Precipitation-based method for determining content of sulfate in urea and used colorimetric tube

Abstract

The invention discloses a precipitation-based method for measuring the content of sulfate in urea and a colorimetric tube used in the method, and relates to the technical field of measurement of the content of impurities in urea, a tube body of the colorimetric tube sequentially comprises a first cylindrical section, a circular truncated cone section, a second cylindrical section and a hemispherical section from top to bottom, the inner diameter of the first cylindrical section is larger than that of the second cylindrical section, and the hemispherical section is a convex lens; during testing, a barium chloride solution is added into a colorimetric tube filled with an acid medium to generate barium sulfate white suspended particles with sulfate ions to be tested, a polyaluminum chloride solution is added, and the mixture is shaken up and then stands, so that the barium sulfate white suspended particles quickly form precipitate aggregation, and bottom precipitate is convenient to observe; the method can determine the range of the sulfate content in the urea according to the calculation process of the visual turbidimetry, improves the accuracy and reproducibility of the test of the sulfate content in the urea, and is simple and easy to operate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of testing the content of impurities in urea, in particular to a method for determining the content of sulfate in urea based on precipitation and a colorimetric tube used. BACKGROUND

[0002] Urea, also known as carbamide or carbamide, has a molecular formula of CH4N2O or CO(NH2)2, is a colorless or white crystal, has no odor, and has a slightly acidic taste. It is a very important organic compound and is widely used in agriculture, industry and medical fields. Industrial-grade urea is used in the urea ammonia system of thermal power plants. Before entering the plant, the quality of each batch should be accepted and the content of main components and impurities should be detected and analyzed. Sulfate is a key impurity. On the one hand, it can combine with metal ions (such as calcium and magnesium) in water to form calcium sulfate, magnesium sulfate and other precipitates, which can cause scaling in pipes and boiler inner walls, reduce thermal efficiency, corrode equipment and increase maintenance costs. On the other hand, direct discharge of industrial wastewater containing high concentrations of sulfate can exacerbate environmental pollution and requires a supporting water treatment process.

[0003] At present, the method for testing the content of sulfate in urea is GB / T 2441.8-2010 "Determination of urea - Part 8: Content of sulfate - Nephelometric method", which adds barium chloride solution to the acid medium to generate white suspended particles of barium sulfate with sulfate ions. The turbidity formed is compared with the standard turbidity. When the content of sulfate in industrial-grade urea is generally not high, the white suspended particles generated by using the above method to compare with the standard turbidity are unstable and have a small content. The formed turbid liquid is difficult to observe and compare visually, which affects the accuracy and reproducibility of the test results.

[0004] The invention patent with the application number 201910826064.X and the title "Method for determining the content of sulfate in urea by spectrophotometry" improves the visual turbidimetry method in the national standard method to spectrophotometry. The turbid liquid formed is determined by absorbance with the standard turbidity liquid, and then the content of low content of sulfate in urea is determined. Although it has high accuracy and good reproducibility, it needs to determine the optimal wavelength and the optimal absorption layer thickness, and the operation is relatively troublesome. Therefore, there is currently no simple and easy-to-operate, high-accuracy and good-reproducibility method for testing the content of sulfate in urea. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a method for determining the content of sulfate in urea based on precipitation and a colorimetric tube used, to solve the problem that the content of sulfate in urea cannot be tested simply, easily, accurately and reproducibly.

[0006] The present application is achieved by the following technical solutions: A colorimetric tube for determining sulfate content in urea, the tube body of the colorimetric tube comprises a first cylindrical segment, a circular truncated cone segment, a second cylindrical segment and a hemispherical segment from top to bottom in sequence; The center of the hemispherical segment is upward, the inner diameter of the first cylindrical segment is larger than that of the second cylindrical segment, the inner diameter of the upper end of the circular truncated cone segment is the same as that of the first cylindrical segment, the inner diameter of the lower end of the circular truncated cone segment is the same as that of the second cylindrical segment, the upper end of the hemispherical segment is smoothly connected with the bottom of the second cylindrical segment, and the hemispherical segment is a convex lens.

