A method for detecting the chloride ion content in hydrolyzate dimethyldimethoxysilane

Abstract

The present invention relates to a method for detecting the chloride ion content in the hydrolyzate of dimethyldimethoxysilane. The hydrolyzate to be tested is placed in a three-necked flask, and an oxidation solution and a chloride ion standard solution are added to the hydrolyzate and mixed thoroughly. The treated hydrolyzate solution is connected to a tail gas absorption device, and sodium hydroxide solution is filled in the tail gas absorption bottle as the collecting liquid. The hydrolyzate treatment liquid is heated, and after 30 - 40 minutes, the heating is stopped. After cooling to room temperature, the tail gas absorption bottle is removed, and the chloride ion content in the solution in the tail gas absorption bottle is measured. The volume of the consumed AgNO3 standard solution is recorded, and the blank value of the sodium chloride standard solution is subtracted, which is the volume consumed by the chloride ions in the hydrolyzate. The present invention avoids the influence of the hydrolyzate itself on the electrode of the potentiometric titrator in the direct titration method, and at the same time, there is no need for digestion, and a large amount of toxic gas will not overflow. The present invention improves the service life of the electrode and the accuracy of the result, has good reproducibility, and also has a certain environmental friendliness.

Description

Technical Field

[0001] The present invention belongs to the technical field of analytical detection, and particularly relates to a method for detecting the chloride ion content in the hydrolysis product of dimethyldimethoxysilane. Background Art

[0002] Dimethyldichlorosilane (C2H6Cl2Si, abbreviated as dimethyl) is the most widely used organosilicon monomer in China at present. The hydrolysis product obtained from dimethyl through hydrolysis can be used to prepare organosilicon intermediates DMC through means such as cracking and polymerization, and then many silicone-based chemicals such as 107 silicone rubber, 110 silicone rubber, and silicone oil can be obtained. Therefore, dimethyl has very broad application prospects. At present, most domestic enterprises still use the hydrolysis product of dimethyl as the raw material for synthesizing products such as 107 silicone rubber, but it is very difficult to control the content of residual chlorine ions in domestic dimethyl hydrolysis products. When the chloride ion content is too high, it will greatly affect the application of a series of products such as 107 silicone rubber (generally, the free chlorine content in the dimethyl hydrolysis product is required to be ≤ 10 ppm). Since the dimethyl hydrolysis product has poor solubility in non-toxic solvents such as water and ethanol, the direct measurement of its chloride ion content results in too large a deviation. At the same time, the dimethyl hydrolysis product will adhere to the electrode during direct measurement, and long-term measurement will seriously reduce the service life of the electrode of the potentiometric titrator; while using digestion and other treatments on the hydrolysis product will generate a large amount of toxic gases, which is relatively dangerous; the detection limit of the mercury colorimetric method for measuring the chloride ion content in the dimethyl hydrolysis product is even worse; the cost of analyzing the hydrolysis product content in the dimethyl hydrolysis product by XRF fluorescence spectrometry is too high, and the reproducibility is poor.

[0003] Since acidic chlorides are not stable in solution, the free chlorine in the dimethyl hydrolysis product is oxidized by a strong oxidant to form acidic chlorides. Through strong mixing for full reaction and heating for full evaporation, an alkaline absorbent is used to absorb the acidic chlorides, which can not only fully absorb the volatilized free chlorine, but also not cause environmental pollution. The absorbent is subjected to potentiometric titration to detect the chloride ion content, and the result is relatively stable, with little impact on the electrode, low cost, and the detection limit can reach 2 ppm, which can meet the basic requirements for the production of dimethyl hydrolysis product (free chlorine content ≤ 20 ppm) and the equipment for synthesizing 107 silicone rubber. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for detecting the chloride ion content in the hydrolysis product of dimethyldimethoxysilane.

