Purification method and purification device for nmp

Abstract

The present invention relates to a method and an apparatus for purifying NMP. Specifically, according to an embodiment of the present invention, a method for purifying NMP includes the steps of: (1) distilling waste NMP in a first distillation column to perform a first purification thereon; (2) discharging a water-containing effluent separated by the first purification out of the system through a top of the first distillation column, and discharging a first bottom liquid through a bottom of the first distillation column; (3) injecting the discharged first bottom liquid into a second distillation column and performing a second purification thereon; (4) discharging purified NMP separated by the second purification out of the system through a top of the second distillation column, and discharging a second bottom liquid through a bottom of the second distillation column; (5) injecting the discharged second bottom liquid into a filtrate recovery apparatus and performing a heat treatment thereon; (6) discharging a tertiary bottom liquid separated by the heat treatment out of the system through a bottom of the filtrate recovery apparatus, and discharging an NMP-containing gas mixture through a top of the filtrate recovery apparatus; and (7) injecting the discharged gas mixture into the second distillation column, and thus improving a recovery rate of NMP recovered from the waste NMP, so as to provide NMP of high purity.

Description

Technical Field

[0001] This invention relates to a method and apparatus for purifying waste NMP. Background Technology

[0002] Recently, with the accelerated development of technologies for portable devices such as mobile phones and cameras, interest in secondary batteries as an energy source is increasing. Among such secondary batteries, research on their recycling is also ongoing, driven by the rapidly growing demand for lithium-ion batteries that exhibit high energy density and operating potential, long cycle life, and low self-discharge rate.

[0003] N-Methyl-2-pyrrolidone (NMP) is an organic solvent with chemical stability, low volatility, and the ability to dissolve a variety of substances. Therefore, it is widely used as a solvent in industries such as petrochemicals, plastics, and pharmaceuticals, and is also used in the manufacturing process of secondary batteries.

[0004] Specifically, lithium-ion secondary batteries consist of a positive electrode and a negative electrode. The positive electrode is manufactured by applying an electrode material comprising a lithium compound (such as lithium cobalt oxide or lithium manganese oxide), a binder (such as polyvinylidene fluoride), and N-methyl-2-pyrrolidone (NMP) as a solvent to a substrate and then calcining the electrode material. The negative electrode is manufactured by applying an electrode material comprising compounds containing carbon, titanium, etc., a binder (such as polyvinylidene fluoride), and water as a solvent to a substrate and then calcining the electrode material. As mentioned above, NMP is used not only as a major material for manufacturing the positive electrode in the electrode manufacturing process but also in the cleaning and drying steps, resulting in significant emissions. Therefore, research on technologies for its efficient recovery continues.

[0005] For example, Korean Patent No. 10-2050990 discloses a system for separating and recovering NMP from NMP gas by making NMP-containing gas with water that has absorbed NMP through gas-liquid contact, whereby NMP in the NMP-containing gas is absorbed by water.

[0006] [Existing Technical Documents] [Patent Literature] Patent Document 1: Korean Patent No. 10-2050990 Summary of the Invention

[0007] Technical issues Therefore, the present invention aims to provide a method and apparatus for purifying NMP, which can improve the recovery rate of NMP from waste NMP and provide high-purity NMP.

[0008] Technical solutions to solve technical problems According to one embodiment of the present invention, a method for purifying NMP includes: (1) distilling waste NMP in a first distillation column for a first purification; (2) discharging an aqueous overhead product separated by the first purification to the outside of the system through the top of the first distillation column and discharging a first bottom product through the bottom of the first distillation column; (3) feeding the discharged first bottom product to a second distillation column for a second purification; (4) discharging purified NMP separated by the second purification to the outside of the system through the top of the second distillation column and discharging a second bottom product through the bottom of the second distillation column; (5) feeding the discharged second bottom product to a filtrate recovery device for heat treatment; (6) discharging a third bottom product separated by the heat treatment to the outside of the system through the bottom of the filtrate recovery device and discharging a gas mixture containing NMP through the top of the filtrate recovery device; and (7) feeding the discharged gas mixture to the second distillation column.

