Permeation tube standard substance for preparing NMP standard gas and preparation method

Abstract

The invention provides a permeation tube standard substance for preparing NMP standard gas and a preparation method thereof. A permeation tube comprises a liquid storage tank and a diffusion barrier film, and the diffusion barrier film is mounted at an opening of the liquid storage tank; the liquid storage tank is made of stainless steel, and the diffusion barrier film is made of polytetrafluoroethylene porous materials. The low-concentration NMP standard gas can be prepared, the traceability requirement of N-methyl-2-pyrrolidone gas concentration and the verification and calibration requirements of N-methyl-2-pyrrolidone gas detection equipment are met, and the current blank situation of NMP gas standard substances is filled up.

Description

Technical Field

[0001] The invention belongs to the technical field of standard substances, and in particular relates to a permeation tube standard substance for preparing NMP standard gas and a preparation method thereof. Background Art

[0002] Gas standard materials, as the metrological standards for measuring gas composition, play an indispensable and important role in gas detection. How to prepare high-precision, accurate and diverse gas standard materials has always been a key challenge and a hot area in gas metrology research. After years of development, in the production of gas standard materials, the commonly used gas distribution methods are divided into two types: static method and dynamic method. Among them, the static method has certain application limitations due to its own principle defects. Compared with the static gas distribution method, the dynamic gas distribution method can produce a larger amount of gas standard materials in a wider concentration range, and has the advantages of eliminating container wall adsorption. It is currently gaining momentum in the preparation of gas standard materials.

[0003] N-methyl-2-pyrrolidone (hereinafter referred to as: NMP), also known as 1-methylpyrrolidone, has the structural formula It is a polar solvent with strong selectivity and good stability. It has the characteristics of high boiling point, strong solubility, good stability, biodegradability, and recyclability. It is widely used in lithium batteries, polymer materials, electronic materials, petrochemicals and other industries. With the proposal of the "dual carbon" goal, the lithium battery industry has developed rapidly, and the scale of NMP consumption has grown rapidly. However, there are safety hazards in the use of NMP. A certain concentration of NMP atmosphere will not only endanger human health, but also pose a risk of combustion and explosion. Therefore, real-time monitoring and early warning of NMP concentration in the air is one of the important safety guarantees. However, due to the lack of low-concentration NMP gaseous standard substances, it is impossible to accurately trace the value of the NMP detection alarm device, and the credibility of the NMP detection results is low, affecting the safe production of enterprises.

[0004] In view of the current blank situation of NMP gas standard materials and the actual urgent need, in order to ensure the traceability and accuracy of NMP and in combination with the use requirements of national standards, a method for providing NMP standard gas is urgently needed. Summary of the invention

[0005] In view of this, the present invention aims to propose a permeation tube standard substance and a preparation method for preparing NMP standard gas, which can prepare low-concentration NMP standard gas, meet the traceability requirements of N-methyl-2-pyrrolidone gas concentration and the verification and calibration requirements of N-methyl-2-pyrrolidone gas detection equipment, and make up for the blank status of NMP gas standard substance.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A permeation tube standard material for preparing NMP standard gas comprises a liquid storage tank and an emission barrier membrane, wherein the emission barrier membrane is installed at the opening of the liquid storage tank; the liquid storage tank is made of stainless steel, and the emission barrier membrane is made of a porous polytetrafluoroethylene material.

[0008] Preferably, the volume of the liquid reservoir is 1.5-2.5 mL, the diameter of the liquid reservoir is 7-9 mm, and the diffusion area of ​​the diffusion barrier membrane is 38-64 mm 2 The pore size of the emission barrier membrane is 0.05-3.0μm and the thickness is 0.01-0.1mm.

[0009] Preferably, the liquid reservoir contains 1.00-2.00 g of N-methyl-2-pyrrolidone.

[0010] Preferably, the purity of N-methyl-2-pyrrolidone is greater than 99.50%.