[0005] A method for detecting the chloride ion content in the hydrolysis product of dimethyldimethoxysilane, the specific steps are as follows:

[0006] (1) Titrating the blank value: Accurately transfer the NaCl standard solution into the titration cup, add deionized water to the scale line, and perform potentiometric titration with the AgNO3 standard solution. Record the volume V0 of the AgNO3 standard solution consumed, and perform parallel determination three times;

[0007] (2) Treat the hydrolyzate to be tested: Weigh accurately a certain amount of hydrolyzate into a volumetric flask, add an oxidizing agent solution, pipette a standard NaCl solution into the volumetric flask, and stir to mix thoroughly;

[0008] (3) Heat and distill the hydrolyzate: Heat the hydrolyzate mixed evenly in step (2) by oil bath, collect the tail gas with sodium hydroxide solution, and weigh the sodium hydroxide solution as m;

[0009] (4) After the collected tail gas is cooled, accurately weigh a certain mass of the tail gas absorption solution m1, add nitric acid solution to make it acidic, and then perform potentiometric titration with AgNO3 standard solution. Record the volume V of the consumed AgNO3 standard solution, and perform parallel determination three times to calculate the chloride ion content;

[0010] The calculation formula for the chloride ion content is as follows:

[0011]

[0012] Among them, V: the volume of the AgNO3 standard solution consumed by the tail gas absorption solution, mL;

[0013] V0: the volume of the AgNO3 standard solution consumed by titrating the NaCl blank solution, mL;

[0014] 35450: the relative atomic mass of chlorine atom × 1000;

[0015] m1: the mass of the sodium hydroxide tail gas absorption solution weighed;

[0016] m: the total mass of the sodium hydroxide solution.

[0017] Preparation and calibration of the AgNO3 standard solution: Weigh accurately a certain amount of analytical pure AgNO3 solid into a 500 mL container, quickly add deionized water to dissolve it, and then quickly transfer it to a brown wide-mouth reagent bottle with a glass stopper; Take another 0.1 - 0.2 g of analytical pure sodium chloride solid that has been weighed to constant weight at 500 - 600 °C for 3 - 6 h, dissolve it with deionized water, use the prepared AgNO3 solution as the titrant, perform precipitation titration on a potentiometric titrator, record the volume of the consumed AgNO3 solution, and perform parallel determination 3 - 5 times to calculate the titration degree of the AgNO3 standard titration solution. The calculation formula for the AgNO3 standard titration solution is as follows:

[0018] ;

[0019] Among them, m: the mass of the weighed sodium chloride, g;

[0020] M: the relative molecular mass of NaCl, taking 58.4 g / mol;

[0021] V: Volume of the consumed AgNO3 standard solution, mL.

[0022] The error of the calculation results of the AgNO3 standard titration solution for 3 - 5 times ≤ ±0.2%.

[0023] The hydrolyzate described in step (2) is a weakly acidic hydrolyzate of dimethyldichlorosilane with a pH of 5 - 6; the oxidant solution is one of nitric acid solution, hydrogen peroxide solution, and potassium permanganate solution; the mass ratio of the oxidant solution to the hydrolyzate is 1:1 - 1:3.

[0024] Preparation of the oxidant solution: Add 20 mL of concentrated sulfuric acid to a 1000 mL volumetric flask, then slowly add a certain amount of deionized water. After complete cooling, add 10 mol of strong oxidant to the 1000 mL volumetric flask and continue to add deionized water to the calibration line. The strong oxidant is nitric acid, hydrogen peroxide, or potassium permanganate.

[0025] Preparation of the sodium chloride standard solution: Accurately weigh a certain amount of analytical pure sodium chloride solid into a 1000 mL beaker, add a certain amount of deionized water to completely dissolve it, then transfer it to a volumetric flask and make up to the calibration line with deionized water, and shake well.

[0026] The mass - volume ratio of the weakly acidic hydrolyzate of dimethyldichlorosilane to the sodium chloride standard solution is 30 - 50:1 - 3 (g:ml).

[0027] During the heating and distillation of the hydrolyzate in step (3), the heating temperature is 140 - 150 °C and the heating time is 25 - 35 min.

