A method for determining residual acrylonitrile content in polyacrylonitrile polymerization solution

Abstract

The present invention provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization liquid, and the residual acrylonitrile content in the polyacrylonitrile polymerization liquid is determined by using a fully automatic potentiometric titrator; the method mainly comprises the steps of preparing a solution to be tested, a blank titration step, and a titration step of the solution to be tested. The present invention is used to provide a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization liquid, which can quickly and accurately determine the titration end point, thereby improving accuracy and timeliness, so as to better guide actual production. Compared with the traditional manual titration method, the present invention is simple to operate, has accurate liquid addition volume, uniform stirring speed, and sensitive endpoint mutation. The instrument can automatically titrate and stop the reaction, so that the test error is small, and the detection efficiency is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of residual acrylonitrile content determination in a polymerization solution, in particular to a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution. Background Art

[0002] Polyacrylonitrile carbon fiber is an important strategic raw material for both military and civilian use. It is known as "black gold". Due to its excellent properties such as high strength and high modulus, it is regarded as the preferred new material in various fields such as aerospace, national defense and military.

[0003] Polyacrylonitrile carbon fiber is mainly produced by polymerization of acrylonitrile and solvents such as dimethyl sulfoxide and sodium thiocyanate under a series of reaction conditions. In order to ensure the quality of carbon fiber products, the residual acrylonitrile content in the polymerization solution needs to be accurately controlled. In order to spin high-quality raw yarn, the residual acrylonitrile content in the polyacrylonitrile polymerization solution should be strictly controlled below 0.1%. If the residual amount is too high, the monomer is very easy to volatilize after hot water drawing, leaving holes and affecting the quality of the raw yarn.

[0004] There is currently no national standard for determining the residual acrylonitrile content in polyacrylonitrile polymerization liquid. In some books such as "Polyacrylonitrile-based Carbon Fiber Production Technology" compiled by Cai Xiaoping et al., the detection method of residual monomers in the polymerization liquid is described. The determination principle is to conduct an addition reaction between acrylonitrile and an aqueous solution of sodium sulfite, generate NaOH and then neutralize it with hydrochloric acid or sulfuric acid solution. The detection method is to use manual indicator titration. In the patent "A method for determining the residual acrylonitrile monomer content of spinning solution in the process of carbon fiber production" (CN 106370773), the residual acrylonitrile content in the polymerization liquid is also determined by manual titration.

[0005] The above method can meet the detection requirements to a certain extent, but there are also certain drawbacks. Because the maximum accuracy requirement of chemical titration is 0.01%, the accuracy of manual titration is close to the limit of chemical titration, and for detection items with higher accuracy requirements, if manual titration is continued, a large error will be introduced, resulting in inaccurate experimental results and unable to correctly guide actual production. At the same time, the manual titration method is adopted, and different operators and different laboratory environmental conditions have a great influence on the detection results of the same sample. This is because the manual titration method determines the titration end point by observing the color change of the indicator, and different people are affected by the laboratory ambient light, experimental equipment materials such as glass thickness and color, indicator concentration, and the solution to be tested itself. The color recognition is affected, and the end point mutation is not very obvious, so that the experimental end point is often due to inaccurate human judgment, which makes the experimental result error larger, so as to bring certain troubles to the precise control of the production process. In addition, if the amount of samples to be detected is large, manual titration takes a long time, cannot be batch tested, and completely occupies the working time of other detection items, with poor timeliness, and also increases the chance of contact between people and acid.

[0006] Therefore, it is necessary to seek a method for determining the residual acrylonitrile content in polyacrylonitrile polymerization solution, which has a fast detection speed, a small error range, and an accurate determination of the endpoint. Summary of the invention

[0007] In view of this, the present invention provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution. The main purpose is to provide a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution that can quickly and accurately determine the titration endpoint, thereby improving accuracy and timeliness, so as to better guide actual production.

[0008] In order to achieve the above object, the present invention mainly provides the following technical solutions:

[0009] On the one hand, an embodiment of the present invention provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, wherein the residual acrylonitrile content in the polyacrylonitrile polymerization solution is determined using a fully automatic potentiometric titrator, which comprises the following steps:

[0010] The step of preparing the solution to be tested is: preparing the solution to be tested by mixing a set mass of polyacrylonitrile polymer solution sample and a set volume of solvent;

[0011] Blank titration step: prepare a set volume of solvent, use a fully automatic potentiometric titrator, and titrate with a base standard solution. The titration stops when the first set pH value is reached. The volume of the base standard solution consumed is recorded as V 02 ;

[0012] Prepare a set volume of solvent, add sodium sulfite solution thereto, then titrate with acid standard solution by a fully automatic potentiometric titrator, and stop titrating when the second set pH value is reached, wherein the volume of the acid standard solution consumed is recorded as V 01 ;

[0013] The test solution titration step: titrate the test solution with an alkali standard solution by a fully automatic potentiometric titrator to a third set pH value, add a sodium sulfite solution thereto, and then titrate with an acid standard solution until the titration reaches a fourth set pH value, and record the volume V of the consumed acid standard solution; according to V, V 01 、V 02 , the concentration of the alkali standard solution C 碱 , the concentration of acid standard solution C 酸 The residual acrylonitrile content in the polyacrylonitrile polymerization liquid sample is calculated based on the mass m of the polyacrylonitrile polymerization liquid sample.

