JP7106474B2 - N-methyl-2-pyrrolidone purification method, purification device, recovery purification method, and recovery purification system - Google Patents

Description

The present invention provides a method and apparatus for purifying water-containing N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as NMP; also called N-methyl-2-pyrrolidinone, 1-methyl-2-pyrrolidone, etc.). In particular, it relates to a method and apparatus for purifying hydrous NMP containing N-methylsuccinimide and γ-butyrolactone as impurities, and a method and system for recovering and purifying NMP.

NMP is widely used as a dispersion medium when producing electrodes, particularly positive electrodes, of lithium ion secondary batteries. Electrode active materials, current collectors, and binders are the main constituent materials of each electrode, ie, positive electrode and negative electrode, of a lithium ion secondary battery. As the binder, it is common to use polyvinylidene fluoride (PVDF) dissolved in NMP as a dispersion medium. The electrode is manufactured by applying a slurry obtained by mixing an electrode active material and a binder onto a current collector and evaporating NMP by heating in air, ie, in the presence of oxygen. NMP used for electrode production is recovered by a recovery device because it is released into the air. NMP has the property of being miscible with water, and the recovered NMP contains, for example, up to about 20% by mass of water. Also, when NMP is heated in air, N-methylsuccinimide, which is a reaction product with oxygen in the air, is produced. Therefore, for example, NMP recovered from the electrode manufacturing process of lithium ion secondary batteries contains N-methylsuccinimide. In addition, since NMP is industrially produced using a dehydration condensation reaction between γ-butyrolactone and methylamine, γ-butyrolactone may remain in product NMP. Even if NMP is heated in the air, it is considered that γ-butyrolactone is hardly generated newly, but since γ-butyrolactone continues to remain in NMP during the electrode manufacturing process, γ-butyrolactone is also included in recovered NMP. may be included, and the concentration of γ-butyrolactone may relatively increase as NMP decreases due to oxidation or the like.

NMP used in the production of lithium ion secondary batteries is required to be of high purity from which impurities such as moisture and metals have been removed. It is preferable to reuse the NMP recovered from the electrode manufacturing process of the lithium ion secondary battery, but the recovered NMP contains the above-mentioned N-methylsuccinimide, γ-butyrolactone, other organic impurities, and metal impurities. etc. are included. For reuse, it is necessary to purify recovered NMP, and various purification methods suitable for NMP recycling have been proposed. For example, US Pat. No. 6,200,001 discloses the removal of amines and metal ions from N-substituted lactams such as NMP by using strongly acidic macroporous cation exchangers with sulfonic acid groups as anchor groups. Patent document 2 discloses purifying recovered NMP by distillation. Further, Patent Document 2 describes, as examples of impurities contained in recovered NMP, low-boiling components such as formic acid having a boiling point between the boiling point of water and the boiling point of NMP, γ-butyl lactone derived from NMP, N - with high boiling components such as methylsuccinimide.

In Patent Document 3, in order to prevent coloration when PVDF or the like is dissolved in NMP, basic substances that are impurities that cause coloration are neutralized with an acidic substance or adsorbed with a porous substance. It discloses pre-removal from the NMP by means of In Patent Document 3, an ion exchange resin is mentioned as an example of an acidic substance, and an anion exchange resin is also included in the ion exchange resin. you can't. The NMP to be treated in Patent Document 3 is obtained by the reaction of, for example, γ-butyrolactone and ammonia or amines, and basically contains almost no water. Patent Literature 4 discloses passing NMP through an anion exchange resin in order to remove corrosive acids from NMP. As a preferred embodiment, an example using Amberlite® IRA458, an acrylic strongly basic anion exchange resin, is shown.

JP-A-2000-256314 JP 2012-188369 A JP-A-11-71346 GB 2088850

NMP used in the production of lithium ion secondary batteries, etc. is required to be of high purity, so when reusing NMP recovered from the process, N-methylsuccinimide and γ-butyrolactone contained in the recovered NMP It is necessary to remove impurities such as In principle, N-methylsuccinimide can be removed by a distillation method such as that shown in Patent Document 2, but the boiling point of NMP is 202° C. It is 235° C. and the temperature difference between the boiling points of both is small. Similarly, the boiling point of .gamma.-butyrolactone is 204.degree. Therefore, when distilling an NMP solution containing water (boiling point: 100° C.) to obtain dehydrated NMP, in order to reduce the concentration of N-methylsuccinimide and γ-butyrolactone in the dehydrated NMP, a complicated distillation operation is required. Is required. In particular, γ-butyrolactone is difficult to remove by distillation because its boiling point is very close to that of NMP. When NMP is purified by a distillation method and used repeatedly, γ-butyrolactone remains as an impurity in NMP, and when NMP decreases due to oxidation or the like, γ-butyrolactone relatively increases. Therefore, it is desirable to remove N-methylsuccinimide and γ-butyrolactone from the NMP solution prior to distillation. There is also a method of using pervaporation as a method for dehydrating the NMP solution, but since NMP and N-methylsuccinimide cannot be separated by pervaporation, N- Methylsuccinimide should be removed.

Patent Documents 1, 3, and 4 disclose the removal of basic substances, acids, amines, metal ions, etc. contained in NMP. In particular, the removal of N-methylsuccinimide and γ-butyrolactone from NMP solutions containing water is neither disclosed nor suggested.

An object of the present invention is to provide a purification method and a purification apparatus capable of efficiently removing N-methylsuccinimide and γ-butyrolactone as impurities from an NMP solution containing water, and recovering and reusing the NMP solution from the manufacturing process and the like. It is to provide a recovery and purification method and a recovery and purification system for refining for use.

The purification method of the present invention is a purification method for purifying a water-containing N-methyl-2-pyrrolidone (NMP) solution containing at least one of N-methylsuccinimide and γ-butyrolactone as impurities, wherein the NMP solution is It is characterized by having a step of removing impurities through a strongly basic anion exchange resin of the system.

