JP7217648B2 - Dehydrating apparatus and dehydrating method for mixed liquid containing organic solvent and water - Google Patents

Description

TECHNICAL FIELD The present invention relates to a dehydrating apparatus and a dehydrating method for a mixed liquid containing an organic solvent and water.

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 module 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.

Patent Literature 1 discloses an NMP aqueous solution purification system in which a plurality of stages of pervaporation membrane modules are provided in series. The NMP aqueous solution dehydrated and concentrated in the upstream pervaporation membrane module is supplied to the subsequent pervaporation membrane module to further remove moisture. Permeated vapor that permeates the permeation chamber of each pervaporation membrane module is condensed in a heat exchanger connected to the permeation chamber to become permeated water. The downstream pervaporation membrane module has a lower moisture removal efficiency than the upstream pervaporation membrane module and a relatively large amount of NMP leaks into the permeation chamber. Therefore, in order to suppress the loss of NMP, the permeated water generated from the downstream pervaporation membrane module is again supplied to the upstream pervaporation membrane module. In addition, the heat exchanger connected to the downstream pervaporation membrane module cools the permeated vapor using a cooling liquid (refrigerant) having a lower temperature than the upstream. This increases the negative pressure in the permeation chamber and increases the water removal efficiency of the downstream pervaporation membrane module.

WO2018/207431

In the NMP aqueous solution purification system described in Patent Document 1, permeated water is temporarily stored in a permeated water tank, and the permeated water stored in the permeated water tank is returned to the upstream pervaporation membrane module. Since the permeate tank is depressurized, it is desirable to release the depressurization of the permeate tank when returning the permeate. For this reason, the operation of returning the permeated water is performed intermittently. On the other hand, since the permeated water is cooled by the low-temperature refrigerant, the temperature of the NMP aqueous solution supplied from the permeated water tank to the pervaporation membrane module temporarily decreases when returning the permeated water to the pervaporation membrane module. This may reduce the dehydration performance of the pervaporation membrane module. The above points are the same for mixed liquids containing organic solvents other than NMP and water.

The present invention provides a dehydrator for a mixed liquid containing an organic solvent and water in which permeated water generated in a pervaporation membrane module is returned to an upstream pervaporation membrane module. The purpose is to suppress the decline.

The dehydrator of the present invention includes a first pervaporation membrane module that removes part of water from a mixed liquid containing an organic solvent and water to produce a concentrated liquid of the organic solvent, and the first pervaporation membrane module. A second pervaporation membrane module located downstream for further removing moisture from the concentrated liquid of the organic solvent, and communicating with the permeation chamber of the second pervaporation membrane module to cool and condense the permeated vapor that has permeated the permeation chamber. a permeate tank in communication with the cooler downstream of the cooler and capable of being maintained at a negative pressure therein and capable of storing the permeate; and located downstream of the permeate tank. , a heater for heating the permeated liquid, a return line for returning the permeated liquid heated by the heater to the inlet side of the first pervaporation membrane module, connected to the permeation chamber of the first pervaporation membrane module, and cooling water A heat exchanger that cools the permeated vapor that has permeated the permeation chamber of the first pervaporation membrane module by heat exchange, and discharges cooling waste water that has a higher temperature than the permeate discharged from the permeate tank, and a cooling waste water discharge line and the heater heats the permeate by heat exchange with the cooling waste water flowing through the discharge line.

According to the present invention, since the permeated liquid heated by the heater is returned to the inlet side of the first pervaporation membrane module, even if the permeated water of the pervaporation membrane module is at a low temperature, deterioration of dehydration performance can be suppressed. can be done.

1 is a schematic configuration diagram of an NMP aqueous solution purification system according to an embodiment of the present invention; FIG. 1 is a schematic configuration diagram of a dehydrator 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. An NMP concentrated liquid impurity discharge line L309 provided with a valve V304 branches off from the circulation line L303.

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 311 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 311 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. Peroxides of NMP 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.

