Method for improving purity of N-methyl pyrrolidone

Abstract

The invention discloses a method for improving the purity of N-methyl pyrrolidone, and belongs to the technical field of purification of N-methyl pyrrolidone, and the method for improving the purity of N-methyl pyrrolidone is characterized by comprising the following steps: adding liquid caustic soda into water, fully mixing, adding sodium hydroxide into the water, and stirring to obtain a mixed solution; and adding an N-methyl pyrrolidone stock solution, stirring, sampling the mixed solution, carrying out gas chromatography detection, and rectifying the mixed solution with the gamma-butyrolactone content of zero in the mixed solution to obtain an N-methyl pyrrolidone finished product, thereby achieving the effect of conveniently and quickly reducing the gamma-butyrolactone content in the N-methyl pyrrolidone.

Description

Technical Field

[0001] The invention relates to the technical field of N-methylpyrrolidone purification, in particular to a method for improving the purity of N-methylpyrrolidone. Background Art

[0002] N-methylpyrrolidone, referred to as NMP, is a commonly used organic solvent with the advantages of high solubility, high boiling point, low toxicity, high solvent performance, excellent chemical stability and thermal stability. It is widely used in electronics, chemical industry, textile, pharmaceutical and other fields. Moreover, N-methylpyrrolidone is one of the most commonly used auxiliary materials for lithium batteries. N-methylpyrrolidone is a solvent for PVDF binder. When making electrode sheets, N-methylpyrrolidone is used as a solvent to fuse various electrode materials such as binder, positive electrode active material, conductive agent, etc. together, so that the binder is in full contact with other materials and evenly distributed. As a solvent, the purity of N-methylpyrrolidone directly affects the quality of lithium-ion battery slurry coating. Therefore, improving the purity of N-methylpyrrolidone can effectively ensure the quality of N-methylpyrrolidone.

[0003] Existing methods for removing the impurity γ-butyrolactone in N-methylpyrrolidone include distillation, extraction, adsorption, chemical reaction (converting γ-butyrolactone into other easily separable substances through chemical reaction and then separating them), membrane separation technology, etc. However, since γ-butyrolactone and N-methylpyrrolidone have similar boiling points and structures, it is difficult to completely separate them when using distillation purification technology, thereby limiting the application of N-methylpyrrolidone products as electronic grade products in related fields. Other impurity removal methods are not only relatively complicated to operate, but also may introduce new impurities (such as by-products that may be produced during the reaction process of the chemical reaction method). Therefore, it is urgent to find a simple and effective impurity removal method. Summary of the invention

[0004] In order to solve the problems in the prior art, the present invention provides a method for improving the purity of N-methylpyrrolidone, which can conveniently and quickly reduce the content of gamma-butyrolactone in N-methylpyrrolidone.

[0005] The present invention provides a method for improving the purity of N-methylpyrrolidone using the following technical solution: A method for improving the purity of N-methylpyrrolidone comprises the following steps: adding liquid alkali into water, mixing thoroughly, adding N-methylpyrrolidone stock solution, stirring, sampling the mixed solution, performing gas chromatography detection, and distilling the mixed solution containing zero gamma-butyrolactone to obtain the N-methylpyrrolidone finished product.

[0006] In a preferred embodiment, in the mixed solution, the liquid alkali accounts for 0.05-0.1wt%, the water accounts for 5-15wt%, and the balance is N-methylpyrrolidone stock solution.

[0007] In a preferred embodiment, the liquid alkali accounts for 0.1 wt%, water accounts for 5-15 wt%, and the balance is N-methylpyrrolidone stock solution.

[0008] In a preferred embodiment, the liquid alkali accounts for 0.1 wt%, water accounts for 10-15%, and the balance is N-methylpyrrolidone stock solution.

[0009] In a preferred embodiment, the liquid alkali accounts for 0.1 wt %, water accounts for 10%, and the balance is N-methylpyrrolidone stock solution.

[0010] In a preferred embodiment, the concentration of the liquid caustic soda is 30wt%.

[0011] In a preferred embodiment, the purity of the finished N-methylpyrrolidone is >99.9%.

[0012] In a preferred embodiment, the stirring time is 10-30 min.