[0014] Preferably, the first set pH value is 10.60-10.65, preferably 10.62.

[0015] Preferably, the second set pH value is 10.50-10.57, preferably 10.55.

[0016] Preferably, the third set pH value is 10.60-10.65, preferably 10.62.

[0017] Preferably, the fourth set pH value is 10.38-10.47, preferably 10.40-10.45; preferably, if the polyacrylonitrile polymerization solution is a polymerization solution that has not been stripped of single atoms, the fourth set pH value is 10.38-10.42, preferably 10.40; if the polyacrylonitrile polymerization solution is a polymerization solution that has been stripped of single atoms, the fourth set pH value is 10.43-10.47, preferably 10.45.

[0018] Preferably, in the step of preparing the test solution: the set mass is 0.5-2g; preferably, if the polyacrylonitrile polymerization liquid sample is a sample in the early stage of polymerization, the set mass is 0.4-0.6g, preferably 0.5g; preferably, if the polyacrylonitrile polymerization liquid sample is a sample in the late stage of polymerization, the set mass is 1.4-1.6g, preferably 1.5g; preferably, if the polyacrylonitrile polymerization liquid sample is a sample after stripping, the set mass is 1.9-2.1g, preferably 2g.

[0019] Preferably, in the step of preparing the test solution and the blank titration step: the solvent includes DMSO and water; preferably, in the set volume of the solvent: the volume of DMSO is 28-35 mL, preferably 30 mL; the volume of water is 45-55 mL, preferably 50 mL.

[0020] Preferably, in the step of preparing the test solution: placing the polyacrylonitrile polymer solution sample in a container, then adding DMSO thereto, sealing the container, and stirring to dissolve; after the polyacrylonitrile polymer solution sample is completely dissolved, opening the container mouth, adding water thereto, shaking well, to obtain the test solution; then sealing the container for standby use; preferably, sealing with a sealing film; preferably, the container is a beaker; preferably, firstly placing the polyacrylonitrile polymer solution at the bottom of the container by a sampling spoon, and ensuring that the polyacrylonitrile polymer solution does not touch the side wall of the container; preferably, the stirring and dissolving time is 25-30 minutes; preferably, a polytetrafluoroethylene rotor is placed in the container for stirring and dissolving.

[0021] Preferably, in the blank titration step and the test solution titration step: the concentration of the alkali standard solution is 0.05-0.1 mol / L, and the concentration of the acid standard solution is 0.05-0.1 mol / L; and / or the alkali standard solution is a NaOH standard solution; the acid standard solution is a 1 / 2H 2 SO 4 standard solution; and / or in the blank titration step, the concentration of the added sodium sulfite solution is 1±0.05mol / L and the volume is 20±0.1mL; and / or in the test solution titration step, the concentration of the added sodium sulfite solution is 1±0.05mol / L and the volume is 20±0.1mL.

[0022] Preferably, in the blank titration step: DMSO and water are added to a container in sequence to prepare a set volume of solvent; preferably, the container is a beaker to facilitate titration by a fully automatic potentiometric titrator.

[0023] Preferably, in the blank titration step and the test solution titration step: the setting conditions of the fully automatic potentiometric titrator are: the pre-added volume in the burette is 20 mL, the stirring time after pre-titration is 50-60 s, and the stirring speed is 6-8 r / s.

[0024] Preferably, the fully automatic potentiometric titrator is a Swiss Metrohm 855 fully automatic potentiometric titrator, but is not limited thereto, and other fully automatic titrators are also applicable.

[0025] Preferably, before the test solution titration step, the method further comprises:

[0026] Method setting steps: Input the concentration value C of the alkali standard solution on the fully automatic potentiometric titrator. 碱 , the concentration value of the acid standard solution C 酸 , a calculation formula for residual acrylonitrile content, and a method for determining residual acrylonitrile content is set; wherein the calculation formula for residual acrylonitrile content is as follows:

[0027]

[0028] Wherein, X is the residual acrylonitrile content in the polyacrylonitrile polymerization liquid sample, in %;

[0029] m is the mass of the polyacrylonitrile polymerization liquid sample, in g;

[0030] V is the volume of the acid standard solution consumed, in mL;

[0031] C 酸 is the concentration of the acid standard solution, in mol / L;

[0032] C 碱 is the concentration of the alkali standard solution, in mol / L;

[0033] V 01 is the volume of acid standard solution consumed in the blank titration step, in mL;

[0034] V 02 is the volume of the alkali standard solution consumed in the blank titration step, in mL;

[0035] 0.053 is the mass number equivalent to each millimole of acrylonitrile, and the unit is g / mmol.

[0036] Preferably, in the test solution titration step: a residual acrylonitrile content determination method is selected on the fully automatic potentiometric titrator, and start is clicked; then, the test solution is first titrated with an alkali standard solution to a third set pH value, a sodium sulfite solution is added thereto, and then titrated with an acid standard solution to a fourth set pH value; the fully automatic potentiometric titrator automatically records the volume V of the consumed acid standard solution, and automatically calculates the residual acrylonitrile content in the polyacrylonitrile polymerization solution sample based on the input data and the automatically recorded data.