[0007] The further improvement of the present application is that: The inner diameter of the first cylindrical segment is 3-5 times of that of the second cylindrical segment.

[0008] The hemispherical segment is a solid structure.

[0009] The capacity of the second cylindrical segment is 0.8-1.2 mL, and the inner diameter is 0.8-1.2 cm.

[0010] A precipitation-based method for determining sulfate content in urea, based on the colorimetric tube for determining sulfate content in urea according to any one of the preceding items, comprising the following steps: Step 1, dissolving the urea to be measured in a colorimetric tube containing deionized water, adding hydrochloric acid and mixing to obtain a mixed solution, then adding deionized water to the colorimetric tube to a volume of V o , and then adding hydrochloric acid to the colorimetric tube to a volume of V , to obtain a first test solution; When the mixed solution is turbid, filter it, wash the filter cake with deionized water, and then combine the filtrate and the washing liquid in the colorimetric tube to a volume of Vo , to obtain a second test solution, the hydrochloric acid content in the first test solution and the second test solution is the same as that in the standard turbidity solution; Step 2, loading the standard turbidity solution into the corresponding colorimetric tube, and simultaneously adding barium chloride solution and polyaluminum chloride solution to the first test solution or the second test solution in the colorimetric tube under constant shaking, and then shaking and standing; Step 3, comparing the precipitates generated by the first test solution or the second test solution with the precipitates generated by the standard turbidity solution, and then determining the range of sulfate content in urea according to the calculation process of the visual turbidimetry, to complete the determination of the sulfate content in urea.

[0011] The mass of the urea to be measured in step 1, the concentration of hydrochloric acid, and the concentration and amount of barium chloride solution in step 2 are all standards of the visual turbidimetry.

[0012] The volume of the polyaluminum chloride solution is 0.8-1.2 mL.

[0013] In step 1, the urea to be measured is dissolved in 25-30 mL of deionized water at 60-80℃, and then hydrochloric acid is added to boil for 2-3 min to obtain a mixed solution.

[0014] In step 1, when the mixed solution is turbid, it is filtered with a tight filter paper, and the obtained filter cake is washed with 60-80 DEG C deionized water for 3-5 times, and then the filter solution and the washing solution are combined.

[0015] The standing time in step 2 is 10-15 min.

[0016] Compared with the prior art, the present application has the following beneficial technical effects: The colorimetric tube for determining the sulfate content in urea is based on the principle that barium chloride solution is added in an acidic medium to generate white barium sulfate suspended particles with sulfate ions to be measured, and polyaluminum chloride solution is added to quickly form precipitated aggregates of the white barium sulfate suspended particles. The tube body of the colorimetric tube is designed to sequentially include a first cylindrical segment, a circular segment, a second cylindrical segment and a hemispherical segment from top to bottom. Since the inner diameter of the first cylindrical segment is larger than that of the second cylindrical segment, the space required for observing the precipitate can be reduced. Since the precipitate is close to the hemispherical segment as a convex lens, the precipitate can be further enlarged, facilitating the observation of the bottom precipitate, and thus improving the accuracy and reproducibility of the sulfate content test in urea.

[0017] The method for determining the sulfate content in urea based on precipitation is also based on the principle that barium chloride solution is added in an acidic medium to generate white barium sulfate suspended particles with sulfate ions to be measured, and polyaluminum chloride solution is used to agglomerate, adsorb and precipitate the white barium sulfate suspended particles due to its strong bridging adsorption performance, to quickly form precipitated aggregates. Therefore, the urea to be measured is dissolved in a colorimetric tube containing deionized water, mixed with hydrochloric acid, and then diluted to volume. When the mixed solution is turbid, it needs to be filtered. The obtained filter cake is washed with deionized water, and then the filter solution and the washing solution are combined. Then, the standard turbidimetric solution is loaded into the corresponding colorimetric tube. The barium chloride solution and the polyaluminum chloride solution are added into the colorimetric tube containing the test solution under continuous shaking. After shaking, the test solution is allowed to stand. The polyaluminum chloride converts the original weak suspended state into a significant and easily observable precipitated aggregate state, which is further enlarged by the convex lens at the bottom of the colorimetric tube, facilitating the observation of the bottom precipitate, and thus improving the accuracy and reproducibility of the sulfate content test in urea. The method is simple and easy to operate, avoids the disadvantage that it is difficult to observe and judge when the turbidity content is low, has high accuracy and good result reproducibility. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The figure shows the structure of the improved colorimetric tube.

