JP2020146635A - Dehydrator and dehydration method for liquid mixture including organic solvent and water - Google Patents

Abstract

To restrain deterioration of dehydration performance even if a permeable water from the permeable vapor of a pervaporation membrane module is in a low temperature area in a dehydrator for liquid mixture including an organic solvent and water.SOLUTION: A dehydrator 600 comprises: a first pervaporation membrane module 202 removing a part of moisture from a liquid mixture to generate the concentrated liquid of an organic solvent; a second pervaporation membrane module 203 located at the downstream of the module 202 and further removing the moisture from the above concentrated liquid; a chiller 212 communicating with a permeation chamber 203b of the module 203 and cooling/condensing the permeable vapor passed through the permeation chamber 203b to generate a permeation liquid; a permeation tank 215 communicating with the chiller 212 at the downstream thereof, having an inside maintainable at a negative pressure and capable of storing the permeation liquid; a heater 220 located at the downstream of the permeation tank 215 to heat the permeation liquid; and a return line L205 returning the permeation liquid heated by the heater 220 to the inlet side of the first pervaporation membrane module 202.SELECTED DRAWING: Figure 2

Description

The present invention relates to a dehydrator and a dehydration method for a mixed solution containing an organic solvent and water.

Conventionally, a method of separating NMP from a mixed solution of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) and water (hereinafter referred to as NMP aqueous solution) by an osmotic vaporization method (PV method) has been 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 (vacuum distillation method). In the PV method, an osmotic vaporization membrane module provided with a separation membrane (osmotic vaporization membrane) having an affinity for water is used. By supplying the NMP aqueous solution to the inlet side of the osmotic vaporization membrane and reducing the pressure on the permeation side, a driving force for moving the NMP aqueous solution from the inlet side to the permeation side can be obtained. At this time, due to the difference in permeation rate between NMP and water, water mainly moves to the permeation side, and NMP and water are separated.

Patent Document 1 discloses a purification system for an NMP aqueous solution in which a plurality of osmotic vaporization membrane modules are provided in series. The NMP aqueous solution dehydrated and concentrated in the upstream osmotic membrane module is supplied to the subsequent osmotic membrane module to further remove water. The permeated vapor permeating through the permeation chamber of each permeation vaporization membrane module is condensed by a heat exchanger connected to the permeation chamber to become permeated water. The downstream osmotic vaporization membrane module has a lower water removal efficiency than the upstream osmotic vaporization membrane module, and the amount of NMP leaking into the permeation chamber is relatively large. Therefore, in order to suppress the loss of NMP, the permeated water generated from the downstream osmotic vaporization membrane module is supplied to the upstream osmotic vaporization membrane module again. Further, the heat exchanger connected to the osmotic vaporization membrane module on the downstream side cools the permeated vapor by using a coolant (refrigerant) having a lower temperature than that on the upstream side. As a result, the negative pressure in the permeation chamber is increased, and the water removal efficiency of the downstream osmotic vaporization membrane module is enhanced.

International Publication No. 2018/207431

In the NMP aqueous solution purification system described in Patent Document 1, the permeated water is once stored in the permeated water tank, and the permeated water stored in the permeated water tank is returned to the upstream permeation vaporization membrane module. Since the permeated water tank is decompressed, it is desirable to release the decompression of the permeated water tank when returning the permeated water. Therefore, the operation of returning the permeated water is performed intermittently. On the other hand, since the permeated water is cooled by a low-temperature refrigerant, the temperature of the NMP aqueous solution supplied from the permeated water tank to the permeated vaporization membrane module temporarily drops when the permeated water is returned to the permeated vaporization membrane module. This may reduce the dehydration performance of the osmotic vaporization membrane module. The above points are the same for the mixed solution containing an organic solvent other than NMP and water.

The present invention is a dehydrator of a mixed solution containing an organic solvent and water in which the permeated water generated by the osmotic vaporization membrane module is returned to the upstream osmotic vaporization membrane module. The purpose is to suppress the decrease.

The dehydrator of the present invention comprises a first permeable vaporization film module and a first permeable vaporization film module that remove a part of water from a mixed solution containing an organic solvent and water to generate a concentrated solution of the organic solvent. It communicates with the permeation chamber of the second permeation vaporization film module, which is located downstream and further removes water from the concentrated solution of the organic solvent, and the permeation chamber of the second permeation vaporization membrane module, and cools and condenses the permeated vapor that has permeated through the permeation chamber. It is located downstream of the permeate tank and the permeate tank that communicates with the cooler downstream of the cooler to generate permeate and can maintain a negative pressure inside and can store the permeate. It has a heater for heating the permeate and a return line for returning the permeate heated by the heater to the inlet side of the first permeation vaporization film module.