[0009] An apparatus for purifying NMP according to another embodiment of the present invention comprises: a supply unit for supplying waste NMP; a first distillation column for performing a first purification of the supplied waste NMP by distillation, thereby discharging an aqueous overhead product separated by the first purification to the outside of the system through its top and discharging a first bottom product through its bottom; a second distillation column for performing a second purification of the first bottom product by distillation, thereby discharging purified NMP separated by the second purification to the outside of the system through its top and discharging a second bottom product through its bottom; and a filtrate recovery device for heat-treating the second bottom product, discharging a third bottom product separated by the heat treatment to the outside of the system through its bottom and discharging a gaseous mixture containing NMP through its top.

[0010] Advantages of the present invention A method for purifying NMP according to an embodiment of the present invention includes: (1) distilling waste NMP in a first distillation column for a first purification; (2) discharging an aqueous overhead product separated by the first purification to the outside of the system through the top of the first distillation column and discharging a first bottom product through the bottom of the first distillation column; (3) feeding the discharged first bottom product to a second distillation column for a second purification; (4) discharging purified NMP separated by the second purification to the outside of the system through the top of the second distillation column and discharging a second bottom product through the bottom of the second distillation column; (5) feeding the discharged second bottom product to a filtrate recovery device for heat treatment; (6) discharging a third bottom product separated by the heat treatment to the outside of the system through the bottom of the filtrate recovery device and discharging a gas mixture containing NMP through the top of the filtrate recovery device; and (7) feeding the discharged gas mixture to the second distillation column. Therefore, the recovery rate of NMP from waste NMP can be improved, and high-purity NMP can be provided.

[0011] Specifically, water in waste NMP can be effectively removed through the first purification process, and substances with boiling points higher than those of NMP, which may be contained in the bottom product of the third column discharged through the second purification, can be effectively removed through heat treatment in the filtrate recovery unit. Furthermore, the recovery rate and purity of NMP can be further improved by refeeding the NMP-containing gas mixture separated by heat treatment in the filtrate recovery unit to the second distillation column. Attached Figure Description

[0012] Figure 1 A flowchart illustrating an NMP purification method according to one embodiment of the present invention is shown schematically.

[0013] Figure 2 An example of an NMP purification apparatus according to another embodiment of the present invention is shown. Detailed Implementation

[0014] The present invention will be described in detail below. The present invention is not limited to the disclosure given below, but can be modified in various ways as long as the essential points of the invention remain unchanged.

[0015] Throughout this specification, when a component is referred to as "including" an element, it should be understood that, unless otherwise specifically stated, other elements may be included, rather than excluded.

[0016] Unless otherwise stated, all figures and expressions relating to the amounts of components, reaction conditions, etc., used herein should be understood to be modified by the term “about”.

[0017] In this specification, when it is mentioned that an element is formed "on" or "below" another element, it means not only that an element is formed directly "on" or "below" another element, but also that an element is formed indirectly on or below another element, with other elements inserted between them.

[0018] Throughout this specification, the terms first, second, etc., are used to describe various components. However, these components should not be limited by these terms. These terms are used only for the purpose of distinguishing one component from another.

[0019] NMP purification method According to one embodiment of the present invention, a method for purifying NMP includes: (1) distilling waste NMP in a first distillation column for a first purification; (2) discharging an aqueous overhead product separated by the first purification to the outside of the system through the top of the first distillation column and discharging a first bottom product through the bottom of the first distillation column; (3) feeding the discharged first bottom product to a second distillation column for a second purification; (4) discharging purified NMP separated by the second purification to the outside of the system through the top of the second distillation column and discharging a second bottom product through the bottom of the second distillation column; (5) feeding the discharged second bottom product to a filtrate recovery device for heat treatment; (6) discharging a third bottom product separated by the heat treatment to the outside of the system through the bottom of the filtrate recovery device and discharging a gas mixture containing NMP through the top of the filtrate recovery device; and (7) feeding the discharged gas mixture to the second distillation column.

