Method for determining purity of acrylonitrile raw material

Abstract

The invention relates to the field of chemical testing, in particular to a method for measuring the purity of an acrylonitrile raw material, which comprises the following steps: preparing and calibrating a standard solution, weighing a sample, transferring the sample, carrying out sample titration analysis, carrying out blank titration analysis and calculating a result, thereby obtaining the purity of the acrylonitrile raw material. According to the method, the problems of high cost and overlong detection time of instruments required for detecting the purity of acrylonitrile by a gas chromatographic method are solved, the volatilization loss caused by sample transferring is avoided, the detection efficiency and the test accuracy are improved, and the real purity value of acrylonitrile can be reflected more accurately.

Description

Technical Field

[0001] The present invention relates to a chemical testing method, and in particular to a method for determining the purity of acrylonitrile raw materials. Background Art

[0002] Polyacrylonitrile-based carbon fiber has excellent properties such as high temperature resistance, friction resistance, thermal conductivity, electrical conductivity and corrosion resistance, and is widely used in defense and military industry, civilian industry and other fields. The raw material of polyacrylonitrile-based carbon fiber is acrylonitrile. The presence of organic substances such as acetaldehyde, acetone, benzene, acetonitrile, thiazole, etc. will reduce the purity of acrylonitrile, affect the conversion rate of polymerization reaction, and increase production and operation costs.

[0003] At present, there are two methods for detecting the residual acrylonitrile monomer content in the spinning solution during the production of carbon fiber: the film weighing method and the titration method; and there is a gas chromatography method for detecting the purity of industrial acrylonitrile. However, the gas chromatography method requires nearly 40 minutes of peak time, which is time-consuming and requires the purchase of precision instruments, which increases the detection cost. Therefore, it is very necessary to invent an acrylonitrile purity detection method with accurate data, convenient operation and high efficiency. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings in the prior art and provide a method for determining the purity of acrylonitrile raw materials. The method is simple and convenient to operate and has good accuracy and repeatability.

[0005] According to a first aspect of an exemplary embodiment of the present disclosure, a method for determining the purity of an acrylonitrile raw material is provided, comprising the following steps:

[0006] S1. Solution preparation and calibration: prepare reaction solution and standard solution;

[0007] S2. Sample weighing: Weigh the acrylonitrile raw material using an ampoule ball;

[0008] S3. Sample transfer: The reaction solution was measured and added to an iodine volumetric flask, and then the ampoule ball containing the acrylonitrile raw material was transferred to the iodine volumetric flask;

[0009] S4. Sample titration analysis;

[0010] S5. Blank titration analysis;

[0011] S6. Calculation of results.

[0012] The reaction principle involved in the method for determining the purity of acrylonitrile raw materials in this application is as follows:

[0013] Acrylonitrile reacts with sodium sulfite to precipitate the same amount of sodium hydroxide. The amount of sodium hydroxide produced is titrated with a standard hydrochloric acid solution, and the end point is indicated by a mixed indicator of alizarin and thymolphthalein for determination. The reaction mechanism of sodium sulfite and acrylonitrile is as follows:

[0014] Na2SO3+CH2CHCN+H2O→NaSO3CH2CH2CN+NaOH,

[0015] NaOH+HCl→NaCl+H2O

[0016] In some exemplary embodiments, the reaction solution in step S1 is a sodium sulfite solution with a concentration of 0.8 to 1.2 mol / L; and the standard solution is a hydrochloric acid solution with a concentration of 0.3 to 0.5 mol / L.

[0017] In some exemplary embodiments, the method of weighing the acrylonitrile raw material using an ampoule ball in step S2 is specifically as follows: weigh the weight of the empty ampoule ball and record it as m1g; use an alcohol lamp to quickly burn the spherical end of the ampoule ball back and forth 5-6 times for 3-5s, place the capillary end of the ampoule ball into the test sample, automatically absorb to 1 / 4-1 / 3 of the ampoule ball, and then heat the capillary end of the ampoule ball with an alcohol lamp to cause the capillary to automatically curl and seal, weigh the ampoule ball and the sample, and record it as m2g.

[0018] The estimation method of the 1 / 4-1 / 3 position of the ampoule spherical shape is visual inspection, which means sucking to about 1 / 4-1 / 3 of the diameter of the ampoule ball.