[0028] In step (4), adjust the pH of the tail gas absorption solution within the range of 3 - 5.

[0029] The measured chloride ion content is in the range of 2 - 20 ppm.

[0030] The present invention has the advantages of high precision, good reproducibility, high accuracy, and good repeatability, avoiding the poor solubility of dimethyl hydrolyzate and the influence on the service life of the electrode, which can increase the service life of the electrode and ensure the use accuracy of the instrument. Detailed Embodiment

[0031] To more detailedly explain the present invention, the following examples are now combined to further elaborate on the present invention. The preparation of the standard solutions required in the present invention is as follows:

[0032] (1) Preparation of strong oxidation solution: Add 20 mL of concentrated sulfuric acid (sulfuric acid content 98%) into a 1000 mL volumetric flask, then slowly add a certain amount of deionized water. After complete cooling, add 10 mol of strong oxidant (nitric acid content 70%, hydrogen peroxide content 33%, potassium permanganate is of analytical purity) into the 1000 mL volumetric flask, and continue to add deionized water to volume to the scale line;

[0033] (2) Preparation of sodium hydroxide solution: Accurately weigh 40 g of solid sodium hydroxide of analytical purity into a 1000 mL beaker, add a certain amount of deionized water to completely dissolve it, then transfer it to a volumetric flask, and use deionized water to volume to the scale line and shake well;

[0034] (3) Preparation of sodium chloride standard solution: Accurately weigh 5.84 g of solid sodium chloride of analytical purity into a 1000 mL beaker, add a certain amount of deionized water to completely dissolve it, then transfer it to a volumetric flask, and use deionized water to volume to the scale line and shake well;

[0035] (4) Preparation and calibration of AgNO3 standard solution: Accurately weigh a certain amount of solid AgNO3 of analytical purity into a 500 mL beaker, quickly add deionized water to dissolve it, then quickly transfer it to a brown wide-mouth reagent bottle with a glass stopper; Take another 0.1 g of solid sodium chloride of analytical purity that has been weighed to constant weight at 500 - 600 °C for 6 h, dissolve it with deionized water, use the prepared AgNO3 solution as the titrant, conduct precipitation titration on a potentiometric titrator, record the volume of the consumed AgNO3 solution, and perform parallel determination 3 - 5 times. Calculate the titration degree of the AgNO3 standard titration solution to be 0.01027 mol / L.

[0036] (5) Titration blank value: Accurately pipette 1 mL of the prepared NaCl standard solution into a 100 mL titration cup, add deionized water to the 40 mL scale line, conduct titration with a potentiometric titrator, the titrant is the calibrated AgNO3 standard solution, record the volume of the consumed AgNO3 standard solution, perform parallel determination three times, and the average value of the consumed volume is 11.0210 mL;

[0037] Example 1

[0038] There is a batch of dimethyl hydrolysis product raw materials for synthesizing DMC, and it is necessary to measure the free chlorine content. The specific steps are as follows:

[0039] (1) Treatment of the hydrolyzate to be measured: Accurately weigh 35.0547 g of the hydrolyzate into a three-necked flask, add 35.0017 g (excess nitric acid) of the prepared nitric acid solution, and at the same time accurately pipette 1 mL of the NaCl standard solution into the three-necked flask, and use a magnetic heating stirrer to stir for full mixing;

[0040] (2) Heat distillation of the hydrolyzate: Place the well-mixed hydrolyzate on an oil bath, heat at a temperature of 145 °C for 30 min. After sufficient heating, condense the tail gas and discharge it into a tail gas absorption bottle, and add 120.0500 g of sodium hydroxide solution accurately weighed into the tail gas absorption bottle;

[0041] (3) After the tail gas absorption bottle has cooled sufficiently, weigh and tare the tail gas absorption liquid, which is 162.0147 g in total. Take m1 g of the tail gas absorption liquid, which are 30.1472 g, 30.0017 g, and 30.1003 g respectively. Add nitric acid solution to make the pH of the three solutions 3, and titrate with a calibrated AgNO3 standard solution potentiometric titrator. Record the volume V of the AgNO3 standard solution consumed, which are 11.0635 mL, 11.0623 mL, and 11.0637 mL respectively. Calculate the chloride ion content (the result is reserved to two decimal places), which are 2.75 ppm, 2.70 ppm, and 2.77 ppm respectively.

