Method for purifying waste N-methyl-2-pyrrolidone mixed liquor

Abstract

The present invention relates to a method for purifying a waste N-methyl-2-pyrrolidone (hereinafter referred to as NMP) mixed solution, and more particularly, to a method for purifying the waste NMP mixed solution using alkali. According to the present invention, alkali is applied to the waste NMP mixed solution to simultaneously remove NMS and GBL, thereby recovering high-purity NMP.

Description

Technical Field

[0001] The present invention relates to a method for purifying a waste N-methyl-2-pyrrolidone (hereinafter referred to as NMP) mixed liquid, and more particularly to a method for purifying the waste NMP mixed liquid by using alkali. Background Art

[0002] N-Methyl-2-pyrrolidone (NMP) is a low viscosity, colorless, non-toxic organic solvent with excellent heat resistance. NMP is a solvent with good chemical stability and high polarity, so it is very helpful for various chemical reactions that require an inert medium.

[0003] As environmental regulations are tightened, NMP is increasingly in demand as an environmentally friendly, non-toxic product in the fields of polymer polymerization and processing solvents, paint manufacturing solvents, metal surface cleaning agents, pharmaceutical synthesis and purification solvents, semiconductor and electronic material processing solvents, and lithium secondary battery manufacturing solvents.

[0004] In particular, in the manufacturing process of the anode and cathode in the secondary battery manufacturing process, NMP can be included in the binder as a solvent for forming active materials. NMP can be used as a dispersing solvent in the active material mixing tank, and after the electrode is formed, it can be recovered in the form of vapor in the drying process. At this time, the waste NMP can contain about 30wt% of water.

[0005] In addition, when the waste NMP is recovered and reused in the process, it is not only economically beneficial, but also has a great effect of reducing the emission of environmental pollution sources. Therefore, research on methods for purifying high-purity NMP by purifying the waste NMP is being actively carried out.

[0006] During the synthesis process of NMP, a certain amount of GBL (gamma-butyrolactone, γ-butyrolactone) will remain. During the purification process by distillation, the boiling points of NMP (boiling point 202°C) and GBL (boiling point 204°C) as an impurity are very similar, making it difficult to remove GBL. Therefore, all NMP products contain about 200 to 400 wtppm of GBL.

[0007]

[0008] Moreover, during storage, transportation and use, NMP is oxidized by oxygen in the air, thereby generating a considerable amount of NMS (N-methylsuccinimide, boiling point 234°C), so that the NMP product also contains a considerable amount of NMS, and the waste NMP may also contain 200 to 500 wtppm or more of NMS. Although the boiling point of NMS is quite different from that of NMP, it has the problem that it cannot be completely removed in the purification process of the waste NMP mixed liquid by distillation. In particular, in industries that require high-purity NMP of 99.9% by weight or more as a processing solvent for semiconductors and electronic materials and a solvent for lithium battery manufacturing, it is necessary to remove NMS and GBL, etc., but a solution has not yet been proposed.

[0009] In addition, in the NMP product and the waste NMP mixed liquid, 1,3-DMP (1,3-dimethyl-2-pyrrolidone) and 1,4-DMP (1,4-dimethyl-2-pyrrolidone) which are not removed by fractionation usually remain at about 300 to 350 wtppm each. Therefore, in order to purify and recover high-purity NMP from the waste NMP mixed liquid, it is necessary to remove NMS and GBL.

[0010] Korean Patent Publication No. 10-2015-0085065 discloses a method for purifying and reusing N-alkylpyrrolidone to be purified by adding an alkaline compound and distilling the mixture. Patent Publication No. 10-2018-0069284 discloses a method for purifying high-purity NMP by adding an alkaline compound to a waste NMP mixed liquid to simultaneously remove NM3P (N-methyl-3-pyrrolin-2-one) and NMS (N-methylsuccinimide). US Pat. No. 2,964,535 discloses a method for removing GBL as an impurity contained in NMP.

[0011] However, a method for purifying the waste NMP mixed liquid by simultaneously removing NMS (N-methylsuccinimide) and GBL (gamma-butyrolactone, γ-butyrolacton) as impurities remaining in the waste NMP mixed liquid has not been proposed.

[0012] [Prior art literature]

[0013] 1. Korean Patent Publication No. 10-2015-0085065 (published on July 22, 2015)

[0014] 2. Korean Patent Publication No. 10-2018-0069284 (published on June 25, 2018)

[0015] 3. U.S. Patent 2,964,535 (granted on December 13, 1960) Summary of the invention

[0016] Technical issues solved

[0017] The technical problem to be solved by the present invention is to provide a method for recovering high-purity NMP by applying a fractionation process after simultaneously removing NMS and GBL as impurities remaining in a waste NMP mixed liquid.