[0019] In some exemplary embodiments, in step S3, 20-30 ml of Na2SO3 solution is measured and added to an iodine volumetric flask, and then the ampoule ball containing acrylonitrile raw material is put into the iodine volumetric flask, the ampoule ball is crushed with a glass rod, and the inner wall of the iodine volumetric flask and the glass rod are rinsed with 1.5-2.5 mL of secondary water; the stopper is tightly closed, the mouth of the iodine volumetric flask is sealed with water, and then placed on a magnetic stirrer and stirred for 2-4 minutes.

[0020] In some exemplary embodiments, the rotation speed of the magnetic stirrer is 500-600 r / min.

[0021] In some exemplary embodiments, an ampoule ball with a ball diameter of 15-16 mm is selected, and the material is high borosilicate glass. Through experiments, it is found that different specifications of ampoule balls will affect the accuracy of the measurement results and the measurement efficiency. In addition, the rotation speed needs to be controlled within a certain range, otherwise it will cause the sample solution actually involved in the titration process to be inaccurate, resulting in inaccurate titration results.

[0022] In some exemplary embodiments, the specific operation of step S4 is: open the stopper of the iodine volumetric flask, vertically drip 3 to 4 drops of a mixed indicator of alizarin yellow and thymolphthalein, and titrate with the standard solution until the color of the solution changes from purple to light yellow, which is the end point, record the volume V of the consumed HCl standard solution, and turn off the magnetic stirrer after the titration is completed.

[0023] In some exemplary embodiments, in step S4, potentiometric titration is used to determine the purity of acrylonitrile; after completing steps S1 to S3, the iodine volume bottle is placed on a magnetic stirrer and magnetically stirred for 1-3 minutes, and then the liquid is poured into a beaker, and the iodine volume bottle is washed; titration is performed using a potentiometric titrator; when the titration endpoint is reached, the titration stops automatically and the acrylonitrile concentration is recorded.

[0024] In some exemplary embodiments, the specific operation of step S5 is: titrating with the standard solution in an iodine volume flask containing the reaction solution and water but without the sample, and recording the volume V0 of the standard hydrochloric acid solution consumed in the blank test.

[0025] In some exemplary embodiments, in step S6, the result calculation includes:

[0026]

[0027] Where:

[0028] AN%——acrylonitrile purity in raw material sample, %;

[0029] V——The volume of hydrochloric acid standard solution consumed in titrating the raw material sample, ml;

[0030] V0——the volume of hydrochloric acid standard solution consumed in titrating the blank sample, ml;

[0031] M——molar mass of acrylonitrile, g / mol (M=53.06);

[0032] c——concentration of hydrochloric acid standard solution, mol / L.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The method for determining the purity of acrylonitrile raw materials provided in the present disclosure uses an ampoule ball to absorb the sample, seal it, and move it to an iodine volume bottle and seal it. During the process, the sample sampling amount can be ensured to be accurate; the sample solution is further controlled at an appropriate concentration and a suitable stirring speed is set to ensure the accuracy of the titration result. In addition, the method does not introduce reagents such as dimethyl sulfoxide that affect the color mutation of the indicator, and the color change and jump at the re-titration endpoint are obvious. The detection method is simple to operate, has high detection efficiency and high accuracy; and can avoid the harm to the human body caused by the volatilization of acrylonitrile, and is suitable for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solution of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 It is a schematic diagram of a method for determining the purity of acrylonitrile raw materials according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with the specific embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other in the absence of conflict. The present application will be described in detail below in conjunction with the embodiments.

[0038] Reference to an "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present disclosure. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0039] In the related technology, inaccurate sampling volume will lead to obvious test errors, while using ampoule balls for sampling and sealing can avoid the volatilization loss of acrylonitrile; at the same time, controlling the sampling and titration operation parameters can improve the accuracy and repeatability of the test; at the same time, it can avoid the use of dimethyl sulfoxide in the test process, which will reduce the color mutation of the indicator, making the indicator's color mutation ability insufficient and interfering with the judgment of the true endpoint color of the titration.

[0040] Based on this, the exemplary embodiment of the present disclosure provides a method for detecting the purity of acrylonitrile raw materials. The schematic diagram of the determination method is as follows: Figure 1 The following is a specific example of the method for determining the purity of acrylonitrile raw materials according to the present application.

[0041] Example 1

[0042] S1. Solution preparation and calibration; the concentration of sodium sulfite solution is 1.0 mol / L, and the concentration of hydrochloric acid standard solution is 0.3573 mol / L.