[0042] The calculation formula for the chloride ion content is as follows:

[0043]

[0044] Where, V: the volume of the AgNO3 standard solution consumed by the tail gas absorption liquid, mL;

[0045] V0: the volume of the AgNO3 standard solution consumed by titrating the NaCl blank solution, mL;

[0046] 35450: the relative atomic mass of chlorine atom × 1000;

[0047] m1: the mass of the sodium hydroxide solution weighed;

[0048] m: the total mass of the sodium hydroxide solution.

[0049] Taking the first result as an example, the calculation process of the chloride ion content result is as follows:

[0050]

[0051] Example 2

[0052] There is a batch of dimethyl hydrolyzate raw materials for synthesizing 107 silicone rubber, and it is necessary to measure the free chlorine content. The specific steps are as follows:

[0053] A method for detecting the chloride ion content in dimethyldimethoxysilane hydrolyzate, the specific steps are as follows:

[0054] (1)Treat the hydrolyzate to be measured: Accurately weigh 40.0780 g of the hydrolyzate into a three-necked flask, add 40.0144 g of the prepared hydrogen peroxide solution (hydrogen peroxide in excess), and at the same time accurately pipette 1 mL of the NaCl standard solution into the three-necked flask, and use a magnetic heating stirrer to stir for thorough mixing;

[0055] (2)Heat and distill the hydrolyzate: Place the well-mixed hydrolyzate on an oil bath, heat at 140 °C for 35 min. After sufficient heating, condense the tail gas and discharge it into the tail gas absorption bottle, and add 140.0033 g of sodium hydroxide solution accurately weighed into the tail gas absorption bottle;

[0056] (3)After the tail gas absorption bottle has cooled sufficiently, weigh and tare the tail gas absorption liquid, which is 176.3778 g in total. Weigh m1 g of the tail gas absorption liquid, which are 30.1014 g, 30.5547 g, and 30.0531 g respectively. Add nitric acid solution to make the pH of the three solutions 3, and titrate with a calibrated AgNO3 standard solution potentiometric titrator, record the volume V of the consumed AgNO3 standard solution, which are 11.0871 mL, 11.0900 mL, and 11.0861 mL respectively, and calculate the chloride ion content (the result is reserved to two decimal places), which are 4.68 ppm, 4.74 ppm, and 4.63 ppm respectively.

[0057] The calculation formula for the chloride ion content is as follows:

[0058]

[0059] Among them, V: the volume of the AgNO3 standard solution consumed by the tail gas absorption liquid, mL;

[0060] V0: the volume of the AgNO3 standard solution consumed by titrating the NaCl blank solution, mL;

[0061] 35450: the relative atomic mass of chlorine atoms × 1000;

[0062] m1: the mass of the sodium hydroxide solution weighed;

[0063] m: the total mass of the sodium hydroxide solution.

[0064] Taking the first result as an example, the calculation process of the chloride ion content result is as follows:

[0065]

[0066] Example 3

[0067] There is a batch of hot dimethyl hydrolyzate raw materials just produced in the workshop, and it is necessary to measure the free chlorine content. The specific steps are as follows:

[0068] A method for detecting the chloride ion content in dimethyldimethoxysilane hydrolyzate, the specific steps are as follows:

[0069] (1) Treat the hydrolyzate to be tested: Cool the hydrolyzate to be tested to room temperature, accurately weigh 35.2789 g of the hydrolyzate into a three-necked flask, add 38.0980 g of the prepared acidic potassium permanganate solution (excess potassium permanganate), and at the same time accurately pipette 1 mL of the NaCl standard solution into the three-necked flask, and use a magnetic heating stirrer to stir for sufficient mixing;

