JP7220597B2 - Organic solvent distillation purification device and distillation purification method - Google Patents

Description

The present invention relates to an organic solvent distillation purification apparatus and a distillation purification method.

Conventionally, a method of separating NMP from a mixture of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) and water (hereinafter referred to as NMP aqueous solution) using pervaporation method (PV method) is known. there is The PV method is superior in energy saving performance as compared with the method of distilling the NMP aqueous solution under reduced pressure (reduced pressure distillation method). In the PV method, a pervaporation membrane device having a separation membrane (pervaporation membrane) having an affinity for water is used. By supplying the NMP aqueous solution to the inlet side of the pervaporation membrane and reducing the pressure on the permeate side, a driving force for moving the NMP aqueous solution from the inlet side to the permeate side can be obtained. At this time, due to the difference in permeation speed between NMP and water, mainly water moves to the permeation side, and NMP and water are separated.

Since the NMP aqueous solution (NMP concentrate) from which water has been separated contains a small amount of fine particles and ion components, it is further distilled in a distillation purification device located downstream of the pervaporation membrane device to remove these impurities. Patent Document 1 discloses an NMP distillation purification apparatus equipped with an evaporator that evaporates an NMP concentrated liquid to generate an NMP purified gas and a condenser that condenses the NMP purified gas to produce an NMP purified liquid. there is A vacuum pump is connected to the condenser to maintain a negative pressure in the distillation purification apparatus.

WO2018/207431

If the cooling capacity of the condenser is reduced for some reason, the NMP purified gas remaining in the condenser without being condensed increases. This increases the amount of NMP drawn by the vacuum pump from the condenser. The purified NMP gas in the condenser has extremely high purity, and once it is sucked by the vacuum pump, it is discharged outside the system without being recovered. It is not preferable from the point of view. The above points are the same for concentrated liquids of organic solvents other than NMP.

SUMMARY OF THE INVENTION An object of the present invention is to provide a distillation purification apparatus capable of suppressing the loss of an organic solvent when producing a purified liquid of the organic solvent.

The organic solvent distillation purification apparatus of the present invention comprises an evaporator for evaporating the organic solvent, a condenser for condensing the vapor of the organic solvent generated in the evaporator, a vacuum pump communicating with the gas phase portion of the condenser, a condenser and the vacuum. a gas cooler provided between the pump and condensing the vapor flowing in from the gas phase by the negative pressure generated by the vacuum pump; and a circulation line connected to the bottom and top of the evaporator to form a circulation path including the evaporator , an impurity discharge line that branches off from the circulation line and discharges the organic solvent containing impurities accumulated at the bottom of the evaporator, and a cooling waste water discharge line that is connected to the condenser and discharges the cooling waste water after cooling the vapor of the organic solvent. and a heat exchanger provided in the impurity discharge line for cooling the organic solvent containing the impurities by heat exchange with the cooling waste water flowing through the cooling waste water discharge line. A valve is provided in each of the circulation line and the impurity discharge line, and one of the valve of the circulation line and the valve of the impurity discharge line is closed when the other is opened.

According to the invention, the vapor coming from the vapor phase of the condenser is condensed by the underpressure created by the vacuum pump before being drawn by the vacuum pump. Therefore, according to the present invention, it is possible to provide a distillation purification apparatus capable of suppressing the loss of the organic solvent when producing the purified liquid of the organic solvent.

1 is a schematic configuration diagram of an NMP aqueous solution distillation purification system according to an embodiment of the present invention. FIG.

Examples of organic solvents applicable to the present invention include alcohols such as methanol, ethanol, and 2-propanol. An organic solvent having a boiling point under atmospheric pressure of 120° C. or higher, which is the general operating temperature of a pervaporation membrane device, can be mentioned. Examples of such organic solvents are shown in Table 1.

FIG. 1 shows a schematic configuration diagram of an NMP aqueous solution purification system 1 according to one embodiment of the present invention. In the figure, CW means cooling water, BR1 and BR2 means brine, and ST means high temperature steam.