[0019] In the figure, 1 is a tube body, 2 is a convex lens, and 3 is a tube plug. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with examples, which are the explanation but not limitation of the present application.

[0021] The present application is a precipitation-based method for determining the sulfate content in urea, in which barium chloride solution is added to an acidic medium to form barium sulfate white suspended particles with the sulfate ions to be measured, and polyaluminum chloride solution is added to make the barium sulfate white suspended particles quickly form a precipitate aggregation, and the formed precipitate is compared with a standard precipitate. The method comprises the following steps: Firstly, 0, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL and 3.50 mL of sulfate standard solution (0.1 mg / mL) are respectively added to 8 25 mL cuvettes, 2 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water) is added, and deionized water is added to 20 mL to obtain standard turbidity liquid for standby.

[0022] Secondly, about 10 g of laboratory sample (accurate to 0.1 g) is weighed, the sample is dissolved in 25 mL~30 mL of 60~80℃ deionized water, 10 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water) is added, and heated to boiling for 2~3 min. If the solution is turbid, it is filtered with a tight filter paper, and the filter cake is washed with 2~3 mL of 60~80℃ deionized water for 3~5 times, the filtrate and washing liquid are collected in a 50 mL volumetric flask, cooled to room temperature, diluted to the mark with deionized water, and mixed to obtain a test solution.

[0023] Thirdly, 10.0 mL of the test solution is taken in a 25 mL cuvette, deionized water is added to 20 mL, 1 mL of barium chloride solution (250 g / L) is added dropwise under continuous shaking, and 1 mL of polyaluminum chloride solution with a concentration of 8~12 g / L is diluted to the mark with deionized water, shaken well and placed for 10~15 min, and the precipitate in the first step cuvette is compared.

[0024] In order to facilitate observation of the bottom precipitate, the present application improves the cuvette, and the cuvette body 1 is designed into four sections, as shown in Figure 1As shown, from top to bottom are a first cylindrical segment, a circular truncated cone segment, a second cylindrical segment and a hemispherical segment, the center of the hemispherical segment is upward, a tube plug 3 is arranged on the first cylindrical segment, the position close to the bottom of the tube plug 3 is a 25mL scale line, the inner diameter of the first cylindrical segment is 3-5 times of the second cylindrical segment, the upper end inner diameter of the circular truncated cone segment is the same as that of the first cylindrical segment, the lower end inner diameter of the circular truncated cone segment is the same as that of the second cylindrical segment, the capacity of the second cylindrical segment is 1mL and is marked with a scale line, the inner diameter is 0.1cm, the hemispherical segment is a solid convex lens 2, which is smoothly connected with the bottom of the second cylindrical segment, has a magnifying effect, can replace the previous cuvette and is convenient for observing the bottom precipitate.

[0025] Fourthly, the sulfate concentration is calculated according to the following formula: In the formula, w=v(0.1 / 1000) / [(10 / 50)m]=0.05v / m v is the value of the volume of the sulfate standard solution in the standard turbidity solution with the same turbidity as the test part, in milliliter (mL); m is the value of the mass of the sample, in gram (g).

[0026] The calculation result is expressed to four decimal places.