[0011] Preferably, the permeability of the permeation tube is 1.0-20.0 μg / min (50.0°C ± 0.1°C), and the relative expansion uncertainty is U rel =6% (k=2).

[0012] The present invention also provides a method for preparing the permeation tube as described above, comprising the following steps: fully cleaning a pipette tip, a liquid storage tank, and an emission barrier film, rinsing with ultrapure water for 3-5 times, placing in an oven and heating to 45-70°C, and maintaining for 1-3 hours, placing the dried items in a dryer and cooling for standby use; weighing 1.00-2.00 g of N-methyl-2-pyrrolidone, adding liquid N-methyl-2-pyrrolidone into the liquid storage tank, installing a porous emission barrier film at the tank mouth, and sealing to form a permeation tube, ensuring that the permeation tube is naturally placed without leakage.

[0013] The present invention also provides a method for preparing NMP standard gas using the above-mentioned permeation tube standard material, wherein the permeation cell temperature is 40-60° C. and the constant total nitrogen flow rate is 50-4000 mL / min.

[0014] Preferably, the carrier gas flow rate of the permeation cell is 50 mL / min, and the dilution gas flow rate is 0-3950 mL / min.

[0015] The present invention also provides the use of the permeation tube standard material as described above, the permeation tube standard material prepared by the preparation method as described above, or the method for preparing NMP standard gas as described above in preparing low-concentration NMP standard gas.

[0016] Preferably, the low-concentration NMP standard gas refers to an NMP standard gas having a concentration of 1-300 ppm.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] In view of the blank status of NMP gas standard materials and the actual urgent need, and in combination with the use requirements of national standards, the present invention provides an NMP permeation tube standard material and a preparation method thereof. When the carrier gas flow rate of the permeation cell is 50 mL / min and the dilution gas flow rate is 300 mL / min, the permeability of the NMP permeation tube is 3.60 μg / min (50.0°C ± 0.1°C), and the relative expanded uncertainty is U rel =6% (k=2), NMP permeation tube standard material can be used to prepare low-concentration NMP standard gas through permeation method, which can realize the practical preparation of low-concentration NMP gas, meet the traceability requirements of NMP gas concentration and the verification and calibration requirements of NMP gas detection equipment. Among them, according to the national metrology technical specification JJF 1343-2012 "General Principles and Statistical Principles of Standard Material Value", the corresponding research was carried out, and the permeability of DEC permeation tube standard material was determined by weight method, and the uncertainty was evaluated. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the permeation tube;

[0020] Figure 2 This is a physical picture of the permeation tube standard material used to prepare NMP standard gas;

[0021] Figure 3 This is the principle diagram of the permeation gas distribution method;

[0022] 1. Emission barrier film; 2. First sealing ring; 3. Container cover; 4. Second sealing ring; 5. Liquid NMP; 6. Liquid storage tank. DETAILED DESCRIPTION

[0023] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified. The purchase of some reagents and instruments is as follows:

[0024] N-methyl-2-pyrrolidone (CAS: 872-50-4), raw material purity 99.70%, purchased from Sigma-Aldrich;

[0025] Electronic balance: Sartorius, MSA225S-1CE-DU;

[0026] Electronic stopwatch: CASIO, HS-3;

[0027] The present invention will be described in detail below with reference to the embodiments.

[0028] The permeation gas distribution method is a commonly used dynamic gas distribution method. It is a gas distribution method based on weighing. Its principle is as follows: Figure 3 As shown, the permeation tube containing the substance to be prepared is placed under a certain temperature and pressure, and the components contained in the permeation tube diffuse to the outside of the permeation tube at a certain diffusion rate, and trace gases of different concentrations are obtained by the continuous and stable flow of dilution gas through the permeation tube.