[0037] Compared with the prior art, the method for determining the residual acrylonitrile content in the polyacrylonitrile polymerization solution of the present invention has at least the following beneficial effects:

[0038] The method for determining the residual acrylonitrile content in the polyacrylonitrile polymerization liquid provided in the embodiment of the present invention is a new method based on manual titration and combined with a fully automatic potentiometric titrator. Through a large number of studies, the endpoint pH value of the titration (as well as the endpoint pH value of different polymerization liquid samples) is found, and the operating points of the method are proposed. Here, the embodiment of the present invention uses a fully automatic potentiometric titrator to detect the residual acrylonitrile content in the polymerization liquid, avoiding the disadvantage that the indicator color change endpoint in the traditional titration method is difficult to determine, greatly reducing the subjective error caused by human beings, improving the accuracy of the detection data, and providing accurate data guarantee for the research and development of the polymerization production process. In addition, since the instrument titration is used instead of manual titration, the labor intensity of the detection personnel is greatly reduced and the detection time is shortened.

[0039] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. DETAILED DESCRIPTION

[0040] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention application are described in detail below in combination with the preferred embodiments. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0041] The embodiment of the present invention provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution. The method can quickly and accurately determine the titration endpoint and completely replace the manual titration method, thereby improving the accuracy and timeliness of the detection data to better guide actual production.

[0042] Here, the proposal of the present invention is a creative effort, which is specifically described as follows:

[0043] First, the acid-base titration of the prior art and the problems therein are explained as follows:

[0044] In the prior art, the difficulty of manual titration is that the sample is turbid at the end point of titration, and the color change from light blue to yellow-green is not obvious. In addition, there are color differences in the color judgment of individual testers, and the stoppered conical flasks used have color interference caused by different glass colors and thicknesses due to different production batches. During the test, the titration often fails to reach the end point or exceeds the end point, resulting in large deviations in the test results. Even if the same sample is titrated by the same person, the test results will also be biased.

[0045] Simple acid-base titration does not require setting the pH value during the titration process. As long as the titration endpoint is reached, the instrument automatically displays the mutation point and can read the volume of the mutation point. However, the polymer solution is an organic solution containing other impurities. It is not a simple acid-base reaction, but an addition reaction first and then an acid-base reaction. There are other organic substances in the solution that interfere. The titration process will not automatically have a mutation point, and the endpoint value may also be different from the simple acid-base titration endpoint. The endpoint can only be confirmed by determining the pH value.

[0046] Second, the difficulty of using a fully automatic potentiometric titrator for titration is how to determine the pH value. For this reason, in the prior art, there is no method for determining the residual acrylonitrile content in a polymerization solution using a fully automatic potentiometric titrator. The inventor of the present invention also determined the pH value through some experience, but did not successfully titrate using the fully automatic potentiometric titrator using the pH value for endpoint determination.

[0047] Based on this, the inventors of the present invention determined the pH value after a lot of research, and the general method is as follows:

[0048] Let's speculate on the principle first. The indicator used in the manual titration process is Alizarin Yellow R-Thymolphthalein indicator, the preparation ratio is 0.05g:0.1g, and the color change range of the two indicators is shown in Table 1.

[0049] Table 1

[0050] Alizarin Yellow R Thymolphthalein pH color change point 1.9-3.1 9.0-10.2 Color Change Red-Yellow None-Blue

[0051] According to the color change range of the mixed indicator and the design principle of chemical manual titration, the inventors took into account that: when the alkali is dropped, since the solution is weakly acidic, the solution is light yellow after adding the indicator, and the alkali is dropped to light blue, and the pH value of the solution is expected to be greater than 10.6. When the acid is dropped, the color is blue after adding the indicator, and it is necessary to titrate with acid to yellow-green. This pH value should be lower than the pH value when the alkali is dropped. On this basis, the inventors combined the actual color change of the sample, through repeated manual titration, estimated pH value and comparison with the actual measured value of the acidometer, and then compared the titration test with the titrator, and found the appropriate reaction color change point (this process is not a simple conventional experiment and orthogonal experiment, but after a lot of research, according to the principle, find out the idea, and then combine the actual sample, and conduct repeated research).

[0052] The specific scheme of the present invention comprises the following steps:

[0053] Weighing and dissolving steps of polyacrylonitrile polymer solution sample:

[0054] Accurately and quickly weigh the polyacrylonitrile polymer solution sample in a beaker (preferably, the capacity of the beaker is 250 mL), with a mass of m. Then add DMSO (preferably add 30 mL of DMSO), seal the mouth of the beaker with a sealing film, and place it on a magnetic stirrer to fully stir and dissolve. After the polyacrylonitrile polymer solution sample is completely dissolved, remove the sealing film, add ultrapure water (preferably 50 mL of ultrapure water) along the wall of the beaker, shake well, obtain a solution to be tested, and finally seal it with a sealing film for standby use.