[0027] The sulfate content determination method based on precipitation of the urea of the application uses the improved cuvette, wherein the inner diameter of the first cylindrical segment is 4 times of the second cylindrical segment, for the convenience of description, the following embodiments are uniformly expressed as cuvettes. Example 1 Firstly, 0, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL and 3.50 mL of sulfate standard solution are respectively added into 8 cuvettes, 2mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water) is added, deionized water is added to 20mL, and the mixture is prepared.

[0028] Secondly, about 10.1g of laboratory sample (accurate to 0.1g) is weighed, the sample is dissolved in 25mL of 60℃ deionized water, 10mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water) is added, and the mixture is heated and boiled for 2min, at this time, the solution is turbid, the solution is filtered with a tight filter paper, and the filter paper is washed with 3mL of 60℃ deionized water for 3 times, the filtrate and the washing liquid are collected in a 50mL volumetric flask, and the mixture is cooled to room temperature, diluted with deionized water to the scale, and mixed uniformly.

[0029] Third step: Take 10.0 mL of the test solution in a 25 mL cuvette, add deionized water to 20 mL, and add 1 mL of barium chloride solution (250 g / L) dropwise while constantly shaking, and add 1 mL of polyaluminum chloride solution with a concentration of 10 g / L diluted to the mark with deionized water. Shake well and let stand for 10 min. Compare the precipitate with that in the cuvette of the first step.

[0030] Visually compare the sample precipitate with the 0.50 mL standard sample precipitate.

[0031] Fourth step: Calculate the sulfate concentration according to the following formula: w = v(0.1 / 1000) / [(10 / 50)m] = 0.05v / m In the formula: v - the numerical value of the volume of the sulfate standard solution in the standard turbidity solution with the same turbidity as the test part, in milliliters (mL); m - the numerical value of the mass of the sample, in grams (g).

[0032] The calculation result is expressed to four decimal places.

[0033] The calculation result is less than 0.0025%.

[0034] Example 2 First step: In 8 25 mL cuvettes, add 0, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL, and 3.50 mL of sulfate standard solution, respectively, add 2 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water), and add deionized water to 20 mL. Wait for use.

[0035] Second step: Weigh about 10.0 g of laboratory sample (accurate to 0.1 g), dissolve the sample in 30 mL of 80°C deionized water, add 10 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water), heat and boil for 2 min, at which time the solution is turbid, filter with a tight filter paper, and wash with 2 mL of 80°C deionized water 3 times. Collect the filtrate and wash in a 50 mL volumetric flask, cool to room temperature, dilute to the mark with deionized water, and mix well.

[0036] Third step: Take 10.0 mL of the test solution in a 25 mL cuvette, add deionized water to 20 mL, and add 1 mL of barium chloride solution (250 g / L) dropwise while constantly shaking, and add 1 mL of polyaluminum chloride solution with a concentration of 10 g / L diluted to the mark with deionized water. Shake well and let stand for 10 min. Compare the precipitate with that in the cuvette of the first step.

[0037] Visually compare the sample precipitate to less than 2.00 mL of the standard sample precipitate.

[0038] Fourth Step Calculate the sulfate concentration according to the following formula: w = v(0.1 / 1000) / [(10 / 50)m] = 0.05v / m In the formula: v - the value of the volume of the sulfate standard solution in the standard turbidity test portion, in milliliters (mL); m - the value of the mass of the sample, in grams (g).

[0039] The calculation result is expressed to four decimal places.

[0040] The calculation result is less than 0.0100%.

[0041] Example 3 First Step In 8 25 mL cuvettes, respectively add 0, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL, 3.50 mL of the sulfate standard solution, add 2 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water), and add deionized water to 20 mL, ready for use.

[0042] Second Step Weigh about 10.0 g of the laboratory sample (accurate to 0.1 g), dissolve the sample in 25 mL of 70°C deionized water, add 10 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water), heat and boil for 2 min, at which time the solution is turbid, filter with a tight filter paper, and wash 3 times with 3 mL of 70°C deionized water, collect the filtrate and wash in a 50 mL volumetric flask, cool to room temperature, dilute to the mark with deionized water, and mix well.