[0070] (2) Heat and distill the hydrolyzate: Place the well-mixed hydrolyzate on an oil bath, heat at a temperature of 150 °C for 35 minutes. After sufficient heating, condense the tail gas and discharge it into a tail gas absorption bottle, and add 128.0017 g of sodium hydroxide solution accurately weighed into the tail gas absorption bottle;

[0071] (3) After the tail gas absorption bottle is fully cooled, weigh and tare the tail gas absorption liquid to a total of 180.1475 g. Weigh m1 g of the tail gas absorption liquid, which are 35.0147 g, 35.8841 g, and 36.0778 g respectively. Add nitric acid solution to make the pH of the three solutions 3, and use a calibrated AgNO3 standard solution potentiometric titrator for titration. Record the volume V of the consumed AgNO3 standard solution, which are 11.2114 mL, 11.2217 mL, and 11.2377 mL respectively. Calculate the chloride ion content (the result is reserved to two decimal places), which are 10.18 ppm, 10.22 ppm, and 10.28 ppm respectively.

[0072] The calculation formula for the chloride ion content is:

[0073]

[0074] Among them, V: the volume of the AgNO3 standard solution consumed by the tail gas absorption liquid, mL;

[0075] V0: the volume of the AgNO3 standard solution consumed by titrating the NaCl blank solution, mL;

[0076] 35450: the relative atomic mass of chlorine atom × 1000;

[0077] m1: the mass of the sodium hydroxide solution weighed;

[0078] m: the total mass of the sodium hydroxide solution.

[0079] Taking the first result as an example, the calculation process of its chloride ion content result is:

[0080]

[0081] Spiked recovery experiment

[0082] In the present invention, the addition of the NaCl standard solution is to better amplify the titration effect when the free chlorine content in the dimethyl hydrolyzate is low. To verify that the addition of the NaCl standard solution does not affect the sample results, 40 g of the dimethyl hydrolyzate samples 1 - 5 in Example 3 were accurately weighed into 250 mL three-necked flasks respectively. 40 g of acidic potassium permanganate solution was added to each hydrolyzate. Then, 0.5 mL, 1 mL, 1.5 mL, 2 mL, and 2.5 mL of the NaCl standard solution were respectively pipetted into the 5 three-necked flasks, and the 5 samples were numbered 1, 2, 3, 4, and 5 respectively. After that, they were mixed evenly by a magnetic stirrer and distilled for 35 min using a heating distillation device. The heating temperature was set at 145 °C, and 100 g of NaOH solution was placed in each tail gas absorption flask. After distillation and cooling to room temperature, 35 g of the absorption solution was weighed, and the chloride ion content was titrated using a potentiometric titrator.

[0083] Table 1 Spiked recovery data

[0084]

[0085] From the above data, it can be seen that the recovery rate of the sample is stable in the range of 99% - 101%, which can meet the accuracy requirements. Therefore, the present invention can be used as a detection method for chloride ions in dimethyl hydrolyzate.

[0086] Example 4

[0087] To verify the precision and good reproducibility of the present invention, 12 portions of the dimethyl hydrolyzate samples in Example 3, each weighing 5 g, were placed in 12 150 mL titration cups respectively, and the 12 samples were numbered A1, A2, A3, A4, A5, A6, A7, A8, A9, A 10 , A 11 , A 12 , A 13 , A 14 , where A1 - A3 were processed and measured according to the steps in Example 3, A4 - A6 were processed and measured according to the steps in Example 3, but without adding a strong oxidant (i.e., without adding potassium permanganate solution for oxidation in step 1 and directly heating), and A7 - A9 were processed and measured according to the steps in Example 3, but without heating (i.e., only adding potassium permanganate solution for oxidation in step 1 and not performing step 2).