[0055] In this step, the mass of the polyacrylonitrile polymerization liquid sample is 0.5-2g. If the polyacrylonitrile polymerization liquid sample is a sample in the early stage of polymerization, the mass of the polyacrylonitrile polymerization liquid sample is 0.4-0.6g, preferably 0.5g. If the polyacrylonitrile polymerization liquid sample is a sample in the late stage of polymerization, the mass of the polyacrylonitrile polymerization liquid sample is 1.4-1.6g, preferably 1.5g; if the polyacrylonitrile polymerization liquid sample is a sample after de-singling, the mass of the polyacrylonitrile polymerization liquid sample is 1.9-2.1g, preferably 2g.

[0056] In addition, in this step, please note:

[0057] 1) The polyacrylonitrile polymerization liquid sample should be uniform and free of lumps.

[0058] 2) The taken out polyacrylonitrile polymer liquid sample should be placed on the bottom of the beaker with a medicine spoon, and make sure that the polyacrylonitrile polymer liquid does not stick to the side wall of the beaker.

[0059] 3) During the determination process, the acid blank, base blank and sample should be prepared in parallel;

[0060] 4) Since the residual monomers in the polyacrylonitrile polymerization liquid sample are volatile, the weighing process should be shortened as much as possible, and the initial stable value of the balance should be read. After the weighing is completed, the sample bottle should be sealed with a sealing film in time;

[0061] 5) Keep the beaker mouth sealed with sealing film while stirring with the stirrer;

[0062] 6) The time for stirring to accelerate dissolution is about 25-30 minutes, and a polytetrafluoroethylene rotor needs to be added to the beaker;

[0063] 7) The amount of DMSO added in the step is 30 mL;

[0064] 8) The reaction vessel used in the titration process is a beaker, not a conical flask.

[0065] Method setup steps:

[0066] First, input the calibrated alkali standard solution (NaOH standard solution) and acid standard solution (1 / 2H 2 SO 4The actual concentration of the standard solution) C 碱 , C 酸 , then input the calculation formula for determining the residual acrylonitrile content in the polymerization liquid and set the method.

[0067] The calculation formula is as follows:

[0068] The residual acrylonitrile mass percentage X (%) in the polymerization solution is calculated according to formula (1):

[0069]

[0070] Among them, in formula (1):

[0071] X is the residual acrylonitrile content in the polyacrylonitrile solution, %;

[0072] m is the mass of the polyacrylonitrile polymerization liquid sample, in g;

[0073] V is the volume of acid standard solution consumed by the sample, in mL;

[0074] C 酸 is the concentration of the acid standard solution, in mol / L;

[0075] C 碱 is the concentration of the alkali standard solution, in mol / L;

[0076] V 01 is the volume of acid standard solution consumed in the blank titration step, in mL;

[0077] V 02 is the volume of the alkali standard solution consumed in the blank titration step, in mL;

[0078] 0.053 is the mass number equivalent to each millimole of acrylonitrile, and the unit is g / mmol.

[0079] Blank titration steps:

[0080] Alkali dropping step: in a beaker (preferably, the capacity of the beaker is 250 mL), add 30 mL of DMSO and 50 mL of ultrapure water in sequence, shake well, and use a fully automatic potentiometric titrator to titrate with 0.1 mol / L alkali standard solution (NaOH standard solution) to the first set pH value (preset) to stop the reaction, and the volume of the consumed alkali standard solution (NaOH standard solution) is recorded as V 02 .

[0081] Acid drop step: In a beaker (preferably, the capacity of the beaker is 250 mL), add 30 mL of DMSO and 50 mL of ultrapure water in sequence, shake well, then add 20 mL of 1 mol / L sodium sulfite, and use a fully automatic potentiometric titrator to titrate with 0.1 mol / L acid standard solution (1 / 2H 2 SO 4 The reaction stops when the acid standard solution (1 / 2H 2 SO 4 The volume of the standard solution is recorded as V 01 .

[0082] Titration steps of the test solution:

[0083] The residual acrylonitrile content of the solution to be tested is determined by a fully automatic potentiometric titrator. Select the setting method, click Start, and titrate with 0.1 mol / L alkali standard solution (NaOH standard solution) to the third set pH value, then add 20 mL of 1 mol / L sodium sulfite, and then use 0.1 mol / L acid standard solution (1 / 2H 2 SO 4 When the acid standard solution (1 / 2H) is titrated to the fourth set pH value, the fully automatic potentiometric titrator automatically stops and automatically records the acid standard solution (1 / 2H 2 SO 4 The volume V of the standard solution is automatically calculated according to the formula to obtain the residual acrylonitrile content.

[0084] In addition, in the above determination steps: (1) the setting conditions of the fully automatic potentiometric titrator are: the pre-added volume in the burette is 20 mL, the stirring time after pre-titration is 50-60 s, and the stirring speed is 6-8 r / s. (2) The titration endpoint pH value is 10.30-10.65; preferably, the alkali blank endpoint pH value is 10.62, and the acid blank endpoint pH value is 10.55. The titration endpoint pH value of the polyacrylonitrile polymerization liquid sample that has not been stripped is 10.40, and the endpoint pH value of the polyacrylonitrile polymerization liquid sample that has been stripped is 10.45.