[0043] S2. Sample weighing: Weigh the empty ampoule ball to 0.453g, use an alcohol lamp to quickly burn the spherical end of the ampoule ball back and forth 5 times, put the thin tube end of the ampoule ball into the test sample, automatically absorb the sample to about 1 / 4 of the ampoule ball, and then heat the thin tube end of the ampoule ball with an alcohol lamp to make the thin tube automatically curl and seal, weigh the ampoule ball and the sample weight to 0.748g, and use the difference to obtain the sample weight of 0.295g.

[0044] S3. Sample transfer: Measure 25 ml of Na2SO3 solution and add it to the iodine volume flask, then put the ampoule ball containing the sample into the iodine volume flask, quickly crush the ball with a glass rod, rinse the inner wall of the iodine volume flask and the residual sample on the glass rod with about 2 mL of secondary water, cover the stopper, add water to the mouth of the iodine volume flask to seal it, and place the iodine volume flask on a magnetic stirrer and stir at a speed of 500 r / min for 2 minutes.

[0045] S4. Sample titration analysis: open the stopper of the iodine volumetric flask, vertically drip 3 drops of the mixed indicator of alizarin yellow and thymolphthalein, and titrate with 0.3573 mol / L hydrochloric acid standard solution until the color of the solution changes from purple to light yellow, record the volume of HCl standard solution consumed (15.52 ml), and turn off the magnetic stirrer.

[0046] S5. Blank titration analysis, consuming 0 ml of hydrochloric acid standard solution;

[0047] S6. According to the formula, the purity of acrylonitrile raw material is calculated to be 99.74%.

[0048] Example 2

[0049] S1. Solution preparation and calibration: The concentration of sodium sulfite solution is 1.0 mol / L, and the concentration of hydrochloric acid standard solution is 0.3497 mol / L.

[0050] S2. Sample weighing: Weigh the empty ampoule ball to 0.397g, use an alcohol lamp to quickly burn the spherical end of the ampoule ball back and forth 6 times, put the thin tube end of the ampoule ball into the test sample, automatically absorb the sample to about 1 / 3 of the ampoule ball, and then heat the thin tube end of the ampoule ball with an alcohol lamp to make the thin tube automatically curl and seal, weigh the ampoule ball and the sample weight to 0.699g, and use the difference to obtain the sample weight of 0.302g.

[0051] S3. Sample transfer: Measure 25 ml of Na2SO3 solution and add it to the iodine volume flask, then put the ampoule ball containing the sample into the iodine volume flask, quickly crush the ball with a glass rod, rinse the inner wall of the iodine volume flask and the residual sample on the glass rod with about 2 mL of secondary water, cover the stopper, add water to the mouth of the iodine volume flask to seal it, and place the iodine volume flask on a magnetic stirrer and stir at a speed of 500 r / min for 3 minutes.

[0052] S4. Sample titration analysis: open the stopper of the iodine volumetric flask, vertically drip 3 drops of the mixed indicator of alizarin yellow and thymolphthalein, and titrate with 0.3497 mol / L hydrochloric acid standard solution until the color of the solution changes from purple to light yellow, record the volume of HCl standard solution consumed (16.23 ml), and turn off the magnetic stirrer.

[0053] S5. Blank titration analysis, consuming 0 ml of hydrochloric acid standard solution;

[0054] S6. According to the formula, the purity of the acrylonitrile raw material is calculated to be 99.72%.

[0055] Example 3

[0056] S1. Solution preparation and calibration: The concentration of sodium sulfite solution is 1.0 mol / L, and the concentration of hydrochloric acid standard solution is 0.3573 mol / L.

[0057] S2. Sample weighing: Weigh the empty ampoule ball to 0.408g, use an alcohol lamp to quickly burn the spherical end of the ampoule ball back and forth 5 times, put the thin tube end of the ampoule ball into the test sample, automatically absorb the sample to about 1 / 4 of the ampoule ball, and then heat the thin tube end of the ampoule ball with an alcohol lamp to make the thin tube automatically curl and seal, weigh the ampoule ball and the sample weight to 0.691g, and use the difference to obtain the sample weight of 0.283g.