The purifier of the present invention is a purifier for purifying a water-containing NMP solution that contains at least one of N-methylsuccinimide and γ-butyrolactone as an impurity, and is filled with a styrene-based strongly basic anion exchange resin. An exchange device is provided, and the NMP solution is passed through the ion exchange device.

The recovery and purification method of the present invention is a recovery and purification method for recovering and purifying N-methyl-2-pyrrolidone for reuse from the NMP use step using N-methyl-2-pyrrolidone, in which, from the NMP use step, An NMP recovery step of recovering N-methyl-2-pyrrolidone in the form of an N-methyl-2-pyrrolidone solution containing water and passing the N-methyl-2-pyrrolidone solution through a styrenic strongly basic anion exchange resin. and a liquid impurity removal step, wherein at least one of N-methylsuccinimide and γ-butyrolactone is removed from the N-methyl-2-pyrrolidone solution in the impurity removal step.

The recovery and purification method of the present invention is a recovery and purification system for recovering and purifying N-methyl-2-pyrrolidone for reuse from an NMP-using system using N-methyl-2-pyrrolidone, from the NMP-using system, NMP recovery means for recovering N-methyl-2-pyrrolidone in the form of N-methyl-2-pyrrolidone solution containing water, and N-methyl-2-pyrrolidone filled with styrene-based strongly basic anion exchange resin and an ion exchange device through which the solution flows, wherein at least one of N-methylsuccinimide and γ-butyrolactone is removed from the N-methyl-2-pyrrolidone solution in the ion exchange device.

According to the present invention, by passing the NMP solution through a styrene-based strongly basic anion exchange resin, N-methylsuccinimide and γ-butyrolactone in the NMP solution are removed, as will be apparent from the examples described later. can be removed efficiently.

It is a figure which shows the structure of the refiner|purifier of one form of implementation of this invention. It is a figure which shows the structure of the refiner|purifier of another embodiment provided with a distillation apparatus. It is a figure which shows the structure of the refiner|purifier of another embodiment provided with a pervaporation apparatus. It is a figure which shows an example of a structure of a collection|recovery refinement system of NMP. FIG. 4 is a diagram showing another example of the configuration of the NMP recovery and purification system;

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a refiner according to one embodiment of the present invention. The purification apparatus shown in FIG. 1 is composed of an impurity removal apparatus 10 for removing impurities such as N-methylsuccinimide and γ-butyrolactone from an NMP solution containing water. The impurity removal device 10 includes an ion exchange resin tower 11 which is an ion exchange device, and the ion exchange resin tower 11 is filled with an ion exchange resin 12 . The ion-exchange resin tower 11 is connected to a supply pipe 13 for supplying the NMP solution containing water to the ion-exchange resin tower 11 and a discharge pipe 14 for discharging the NMP solution that has passed through the ion-exchange resin tower 11. .

The ion exchange resin 12 packed in the ion exchange resin tower 11 will be described. The ion exchange resin tower 11 is filled with at least a styrene-based strongly basic anion exchange resin. The styrene-based strongly basic anion-exchange resin 12 is a strongly basic anion-exchange resin in which the skeleton of the resin is formed by a styrene polymer or a copolymer containing styrene. The ion-exchange resin tower 11 may be filled with a mixture of a styrene-based strongly basic anion-exchange resin and a cation-exchange resin. Styrenic strongly basic anion exchange resins that can be used in the present invention include Amberjet (registered trademark) 4002 manufactured by Dow Chemical Company, Amberlite (registered trademark) IRA900 manufactured by Dow Chemical Company, and DOWEX MARATHON (manufactured by Dow Chemical Co., Ltd.). registered trademark) MSA, DIAION (registered trademark) PA308 manufactured by Mitsubishi Chemical Corporation, and the like. The form of the styrene-based strongly basic anion exchange resin may be gel type or MR type (macroporous type). A mold is preferred.

Next, purification of the NMP solution using the purification apparatus shown in FIG. 1 will be described. Here, a case of purifying a used NMP solution collected from the electrode manufacturing process of a lithium ion secondary battery will be described. The used NMP solution contains the water used during recovery. In addition, in the electrode manufacturing process of a lithium ion secondary battery, NMP is vaporized by heating in the atmosphere, that is, in the presence of oxygen, so part of NMP is oxidized to form N-methylsuccinimide. Therefore, the spent NMP solution contains N-methylsuccinimide as an impurity. In addition, there is a possibility that γ-butyrolactone, which remains unreacted during the production of NMP, is included as an impurity. The used NMP solution is sent to the supply pipe 13 and supplied to the ion exchange resin tower 11 . The NMP solution supplied to the ion-exchange resin tower 11 flows while diffusing in the ion-exchange resin 12. At this time, N-methylsuccinimide and γ-butyrolactone contained as impurities in the NMP solution are adsorbed on the anion-exchange resin. , is removed from the NMP solution. As a result, the NMP solution from which N-methylsuccinimide and γ-butyrolactone have been removed is removed from the discharge pipe 14 .

The amount of the NMP solution supplied to the ion exchange resin tower 11 is preferably 10 hr or less, that is, ¹ hour, in terms of the space velocity SV (space velocity) of the NMP solution passing through the ion exchange resin tower 11. The volume is set to be 10 times or less of the volume of the ion exchange resin 12 per unit.