(Dehydration device 600)
Next, the dehydrator of the NMP aqueous solution purification system will be described. FIG. 2 is a schematic configuration diagram of the dewatering device 600. As shown in FIG. The dehydrator 600 includes the first to third pervaporation membrane modules 202 to 204 of the second subsystem 200 and their incidental equipment. Heaters 220 and 221 for heating the permeated liquid are provided downstream of the second and third permeated liquid tanks 215 and 216 . The configuration of the heaters 220 and 221 is not limited as long as the permeating liquid can be heated, and may be electric heaters, for example. In this embodiment, the heaters 220 and 221 are the heat exchangers 220 and 221 in order to use the cooling waste water of the first heat exchanger 211 as the heat source. Therefore, the heat exchangers 220 and 221 are connected to a first cooling water discharge line L220 for discharging the cooling water discharged from the first heat exchanger 211. As shown in FIG. As described above, the first heat exchanger 211 is connected to the first permeation chamber 202b of the first pervaporation membrane module 202, and heats the permeated vapor that has permeated the first permeation chamber 202b with the cooling water CW. Cool by exchange. The heaters 220, 221 heat the permeated liquid generated in the second and third pervaporation membrane modules 203, 204 by heat exchange with the cooling waste water flowing through the first cooling water discharge line L220 and the cooling water discharge line L221. do. The permeated liquid heated by the heat exchangers 220 and 221 is recovered by a permeated liquid recovery line L205, which is a return line that returns the permeated liquid to the inlet side of the first pervaporation membrane module 202.

The temperature of the permeated liquid in the first to third permeated liquid tanks 214, 215, 216 decreases in the order of the first permeated liquid tank 214, the second permeated liquid tank 215, and the third permeated liquid tank 216. there is This is because the water content in the NMP aqueous solution decreases and the NMP concentration increases in the subsequent pervaporation membrane module. In order to dehydrate the NMP aqueous solution with a small water content, it is necessary to increase the pressure difference between the inlet side and the permeation side of the pervaporation membrane module. Since the pressure on the permeate side is equal to the saturated vapor pressure of water, it is necessary to lower the temperature on the permeate side and lower the saturated vapor pressure of water in order to increase the pressure difference between the inlet side and the permeate side. Therefore, while normal temperature water can be used as cooling water in the first heat exchanger 211, the second heat exchanger 212 uses a lower temperature refrigerant, brine BR1, and the third heat exchanger 213 uses brine BR1. Brine BR2, which is an even lower temperature refrigerant, is used. In one example, this results in a permeate temperature of about 40° C. in first permeate tank 214 , about 2° C. in second permeate tank 215 , and about −10° C. in third permeate tank 216 . In one example, the temperature of cooling water flowing through the first cooling water discharge line L220 and the cooling water discharge line L221 is approximately 37°C. Therefore, the cooling waste water flowing through the first cooling water discharge line L220 and the cooling water discharge line L221 has sufficient thermal energy to heat the permeated water in the second and third permeated liquid tanks 215,216. The permeate is preferably heated to a temperature above 20°C. In addition, since the cooling water flowing through the first cooling water discharge line L220 is cooled to near room temperature and discarded, auxiliary equipment such as a cooling tower for cooling the cooling water is not required, or the size can be reduced.

Here, the reason for heating the permeated water in the second and third permeated liquid tanks 215 and 216 will be described. The permeated water of the second and third permeated liquid tanks 215 and 216 is discharged from the second and third permeated water discharge lines L211 and L214 to the upstream side of the first pervaporation membrane module 202 (the primary treated liquid in this embodiment). When returning to the tank 106), as will be described later, the pressure of the inert gas pushes out the permeated water. As a result, the negative pressure in the second and third permeate tanks 215, 216 and the negative pressure in the second and third permeation chambers 203b, 204b are released, and the second and third pervaporation membrane modules 203, 204 performance is degraded. Therefore, this operation cannot be performed continuously. Therefore, it is necessary to store the permeated water in the second and third permeated liquid tanks 215 and 216 , temporarily release the negative pressure, and return the permeated water to the primary treatment liquid tank 106 . Using a pump instead of an inert gas could potentially allow the permeate to be continuously drained, however, the second and third permeate tanks 215, 216 and the pump should be separated in order to ensure the suction head of the pump. It is necessary to provide a large height difference between them, which is not realistic. For this reason, the permeated water stored in the second and third permeated liquid tanks 215 and 216 is intermittently returned to the primary treated liquid tank 106 .