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

It is a schematic block diagram of the purification system of the NMP aqueous solution which concerns on one Embodiment of this invention. It is a schematic block diagram of the dehydration apparatus which concerns on one Embodiment of this invention.

As the organic solvent applicable to the present invention, in addition to alcohols such as methanol, ethanol and 2-propanol, the boiling point at atmospheric pressure (0.1013 Mpa) is higher than the boiling point of water (100 ° C.), preferably large. Examples thereof include organic solvents having a boiling point under atmospheric pressure of 120 ° C. or higher, which is a general operating temperature of a permeation vaporization film device. Table 1 shows examples of such organic solvents.

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

NMP is one of the organic solvents having high solubility in water. For example, in the manufacturing process of a lithium ion secondary battery, NMP is used as a dispersion medium for a slurry when a slurry in which particles such as an electrode active material are dispersed is applied onto an electrode current collector and dried to form an electrode. Widely used. NMP is recovered when the slurry is dried, and the recovered NMP can be reused after purification. The NMP is recovered as a mixed solution (NMP aqueous solution) in which NMP and water are mixed using, for example, 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 uses a first subsystem 100 for removing fine particles, dissolved oxygen, ionic components, etc. from the NMP aqueous solution, and a permeation vaporization film device for removing fine particles, dissolved oxygen, ionic components, etc. from the NMP aqueous solution. 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 an NMP purified solution. The configuration of each subsystem will be described below.

(First subsystem 100)
The first subsystem 100 has a receiving unit 101 that receives the NMP aqueous solution to be processed that has been recovered as described above. The NMP aqueous solution is supplied to the receiving unit 101 by a first NMP aqueous solution supply line L101 connected to an 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 stock solution of the NMP aqueous solution supplied to the purification system 1. It is possible to switch 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 for 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 to the first microfiltration membrane device 102 that removes fine particles contained in the NMP aqueous solution via the second NMP aqueous solution supply line L102. 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 is downstream of the membrane degassing device 103, that is, the membrane degassing device 103 and the ion exchange device 104 (described later). It may be provided in between, or may be provided both upstream of the membrane degassing device 103 and between the membrane degassing device 103 and the ion exchange device 104.

The first microfiltration membrane device 102 is connected to the membrane degassing device 103 that removes the dissolved oxygen of the NMP aqueous solution via the third NMP aqueous solution supply line L103. As will be described later, the NMP aqueous solution is heated to about 120 ° C. before being introduced into the osmotic vaporization membrane device 201. In the NMP aqueous solution heated to about 120 ° C., the dissolved oxygen contained in the NMP aqueous solution becomes hydrogen peroxide, and this hydrogen peroxide may oxidize and deteriorate the 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, a dissolved oxygen meter (not shown) is provided at the inlet line L103 and the outlet line L104 of the membrane degassing device 103. Further, the inlet line L103 of the membrane degassing device 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 portion 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 rate adjusting valve V103 for adjusting the flow rate of high temperature steam.

The degassing film of the membrane degassing device 103 can be formed from polyolefin, polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), polyurethane, epoxy resin and the like. Since NMP has the property of dissolving some organic materials, the degassing membrane is preferably formed of polyolefin, PTFE or PFA. The degassed membrane is preferably non-porous. Degassing, that is, removal of dissolved oxygen, is performed by moving the dissolved oxygen of the NMP aqueous solution flowing inside the hollow filament-shaped degassing membrane to the outside of the degassing membrane whose negative pressure is applied by the vacuum pump 109. The oxygen partial pressure may be lowered by sweeping an inert gas such as nitrogen gas on the outside (gas permeation side) of the degassing membrane, or the vacuum method and the sweep method may be used in combination.

The membrane degassing device 103 is connected to an ion exchange device 104 that removes an ionic component of the NMP aqueous solution via a fourth NMP aqueous solution supply line L104. The ion exchange device 104 is filled with an anion exchange resin or a cation exchange resin in a single bed, or an anion exchange resin and a cation exchange resin in a mixed bed or a multi-layer bed. The type of ion exchange resin may be either a gel type or an 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 the resin that may flow out from the ion exchange device 104 and prevents the resin from flowing out downstream. The second microfiltration membrane device 105 is connected to the primary treatment liquid tank 106 via the 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 receives the NMP aqueous solution. It is supplied to the permeation vaporization membrane device 201. Hereinafter, the NMP aqueous solution stored in the primary treatment liquid tank 106 and supplied to the osmotic vaporization membrane device 201 may be referred to as the primary treatment liquid.

