass of the heat-treated filtrate.

[0014] Furthermore, in step 5, the strong base-weak acid salt includes sodium bicarbonate; Furthermore, sodium bicarbonate is added to the filtrate from which organic matter has been removed until the filtrate changes from colorless to light red.

[0015] Further, in step 5, nitric acid is added to the filtrate from which the organic matter has been removed until the filtrate changes from light red to colorless.

[0016] Further, in step 6, the step of detecting the chloride ion content in the test solution by the silver nitrate molar method includes: adding 1.0 mL of potassium chromate indicator to the test solution, and titrating with 0.05 mol / L silver nitrate standard solution against a white background until a brick red color just appears.

[0017] Further, in step 6, the detection formula for the silver nitrate molar method is: C1 = C2 × (V1 - V0) × M × 1000 / V; In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution; V: Volume of hydrolyzed wastewater; M: Molar mass of chlorine.

[0018] On the other hand, the present invention provides a kit for measuring chloride ion content in urea hydrolyzer sludge, the kit comprising organic filter paper, nitric acid, pH test paper, H2O2, strong base-weak acid salt, phenolphthalein indicator, potassium chromate indicator, and silver nitrate standard solution.

[0019] On the other hand, the present invention provides the application of the above-mentioned detection method or the above-mentioned kit in detecting the chloride ion content in the urea hydrolyzer sludge.

[0020] The technical solution of this invention has the following advantages: (1) The method for detecting chloride ion content in urea hydrolyzer sludge provided by the present invention firstly filters the water sample to remove mechanical impurities and some organic matter; then neutralizes and adjusts the filtrate and heats it to boiling to effectively eliminate the interference of ammonium ions and hydroxide ions on the detection; then digests the water sample to further remove the trace organic matter remaining in the system; finally, the pH value of the system is adjusted by using strong base weak acid salt sodium bicarbonate to avoid introducing a large amount of hydroxide ions during the pH adjustment process, reduce the side reaction between hydroxide ions and titration standard solution, thereby reducing the adverse effects on indicator color development and titration endpoint judgment.

[0021] (2) The method for detecting chloride ion content in urea hydrolyzer sludge provided by the present invention can effectively avoid various interference factors such as mechanical impurities, ammonium ions, hydroxide ions, and organic matter in water samples, and greatly improve the accuracy and reliability of chloride ion content determination results. Detailed Implementation

[0022] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0023] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] Example 1. A method for detecting chloride ion content in urea hydrolysate from a urea hydrolyzer. This embodiment aims to provide a method for detecting the chloride ion content in the hydrolysis effluent of a urea hydrolyzer. The steps of the detection method are as follows: (1) Take the urea hydrolysis sludge from the urea hydrolyzer (taken from the urea hydrolysis workshop of a coal-fired power plant), filter it with organic filter paper (purchased from Hangzhou Special Paper Co., Ltd., with a filtration accuracy of 0.45 μm) to remove mechanical impurities and some organic matter, and collect the filtrate.

[0025] (2) Accurately transfer 50 mL of the filtrate into an Erlenmeyer flask, and add nitric acid (98% pure nitric acid diluted with water in a 1:1 volume ratio) to neutralize the OH- in the filtrate. - While adding nitric acid, stir and measure the pH value of the filtrate with pH test paper. Stop adding nitric acid when the pH value of the filtrate is 2, and obtain the neutralized filtrate.

[0026] (3) The neutralized filtrate was placed on an electric furnace and heated to boiling for 10 minutes to completely expel the NH3 produced by the further decomposition of ammonium carbamate, an intermediate product of urea hydrolysis, and the free NH3 produced by urea hydrolysis, while also promoting the complete volatilization of other volatile gases in the neutralized filtrate. After boiling, the filtrate was allowed to cool to room temperature to obtain the heat-treated filtrate.

[0027] (4) Add H2O2 to the filtrate after heat treatment (the amount of H2O2 added to the filtrate after heat treatment is 30% of the total mass of the filtrate after heat treatment) to dissolve some of the residual organic matter and obtain a filtrate with the organic matter removed.

[0028] (5) Add 2 drops of phenolphthalein indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., product number 73202067) to the filtrate after removing organic matter. Since the filtrate after removing organic matter is acidic, it will be colorless. Then add NaHCO3 to adjust the filtrate after removing organic matter to be light red and stop adding. Then add nitric acid (98% pure nitric acid diluted with water in a volume ratio of 1:100) until the light red color just turns colorless, and the test solution is obtained.

