Method for measuring content of residual acrylonitrile in polyacrylonitrile polymer liquid

Abstract

The invention relates to a method for measuring the content of residual acrylonitrile in polyacrylonitrile polymer liquid, and relates to the technical field of chemical analysis. The method comprises the following steps: stirring and dissolving a polyacrylonitrile polymerization liquid sample with an organic solvent, and diluting with water to obtain a sample solution; adding a salting-out agent into the sample solution, stirring and dissolving, and standing for a set time to obtain a solution added with the salting-out agent; adding a sodium sulfite solution into the solution in which the salting-out agent is added, carrying out addition reaction on sodium sulfite and acrylonitrile AN under a heating condition, and cooling after the reaction is carried out for a set time to terminate the reaction, so as to obtain a reaction product mixture; carrying out solid-liquid separation on the reaction product mixture to obtain filtrate; and titrating the filtrate and the blank sample by adopting an acid-base back titration method, and then calculating the content of residual acrylonitrile in the polyacrylonitrile polymer liquid according to experimental data. The method disclosed by the invention has the advantages of high accuracy, good repeatability and convenience in operation.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis technology, and in particular to a method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solutions. Background Technology

[0002] Polyacrylonitrile (PAN) carbon fiber is widely used in aerospace and other fields due to its excellent properties. Its preparation involves three main processes: polymerization, spinning, and carbonization. Among these, polymerization is the starting point of carbon fiber production and a key step in producing high-quality precursor fibers. Therefore, it is essential to accurately measure the residual acrylonitrile content in the polyacrylonitrile polymerization solution to better guide on-site process adjustments and ultimately improve the quality of the finished carbon fiber.

[0003] In existing technologies, the determination of residual acrylonitrile content in polyacrylonitrile polymerization solutions almost exclusively employs chemical titration methods, such as CN 106370773. The main principle of this method is that acrylonitrile undergoes an addition reaction with sodium sulfite in an aqueous solution, generating a quantitative amount of NaOH solution. Alizarin Yellow R-vanillin phthalide is used as an indicator, and titration is performed with a standard sulfuric acid solution. The residual acrylonitrile content is calculated based on the volume of standard sulfuric acid solution consumed. This method is currently the most widely used due to its simplicity, but it has certain drawbacks, mainly as follows: Traditional methods for detecting residual acrylonitrile in polyacrylonitrile polymerization solutions typically involve directly dissolving the polymerization sample in DMSO, adding a certain amount of water, and then performing subsequent testing. However, upon adding water, the local osmotic pressure of the solution changes, causing PAN chains to aggregate and even precipitate. Due to the entanglement of the PAN polymer chains, some AN ​​monomers are physically "encapsulated," making it difficult to fully react with sodium sulfite, resulting in lower detection results. Furthermore, the release of this AN portion takes a considerable amount of time, failing to provide timely and effective guidance for on-site process adjustments. Furthermore, the indicator used in this method is Alizarin Yellow R-thymolphthalein, which has a wide color change range; the solution color changes from pale blue to yellowish-green before and after titration, but the color change is not very obvious. Moreover, interference from PAN precipitated from the high-viscosity polymerization solution, impurities in the DMSO solution, and by-products from the addition reaction are significant. This exacerbates the operator's reliance on the endpoint color change, leading to large titration errors and inaccurate experimental results.

[0004] In addition, there is a related technology (CN 115616144 B) that uses a fully automated potentiometric titrator to determine the residual acrylonitrile content in polyacrylonitrile polymerization solution. It uses a potential jump or a fixed endpoint pH value to determine the reaction endpoint, achieving an AN content detection accuracy of 0.1%. However, the fully automated potentiometric titrator used in this method uses an open beaker as the titration container, which has poor sealing. AN is easily volatilized during the reaction, leading to inaccurate results, and AN residues may remain in the environment, affecting human health. Furthermore, operators require a certain amount of training before they can operate the instrument, resulting in high labor costs and a long testing time.

[0005] Therefore, there is an urgent need to develop a novel method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solutions in order to improve the accuracy of detection. Summary of the Invention

[0006] In view of this, the present invention provides a method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution, the main purpose of which is to improve the accuracy of detection.

[0007] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0008] On one hand, embodiments of the present invention provide a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, comprising the following steps:

[0009] Sample solution preparation steps: Dissolve the polyacrylonitrile polymer solution sample in an organic solvent by stirring, and then dilute with water to obtain the sample solution;

[0010] Adding salting-out agent step: Add salting-out agent to the sample solution, stir to dissolve, and let stand for a set time to allow acrylonitrile to accumulate and be released from the PAN chain, thus obtaining the solution after adding salting-out agent;

[0011] Addition reaction step: Add sodium sulfite solution to the solution after adding salting-out agent, and allow sodium sulfite to react with acrylonitrile AN under heating conditions. After a set reaction time, cool to terminate the reaction and obtain a mixture of reaction products; perform solid-liquid separation on the mixture of reaction products to obtain filtrate;

[0012] Acid-base back titration method steps: The filtrate and blank sample are titrated using the acid-base back titration method, and then the residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated based on the experimental data.

[0013] Preferably, in the step of preparing the sample solution, the organic solvent is one or more of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0014] Preferably, in the step of adding the salting-out agent: the salting-out agent is any one or more of the following: solid sodium chloride, sodium chloride solution, solid ammonium sulfate, ammonium sulfate solution, solid potassium chloride, and potassium chloride solution.

[0015] Preferably, in the step of adding the salting-out agent: if the salting-out agent is a liquid, the concentration of the salting-out agent in the solution after adding the salting-out agent should be 0.3 mol / L to 0.7 mol / L.

[0016] Preferably, in the step of adding the salting-out agent: if the salting-out agent is a liquid, the concentration of the salting-out agent in the solution after adding the salting-out agent should be 0.5 mol / L.

[0017] Preferably, in the step of adding the salting-out agent: if the salting-out agent is a solid, then 1.46g to 4.38g of salting-out agent needs to be added to every 80mL of sample solution.

[0018] Preferably, in the step of adding the salting-out agent: if the salting-out agent is a solid, then 2.34 g of salting-out agent needs to be added to every 80 mL of sample solution.

[0019] Preferably, in the step of adding the salting-out agent:

[0020] If the salting-out agent is a liquid, it must be added drop by drop while stirring when adding it to the sample solution;

[0021] If the salting-out agent is a solid, it needs to be added to the sample solution in multiple batches; after the previous batch of salting-out agent has dissolved, the next batch of salting-out agent should be added.

[0022] Preferably, in the step of adding the salting-out agent: the salting-out agent is added to the sample solution, and after the salting-out agent is stirred and dissolved, it needs to stand for 5 min to 15 min to allow acrylonitrile to accumulate and be released from the PAN chain.

[0023] Preferably, in the addition reaction step: the temperature of the addition reaction is 45 ℃ to 55 ℃; and the time of the addition reaction is 5 min to 15 min.