[0085] The present invention is further described below by specific experimental examples:

[0086] Example 1

[0087] This embodiment provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, wherein the polyacrylonitrile polymerization solution sample is sampled from the polyacrylonitrile polymerization solution in the polymerization process. The method mainly comprises the following steps:

[0088] 1) Set the "Residual acrylonitrile content detection method" on the fully automatic potentiometric titrator in advance. The setting conditions are: the pre-added volume in the burette is 20mL, the stirring time after pre-titration is 60s, the stirring speed is 8r / s; the titration endpoint pH value is 10.40, the alkali blank endpoint pH value is 10.62, and the acid blank endpoint pH value is 10.55.

[0089] 2) Weigh two parallel samples, with masses of 0.5020g and 0.5068g (accurate to 0.1mg), respectively, and place the two parallel samples in 250mL beakers, then add 30mL of DMSO to each, add a polytetrafluoroethylene rotor to the beaker, seal the beaker mouth with a sealing film, and place it on a magnetic stirrer to stir and dissolve for 30 minutes. Remove the sealing film, add 50mL of ultrapure water along the wall of the stirred sample solution, shake well, obtain the test solution, and then seal it with a sealing film for standby use.

[0090] 3) Alkali dropping step: 30 mL of DMSO and 50 mL of ultrapure water were added to a 250 mL beaker in sequence, and titrated with 0.1 mol / L alkali standard solution (NaOH standard solution) using a fully automatic potentiometric titrator. When the pH value of the solution reaches 10.62, titrate to the endpoint. The volume of the consumed alkali standard solution (NaOH standard solution) is recorded as V 02 .

[0091] Acid titration steps: 30 mL of DMSO, 50 mL of ultrapure water, and 20 mL of sodium sulfite were added to a 250 mL beaker in sequence, and then a 0.1 mol / L acid standard solution (1 / 2H 2 SO 4 When the pH value of the solution reaches 10.55, titrate to the end point, consuming the acid standard solution (1 / 2H 2 SO 4 The volume of the standard solution is recorded as V 01 .

[0092] 4) Select the method "Residual acrylonitrile content detection method" on the fully automatic potentiometric titrator, click to enter the calibrated alkali standard solution (NaOH standard solution) and acid standard solution (1 / 2H 2 SO 4 The actual concentration of the standard solution) C 碱 , C 酸 Remove the sealing film on the beaker with dissolved sample, click the "Start" button, titrate with 0.1mol / L alkali standard solution (NaOH standard solution) to the set pH value of 10.62, add 20mL of 1mol / L sodium sulfite, stir for a while, and then add 0.1mol / L acid standard solution (1 / 2H 2 SO 4When the pH value reaches the set value of 10.40, the fully automatic potentiometric titrator stops automatically and automatically records the consumption of the acid standard solution (1 / 2H 2 SO 4 The volume V of the standard solution is titrated and the residual acrylonitrile content is automatically calculated.

[0093]

[0094] In the above formula:

[0095] X is the residual acrylonitrile content in the polyacrylonitrile solution, %;

[0096] m is the mass of the polyacrylonitrile polymerization liquid sample, in g;

[0097] V is the volume of acid standard solution consumed by the sample, in mL;

[0098] C 酸 is the concentration of the acid standard solution, in mol / L;

[0099] C 碱 is the concentration of the alkali standard solution, in mol / L;

[0100] V 01 is the volume of acid standard solution consumed in the blank titration step, in mL;

[0101] V 02 is the volume of the alkali standard solution consumed in the blank titration step, in mL;

[0102] 0.053 is the mass number equivalent to each millimole of acrylonitrile, and the unit is g / mmol.

[0103] Table 2 shows the test results of the residual acrylonitrile content in the polyacrylonitrile-based polymer solution sample after 5 hours of polymerization reaction using the method of Example 1 and the existing manual titration method.

[0104] Table 2 Comparison of experimental data of residual acrylonitrile content in polymerization solution samples after 5 hours of polymerization

[0105]

[0106] Example 2

[0107] This embodiment provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization liquid, wherein the polyacrylonitrile polymerization liquid sample is sampled from the polyacrylonitrile polymerization liquid after the monomer removal. The method mainly comprises the following steps:

[0108] 1) Set the "Residual acrylonitrile content detection method (single sample)" on the fully automatic potentiometric titrator in advance. The setting conditions are as follows: the pre-added volume in the burette is 20 mL, the stirring time after pre-titration is 60 s, the stirring speed is 8 r / s, the titration endpoint pH value is 10.45, the alkaline blank endpoint pH value is 10.62, and the acid blank endpoint pH value is 10.55.

[0109] 2) Weigh two parallel samples, the mass is 2.1943g, 2.1009g (accurate to 0.1mg), and then place the two parallel samples in 250mL beakers, add 30mL of DMSO to each of the two beakers, and put in polytetrafluoroethylene rotors, seal the beakers with sealing film, and place them on a magnetic stirrer to stir and dissolve for 30min. Remove the sealing film, add 50mL of ultrapure water along the wall of the stirred sample solution, shake well, obtain the test solution, and then seal it with sealing film.

[0110] 3) Alkali dropping step: 30 mL of DMSO and 50 mL of ultrapure water were added to a 250 mL beaker in sequence, and titrated with 0.1 mol / L alkali standard solution (NaOH standard solution) using a fully automatic potentiometric titrator. When the pH value of the solution reaches 10.62, titrate to the endpoint. The volume of the consumed alkali standard solution (NaOH standard solution) is recorded as V 02 .