Therefore, when the permeated water in the second and third permeated liquid tanks 215 and 216 is not heated, the low-temperature permeated water is temporarily returned to the primary treated liquid tank 106 and stored in the primary treated liquid tank 106. The temperature of the NMP aqueous solution will drop. The NMP aqueous solution is heated by the first heater 205 and the waste heat recovery heat exchanger 206. The first heater 205 and the waste heat recovery heat exchanger 206 are controlled so as to heat the NMP aqueous solution to about 120°C. It is difficult. Therefore, the temperature of the NMP aqueous solution supplied to the first pervaporation membrane module 202 temporarily falls below 120° C., the temperature of the dehydration membrane of the first pervaporation membrane module 202 and the temperature on the permeation side fluctuate, and the dehydration Performance becomes unstable. In the present embodiment, since the permeated water in the second and third permeated liquid tanks 215 and 216 is heated, the temperature change of the NMP aqueous solution supplied to the first pervaporation membrane module 202 is suppressed, resulting in more stable dehydration. performance can be obtained.

Heating the permeated water in the second and third permeated liquid tanks 215 and 216 also facilitates maintaining the performance of the measuring instruments 222 and 223 . Although the type of the measuring instrument 222 is not limited, in this embodiment, the measuring instrument 222 is a flow meter 222A and a moisture concentration meter 222B provided in the second permeated water discharge line L211, and the measuring instrument 223 is a third permeation A flow meter 223A and a moisture concentration meter 223B provided in the water discharge line L214. These measuring instruments 222 and 223 are often not guaranteed to operate with liquids below 0° C., and their use with low-temperature liquids is disadvantageous in terms of reliability. In this embodiment, since the permeated water is heated to a temperature close to normal temperature, it is easy to maintain the performance of the measuring instruments 222 and 223 .

Next, a method for discharging the permeated liquid from the first to third permeated liquid tanks 214, 215 and 216 will be described. As described above, the inert gas supply means, that is, the inert gas supply lines L406A, 406B branched from the inert gas supply mother pipe L401 are provided in the upper portions of the first to third permeate tanks 214, 215, 216. 406C is connected. Further, first to third shutoff valves V207, V208 and V209 are provided in the first to third permeated liquid discharge lines L206, L209 and L212, respectively. The first to third shutoff valves V207, V208, V209 are respectively the first to third permeate tanks 214, 215, 216 and the permeation chambers 202b of the first to third pervaporation membrane modules 202, 203, 204, This is an example of means for blocking communication with 203b and 204b. For example, when discharging the permeated liquid from the second permeated liquid tank 215, first, the second cutoff valve V208 is closed to block the communication between the second permeated liquid tank 215 and the permeation chamber 203b. At the same time, the second vacuum pump 218 is stopped. Next, an inert gas is supplied from the inert gas supply line 406B. The inert gas supply line 406B can apply to the second permeated liquid tank 215 a pressure capable of discharging the permeated liquid stored inside the second permeated liquid tank 215 to the permeated liquid recovery line L205. This causes the permeate from the second permeate tank 215 to be returned to the primary treatment liquid tank 106 . Although part of the inert gas may flow into the primary treatment liquid tank 106, there is no problem because the gas phase portion of the primary treatment liquid tank 106 is replaced with the inert gas as described above.

As indicated by broken lines in FIG. 2, pumps for discharging the permeated liquid are provided between the second permeated liquid tank 215 and the heat exchanger 220 and between the third permeated liquid tank 216 and the heat exchanger 221. It is also possible to provide P. In this case, the inert gas only needs to release the vacuum inside the first to third permeate tanks 214, 215, 216, and pressurization capability for discharge is not required. Therefore, the installation of the pump P is effective when the pressure of the inert gas cannot be sufficiently secured. However, since the permeated liquid is transferred at a low temperature of about -10°C, there is a possibility that the pump P may be damaged due to freezing of the permeated liquid, and the installation cost of the pump P itself is high. It is preferable to transfer

Although three pervaporation membrane modules 202 to 204 are used in this embodiment, the number of pervaporation membrane modules is not limited. Therefore, more generally, at least one or more of the pervaporation modules 202, 203 are arranged in series with the first and second pervaporation modules 202, 203 downstream of the second pervaporation module 203 to further remove water from the organic solvent concentrate. One other pervaporation membrane module can be arranged. At least one further cooler is provided in communication with the permeate chambers of the other pervaporation membrane modules, respectively, for cooling and condensing the permeated vapor that permeates the permeate chambers of the other pervaporation membrane modules. to generate a permeate. Furthermore, at least one other permeate tank is provided downstream of the other cooler, each in communication with the other cooler. The other permeate tank can maintain a negative pressure inside and store the permeate. At least one further heater for heating the permeate is provided downstream of each of the other permeate tanks. The cooling water discharge line has branch lines connected to each of the other heaters, and the other heaters heat the permeate by heat exchange with cooling water flowing through the branch lines.