NMP is one of the organic solvents with high solubility in water. For example, in the manufacturing process of a lithium ion secondary battery, NMP is used as a slurry dispersion medium when forming an electrode by applying a slurry in which particles such as an electrode active material are dispersed on an electrode current collector and drying it. Widely used. NMP is recovered when the slurry is dried, and the recovered NMP can be reused after purification. NMP is recovered as a mixed solution (NMP aqueous solution) in which NMP and water are mixed, for example, using a water scrubber. The NMP concentration in the recovered NMP aqueous solution is about 70 to 99% by weight.

The NMP aqueous solution purification system 1 includes a first subsystem 100 that removes fine particles, dissolved oxygen, ionic components, etc. from the NMP aqueous solution, and a pervaporation membrane device from the NMP aqueous solution from which fine particles, dissolved oxygen, ionic components, etc. have been removed. It has a second subsystem 200 that removes most of the water to produce an NMP concentrate and a third subsystem 300 that distills the NMP concentrate to produce a purified NMP liquid. The configuration of each subsystem will be described below.

(First subsystem 100)
The first subsystem 100 has a receiving section 101 that receives the NMP aqueous solution to be treated that has been collected as described above. The NMP aqueous solution is supplied to the receiving section 101 through a first NMP aqueous solution supply line L101 connected to NMP recovery means (not shown) such as a water scrubber. The receiving unit 101 has a plurality of containers (first to third containers 101a, 101b, 101c), and these containers 101a, 101b, 101c receive, analyze, and analyze the undiluted NMP aqueous solution supplied to the purification system 1. It can be switched according to the purpose such as transportation. If there is no problem as a result of the analysis, the NMP aqueous solution is transferred to the subsequent stage and subjected to purification treatment, and if it is not suitable for purification treatment, it is transferred to a waste liquid tank (not shown). The receiving unit 101 is connected via a second NMP aqueous solution supply line L102 to a first microfiltration membrane device 102 that removes 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 L102. 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 L103 to a membrane degassing device 103 that removes dissolved oxygen from 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 . In the NMP aqueous solution heated to about 120° C., dissolved oxygen contained in the NMP aqueous solution becomes hydrogen peroxide, and this hydrogen peroxide may oxidize and deteriorate NMP. Oxidation of NMP can be suppressed by removing dissolved oxygen in the NMP aqueous solution in advance. In order to monitor the concentration of dissolved oxygen, the inlet line L103 and the outlet line L104 of the membrane deaerator 103 are provided with dissolved oxygen meters (not shown). In addition, the inlet line L103 of the membrane deaerator 103 is provided with a moisture concentration meter and a resistivity meter (both not shown). A heater 108 is provided between the pump 107 downstream of the receiving section 101 and the first microfiltration membrane device 102 . High-temperature steam is supplied to the heater 108, and the NMP aqueous solution is heated by the high-temperature steam. The steam pipe is provided with a flow control valve V103 for adjusting the flow rate of the high-temperature steam.

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 deaerator 103 is connected via a fourth NMP aqueous solution supply line L104 to an ion exchange device 104 that removes ion components from the NMP aqueous solution. The ion exchange unit 104 is packed with a single bed of anion exchange resin or cation exchange resin, or mixed or multiple beds of anion exchange resin and cation exchange resin. The type of ion exchange resin may be either gel type or MR type. The ion exchange device 104 is connected to the second microfiltration membrane device 105 via a fifth NMP aqueous solution supply line L105. 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 L106. 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.