FIG. 2 shows a purifier according to another embodiment of the invention. This purifying apparatus is the purifying apparatus shown in FIG. 1, in which a distillation column 20 is arranged as a distillation device after the ion exchange resin column 11, and water and impurities are removed from the NMP solution by distillation to obtain purified NMP. there is The discharge end of discharge line 14 is connected to the inlet of distillation column 20 . In this refiner, the NMP solution from which N-methylsuccinimide and γ-butyrolactone have been removed in the ion-exchange resin column 11 is supplied to the distillation column 20, so that the distillation column 20 can be of a simpler structure while being simple. A high-purity NMP containing almost no impurities such as N-methylsuccinimide and γ-butyrolactone can be obtained from the distillation column 20 by such a distillation operation.

FIG. 3 shows a purifier according to yet another embodiment of the invention. This purifying apparatus is similar to the purifying apparatus shown in FIG. 1, except that a pervaporation apparatus 30 is arranged after the ion-exchange resin column 11, and water is removed from the NMP solution by pervaporation treatment to obtain purified NMP. A pervaporation membrane 31 made of, for example, zeolite is provided inside the pervaporation device 30 . The NMP solution discharged from the ion exchange resin tower 11 is supplied to the pervaporation device 30 through the discharge pipe 14 . Water permeates the pervaporation membrane 31, but other components do not permeate the pervaporation membrane 31, so that water is discharged as water vapor from the permeation side outlet of the permeation vaporization device 30, and purified NMP is discharged from the concentration side outlet. be done. In this refiner, the NMP solution from which N-methylsuccinimide and γ-butyrolactone have been removed in the ion-exchange resin tower 11 is supplied to the pervaporation device 30, so that N-methylsuccinimide and γ- It is possible to obtain purified NMP of high purity which contains almost no butyrolactone. Purified NMP obtained from the concentration-side outlet of the pervaporation device 30 may be supplied to a distillation device to obtain purified NMP of higher purity.

In the above, the purification apparatus based on the present invention has been described by taking as an example the case of purifying the used NMP solution recovered from the electrode manufacturing process of the lithium ion secondary battery. However, the NMP solution targeted by the refining device according to the present invention is not limited to that recovered from the electrode manufacturing process of the lithium ion secondary battery. For example, when NMP is produced using a dehydration condensation reaction between γ-butyrolactone and methylamine, unreacted γ-butyrolactone contained in the produced NMP is removed to increase the purity of the product NMP. can also be used.

Next, an NMP recovery and purification system using the purification apparatus according to the present invention will be described. The NMP purification and recovery system is a system for recovering and purifying NMP from an NMP use system such as a lithium ion secondary battery manufacturing system or an NMP use process for the purpose of reuse. FIG. 4 shows an example of the configuration of an NMP recovery and purification system. The illustrated recovery and purification system recovers NMP discharged in gaseous form from the NMP use system 50, purifies the recovered NMP, and supplies it to the NMP use system 50 for reuse.

NMP is discharged from the NMP use system 50 through a pipe 51 . This recovery and purification system recovers and purifies this NMP, but if the recovered NMP is gaseous, it is difficult to treat it with an ion exchange resin, so a water scrubber 52 is provided as NMP recovery means. The recovered NMP sent from the NMP use system 50 through the pipe 51 comes into contact with water in the water scrubber 52 and is absorbed by the water. As a result, the NMP solution containing water is discharged from the water scrubber 52 . This water-containing NMP solution is supplied through the supply pipe 13 to the impurity removal device 10 of the refiner described with reference to FIG. As a result, impurities such as N-methylsuccinimide and γ-butyrolactone contained in the recovered NMP are removed by the impurity remover 10 , and the NMP solution from which the impurities have been removed is discharged from the discharge pipe 15 . When NMP recovered from the NMP use system 50 is reused, it is generally necessary to remove water contained in the NMP. As the dehydrator 55, for example, one using distillation or one using a pervaporation membrane can be used. The NMP dehydrated by the dehydrator 55 is supplied to the NMP use system 50 via the pipe 56 as purified NMP.

FIG. 5 shows a more specific example of a recovery and purification system incorporating a purification device according to the invention. Here, a case will be described in which NMP is recovered from the lithium secondary battery manufacturing system, purified, and the refined NMP is supplied again to the lithium secondary battery manufacturing system. Here, the NMP recovered in a gaseous state from the lithium secondary battery production system has already been treated by an NMP recovery means (not shown in FIG. 5) such as a water scrubber, and as a result, an NMP aqueous solution containing impurities is produced. shall be supplied in the form The purified NMP supplied to the lithium secondary battery manufacturing system must be anhydrous, and the recovery and purification system removes impurities in the recovered NMP aqueous solution and purifies it, and then dehydrates the NMP aqueous solution. conduct. In the figure, CW means cooling water, BR1 and BR2 means brine, and ST means high temperature steam.

The recovery and purification system 1 includes a first subsystem 100 that removes impurities such as fine particles, dissolved oxygen, and ionic components from the recovered NMP aqueous solution, and particularly removes N-succinimide and γ-butyrolactone as impurities; A second subsystem 200 that removes most of the water from the removed NMP aqueous solution by a pervaporation membrane device to produce an NMP concentrate, and a third subsystem that further distills the NMP concentrate to produce a purified NMP liquid. a system 300; The configuration of each subsystem will be described below.

(First subsystem 100)
The first subsystem 100 includes a stock solution tank 101, and the NMP aqueous solution to be treated recovered from the lithium ion secondary battery manufacturing system is connected to NMP recovery means (not shown) such as a water scrubber. It is supplied to the stock solution tank 101 through the first NMP aqueous solution supply line 151 . The undiluted solution tank 101 is connected via a second NMP aqueous solution supply line 152 to the first microfiltration membrane device 102 for removing fine particles contained in the NMP aqueous solution. A pump 107 for pumping the NMP aqueous solution is provided on the second NMP aqueous solution supply line 152 . The first microfiltration membrane device 102 is provided upstream of the membrane degassing device 103 (described later), but downstream of the membrane degassing device 103, that is, between the membrane degassing device 103 and the ion exchange device 104 (described later). Alternatively, it may be provided both upstream of the membrane degasser 103 and between the membrane degasser 103 and the ion exchange device 104 .