[0029] The permeation tube gas distribution method is a standard gas preparation method based on Fick's diffusion law. The liquid compound is placed in a stainless steel bottle, and a porous diffusion barrier membrane (permeation membrane) is installed at the bottle mouth to make a permeation tube. The permeability calculation formula of the diffusion component gas is:

[0030]

[0031] Where: R m ——Permeability of the diffusion component gas, μg / min;

[0032] D——diffusion component gas diffusion coefficient, cm 3 / s;

[0033] M——molar mass of diffusion component gas, g / mol;

[0034] S——Diffusion area of ​​radiant barrier film, cm 2 ;

[0035] L——thickness of emission barrier film, cm;

[0036] R——gas constant, J / (mol·K);

[0037] T——permeation pool temperature, K;

[0038] P——total pressure at the infiltration pool, Pa;

[0039] P v ——Partial pressure of the diffusing component at temperature T, Pa.

[0040] For a specific permeation tube, the diffusion area S and thickness L of the diffusion barrier are fixed values, and the permeability R of the component m Only with the diffusion coefficient D, the diffusion component partial pressure P v It is related to the total pressure P at the diffusion cell outlet. Under the condition of constant temperature T, the diffusion coefficient D of the component and the partial pressure P of the diffusion component v When the dilution gas flow rate is constant, the total pressure P at the diffusion cell outlet is also constant. Therefore, when the temperature and dilution gas flow rate are constant, the permeability R of the diffusion component gas is m Is a fixed value.

[0041] The preparation process of the permeation tube for preparing NMP standard gas includes the following steps: Step 1, selecting N-methyl-2-pyrrolidone (NMP) with a purity greater than 99.50%; Step 2, selecting a well-sealed stainless steel permeation tube reservoir (volume of 2.00 mL, diameter of 8 mm), a polytetrafluoroethylene porous diffusion barrier membrane (pore size of 0.22 μm, diffusion area of ​​50 mm 2 , thickness is 0.02mm); Step 3, preparation of pipette, permeation tube reservoir, and emission barrier membrane: After the pipette tip, stainless steel reservoir, and emission barrier membrane are fully cleaned, rinse with ultrapure water 3 times, put into an oven and heat to 60°C, and keep for more than 1h, put the dried items into a dryer to cool for standby use; Step 4, weigh 1.00-1.50g of N-methyl-2-pyrrolidone (NMP), add liquid N-methyl-2-pyrrolidone (NMP) into the stainless steel permeation tube reservoir, install a porous emission barrier membrane at the pool mouth, and seal it to make N-methyl-2-pyrrolidone (NMP) permeation tube standard material; Step 5, store the assembled permeation tube at 4°C for 7 days and then check for leaks to confirm that the sealing ring firmly fixes the emission barrier membrane on the reservoir and there is no obvious leakage in the permeation tube.

[0042] The permeation tube standard material used to prepare the NMP standard gas is placed in the permeation method standard gas generator. One side of the permeation membrane is NMP saturated vapor, and the other side is an environment where the NMP concentration can be ignored. When the temperature and pressure are constant, the concentration of NMP saturated vapor is a constant value. The NMP vapor stably diffuses through the permeation membrane to the outside of the permeation tube, and is then carried away by a certain flow of carrier gas, thereby obtaining a stable concentration of NMP standard gas.

[0043] In this embodiment, the conditions of the permeation cell temperature of 50°C ± 0.1°C and the constant total nitrogen flow rate of 350 mL / min (the permeation cell carrier gas flow rate of 50 mL / min and the dilution gas flow rate of 300 mL / min) are adopted.

[0044] Study on the Stability of Material Selection for Permeation Tubes

[0045] During the entire use cycle of the reference material, stainless steel is in long-term contact with NMP. Upon inquiry, no reports of chemical reactions between NMP and stainless steel were found.