[0013] In summary, the present invention has the following beneficial effects: 1. The present application mixes N-methylpyrrolidone stock solution with liquid alkali and water to hydrolyze γ-butyrolactone in the N-methylpyrrolidone stock solution to generate small molecules in an alkaline environment, and then removes the small molecules by distillation, thereby achieving the effect of purifying the N-methylpyrrolidone stock solution. In addition, the purification method of the present application is simple and easy to operate, thereby improving the efficiency of N-methylpyrrolidone purification.

[0014] 2. The present application performs gas chromatography detection after mixing liquid alkali, water and N-methylpyrrolidone stock solution and stirring to see whether the content of γ-butyrolactone in the N-methylpyrrolidone stock solution is reduced, and performs gas chromatography detection again after stirring for a period of time to see whether the content of γ-butyrolactone is reduced. If the content of γ-butyrolactone still does not decrease after stirring for 30 minutes, the content of γ-butyrolactone can be reduced by adjusting the content of water and / or alkali, and then after distillation, γ-butyrolactone can be completely eliminated from the N-methylpyrrolidone stock solution, thereby improving the purity of the N-methylpyrrolidone stock solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the gas chromatogram of Example 1.1 of the present application after stirring for 10 minutes.

[0016] Figure 2 This is the gas chromatogram of Example 1.2 of the present application after stirring for 20 minutes.

[0017] Figure 3This is the gas chromatogram of Example 1.3 of the present application after stirring for 30 minutes.

[0018] Figure 4 This is the gas chromatogram of Example 2.1 of the present application after stirring for 10 minutes.

[0019] Figure 5 This is the gas chromatogram of Example 2.2 of the present application after stirring for 20 minutes.

[0020] Figure 6 This is the gas chromatogram of Example 2.3 of the present application after stirring for 30 minutes.

[0021] Figure 7 This is the gas chromatogram of Example 3.1 of the present application after stirring for 10 minutes.

[0022] Figure 8 This is the gas chromatogram of Example 3.2 of the present application after stirring for 20 minutes.

[0023] Fig. 9 This is the gas chromatogram of Example 3.3 of the present application after stirring for 30 minutes.

[0024] Fig.10 This is the gas chromatogram of Example 4 of the present application after stirring for 10 minutes.

[0025] Fig.11 This is a gas chromatogram of the mixed liquid after distillation after stirring for 10 minutes in Example 4 of the present application.

[0026] Fig.12 This is the gas chromatogram of Example 5.1 of the present application after stirring for 10 minutes.

[0027] Fig.13 This is the gas chromatogram of Example 5.2 of the present application after stirring for 20 minutes.

[0028] Fig.14 This is the gas chromatogram of Example 5.3 of the present application after stirring for 30 minutes.

[0029] Fig.15 This is the gas chromatogram of Example 6.1 of the present application after stirring for 10 minutes.

[0030] Fig.16 This is the gas chromatogram of Example 6.2 of the present application after stirring for 20 minutes.

[0031] Fig.17 This is the gas chromatogram of Example 7 of the present application after stirring for 10 minutes.

[0032] Fig.18 This is the gas chromatogram of N-methylpyrrolidone stock solution. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0034] A method for improving the purity of N-methylpyrrolidone comprises the following steps: adding liquid alkali into water, mixing thoroughly, adding N-methylpyrrolidone stock solution, stirring, sampling the mixed solution, performing gas chromatography detection, and distilling the mixed solution containing zero gamma-butyrolactone to obtain the N-methylpyrrolidone finished product.

[0035] In a preferred embodiment, in the mixed solution, the liquid alkali accounts for 0.05-0.1wt%, the water accounts for 5-15wt%, and the balance is N-methylpyrrolidone stock solution.

[0036] In a preferred embodiment, the liquid alkali accounts for 0.1 wt%, water accounts for 5-15 wt%, and the balance is N-methylpyrrolidone stock solution.

[0037] In a preferred embodiment, the liquid alkali accounts for 0.1 wt%, water accounts for 10-15%, and the balance is N-methylpyrrolidone stock solution.

[0038] In a preferred embodiment, the liquid alkali accounts for 0.1 wt %, water accounts for 10%, and the balance is N-methylpyrrolidone stock solution.