[0024] Preferably, in the addition reaction step: the temperature of the addition reaction is 50°C; and the time of the addition reaction is 10 min.

[0025] Preferably, in the addition reaction step, the cooling method is an ice bath or a cold water bath.

[0026] Preferably, the acid-base back titration step includes:

[0027] Step 1): Transfer all the filtrate obtained in the addition reaction step to a volumetric flask, and then add water to the set mark. The volume obtained is V. 总 A diluted solution;

[0028] Step 2): From the volume V 总 A volume of V was taken from the diluted solution. 移 The diluted solution was transferred to a titration vessel. Using reverse titration, an excess of a known concentration of acid standard solution was first added to the titration vessel, followed by the addition of a pH indicator. Then, titration was performed with a known concentration of alkali standard solution. Titration was stopped when the solution color changed from pale pink to green, and the volume of alkali standard solution consumed was recorded as V. 样 ;

[0029] Step 3): Using the reverse titration method, first add an excess of acid standard solution of known concentration to the blank sample, then add a pH indicator, and then titrate with a base standard solution of known concentration. Stop the titration when the solution color changes from light pink to green, and record the volume V of base standard solution consumed in the blank experiment. 白 ;

[0030] Step 4): Based on the mass m of the polyacrylonitrile polymerization solution sample 样 V 总 V 移 V 样 V 白 The residual acrylonitrile content in the polyacrylonitrile polymerization solution was calculated.

[0031] Preferably, in the back titration step: V 移 / V 总 The ratio is 1:10 to 1:1.

[0032] Preferably, in the back titration step: the pH indicator is a mixed solution comprising methyl red and bromocresol green; wherein the mass ratio of methyl red to bromocresol green is 1:1 to 3:1.

[0033] Preferably, in the back titration step, the mass ratio of methyl red to bromocresol green is 2:1.

[0034] Preferably, in the back titration step, the pH indicator further includes an ethanol solvent.

[0035] Preferably, in step 4), the residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula:

[0036]

[0037] Where: V 样The volume of alkaline standard solution consumed in step 2) is in mL.

[0038] V 白 The volume of alkaline standard solution consumed in step 3) is in mL.

[0039] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0040] m 样 The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams.

[0041] V 总 This represents the total volume of the solution after dilution, in mL.

[0042] V 移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution is expressed in mL.

[0043] Among them, V 移 / V 总 This refers to the proportion of solution transferred.

[0044] 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

[0045] Compared with the prior art, the method for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquor of the present invention has at least the following beneficial effects:

[0046] This invention provides a method for determining the residual acrylonitrile content in polyacrylonitrile (PAI) polymerization solutions. It introduces for the first time a salting-out agent step, utilizing the salting-out effect to effectively separate acrylonitrile (AN) from the matrix, forcing AN to dissociate from the PAN chains and enter the solution phase. This allows for a more complete addition reaction with sodium sulfite, significantly improving the detection sensitivity and accuracy of AN. Furthermore, in the addition reaction step, the invention accelerates the reaction by heating, shortening the detection time, followed by immediate cooling (ice bath) to reduce side reactions. Additionally, the invention employs filtration after the addition reaction to effectively separate impurities and obtain a clear solution, facilitating subsequent titration endpoint determination.

[0047] Furthermore, this embodiment of the invention provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution. The pH indicator used in the acid-base back titration step is a methyl red-bromocresol green indicator. The sulfonic acid group of methyl red remains dissociated in the DMSO-water system and is not inhibited by organic solvents. The bromine atoms of bromocresol green can enhance the electron cloud density, making the green color still visible in the turbid liquid. These two advantages ensure that the solution color changes from light pink to green at the titration endpoint, the solution color difference is obvious, and the visual recognition is greatly improved.

[0048] In summary, this invention employs salting-out separation and back titration, effectively solving the problems of inaccurate endpoint color determination and significant interference in the solution system in traditional titration methods. It has the advantages of high accuracy, good repeatability, and convenient operation.

[0049] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0050] Figure 1 This is a flowchart illustrating a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, as provided in an embodiment of the present invention.

[0051] Figure 2 This is a comparison chart of the color change of the pH indicator before and after titration in Example 2 and Comparative Example 2; wherein, the pH indicator used in Comparative Example 2 is Alizarin Yellow R-thymolphthalein indicator; and the pH indicator used in Example 2 is Methyl Red-Bromocresol Green indicator. Detailed Implementation

[0052] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0053] This invention primarily addresses the low detection sensitivity caused by AN encapsulation in traditional methods, further resolving issues such as difficulty in identifying the titration endpoint color and complex operation. The core innovations of this invention lie in addressing the pain points of determining residual AN content in high-viscosity polyacrylonitrile polymerization solutions through methods such as adding a salting-out agent to release encapsulated AN, heating to accelerate the addition reaction rate, cooling to suppress side reactions, and replacing the mixed indicator. The main solutions of this invention are as follows:

[0054] This invention provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, comprising the following steps:

[0055] Sample solution preparation steps: Take the polyacrylonitrile polymerization solution sample (mass denoted as m) 样 Dissolve the sample by stirring with an organic solvent and then dilute with water to obtain the sample solution.

[0056] The organic solvent is one or more of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0057] Adding salting-out agent step: Add salting-out agent to the sample solution, stir to dissolve, and let stand for a set time (5min~15min) to allow acrylonitrile to accumulate and be released from the PAN chain, thus obtaining the solution after adding salting-out agent.

[0058] The salting-out agent is any one or more of the following: solid sodium chloride, sodium chloride solution, solid ammonium sulfate, ammonium sulfate solution, solid potassium chloride, and potassium chloride solution.

[0059] If the salting-out agent is a liquid, the concentration of the salting-out agent in the solution after adding the salting-out agent should be 0.3 mol / L to 0.7 mol / L, preferably 0.5 mol / L.

[0060] If the salting-out agent is a solid, then 1.46g to 4.38g (preferably 2.34g) of salting-out agent needs to be added to every 80mL of sample solution.

[0061] If the salting-out agent is a liquid, it must be added drop by drop while stirring when adding it to the sample solution;

[0062] If the salting-out agent is a solid, it should be added to the sample solution in multiple batches. After the previous batch of salting-out agent has dissolved, the next batch of salting-out agent should be added (preferably, it should be added in three batches; after the first batch is added, stir for a few minutes until it is completely dissolved, then add the second batch, stir until it is dissolved, and then add the last batch).

[0063] In this step, the volume of organic solvent added is 30 mL ± 1 mL, and the volume of water added is 50 mL ± 1 mL.

[0064] Addition reaction steps: Add sodium sulfite solution to the solution after adding salting-out agent, and allow sodium sulfite to undergo an addition reaction with acrylonitrile AN under heating conditions. After a set reaction time, cool to terminate the reaction and obtain a mixture of reaction products. Perform solid-liquid separation on the mixture of reaction products to obtain filtrate.

[0065] The addition reaction is carried out at a temperature of 45°C to 55°C (preferably 50°C) and for a duration of 5 min to 15 min (preferably 10 min).