An inlet line L104 and an outlet line L105 of the ion exchange device 104 are provided with resistivity meters (not shown). When the specific resistance of the NMP aqueous solution treated by the ion exchange device 104 is less than a predetermined value, that is, when the ion components are not sufficiently removed, the NMP aqueous solution can be circulated along a loop passing through the ion exchange device 104. . Specifically, a return line L107 branched from the fifth NMP aqueous solution supply line L105 and connected to the receiving portion 101 is provided. Normally, the valve V101 of the fifth NMP aqueous solution supply line L105 is opened, and the valve V102 of the return line L107 is closed. Close valve V101 of L105 and open valve V102 of return line L107. Thereby, a circulation loop passing through the receiving section 101, the first microfiltration membrane device 102, the membrane degassing device 103, and the ion exchange device 104 is formed. The ionic components contained in the NMP aqueous solution are sufficiently removed by flowing the NMP aqueous solution along this circulation loop.

In addition, when the dissolved oxygen in the NMP aqueous solution treated by the membrane deaerator 103 is larger than a predetermined value, that is, when the dissolved oxygen is not sufficiently removed, NMP Aqueous solutions can be circulated. Thereby, the dissolved oxygen contained in the NMP aqueous solution is also sufficiently removed.

(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. The primary treatment liquid tank 106 is connected to the pervaporation membrane device 201 via the seventh NMP aqueous solution supply line L201. A pump 224 and a valve V201 are provided in the seventh NMP aqueous solution supply line L201. 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 L201. , 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 supplied to the pervaporation membrane device 201 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 L201 and the NMP concentrated liquid flowing through the NMP concentrated liquid discharge line L204. A first heater 205 heats the NMP aqueous solution with high temperature steam supplied from an external steam source (not shown). A steam supply line of the first heater 205 is provided with a valve V202 for adjusting the amount of steam supply. A temperature alarm indicator 223 is provided downstream of the first heater 205 . The opening of the valve V202 is adjusted based on the temperature detected by the temperature alarm indicator 223, and the temperature of the NMP aqueous solution is controlled to about 120.degree. A flow rate alarm indicator 225 is provided upstream of the waste heat recovery heat exchanger 206 in the seventh NMP aqueous solution supply line L201. The opening of the valve V201 is adjusted based on the flow rate detected by the flow rate alarm indicator 225, and the flow rate of the NMP aqueous solution is controlled within a predetermined range.

A pervaporation membrane device 201 has a plurality of pervaporation membrane modules 202 to 204 connected in series. In this embodiment, three pervaporation membrane modules, that is, a first pervaporation membrane module 202, a second pervaporation membrane module 203, and a third pervaporation membrane module 204 are connected in series from upstream to downstream. However, 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 L202. The second pervaporation membrane module 203 is connected to the third pervaporation membrane module 204 via a second connection line L203. 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 (moisture content less than 0.01%) with an NMP concentration increased to approximately 99.99% 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 L202 and the second connection line L203 are provided with a second heater 207 and a 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 steam supply lines of the second and third heaters 207, 208 are provided with valves V203, V204 for adjusting the amount of steam supply, respectively. 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 L204. As described above, the NMP concentrated liquid flowing through the NMP concentrated liquid discharge line L204 is heat-exchanged with the NMP aqueous solution flowing through the seventh NMP aqueous solution supply line L201 by the waste heat recovery type heat exchanger 206, and NMP Preheat the aqueous solution.

An NMP concentrate return line L215 branched from the NMP concentrate discharge line L204 and connected to the primary treatment liquid tank 106 is provided. Normally, the valve V205 of the NMP concentrate discharge line L204 is opened, the valve V206 of the return line L215 is closed, and the NMP concentrate is supplied to the relay tank 301. On the other hand, when the NMP concentrate cannot be supplied to the relay tank 301, the valve V205 is closed and the valve V206 is opened to return the NMP concentrate to the primary treatment liquid tank . When the NMP concentrate is returned to the primary treatment liquid tank 106, the cooler 226 provided in the return line L215 sets the temperature of the NMP concentration to the same level as the temperature of the NMP aqueous solution (primary treatment liquid). Cool with cooling water.