[0088] A 10 ~A 14The chloride ion content is titrated by a conventional method. Specifically, 35.2038 g of the sample to be tested of the hydrolyzate of dimethyldichlorosilane is added to 40 mL of an ethanol-aqueous solution (the volume ratio of ethanol to water is 1:1), 5 mL of a 5 wt% acetic acid solution, and 1 mL of a sodium chloride standard solution, stirred evenly, and then titrated. The results are compared with the sample data in Example 3.

[0089] Table 1 Comparative test data

[0090]

[0091] From the above data, it can be seen that: if a strong oxidant is not added, heating alone cannot separate chloride ions from the dimethyl hydrolyzate; if only an oxidant is added and no heating is carried out, the chloride ions in the dimethyl hydrolyzate cannot be completely separated; using the conventional titration method to measure the dimethyl hydrolyzate has very poor reproducibility and cannot meet the accuracy requirements of actual production. However, the sample test results of the present invention have higher accuracy, and at the same time, chloride ions can be better separated from the dimethyl hydrolyzate. Therefore, the present invention can be used as a detection method for chloride ions in the dimethyl hydrolyzate.

[0092] Example 5

[0093] Through comparative experiments, it can be found that heating has a greater impact on the test results of the present invention. To verify the heating temperature of the present invention, 7 samples of the dimethyl hydrolyzate in Example 3, each weighing 5 g, are placed in 7 150 mL titration cups respectively, numbered B1, B2, B3, B4, B5, B6, and B7, and processed and titrated according to the steps in Example 3. However, the heating temperatures in step 2 are 50 °C, 85 °C, 120 °C, 130 °C, 140 °C, 150 °C, and 170 °C respectively, and the results are compared with the sample data in Example 3.

[0094] Table 2 Verification experiment data

[0095]

[0096] From the above data, it can be seen that when the heating temperature ≥ 140 °C, the measurement results are basically stable. Considering the actual consumption problem, it is feasible and reasonable to set the heating temperature at 140 °C - 150 °C.

[0097] Example 6

[0098] To verify the optimal heating time of the present invention, 7 portions of the dimethyl hydrolyzate sample in Example 3, each portion being 5 g, were placed in 7 150 mL titration flasks respectively, numbered C1, C2, C3, C4, C5, C6, and C7, and were processed and titrated according to the steps in Example 3, but the heating times in Step 2 were 10 min, 20 min, 22 min, 25 min, 30 min, 35 min, and 40 min respectively, and the results were compared with the sample data in Example 3.

[0099] Table 3 Verification experiment data

[0100]

[0101] It can be seen from the above data that only sufficient heating can make all the chlorides be absorbed. When the heating time ≥ 30 min, the measurement results are basically stable. Considering the actual consumption problem, it is feasible and reasonable to set the heating time at 30 - 40 °C.

[0102] Example 7

[0103] To verify the optimal addition amount of the oxidant in the present invention, 5 portions of the dimethyl hydrolyzate sample in Example 3, each portion being 25 g, were placed in 5 150 mL titration flasks respectively, numbered C1, C2, C3, C4, and C5, and were processed and titrated according to the steps in Example 3, but the amounts of potassium permanganate solution (concentration 0.5 mol / L) in Step 1 were 10 g, 15 g, 25 g, 50 g, and 55 g respectively, and the results were compared with the sample data in Example 3.

[0104] Table 3 Verification experiment data

[0105]

[0106] It can be seen from the above data that only by adding a sufficient amount of oxidant can all the chloride ions be converted and absorbed. When the mass ratio of it to the addition amount of the hydrolyzate ≥ 1:1, the measurement results are basically stable. Considering the actual consumption problem, it is feasible and relatively reasonable to set the ratio of the hydrolyzate to the oxidant at 1:1 - 1:3.