[0066] The cooling method is an ice bath or a cold water bath (preferably an ice bath for 5 minutes) to reduce the occurrence of side reactions.

[0067] For solid-liquid separation, filtration or centrifugation is used.

[0068] Acid-base back titration method steps: The filtrate and blank sample are titrated using the acid-base back titration method, and then the residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated based on the experimental data.

[0069] Step 1): Transfer all the filtrate obtained in the addition reaction step to a volumetric flask, and then add water to the set mark. The volume obtained is V. 总 A solution that has been brought to a constant volume.

[0070] Step 2): From the volume V 总 A volume of V was taken from the diluted solution. 移 The diluted solution was transferred to a titration vessel. Using reverse titration, an excess of a known concentration of acid standard solution was first added to the titration vessel, followed by the addition of a pH indicator. Then, titration was performed with a known concentration of alkali standard solution. Titration was stopped when the solution color changed from pale pink to green, and the volume of alkali standard solution consumed was recorded as V. 样 .

[0071] Among them, V 移 The value of V can be adjusted according to the residual acrylonitrile content in the sample to be tested. 移 / V 总 This is the solution transfer ratio, which is between 1:10 and 1:1.

[0072] The pH indicator is a mixed solution comprising methyl red and bromocresol green; wherein the mass ratio of methyl red to bromocresol green is 1:1 to 3:1, preferably 2:1.

[0073] In the back titration step, the mass ratio of methyl red to bromocresol green is 2:1.

[0074] In the back titration step, the pH indicator further includes an ethanol solvent. Preferably, the formulation step of the pH indicator includes: dissolving 0.1 g ± 0.001 g bromocresol green and 0.2 g ± 0.001 g methyl red in 100 mL ± 1 mL of 95% ± 1% ethanol, mixing, and shaking well.

[0075] In simple acid-base titrations, the endpoint color of the pH indicator changes abruptly from light pink, red, or orange-red to green, yellow-green, or gray-green. However, in the titration system of this invention, the endpoint color of the pH indicator changes from light pink to green.

[0076] Step 3): Using the reverse titration method, first add an excess of a known acid standard solution to the blank sample, then add a pH indicator, and then titrate with a known concentration of alkali standard solution. Stop the titration when the solution color changes from light pink to green, and record the volume V of alkali standard solution consumed in the blank experiment. 白 .

[0077] In this step, it should be noted that the blank sample and the sample with a volume of V 移 The difference between the prepared solution and the blank sample is that the blank sample does not contain the original sample. The preparation steps for the blank sample are as follows:

[0078] 1) Mix the organic solvent and water to obtain a blank solution. The difference between the blank solution and the sample solution is that the blank solution does not contain the sample. However, the blank solution and the sample solution use the same amount of organic solvent and the same amount of water.

[0079] 2): Same as the above steps for adding salting-out agent.

[0080] 3): Same as the addition reaction steps described above.

[0081] 4): Transfer all the filtrate obtained in the addition reaction step to a volumetric flask, and then add water to the set mark. The volume obtained is V. 总 The blank solution.

[0082] From the volume of V 总 A volume of V was taken from the blank solution. 移 The diluted solution was used as a blank sample.

[0083] Step 4): Based on the mass m of the polyacrylonitrile polymerization solution sample 样 V 总 V 移 V 样 V 白 The residual acrylonitrile content in the polyacrylonitrile polymerization solution was calculated.

[0084] In the calculation step, the residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula:

[0085]

[0086] Where: V 样 The volume of alkaline standard solution consumed in the back titration step is expressed in mL.

[0087] V 白 The volume of alkaline standard solution consumed in the blank experimental step is expressed in mL.

[0088] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0089] m 样 The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams.

[0090] V 总 This represents the total volume of the solution after dilution, in mL.

[0091] V 移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution, expressed in mL; V 移 / V 总 This refers to the proportion of solution transferred.

[0092] 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

[0093] This invention provides a method for determining the residual acrylonitrile content in polyacrylonitrile (PAI) polymerization solutions. A salting-out agent is added to the sample solution, utilizing the salting-out effect to effectively separate AN from the matrix, forcing AN to dissociate from the PAN chains and enter the solution phase. This allows for a more complete addition reaction with sodium sulfite, significantly improving the detection sensitivity and accuracy of AN. Furthermore, this invention accelerates the addition reaction by heating, shortening the detection time, followed by immediate cooling (ice bath) to reduce side reactions. Additionally, filtration after the addition reaction effectively separates impurities, yielding a clear solution that facilitates easier determination of the titration endpoint. Furthermore, the methyl red-bromocresol green indicator used in this invention utilizes the fact that the sulfonic acid groups of methyl red remain dissociated in the DMSO-water system, unaffected by organic solvents, while the bromine atoms of bromocresol green enhance electron cloud density, making the green color visible even in turbid solutions. These two advantages ensure that the solution color changes from light pink to green at the titration endpoint, with a clear color difference and significantly improved visual visibility.

[0094] The present invention will be further illustrated below with specific embodiments:

[0095] Example 1

[0096] This embodiment provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, which includes the following steps:

[0097] Sample solution preparation steps: Weigh 1.5021g, 1.4932g, 1.4336g, and 1.4203g of polyacrylonitrile polymerization solution samples and place them into four 250mL Erlenmeyer flasks respectively, and quickly cap the flasks. Then add 30mL of DMSO solution to each of the four Erlenmeyer flasks, place the flasks on a magnetic stirrer, and stir magnetically at 30℃ for 15min until the polyacrylonitrile polymerization solution is completely dissolved. Then add 50mL of ultrapure water to each of the four Erlenmeyer flasks, shake well, and you will get four sample solutions.

[0098] Adding salting-out agent: Add 2.34g of solid sodium chloride to each of the four sample solutions (in three portions, stirring as you add). After all the sodium chloride has been added, let it stand for 5 minutes to obtain four solutions with added salting-out agent.

[0099] Addition reaction steps: Add 20 mL of 0.1 mol / L Na2SO3 solution to each of the four solutions after adding the salting-out agent, then heat at 50 °C for 10 minutes, and immediately place in an ice bath for 5 minutes to terminate the reaction and obtain a mixture of reaction products; perform solid-liquid separation on the mixture of reaction products to obtain four filtrate samples.

[0100] Acid-base back titration procedure: Transfer each filtrate sample to four separate 100 mL volumetric flasks, and dilute to the mark with ultrapure water to obtain four volumes of V. 总 A diluted solution; wherein, V 总 =100mL.

[0101] Take V from each of the four solutions that have been brought to a constant volume. 移 25 mL of solution was poured into four Erlenmeyer flasks. 18 mL of 0.1 mol / L H₂SO₄ standard solution was added to each flask, followed by 5 drops of methyl red-bromocresol green indicator. Titration with 0.1 mol / L sodium hydroxide standard solution continued until the solution changed abruptly from light pink to green. The volumes of sodium hydroxide standard solution consumed were 15.81 mL, 15.83 mL, 15.93 mL, and 15.96 mL, respectively.