[0029] (6) Add 1.0 mL of potassium chromate indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the solution to be tested. Titrate with 0.05 mol / L silver nitrate standard solution against a white background until a brick-red color just appears. Perform parallel and blank tests simultaneously. The volume of silver nitrate standard solution consumed when titrating the water sample is a mL, and the volume of silver nitrate standard solution consumed when titrating the blank water sample is b mL. The calculation formula is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V; In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution, 0.05 mol / L; V: Volume of hydrolysis effluent, 50 mL; M: Molar mass of chlorine, 35.5 g / mol.

[0030] (7) The volume of silver nitrate standard solution consumed when titrating the blank water sample was 0.29 mL. The volumes of silver nitrate standard solution consumed when titrating the water sample in the parallel tests were 3.54 mL and 3.62 mL, respectively. The chloride ion content in the urea hydrolyzer sludge of the two sets of parallel tests was calculated to be 115.375 mg / L and 118.215 mg / L, respectively.

[0031] Experimental Example 1: Determining the accuracy of the detection method in Example 1 using the standard increment method (1) Take a certain amount of urea hydrolyzer sludge (the same sludge as in Example 1), filter it with organic filter paper (purchased from Hangzhou Special Paper Co., Ltd., filtration accuracy 0.45 μm) to remove mechanical impurities and some organic matter, and collect the filtrate as filtrate.

[0032] (2) Accurately transfer 50 mL of the filtrate into an Erlenmeyer flask, add 0.8239 mg of analytical grade NaCl, which dissolves in the filtrate, meaning that 0.5 mg of Cl is added to the filtrate. - Cl - The concentration increased by 10 mg / L. Nitric acid (98% purity nitric acid diluted with water at a volume ratio of 1:1) was then added to neutralize the OH- in the filtrate. - While adding nitric acid, stir and measure the pH value of the filtrate with pH test paper. Stop adding nitric acid when the pH value of the filtrate is 2, and obtain the neutralized filtrate.

[0033] (3) The neutralized filtrate is heated to boiling on an electric furnace for 10 minutes to completely remove the NH3 produced by the further decomposition of ammonium carbamate, an intermediate product of urea hydrolysis, and the free NH3 produced by urea hydrolysis. This also facilitates the complete volatilization of other volatile gases in the neutralized filtrate. After the neutralized filtrate is cooled to room temperature, the heated filtrate is obtained.

[0034] (4) Add H2O2 to the filtrate after heat treatment (the amount of H2O2 added to the filtrate after heat treatment is 30% of the total mass of the filtrate after heat treatment) to dissolve some of the residual organic matter and obtain a filtrate with the organic matter removed.

[0035] (5) Add 2 drops of phenolphthalein indicator to the filtrate after removing organic matter. Since the filtrate after removing organic matter is acidic, it will be colorless. Then add NaHCO3 to adjust the filtrate after removing organic matter to be light red and stop adding. Then add nitric acid (98% pure nitric acid diluted with water in a volume ratio of 1:100) to make the light red just turn colorless, so as to avoid the formation of carbonate and silver ions into precipitates and to inhibit the side reaction of hydroxide and silver nitrate to form silver oxide precipitate, thus obtaining the test solution.

[0036] (6) Add 1.0 mL of potassium chromate indicator to the solution to be tested. Titrate with 0.05 mol / L silver nitrate standard solution against a white background until a brick-red color just appears. Perform parallel and blank tests simultaneously. The volume of silver nitrate standard solution consumed when titrating the water sample is a mL, and the volume of silver nitrate standard solution consumed when titrating the blank water sample is b mL. The calculation formula is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution, 0.05 mol / L; V: Volume of hydrolysis effluent, 50 mL; M: Molar mass of chlorine, 35.5 g / mol.

[0037] (7) The volume of silver nitrate standard solution consumed when titrating the blank water sample was 0.28 mL. The volumes of silver nitrate standard solution consumed when titrating the water sample in the parallel tests were 3.81 mL and 3.88 mL, respectively. The chloride ion content in the urea hydrolyzer sludge of the two sets of parallel tests was calculated to be 125.315 mg / L and 127.642 mg / L, respectively.

[0038] Therefore, when the chloride ion content in the urea hydrolyzer sludge is increased by the standard incremental method and the incremental chloride ion content is 10 mg / L, the incremental chloride ion content in Example 2 compared with Example 1 is also about 10 mg / L, indicating that this method has high accuracy in detecting the chloride ion content in the hydrolyzer sludge.