Claims

1. A method for detecting the chloride ion content in hydrolyzate dimethyldimethoxysilane, characterized in that: It includes the following steps: (1) Titrating the blank value: Accurately pipette the NaCl standard solution into the titration cup, add deionized water to the calibration line, perform potentiometric titration with the AgNO3 standard solution, record the volume V0 of the consumed AgNO3 standard solution, and perform parallel determinations three times. (2) Treating the hydrolyzate to be measured: Accurately weigh a certain amount of the hydrolyzate into a volumetric flask, add the oxidant solution, pipette the NaCl standard solution into the volumetric flask, and stir to mix thoroughly; the mass ratio of the oxidant solution to the hydrolyzate is 1:1 to 1:3; the hydrolyzate is a weakly acidic hydrolyzate of dimethyldichlorosilane with a pH of 5 - 6. The preparation of the oxidant solution: Add 20 mL of concentrated sulfuric acid to a 1000 mL volumetric flask, then slowly add a certain amount of deionized water. After complete cooling, add 10 mol of the oxidant to the 1000 mL volumetric flask, and continue to add deionized water to volume to the calibration line. The oxidant is one of nitric acid, hydrogen peroxide, and potassium permanganate. (3) Heating and distilling the hydrolyzate: Perform oil bath heating on the hydrolyzate mixed evenly in step (2), with the heating temperature being 140 - 150 °C and the heating time being 25 - 35 min. Use sodium hydroxide solution to collect the tail gas, and weigh the sodium hydroxide solution as m. (4) After the collected tail gas cools down, accurately weigh a certain mass m1 of the tail gas absorption solution, add nitric acid solution to make it acidic, then perform potentiometric titration with the AgNO3 standard solution, record the volume V of the consumed AgNO3 standard solution, perform parallel determinations three times, and calculate the chloride ion content. The calculation formula for the chloride ion content is: Where, V: the volume of the AgNO3 standard solution consumed by the tail gas absorption solution, mL; V0: the volume of the AgNO3 standard solution consumed by titrating the NaCl standard solution, mL; 35450: the relative atomic mass of chlorine atom × 1000; m1: the mass of the sodium hydroxide tail gas absorption solution weighed; m: the total mass of the sodium hydroxide solution.

2. The method according to claim 1, characterized in that: Preparation and calibration of the AgNO3 standard solution: Accurately weigh a certain amount of analytical pure AgNO3 solid into a 500 mL container, quickly add deionized water to dissolve it, and then quickly transfer it to a brown wide-mouth reagent bottle with a glass stopper; separately take 0.1 - 0.2 g of analytical pure sodium chloride solid that has been weighed to constant weight at 500 - 600 °C for 3 - 6 h, dissolve it with deionized water, use the prepared AgNO3 solution as the titrant, perform precipitation titration on a potentiometric titrator, record the volume of the consumed AgNO3 solution, perform parallel determinations 3 - 5 times, and calculate the molar concentration of the AgNO3 standard titration solution. The calculation formula for the molar concentration is: ； Where, m(NaCl): the mass of the weighed sodium chloride, g; M(NaCl): the relative molecular mass of NaCl, taking 58.4 g / mol; V(AgNO3): the volume of the consumed AgNO3 standard solution, mL.

3. The method according to claim 1, wherein: The error of the 3 - 5 calculation results of the AgNO3 standard titration solution ≤ ±0.2%.

4. The method according to claim 1, wherein: Preparation of the sodium chloride standard solution: Weigh accurately a certain amount of analytical pure sodium chloride solid into a 1000 mL beaker, add a certain amount of deionized water to completely dissolve it, then transfer it to a volumetric flask, and make up the volume to the calibration line with deionized water, and shake well.

5. The method according to claim 4, wherein: The mass-volume ratio of the weak acid hydrolysis product of dimethyldichlorosilane to the sodium chloride standard solution is 30 - 50: 1 - 3 g / ml.

6. The method according to claim 1, wherein: In step (4), adjust the pH of the tail gas absorption liquid within the range of 3 - 5.

7. The method according to any one of claims 1 to 6, characterized in that: The measured chloride ion content is in the range of 2 - 20 ppm.

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