[0102] Blank Experiment: Take 30 mL of DMSO solution in an Erlenmeyer flask and stir magnetically for 15 minutes at 30°C. Add 50 mL of ultrapure water and shake well to obtain a blank solution. Add 2.34 g of solid sodium chloride to the blank solution in three portions, stirring continuously. After all the sodium chloride has been added, let stand for 5 minutes to obtain the solution with added salting-out agent. Add 20 mL of 0.1 mol / L Na₂SO₃ solution to the solution with added salting-out agent, heat at 50°C for 10 minutes, and then immediately place in an ice bath for 5 minutes to obtain the product solution. Filter the product solution and transfer it to a 100 mL volumetric flask. Dilute to the mark with ultrapure water. 总 =100mL. Accurately transfer V 移 Add 25 mL of diluted solution to an Erlenmeyer flask, then add 18 mL of 0.1 mol / L H₂SO₄ standard solution, followed by 5 drops of methyl red-bromocresol green indicator. Titrate with 0.1 mol / L sodium hydroxide standard solution until the solution changes abruptly from light pink to green. The volume of sodium hydroxide standard solution consumed is V. 白 =17.70mL.

[0103] Calculation steps: The residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula.

[0104]

[0105] Where: V 样 The volume of alkaline standard solution consumed in the back titration step is expressed in mL.

[0106] V 白 The volume of alkaline standard solution consumed in the blank experimental step is expressed in mL.

[0107] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0108] m 样 The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams.

[0109] V 总 This represents the total volume of the solution after dilution, in mL.

[0110] V 移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution, expressed in mL; V 移 / V 总 This refers to the proportion of solution transferred.

[0111] 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

[0112] Table 1 shows the experimental data for this embodiment.

[0113] Table 1

[0114]

[0115] Comparative Example 1

[0116] Comparative Example 1 uses a conventional method to determine the residual acrylonitrile content in the polyacrylonitrile polymerization solution, which includes the following steps:

[0117] Sample solution preparation steps: Weigh 1.4429 g, 1.4816 g, 1.3233 g, and 1.3403 g of polyacrylonitrile polymerization solution samples and place them into four 250 mL Erlenmeyer flasks, respectively, and quickly cap them. Then, add 30 mL of DMSO solution to each of the four Erlenmeyer flasks, place the flasks on a magnetic stirrer, and stir at room temperature until the polyacrylonitrile polymerization solution is completely dissolved. Then, add 50 mL of ultrapure water to each of the four Erlenmeyer flasks, shake well, and you will have four sample solutions.

[0118] Direct titration procedure: Add 5 drops of Alizarin Yellow R-thymolphthalein indicator to each of the four sample solutions. First, titrate with 0.1 mol / L sodium hydroxide standard solution until the solution turns pale blue. Then, add 20 mL of 0.1 mol / L Na2SO3 solution to each of the four conical flasks, shake well, and after the reaction is complete, titrate with 0.1 mol / L H2SO4 standard solution until the solution turns yellow-green. The titration volumes of acid standard solution (1 / 2 H2SO4 standard solution) consumed at this time are 6.66 mL, 6.82 mL, 5.97 mL, and 6.14 mL, respectively.

[0119] Blank alkaline titration procedure: Add 30 mL of DMSO and 50 mL of ultrapure water sequentially to a 250 mL Erlenmeyer flask, then add 5 drops of Alizarin Yellow R-thymolphthalein indicator, and titrate with sodium hydroxide standard solution (0.1 mol / L) until a light blue endpoint is reached. Record the volume of alkaline solution consumed as 0.10 mL.

[0120] Blank acid titration procedure: Add 30 mL of DMSO and 50 mL of ultrapure water sequentially to a 250 mL Erlenmeyer flask, then add 20 mL of sodium sulfite, followed by 5 drops of alizarin yellow R-thymolphthalein indicator. Titrate with sulfuric acid standard solution (0.1 mol / L) until the endpoint is yellow-green, consuming 0.36 mL of acid solution.

[0121]

[0122] In the above formula:

[0123] X represents the residual acrylonitrile content in the polyacrylonitrile solution, % .

[0124] m represents the mass of the polyacrylonitrile polymerization solution sample, in grams.

[0125] V is the volume of acid standard solution consumed by the sample, in mL;

[0126] C 酸 This represents the concentration of the acid standard solution, expressed in mol / L.

[0127] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0128] V 01 The volume of acid standard solution consumed in the blank titration step is expressed in mL.

[0129] V 02 The volume of alkaline standard solution consumed in the blank titration step is expressed in mL.

[0130] 0.053 is the mass number equivalent to one millimole of acrylonitrile, expressed in g / mmol.

[0131] Table 2 shows the experimental data for Comparative Example 1.

[0132] Table 2

[0133]

[0134] As can be seen from Tables 1 and 2 above:

[0135] The average AN content measured in Comparative Example 1 (conventional method) was 2.623%, while the average AN content measured in Example 1 was 2.621%. The relative standard deviation (RSD) of the method described in Comparative Example 1 was 1.27%, and that of the method described in Example 1 was 1.24%. The mean and RSD of the residual acrylonitrile content in the polyacrylonitrile polymerization solution measured by both methods were almost identical (Example 1 showed slightly higher accuracy). This indicates that when the residual acrylonitrile content in the polymerization solution is high, the accuracy of the two detection methods is almost the same, and it is also possible that the absolute AN content is high at high concentrations. Although the absolute deviation value exists due to incomplete AN release caused by polymer encapsulation in the conventional method, its relative error as a percentage of the total measurement is diluted. This error is on the same order of magnitude as random errors such as burette readings and environmental fluctuations, thus statistically masking the systematic differences between different methods, leading to numerical convergence. High-concentration samples require lower sensitivity from the detection system. In this case, even the conventional titration method produces a sufficiently strong signal to provide good precision.

[0136] Example 2

[0137] This embodiment measures the residual acrylonitrile content in the polyacrylonitrile polymerization solution after monomer removal, and mainly includes the following steps:

[0138] Sample solution preparation steps: Weigh 2.1060 g, 2.0498 g, 2.0321 g, 2.0024 g, and 2.1692 g of polyacrylonitrile polymerization solution samples and place them into five 250 mL Erlenmeyer flasks, respectively, and quickly cap them. Then, add 30 mL of DMSO solution to each of the five Erlenmeyer flasks, place the flasks on a magnetic stirrer, and stir magnetically at 30 °C for 15 min until the polyacrylonitrile polymerization solution is completely dissolved. Then, add 50 mL of ultrapure water to each of the five Erlenmeyer flasks, shake well, and you will have five sample solutions.

[0139] Steps for adding salting-out agent: Add 2.34g of solid sodium chloride to each of the five sample solutions (in three portions, stirring as you add). After all the sodium chloride has been added, let it stand for 5 minutes to obtain five solutions with added salting-out agent.