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 600 Dehydrator V207, V208, V209 first to Third shut-off valve

Claims (6)

a first pervaporation membrane module that removes part of water from a liquid mixture containing an organic solvent and water to produce a concentrated liquid of the organic solvent;
a second pervaporation membrane module located downstream of the first pervaporation membrane module for further removing water from the organic solvent concentrate;
a cooler that communicates with the permeation chamber of the second pervaporation membrane module and cools and condenses the permeated vapor that has permeated the permeation chamber to produce a permeate;
a permeate tank in communication with the cooler downstream of the cooler and capable of being maintained at a negative pressure therein and capable of storing the permeate;
a heater positioned downstream of the permeate tank to heat the permeate;
a return line for returning the permeated liquid heated by the heater to the inlet side of the first pervaporation membrane module ;
It is connected to the permeation chamber of the first pervaporation membrane module, cools the permeated vapor that has permeated the permeation chamber of the first pervaporation membrane module by heat exchange with cooling water, and is discharged from the permeate tank a heat exchanger that discharges cooling waste water that is hotter than the permeated liquid;
and a discharge line for the cooling waste water,
The dewatering device, wherein the heater heats the permeated liquid by heat exchange with the cooling waste water flowing through the discharge line . at least one other pervaporation module arranged in series with the first and second pervaporation modules downstream of the second pervaporation module to further remove water from the organic solvent concentrate; ,
at least one other cooler, each in communication with the permeate chamber of the other pervaporation membrane module, for cooling and condensing the permeated vapor that has permeated the permeate chamber of the other pervaporation membrane module to produce a permeate;
at least one further permeate tank downstream of and in communication with each of said other coolers, capable of being maintained at a negative pressure therein and capable of storing said permeate;
at least one other heater located downstream of each of said other permeate tanks for heating said permeate;
3. The cooling wastewater discharge line has a branch line connected to each of said other heaters, and said other heater heats said permeated liquid by heat exchange with said cooling wastewater flowing through said branch line. 2. The dehydrator according to 1 . means for blocking communication between the permeate tank and the permeation chamber of the second pervaporation membrane module;
an inert gas supply means connected to the permeate tank;
The inert gas supply means provides a pressure capable of discharging the permeated liquid stored inside the permeated liquid tank to the return line when the communication between the permeated liquid tank and the permeation chamber is cut off. 3. A dehydrator according to claim 1 or 2 , applicable to the permeate tank. 4. The dehydrator according to any one of claims 1 to 3 , wherein said organic solvent is NMP. removing part of water from a mixture containing an organic solvent and water by a first pervaporation membrane module to produce a concentrated liquid of the organic solvent;
A heat exchanger connected to the permeation chamber of the first pervaporation membrane module cools the permeated vapor that has permeated the permeation chamber of the first pervaporation membrane module by heat exchange with cooling water, and permeates discharging cooling waste water having a higher temperature than the permeated liquid discharged from the liquid tank;
further removing water from the organic solvent concentrate by a second pervaporation membrane module located downstream of the first pervaporation membrane module;
cooling and condensing the permeated vapor permeated into the permeate chamber by a cooler in communication with the permeate chamber of the second pervaporation membrane module to produce a permeate;
transferring the permeate to the permeate tank in communication with the cooler downstream of the cooler and maintained at a negative pressure therein;
heating the permeate discharged from the permeate tank with a heater;
returning the heated permeate to the inlet side of the first pervaporation membrane module;
has
A method for dehydrating a mixed liquid containing an organic solvent and water using a pervaporation membrane module, wherein the heater heats the permeated liquid by heat exchange with the cooling waste water. Additional water is removed from the organic solvent concentrate by at least one other pervaporation module arranged in series with the first and second pervaporation modules downstream of the second pervaporation module. and
Cooling and condensing the permeated vapor permeated through the permeate chambers of the other pervaporation membrane modules by at least one other cooler respectively communicating with the permeate chambers of the other pervaporation membrane modules to form a permeate. and,
storing the permeate in at least one other permeate tank downstream of and in communication with each of the other coolers and maintained at a negative pressure therein;
at least one other heater located downstream of each of said other permeate tanks for heating said permeate;
3. The cooling wastewater discharge line has a branch line connected to each of said other heaters, and said other heater heats said permeated liquid by heat exchange with said cooling wastewater flowing through said branch line. 5. The dehydration method according to 5.

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