[0020] Figure 1 A flowchart illustrating an NMP purification method according to one embodiment of the present invention is shown schematically. Figure 2 An example of an NMP purification apparatus according to another embodiment of the present invention is shown. Specifically, Figure 2 An NMP purification apparatus consisting of a supply unit (SD), a first distillation column (D1), a second distillation column (D2), and a filtrate recovery unit (R) is shown.

[0021] In the following text, reference will be made to Figure 1 and Figure 2 A method for purifying NMP according to one embodiment of the present invention is described.

[0022] Step (1): Distill waste NMP in a first distillation column for first purification. A method for purifying NMP according to one embodiment of the present invention includes the step of distilling waste NMP in a first distillation column to perform a first purification.

[0023] Waste NMP can be recycled once it has been used in the manufacturing process of lithium-ion batteries. For example, waste NMP can be recycled once it has been used as a raw material for lithium-ion batteries, but it is not limited to this.

[0024] Waste NMP may contain 70% by weight or more of NMP. For example, based on the total weight of the waste NMP, the NMP content in the waste NMP may be 72% by weight or more, 75% by weight or more, 78% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more.

[0025] In addition, waste NMP may contain water. For example, based on the total weight of waste NMP, the water content in waste NMP may be 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less.

[0026] In step (1), the waste NMP can be fed to the middle or upper part of the first distillation column. Specifically, it is preferable to feed the waste NMP to the middle or upper part of the first distillation column to perform the first purification more effectively, but it is not limited thereto.

[0027] The first purification in step (1) can be carried out at a temperature of 50°C to 150°C and a pressure of 100 Torr to 130 Torr. For example, the first purification can be carried out at a temperature of 52°C to 145°C or 55°C to 143°C and a pressure of 105 Torr to 130 Torr or 110 Torr to 125 Torr. When the temperature and pressure conditions of the first purification meet the above ranges, water contained in waste NMP can be effectively removed.

[0028] Step (2): The aqueous top product separated by the first purification is discharged through the top of the first distillation column. The product is discharged to the outside of the system and through the bottom of the first distillation column. According to one embodiment of the present invention, a method for purifying NMP includes the following steps: discharging an aqueous overhead product separated by a first purification process to the outside of the system through the top of a first distillation column; and discharging a first bottom product through the bottom of the first distillation column.

[0029] Specifically, in step (2), the water-containing overhead product separated from the waste NMP in the first purification in step (1) is discharged outside the system, which reduces the water content and thus improves the purity of the waste NMP.

[0030] The water content in the first bottom product can be 0.01% or less. For example, the water content in the first bottom product can be 0.008% or less, 0.006% or less, or 0.005% or less.

[0031] Furthermore, the first bottoms product may contain 99.9% by weight or more of NMP. For example, based on the total weight of the first bottoms product, the NMP content in the first bottoms product may be 99.92% by weight or more, 99.94% by weight or more, or 99.95% by weight or more. Since most of the water in the waste NMP is effectively removed in the above-described first purification, the purity of NMP in the first bottoms product can be further improved.

[0032] Step (3): Feed the discharged bottom product from the first distillation column to the second distillation column for secondary purification. According to one embodiment of the present invention, a method for purifying NMP includes the step of feeding the discharged first bottom product into a second distillation column for a second purification.

[0033] The purity of NMP can be improved through a second purification. Specifically, waste NMP may contain NMP and components with boiling points higher than NMP. Since water has been removed from the bottom product of the first column in the first purification, the second purification of the bottom product of the first column in step (3) can effectively remove components with boiling points higher than NMP, thereby further improving the purity of NMP.

[0034] In step (3), the bottom product of the first column can be fed into the middle or lower part of the second distillation column. Specifically, it is preferable to feed the bottom product of the first column into the middle or lower part of the second distillation column in order to perform the second purification more effectively, but it is not limited thereto.