[0039] Comparative Example 1. (1) Take a certain amount of urea hydrolysis wastewater (taken from the urea hydrolysis workshop of a coal-fired power plant), accurately transfer 50 mL into an Erlenmeyer flask, and add nitric acid (98% pure nitric acid diluted with water in a volume ratio of 1:1) to neutralize the OH- in the urea hydrolysis wastewater. - Nitric acid was added while stirring, and the pH value of the urea hydrolysate was measured with pH test paper. Nitric acid was stopped when the pH value of the urea hydrolysate was 2, and the neutralized filtrate was obtained.

[0040] (2) The neutralized filtrate was heated to boiling on an electric furnace for 10 minutes to completely expel the NH3 produced by the further decomposition of ammonium carbamate, an intermediate product of urea hydrolysis, and the free NH3 produced by urea hydrolysis, while also promoting the complete volatilization of other volatile gases in the neutralized filtrate. After the neutralized filtrate was cooled to room temperature, the heated filtrate was obtained.

[0041] (3) Add H2O2 to the filtrate after heat treatment (the amount of H2O2 added to the filtrate after heat treatment is 30% of the total mass of the filtrate after heat treatment) to dissolve some of the residual organic matter and obtain a filtrate with the organic matter removed.

[0042] (4) Add 2 drops of phenolphthalein indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the filtrate after removing organic matter. Since the filtrate after removing organic matter is acidic, it will be colorless. Then add NaHCO3 to adjust the filtrate after removing organic matter to be light red and stop adding. Then add nitric acid (98% pure nitric acid diluted with water in a volume ratio of 1:100) until the light red color just turns colorless, and the test solution is obtained.

[0043] (5) Add 1.0 mL of potassium chromate indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the solution to be tested. Titrate with 0.05 mol / L silver nitrate standard solution against a white background until a brick-red color just appears. Perform parallel and blank tests simultaneously. The volume of silver nitrate standard solution consumed when titrating the water sample is a mL, and the volume of silver nitrate standard solution consumed when titrating the blank water sample is b mL. The calculation formula is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution, 0.05 mol / L; V: Volume of hydrolysis effluent, 50 mL; M: Molar mass of chlorine, 35.5 g / mol.

[0044] (6) The volume of silver nitrate standard solution consumed when titrating the blank water sample was 0.29 mL. The volumes of silver nitrate standard solution consumed when titrating the water sample in the parallel tests were 3.99 mL and 4.05 mL, respectively. The chloride ion content in the urea hydrolyzer sludge of the two sets of parallel tests was calculated to be 131.254 mg / L and 133.425 mg / L, respectively.

[0045] The standard incremental method was verified according to the method of Experiment Example 1. The difference from Experiment Example 1 is that step (1) is missing. The chloride ion content in the urea hydrolyzer sludge of the two parallel experiments was calculated to be 144.364 mg / L and 147.793 mg / L, respectively.

[0046] Comparative Example 2. (1) Take a certain amount of urea hydrolyzer sludge (taken from the urea hydrolysis workshop of a coal-fired power plant), filter it with organic filter paper (purchased from Hangzhou Special Paper Co., Ltd., filtration accuracy 0.45 μm) to remove mechanical impurities and some organic matter, and collect the filtrate.

[0047] (2) Accurately transfer 50 mL of the filtrate into an Erlenmeyer flask, place the filtrate on an electric stove and heat to boiling for 10 minutes. This will completely expel the NH3 produced by the further decomposition of ammonium carbamate, an intermediate product of urea hydrolysis, and the free NH3 produced by urea hydrolysis, while also promoting the complete volatilization of other volatile gases in the filtrate. After boiling, allow it to cool to room temperature to obtain the heat-treated filtrate.

[0048] (3) Add H2O2 to the filtrate after heat treatment (the amount of H2O2 added to the filtrate after heat treatment is 30% of the total mass of the filtrate after heat treatment) to dissolve some of the residual organic matter and obtain a filtrate with the organic matter removed.

[0049] (4) Add 2 drops of phenolphthalein indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., product number 73202067) to the filtrate after removing organic matter. Since the filtrate after removing organic matter is acidic, it will be colorless. Then add NaHCO3 to adjust the filtrate after removing organic matter to be light red and stop adding. Then add nitric acid (98% pure nitric acid diluted with water in a volume ratio of 1:100) until the light red color just turns colorless, and the test solution is obtained.