[0046] To verify the stability of stainless steel in NMP environment, the stainless steel storage tank was immersed in NMP and placed in an environment of 50.0℃. The mass of the stainless steel storage tank was weighed every week. After 6 months of continuous immersion, the mass measurement results of the stainless steel storage tank are shown in Table 1. The results show that the quality of the stainless steel storage tank is stable under NMP immersion conditions and there is no obvious change.

[0047] Table 1 Stainless steel storage tank quality measurement results

[0048]

[0049]

[0050] To verify the stability of PTFE in NMP environment, the PTFE membrane was immersed in NMP and placed in an environment of 50.0℃. The mass of the PTFE membrane was weighed every week. After continuous immersion for 6 months, the mass measurement results of the PTFE membrane are shown in Table 2. The results show that the quality of the PTFE membrane is stable under NMP immersion conditions, and there is no obvious dissolution or breakage.

[0051] Table 2 PTFE membrane quality measurement results

[0052]

[0053] Example 1: Preparation of permeation tube standard material for preparing NMP standard gas

[0054] Step 1. Preparation of pipette, permeation tube reservoir, and emission barrier membrane: After thoroughly cleaning the pipette tip, stainless steel reservoir, and emission barrier membrane, rinse them with ultrapure water for 3 times, heat them in an oven to 60°C and keep it for more than 1 hour, and place the dried items in a dryer to cool down for later use.

[0055] Step 2: Use a pipette to add 1.00 g of liquid NMP (purity>99.50%) into a 2.0 mL stainless steel permeation tube reservoir;

[0056] Step 3: Install a polytetrafluoroethylene emission barrier film with a pore size of 0.22 μm and a thickness of 0.02 mm at the pool port;

[0057] Step 4, using a polytetrafluoroethylene sealing ring to compress the emission barrier film and seal it to make an N-methyl-2-pyrrolidone (NMP) permeation tube standard material;

[0058] Step 5: Store the assembled permeation tube at 4°C for 7 days and then check for leaks. Confirm that the fixing ring firmly fixes the membrane on the stainless steel container and ensure that the permeation tube is placed naturally without leakage.

[0059] Permeability of NMP permeation tube standard material

[0060] Install the NMP permeation tube into the permeation cell of the permeation method standard generator. Under the conditions of constant temperature and carrier gas flow in the permeation cell, use an electronic balance to measure the mass change of the NMP permeation tube at certain time intervals. The mass of NMP permeated per unit time is calculated as the average permeability of the NMP permeation tube.

[0061] R m =Δm / Δt Formula (2)

[0062] Where: R m ——Permeability of the diffusion component gas, μg / min;

[0063] Δm——mass of NMP permeated, μg;

[0064] Δt——weighing interval time, min.

[0065] Evaluation of NMP dosage

[0066] 0.50-1.75g ​​of liquid NMP was added to the permeation tube reservoir with a pipette to make permeation tubes with different NMP contents, and the effect of different NMP dosages on the permeability of the NMP permeation tubes was evaluated. The experimental results show that when the NMP dosage is within the range of 0.50-1.75g, as shown in Table 3, there is no significant difference in the permeability of different NMP permeation tubes. Since the service life of the NMP permeation tube is shortened when the NMP dosage is small, and when the NMP dosage is too much, it is easy to cause NMP to splash onto the permeation membrane during the taking process, affecting the permeability, therefore, 1.00-1.50g is selected as the NMP dosage range.

[0067] Table 3 Evaluation of NMP dosage

[0068]

[0069]

[0070] Evaluation of polytetrafluoroethylene membranes with different pore sizes

[0071] 1.00g of liquid NMP was added to the permeation tube reservoir with a pipette, and polytetrafluoroethylene permeation membranes with different pore sizes were selected to make different permeation tubes. The effect of different permeation membrane pore sizes on the permeability of the NMP permeation tube was evaluated. The experimental results are shown in Table 4. The results show that when other conditions such as the reservoir caliber, permeation membrane thickness, and permeation cell temperature remain unchanged, the larger the permeation membrane pore size, the greater the permeability. Finally, a permeation membrane with a pore size of 0.22μm and a smaller permeability was selected for subsequent research.