[0035] The second purification can be carried out at a temperature of 120°C to 150°C and a pressure of 50 Torr to 90 Torr. For example, the second purification can be carried out at a temperature of 122°C to 148°C or 126°C to 145°C and a pressure of 55 Torr to 85 Torr or 65 Torr to 80 Torr. When the temperature and pressure conditions of the second purification meet the above ranges, components with boiling points higher than NMP and contained in the bottom product of the first column can be effectively removed.

[0036] Step (4): The purified NMP separated by the second purification process is discharged from the system through the top of the second distillation column. The product from the bottom of the second distillation column is discharged through the bottom of the second distillation column. According to one embodiment of the present invention, a method for purifying NMP includes the following steps: discharging purified NMP separated by a second purification process to the outside of the system through the top of a second distillation column; and discharging the bottom product of the second distillation column through the bottom of the second distillation column.

[0037] Specifically, in step (4), purified NMP can be obtained as the second bottom product containing components with boiling points higher than NMP is separated from and discharged from the first bottom product through the second purification in step (3).

[0038] The second bottom product may contain 1.0% by weight or less of a component with a boiling point higher than that of NMP. For example, based on the total weight of the second bottom product, the content of the component with a boiling point higher than that of NMP in the second bottom product may be 0.8% by weight or less, 0.6% by weight or less, or 0.4% by weight or less.

[0039] Purified NMP can have a purity of 99.9% or higher. For example, the purity of purified NMP can be 99.92% or higher, 99.94% or higher, or 99.95% or higher.

[0040] Step (5): Feed the discharged second bottom product to the filtrate recovery unit for heat treatment. A method for purifying NMP according to one embodiment of the present invention includes the step of feeding the discharged second bottom product to a filtrate recovery unit for heat treatment.

[0041] Even if the water and components with boiling points higher than NMP contained in the waste NMP are removed through the first and second purification steps described above, the second bottom product discharged through the second purification may still contain NMP.

[0042] The second bottom product may contain 99% by weight or more of NMP. For example, based on the total weight of the second bottom product, the NMP content in the second bottom product may be 99.2% by weight or higher, 99.4% by weight or higher, or 99.6% by weight or higher.

[0043] Since the method for purifying NMP according to one embodiment of the present invention includes the steps of feeding a second bottom product to a filtrate recovery unit and subjecting it to heat treatment, the NMP contained in the second bottom product can be separated in gaseous form. When fed to a second distillation column for a second purification, the recovery rate of NMP can be improved.

[0044] In step (5), heat treatment can be carried out at a temperature of 110°C to 140°C and a pressure of 60 Torr to 100 Torr, with stirring at 20 rpm to 80 rpm. For example, heat treatment can be carried out at a temperature of 115°C to 140°C, 125°C to 138°C, or 128°C to 135°C and a pressure of 65 Torr to 95 Torr or 75 Torr to 85 Torr, with stirring at 25 rpm to 70 rpm or 30 rpm to 60 rpm. As the heat treatment conditions meet the above ranges, the recovery rate of NMP can be further improved.

[0045] Step (6): The bottom product of the third column, separated by heat treatment, is discharged to the system through the bottom of the filtrate recovery device. The system is external; and the NMP-containing gas mixture is discharged through the top of the filtrate recovery unit. A method for purifying NMP according to one embodiment of the present invention includes the following steps: discharging a third bottom product separated by heat treatment to the outside of the system through the bottom of a filtrate recovery device; and discharging a gas mixture containing NMP through the top of the filtrate recovery device.

[0046] Specifically, in step (6), the third bottom product is discharged through the heat treatment in step (5), the component with a boiling point higher than that of NMP can be separated from the second bottom product again, and a gas mixture containing NMP can be obtained from the second bottom product.

[0047] The third bottom product may contain 1.5% by weight or less of a component with a boiling point higher than that of NMP. For example, based on the total weight of the third bottom product, the content of a component with a boiling point higher than that of NMP in the third bottom product may be 1.0% by weight or less, 0.8% by weight or less, or 0.6% by weight or less.