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 L206, L209, L212, 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 201b, 202b, and 203b, and the inside of the permeation chambers 201b, 202b, and 203b 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 flow through cooling jackets (not shown) surrounding first to third permeate tanks 214, 215 and 216, respectively, to produce vapor phase water and NMP. and further through the cooling lines L207, L210, L213 to the first to third heat exchangers 211, 212, 213 provided in the first to third permeated liquid discharge lines L206, L209, L212 It condenses water and NMP in the gas phase. The temperature of the brines BR1 and BR2 is preferably about 0 to -20°C.

The first to third heat exchangers 211, 212, 213 are respectively connected to the first to third pervaporation membrane modules 202, 203, 204 through the first to third permeate discharge lines L206, L209, L212. permeation chambers 202b, 203b, 204b. The first to third heat exchangers 211, 212, 213 are coolers that cool and condense the permeated vapor that has permeated the permeation chambers 202b, 203b, 204b to produce a permeated liquid. The permeate chambers 202b, 203b, 204b are in communication with the first to third permeate tanks 214, 215, 216 downstream of the first to third heat exchangers 211, 212, 213, respectively.

First to third permeate discharge lines L208, L211 and L214 are connected to the bottoms of the first to third permeate tanks 214, 215 and 216, respectively. Inert gas supply lines L406A, 406B, 406C branched from an inert gas supply mother pipe L401, which will be described later, are connected to the upper portions of the first to third permeate tanks 214, 215, 216, respectively. The condensed water and a small amount of NMP are temporarily stored in the first to third permeate tanks 214, 215, 216, and the inert gas supplied from the inert gas supply lines L406A, 406B, 406C. By pressurizing the interiors of the to third permeate tanks 214, 215 and 216, the first to third permeate tanks 214, 215 and 216 are discharged. 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 gaseous water collected in the first permeate tank 214 and the cooling water CW obtained by cooling a small amount of NMP are discharged to the first cooling water discharge line L220. Part of the cooling water flowing through the first cooling water discharge line L220 passes through the cooling water discharge line L221 branched from the first cooling water discharge line L220, and flows through the heat provided in the second permeated water discharge line L211. Heats the NMP-containing permeate supplied to the exchanger 220 and flowing through the second permeate discharge line L211. The remainder of the cooling water is supplied to the heat exchanger 221 provided in the third permeate discharge line L214 to heat the NMP-containing permeate flowing through the third permeate discharge line L214. Measuring instruments 222, 223 for measuring water concentration, flow rate, etc. are provided downstream of the heat exchangers 220, 221 of the second and third permeate discharge lines L211, L214.

The most upstream pervaporation membrane module, that is, the first pervaporation membrane module 202 has a pervaporation membrane 202c made of CHA-type, T-type, Y-type or MOR-type zeolite. The pervaporation membrane modules other than the most upstream pervaporation membrane module, that is, the second and third 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, the pervaporation membrane 202c of the first pervaporation membrane module 202 that processes an NMP aqueous solution containing 10 to 20% by weight of water is made of CHA type, T type, Y type or MOR type zeolite, and contains 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 a small amount of NMP aqueous solution. It is not necessary that all of the plurality of pervaporation membranes constituting the first pervaporation membrane module 202 are made of CHA-, T-, Y-, or MOR-type zeolite. may consist of

A cooler 209 and a mechanical booster pump 210 are provided in the third permeated liquid discharge line L212. Cooler 209 pre-cools the permeated liquid discharged from third pervaporation membrane module 204 . A mechanical booster pump 210 and a cooler 209 are provided to apply a large negative pressure to the permeation chamber 204 b of the third pervaporation membrane module 204 . Since the water content of the NMP aqueous solution supplied to the third pervaporation membrane module 204 is very low, by applying a sufficient negative pressure with the mechanical booster pump 210 in addition to the third vacuum pump 219, the water is It can be efficiently separated from the NMP aqueous solution. Cooler 209 and mechanical booster pump 210 can be omitted. A pod (not shown) for storing the permeated water condensed by the cooler 209 can also be provided between the cooler 209 and the mechanical booster pump 210 .