[0140] Addition reaction steps: Add 20 mL of 0.1 mol / L Na2SO3 solution to each of the five solutions after adding the salting-out agent, then heat at 50 °C for 10 minutes, and immediately place in an ice bath for 5 minutes to terminate the reaction and obtain a mixture of reaction products; perform solid-liquid separation on the mixture of reaction products to obtain five filtrate samples.

[0141] Acid-base back titration procedure: Transfer each filtrate sample to five separate 100 mL volumetric flasks, and dilute to the mark with ultrapure water to obtain five volumes of V. 总 A diluted solution; wherein, V 总 =100mL.

[0142] All five diluted solutions were transferred to five separate Erlenmeyer flasks. 5 mL of 0.1 mol / L H₂SO₄ standard solution was added to each flask, followed by 5 drops of methyl red-bromocresol green indicator. Titration with 0.1 mol / L sodium hydroxide standard solution continued until the solution changed abruptly from light pink to green. The volumes of sodium hydroxide standard solution consumed were 4.42 mL, 4.43 mL, 4.44 mL, 4.45 mL, and 4.42 mL, respectively.

[0143] Blank Experiment: Take 30 mL of DMSO solution in an Erlenmeyer flask and stir magnetically for 15 minutes at 30°C. Add 50 mL of ultrapure water and mix well to obtain a blank solution. Add 2.34 g of solid sodium chloride to the blank solution in three portions, stirring continuously. After all the sodium chloride has been added, let stand for 5 minutes to obtain the solution with added salting-out agent. Add 20 mL of 0.1 mol / L Na₂SO₃ solution to the solution with added salting-out agent, heat at 50°C for 10 minutes, and then immediately place in an ice bath for 5 minutes to obtain the product solution. Filter the product solution and transfer it to a 100 mL volumetric flask. Dilute to the mark with ultrapure water. 总 =100mL. Transfer the entire diluted solution to an Erlenmeyer flask, add 5mL of 0.1mol / L H2SO4 standard solution, then add 5 drops of methyl red-bromocresol green indicator. Titrate with 0.1mol / L sodium hydroxide standard solution until the solution changes abruptly from light pink to green. The volume of sodium hydroxide standard solution consumed is V. 白 =4.68mL.

[0144] Calculation steps: The residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula.

[0145]

[0146] Where: V 样 The volume of alkaline standard solution consumed in the back titration step is expressed in mL.

[0147] V 白 The volume of alkaline standard solution consumed in the blank experimental step is expressed in mL.

[0148] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0149] m 样 The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams.

[0150] V 总 This represents the total volume of the solution after dilution, in mL.

[0151] V 移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution, expressed in mL; V 移 / V 总 This refers to the proportion of solution transferred.

[0152] 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

[0153] Table 3 shows the experimental data for determining the residual acrylonitrile content in the polyacrylonitrile polymerization solution after monomer removal in Example 2.

[0154] Table 3

[0155]

[0156] Comparative Example 2

[0157] Comparative Example 2 used a conventional method to determine the residual acrylonitrile content in the polyacrylonitrile polymerization solution after monomer removal, including the following steps:

[0158] Sample solution preparation steps: Weigh 2.3719 g, 2.1044 g, 2.0659 g, 2.1532 g, and 2.0523 g of polyacrylonitrile polymerization solution samples and place them into five 250 mL Erlenmeyer flasks, respectively, and quickly cap them. Then, add 30 mL of DMSO solution to each of the five Erlenmeyer flasks, place the flasks on a magnetic stirrer, and stir at room temperature until the polyacrylonitrile polymerization solution is completely dissolved. Then, add 50 mL of ultrapure water to each of the five Erlenmeyer flasks, shake well, and you will have five sample solutions.

[0159] Titration procedure: Add 5 drops of Alizarin Yellow R-thymolphthalein indicator to each of the five sample solutions. First, titrate with 0.1 mol / L sodium hydroxide standard solution until the solution turns pale blue. Then, add 20 mL of 0.1 mol / L Na2SO3 solution to each of the five conical flasks, shake well, and after the reaction is complete, titrate with 0.1 mol / L H2SO4 standard solution until the solution turns yellow-green. The titration volumes of acid standard solution consumed at this time are 0.56 mL, 0.55 mL, 0.52 mL, 0.54 mL, and 0.52 mL, respectively.

[0160] Blank alkaline titration procedure: Add 30 mL of DMSO and 50 mL of ultrapure water sequentially to a 250 mL Erlenmeyer flask, then add 5 drops of Alizarin Yellow R-thymolphthalein indicator, and titrate with sodium hydroxide standard solution (0.1 mol / L) until a light blue endpoint is reached. Record the volume of alkaline solution consumed as 0.10 mL.

[0161] Blank acid titration procedure: Add 30 mL of DMSO and 50 mL of ultrapure water sequentially to a 250 mL Erlenmeyer flask, then add 20 mL of sodium sulfite, followed by 5 drops of alizarin yellow R-thymolphthalein indicator. Titrate with sulfuric acid standard solution (0.1 mol / L) until the endpoint is yellow-green, consuming 0.40 mL of acid solution.

[0162]

[0163] In the above formula:

[0164] X represents the residual acrylonitrile content in the polyacrylonitrile solution, % .

[0165] m represents the mass of the polyacrylonitrile polymerization solution sample, in grams.

[0166] V is the volume of acid standard solution consumed by the sample, in mL;

[0167] C 酸 This represents the concentration of the acid standard solution, expressed in mol / L.

[0168] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0169] V 01 The volume of acid standard solution consumed in the blank titration step is expressed in mL.

[0170] V 02 The volume of alkaline standard solution consumed in the blank titration step is expressed in mL.

[0171] 0.053 is the mass number equivalent to one millimole of acrylonitrile, expressed in g / mmol.

[0172] Table 4 shows the experimental data (conventional method) for determining the residual acrylonitrile content in the polyacrylonitrile polymerization solution after monomer removal in Comparative Example 2.

[0173] Table 4

[0174]

[0175] As can be seen from Tables 3 and 4 above:

[0176] Compared with the determination method of Comparative Example 2 (conventional titration), the method of Example 2 showed little deviation in the average value of residual AN content in the polyacrylonitrile polymer solution after monomer removal. However, the relative standard deviation of the determination method (conventional titration) was 4.71%, while the relative standard deviation of the method of Example 2 was even smaller, at 2.81%. This indicates that when the amount of residual acrylonitrile is low, the determination method of the present invention has better precision, allowing the testing personnel to better determine the reaction titration endpoint. This is because the conventional method directly titrates a complex polymer dilution solution, resulting in a low residual acrylonitrile content in the polyacrylonitrile polymer solution after monomer removal. Furthermore, the comonomers (such as itaconic acid and azo dyes), polymers, and solvents in the solution significantly interfere with the determination of the titration endpoint color, increasing the visual recognition of color changes and introducing measurement errors. In contrast, the method of the present invention adds a salting-out agent before the addition reaction, utilizing the "salting-out effect" of the salting-out agent to release the residual acrylonitrile monomers from the polyacrylonitrile polymer solution after monomer removal. The AN is then separated from most of the polymer matrix and impurities through a filtration step. This step is equivalent to purifying the sample, providing a clearer titration solution for subsequent titration. This reduces operational and environmental interference during titration, resulting in more accurate titration results. Additionally, when the residual acrylonitrile content in the polyacrylonitrile polymerization solution after monomer removal is low, see [reference needed]. Figure 2 The indicator color change of the method of the present invention changes from pink to green, which is more visually identifiable than the traditional method of changing from light blue to yellowish-green, making it easier to determine the titration endpoint and more accurate in the measurement results.