[0050] (5) Add 1.0 mL of potassium chromate indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the solution to be tested. Titrate with 0.05 mol / L silver nitrate standard solution against a white background until a brick-red color just appears. Perform parallel and blank tests simultaneously. The volume of silver nitrate standard solution consumed when titrating the water sample is a mL, and the volume of silver nitrate standard solution consumed when titrating the blank water sample is b mL. The calculation formula is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution, 0.05 mol / L; V: Volume of hydrolysis effluent, 50 mL; M: Molar mass of chlorine, 35.5 g / mol.

[0051] (6) The volume of silver nitrate standard solution consumed when titrating the blank water sample was 0.29 mL. The volumes of silver nitrate standard solution consumed when titrating the water samples in the parallel tests were 4.72 mL and 4.78 mL, respectively. The chloride ion content in the urea hydrolyzer sludge of the two sets of parallel tests was calculated to be 157.321 mg / L and 159.463 mg / L, respectively.

[0052] The standard incremental method was verified according to the method of Experiment Example 1. The difference from Experiment Example 1 is that step (2) is missing. The chloride ion content in the urea hydrolyzer sludge of the two parallel experiments was calculated to be 171.275 mg / L and 172.639 mg / L, respectively.

[0053] Comparative Example 3. (1) Take a certain amount of urea hydrolyzer sludge and filter it with organic filter paper (purchased from Hangzhou Special Paper Co., Ltd., filtration accuracy 0.45 μm) to remove mechanical impurities and some organic matter, and collect the filtrate.

[0054] (2) Accurately transfer 50 mL of the filtrate into an Erlenmeyer flask, and add nitric acid (98% pure nitric acid diluted with water in a 1:1 volume ratio) to neutralize the OH- in the filtrate. - While adding nitric acid, stir and measure the pH value of the filtrate with pH test paper. Stop adding nitric acid when the pH value of the filtrate is 2, and obtain the neutralized filtrate.

[0055] (3) Add H2O2 to the neutralized filtrate (the amount of H2O2 added to the heated filtrate is 30% of the total mass of the heated filtrate) to dissolve some of the residual organic matter and obtain a filtrate with the organic matter removed.

[0056] (4) Add 2 drops of phenolphthalein indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the filtrate after removing organic matter. Since the filtrate after removing organic matter is acidic, it will be colorless. Then add NaHCO3 to adjust the filtrate after removing organic matter to be light red and stop adding. Then add nitric acid (the dilution ratio of nitric acid to water is 1:100) until the light red color just turns colorless, and the test solution is obtained.

[0057] (5) Add 1.0 mL of potassium chromate indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the solution to be tested. Titrate with 0.05 mol / L silver nitrate standard solution against a white background until a brick-red color just appears. Perform parallel and blank tests simultaneously. The volume of silver nitrate standard solution consumed when titrating the water sample is a mL, and the volume of silver nitrate standard solution consumed when titrating the blank water sample is b mL. The calculation formula is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution, 0.05 mol / L; V: Volume of hydrolysis effluent, 50 mL; M: Molar mass of chlorine, 35.5 g / mol.

[0058] (6) The volume of silver nitrate standard solution consumed when titrating the blank water sample was 0.29 mL. The volumes of silver nitrate standard solution consumed when titrating the water samples in the parallel tests were 4.37 mL and 4.42 mL, respectively. The chloride ion content in the urea hydrolyzer sludge of the two sets of parallel tests was calculated to be 144.875 mg / L and 146.467 mg / L, respectively.

[0059] The standard incremental method was verified according to the method of Experiment Example 1. The difference from Experiment Example 1 is that step (3) is missing. The chloride ion content in the urea hydrolyzer sludge of the two parallel experiments was calculated to be 153.753 mg / L and 155.547 mg / L, respectively.

[0060] Comparative Example 4. (1) Take a certain amount of urea hydrolyzer sludge (taken from the urea hydrolysis workshop of a coal-fired power plant), filter it with organic filter paper (purchased from Hangzhou Special Paper Co., Ltd., filtration accuracy 0.45 μm) to remove mechanical impurities and some organic matter, and collect the filtrate.