[0043] Third Step Take 10.0 mL of the test solution in a 25 mL cuvette, add deionized water to 20 mL, and at the same time as the cuvettes in the first step, add 1 mL of barium chloride solution (250 g / L) dropwise with constant shaking, add 1 mL of polyaluminum chloride solution with a concentration of 10 g / L diluted to the mark with deionized water, shake well, and let stand for 10 min, and compare the precipitate with the precipitate in the cuvettes in the first step.

[0044] Visually compare the sample precipitate to less than 0.50 mL of the standard sample precipitate.

[0045] Fourth Step Calculate the sulfate concentration according to the following formula: w = v(0.1 / 1000) / [(10 / 50)m] = 0.05v / m In the formula: v - the value of the volume of the sulfate standard solution in milliliters (mL) in the standard turbidimetric solution with the same turbidity as the test portion; m - the value of the mass of the test sample in grams (g).

[0046] The result of the calculation is indicated to four decimal places.

[0047] The result of the calculation is less than 0.0025%.

[0048] Example 4 First step In eight 25 mL cuvettes, 0, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL, 3.50 mL of the sulfate standard solution were added, respectively, 2 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water) was added, and deionized water was added to 20 mL, ready for use.

[0049] Second step About 10.0 g of the laboratory sample was weighed (accurate to 0.1 g), the test sample was dissolved in 25 mL of 70°C deionized water, 10 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water) was added, and heated to boiling for 2 min, at which time the solution was turbid, filtered with a tight filter paper, and washed with 3 mL of 70°C deionized water 3 times, the filtrate and wash were collected in a 50 mL volumetric flask, cooled to room temperature, diluted to the mark with deionized water, and mixed well.

[0050] Third step 10.0 mL of the test solution was taken in a 25 mL cuvette, deionized water was added to 20 mL, 1 mL of barium chloride solution (250 g / L) was added dropwise under constant shaking, 1 mL of polyaluminum chloride solution with a concentration of 10 g / L was diluted to the mark with deionized water, shaken well, and placed for 10 min, and the precipitate was compared with that in the cuvettes of the first step.

[0051] Visually compare the sample precipitate with the precipitate of the 3.50 mL standard sample.

[0052] Fourth step The sulfate concentration was calculated according to the following formula: w = v (0.1 / 1000) / [(10 / 50) m] = 0.05 v / m In the formula: v - the value of the volume of the sulfate standard solution in milliliters (mL) in the standard turbidimetric solution with the same turbidity as the test portion; m - the value of the mass of the test sample in grams (g).

[0053] The result of the calculation is indicated to four decimal places.

[0054] The result of the calculation is greater than 0.0175%.

[0055] Example 5 First Step In 8 25 mL cuvettes, respectively, add 0, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL, 3.50 mL sulfate standard solution, add 2 mL hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water), add deionized water to 20 mL, and wait for use.

[0056] Second Step Weigh about 10.0 g laboratory sample (accurate to 0.1 g), dissolve the sample in 25 mL of 70°C deionized water, add 10 mL of hydrochloric acid (1 volume of concentrated hydrochloric acid and 1 volume of deionized water), heat and boil for 2 min, at which time the solution is turbid, filter with tight filter paper, and wash 3 times with 3 mL of 70°C deionized water, collect the filtrate and wash in a 50 mL volumetric flask, cool to room temperature, dilute to the mark with deionized water, and mix well.

[0057] Third Step Take 10.0 mL of the test solution in a 25 mL cuvette, add deionized water to 20 mL, and at the same time as the cuvettes in the first step, add 1 mL of barium chloride solution (250 g / L) dropwise with constant shaking, add 1 mL of polyaluminum chloride solution with a concentration of 10 g / L diluted to the mark with deionized water, shake well, and let stand for 15 min, and compare the precipitate with that in the cuvettes in the first step.

[0058] Visually compare the sample precipitate with less than 3.00 mL of the standard sample precipitate.