[0177] Comparative Example 3

[0178] Comparative Example 3 determined the residual acrylonitrile content in the polyacrylonitrile polymerization solution. The method in Comparative Example 3, compared to Example 1, did not include the addition of a salting-out agent. The determination method in Comparative Example 3 included the following steps:

[0179] Sample solution preparation steps: Weigh 1.5741g, 1.5860g, 1.5306g, and 1.5727g of polyacrylonitrile polymerization solution samples and place them into four 250mL Erlenmeyer flasks respectively, and quickly cap the flasks. Then add 30mL of DMSO solution to each of the four Erlenmeyer flasks, place the flasks on a magnetic stirrer, and stir magnetically at 30℃ for 15min until the polyacrylonitrile polymerization solution is completely dissolved. Then add 50mL of ultrapure water to each of the four Erlenmeyer flasks and shake well to obtain four sample solutions.

[0180] Addition reaction procedure: Add 20 mL of 0.1 mol / L Na₂SO₃ solution to each of the four sample solutions, then heat at 50 °C for 10 minutes, immediately followed by an ice bath for 5 minutes to terminate the reaction and obtain the reaction product. Perform solid-liquid separation on the mixture of reaction products to obtain four filtrate samples.

[0181] Acid-base back titration procedure: Transfer each filtrate sample to four separate 100 mL volumetric flasks, and dilute to the mark with ultrapure water to obtain four volumes of V. 总 A diluted solution; wherein, V 总 =100mL.

[0182] Take V from each of the four solutions that have been brought to a constant volume. 移 25 mL of solution was poured into four Erlenmeyer flasks. 18 mL of 0.1 mol / L H₂SO₄ standard solution was added to each flask, followed by 5 drops of methyl red-bromocresol green indicator. Titration with 0.1 mol / L sodium hydroxide standard solution continued until the solution changed abruptly from light pink to green. The volumes of sodium hydroxide standard solution consumed were 15.74 mL, 15.68 mL, 15.80 mL, and 15.75 mL, respectively.

[0183] Blank experiment: Take 30 mL of DMSO solution in an Erlenmeyer flask, stir magnetically for 15 minutes at 30 °C, add 50 mL of ultrapure water, and shake well to obtain a blank solution. Add 20 mL of 0.1 mol / L Na₂SO₃ solution to the blank solution, heat at 50 °C for 10 minutes, and then immediately place in an ice bath for 5 minutes to obtain the product solution. Filter the product solution and transfer it to a 100 mL volumetric flask, then dilute to the mark with ultrapure water. 总 =100mL. Accurately transfer V 移 Add 25 mL of diluted solution to an Erlenmeyer flask, then add 18 mL of 0.1 mol / L H₂SO₄ standard solution, followed by 5 drops of methyl red-bromocresol green indicator. Titrate with 0.1 mol / L sodium hydroxide standard solution until the solution changes abruptly from light pink to green. The volume of sodium hydroxide standard solution consumed is V. 白 =17.69mL.

[0184] Calculation steps: The residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula.

[0185]

[0186] Where: V 样 The volume of alkaline standard solution consumed in the back titration step is expressed in mL.

[0187] V 白 The volume of alkaline standard solution consumed in the blank experimental step is expressed in mL.

[0188] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0189] m 样The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams.

[0190] V 总 This represents the total volume of the solution after dilution, in mL.

[0191] V 移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution, expressed in mL; V 移 / V 总 This refers to the proportion of solution transferred.

[0192] 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

[0193] Table 5 shows the experimental data for Comparative Example 3.

[0194] Table 5

[0195]

[0196] As can be seen from Tables 1 and 5 above:

[0197] The average AN content measured in Example 1 was 2.621%, and the average AN content measured in Comparative Example 3 was 2.623%. The relative standard deviation of the determination method in Example 1 was 1.24%, and the relative standard deviation of the determination method in Comparative Example 3 was 1.28%. When the residual acrylonitrile content in the polyacrylonitrile polymerization solution was high, there was no significant difference in the determination results of the determination methods in Comparative Example 3, Comparative Example 1, and Example 1. The main reasons are as follows:

[0198] When the residual acrylonitrile content is high, the absolute amount of the analyte is large. In traditional methods or without salting-out agents, the incomplete release of AN due to polymer encapsulation results in an absolute error, but its relative error to the total measurement is small and easily masked by random experimental errors. Furthermore, high-concentration samples have lower sensitivity requirements for the measurement system; traditional direct titration and the absence of salting-out agents are sufficient to provide acceptable precision. Therefore, the advantages of Example 1 are not fully realized.

[0199] Comparative Example 4

[0200] Comparative Example 4 determined the residual acrylonitrile content in the polyacrylonitrile polymerization solution. Compared with Example 1, in the addition reaction step, Comparative Example 4 did not use an ice bath to terminate the reaction after the addition reaction was completed. The determination method in Comparative Example 4 included the following steps:

[0201] Sample solution preparation steps: Weigh 1.4555g, 1.4276g, 1.4749g, and 1.3986g of polyacrylonitrile polymerization solution samples, respectively, and place them into four 250mL Erlenmeyer flasks, then quickly cap them. Next, add 30mL of DMSO solution to each of the four flasks. Place the flasks on a magnetic stirrer and stir magnetically at 30℃ for 15 minutes until the polyacrylonitrile polymerization solution is completely dissolved. Then, add 50mL of ultrapure water to each of the four flasks and shake well to obtain four sample solutions.

[0202] Adding salting-out agent: Add 2.34g of solid sodium chloride to each of the four sample solutions (in three portions, stirring as you add). After all the sodium chloride has been added, let it stand for 5 minutes to obtain four solutions with added salting-out agent.

[0203] Addition reaction steps: Add 20 mL of 0.1 mol / L Na2SO3 solution to each of the four solutions after adding the salting-out agent, then heat at 50 °C for 10 minutes, and then cool naturally to room temperature to obtain a mixture of reaction products; perform solid-liquid separation on the mixture of reaction products to obtain four filtrate samples.

[0204] Acid-base back titration procedure: Transfer each filtrate sample to four separate 100 mL volumetric flasks, and dilute to the mark with ultrapure water to obtain four volumes of V. 总 A diluted solution; wherein, V 总 =100mL.