[0048] Furthermore, the gas mixture may contain 98.5% by weight or more of NMP. For example, based on the total weight of the gas mixture, the NMP content in the gas mixture may be 99.0% by weight or higher, 99.2% by weight or higher, or 99.4% by weight or higher.

[0049] Step (7): Feed the discharged gas mixture into the second distillation column. A method for purifying NMP according to one embodiment of the present invention includes the step of feeding the discharged gas mixture into a second distillation column.

[0050] In step (7), the gas mixture may be fed into the middle or lower part of the second distillation column. Specifically, it is preferable to feed the gas mixture into the middle or lower part of the second distillation column for more efficient purification, but this is not a limitation.

[0051] More specifically, the position where the gas mixture is fed into the second distillation column in step (7) can be the same as or lower than the position where the bottom product of the first column is fed into the second distillation column in step (3). When the position where the gas mixture is fed into the second distillation column in step (7) is the same as or lower than the position where the bottom product of the first column is fed into the second distillation column in step (3), NMP can be purified more effectively. In particular, since the high-purity NMP, as the final product, is discharged to the outside of the system through the top of the second distillation column, the bottom product of the first column and the gas mixture must be fed into the middle or lower position of the second distillation column to improve the efficiency of NMP purification. Since the feed position of the gas mixture with low NMP content is set relatively lower than the feed position of the bottom product of the first column, more efficient purification can be achieved.

[0052] NMP purification device An apparatus for purifying NMP according to another embodiment of the present invention includes: a supply unit for supplying waste NMP; a first distillation column for performing a first purification of the supplied waste NMP by distillation, thereby discharging an aqueous overhead product separated by the first purification to the outside of the system through its top and discharging a first bottom product through its bottom; a second distillation column for performing a second purification of the first bottom product by distillation, thereby discharging purified NMP separated by the second purification to the outside of the system through its top and discharging a second bottom product through its bottom; and a filtrate recovery device for heat-treating the second bottom product, discharging a third bottom product separated by the heat treatment to the outside of the system through its bottom and discharging a gaseous mixture containing NMP through its top.

[0053] Figure 2 An example of an NMP purification apparatus according to another embodiment of the present invention is shown. Specifically, Figure 2 An NMP purification apparatus consisting of a supply unit (SD), a first distillation column (D1), a second distillation column (D2), and a filtrate recovery unit (R) is shown.

[0054] First, waste NMP is supplied to the first distillation column (D1) via the supply unit (SD). This supply can be made via the first pump (P1). In this case, the waste NMP can be preheated via the preheater (B1).

[0055] The first distillation column (D1) performs a first purification by distilling the supplied waste NMP. The aqueous overhead product separated by the first purification is discharged outside the system through the top of the first distillation column (D1) (T-1), and the first bottom product is discharged through the bottom of the first distillation column (D1) (Y-1). The discharged first bottom product can be transferred to the second distillation column (D2) (X-1) by the second pump (P2) and can be recycled back to the first distillation column (D1) (S-1). In this case, the first bottom product can be preheated by the first reboiler (B2) before being sent back to the first distillation column (D1).

[0056] The second distillation column (D2) performs a second purification by distilling the bottom product of the feed from the first column. The purified NMP separated by the second purification is discharged outside the system through the top of the second distillation column (D2) (T-2), and the second bottom product is discharged through the bottom of the second distillation column (D2) (Y-2). The purified NMP discharged from the system can be stored in a storage tank. Furthermore, the discharged second bottom product can be transferred to the filtrate recovery unit (R) (X-2) by a third pump (P3) and can be recycled back to the second distillation column (D2) (S-2). In this case, the second bottom product can be preheated by the second reboiler (B3) before being sent back to the second distillation column (D2).

[0057] The filtrate recovery unit (R) heat-treats the second bottom product of the feed. The third bottom product separated by heat treatment is discharged to the outside of the system (Y-3) through the bottom of the filtrate recovery unit (R). In addition, the gas mixture containing NMP separated by heat treatment can be discharged through the top of the filtrate recovery unit (R) and recycled to the second distillation column (D2) (S-3).

