Rapid detection method for urotropine in glycine mother liquor

Abstract

The invention provides a rapid detection method for urotropine in glycine mother liquor, which adopts an ultraviolet spectrophotometer for detection and comprises the following steps: (1) drawing a formaldehyde standard curve; (2) testing the glycine mother liquor: taking the glycine mother liquor, adding acid to adjust the pH value to obtain an acidic mother liquor A, and measuring the absorbance A1 of the acidic mother liquor A; (3) heating the acidic mother liquor A for reaction until urotropin in the acidic mother liquor is completely decomposed into formaldehyde to obtain decomposed mother liquor B, and measuring the absorbance A2 of the mother liquor B; (4) substituting the absorbance A1 and the absorbance A2 into a formaldehyde standard curve, and calculating the formaldehyde concentration rho0 of the mother liquor A and the formaldehyde concentration rhon of the mother liquor B; according to the formula rho tropine = (rho n-rho 0) * k, the mass concentration rho tropine of urotropine in the glycine mother liquor is obtained, and k is equal to 0.778. The detection method disclosed by the invention is low in cost, short in detection time, simple to operate and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of glycine production, and specifically to a method for detecting the hexamethylenetetramine content in glycine mother liquor by decomposition reaction and ultraviolet spectrophotometry. Background Technology

[0002] Glycine is an important raw material for products such as glyphosate and glycine ethyl hydrochloride, and can also be refined into food-grade glycine for use. Currently, the traditional domestic process for producing glycine via aqueous chloroacetic acid ammonolysis is as follows: A 25% aqueous solution of hexamethylenetetramine (catalyst) is added to a reactor with cooling water, while an 80% aqueous solution of chloroacetic acid is added dropwise and ammonia gas is introduced. The ammonolysis reaction is carried out at pH=7 and a reaction temperature of approximately 80℃. After the reaction, the ammonolysis reaction solution containing glycine and ammonium chloride is obtained, and the glycine product is separated by methanol precipitation.

[0003] However, existing methods for producing glycine have several problems. First, the catalyst, hexamethylenetetramine, is a single-use substance; once added, it is not recycled and ultimately ends up in the wastewater and the final product, leading to excessive costs and subsequent environmental problems. Second, in current technology, the ammonium chloride mother liquor is recycled in the mother liquor concentration process. Because hexamethylenetetramine decomposes into formaldehyde and ammonia during concentration at high temperatures, and formaldehyde readily reacts with other components in the mother liquor, the ammonium chloride mother liquor becomes highly complex after multiple recycling processes. It appears as a reddish, viscous liquid, commonly known in the industry as "red water," and is extremely difficult to treat.

[0004] To address these issues, a method for detecting the hexamethylenetetramine content in glycine mother liquor needs to be established.

[0005] CN120084897A discloses a method for detecting glycine and hexamethylenetetramine content in glycine wastewater. This method utilizes standard solutions of glycine and hexamethylenetetramine, employing high-performance liquid chromatography (HPLC) with isocratic elution to obtain a working curve exhibiting good linear correlation, thereby improving the accuracy of the test. However, this method still requires optimization of chromatographic conditions during HPLC testing, necessitating further adjustments to the composition and ratio of the mobile phase, and optimization of the chromatographic column type and specifications.

[0006] CN118465129A proposes a method for detecting hexamethylenetetramine in glycine. This method uses a 30m × 0.32mm × 0.25μm HP-5 capillary column for gas chromatography analysis of glycine samples. By limiting the gas chromatography temperature program and the temperatures of the injection port and detector, the peak response intensities of the test and reference solutions are improved, thereby enhancing the detection accuracy. However, there is still room for optimization in the gas chromatography conditions, and further improvements in the peak response intensities of the test and reference solutions are needed.