[0205] Take V from each of the four solutions that have been brought to a constant volume. 移 25 mL of solution was poured into four Erlenmeyer flasks. 18 mL of 0.1 mol / L H₂SO₄ standard solution was added to each flask, followed by 5 drops of methyl red-bromocresol green indicator. Titration with 0.1 mol / L sodium hydroxide standard solution continued until the solution changed abruptly from light pink to green. The volumes of sodium hydroxide standard solution consumed were 15.87 mL, 15.94 mL, 15.88 mL, and 16.10 mL, respectively.

[0206] Blank Experiment: Take 30 mL of DMSO solution in an Erlenmeyer flask and stir magnetically for 15 minutes at 30°C. Add 50 mL of ultrapure water and shake well to obtain a blank solution. Add 2.34 g of solid sodium chloride to the blank solution in three portions, stirring continuously. After all the sodium chloride has been added, let stand for 5 minutes to obtain the solution with added salting-out agent. Add 20 mL of 0.1 mol / L Na₂SO₃ solution to the solution with added salting-out agent, heat at 50°C for 10 minutes, and then allow to cool naturally to room temperature to obtain the product solution. Filter the product solution and transfer it to a 100 mL volumetric flask. Dilute to the mark with ultrapure water.总 =100mL. Accurately transfer V 移 Dilute 25 mL of solution to volume in an Erlenmeyer flask. Add 18 mL of 0.1 mol / L H₂SO₄ standard solution to the Erlenmeyer flask, then add 5 drops of methyl red-bromocresol green indicator. Titrate with 0.1 mol / L sodium hydroxide standard solution until the solution changes abruptly from light pink to green. The volume of sodium hydroxide standard solution consumed is V. 白 =17.72mL.

[0207] Calculation steps: The residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula.

[0208]

[0209] Where: V 样 The volume of alkaline standard solution consumed in the back titration step is expressed in mL.

[0210] V 白 The volume of alkaline standard solution consumed in the blank experimental step is expressed in mL.

[0211] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0212] m 样 The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams.

[0213] V 总 This represents the total volume of the solution after dilution, in mL.

[0214] V 移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution, expressed in mL; V 移 / V 总 This refers to the proportion of solution transferred.

[0215] 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

[0216] Table 6 shows the experimental data for Comparative Example 4.

[0217] Table 6

[0218]

[0219] As can be seen from Tables 1 and 6 above:

[0220] The average AN content measured in Example 1 was 2.621%, while the average AN content measured in Comparative Example 4 was 2.597%. The relative standard deviation of the determination method in Example 1 was 1.24%, while the relative standard deviation of the determination method in Comparative Example 4 was 4.04%. Compared with the determination method in Example 1, the determination method in Comparative Example 4 (without ice bath cooling) showed a lower average residual AN content in the polyacrylonitrile polymerization solution with significant fluctuations, and even the residual acrylonitrile content in the polyacrylonitrile polymerization solution was lower than that of the traditional method. The main reasons are as follows:

[0221] During natural, slow cooling, the reaction system remains at a relatively high temperature for an extended period, making it more susceptible to side reactions such as hydrolysis or self-polymerization of AN monomers. This reduces the amount of AN actually participating in the main reaction, leading to lower measured results. Furthermore, natural cooling is an uncontrollable process, significantly affected by factors such as ambient temperature, test tube position, and airflow. Each sample exhibits a different cooling profile, resulting in varying degrees of reaction progression. Consequently, even parallel experiments using the same sample will yield highly dispersed results with poor reproducibility. However, ice bath cooling can rapidly lower the reaction system to a low temperature, halting the reaction process and ensuring that each sample reacts under identical conditions, thus reducing the rate of side reactions.

[0222] Comparative Example 5

[0223] Comparative Example 5 determined the residual acrylonitrile content in the polyacrylonitrile polymerization solution after monomer removal. Compared with Example 2, the method of Comparative Example 5 did not include the addition of a salting-out agent. The determination method of Comparative Example 5 included the following steps:

[0224] Sample solution preparation steps: Weigh 2.0073g, 2.0306g, 2.0845g, 2.0727g, and 2.0155g of polyacrylonitrile polymerization solution samples and place them into five 250mL Erlenmeyer flasks, respectively, and quickly cap them. Then, add 30mL of DMSO solution to each of the five Erlenmeyer flasks, place the flasks on a magnetic stirrer, and stir magnetically at 30℃ for 15min until the polyacrylonitrile polymerization solution is completely dissolved. Then, add 50mL of ultrapure water to each of the five Erlenmeyer flasks, shake well, and you will have five sample solutions.

[0225] Addition reaction procedure: 20 mL of 0.1 mol / L Na₂SO₃ solution was added to each of the five sample solutions. The mixture was then heated at 50 °C for 10 minutes, followed immediately by an ice bath for 5 minutes to terminate the reaction and obtain the reaction product. The mixture of reaction products was subjected to solid-liquid separation to obtain four filtrate samples.

[0226] Acid-base back titration procedure: Transfer each filtrate sample to five separate 100 mL volumetric flasks, and dilute to the mark with ultrapure water to obtain five volumes of V.总 A diluted solution; wherein, V 总 =100mL.

[0227] All five diluted solutions were transferred to five separate Erlenmeyer flasks. 5 mL of 0.1 mol / L H₂SO₄ standard solution was added to each flask, followed by 5 drops of methyl red-bromocresol green indicator. Titration with 0.1 mol / L sodium hydroxide standard solution continued until the solution changed abruptly from light pink to green. The volumes of sodium hydroxide standard solution consumed were 4.46 mL, 4.45 mL, 4.43 mL, 4.43 mL, and 4.45 mL, respectively.

[0228] Blank experiment: Take 30 mL of DMSO solution in an Erlenmeyer flask, stir magnetically for 15 minutes at 30 °C, add 50 mL of ultrapure water, and shake well to obtain a blank solution. Add 20 mL of 0.1 mol / L Na₂SO₃ solution to the blank solution, heat at 50 °C for 10 minutes, and then immediately place in an ice bath for 5 minutes to obtain the product solution. Transfer the product solution to a 100 mL volumetric flask and dilute to the mark with ultrapure water. 总 =100mL. Transfer the entire diluted solution to an Erlenmeyer flask, add 5mL of 0.1mol / L H2SO4 standard solution, then add 5 drops of methyl red-bromocresol green indicator. Titrate with 0.1mol / L sodium hydroxide standard solution until the solution changes abruptly from light pink to green. The volume of sodium hydroxide standard solution consumed is V. 白 =4.67mL.

[0229] Calculation steps: The residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula.

[0230]

[0231] Where: V 样 The volume of alkaline standard solution consumed in the back titration step is expressed in mL.

[0232] V 白 The volume of alkaline standard solution consumed in the blank experimental step is expressed in mL.

[0233] C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L.

[0234] m 样 The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams.

[0235] V 总 This represents the total volume of the solution after dilution, in mL.

[0236] V移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution, expressed in mL; V 移 / V 总 This refers to the proportion of solution transferred.

[0237] 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

[0238] Table 7 shows the experimental data for determining the residual acrylonitrile content in the polyacrylonitrile polymerization liquor after monomer removal in Comparative Example 5.