[0072] Table 4 Evaluation of polytetrafluoroethylene permeable membranes with different pore sizes

[0073] serial number 1 2 3 Membrane pore size / μm 0.22 0.46 1.0 Permeability measured value / (μg / min) 3.62 7.37 14.90

[0074] Stability Check

[0075] The stability test of the standard substance is used to determine whether the characteristic value of the standard substance can be stable within the specified range under the specified storage conditions and within a certain period of time. Therefore, the stability test was carried out by continuously measuring the permeability of the NMP permeation tube. Since the expected shelf life of the NMP permeation tube standard substance is 6 months, the permeability of the NMP permeation tube was measured every 7 days. The permeability of the NMP permeation tube was continuously measured within 6 months (n=27), as shown in Table 5. β1 Compared with the critical value of the two-tailed Student's t distribution with n-2 degrees of freedom at a 95% confidence level, t β1 Less than t 0.05,25 , indicating that the permeability of the NMP permeation tube standard material within 6 months had no significant difference at the confidence probability level of 95%, and the NMP permeation tube standard material was stable for 6 months.

[0076] Table 5 Long-term stability monitoring results of NMP permeation tube standard substances

[0077]

[0078]

[0079] Fixed value

[0080] The permeability of the NMP permeation tube (n=6) was measured for 6 consecutive months. According to the measurement results (see Table 4), the average permeability of the prepared NMP permeation tube can be calculated as R m =3.60μg / min.

[0081] Table 6 NMP permeation tube standard material permeability measurement results

[0082]

[0083]

[0084] Measurement verification

[0085] 1) Spectrophotometric method for measuring NMP concentration in water

[0086] NMP has strong absorption in near-ultraviolet light, so a test wavelength of 210 nm was selected for the experiment, and the calibration curve method was used to confirm the spectrophotometric method. Prepare 32 standard solutions of different concentrations (0.0 mg / L, 1.0 mg / L, 2.0 mg / L, 3.0 mg / L, 4.0 mg / L, 5.0 mg / L, 6.0 mg / L, 7.0 mg / L, 8.0 mg / L, 9.0 mg / L, 10.0 mg / L, 12.0 mg / L, 14.0 mg / L, 16.0 mg / L, 18.0 mg / L, 20.0 mg / L, 25.0 mg / L, 30.0 mg / L, 35.0 mg / L , 40.0mg / L, 45.0mg / L, 50.0mg / L, 55.0mg / L, 60.0mg / L, 65.0mg / L, 70.0mg / L, 75.0mg / L, 80.0mg / L, 85.0mg / L, 90.0mg / L, 95.0mg / L, 100.0mg / L), each concentration was measured 6 times from low to high at a wavelength of 210nm. The measurement results are shown in Table 7, so as to draw the absorbance standard curve and obtain the regression equation and r 2 The NMP concentration of the solution can be determined by testing the absorbance of the NMP solution.

[0087] Table 7 Calibration curve measurement results at 210nm

[0088]

[0089]

[0090] 2) Verification method

[0091] Use spectrophotometry to verify the permeability of the NMP permeation tube. Place the permeation tube in the permeation pool of the permeation gas distribution system, and pass the NMP standard gas prepared by the dynamic method into the gas absorption device. Put about 100mL of ultrapure water in each absorption tube of the gas absorption device. After ventilation for a certain period of time, transfer all the liquids in the three absorption tubes to a 500mL volumetric flask. Wash the absorption tube with ultrapure water at least three times, and transfer all the solutions to a 500mL volumetric flask. After constant volume, take an appropriate amount of solution and measure the NMP concentration in the water by spectrophotometry.