[0111] Acid drop step: add 30mL of DMSO and 50mL of ultrapure water to a 250mL beaker, then add 20mL of 1mol / L sodium sulfite, and then use a fully automatic potentiometric titrator to titrate with 0.1mol / L acid standard solution (1 / 2H 2 SO 4 When the pH of the solution reaches 10.55, titrate to the end point, consuming the acid standard solution (1 / 2H 2 SO 4 The volume of the standard solution is recorded as V 01 .

[0112] 4) Select the method "Residual acrylonitrile content detection method (single sample)" on the fully automatic potentiometric titrator, click to enter the calibrated alkali standard solution (NaOH standard solution) and acid standard solution (1 / 2H 2 SO 4 The actual concentration of the standard solution) C 碱 , C 酸 , remove the sealing film on the beaker with dissolved sample, click the "Start" button, titrate with 0.1mol / L alkali standard solution (NaOH standard solution) to the set pH value of 10.62, add 20mL of 1mol / L sodium sulfite, stir for a while, and then add 0.1mol / L acid standard solution (1 / 2H2 SO 4 When the pH value of the sample reaches the set value of 10.45, the fully automatic potentiometric titrator stops automatically and automatically records the consumption of the acid standard solution (1 / 2H 2 SO 4 The volume V of the standard solution is automatically calculated to obtain the residual acrylonitrile content.

[0113]

[0114] In the above formula:

[0115] X is the residual acrylonitrile content in the polyacrylonitrile solution, %;

[0116] m is the mass of the polyacrylonitrile polymerization liquid sample, in g;

[0117] V is the volume of acid standard solution consumed by the sample, in mL;

[0118] C 酸 is the concentration of the acid standard solution, in mol / L;

[0119] C 碱 is the concentration of the alkali standard solution, in mol / L;

[0120] V 01 is the volume of acid standard solution consumed in the blank titration step, in mL;

[0121] V 02 is the volume of the alkali standard solution consumed in the blank titration step, in mL;

[0122] 0.053 is the mass number equivalent to each millimole of acrylonitrile, and the unit is g / mmol.

[0123] Table 3 shows the test results of the residual acrylonitrile content in the polymer solution sample after the removal of monomers by the method of Example 2 and the existing manual titration method.

[0124] Table 3 Comparison of experimental data of residual acrylonitrile content in the polymerization solution after removal of single

[0125]

[0126] As can be seen from the above-described embodiment: when utilizing the full-automatic potentiometric titrator to measure the residual acrylonitrile content in the polyacrylonitrile, because the method of the embodiment of the present invention is not based on the indicator color change, only by the instrument detecting the setting pH value, stop titration to judge the reaction end point, its measurement result is little deviation compared with the manual titration method, because the acid volume reading is more accurate during instrument titration, it is more sensitive to the terminal point judgment, and its detection result is more accurate. Like this, both eliminated the artificial difference brought due to reading and color judgment between different operators, simultaneously because the minimum titration graduation of the titrator is 0.0002mL, and the minimum titration graduation of the microburette for manual titration is 0.02mL, compared with manual titration, detection accuracy can improve about 100 times. In addition because the automation degree of the instrument is high, the parameter setting is convenient, the instrument can automatically titrate, and the reaction is automatically stopped during the terminal point, and finally also to print out the experimental result report sheet, can greatly save manpower and time like this, is the more ideal method for measuring the residual acrylonitrile content in the polymer solution.

[0127] Comparative Example 1

[0128] Comparative Example 1 provides a method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution, wherein the polyacrylonitrile polymerization solution sample is sampled from the polyacrylonitrile polymerization solution after the removal of monomers. The method mainly comprises the following steps:

[0129] 1) Set the "Residual acrylonitrile content detection method (de-acrylonitrile sample)" in advance on the fully automatic potentiometric titrator. The setting conditions are as follows: the pre-added volume in the burette is 20 mL, the stirring time after pre-titration is 60 s, the stirring speed is 8 r / s, the titration endpoint pH value is 10.67, the alkaline blank endpoint pH value is 10.62, and the acid blank endpoint pH value is 10.55.

[0130] 2) Weigh two parallel samples, the masses are 1.9804g and 2.0836g (accurate to 0.1mg), and then place the two parallel samples in 250mL beakers, add 30mL of DMSO to each of the two beakers, and place polytetrafluoroethylene rotors in each beaker, seal the beaker mouth with sealing film, and place it on a magnetic stirrer to stir and dissolve for 30 minutes. Remove the sealing film, add 50mL of ultrapure water along the wall of the stirred sample solution, shake well, obtain the test solution, and then seal it with sealing film.

[0131] 3) Alkali dropping step: 30 mL of DMSO and 50 mL of ultrapure water were added to a 250 mL beaker in sequence, and titrated with 0.1 mol / L alkali standard solution (NaOH standard solution) using a fully automatic potentiometric titrator. When the pH value of the solution reaches 10.62, titrate to the endpoint. The volume of the consumed alkali standard solution (NaOH standard solution) is recorded as V 02 .