[0018] Technical Solution

[0019] In a specific example of the present invention, a method for purifying a waste NMP mixed liquid is provided, wherein a base is added to the waste NMP mixed liquid to simultaneously remove N-methylsuccinimide (N-methylsuccinimide) and GBL (gamma-Butyrolactone) as by-products of NMP that are already present in the waste NMP mixed liquid or generated during the purification process. The base may be SBH (NaBH4).

[0020] In a method for purifying a waste NMP mixed liquid according to another specific example of the present invention, the SBH may be added in an amount of 0.05 to 0.10 wt % relative to the total weight of the waste NMP mixed liquid.

[0021] In a method for purifying a waste NMP mixed liquid according to another specific example of the present invention, water is added at a content of 5 to 20 weight % relative to the total weight of the reactants, the reaction temperature is 100 to 150° C., and the reaction time can be 10 to 60 minutes.

[0022] In a method for purifying a waste NMP mixed liquid according to another specific example of the present invention, the SBH can be added in a form of being dissolved in NaOH having a concentration of 10% (w / v).

[0023] Effects of the Invention

[0024] According to a method for purifying waste NMP of the present invention, NMS and GBL can be removed simultaneously by using an alkali and high-purity NMP can be recovered. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1The results of GC (gas chromatography) analysis of a waste NMP mixed liquid containing NMS and GBL as impurities.

[0026] Figure 2 The GC analysis results of the waste NMP mixture after SBH treatment are shown in FIG. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0028] In the description of the constituent elements of the present invention, terms such as 1st, 2nd, 3rd, 1st, 2nd, A, B, (a), (b) etc. may be used. These terms are only used to distinguish the constituent elements from other constituent elements, and do not limit the nature, order or sequence of the corresponding constituent elements due to their terms. Moreover, in the description of the present invention, when it is judged that the detailed description of the relevant known structure or function may confuse the gist of the present invention, its detailed description will be omitted.

[0029] Unless otherwise defined, the meanings of all terms in this specification are the same as the general meanings of the terms understood by ordinary technicians in the field to which the present invention belongs. When there is a conflict with the meaning of the terms used in this specification, the definitions used in this specification shall prevail. In the overall specification, unless there is a special record to the contrary, when it is mentioned that a part "includes" a certain constituent element, it means that other constituent elements are also included rather than excluding other constituent elements.

[0030] In a specific example of one embodiment of the present invention, a method for purifying a waste NMP mixed liquid is provided, wherein an alkali is added to the waste NMP mixed liquid to simultaneously remove N-methylsuccinimide (N-Methylsuccinimide) and GBL (gamma-Butyrolactone) as by-products of NMP remaining in the waste NMP mixed liquid.

[0031] pass Figure 1 It is clear that the waste NMP mixed liquid contains N-methylsuccinimide and GBL (gamma-butyrolactone) as impurities. Figure 1 The GC (Gas Chromatography) analysis results of the waste NMP mixed liquid are shown in Table 1. Figure 1 , peaks were observed in N-Methylsuccinimide and GBL (γ-butyrolactone).

[0032] According to the present invention, NMS and GBL as impurities can be completely removed at the same time by reacting the waste NMP mixed liquid with a reducing agent such as SBH. That is, as shown in the following reaction formula 1, NMS (boiling point: 234°C) contained in the waste NMP reacts with SBH and is converted into 5-hydroxy-N-methyl-2-pyrrolidone (boiling point: 276°C), and as shown in the following reaction formula 2, GBL (boiling point: 204°C) contained in the waste NMP reacts with SBH and is converted into 1,4-butanediol (boiling point: 230°C).

[0033] The boiling point of NMP is 202°C, which is similar to that of GBL. Therefore, when waste NMP is directly fractionated, it is difficult to remove GBL, but when reacted with SBH as in the present invention, it can be converted into a high-boiling substance compared to NMP, so that the converted substance can be fractionated and removed. This can be achieved by Figure 2 Get confirmation.

[0034] Figure 2 The GC analysis results of the waste NMP mixture after SBH treatment are shown. Figure 1 In contrast, no peaks for GBL or NMS were observed.

[0035] [Reaction 1]

[0036]

[0037] [Reaction 2]

[0038]

[0039] In addition, in a method for purifying a waste NMP mixed liquid according to a specific example of the present invention, the alkali may be SBH (sodium borohydride (NaBH4)).

[0040] Generally, reduction reactions in organic chemical reactions are reactions that combine with hydrogen or reduce the oxidation state. The reducing agents that cause the reduction reactions include metal hydrides that directly provide hydrogen ions (H-, hydride), representative of which are lithium aluminum hydride (Lithium Aluminum Hydride (LAH, LiAlH4) and sodium borohydride (Sodium Borohydride (SBH, NaBH4).