[0061] (2) Accurately transfer 50 mL of the filtrate into an Erlenmeyer flask, and add nitric acid (98% pure nitric acid diluted with water in a 1:1 volume ratio) to neutralize the OH- in the filtrate. - While adding nitric acid, stir and measure the pH value of the filtrate with pH test paper. Stop adding nitric acid when the pH value of the filtrate is 2, and obtain the neutralized filtrate.

[0062] (3) The neutralized filtrate was placed on an electric furnace and heated to boiling for 10 minutes to completely expel the NH3 produced by the further decomposition of ammonium carbamate, an intermediate product of urea hydrolysis, and the free NH3 produced by urea hydrolysis, while also promoting the complete volatilization of other volatile gases in the neutralized filtrate. After boiling, the filtrate was allowed to cool to room temperature to obtain the heat-treated filtrate.

[0063] (4) Add 2 drops of phenolphthalein indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the filtrate after heat treatment, then add NaHCO3 to adjust to a light red color and stop adding. Then add nitric acid (98% pure nitric acid diluted with water at a volume ratio of 1:100) until the light red color just turns colorless, and obtain the test solution.

[0064] (5) Add 1.0 mL of potassium chromate indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the solution to be tested. Titrate with 0.05 mol / L silver nitrate standard solution against a white background until a brick-red color just appears. Perform parallel and blank tests simultaneously. The volume of silver nitrate standard solution consumed when titrating the water sample is a mL, and the volume of silver nitrate standard solution consumed when titrating the blank water sample is b mL. The calculation formula is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution, 0.05 mol / L; V: Volume of hydrolysis effluent, 50 mL; M: Molar mass of chlorine, 35.5 g / mol.

[0065] (6) The volume of silver nitrate standard solution consumed when titrating the blank water sample was 0.29 mL. The volumes of silver nitrate standard solution consumed when titrating the water sample in the parallel tests were 3.83 mL and 3.89 mL, respectively. The chloride ion content in the urea hydrolyzer sludge of the two sets of parallel tests was calculated to be 125.634 mg / L and 127.638 mg / L, respectively.

[0066] The standard incremental method was verified according to the method of Experiment Example 1. The difference from Experiment Example 1 is that step (4) is missing. The chloride ion content in the urea hydrolyzer sludge of the two parallel experiments was calculated to be 138.548 mg / L and 139.537 mg / L, respectively.

[0067] Comparative Example 5. (1) Take a certain amount of urea hydrolyzer sludge (taken from the urea hydrolysis workshop of a coal-fired power plant), filter it with organic filter paper (purchased from Hangzhou Special Paper Co., Ltd., filtration accuracy 0.45 μm) to remove mechanical impurities and some organic matter, and collect the filtrate.

[0068] (2) Accurately transfer 50 mL of the filtrate into an Erlenmeyer flask, and add nitric acid (98% pure nitric acid diluted with water in a 1:1 volume ratio) to neutralize the OH- in the filtrate. - While adding nitric acid, stir and measure the pH value of the filtrate with pH test paper. Stop adding nitric acid when the pH value of the filtrate is 2, and obtain the neutralized filtrate.

[0069] (3) The neutralized filtrate was placed on an electric furnace and heated to boiling for 10 minutes to completely expel the NH3 produced by the further decomposition of ammonium carbamate, an intermediate product of urea hydrolysis, and the free NH3 produced by urea hydrolysis, while also promoting the complete volatilization of other volatile gases in the neutralized filtrate. After boiling, the filtrate was allowed to cool to room temperature to obtain the heat-treated filtrate.

[0070] (4) Add H2O2 to the filtrate after heat treatment (the amount of H2O2 added to the filtrate after heat treatment is 30% of the total mass of the filtrate after heat treatment) to dissolve the remaining organic matter and obtain the solution to be tested.

[0071] (5) Add 1.0 mL of potassium chromate indicator (purchased from Sinopharm Chemical Reagent Co., Ltd., item number 73203064) to the solution to be tested. Titrate with 0.05 mol / L silver nitrate standard solution against a white background until a brick-red color just appears. Perform parallel and blank tests simultaneously. The volume of silver nitrate standard solution consumed when titrating the water sample is a mL, and the volume of silver nitrate standard solution consumed when titrating the blank water sample is b mL. The calculation formula is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution, 0.05 mol / L; V: Volume of hydrolysis effluent, 50 mL; M: Molar mass of chlorine, 35.5 g / mol.