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 L211 and L214 are connected to the permeated liquid recovery line L205, and the permeated liquid recovery line L205 is connected to the primary treatment liquid tank . The permeated liquid discharged from the second and third permeated liquid discharge lines L211 and L214 has a higher NMP content than the permeated liquid discharged from the first permeated liquid discharge line L208. , 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 permeated liquid of the most downstream pervaporation membrane module (third pervaporation membrane module 204) may be recovered upstream of the pervaporation membrane device 201 . The permeated liquid may be recovered in the receiving part 101, or may be selectively recovered in the primary treatment liquid tank 106 and the receiving part 101 by providing a branch line (not shown) in the permeated liquid recovery line L205. 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. The third subsystem 300 produces a purified NMP liquid by distilling and condensing the NMP concentrate, and thus functions as an NMP concentrate distiller and purifier. 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. For example, a precision distillation method can also be used. However, the simple distillation method is preferable for reasons such as low energy consumption, small equipment size, and simple operation. 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.

As described above, the NMP concentrate is temporarily stored in the relay tank 301 . 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 the relay tank 301, it is possible to operate the second subsystem 200 and the third subsystem 300 more flexibly while maintaining mutual independence. The relay tank 301 is connected to the regenerator 302 via the first NMP concentrate supply line L301. A pump 306 and a valve V301 are provided in the first NMP concentrate supply line L301. 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. The regenerator 302 is connected to the evaporator 303 via a second NMP concentrate supply line L302. Evaporator 303 heats and vaporizes the NMP concentrate with hot steam supplied from an external steam source (not shown). A steam supply line of the evaporator 303 is provided with a valve V302 for adjusting the amount of steam supply. 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 L303 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 L303. 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 concentrated liquid withdrawal line L306 that merges with the circulation line L303 is provided at the bottom of the vapor withdrawal can 304 (described later). The NMP concentrate remaining at the bottom of the steam take-out can 304 is also returned to the evaporator 303 through the NMP concentrate take-out line L306 and the circulation line L303 and heated again. A circulation pump 307 and a valve V303 are provided in the circulation line L303. From the circulation line L303, an NMP concentrated liquid impurity discharge line L309 provided with a valve V304 branches off.

The purified NMP 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 through the first NMP-purified gas take-out line L304. Vapor removal can 304 is connected to regenerator 302 via second NMP purified gas removal line L305. 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 L307, 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 the negative pressure line L310, 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. A gas cooler 310 is provided between the condenser 305 of the negative pressure line L310 and the vacuum pump 309 to cool the gas containing NMP purified gas discharged from the condenser 305 to the vacuum pump 309 . The cooling water of the condenser 305 is discharged to the cooling water drainage line L311 connected to the condenser 305. A heat exchanger 312 is provided in the cooling water discharge line L311, and the NMP concentrate flowing through the impurity discharge line L309 is cooled by the heat exchanger 312 before being discharged.

An outlet of the condenser 305 is connected to an NMP purified liquid extraction pipe L308. The purified NMP liquid is sent to the payout section 311 by the pump 308 provided in the NMP purified liquid extraction pipe L308. Like the receiving unit 101, the dispensing unit 311 has a plurality of containers (first to third containers 311a, 311b, 311c). It can be switched according to purposes such as acceptance, analysis, and transfer. If there is no problem as a result of the analysis, the purified NMP liquid is transferred to the lithium ion secondary battery manufacturing system through the discharge line L312 and reused in the manufacturing system. If there is a problem, the NMP purified liquid is transferred to a waste tank (not shown).

(Inert gas supply means)
The NMP aqueous solution purification system 1 of the present embodiment further includes an inert gas supply means for filling the gas phase portion of the container with an inert gas. As described above, upstream and downstream of the pervaporation membrane device 201 are provided various containers in which the NMP aqueous solution, the NMP concentrated solution, or the NMP purified solution are stored. Some of these containers form an interface between the NMP aqueous solution, the NMP concentrated solution, or the NMP purified solution and the gas phase portion. Containers that satisfy this condition include the following.