[0058] S3. Sample transfer: Measure 25 ml of Na2SO3 solution and add it to the iodine volume flask, then put the ampoule ball containing the sample into the iodine volume flask, quickly crush the ball with a glass rod, rinse the inner wall of the iodine volume flask and the residual sample on the glass rod with 2.5 mL of secondary water, cover the stopper, add water to the mouth of the iodine volume flask to seal it, and place the iodine volume flask on a magnetic stirrer and stir at a speed of 600 r / min for 2 minutes.

[0059] S4. Sample titration analysis: open the stopper of the iodine volumetric flask, vertically drip 3 drops of mixed indicator of alizarin yellow and thymophthalein, and titrate with 0.3573 mol / L hydrochloric acid standard solution until the color of the solution changes from purple to light yellow, record the volume of HCl standard solution consumed (14.89 ml), and turn off the magnetic stirrer.

[0060] S5. Blank titration analysis, consuming 0 ml of hydrochloric acid standard solution;

[0061] S6. According to the formula, the purity of the acrylonitrile raw material is calculated to be 99.75%.

[0062] In order to explain the technical solution of the present disclosure more clearly, according to the determination method of the purity of acrylonitrile raw materials provided in each exemplary embodiment of the present disclosure, solution preparation and calibration, sample weighing, sample transfer, sample titration analysis, and blank titration analysis are performed. The determination results of potentiometric titration and gas chromatography are compared. The specific determination comparison results are shown in Tables 1 to 3.

[0063] Table 1 Comparative results of Example 1

[0064]

[0065] Table 2 Comparison results of Example 2

[0066]

[0067] Table 3 Comparative results of Example 3

[0068]

[0069] In order to further demonstrate the beneficial effects of the present application, the parameters involved in the measurement method are changed as a comparative example to compare the measurement results. Among them, an ampoule ball with a ball diameter of 20 mm is selected for sampling.

[0070] Comparative Example

[0071] S1. Solution preparation and calibration: The concentration of sodium sulfite solution is 1.0 mol / L, and the concentration of hydrochloric acid standard solution is 0.3573 mol / L.

[0072] S2. Sample weighing: Weigh the empty ampoule ball to 0.513g, use an alcohol lamp to quickly burn the spherical end of the ampoule ball back and forth 5 times, put the thin tube end of the ampoule ball into the test sample, automatically absorb the sample to about 1 / 4 of the ampoule ball, and then heat the thin tube end of the ampoule ball with an alcohol lamp to make the thin tube automatically curl and seal, weigh the ampoule ball and the sample weight to 0.940g, and use the difference to obtain the sample weight of 0.427g.

[0073] S3. Sample transfer: Measure 25 ml of Na2SO3 solution and add it to the iodine volume flask, then put the ampoule ball containing the sample into the iodine volume flask, quickly crush the ball with a glass rod, rinse the inner wall of the iodine volume flask and the residual sample on the glass rod with about 4 mL of secondary water, cover the stopper, add water to the mouth of the iodine volume flask to seal it, and place the iodine volume flask on a magnetic stirrer and stir at a speed of 700 r / min for 3 minutes.

[0074] S4. Sample titration analysis: open the stopper of the iodine volumetric flask, vertically drip 3 drops of the mixed indicator of alizarin yellow and thymophthalein, and titrate with 0.3573 mol / L hydrochloric acid standard solution until the color of the solution changes from purple to light yellow, record the volume of HCl standard solution consumed (22.45 ml), and turn off the magnetic stirrer.

[0075] S5. Blank titration analysis, consuming 0 ml of hydrochloric acid standard solution;

[0076] S6. According to the formula, the purity of acrylonitrile raw material is 99.68%.

[0077] Table 4 Comparative Example 1 Measurement Results

[0078]

[0079] As can be seen from the data in Tables 1-3, the detection method for the purity of acrylonitrile raw materials provided by the exemplary embodiment of the present disclosure, the manual titration method is slightly higher than the other two methods, and the phenomenon of "over titration" is prone to occur, and repeated measurements are required. The results measured by potentiometric titration and gas chromatography are highly consistent, and are consistent with the acrylonitrile purity value provided by the supplier. The accuracy and repeatability of the detection result data obtained by the present method are good. As can be seen from Table 4, the accuracy of the measurement results of the comparative example is lower than that of Examples 1-3, and the specific purity measurement results are lower. Therefore, according to the standard solution concentration selected by the exemplary embodiment of the present disclosure, the sample is weighed according to the appropriate ampoule ball specifications, and the acrylonitrile purity measured by the appropriate parameters can accurately characterize the true purity value of the acrylonitrile raw material. In addition, the detection time using manual titration, potentiometric titration and gas chromatography is 4min, 2min and 45min respectively. Manual titration requires the presence of experimental personnel throughout the process, and the operation is cumbersome and time-consuming. Chromatography needs to wait for the appearance of characteristic peaks such as toluene and crotononitrile before the test can be terminated. Taking all factors into consideration, the potentiometric titration method used in step S4 has high accuracy, good repeatability, short time consumption and high detection efficiency.