[0041] Of the above LAH and SBH, LAH has a much stronger reducing ability than SBH, and can generally convert the hydroxyl groups of all the following carbonyl (C=O) compounds into methylene (CH2). However, SBH has a weaker reducing ability than LAH, so when generally viewed in the order of the following compounds, it is well known that it can only be reduced to ketones.

[0042]

[0043] This reduction reaction is caused by the attack of the negative hydride ion on the C of the partially positively charged hydroxyl group in C=O. It is well known that starting from ester, the positive charge of C is weakened due to the inductive effect of the O adjacent to the C of C=O, so that SBH with weak reducing ability cannot cause the reduction reaction.

[0044] However, in the case of NMS, since there are C=O on both sides of the N-methyl group, electrons can be pulled from both sides, so the C of the C=O on one side becomes more positively charged and is easy to react. However, since NMP has C=O on only one side, it is considered that it cannot cause a reaction.

[0045] In addition, in the case of GBL, it can be inferred that since cyclic esters (lactones) are more reactive than amides, the pentagonal structure is decyclized (strain is relieved) to form a stable structure, and the reaction can still proceed despite being an ester.

[0046] In a method for purifying a waste NMP mixed liquid according to another specific example of the present invention, the SBH may be added in an amount of 0.05 to 0.10 wt % relative to the total weight of the waste NMP mixed liquid. When the content of the added SBH exceeds the above range, NMS and GBL contained in the waste NMP mixed liquid may not be completely removed at the same time.

[0047] In a method for purifying a waste NMP mixed liquid according to another specific example of the present invention, water is added at a content of 5 to 20 weight % relative to the total weight of the reactants, the reaction temperature is 100 to 150° C., and the reaction time can be 10 to 60 minutes. When the reaction conditions exceed the above range, NMS and GBL contained in the waste NMP mixed liquid may not be completely removed at the same time.

[0048] In a method for purifying a waste NMP mixed solution according to another specific example of the present invention, the SBH can be added in the form of being dissolved in NaOH with a concentration of 10% (w / v). When the reaction conditions exceed the above range, NMS and GBL contained in the waste NMP mixed solution may not be completely removed at the same time.

[0049] Hereinafter, an embodiment of a method for purifying a waste NMP mixed liquid according to a specific example of the present invention is described. The following embodiments are only examples for illustrating the present invention, and the scope of the present invention is not limited to these embodiments.

[0050] Examples and Comparative Examples

[0051] <Example 1> to <Example 10>

[0052] After 200 g of a waste NMP mixed liquid containing 200 to 500 wtppm of NMS and 200 to 400 wtppm of GBL relative to the total weight of the waste NMP mixed liquid was added to a 500 mL round-bottom flask, a solution prepared by dissolving SBH in a 10% (w / v) NaOH aqueous solution was added to the waste NMP mixed liquid at 25 to 150° C. and stirred at 200 to 250 rpm. At this time, the composition of the waste liquid, the amount of SBH added, the reaction temperature, etc. are shown in Table 1 below. In Table 1 below, the amount of SBH added is the amount of SBH added relative to the total weight of the waste liquid mixture.

[0053] <Comparative Example 1> to <Comparative Example 11>

[0054] After 200 g of a waste NMP mixed solution containing 200 to 500 wtppm of NMS and 200 to 400 wtppm of GBL relative to the total weight of the waste NMP mixed solution was charged into a 500 mL round-bottom flask, a 10% (w / v) NaOH aqueous solution was charged into the waste NMP mixed solution while stirring at 200 to 250 rpm at 25 to 150° C. At this time, the composition of the waste liquid, the amount of SBH charged, the reaction temperature, etc. are shown in Table 1 below.

[0055] As a result of the reaction according to Examples 1 to 10 and Comparative Examples 1 to 11, the composition of the waste liquid after the reaction is shown in Table 1. In Table 1, the content of each component of the waste liquid, Comparative Examples and Examples is the content in organic matter excluding water.

[0056] [Table 1]

[0057]

[0058] As can be seen from Table 1, when the waste liquid containing about 300 wtppm of NMS and about 250 wtppm of GBL was used, GBL and NMS remained in the comparative example, whereas GBL and NMS were not observed at all in the example of the present invention.

[0059] Therefore, according to the present invention, under the reaction conditions of a moisture content of 5 to 20 wt%, a reaction temperature of 100 to 150°C, and a reaction time of 10 to 60 minutes, when the SBH content is 0.05 to 0.10 wt%, NMS and GBL can be completely removed from the waste NMP mixed liquid at the same time.