[0039] In a preferred embodiment, the concentration of the liquid caustic soda is 30wt%.

[0040] In a preferred embodiment, the purity of the finished N-methylpyrrolidone is >99.9%.

[0041] In a preferred embodiment, the stirring time is 10-30 min.

[0042] Example 1.1 A method for improving the purity of N-methylpyrrolidone comprises the following steps: adding 0.05 g of liquid alkali to 5 g of water, mixing thoroughly, adding 94.95 g of N-methylpyrrolidone stock solution, stirring with a magnetic stirrer for 10 min, sampling the mixed solution, and performing gas chromatography to detect the content of γ-butyrolactone. The detection results are shown in Table 1 and the chromatogram is shown in Table 1. Figure 1 As shown, the gas chromatogram of N-methylpyrrolidone stock solution is as follows Fig.18 shown.

[0043] Example 1.2-1.3 A method for improving the purity of N-methylpyrrolidone, which is different from Example 1.1 in that the mixed solution is sampled after stirring for 20 min and 30 min respectively, and the content of γ-butyrolactone is detected by gas chromatography. The detection results are shown in Table 1, and the chromatogram is shown in Figure 2 and Figure 3 shown.

[0044] Table 1 Test results of examples 1.1-1.3 It can be seen from Table 1 that under the condition of 5wt% water + 0.05wt% liquid alkali, the γ-butyrolactone content in the N-methylpyrrolidone stock solution is significantly reduced, but cannot be completely removed.

[0045] Example 2.1 A method for improving the purity of N-methylpyrrolidone, comprising the following steps: adding 0.1 g of liquid alkali to 5 g of water, mixing thoroughly, adding 94.9 g of N-methylpyrrolidone stock solution, stirring with a magnetic stirrer for 10 min, sampling the mixed solution, and performing gas chromatography to detect the content of γ-butyrolactone. The test results are shown in Table 2, and the chromatogram is shown in Table 2. Figure 4 shown.

[0046] Example 2.2-2.3 A method for improving the purity of N-methylpyrrolidone, which is different from Example 2.1 in that the mixed solution is sampled after stirring for 20 min and 30 min respectively, and the content of γ-butyrolactone is detected by gas chromatography. The detection results are shown in Table 2, and the chromatogram is shown in Figure 5 and Figure 6 shown.

[0047] Table 2 Test results of Examples 2.1-2.3 As can be seen from Table 2, under the condition of 5wt% water + 0.1wt% liquid alkali ratio, the γ-butyrolactone content in the N-methylpyrrolidone stock solution is significantly lower than that in the stock solution, and is also lower than the γ-butyrolactone content under the stirring time corresponding to Examples 1.1-1.3. It can be seen that with the increase of the liquid alkali content, it is helpful to further reduce the γ-butyrolactone content in the N-methylpyrrolidone stock solution, and in Examples 2.1-2.3, the γ-butyrolactone content decreases with the extension of the stirring time, but after more than 20 minutes, the γ-butyrolactone content will no longer decrease. It can be seen that the γ-butyrolactone in the N-methylpyrrolidone stock solution cannot be completely removed under the condition of 5wt% water + 0.1wt% liquid alkali ratio.

[0048] Example 3.1 A method for improving the purity of N-methylpyrrolidone comprises the following steps: adding 0.08 g of liquid alkali to 10 g of water, mixing thoroughly, adding 89.92 g of N-methylpyrrolidone stock solution, stirring with a magnetic stirrer for 10 min, sampling the mixed solution, and performing gas chromatography to detect the content of γ-butyrolactone. The detection results are shown in Table 3 and the chromatogram is shown in Table 3. Figure 7 shown.

[0049] Examples 3.2-3.3 A method for improving the purity of N-methylpyrrolidone, which is different from Example 3.1 in that the mixed solution is sampled after stirring for 20 min and 30 min respectively, and the content of γ-butyrolactone is detected by gas chromatography. The detection results are shown in Table 3, and the chromatogram is shown in Figure 8 and Fig. 9 shown.