[0059] Fourth Step Calculate the sulfate concentration according to the following formula: w = v (0.1 / 1000) / [(10 / 50) m] = 0.05 v / m In the formula: v - the value of the volume of the sulfate standard solution in the standard turbidity solution with the same turbidity as the test part, in milliliters (mL); m - the value of the mass of the sample, in grams (g).

[0060] The calculation result is expressed to four decimal places.

[0061] The calculation result is less than 0.0150%.

Claims

1. A colorimetric tube for determination of sulfate content in urea, characterized in that, The tube body (1) of the cuvette comprises a first cylindrical section, a circular truncated cone section, a second cylindrical section and a hemispherical section from top to bottom in sequence. The center of the hemispherical section is upward, the inner diameter of the first cylindrical section is larger than that of the second cylindrical section, the inner diameter of the upper end of the circular truncated cone section is the same as that of the first cylindrical section, the inner diameter of the lower end of the circular truncated cone section is the same as that of the second cylindrical section, the upper end of the hemispherical section is smoothly connected with the bottom of the second cylindrical section, and the hemispherical section is a convex lens (2).

2. The colorimetric tube for determining sulfate content in urea according to claim 1, characterized in that, The inner diameter of the first cylindrical section is 3-5 times of that of the second cylindrical section.

3. The colorimetric tube for determining sulfate content in urea according to claim 1, characterized in that, The hemispherical section is a solid structure.

4. The colorimetric tube for determining the sulfate content in urea according to claim 3, characterized in that, The capacity of the second cylindrical section is 0.8-1.2 mL, and the inner diameter is 0.8-1.2 cm.

5. A method for determining the sulfate content of a precipitate-based urea, characterized in that, The cuvette for determining the sulfate content in urea according to any one of claims 1-4 comprises the following steps: S1, dissolve the urea to be tested in a colorimetric tube containing deionized water, mix with hydrochloric acid to obtain a mixed solution, and then add deionized water to the mixed solution to obtain a first test solution o dilute to volume, and obtain the first test solution; When the mixed solution is turbid, filtering is performed, the obtained filter cake is washed with deionized water, and then the filter solution and the washing solution are combined into the cuvette and then constant volume is performed according to the set volume Vo to obtain a second test solution, the hydrochloric acid content in the first test solution and the second test solution is the same as that in the standard turbidity solution; S2, the standard turbidity solution is loaded into the corresponding cuvette, and the barium chloride solution and the polyaluminum chloride solution are added dropwise into the first test solution or the second test solution in the cuvette under constant shaking, and then shaking and standing are performed; S3, by comparing the precipitates generated by the first test solution or the second test solution with the precipitates generated by the standard turbidity solution, the range of the sulfate content in urea is determined according to the calculation process of the visual turbidimetry, and the determination of the sulfate content in urea is completed.

6. The precipitation-based urea sulphate content assay of claim 5, wherein, The mass of the urea to be measured, the concentration of the hydrochloric acid in S1, and the concentration and amount of the barium chloride solution in S2 are all standards of the visual turbidimetry, and the concentration of the polyaluminum chloride solution in S2 is 8-12 g / L.

7. The precipitation-based urea sulphate content assay of claim 6, wherein, The volume of the polyaluminum chloride solution is 0.8-1.2 mL.

8. The precipitation-based urea sulphate content assay of claim 6, wherein, In S1, the urea to be measured is dissolved in 25-30 mL of deionized water at 60-80℃, and then hydrochloric acid is added and boiled for 2-3 min to obtain a mixed solution.

9. The precipitation-based urea sulphate content assay of claim 8, wherein, In S1, when the mixed solution is turbid, filtering is performed with tight filter paper, the obtained filter cake is washed with 60-80℃ deionized water for 3-5 times, and then the filter solution and the washing solution are combined.

10. The precipitation-based urea sulphate content assay of claim 5, wherein, The standing time in S2 is 10-15 min.

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