[0132] Acid drop step: add 30mL of DMSO, 50mL of ultrapure water, and then add 20mL of sodium sulfite in a 250mL beaker, and then use a fully automatic potentiometric titrator to titrate with 0.1mol / L acid standard solution (1 / 2H 2 SO 4 When the pH of the solution reaches 10.55, titrate to the end point, consuming the acid standard solution (1 / 2H 2 SO 4 The volume of the standard solution is recorded as V 01 .

[0133] 4) Select the method "Residual acrylonitrile content detection method (single sample)" on the fully automatic potentiometric titrator, click to enter the actual concentration C of the calibrated sodium hydroxide standard solution and sulfuric acid standard solution 碱 , C 酸 , remove the sealing film on the beaker with dissolved sample, click the "Start" button, titrate with 0.1mol / L alkali standard solution (NaOH standard solution) to the set pH value of 10.62, add 20mL of 1mol / L sodium sulfite, stir for a while, and then add 0.1mol / L acid standard solution (1 / 2H 2 SO 4 When the pH value of the sample reaches the set value of 10.67, the fully automatic potentiometric titrator stops automatically and automatically records the consumption of the acid standard solution (1 / 2H 2 SO 4 The volume V of the titration solution (standard solution) is automatically calculated to obtain the residual acrylonitrile content.

[0134]

[0135] In the above formula:

[0136] X is the residual acrylonitrile content in the polyacrylonitrile solution, %;

[0137] m is the mass of the polyacrylonitrile polymerization liquid sample, in g;

[0138] V is the volume of acid standard solution consumed by the sample, in mL;

[0139] C 酸 is the concentration of the acid standard solution, in mol / L;

[0140] C 碱 is the concentration of the alkali standard solution, in mol / L;

[0141] V 01 is the volume of acid standard solution consumed in the blank titration step, in mL;

[0142] V 02is the volume of the alkali standard solution consumed in the blank titration step, in mL;

[0143] 0.053 is the mass number equivalent to each millimole of acrylonitrile, and the unit is g / mmol.

[0144] Table 4 shows the test results of the residual acrylonitrile content in the polymer solution after the removal of single monomers by the method of Comparative Example 1 and the existing manual titration method.

[0145] Table 4 Comparison of experimental data of residual acrylonitrile content in the polymerization solution after removal of single

[0146]

[0147] It can be seen from Table 4 that for the polymerization solution after single-acid removal, when the fourth set pH value is 10.67, the residual acrylonitrile content in the polymerization solution has a significant deviation from the value of manual titration. When the fourth set pH value is 10.45, the residual acrylonitrile content in the polymerization solution is basically equivalent to the value of manual titration.

[0148] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls 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: The residual acrylonitrile content in the polyacrylonitrile polymerization solution is determined by using a fully automatic potentiometric titrator, which comprises the following steps: The step of preparing the solution to be tested is: preparing the solution to be tested by mixing a set mass of polyacrylonitrile polymer solution sample and a set volume of solvent; Blank titration step: prepare a set volume of solvent, use a fully automatic potentiometric titrator, and titrate with a base standard solution. The titration stops when the first set pH value is reached. The volume of the base standard solution consumed is recorded as V 02 ; Prepare a set volume of solvent, add sodium sulfite solution thereto, then titrate with acid standard solution by a fully automatic potentiometric titrator, and stop titrating when the second set pH value is reached, wherein the volume of the acid standard solution consumed is recorded as V 01 ; The test solution titration step: titrate the test solution with an alkali standard solution by a fully automatic potentiometric titrator to a third set pH value, add a sodium sulfite solution thereto, and then titrate with an acid standard solution until the titration reaches a fourth set pH value, and record the volume V of the consumed acid standard solution; according to V, V 01 、V 02 , the concentration of the alkali standard solution C 碱 , the concentration of acid standard solution C 酸 and the mass m of the polyacrylonitrile polymerization liquid sample, calculate the residual acrylonitrile content in the polyacrylonitrile polymerization liquid sample; The first set pH value is 10.60-10.65, the second set pH value is 10.50-10.57, the third set pH value is 10.60-10.65, and the fourth set pH value is 10.38-10.47; Wherein, if the polyacrylonitrile polymerization liquid is a polymerization liquid that has not been de-monomerized, the fourth set pH value is 10.38-10.42; if the polyacrylonitrile polymerization liquid is a polymerization liquid that has been de-monomerized, the fourth set pH value is 10.43-10.

47.

2. The method for measuring the residual acrylonitrile content in the polyacrylonitrile polymerization solution according to claim 1, characterized in that: The first set pH value is 10.62; and / or The second set pH value is 10.55; and / or The third set pH value is 10.62; and / or The fourth set pH value is 10.40-10.45; and / or If the polyacrylonitrile polymerization liquid is a polymerization liquid that has not been stripped of single atoms, the fourth set pH value is 10.40; if the polyacrylonitrile polymerization liquid is a polymerization liquid that has been stripped of single atoms, the fourth set pH value is 10.

45.

3. The method for measuring the residual acrylonitrile content in the polyacrylonitrile polymerization solution according to claim 1, characterized in that: In the step of preparing the test solution: the set mass is 0.5-2g.