[0050] Table 3 Test results of Examples 3.1-3.3 It can be seen from Table 3 that under the conditions of 10wt% water + 0.08wt% liquid caustic soda, after the content of γ-butyrolactone in the mixed solution obtained in Examples 3.1-3.3 is reduced to 0.006%, it no longer decreases with the change of stirring time. It can be seen that under the conditions of 10wt% water + 0.08wt% liquid caustic soda, γ-butyrolactone in N-methylpyrrolidone cannot be completely removed.

[0051] Example 4 A method for improving the purity of N-methylpyrrolidone comprises the following steps: adding 0.1 g of liquid alkali to 10 g of water, mixing thoroughly, adding 89.9 g of N-methylpyrrolidone stock solution, stirring with a magnetic stirrer for 10 min, sampling the mixed solution, and performing gas chromatography to detect the content of γ-butyrolactone. The detection results are shown in Table 4, and the chromatogram is shown in Table 4. Fig.10 shown.

[0052] Table 4 Example 4 Test results table As can be seen from Table 4, at a ratio of 10 wt% water + 0.1 wt% liquid alkali, the γ-butyrolactone in the N-methylpyrrolidone stock solution is completely dissolved after the mixed solution is stirred for 10 min, so the presence of γ-butyrolactone cannot be detected by gas chromatography. Therefore, the mixed solution obtained after stirring for 10 min in Example 4 is distilled, and the N-methylpyrrolidone product obtained by distillation is again subjected to gas chromatography detection. The gas chromatogram is as shown in FIG. Fig.11As shown, no γ-butyrolactone was found in the gas chromatogram, which shows that the γ-butyrolactone in the N-methylpyrrolidone stock solution can be completely removed after stirring for 10 minutes at a ratio of 10wt% water + 0.1wt% liquid alkali.

[0053] Example 5.1 A method for improving the purity of N-methylpyrrolidone comprises the following steps: adding 0.05 g of liquid alkali to 15 g of water, mixing thoroughly, adding 84.95 g of N-methylpyrrolidone stock solution, stirring with a magnetic stirrer for 10 min, sampling the mixed solution, and performing gas chromatography to detect the content of γ-butyrolactone. The detection results are shown in Table 5, and the chromatogram is shown in Table 5. Fig.12 shown.

[0054] Examples 5.2-5.3 A method for improving the purity of N-methylpyrrolidone, which is different from Example 5.1 in that the mixed solution is sampled after stirring for 20 min and 30 min respectively, and the content of γ-butyrolactone is detected by gas chromatography. The detection results are shown in Table 5, and the chromatogram is shown in Fig.13 and Fig.14 shown.

[0055] Table 5 Test results of Examples 5.1-5.3 As can be seen from Table 5, at a ratio of 15wt% water + 0.05wt% liquid caustic soda, the γ-butyrolactone content in the N-methylpyrrolidone obtained in Examples 5.1-5.3 decreases with the extension of the stirring time, but after the stirring time reaches 20 minutes, the γ-butyrolactone content will no longer decrease. It can be seen that the γ-butyrolactone content in N-methylpyrrolidone cannot be completely removed at a ratio of 15wt% water + 0.05wt% liquid caustic soda.

[0056] Example 6.1 A method for improving the purity of N-methylpyrrolidone comprises the following steps: adding 0.08 g of liquid alkali to 15 g of water, mixing thoroughly, adding 84.92 g of N-methylpyrrolidone stock solution, stirring with a magnetic stirrer for 10 min, sampling the mixed solution, and performing gas chromatography to detect the content of γ-butyrolactone. The detection results are shown in Table 6, and the chromatogram is shown in Table 6. Fig.15 shown.

[0057] Example 6.2 A method for improving the purity of N-methylpyrrolidone, which is different from Example 6.1 in that the mixed solution is sampled after stirring for 20 min and 30 min respectively, and the content of γ-butyrolactone is detected by gas chromatography. The detection results are shown in Table 6, and the chromatogram is shown in Fig.16 shown.

[0058] Table 6 Test results of Example 6.1-6.2 It can be seen from Table 6 that at a ratio of 15wt% water + 0.08wt% liquid alkali, the γ-butyrolactone content in the mixed solution obtained in Example 6.1 is lower than that in Example 5.1, and in Example 6.2, with the extension of the stirring time, when the stirring time is 20 minutes, the γ-butyrolactone in N-methylpyrrolidone can be completely removed, and after the mixed solution obtained in Example 6.2 is distilled, the distilled sample is subjected to gas chromatography again and it is found that no γ-butyrolactone appears in the chromatogram, which shows that the γ-butyrolactone in N-methylpyrrolidone has been completely removed.