[0072] (6) The volume of silver nitrate standard solution consumed when titrating the blank water sample was 0.29 mL. The volumes of silver nitrate standard solution consumed when titrating the water samples in the parallel tests were 3.71 mL and 3.77 mL, respectively. The chloride ion content in the urea hydrolyzer sludge of the two sets of parallel tests was calculated to be 121.546 mg / L and 123.546 mg / L, respectively.

[0073] The standard incremental method was verified according to the method of Experiment Example 1. The difference from Experiment Example 1 is that step (5) is missing. The chloride ion content in the urea hydrolyzer sludge of the two parallel experiments was calculated to be 125.574 mg / L and 129.543 mg / L, respectively.

[0074] result: Comparative Examples 1-5 were performed without any of the steps (1), (2), (3), (4), and (5) in Example 1, and then steps (6) and (7) were performed; in addition, the standard incremental method was performed without any of the steps (1), (2), (3), (4), and (5) in Experimental Example 1; the detection results are shown in Table 1.

[0075] Table 1 lacks error rates for key steps and results of spiked recovery tests.

[0076] As shown in Table 1 of the test results, the measured values ​​have a large error rate compared with the background values ​​when any step (1), step (2), step (3), step (4), or step (5) is missing; and the recovery rate of the measured error values ​​after the spike test is also not ideal. This indicates that the absence of any step (1), step (2), step (3), step (4), or step (5) has a significant impact on the accuracy of the test results.

[0077] This invention optimizes the method for determining chloride ion content, reducing the influence of impurities, ammonium ions, hydroxide ions, and organic matter in the hydrolyzer sludge on the determination results, thereby improving the accuracy of the determination results.

[0078] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for detecting chloride ion content in urea hydrolyzer wastewater, characterized in that, The detection method includes: Step 1: Remove mechanical impurities and organic matter from the urea hydrolyzer effluent by filtration to obtain filtrate; Step 2: Add nitric acid to the filtrate to neutralize the OH- in the filtrate. - The neutralized filtrate was obtained. Step 3: Remove NH3 from the neutralized filtrate by heating to obtain a heated filtrate; Step 4: Add H2O2 to the filtrate after heat treatment to remove residual organic matter, thus obtaining a filtrate with organic matter removed; Step 5: First, add an acid-base indicator to the filtrate after removing organic matter, then add a strong base-weak acid salt to adjust the pH value of the filtrate after removing organic matter. Finally, add nitric acid to the filtrate after removing organic matter to obtain the test solution. Step 6: Detect the chloride ion content in the test solution using the silver nitrate molar method.

2. The detection method according to claim 1, characterized in that, In step 1, the filtration is performed using organic filter paper.

3. The detection method according to claim 1, characterized in that, In step 2, the addition of nitric acid is stopped when the pH of the filtrate is 1-2.

4. The detection method according to claim 1, characterized in that, In step 3, the heating is to heat the neutralized filtrate to boiling.

5. The detection method according to claim 1, characterized in that, In step 4, the amount of H2O2 added to the heat-treated filtrate is 30% of the total mass of the heat-treated filtrate.

6. The detection method according to claim 1, characterized in that, In step 5, the strong base-weak acid salt includes sodium bicarbonate; Preferably, sodium bicarbonate is added to the filtrate from which organic matter has been removed until the filtrate changes from colorless to light red.

7. The detection method according to claim 1, characterized in that, In step 5, nitric acid is added to the filtrate from which the organic matter has been removed until the filtrate changes from light red to colorless.

8. The detection method according to claim 1, characterized in that, In step 6, the detection formula for the silver nitrate molar method is as follows: C1 = C2 × (V1 - V0) × M × 1000 / V; In the formula: C1: Chloride ion content in the urea hydrolyzer effluent, mg / L; V1: The volume of silver nitrate standard solution consumed during the titration of the water sample, in mL; V0: The volume of silver nitrate standard solution consumed in the blank test, in mL; C2: Molar concentration of silver nitrate standard solution; V: Volume of hydrolyzed wastewater; M: Molar mass of chlorine.

9. A reagent kit for determining the chloride ion content in the sludge from a urea hydrolyzer, characterized in that, The kit includes organic filter paper, nitric acid, pH test paper, H2O2, strong base-weak acid salt, phenolphthalein indicator, potassium chromate indicator, and silver nitrate standard solution.

10. The application of the detection method according to any one of claims 1-8 or the kit according to the claims in detecting the chloride ion content in the urea hydrolyzer sludge.

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