(1) First to third containers 101a, 101b, and 101c of receiving portion 101 for NMP aqueous solution
(2) Primary treatment liquid tank 106
(3) Relay tank 301
(4) Regenerator 302
(5) Evaporator 303
(6) Steam extraction can 304
(7) Capacitor 305
(8) First to third containers 311a, 311b, and 311c of dispensing unit 311 for purified NMP solution
The gas phase portion of a conventional container (in the following description of the inert gas supply means, containers means containers 101a, 101b, 101c, 106, 301 to 305, 311a, 311b, and 311c) was formed of air. . However, the inventor believes that when these containers are filled with air, NMP combines with the air in the gas phase to form a peroxide of NMP (NMP-O-O-H; 5-hydroperoxo-1 -methyl-2-pyrrolidone) is produced. NMP peroxides are potentially explosive when accumulated. Therefore, in this embodiment, these containers are provided with inert gas supply means. Nitrogen gas is preferable as the inert gas, and argon gas can also be used. The inert gas supply means is installed on the inert gas supply main pipe L401 described below, the inert gas supply line branched from the main pipe L401 and supplying the inert gas to each container, and each inert gas supply line. gas seal unit, and

Specifically, an inert gas supply main pipe L401 is connected to an inert gas supply source (not shown). The dispensing units 311 are connected by inert gas supply lines L402, L403, L404 and L407, respectively. Inert gas supply lines L402, L403, L404, L407 are connected to the top of the vessel. Gas seal units U402, U403, U404 and U405 are provided in inert gas supply lines L402, L403, L404 and L407, respectively. Furthermore, an inert gas supply line L405 for sweeping is connected to the negative pressure line L310 between the condenser 305 (more precisely, the gas cooler 310) and the vacuum pump 309. The inert gas is supplied to the condenser 305 from the inert gas supply line L405, and is also supplied to the regenerator 302, the evaporator 303, and the steam extraction can 304 through lines L307, L302, L304, and L305. . Although not shown, the regenerator 302, the evaporator 303, and the steam extraction can 304 can also be provided with similar vacuum pumps and inert gas supply lines for sweep.

The inert gas is filled into the container when the purification system 1 for NMP aqueous solution is operated for the first time. At this time, since the inside of the container is filled with air, the inert gas is sent into the container through the gas seal units U402, U403, U404 and U405 to forcibly replace the air inside the container with the inert gas. The gas seal units U402, U403, U404, U405 are designed to automatically open when the pressure in the downstream vessel drops to fill the vessel with inert gas. Therefore, when the amounts of the NMP aqueous solution, NMP concentrated liquid, and NMP purified liquid in the container decrease, the pressure in the container decreases, and the inert gas is replenished into the container through the gas seal units U402, U403, U404, and U405. The same applies to other gas seal units.

Filling the container with an inert gas not only reduces the possibility of NMP peroxide explosion, but also suppresses the amount of water and dissolved oxygen dissolved in the NMP aqueous solution, NMP concentrate, and NMP purified solution in the container. can be done. As a result, the load on the pervaporation membrane module can be reduced. In addition, since there is almost no oxygen in the container, an effect of preventing oxidation of the NMP aqueous solution, the NMP concentrated solution, and the NMP purified solution can also be obtained.

(Gas cooler 310)
As mentioned above, third subsystem 300 is provided with gas cooler 310 . The gas cooler 310 is provided between the condenser 305 and the vacuum pump 309 , and condenses the vapor flowing from the gas phase portion of the condenser 305 by the negative pressure generated by the vacuum pump 309 . The condenser 305 condenses the purified NMP gas with the cooling water, but the cooling capacity may be temporarily reduced due to fluctuations in the temperature of the cooling water, the circulation flow rate of the purified NMP gas, and the like. Further, when the flow rate of cooling water decreases due to an increase in pressure loss of the condenser 305 itself over time, the cooling capacity also decreases. This raises the temperature inside the condenser 305 and increases the saturated vapor pressure of NMP. As a result, the amount of NMP purified gas that remains in condenser 305 without condensing increases. Since the vacuum pump 309 is connected to the gas phase portion of the capacitor 305, the amount of NMP sucked from the capacitor 305 by the vacuum pump 309 increases. Also, when using a dry vacuum pump, it is not preferable to suck a large amount of NMP purified gas, because reliability may be lowered if used in an environment where liquid exists. Gas cooler 310 is provided between condenser 305 and vacuum pump 309 to condense NMP purified liquid before vacuum pump 309 draws NMP purified gas, so that the amount of NMP purified gas drawn by vacuum pump 309 can be reduced. can be done.

