Method for determining chloride ions in process of synthesizing methylhydrazine by hydrazine hydrochloride methanol method

Abstract

The invention relates to a method for determining chloride ions in a process of synthesizing methylhydrazine by a hydrazine hydrochloride methanol method, and belongs to the technical field of medical analysis. The method comprises the following steps: (1) precisely weighing a methylhydrazine reaction solution in a beaker, monitoring the pH value of the solution, respectively adjusting the pH value to 3-5, adding water to a constant volume, titrating by using a potentiometric titrator, inserting a glass electrode and a silver electrode into the solution, putting a rotor, starting a stirrer, titrating by using a 0.1 mol / L silver nitrate titrating solution, and measuring the concentration of the silver nitrate titrating solution; recording data; (2) calculating the chlorine content; according to the method, a potentiometric titrator is adopted, the pH value of the solution is adjusted to 3-5, the chlorine ion content can be rapidly and accurately detected in the presence of methylhydrazine and hydrazine hydrate, the method is rapid and simple to operate, high in sensitivity, good in repeatability and accurate in result, and the chlorine ion content of reaction liquid in multiple steps in the methylhydrazine synthesis process can be quantitatively detected.

Description

Technical Field

[0001] This invention relates to a method for determining chloride ions, specifically a potentiometric titration method for chloride ions during the synthesis of methylhydrazine using the hydrazine hydrochloride-methanol method. Background Technology

[0002] Methylhydrazine, an important chemical raw material, has wide applications in aerospace, pharmaceutical, pesticide, and explosives industries. There are numerous methods for preparing methylhydrazine, including the chloramine method, the hydrazine hydrate-methanol method, the hydrazine hydrate-benzaldehyde condensation method, the dimethyl phosphite-dimethyl carbonate-hydrazine hydrate method, and the hydrazine hydrochloride-methanol method. Among these, the hydrazine hydrochloride-methanol method shows promise as a relatively energy-efficient and environmentally friendly approach, although it requires the measurement of chloride ion concentration at several stages.

[0003] Currently, the main methods for determining chloride ions in solution include potentiometric titration, ion chromatography, volumetric titration, and spectrophotometry. Among these, ion chromatography, based on ion exchange and separation techniques, separates different ions using a chromatographic column, and then performs quantitative analysis using a detector. This method offers high selectivity and accuracy, but requires complex equipment and operational techniques, and sample pretreatment is cumbersome and time-consuming. It is suitable for applications requiring high chloride ion concentrations.

[0004] Volumetric methods, such as the ammonium thiocyanate volumetric method, involve decomposing the sample with nitric acid, adding a standard silver nitrate solution to convert chloride ions into silver chloride precipitate, and then titrating the excess silver nitrate with a standard ammonium thiocyanate titrant. This method is relatively complex, time-consuming, and labor-intensive, requiring attention to many details to obtain satisfactory results.

[0005] The instruments used in spectrophotometry are not complicated, but the colorants used are usually toxic, and the method has weak resistance to interference.

[0006] Potentiometric titration has advantages over other methods, such as simple operation, speed, and low instrument cost. However, in the process of synthesizing methylhydrazine by hydrazine hydrochloride-methanol method, hydrazine hydrate and methylhydrazine are present in the system at the same time. The presence of both affects the pH of the system, which in turn affects the accuracy of potentiometric titration of chloride ions. Summary of the Invention

[0007] The purpose of this invention is to provide a method for determining chloride ions in the synthesis of methylhydrazine using the hydrazine hydrochloride-methanol method. This method is rapid, simple, highly sensitive, reproducible, and accurate, and can quantitatively detect the chloride ion content in the reaction solutions of multiple steps in the synthesis of methylhydrazine.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for determining chloride ions during the synthesis of methylhydrazine using the hydrazine hydrochloride-methanol method includes the following steps:

[0010] (1) Accurately weigh the methylhydrazine reaction solution into a beaker, monitor the pH of the solution, adjust the pH to 3-5, add water to make up the volume, titrate with a potentiometric titrator, insert the glass electrode and silver electrode into the solution, put in the rotor, turn on the stirrer, start titration with 0.1 mol / L silver nitrate titrant, and record the data;

[0011] (2) Calculate the chlorine content;

[0012]

[0013] In the formula:

[0014] V—The volume of silver nitrate solution consumed during the titration of chloride ions, in mL;

[0015] Mass of m-methylhydrazine reaction solution, g;

[0016] C—Concentration of silver nitrate solution, mol / L;

[0017] 35.45 — Molar mass of chloride ions, g / mol.

[0018] In the preferred step (1), the pH value is adjusted to 4.

[0019] The titration parameters are as follows:

[0020]

[0021]

[0022] The beneficial effects of adopting the above technical solution are:

[0023] This invention provides a quantitative analysis method for chloride ions in methylhydrazine reaction solution. Using a potentiometric titrator and adjusting the solution pH to 3-5, the method can quickly and accurately detect chloride ion content in the presence of methylhydrazine and hydrazine hydrate. It has high sensitivity and can accurately quantify even low chloride ion content. This method avoids the deviation and large error caused by the small amount of titrant used and the need to estimate the volume in the original volumetric method.