The first microfiltration membrane device 102 is connected via a third NMP aqueous solution supply line 153 to a membrane degassing device 103 that removes dissolved oxygen in the NMP aqueous solution. As will be described later, the NMP aqueous solution is heated to about 120° C. before being introduced into the pervaporation membrane device 201. This heating converts dissolved oxygen contained in the NMP aqueous solution into hydrogen peroxide, and this hydrogen peroxide can oxidize NMP and degrade it. Here, dissolved oxygen in the NMP aqueous solution is removed in advance in order to suppress the oxidation of NMP. The degassing membrane of the membrane deaerator 103 can be made of polyolefin, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyurethane, epoxy resin, or the like. Since NMP has the property of dissolving some organic materials, the degassing membrane is preferably made of polyolefin, PTFE or PFA. The degassing membrane is preferably non-porous. Dissolved oxygen in the NMP aqueous solution flowing inside the hollow fiber-like deaeration membrane moves to the outside of the deaeration membrane, which is made negative by the vacuum pump 109, thereby degassing, that is, removing the dissolved oxygen. An inert gas such as nitrogen gas may be swept to the outside (gas permeation side) of the degassing membrane to lower the oxygen partial pressure, or a vacuum method and a sweep method may be used in combination.

The membrane degassing device 103 is connected to the ion exchange device 104 via a fourth NMP aqueous solution supply line 154 . The ion exchanger 104 is provided to remove ionic components in the NMP aqueous solution, as well as N-methylsuccinimide and γ-butyrolactone. Since N-methylsuccinimide and γ-butyrolactone are removed, the ion exchange unit 104 is filled with at least a styrenic strongly basic anion exchange resin. Furthermore, depending on the type of ion component to be removed, the ion exchange device 104 may be filled with a cation exchange resin. When a cation exchange resin and a styrenic strongly basic anion exchange resin are used in combination, they may be used in a mixed bed or in a multilayer bed. The type of ion exchange resin may be either gel type or MR type, but MR type is preferable because it is intended for NMP aqueous solution.

The ion exchange device 104 is connected to the second microfiltration membrane device 105 via a fifth NMP aqueous solution supply line 155 . The second microfiltration membrane device 105 captures resin that may flow out from the ion exchange device 104 and prevents the resin from flowing downstream. The second microfiltration membrane device 105 is connected to the primary treatment liquid tank 106 via a sixth NMP aqueous solution supply line 156 . The primary treatment liquid tank 106 receives the NMP aqueous solution treated by the first microfiltration membrane device 102, the membrane degassing device 103, the ion exchange device 104 and the second microfiltration membrane device 105, and the received NMP aqueous solution It is supplied to the pervaporation membrane device 201 . Hereinafter, the NMP aqueous solution stored in the primary treatment liquid tank 106 and supplied to the pervaporation membrane device 201 may be referred to as the primary treatment liquid.

(Second subsystem 200)
The primary treatment liquid from which particles, dissolved oxygen, and ion components have been removed and stored in the primary treatment liquid tank 106 is then supplied to the second subsystem 200 to produce an NMP concentrate from which most of the moisture has been removed. be done. The primary treatment liquid tank 106 is connected to the pervaporation membrane device 201 via a seventh NMP aqueous solution supply line 251 . A pump 224 is provided in the seventh NMP aqueous solution supply line 251 . A first heater 205 using external steam and a waste heat recovery heat exchanger 206 located upstream (primary side) of the first heater 205 are installed in the seventh NMP aqueous solution supply line 251. , the NMP aqueous solution is heated to about 120° C. by the first heater 205 and the waste heat recovery heat exchanger 206 . By heating the NMP aqueous solution to about 120° C., the dehydration performance of the pervaporation membrane device 201 can be enhanced. The waste heat recovery heat exchanger 206 exchanges heat between the NMP aqueous solution flowing through the seventh NMP aqueous solution supply line 251 and the NMP concentrated liquid flowing through the NMP concentrated liquid discharge line 254 . A first heater 205 heats the NMP aqueous solution with high temperature steam supplied from an external steam source (not shown).

The pervaporation membrane device 201 has a plurality of pervaporation membrane modules connected in series. In this embodiment, there are three pervaporation membrane modules 202 to 204, that is, the first pervaporation membrane module 202, the second pervaporation membrane module 203, and the third pervaporation membrane module 204 are arranged in series from upstream to downstream. , but the number is not limited to three. The first pervaporation membrane module 202 is connected to the second pervaporation membrane module 203 via a first connection line 252 . The second pervaporation membrane module 203 is connected to the third pervaporation membrane module 204 via a second connection line 253 . The first to third pervaporation membrane devices 202, 203, and 204 are separated by separation membranes (pervaporation membranes) 202c, 203c, and 204c. 204b. Since the separation membranes 202c, 203c, and 204c have affinity for water, water permeates the separation membranes 202c, 203c, and 204c at a higher permeation rate than NMP. By applying a negative pressure to the permeation chambers 202b, 203b, and 204b, water with a high permeation rate and a small amount of NMP with a low permeation rate move to the permeation chambers 202b, 203b, and 204b in the form of vapor (gas phase). of NMP remain in concentrating compartments 202a, 203a and 204a. Using this principle, part of the water is removed from the aqueous NMP solution to produce a concentrate of the aqueous NMP solution. At the outlet of the third pervaporation membrane module 204, an NMP concentrate (water content of less than 0.01% by mass) with an NMP concentration increased to approximately 99.99% by mass is obtained.