[0080] The above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure is described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

[0081] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining the purity of acrylonitrile raw material, characterized in that: The method comprises the following steps: S1. Solution preparation and calibration: prepare reaction solution and standard solution; S2. Sample weighing: Weigh the acrylonitrile raw material using an ampoule ball; S3. Sample transfer: The reaction solution was measured and added to an iodine volumetric flask, and then the ampoule ball containing the acrylonitrile raw material was transferred to the iodine volumetric flask; S4. Sample titration analysis; S5. Blank titration analysis; S6. Calculation of results.

2. The method for determining the purity of acrylonitrile raw material according to claim 1, characterized in that: In step S1, the reaction solution is a sodium sulfite solution with a concentration of 0.8-1.2 mol / L; the standard solution is a hydrochloric acid solution with a concentration of 0.3-0.5 mol / L.

3. The method for determining the purity of acrylonitrile raw material according to claim 1, wherein The method of using an ampoule ball to weigh the acrylonitrile raw material described in step S2 is specifically as follows: weigh the weight of the empty ampoule ball and record it as m1g; use an alcohol lamp to quickly reciprocate the spherical end of the ampoule ball for 5-6 times for 3-5s, put the capillary end of the ampoule ball into the test sample, automatically absorb it to 1 / 4-1 / 3 of the ampoule ball, and then heat the capillary end of the ampoule ball with an alcohol lamp, causing the capillary to automatically curl and seal, weigh the ampoule ball and the sample, and record it as m2g.

4. The method for determining the purity of acrylonitrile raw material according to claim 1, wherein: In step S3, 20-30 ml of Na2SO3 solution is measured and added to an iodine volume bottle, and then an ampoule ball containing acrylonitrile raw material is put into the iodine volume bottle, the ampoule ball is crushed with a glass rod, and the inner wall of the iodine volume bottle and the glass rod are rinsed with 1.5-2.5 ml of secondary water; the bottle stopper is tightly covered, the mouth of the iodine volume bottle is sealed with water, and then placed on a magnetic stirrer and stirred for 2-4 minutes.

5. The method for determining the purity of acrylonitrile raw material according to claim 4, characterized in that: The rotation speed of the magnetic stirrer is 500-600r / min.

6. The method for determining the purity of acrylonitrile raw material according to claim 1, characterized in that: The specific operation of step S4 is: open the stopper of the iodine volume flask, vertically drip 3 to 4 drops of a mixed indicator of alizarin yellow and thymolphthalein, titrate with the standard solution until the color of the solution changes from purple to light yellow, which is the end point, record the volume V of the consumed HCl standard solution, and turn off the magnetic stirrer after the titration is completed.

7. The method for determining the purity of acrylonitrile raw material according to claim 1, characterized in that: In step S4, the purity of acrylonitrile is determined by potentiometric titration. After completing steps S1 to S3, the iodine volume bottle is placed on a magnetic stirrer for magnetic stirring for 1-3 minutes, and then the liquid is poured into a beaker, and the iodine volume bottle is cleaned by washing the bottle; titration is performed using a potentiometric titrator; when the titration end point is reached, the titration stops automatically, and the acrylonitrile concentration is recorded.

8. The method for determining the purity of acrylonitrile raw material according to claim 1, characterized in that: The specific operation of step S5 is: titrating with the standard solution in an iodine volume flask containing the reaction solution and water but without the sample, and recording the volume V0 of the standard hydrochloric acid solution consumed in the blank test.

9. The method for determining the purity of acrylonitrile raw material according to claim 1, characterized in that: In step S6, the result calculation includes: Where: AN%——acrylonitrile purity in raw material sample, %; V——The volume of hydrochloric acid standard solution consumed in titrating the raw material sample, ml; V0——The volume of hydrochloric acid standard solution consumed in titrating the blank sample, ml; M——molar mass of acrylonitrile, g / mol; c——concentration of hydrochloric acid standard solution, mol / L.

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