[0007] The existing technology has the following drawbacks: 1. Traditional methods such as ion chromatography cannot accurately and rapidly detect the content of hexamethylenetetramine in glycine mother liquor, which affects subsequent processing and recovery and cannot meet the needs of rapid and accurate detection. 2. Existing detection methods require further adjustments to the composition and ratio of the mobile phase, and optimization of the chromatographic column type and specifications, in order to improve the accuracy and sensitivity of detection; 3. Current detection methods need further optimization of sample extraction and purification methods to improve sample purity and stability, thereby improving the accuracy and reliability of detection results; 4. Existing detection methods need further optimization of data processing methods and result analysis indicators to improve the reliability and repeatability of the analysis; 5. Traditional detection methods are insufficient in terms of operational complexity and detection time, making it difficult to meet the needs of efficient production and affecting resource utilization efficiency and environmental protection in the glycine production process.

[0008] Therefore, there is an urgent need to develop a new detection method to quickly and accurately detect the hexamethylenetetramine content in glycine mother liquor, thereby providing technical support for improving resource utilization efficiency and environmental protection in the glycine production process. Summary of the Invention

[0009] To address the above problems, this invention provides a rapid detection method for hexamethylenetetramine in glycine mother liquor, using an ultraviolet spectrophotometer, comprising the following steps: (1) Draw the formaldehyde standard curve; (2) Glycine mother liquor sample test: Take glycine mother liquor, add acid to adjust pH to obtain acidic mother liquor A, and measure the absorbance A1 of acidic mother liquor A; (3) The acidic mother liquor A is heated until all the hexamethylenetetramine in the acidic mother liquor is decomposed into formaldehyde, and the decomposed mother liquor B is obtained. The absorbance A2 of the mother liquor B is measured. (4) Substitute absorbances A1 and A2 into the formaldehyde standard curve to calculate the formaldehyde concentration ρ0 of mother liquor A and the formaldehyde concentration ρ of mother liquor B. n According to the formula ρ托品 =(ρ n -ρ0)*k, the mass concentration ρ of hexamethylenetetramine in the glycine mother liquor is calculated. 托品 , where k=0.778.

[0010] Furthermore, the specific steps for plotting the formaldehyde standard curve are as follows: S1. Preparation of acetylacetone solution: Dissolve ammonium acetate, glacial acetic acid and acetylacetone reagent solution in water to obtain acetylacetone solution; S2. Prepare formaldehyde standard solutions of different concentrations, and measure the absorbance of the formaldehyde standard solutions of different concentrations using water as a reference to obtain the standard curve A. r = 0.0245W + 0.0202, R² = 0.9999; where, A r denoted as absorbance, and W as the mass of formaldehyde.

[0011] Furthermore, when measuring absorbance, the detection wavelength was 414 nm.

[0012] Furthermore, the pH in step (2) is 2-3.

[0013] Furthermore, the reaction temperature in step (3) is 60-70℃.

[0014] Furthermore, the reaction time in step (3) is 4-10 min.

[0015] Furthermore, the reaction temperature in step (3) is 60°C.

[0016] Furthermore, the reaction time in step (3) is 5 min.

[0017] Furthermore, the pH in step (2) is 2.2-2.8.

[0018] Furthermore, the acetylacetone solution was prepared according to the ratio of 50g ammonium acetate, 6ml glacial acetic acid, 0.5ml acetylacetone reagent, and 100ml water.

[0019] The beneficial effects of this invention are as follows: This invention adjusts the pH of a mother liquor containing hexamethylenetetramine to between 2 and 3, heats it to 60°C and holds it for 5 minutes to decompose all the hexamethylenetetramine in the mother liquor into formaldehyde. Then, the formaldehyde content before and after decomposition is detected by acetylacetone spectrophotometry. Finally, the content of hexamethylenetetramine is calculated by the differential method. This invention avoids the problem that traditional methods such as ion chromatography cannot detect hexamethylenetetramine accurately and quickly, and achieves the goal of rapid and accurate detection of hexamethylenetetramine content in glycine mother liquor.

[0020] The detection method of this invention, which combines decomposition reaction and ultraviolet spectrophotometry, overcomes the problem of insufficient optimization of chromatographic conditions in the prior art. It eliminates the need to adjust the composition and ratio of the mobile phase, optimize the model and specifications of the chromatographic column, etc., simplifying the operation process and improving the accuracy and sensitivity of detection.