The NMP aqueous solution sequentially flows through the first to third pervaporation membrane modules 202, 203, and 204, and water in the NMP aqueous solution is gradually removed. In order to maintain the moisture removal efficiency, the first connection line 252 and the second connection line 253 are provided with the second heater 207 and the third heater 208, respectively. Like the first heater 205, the second and third heaters 207 and 208 are heat exchangers, and heat the NMP aqueous solution to about 120° C. with high-temperature steam supplied from an external steam source. The NMP concentrate discharged from the third pervaporation membrane module 204 is supplied to the relay tank 301 of the third subsystem 300 through the NMP concentrate discharge line 254 . As described above, the NMP concentrated liquid flowing through the NMP concentrated liquid discharge line 254 is heat-exchanged with the NMP aqueous solution flowing through the seventh NMP aqueous solution supply line 251 by the waste heat recovery type heat exchanger 206, and NMP Preheat the aqueous solution.

The permeation chambers 202b, 203b, 204b of the first to third permeation membrane modules 202, 203, 204 are connected to the first to third permeate tanks by the first to third permeate discharge lines 256, 259, 262, respectively. 214, 215 and 216. Above the first to third permeate tanks 214, 215, and 216, a negative pressure is applied to the permeation chambers 202b, 203b, and 204b, and the inside of the permeation chambers 202b, 203b, and 204b can be maintained at a negative pressure. First to third vacuum pumps 217, 218, 219 are provided. Vapor phase water and a small amount of NMP are condensed by the cooling water or brine and collected as permeate at the bottom of the first to third permeate tanks 214 , 215 and 216 . The first to third permeate tanks 214, 215, 216 can temporarily store the permeate. Specifically, cooling water CW and brines BR1 and BR2 are supplied to first to third heat exchangers 211, 212 and 213 provided in first to third permeate discharge lines 256, 259 and 262, respectively. It condenses water and NMP in the gas phase. The temperature of the brines BR1 and BR2 is preferably about 0 to -20°C. First to third permeate discharge lines 258, 261 and 264 are connected to the bottoms of the first to third permeate tanks 214, 215 and 216, respectively. The permeated water discharged from the first permeated liquid tank 214 is discharged to a waste liquid tank, and the permeated water discharged from the second to third permeated liquid tanks 215 and 216 is reused as described later.

The most upstream, that is, the first pervaporation membrane module 202 has a pervaporation membrane 202c made of CHA, T, Y, or MOR zeolite, and the other pervaporation membrane modules, that is, the second and third The pervaporation membrane modules 203 and 204 have pervaporation membranes 203c and 204c made of A-type zeolite. A-type zeolite is relatively inexpensive and has high dehydration performance, but is prone to leakage and performance degradation when treating an NMP aqueous solution with a high water concentration. On the other hand, zeolites other than type A can maintain their performance for a longer period of time in the above environment. For this reason, CHA type, T type, Y type or MOR type zeolite is used for the pervaporation membrane 202c of the first pervaporation membrane module 202 for treating an NMP aqueous solution containing 10 to 20% by mass of water. A-type zeolite is used for the pervaporation membranes 203c and 204c of the second and third pervaporation membrane modules 203 and 204 for treating the NMP aqueous solution with a small content. It is not necessary that all of the plurality of pervaporation membranes constituting the first pervaporation membrane module 202 are made of CHA type, T type, Y type or MOR type zeolite, and some of the membranes are made of A type zeolite. may consist of

The permeated liquids of the second and third pervaporation membrane modules 203 and 204 are recovered upstream of the pervaporation membrane device 201 . Specifically, the second and third permeated liquid discharge lines 261 and 264 are connected to the permeated liquid recovery line 255 , and the permeated liquid recovery line 255 is connected to the primary treatment liquid tank 106 . Since the permeated liquid discharged from the second and third permeated liquid discharge lines 261 and 264 has a higher NMP content than the permeated liquid discharged from the first permeated liquid discharge line 258, it is recovered , the recovery of NMP can be increased. The pervaporation membrane modules in which the permeated liquid is recovered are not limited to the second and third pervaporation membrane modules 203 and 204, and at least the permeate of the most downstream, that is, the third pervaporation membrane module 204 is the pervaporation membrane device. 201 may be collected upstream. The permeated liquid may be recovered in the raw liquid tank 101, or may be selectively recovered in the primary treatment liquid tank 106 and the raw liquid tank 101 by providing a branch line (not shown) in the permeated liquid recovery line 255. good.

(Third subsystem 300)
The NMP concentrate produced in the second subsystem 200 has most of the water removed. However, since the NMP concentrate contains a small amount of fine particles and ion components of the pervaporation membranes 202c, 203c, and 204c eluted from the pervaporation membrane module and the chromaticity component, the third liquid located downstream of the pervaporation membrane device 201 Distillation in subsystem 300 produces NMP purified liquid. Although the third subsystem 300 described below uses a simple distillation method, the distillation method is not limited as long as the NMP concentrate can be distilled, and for example, a precision distillation method can also be used. The simple distillation method is preferred because it consumes little energy, has a small equipment size, and is easy to operate. Moreover, among the simple distillation methods, the vacuum simple distillation method used in the present embodiment is particularly desirable from the viewpoint of preventing thermal deterioration.