[0058] Figure Labels D1: First Distillation Column D2: Second Distillation Column P1: First pump P2: Second pump P3: Third Pump R: Filtrate recovery device SD: Supply Unit B1: Preheater B2: First Reboiler B3: Second Reboiler T-1, T-2, Y-1, Y-2, Y-3: Discharge steps S-1, S-2, S-3: Cyclic steps X-1, X-2: Feeding steps

Claims

1. A method for purifying NMP, comprising: (1) Waste NMP is distilled in a first distillation column for first purification; (2) The water-containing top product separated by the first purification is discharged to the outside of the system through the top of the first distillation column; and the bottom product is discharged through the bottom of the first distillation column. (3) The product discharged from the bottom of the first column is fed into the second distillation column for second purification; (4) The purified NMP separated by the second purification process is discharged to the outside of the system through the top of the second distillation column; The product from the bottom of the second distillation column is discharged through the bottom of the second distillation column. (5) The discharged second bottom product is fed to the filtrate recovery unit for heat treatment; (6) The third bottom product separated by the heat treatment is discharged to the outside of the system through the bottom of the filtrate recovery device; and a gas mixture containing NMP is discharged through the top of the filtrate recovery device; and (7) Feed the discharged gas mixture into the second distillation column.

2. The method for purifying NMP according to claim 1, wherein the waste NMP contains 70% by weight or more of NMP.

3. The method for purifying NMP according to claim 1, wherein in step (1), the waste NMP is fed into the middle or upper part of the first distillation column.

4. The method for purifying NMP according to claim 1, wherein the first bottom product contains 99.9% by weight or higher of NMP.

5. The method for purifying NMP according to claim 1, wherein the water content in the first bottom product is 0.01% or less.

6. The method for purifying NMP according to claim 1, wherein in step (3), the first bottom product is fed into the middle or lower part of the second distillation column.

7. The NMP purification method according to claim 1, wherein the second bottom product contains 99% by weight or higher of NMP.

8. The method for purifying NMP according to claim 1, wherein in step (7), the gas mixture is fed into the middle or lower part of the second distillation column.

9. The method for purifying NMP according to claim 1, wherein the position where the gas mixture is fed into the second distillation column in step (7) is the same as or lower than the position where the bottom product of the first column is fed into the second distillation column in step (3).

10. The method for purifying NMP according to claim 1, wherein the first purification in step (1) is carried out at a temperature of 50°C to 150°C and a pressure of 100 Torr to 130 Torr, and the second purification in step (3) is carried out at a temperature of 120°C to 150°C and a pressure of 50 Torr to 90 Torr.

11. The method for purifying NMP according to claim 1, wherein in step (5), the heat treatment is carried out with stirring at 20 rpm to 80 rpm, at a temperature of 110°C to 140°C and a pressure of 60 Torr to 100 Torr.

12. The method for purifying NMP according to claim 1, wherein the second bottom product contains 1.0% by weight or less of a component with a boiling point higher than that of NMP.

13. The method for purifying NMP according to claim 1, wherein the third bottom product contains 1.5% by weight or less of a component with a boiling point higher than that of NMP.

14. The method for purifying NMP according to claim 1, wherein the gas mixture contains 98.5% by weight or higher of NMP.

15. The method for purifying NMP according to claim 1, wherein the purified NMP in step (4) has a purity of 99.99% or higher.

16. An apparatus for purifying NMP, comprising: Supply unit, which is used to supply waste NMP; The first distillation column is used to perform a first purification of the supplied waste NMP by distillation, thereby discharging the water-containing overhead product separated by the first purification to the outside of the system through its top and discharging the first bottom product through its bottom. The second distillation column is used to perform a second purification on the bottom product of the first column by distillation, thereby discharging the purified NMP separated by the second purification to the outside of the system through its top and discharging the second bottom product through its bottom. as well as A filtrate recovery device is used to heat-treat the second bottom product, thereby discharging the third bottom product separated by the heat treatment to the outside of the system through its bottom and discharging a gas mixture containing NMP through its top.

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