[0239] Table 7

[0240]

[0241] As can be seen from Tables 3 and 7 above:

[0242] The average residual acrylonitrile content in the polyacrylonitrile polymerization liquor after monomer removal in Example 2 was 0.063%, while the average AN content in Comparative Example 5 was 0.058%. The relative standard deviation of the determination method in Example 2 was 2.81%, and the relative standard deviation of the determination method in Comparative Example 5 was 4.30%. Compared with the determination method in Comparative Example 5 (without the salting-out step), when the residual acrylonitrile content in the polyacrylonitrile polymerization liquor after monomer removal was low, the determination results of Comparative Example 5 were lower than those of Examples 2 and Comparative Example 2. The main reasons are as follows:

[0243] The absence of the salting-out step prevented the complete release of AN monomers from the polymer matrix. Traditional methods titrate in an alkaline environment, while this method titrates in an acidic environment. The acidic environment may exacerbate the polymer's encapsulation or adsorption of AN, causing some AN ​​to be encapsulated and unable to participate in the reaction, resulting in incomplete addition reaction and lower measured values. Furthermore, the high viscosity of the polymer matrix interferes with the titration process, making endpoint determination unclear, reducing reproducibility, and decreasing precision. However, the addition of a salting-out agent causes the polymer to precipitate. Filtration then transforms the test solution into a clear, homogeneous aqueous reaction system, eliminating the interference of the subsequent titration environment on the AN release process, thus ensuring the accuracy and precision of the results.

[0244] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, characterized in that, It includes the following steps: Sample solution preparation steps: Dissolve the polyacrylonitrile polymer solution sample in an organic solvent by stirring, and then dilute with water to obtain the sample solution; Adding salting-out agent step: Add salting-out agent to the sample solution, stir to dissolve, and let stand for a set time to allow acrylonitrile to accumulate and be released from the PAN chain, thus obtaining the solution after adding salting-out agent; Addition reaction step: Add sodium sulfite solution to the solution after adding salting-out agent, and allow sodium sulfite to react with acrylonitrile AN under heating conditions. After a set reaction time, cool to terminate the reaction and obtain a mixture of reaction products; perform solid-liquid separation on the mixture of reaction products to obtain filtrate; Acid-base back titration method steps: The filtrate and blank sample are titrated using the acid-base back titration method, and then the residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated based on the experimental data.

2. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 1, characterized in that, In the step of preparing the sample solution: The organic solvent is one or more of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

3. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 1, characterized in that, In the step of adding the salting-out agent: The salting-out agent is any one or more of the following: solid sodium chloride, sodium chloride solution, solid ammonium sulfate, ammonium sulfate solution, solid potassium chloride, and potassium chloride solution.

4. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 3, characterized in that, In the step of adding the salting-out agent: If the salting-out agent is a liquid, the concentration of the salting-out agent in the solution after its addition must be 0.3 mol / L to 0.7 mol / L.

5. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 4, characterized in that, In the step of adding the salting-out agent: If the salting-out agent is a liquid, the concentration of the salting-out agent in the solution after its addition must be 0.5 mol / L.

6. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 3, characterized in that, In the step of adding the salting-out agent: If the salting-out agent is a solid, then 1.46 g to 4.38 g of salting-out agent needs to be added to every 80 mL of sample solution.

7. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 3, characterized in that, In the step of adding the salting-out agent: If the salting-out agent is a solid, then 2.34 g of salting-out agent needs to be added to every 80 mL of sample solution.

8. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 3, characterized in that, In the step of adding the salting-out agent: If the salting-out agent is a liquid, it must be added drop by drop while stirring when adding it to the sample solution; If the salting-out agent is a solid, it needs to be added to the sample solution in multiple batches; after the previous batch of salting-out agent has dissolved, the next batch of salting-out agent should be added.

9. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquor according to claim 1, characterized in that, In the step of adding the salting-out agent: the salting-out agent is added to the sample solution. After the salting-out agent is stirred and dissolved, it needs to stand for 5 min to 15 min to allow acrylonitrile to accumulate and be released from the PAN chain.

10. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 1, characterized in that, In the addition reaction step: The addition reaction is carried out at a temperature of 45°C to 55°C for 5 minutes to 15 minutes.

11. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquor according to claim 10, characterized in that, In the addition reaction step: the temperature of the addition reaction is 50°C; the time of the addition reaction is 10 min.

12. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 1, characterized in that, In the addition reaction step, the cooling method is an ice bath or a cold water bath.

13. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution according to claim 1, characterized in that, The acid-base back titration method includes the following steps: Step 1): Transfer all the filtrate obtained in the addition reaction step to a volumetric flask, and then add water to the set mark. The volume obtained is V. 总 A diluted solution; Step 2): From the volume V 总 A volume of V was taken from the diluted solution. 移 The diluted solution was transferred to a titration vessel. Using reverse titration, an excess of a known concentration of acid standard solution was first added to the titration vessel, followed by the addition of a pH indicator. Then, titration was performed with a known concentration of alkali standard solution. Titration was stopped when the solution color changed from pale pink to green, and the volume of alkali standard solution consumed was recorded as V. 样 ; Step 3): Using the reverse titration method, first add an excess of acid standard solution of known concentration to the blank sample, then add a pH indicator, and then titrate with a base standard solution of known concentration. Stop the titration when the solution color changes from light pink to green, and record the volume V of base standard solution consumed in the blank experiment. 白 ; Step 4): Based on the mass m of the polyacrylonitrile polymerization solution sample 样 V 总 V 移 V 样 V 白 The residual acrylonitrile content in the polyacrylonitrile polymerization solution was calculated.

14. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquor according to claim 13, characterized in that, V 移 / V 总 The ratio is 1:10 to 1:

1.

15. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquor according to claim 13, characterized in that, The pH indicator is a mixed solution comprising methyl red and bromocresol green; wherein the mass ratio of methyl red to bromocresol green is 1:1 to 3:

1.

16. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquor according to claim 15, characterized in that, The mass ratio of methyl red to bromocresol green is 2:

1.

17. The method for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquor according to claim 15, characterized in that, The pH indicator also includes an ethanol solvent.

18. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 15, characterized in that, In step 4), the residual acrylonitrile content in the polyacrylonitrile polymerization solution is calculated using the following formula: ； Where: V 样 The volume of alkaline standard solution consumed in step 2) is in mL. V 白 The volume of alkaline standard solution consumed in step 3) is in mL. C 碱 This represents the concentration of the alkaline standard solution, expressed in mol / L. m 样 The mass of the polyacrylonitrile polymer solution sample in the sample solution preparation step is expressed in grams. V 总 This represents the total volume of the solution after dilution, in mL. V 移 To obtain from the volume V 总 The volume of solution transferred from the final volume of the solution is expressed in mL. Among them, V 移 / V 总 This refers to the proportion of solution transferred. 0.053 is the millimolecular mass of acrylonitrile, expressed in g / mmol.

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