[0021] This invention directly converts hexamethylenetetramine in the mother liquor into formaldehyde through a decomposition reaction, avoiding complex operations in the sample pretreatment process, improving the purity and stability of the sample, and thus improving the accuracy and reliability of the detection results.

[0022] This invention uses the differential method to calculate the hexamethylenetetramine content by comparing the formaldehyde content before and after decomposition, which simplifies the data processing and result analysis process and improves the reliability and repeatability of the analysis.

[0023] The detection method of the present invention is low in cost, short in detection time, simple to operate, and suitable for industrial production, effectively improving the resource utilization efficiency and environmental protection level in the glycine production process. Attached Figure Description

[0024] Figure 1 The formaldehyde standard curve used in the detection method of this invention.

[0025] Figure 2 A graph showing the decomposition of urotropine into formaldehyde over time. Detailed Implementation

[0026] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0027] Example 1 S1. Dissolve 200 mg of hexamethylenetetramine solid in 1 L of ultrapure water.

[0028] S2. Add 0.1 mol / L hydrochloric acid solution to adjust the pH of the mother liquor to 2.4 to obtain acidic mother liquor A.

[0029] S3. Detect the absorbance value using ultraviolet spectrophotometry. S301. Take 10 mL of acidic mother liquor A, heat it to 60℃ and keep it at a constant temperature for 6 minutes to decompose hexamethylenetetramine in the mother liquor into formaldehyde. During the constant temperature reaction of acidic mother liquor A at 60℃, use the acetylacetone spectrophotometer to detect the absorbance of acidic mother liquor A every minute. Measure each sample 3 times. The specific measurement steps are as follows: a) Prepare acetylacetone solution: Dissolve 50g ammonium acetate, 6ml glacial acetic acid and 0.5ml acetylacetone reagent solution in 100ml water.

[0030] b) Blank test: Take a 10ml stoppered colorimetric tube, add water to make up to 10ml, add 1.00ml of acetylacetone solution to the colorimetric tube, and shake well. Heat in a water bath at (60±2)℃ for 15min, then remove and cool. Using a 10mm cuvette, measure the absorbance value A at a wavelength of 414nm, with water as a reference. b .

[0031] c) Plot the standard curve: Take several 10ml stoppered colorimetric tubes and add 0.20, 0.40, 1.20, 2.00, and 3.20ml of formaldehyde standard solution (10mg / L) respectively. Add water to each tube to a final volume of 10ml. Add 1.00ml of acetylacetone solution to each tube and mix well. Heat in a water bath at (60±2)℃ for 15min, then remove and cool. Measure the absorbance at 414nm using a 10mm cuvette, with water as a reference. Calculate the absorbance A obtained from the series of calibration solutions. s Value minus the absorbance A of the blank test b The value is used to obtain the corrected absorbance A. r To correct absorbance A r Plot a standard curve with the formaldehyde content W in 10 ml of calibration solution as the x-axis, or calculate the regression equation using the least squares method, to obtain: A r =bW+a(1) In the formula: A r —Correct absorbance; W – Formaldehyde content, μg; a — the intercept of the regression equation; b — Slope of the regression equation; The standard curve A was obtained by fitting. r =0.0245W+0.0202 (R² = 0.9999); d) Sample testing: Accurately transfer 0.1 ml of acidic mother liquor A sample into a 10 ml stoppered colorimetric tube and dilute with water to the mark. Perform the test according to the steps in c), and determine the formaldehyde content in the sample from the standard curve or calculate the formaldehyde content using the regression equation.

[0032] S302. Record the measurement data as shown in Table 1. Table 1 shows the absorbance of each sample when plotting the standard curve, as well as the absorbance of samples taken every minute during the constant temperature reaction of acidic mother liquor A at 60℃ for 6 minutes.