[0092] 3) Confirmation of the reliability of the gas absorption method

[0093] The permeation tube was placed in the permeation pool of the permeation gas distribution system, and the NMP standard gas prepared by the dynamic method was passed into the gas absorption device. After 24 hours of absorption, the NMP concentrations in the three absorption tubes were measured by spectrophotometry. The NMP concentrations in the three absorption tubes were: first level: 54.2 mg / L; second level: undetectable (based on the detection limit MDL = 0.3 mg / L); third level: undetectable. The results showed that more than 99.9% of NMP could be absorbed through the three-level absorption tube, and the gas absorption method was reliable.

[0094] 4) Verify the value

[0095] The concentration of the NMP solution in the absorption tube can be obtained by spectrophotometry, and then the permeability of the NMP permeation tube standard material can be calculated. At the same time, the permeability of the NMP permeation tube standard material can be calculated according to formula (1). The measurement was performed 7 times, and the measurement results are shown in Table 8. After t verification, it can be determined that the permeability of the developed NMP permeation tube standard material is accurate and reliable, and the value verification has passed.

[0096] Table 8 t test results

[0097]

[0098] From the above analysis results, it can be seen that the permeability of the prepared NMP permeation tube standard material is stable, reliable and highly repeatable.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A permeation tube standard substance for preparing NMP standard gas, characterized in that: It includes a liquid storage tank and an emission barrier membrane, which is installed at the mouth of the liquid storage tank; the liquid storage tank is made of stainless steel, and the emission barrier membrane is made of porous polytetrafluoroethylene.

2. The permeation tube standard material for preparing NMP standard gas according to claim 1, characterized in that: The volume of the reservoir is 1.50-2.50mL, the diameter of the reservoir is 7-9mm, and the diffusion area of ​​the diffusion barrier membrane is 38-64mm 2 The pore size of the emission barrier membrane is 0.05-3.0μm and the thickness is 0.01-0.1mm.

3. The permeation tube standard material for preparing NMP standard gas according to claim 1, characterized in that: The reservoir contained 1.00-2.00 g of N-methyl-2-pyrrolidone.

4. The permeation tube standard material for preparing NMP standard gas according to claim 1, characterized in that: The purity of N-methyl-2-pyrrolidone is greater than 99.50%.

5. The permeation tube standard material for preparing NMP standard gas according to claim 1, characterized in that: The permeability of the permeation tube is 1.0-20.0 μg / min (50.0°C ± 0.1°C), and the relative expanded uncertainty is Urel = 6% (k = 2).

6. A method for preparing a permeation tube standard substance as claimed in any one of claims 1 to 5, characterized in that: The method comprises the following steps: fully cleaning a pipette tip, a liquid storage tank and an emission barrier film, rinsing with ultrapure water for 3-5 times, placing in an oven and heating to 45-70°C and maintaining for 1-3 hours, placing the dried items in a dryer and cooling for standby use; weighing 1.00-2.00 g of N-methyl-2-pyrrolidone, adding liquid N-methyl-2-pyrrolidone into the liquid storage tank, installing a porous emission barrier film at the tank mouth, sealing to form a permeation tube, and ensuring that the permeation tube is naturally placed without leakage.

7. A method for preparing NMP standard gas using the permeation tube standard substance according to any one of claims 1 to 5, characterized in that: The permeation cell temperature is 40-60°C; the constant total nitrogen flow rate is 50-4000mL / min.

8. The method for preparing NMP standard gas as claimed in claim 7, characterized in that: The carrier gas flow rate of the permeation cell is 50 mL / min, and the dilution gas flow rate is 0-3950 mL / min.

9. The permeation tube standard material as described in any one of claims 1 to 5, the permeation tube standard material prepared by the preparation method as described in claim 6, or the method for preparing NMP standard gas as described in claim 7 or 8 are used in preparing low-concentration NMP standard gas.

10. According to the application of claim 9, the low-concentration NMP standard gas refers to an NMP standard gas with a concentration of 1-300 ppm.

Images