[0059] Example 7 A method for improving the purity of N-methylpyrrolidone, comprising the following steps: adding 0.1 g of liquid alkali to 15 g of water, mixing thoroughly, adding 84.9 g of N-methylpyrrolidone stock solution, stirring with a magnetic stirrer for 10 min, sampling the mixed solution, and performing gas chromatography to detect the content of γ-butyrolactone. The test results are shown in Table 7, and the chromatogram is shown in Fig.17 shown.

[0060] Table 7 Example 7 Test results table It can be seen from Table 7 that at a ratio of 15wt% water + 0.1wt% liquid caustic soda, the γ-butyrolactone in the N-methylpyrrolidone stock solution is completely dissolved after the mixed solution is stirred for 10min, so the presence of γ-butyrolactone cannot be detected by gas chromatography. Therefore, the mixed solution obtained after stirring for 10min in Example 7 is distilled, and the N-methylpyrrolidone product obtained by distillation is again subjected to gas chromatography detection, and it is found that no γ-butyrolactone appears in the gas chromatogram. It can be seen that the γ-butyrolactone in the N-methylpyrrolidone stock solution can be completely removed after stirring for 10min at a ratio of 15wt% water + 0.1wt% liquid caustic soda.

[0061] In summary, the schemes of Example 4 (10wt% water + 0.1wt% liquid alkali, stirring for 10min), Example 6.2 (15wt% water + 0.08wt% liquid alkali, stirring for 20min) and Example 7 (15wt% water + 0.1wt% liquid alkali, stirring for 10min) of the present application can completely remove γ-butyrolactone in the N-methylpyrrolidone stock solution, and after distillation treatment and gas chromatography detection of the distilled sample, no γ-butyrolactone appears in the chromatogram, and the purity of the N-methylpyrrolidone obtained after distillation reaches 99.93%, which meets the requirements of the electronic grade product standard. It can be seen that the above conditions can completely remove γ-butyrolactone in the N-methylpyrrolidone stock solution. From the perspective of reducing costs, 10wt% water + 0.1wt% liquid alkali can be preferably used to remove γ-butyrolactone in the N-methylpyrrolidone stock solution.

[0062] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the purity of N-methylpyrrolidone, characterized in that: The method comprises the following steps: adding liquid alkali into water, fully mixing, adding N-methyl pyrrolidone stock solution, stirring, sampling the mixed solution for gas chromatography detection, and distilling the mixed solution containing zero gamma-butyrolactone to obtain the N-methyl pyrrolidone finished product.

2. A method for improving the purity of N-methylpyrrolidone according to claim 1, characterized in that: In the mixed solution, the proportion of liquid alkali is 0.05-0.1wt%, the proportion of water is 5-15wt%, and the balance is N-methylpyrrolidone stock solution.

3. A method for improving the purity of N-methylpyrrolidone according to claim 2, characterized in that: The liquid alkali accounts for 0.1wt%, water accounts for 5-15wt%, and the balance is N-methylpyrrolidone stock solution.

4. A method for improving the purity of N-methylpyrrolidone according to claim 2, characterized in that: The liquid alkali accounts for 0.1wt%, water accounts for 10-15%, and the balance is N-methylpyrrolidone stock solution.

5. A method for improving the purity of N-methylpyrrolidone according to claim 2, characterized in that: The liquid alkali accounts for 0.1wt%, water accounts for 10%, and the balance is N-methylpyrrolidone stock solution.

6. A method for improving the purity of N-methylpyrrolidone according to claim 2, characterized in that: The concentration of the liquid caustic soda is 30wt%.

7. A method for improving the purity of N-methylpyrrolidone according to claim 2, characterized in that: The purity of the N-methylpyrrolidone finished product is >99.9%.

8. A method for improving the purity of N-methylpyrrolidone according to claim 1, characterized in that: The stirring time is 10-30 min.

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