[0060] Furthermore, it can be seen from the results of Comparative Examples 1 to 11 in Table 1 that when the experimental conditions are outside the range of Examples 1 to 10, NMS and GBL cannot be completely removed from the waste NMP mixed liquid at the same time.

[0061] <Example 11>

[0062] This is the case where waste NMP containing 0.12 wt% of NMS and about 270 wtppm of GBL was treated with a 10% (w / v) NaOH aqueous solution in which SBH was dissolved at a reaction temperature of 100°C.

[0063] <Comparative Example 12> to <Comparative Example 14>

[0064] The procedure was the same as in Example 11 except that a 10% (w / v) NaOH aqueous solution in which SBH was not dissolved was used.

[0065] When the waste liquid was treated according to Example 11 and Comparative Examples 12 to 14, the composition of the mixture after treatment was as shown in Table 2 below.

[0066] [Table 2]

[0067]

[0068] As can be seen from Table 2, in Comparative Examples 12 and 13, NMS and GBL were hardly removed from the waste liquid, and in Comparative Example 14, although NMS and GBL were removed more than in Comparative Examples 12 and 13, they were not completely removed. On the contrary, in Example 11 of the present invention, it was confirmed that NMS and GBL in the waste NMP mixed liquid were completely removed.

[0069] <Example 12> Fractionation using a distillation tower

[0070] In Examples 7 and 12, SBH was applied to a waste NMP mixed liquid containing NMS and GBL, thereby completely removing NMS and GBL at the same time to obtain a waste NMP mixed liquid, and the waste NMP mixed liquid was fractionated using a 30-layer sieve tray distillation tower of a 5L pilot scale at a pressure of 40 to 100 mmHg to remove 0 to 15% of water and low-boiling impurities, and recover 15 to 80% of purified NMP. The results are shown in Table 3 below. In Table 3 below, the contents of each component in the waste liquid and the examples are the contents in organic matter other than water.

[0071] [Table 3]

[0072]

[0073] As can be seen from Table 3, in the case of Examples 7 and 12 of the present invention, NMS and GBL were not present in the mixture obtained by fractionation. Therefore, it can be seen that according to the present invention, if the waste NMP mixed liquid is treated with SBH and then fractionated, impurities such as GBL and NMS can be removed.

[0074] The above description is only for illustration, and any person skilled in the art to which the present invention belongs can make various modifications without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in this specification are not intended to limit the present invention, but to illustrate the present invention, and the idea and scope of the present invention will not be limited by such embodiments. The protection scope of the present invention should be interpreted according to the protection scope of the invention claims, and all technologies within the equivalent scope should be interpreted as included in the protection scope of the present invention.

[0075] Cross-references to related patent applications

[0076] This patent application claims priority under 35 U.S.C. §119 to §121, §365 to Patent Application No. 10-2019-0082112 filed in Korea on July 8, 2019, the entire contents of which are incorporated herein by reference. In addition, if this patent application claims priority in other countries besides the United States for the same reason, the entire contents of which are incorporated herein by reference.

Claims

1. A method for purifying a waste N-methyl-2-pyrrolidone mixed solution, wherein the waste N-methyl-2-pyrrolidone mixed solution contains N-methylsuccinimide and γ-butyrolactone as by-products of N-methyl-2-pyrrolidone, wherein an alkali is added to the waste N-methyl-2-pyrrolidone mixed solution to simultaneously remove the N-methylsuccinimide and γ-butyrolactone, characterized in that: The base is NaBH4, The N-methylsuccinimide reacts with the NaBH4 to be converted into 5-hydroxy-N-methyl-2-pyrrolidone, and the γ-butyrolactone reacts with the NaBH4 to be converted into 1,4-butanediol. The amount of NaBH4 added is 0.05-0.10 wt % relative to the total weight of the waste N-methyl-2-pyrrolidone mixed solution, and the amount of water added is 5-20 wt % relative to the total weight of the reactants. The reaction temperature is 100-150° C. and the reaction time is 10-60 minutes.

2. The method for purifying the waste N-methyl-2-pyrrolidone mixed solution according to claim 1, characterized in that: The NaBH4 was added in a form dissolved in NaOH having a concentration of 10% w / v.

3. The method for purifying the waste N-methyl-2-pyrrolidone mixed solution according to claim 1, characterized in that: The 5-hydroxy-N-methyl-2-pyrrolidone is formed by the following reaction formula 1: The 1,4-butanediol is formed by the following reaction formula 2: [Reaction formula 1] [Reaction 2] 4. The method for purifying the waste N-methyl-2-pyrrolidone mixed solution according to claim 1, characterized in that: The waste N-methyl-2-pyrrolidone mixed liquid is derived from waste liquid used in the secondary battery preparation process.

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