[0033] Table 1

[0034] S4. Calculate the content of urotropine using the difference method. S401. Using equation (1), the regression equation is calculated as follows: Ar = 0.0245W + 0.0202 (R² = 0.9999)(2) The coefficient of determination R² of the regression equation is greater than 0.99, indicating that the standard curve has excellent linearity and the method has superior accuracy.

[0035] S402, formaldehyde mass concentration ρ in the sample 甲醛 Calculate according to formula (3): (3) In the formula: ρ 甲醛 —The mass concentration of formaldehyde in the sample; W—the amount of formaldehyde obtained from the standard curve or calculated using the regression equation, in μg; V — Volume of the sample; The formaldehyde concentrations in acidic mother liquor A at 0, 1, 2, 3, 4, 5, and 6 minutes were 0.33 mg / L, 128.98 mg / L, 190.27 mg / L, 226.77 mg / L, 256.84 mg / L, 256.84 mg / L, and 256.84 mg / L, respectively.

[0036] S403, Mass concentration of hexamethylenetetramine in the sample ρ 托品 Calculate according to formula (4): ρ 托品 =(ρ n -ρ0)*k(4) In the formula: ρ 托品 —The mass concentration of tropine in the sample; ρ n —Formaldehyde concentration in the sample after decomposition, mg / L; ρ0 — Formaldehyde concentration in the sample before decomposition, mg / L; k—k=0.778, meaning that for every 1 gram of formaldehyde produced, 0.778 grams of hexamethylenetetramine needs to be decomposed.

[0037] ρ was measured according to the formula. 托品 =199.56mg / L, compared with the mass concentration ρ of urotropine in acidic mother liquor A. 托品 The high agreement of 200 mg / L indicates that the method is highly accurate.

[0038] Example 2 S1. Take the glycine mother liquor and measure its initial pH value to be 7.2; add 0.1 mol / L hydrochloric acid solution to adjust the pH value of the mother liquor to 2.8, and obtain acidic mother liquor A; S2. Take 10 mL of acidic mother liquor A, heat it to 60°C and keep it at a constant temperature for 5 minutes to decompose all the hexamethylenetetramine in the mother liquor into formaldehyde, and obtain the decomposed mother liquor B. S3. The absorbance values ​​before and after decomposition were determined using ultraviolet spectrophotometry. S301, the same as S301 in Example 1 S302. Record the measurement data as shown in Table 2 below. Table 2 shows the absorbance data of acidic mother liquor A before and after the constant temperature reaction.

[0039] Table 2

[0040] S4. Calculate the content of urotropine using the difference method. S401, the same as S401 in Example 1 S402, the same as S402 in Example 1 The formaldehyde concentrations in the acidic mother liquor A before and after decomposition were 79.510 mg / L and 178.286 mg / L, respectively.

[0041] S403, the same as S403 in Example 1 The mass concentration ρ of hexamethylenetetramine in acidic mother liquor A 托品 =76.848 mg / L.

[0042] Example 3 S1. Take the glycine mother liquor and measure its initial pH value to be 6.8; add 0.05 mol / L sulfuric acid solution to adjust the pH value of the mother liquor to 2.5, and obtain acidic mother liquor A; S2. Take 10 mL of acidic mother liquor A, heat it to 60°C and keep it at a constant temperature for 5 minutes to decompose all the hexamethylenetetramine in the mother liquor into formaldehyde, and obtain the decomposed mother liquor B. S3. The absorbance values ​​before and after decomposition were determined using ultraviolet spectrophotometry. S301, the same as S301 in Example 1 S302. Record the measurement data as shown in Table 3 below. Table 3 shows the absorbance data of acidic mother liquor A before and after the constant temperature reaction.

[0043] Table 3

[0044] S4. Calculate the content of urotropine using the difference method. S401, the same as S401 in Example 1 S402, the same as S402 in Example 1 The formaldehyde concentrations in the acidic mother liquor A before and after decomposition were 115.837 mg / L and 266.857 mg / L, respectively.

[0045] S403, the same as S403 in Example 1 The mass concentration of hexamethylenetetramine (ρtropine) in acidic mother liquor A is 117.494 mg / L.