The third subsystem 300 is a subsystem independent from the second subsystem 200. For example, the operation of temporarily stopping the operation of the third subsystem 300 while the second subsystem 200 is operating is performed. may be done. Therefore, by providing a relay tank 301 that temporarily stores the NMP concentrate, the second subsystem 200 and the third subsystem 300 can be operated more flexibly while maintaining mutual independence. becomes. Relay tank 301 is connected to regenerator 302 via first NMP concentrate supply line 351 . A pump 306 is provided in the first NMP concentrate supply line 351 . The regenerator 302 is a heat exchanger that exchanges heat with the concentrated NMP liquid (hereinafter referred to as NMP purified gas) evaporated in the evaporator 303, which will be described later. Thereby, the heat load of the evaporator 303 can be reduced. Regenerator 302 is connected to evaporator 303 via second NMP concentrate supply line 352 . Evaporator 303 heats and vaporizes the NMP concentrate with hot steam supplied from an external steam source (not shown). At the bottom of the evaporator 303, the high-temperature liquid-phase NMP concentrated liquid stays, and the gas-phase NMP purified gas from which fine particles are removed is formed at the upper part. Since the chromaticity component contained in the NMP concentrate in the liquid phase is also difficult to evaporate, it accumulates at the bottom of the evaporator 303 . As the evaporator 303 in the present embodiment, a liquid film flow type evaporator will be described below as an example. may be used. A circulation line 353 is connected to the bottom and top of the evaporator 303 , and a circulation path including the evaporator 303 is formed by the circulation line 353 . On the circulation path, the liquid-phase NMP concentrated liquid is taken out, returned to the evaporator 303, and heated again under liquid film flow, and this cycle is repeated. An NMP concentrate withdrawal line 356 that merges with the circulation line 353 is provided at the bottom of the steam withdrawal can 304 (described later). The NMP concentrate remaining at the bottom of the vapor take-out can 304 is also returned to the evaporator 303 through the NMP concentrate take-out line 356 and the circulation line 353 and heated again. A circulation pump 307 is provided in the circulation line 353 .

The NMP purified gas in the evaporator 303 is taken out from the gas phase portion of the evaporator 303 and taken out to the steam take-out can 304 by the first NMP-purified gas take-out line 354 . Steam take-off can 304 is connected to regenerator 302 via second NMP purified gas take-off line 355 . The heat of the NMP purified gas is heat exchanged with the liquid phase NMP concentrate in the regenerator 302 . The purified NMP gas exiting the regenerator 302 is further introduced into the condenser 305 through the third NMP purified gas extraction line 357, where it is condensed by the cooling water CW to become purified NMP liquid. Inside the condenser 305, NMP purified liquid is stored at the bottom, and above it is a gas phase portion composed of NMP purified gas. The gas phase portion of the capacitor 305 communicates with the vacuum pump 309 through a negative pressure line 360 , and the gas phase portion of the capacitor 305 is made negative by the vacuum pump 309 . The gas phase portion of the third subsystem 300 including the evaporator 303 is also brought to a negative pressure by the vacuum pump 309, and the reduced pressure evaporation is performed in the evaporator 303. This facilitates evaporation of the NMP concentrate. An NMP purified liquid extraction pipe 358 is connected to the outlet of the condenser 305 . The purified NMP liquid is sent to the purified liquid tank 311 by the pump 308 provided in the NMP purified liquid take-out pipe 358 . The NMP purified liquid temporarily stored in the purified liquid tank 311 is transferred through the discharge line 362 to the lithium ion secondary battery manufacturing system and reused in the manufacturing system.

Next, the present invention will be described in more detail based on examples and comparative examples.

[Example 1: Using a styrene-based strongly basic anion exchange resin]
Experiments were performed on the removal of N-methylsuccinimide from NMP solutions. Ultrapure water was added to N-methyl-2-pyrrolidinone (manufactured by Kanto Kagaku) so as to make it 3 mass%, and N-methylsuccinimide (manufactured by Tokyo Kasei Kogyo) was added so that it became 0.1 mass%. An NMP solution was prepared. A column made of polytetrafluoroethylene was filled with 100 mL of a styrene-based strongly basic anion exchange resin Amberlite (registered trademark) IRA900 (OH) manufactured by Dow Chemical Co. to prepare an ion exchange resin column. After filling the column, the anion exchange resin in the column was washed with water, and after washing, the previously prepared NMP solution was passed through the column at 100 mL/hr, that is, SV=1 (hr ^-1 ). After blowing 100 mL of the liquid discharged from the column until the water in the column is replaced with the NMP solution, the NMP solution discharged from the column is sampled and analyzed by gas chromatography to determine the NMP concentration and N-methylsuccinimide concentration was determined. A gas chromatograph GC-2014 manufactured by Shimadzu Corporation was used for the gas chromatography analysis. Analysis conditions are as shown in Table 1. Table 2 shows the NMP and N-methylsuccinimide concentrations obtained.

Since moisture cannot be detected with a flame ionization detector, the concentrations of NMP and N-methylsuccinimide are calculated from the peak area ratios of NMP, N-methylsuccinimide, and γ-butyrolactone excluding moisture in the obtained gas chromatogram. did. γ-Butyrolactone is a raw material for synthesizing NMP and is derived from NMP.

Similarly, the NMP solution was passed through the column so that the flow rate was SV = 2, 3, 4, 5, 6, 7, 8, 9, 10 (hr ^-1 ), and in each case , NMP concentration and N-methylsuccinimide concentration in the NMP solution discharged from the column were determined by gas chromatography analysis. Separately, the NMP concentration and the N-methylsuccinimide concentration in the NMP solution before passing through the column were determined by gas chromatography analysis. These results are also shown in Table 2. As shown in Table 2, when a styrene-based strongly basic anion exchange resin was used and the amount of liquid passed through the anion exchange resin was SV10 or less, the N-methylsuccinimide concentration represented by the NMP area ratio was 0.00. was less than 0.2%. From this, it was found that N-methylsuccinimide in the NMP solution can be removed by passing the NMP solution through a styrene-based strongly basic anion exchange resin.

[Comparative Example 1: Using an acrylic strongly basic anion exchange resin]
As the anion exchange resin to be packed in the column, a liquid flow test of NMP solution was performed in the same manner as in Example 1 except that Amberlite (registered trademark) IRA458 manufactured by Dow Chemical Co., Ltd., which is an acrylic strongly basic anion exchange resin, was used. was performed, and the NMP concentration and the N-methylsuccinimide concentration in the NMP solution discharged from the column were determined by gas chromatography analysis. Table 3 shows the results. Unlike Example 1, N-methylsuccinimide could not be removed by adsorption.