4. The method for determining the residual acrylonitrile content in the polyacrylonitrile polymerization solution according to claim 3, characterized in that: In the step of preparing the test solution: If the polyacrylonitrile polymerization liquid sample is a sample in the early stage of polymerization, the mass is set to 0.4-0.6 g; If the polyacrylonitrile polymerization liquid sample is a sample in the late stage of polymerization, the mass is set to 1.4-1.6 g; If the polyacrylonitrile polymerization liquid sample is a sample after being stripped, the mass is set to 1.9-2.1 g.

5. The method for determining the residual acrylonitrile content in the polyacrylonitrile polymerization solution according to claim 4, characterized in that: In the step of preparing the solution to be tested: If the polyacrylonitrile polymerization liquid sample is a sample in the early stage of polymerization, the mass is set to 0.5 g.

6. The method for determining the residual acrylonitrile content in the polyacrylonitrile polymerization solution according to claim 4, characterized in that: In the step of preparing the solution to be tested: If the polyacrylonitrile polymerization liquid sample is a sample in the late stage of polymerization, the mass is set to 1.5 g.

7. The method for determining the residual acrylonitrile content in the polyacrylonitrile polymerization solution according to claim 4, characterized in that: In the step of preparing the solution to be tested: If the polyacrylonitrile polymerization liquid sample is a sample after stripping, the mass is set to 2 g.

8. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 1, characterized in that: In the step of preparing the test solution and the blank titration step: the solvent includes DMSO and water.

9. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 8, characterized in that: In the set volume of solvent: the volume of DMSO is 28-35 mL; the volume of water is 45-55 mL.

10. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 9, characterized in that: In the set volume of solvent: the volume of DMSO is 30 mL, and the volume of water is 50 mL.

11. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 1, characterized in that: In the step of preparing the solution to be tested: Place the polyacrylonitrile polymer solution sample in a container, then add DMSO thereto, seal the container, and stir to dissolve; after the polyacrylonitrile polymer solution sample is completely dissolved, open the container, add water thereto, shake well to obtain a solution to be tested; then seal the container for standby use.

12. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 11, characterized in that: In the step of preparing the solution to be tested: Sealed with parafilm; and / or The container is a beaker; and / or First, use a sampling spoon to place the polyacrylonitrile polymer solution on the bottom of the container, and ensure that the polyacrylonitrile polymer solution does not touch the side wall of the container; and / or The stirring and dissolving time is 25-30 minutes; and / or A polytetrafluoroethylene rotor is placed in the container for stirring and dissolving.

13. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 1, characterized in that: In the blank titration step and the test solution titration step: The concentration of the base standard solution is 0.05-0.1 mol / L, and the concentration of the acid standard solution is 0.05-0.1 mol / L; and / or The base standard solution is selected from NaOH standard solution; the acid standard solution is selected from 1 / 2H2SO4 standard solution; and / or In the blank titration step, the concentration of the added sodium sulfite solution is 1±0.05 mol / L and the volume is 20±0.1 mL; and / or In the step of titrating the solution to be tested, the concentration of the added sodium sulfite solution is 1±0.05 mol / L and the volume is 20±0.1 mL.

14. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 1, characterized in that: During the blank titration step: DMSO and water are added to a container in sequence to prepare a set volume of solvent.

15. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 14, characterized in that: During the blank titration step: The container is a beaker, so as to facilitate titration by a fully automatic potentiometric titrator.

16. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 1, characterized in that: In the blank titration step and the test solution titration step: The setting conditions of the fully automatic potentiometric titrator are: the pre-added volume in the burette is 20 mL, the stirring time after pre-titration is 50-60 s, and the stirring speed is 6-8 r / s; and / or The fully automatic potentiometric titrator is a Swiss Metrohm 855 fully automatic potentiometric titrator.

17. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 1, characterized in that: Before the test solution titration step, the method further comprises: Method setting steps: Input the concentration value C of the alkali standard solution on the fully automatic potentiometric titrator. 碱 , the concentration value of the acid standard solution C 酸 , a calculation formula for residual acrylonitrile content, and a method for determining residual acrylonitrile content is set; wherein the calculation formula for residual acrylonitrile content is as follows: Wherein, X is the residual acrylonitrile content in the polyacrylonitrile polymerization liquid sample, in %; m is the mass of the polyacrylonitrile polymerization liquid sample, in g; V is the volume of the acid standard solution consumed, in mL; C 酸 is the concentration of the acid standard solution, in mol / L; C 碱 is the concentration of the alkali standard solution, in mol / L; V 01 is the volume of the acid standard solution consumed in the blank titration step, in mL; V 02 is the volume of the alkali standard solution consumed in the blank titration step, in mL; 0.053 is the mass number equivalent to each millimole of acrylonitrile, and the unit is g / mmol.

18. The method for determining the residual acrylonitrile content in a polyacrylonitrile polymerization solution according to claim 17, characterized in that: In the test solution titration step: Select the residual acrylonitrile content determination method on the full-automatic potentiometric titrator and click start; then, first titrate the test solution with the alkali standard solution to the third set pH value, add the sodium sulfite solution thereto, and then titrate with the acid standard solution to the fourth set pH value; the full-automatic potentiometric titrator automatically records the volume V of the consumed acid standard solution, and automatically calculates the residual acrylonitrile content in the polyacrylonitrile polymerization solution sample based on the input data and the automatically recorded data.

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