The structure of the gas cooler 310 is not limited as long as the NMP purified gas can be condensed, but a general shell-and-tube heat exchanger using cooling water can be used. Although illustration is omitted, the cooling water can be shared with the cooling water of the condenser 305 . In addition, the cooling wastewater can be reused together with the cooling wastewater from the condenser 305 by the method described below.

(Heat exchanger 31 2 of impurity discharge line L309)
Since the evaporator 303 evaporates the NMP concentrated liquid circulating in the circulation line L303, the NMP concentrated liquid containing impurities such as high boiling point chromaticity components and metal ions at high density stays at the bottom of the evaporator 303. Impurities contained in the staying NMP concentrated liquid may scatter and be mixed with the NMP concentrated liquid circulating in the circulation line L303, so the NMP concentrated liquid containing impurities at the bottom of the evaporator 303 must be discharged. . Since the circulation line L303 is open to the atmosphere during discharge, the discharge operation is performed intermittently. Specifically, by closing the normally open valve V303 of the circulation line L303 and opening the normally closed valve V304 of the impurity discharge line L309, the NMP concentrated liquid circulating in the circulation line L303 is removed from the impurity discharge line L309. Eject from However, since the NMP concentrate circulating through the circulation line L303 is heated to a high temperature (approximately 80 to 120° C.), it is not preferable to discharge it as it is. For example, when a receiving tank is provided, it is necessary to ensure the heat resistance of the receiving tank, and when a meter such as a flow meter is provided in the impurity discharge line L309, it may be difficult to ensure the reliability of the meter.

In this embodiment, the heat exchanger 312 is provided on the impurity discharge line L309, and the NMP concentrated liquid is cooled by heat exchange with the cooling waste water flowing through the cooling waste water discharge line L311. The cooling water of the condenser 305 is also circulated when the NMP concentrate is discharged. Since the valve V303 of the circulation line L303 is closed, the circulation of the NMP concentrate in the circulation line L303 is not performed. For this reason, almost no NMP purified gas is supplied to the condenser 305, and the cooling waste water is discharged from the condenser 305 without a significant temperature rise. That is, the NMP concentrate is cooled not by warmed cooling waste water, but by relatively low-temperature cooling waste water, so that the cooling efficiency is enhanced. Even if the cooling water supply line for the condenser 305 is provided in parallel with the cooling water supply line for the heat exchanger 312 , the cooling efficiency is substantially the same. However, as in this embodiment, the cooling water supply line is composed of one line L311 that sequentially passes through the condenser 305 and the heat exchanger 312 , and the valve V303 of the circulation line L303 and the valve V304 of the impurity discharge line L309 are By ensuring that one is closed when the other is open, piping and valve costs can be reduced.