[Comparative Example 2: Using Weakly Basic Anion Exchange Resin]
As the anion exchange resin to be packed in the column, the NMP solution passage test was performed in the same manner as in Example 1 except that Amberlite (registered trademark) IRA96SB manufactured by Dow Chemical Co., Ltd., which is an acrylic weakly basic anion exchange resin, was used. was performed, and the NMP concentration and the N-methylsuccinimide concentration in the NMP solution discharged from the column were determined by gas chromatography analysis. Table 4 shows the results. Unlike Example 1, N-methylsuccinimide could not be removed by adsorption.

From the results of Example 1 and Comparative Examples 1 and 2, when removing N-methylsuccinimide contained as an impurity in the NMP solution, the differences in the skeleton of the polymer that is the base of the anion exchange resin caused a large difference in the results. Although N-methylsuccinimide could be removed with a styrene-based strongly basic anion exchange resin, N-methylsuccinimide could not be removed even with an acrylic strongly basic anion-exchange resin. , found it necessary to use a styrenic one as the strongly basic anion exchange resin.

[Example 2: Using a styrene-based strongly basic anion exchange resin]
Experiments were conducted on the removal of γ-butyrolactone from NMP solutions. NMP obtained by adding ultrapure water to N-methyl-2-pyrrolidinone (manufactured by Kanto Kagaku) to a concentration of 3% by mass, and further adding γ-butyrolactone (manufactured by Kanto Kagaku) to a concentration of 0.1% by mass. A solution was prepared. A column made of polytetrafluoroethylene was filled with 100 mL of a styrene-based strongly basic anion exchange resin Amberlite (registered trademark) IRA900 (OH) manufactured by Dow Chemical Co. to prepare an ion exchange resin column. After filling the column, the anion exchange resin in the column was washed with water, and after washing, the previously prepared NMP solution was passed through the column at 100 mL/hr, that is, SV=1 (hr ^-1 ). Of the liquid discharged from the column, after blowing 100 mL until the water in the column is replaced with the NMP solution, the NMP solution discharged from the column is collected and analyzed by gas chromatography in the same manner as in Example 1. was performed to determine the NMP concentration and the γ-butyrolactone concentration. Analysis conditions are as shown in Table 1. Since moisture cannot be detected with a hydrogen flame ionization detector, as in Example 1, from the area ratio of the peaks of NMP excluding moisture, γ-butyrolactone, and other components in the gas chromatogram obtained, NMP and The concentration of γ-butyrolactone was calculated. Table 5 shows the NMP and γ-butyrolactone concentrations obtained.

Similarly, the NMP solution was passed through the column so that the flow rate was SV = 5 and 10 (hr ^-1 ), respectively. Butyrolactone concentration was determined by gas chromatographic analysis. Separately, the NMP concentration and the γ-butyrolactone concentration in the NMP solution before passing through the column were determined by gas chromatography analysis. These results are also shown in Table 5. As shown in Table 5, when a styrene-based strongly basic anion exchange resin was used and the amount of liquid passed through the anion exchange resin was set to SV10 or less, the γ-butyrolactone concentration represented by the NMP area ratio was 0.03. %. In particular, γ-butyrolactone could be almost completely adsorbed and removed when the flow rate was SV5 or less. From this, it was found that γ-butyrolactane in the NMP solution can be removed by passing the NMP solution through a styrene-based strongly basic anion exchange resin.

[Comparative Example 3: Using an acrylic strongly basic anion exchange resin]
As the anion exchange resin to be packed in the column, the liquid flow test of the NMP solution was performed in the same manner as in Example 2 except that Amberlite (registered trademark) IRA458 manufactured by Dow Chemical Co., Ltd., which is an acrylic strongly basic anion exchange resin, was used. was performed, and the NMP concentration and γ-butyrolactone concentration in the NMP solution discharged from the column were determined by gas chromatography analysis. Table 6 shows the results. Unlike Example 2, although some adsorption and removal were possible in the region where the flow rate was very small, γ-butyrotactone could not be sufficiently adsorbed and removed as a whole.

[Comparative Example 4: Using weakly basic anion exchange resin]
As the anion exchange resin packed in the column, the NMP solution passage test was performed in the same manner as in Example 2 except that Amberlite (registered trademark) IRA96SB manufactured by Dow Chemical Co., Ltd., which is an acrylic weakly basic anion exchange resin, was used. was performed, and the NMP concentration and γ-butyrolactone concentration in the NMP solution discharged from the column were determined by gas chromatography analysis. Table 7 shows the results. Unlike Example 2, although some adsorption and removal were possible in the region where the flow rate was very small, γ-butyrotactone could not be sufficiently adsorbed and removed as a whole.

[Example 4: Use of styrene-based strongly basic anion exchange resin]
Experiments were conducted on the simultaneous removal of N-methylsuccinimide and γ-butyrolactone from NMP solutions. Ultrapure water was added to N-methyl-2-pyrrolidinone (manufactured by Kanto Chemical Co., Ltd.) to make it 3% by mass, and N-methylsuccinimide (manufactured by Tokyo Chemical Industry Co., Ltd.) and γ-butyrolactone (manufactured by Kanto Chemical Industry) were added respectively. An NMP solution was prepared with addition of 0.025% by mass. A column made of polytetrafluoroethylene was filled with 100 mL of a styrene-based strongly basic anion exchange resin Amberlite (registered trademark) IRA900 (OH) manufactured by Dow Chemical Co. to prepare an ion exchange resin column. After filling the column, the anion exchange resin in the column was washed with water, and after washing, the previously prepared NMP solution was passed through the column at 1000 mL/hr, that is, SV=10 (hr ^-1 ). Of the liquid discharged from the column, after blowing 100 mL until the water in the column is replaced with the NMP solution, the NMP solution discharged from the column is collected and analyzed by gas chromatography in the same manner as in Example 1. was carried out to determine the respective concentrations of NMP, N-methylsuccinimide and γ-butyrolactone. Analysis conditions are as shown in Table 1. Since moisture cannot be detected with a flame ionization detector, NMP was determined from the area ratio of the peaks of NMP, γ-butyrolactone, and N-methylsuccinimide excluding moisture in the gas chromatogram obtained in the same manner as in Example 1. , N-methylsuccinimide and γ-butyrolactone concentrations were calculated. The concentrations obtained are shown in Table 8.