[0024] This invention employs potentiometric titration. In the presence of methylhydrazine and hydrazine hydrate, the solution is alkaline and the pH needs to be adjusted to 3-5 to ensure data accuracy. It is suitable for the quantitative analysis of chloride ions in the presence of methylhydrazine reaction solution, hydrazine hydrate, and methylhydrazine. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] (1) Sample testing:

[0028] Accurately weigh 0.25 g of methylhydrazine reaction solution into a 150 mL beaker, adjust the pH to 4, add water to about 60 mL, and titrate with a potentiometric titrator. Insert the glass electrode and silver electrode into the solution, place the rotor, start the stirrer, and begin titrating with 0.1 mol / L silver nitrate titrant. Record the data.

[0029] Titration parameters:

[0030] Instrument manufacturer: Beijing Pioneer Weifeng Technology Development Co., Ltd.; Model: ZDJ-2D+S / N:2270538;

[0031] model 0(0:D, 1:C) Maximum increment 0.400ml Minimum Increment 0.020ml Maximum waiting time 30.0 seconds Minimum waiting time 10.0 seconds Signal drift value 30.0 mv / min polarization voltage 0mv Pre-filled volume 5ml Waiting time 10 seconds Potential change threshold 8.0mv Sampling period 2 seconds Titration speed 15.0 ml / min Equivalent points 1 threshold 300 safe volume 40.000ml Results and Number of Formulas 1(1，2，3)

[0032] (2) Calculate the chlorine content

[0033] Calculation formula:

[0034]

[0035] In the formula:

[0036] V—volume of silver nitrate solution consumed during chloride titration, mL; m—mass of methylhydrazine reaction solution, g;

[0037] C—Concentration of silver nitrate solution, mol / L;

[0038] 35.45 — Molar mass of chloride ion, g / mol

[0039] (3) Measurement results

[0040] The above-mentioned test method was used to test three batches of samples (using a self-made methylhydrazine reaction solution, batch numbers respectively).

[0041] The stock solutions 202408005, 202409012, and 202409017 were tested. The results showed that the chlorine content in the stock solution 202408005 was 30.2%, the chlorine content in the stock solution 202409012 was 32.6%, and the chlorine content in the stock solution 202409017 was 29.1% (see Table 1).

[0042] Table 1. Results of chloride ion determination in the original methylhydrazine reaction solution

[0043] batch number m(g) V(mL) C(mol / L) content% 202408005 original solution 0.2549 21.123 0.1028 30.2 202409012 original solution 0.2551 22.82 0.1028 32.6 202409017 original solution 0.2589 20.673 0.1028 29.1

[0044] (4) Methodological validation

[0045] Repeatability experiment:

[0046] Six parallel solutions of the test sample were prepared and measured separately. The RSD of the chlorine content was 1.4%, which is less than 2% (see Table 2), indicating good repeatability.

[0047] Table 2. Results of Repeatability Experiments

[0048]

[0049]

[0050] (5) Linearity and Range Experiment

[0051] Accurately weigh 14.9 g of potassium chloride into a 100 mL volumetric flask to obtain a stock solution. Measure 0.1, 0.5, 0.8, 1.0, 1.2, and 1.5 mL of each solution into a 150 mL beaker, add water to make a final volume of 60 mL, titrate with a potentiometric titrator, and record the results. Plot a standard curve with the concentration (mg / mL) against the volume of titrant consumed. The linear regression equation, correlation coefficient, and other results are shown in Table 3.

[0052] Table 3. Experimental Results of Linearity and Range

[0053]

[0054] Table 4. Summary of Linear Data

[0055] name Linear equations Correlation coefficient (r) Concentration range (mg / mL) Potassium chloride y = 0.13792x + 0.05915 0.99999 14.9242-223.8630

[0056] (6) Limit of Quantitation Experiment

[0057] Accurately weigh 74.5 mg of potassium chloride into a 10 mL volumetric flask, transfer it to a 150 mL beaker, add water to 60 mL, titrate with a potentiometric titrator, and record the results. The chloride ion concentration of 3.545 mg / mL is taken as the limit of quantitation. The results are shown in Table 5.

[0058] Table 5. Results of the Limit of Quantitation Experiment

[0059]

[0060]

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for determining chloride ions during the synthesis of methylhydrazine via the hydrazine hydrochloride-methanol method, characterized in that: Includes the following steps: (1) Accurately weigh the methylhydrazine reaction solution into a beaker, monitor the pH of the solution, adjust the pH to 3-5, add water to make up the volume, titrate with a potentiometric titrator, insert the glass electrode and silver electrode into the solution, put in the rotor, start the stirrer, start titrating with 0.1 mol / L silver nitrate titrant, and record the data; (2) Calculate the chlorine content; ； In the formula: V—The volume of silver nitrate solution consumed during the titration of chloride ions, in mL; Mass of m-methylhydrazine reaction solution, g; C—Concentration of silver nitrate solution, mol / L; 35.45 — Molar mass of chloride ions, g / mol.

2. The chloride ion determination method according to claim 1, characterized in that: In step (1), adjust the pH value to 4.

3. The method for determining chloride ions according to claim 1, characterized in that: The titration parameters are as follows: 。

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