[0046] Example 4 S1. Weigh 30 mg, 100 mg, 150 mg, and 250 mg of urotropine into 1 L volumetric flasks respectively, and measure the initial pH values ​​of the urotropine mother liquor, which are 6.7, 6.8, 6.9, and 7.2 respectively; add 0.01 mol / L hydrochloric acid solution to adjust the pH value of the mother liquor to 2.2, and obtain acidic mother liquor A of different concentrations; S2. Take 10 mL of acidic mother liquor A, heat it to 60°C and keep it at a constant temperature for 5 minutes to decompose all the hexamethylenetetramine in the mother liquor into formaldehyde, and obtain the decomposed mother liquor B. S3. The absorbance value after decomposition was detected by ultraviolet spectrophotometry.

[0047] S301 is the same as S301 in Example 1.

[0048] S302. Record the measurement data as follows: Table 4 shows the absorbance data after the acidic mother liquor A has been reacted at a constant temperature for 5 minutes.

[0049] Table 4

[0050] As shown in Table 4, the SD value of urotropine is ≤0.019 and the RSD value is <5%, indicating that the experimental data are reproducible.

[0051] Comparative Example 1 Unlike Example 4, in S1 the pH of mother liquor A was adjusted to 4, otherwise it was the same as in Example 1.

[0052] The absorbance data of mother liquor A after 5 minutes of constant temperature reaction are shown in Table 5.

[0053] Table 5

[0054] Comparative Example 2 Unlike Example 4, in S1 the pH of the mother liquor A was adjusted to 1.5, otherwise it was the same as in Example 1.

[0055] The absorbance data of mother liquor A after 5 minutes of constant temperature reaction are shown in Table 6.

[0056] Table 6

Claims

1. A method for rapid detection of methenamine in glycine mother liquor, characterized in that, The UV spectrophotometer is used for detection, including the following steps: (1) drawing a formaldehyde standard curve; (2) glycine mother liquor sample test: taking the glycine mother liquor, adding acid to adjust pH to obtain an acidic mother liquor A, measuring the absorbance A1 of the acidic mother liquor A; (3) heating reaction of the acidic mother liquor A until the urotropin in the acidic mother liquor is completely decomposed into formaldehyde to obtain a decomposed mother liquor B, measuring the absorbance A2 of the mother liquor B; (4) The absorbance A1 and A2 are substituted into the formaldehyde standard curve, and the formaldehyde concentration p0 of mother liquor A and the formaldehyde concentration p of mother liquor B are calculated n ; according to the formula p 托品 = (p n -p0) * k, the mass concentration p of urotropine in the glycine mother liquor is calculated 托品 , wherein k = 0.

778.

2. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, The specific steps for drawing the formaldehyde standard curve are: S1, preparing an acetylacetone solution: dissolving ammonium acetate, glacial acetic acid and acetylacetone reagent solution in water to obtain an acetylacetone solution; S2, prepare different concentrations of formaldehyde standard solution, take water as reference to measure the absorbance of different concentrations of formaldehyde standard solution, and obtain the standard curve A r = 0.0245W + 0.0202, R² = 0.9999; wherein, A r is absorbance, and W is formaldehyde mass.

3. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, When measuring the absorbance, the detection wavelength is 414 nm.

4. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, The pH in step (2) is 2-3.

5. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, The reaction temperature in step (3) is 60-70 DEG C.

6. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, The reaction time in step (3) is 4-10 min.

7. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, The reaction temperature in step (3) is 60 DEG C.

8. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, The reaction time in step (3) is 5 min.

9. The method for rapid detection of methenamine in glycine mother liquor according to claim 1, characterized in that, The pH in step (2) is 2.2-2.

8.

10. The method for rapid detection of methenamine in glycine mother liquor according to claim 2, characterized in that, The acetylacetone solution is prepared according to the proportion of 50 g of ammonium acetate, 6 ml of glacial acetic acid, 0.5 ml of acetylacetone reagent and 100 ml of water.

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