From the results shown in Table 8, even when the NMP solution contains both γ-butyrolactone and N-methylsuccinimide as impurities, by passing the NMP solution through the styrene-based strongly basic anion exchange resin, both of these It was found that the impurities of In addition, as can be seen from the numerical value of the NMP concentration area ratio, there is a peak that is neither γ-butyrolactone nor N-methylsuccinimide before the passage of the solution. It means that it contains impurities that are not even. On the other hand, in the measurement results after passing the solution through the styrene-based strongly basic anion exchange resin, the area ratio of the peaks other than γ-butyrolactone and N-methylsuccinimide also decreased. Although the chemical species is not specifically specified, this means that the purification method according to the present invention allows the purification of NMP, such as 5-hydroxy-N-methylpyrrolidone, 1,3-dimethylpyrrolidone, and 1,4-dimethylpyrrolidone. It is thought that it is possible to adsorb and remove impurities such as

REFERENCE SIGNS LIST 10 impurity removal device 11 ion exchange resin tower 12 anion exchange resin 13 supply pipe 14 discharge pipe 20 distillation column 30 pervaporation device 31 pervaporation membrane

Claims (13)

In a purification method for purifying a water-containing N-methyl-2-pyrrolidone solution containing at least one of N-methylsuccinimide and γ-butyrolactone as an impurity,
A purification method comprising a step of removing impurities by passing the N-methyl-2-pyrrolidone solution through a styrene-based strongly basic anion exchange resin. 2. The purification method according to claim 1, wherein the N-methyl-2-pyrrolidone in the N-methyl-2-pyrrolidone solution is heated and evaporated in the presence of oxygen. 3. The purification method according to claim 1, wherein the N-methyl-2-pyrrolidone solution is recovered from the electrode manufacturing process of a lithium ion secondary battery. A first step of distilling the N-methyl-2-pyrrolidone solution discharged from the impurity removal step, and a pervaporation membrane for the N-methyl-2-pyrrolidone solution discharged from the impurity removal step. 4. The purification method according to any one of claims 1 to 3, comprising at least one of a second step of selectively separating water from the N-methyl-2-pyrrolidone solution by supplying it to a pervaporation device. . 5. The purification method according to any one of claims 1 to 4, wherein the N-methylsuccinimide concentration in the N-methyl-2-pyrrolidone solution is 0.1% by mass or more. The purification according to any one of claims 1 to 5, wherein the N-methyl-2-pyrrolidone solution is passed through the styrene-based strongly basic anion exchange resin at a space velocity of 10 or less per hour. Method. In a purification apparatus for purifying a water-containing N-methyl-2-pyrrolidone solution containing at least one of N-methylsuccinimide and γ-butyrolactone as an impurity,
Equipped with an ion exchange device filled with styrene-based strongly basic anion exchange resin,
A purification apparatus, wherein the N-methyl-2-pyrrolidone solution is passed through the ion exchange apparatus. 8. The purification apparatus according to claim 7, wherein the N-methyl-2-pyrrolidone solution is passed through the ion exchange apparatus at a space velocity of 10 or less per hour. The purification device according to claim 7 or 8, comprising at least one of a distillation device and a pervaporation membrane after the ion exchange device. In a recovery and purification method for recovering and purifying N-methyl-2-pyrrolidone for reuse from a process using NMP using N-methyl-2-pyrrolidone,
an NMP recovery step of recovering N-methyl-2-pyrrolidone from the NMP use step in the form of a water-containing N-methyl-2-pyrrolidone solution;
an impurity removal step of passing the N-methyl-2-pyrrolidone solution through a styrene-based strongly basic anion exchange resin;
has
The recovery and purification method, wherein at least one of N-methylsuccinimide and γ-butyrolactone is removed from the N-methyl-2-pyrrolidone solution in the impurity removal step. further comprising a dehydration step of dehydrating the N-methyl-2-pyrrolidone solution discharged from the impurity removal step to produce a purified N-methyl-2-pyrrolidone solution;
11. The recovery and purification method according to claim 10, wherein said purified N-methyl-2-pyrrolidone solution is supplied to said step of using NMP. In a recovery and purification system for recovering and purifying N-methyl-2-pyrrolidone for reuse from an NMP-using system using N-methyl-2-pyrrolidone,
NMP recovery means for recovering N-methyl-2-pyrrolidone from the NMP-using system in the form of a water-containing N-methyl-2-pyrrolidone solution;
an ion exchange device filled with a styrene-based strongly basic anion exchange resin and through which the N-methyl-2-pyrrolidone solution flows;
with
A recovery and purification system, wherein at least one of N-methylsuccinimide and γ-butyrolactone is removed from the N-methyl-2-pyrrolidone solution in the ion exchange device. A dehydration means for dehydrating the N-methyl-2-pyrrolidone solution to produce a purified N-methyl-2-pyrrolidone solution is further provided in the subsequent stage of the ion exchange device,
13. The recovery and purification system according to claim 12, wherein the purified N-methyl-2-pyrrolidone liquid is supplied to the NMP use system.

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