1 NMP aqueous solution purification system 100 first subsystem 101 receiving section 101a, 101b, 101c first to third containers of receiving section 102 first microfiltration membrane device 103 membrane degassing device 104 ion exchange device 105 second Microfiltration membrane device 106 Primary treatment liquid tank 107 Pump 108 Heater L101 to L106 First to sixth NMP aqueous solution supply line L107 Return line V101, V102 Valve 200 Second subsystem 201 Pervaporation membrane device 202 to 204 First to third pervaporation membrane modules 202a, 203a, 204a concentration chambers 202b, 203b, 204b permeation chambers 202c, 203c, 204c separation membrane (pervaporation membrane)
205 first heater 206 regenerative heat exchanger 207 second heater 208 third heater 209 cooler 210 mechanical booster pump 211, 212, 213 first to third heat exchangers 214, 215, 216 first to Third permeate tank 217, 218, 219 First to third vacuum pumps 220, 221 Fourth and fifth heat exchangers 223 Temperature alarm indicator 224 Pump 225 Flow rate alarm indicator 226 Cooler L201 Seventh NMP aqueous solution supply lines L202, L203 First and second connection lines L204 NMP concentrated liquid discharge line L205 Permeated liquid recovery lines L206, L209, L212 First to third permeated liquid discharge lines L207, L210, L213 Cooling line L208, L211, L214 First to third permeate discharge lines L215 NMP concentrate return line L220 First cooling water discharge line V201 to V206 Valve 300 Third subsystem 301 Relay tank 302 Regenerator 303 Evaporator 304 Steam extraction Can 305 Condenser 306 Pump 307 Circulation pump 308 Pump 309 Vacuum pump 310 Gas cooler 311 Dispensing section 311a, 311b, 311c First to third containers of distributing section L301 First NMP concentrated liquid supply line L302 Second NMP concentrated liquid supply Line L303 Circulation line L304 First NMP purified gas extraction line L305 Second NMP purified gas extraction line L306 NMP concentrated liquid extraction line L307 Third NMP purified gas extraction line L308 NMP purified liquid extraction pipe L309 Impurity discharge of NMP concentrated liquid Line L310 Negative pressure line L311 Cooling water drainage line V301 to V304 Valve L401 Inert gas supply main pipe L402 to L407 Inert gas supply line U402, U403, U404, U405 Gas seal unit

Claims (3)

an evaporator for evaporating the organic solvent;
a condenser for condensing the vapor of the organic solvent generated in the evaporator;
a vacuum pump in communication with the gas phase of the condenser;
a gas cooler provided between the condenser and the vacuum pump for condensing the vapor flowing in from the gas phase portion by means of negative pressure generated by the vacuum pump;
a circulation line connected to the bottom and top of the evaporator and forming a circulation path including the evaporator;
an impurity discharge line branching from the circulation line and discharging an organic solvent containing impurities accumulated at the bottom of the evaporator;
a cooling wastewater discharge line connected to the condenser for discharging cooling wastewater obtained by cooling the vapor of the organic solvent;
a heat exchanger provided in the impurity discharge line for cooling the organic solvent containing the impurities by heat exchange with the cooling waste water flowing through the cooling waste water discharge line ;
An organic solvent distillation purification apparatus in which a valve is provided in each of the circulation line and the impurity discharge line, and one of the valve of the circulation line and the valve of the impurity discharge line is closed when the other is opened. 2. The distillation purification apparatus according to claim 1 , wherein said organic solvent is NMP. an evaporator for evaporating the organic solvent;
a condenser for condensing the vapor of the organic solvent generated in the evaporator;
a vacuum pump in communication with the gas phase of the condenser;
a gas cooler provided between the condenser and the vacuum pump for condensing the vapor flowing in from the gas phase portion by means of negative pressure generated by the vacuum pump;
a circulation line connected to the bottom and top of the evaporator and forming a circulation path including the evaporator;
an impurity discharge line branching from the circulation line and discharging an organic solvent containing impurities accumulated at the bottom of the evaporator;
a cooling wastewater discharge line connected to the condenser for discharging cooling wastewater obtained by cooling the vapor of the organic solvent;
a heat exchanger provided in the impurity discharge line for cooling the organic solvent containing the impurities by heat exchange with the cooling waste water flowing through the cooling waste water discharge line;
A method for distilling and refining an organic solvent using a distillation refining device in which the circulation line and the impurity discharge line are respectively provided with valves,
A method for distilling and refining an organic solvent , comprising the step of opening one of the valve of the circulation line and the valve of the impurity discharge line and closing the other .

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