A resistivity meter (not shown) is provided at the inlet line L104 and the outlet line L105 of the ion exchange device 104. When the specific resistance of the NMP aqueous solution treated by the ion exchange device 104 is smaller than a predetermined value, that is, when the ionic component is not sufficiently removed, the NMP aqueous solution can be circulated along the 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 unit 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, but when the specific resistance of the NMP aqueous solution is smaller than a predetermined value, the fifth NMP aqueous solution supply line The valve V101 of L105 is closed and the valve V102 of the return line L107 is opened. As a result, a circulation loop is formed through the receiving portion 101, the first microfiltration membrane device 102, the membrane degassing device 103, and the ion exchange device 104. By flowing the NMP aqueous solution along this circulation loop, the ionic components contained in the NMP aqueous solution are sufficiently removed.

Even when the dissolved oxygen of the NMP aqueous solution treated by the membrane degassing device 103 is larger than a predetermined value, that is, when the dissolved oxygen is not sufficiently removed, the NMP is taken along the loop passing through the ion exchange device 104. The aqueous solution can be circulated. As a result, the dissolved oxygen contained in the NMP aqueous solution is sufficiently removed.

(Second subsystem 200)
The primary treatment liquid from which fine particles, dissolved oxygen and ionic components have been removed and stored in the primary treatment liquid tank 106 is then supplied to the second subsystem 200 to generate an NMP concentrate from which most of the water has been removed. To. The primary treatment liquid tank 106 is connected to the osmotic vaporization membrane device 201 via the seventh NMP aqueous solution supply line L201. The seventh NMP aqueous solution supply line L201 is provided with a pump 224 and a valve V201. 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 these first heater 205 and waste heat recovery heat exchanger 206. By heating the NMP aqueous solution supplied to the osmotic vaporization membrane device 201 to about 120 ° C., the dehydration performance of the osmotic vaporization membrane device 201 can be improved. 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 concentrate flowing through the NMP concentrate discharge line L204. The first heater 205 heats the NMP aqueous solution with high-temperature steam supplied from an external steam source (not shown). The steam supply line of the first heater 205 is provided with a valve V202 for adjusting the steam supply amount. A temperature alarm indicator 223 is provided downstream of the first heater 205. The opening degree 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 ° C. A flow rate alarm indicator 225 is provided upstream of the waste heat recovery heat exchanger 206 of the seventh NMP aqueous solution supply line L201. The opening degree 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.

The osmotic vaporization membrane device 201 has a plurality of osmotic vaporization membrane modules 202 to 204 connected in series. In the present embodiment, three osmotic vaporization membrane modules, that is, the first osmotic vaporization membrane module 202, the second osmotic vaporization membrane module 203, and the third osmotic vaporization membrane module 204 are connected in series from upstream to downstream. However, the number is not limited to three. The first osmotic vaporization membrane module 202 is connected to the second osmotic vaporization membrane module 203 via the first connection line L202. The second osmotic vaporization membrane module 203 is connected to the third osmotic vaporization membrane module 204 via the second connection line L203. The first to third osmotic vaporization membrane devices 202, 203, 204 have the separation membranes (osmotic vaporization membranes) 202c, 203c, 204c, and the concentration chambers 202a, 203a, 204a on the upstream side and the permeation chambers 202b, 203b, on the downstream side. It is divided into 204b. Since the separation membranes 202c, 203c, 204c have an affinity for water, water is permeated through the separation membranes 202c, 203c, 204c at a permeation rate higher than that of NMP. By setting the permeation chambers 202b, 203b, 204b side to negative pressure, water having a high permeation velocity moves to the permeation chambers 202b, 203b, 204b in the form of steam (gas phase) together with a small amount of NMP having a low permeation velocity, and most of them. NMP remains in the concentration chambers 202a, 203a, 204a. Using this principle, a part of water is removed from the NMP aqueous solution to produce a concentrated solution of the NMP aqueous solution. At the outlet of the third osmotic vaporization membrane module 204, an NMP concentrate (moisture content is less than 0.01%) having an NMP concentration increased to about 99.99% can be obtained.

The NMP aqueous solution is sequentially circulated through the first to third osmotic vaporization membrane modules 202, 203, and 204, and the water content in the NMP aqueous solution is gradually removed. In order to maintain the water 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. by high-temperature steam supplied from an external steam source. The steam supply lines of the second and third heaters 207 and 208 are provided with valves V203 and V204 for adjusting the steam supply amount, respectively. The NMP concentrated water discharged from the third osmotic vaporization membrane module 204 is supplied to the relay tank 301 of the third subsystem 300 through the NMP concentrated liquid discharge line L204. As described above, the NMP concentrate flowing through the NMP concentrate discharge line L204 exchanges heat 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.

A return line L215 for the NMP concentrate, which branches off from the NMP concentrate discharge line L204 and is 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, the valve V206 is opened, and the NMP concentrate is returned to the primary treatment liquid tank 106. When the NMP concentrate is returned to the primary treatment liquid tank 106, the temperature of the NMP concentrate is set to the same level as the temperature of the NMP aqueous solution (primary treatment liquid) by the cooler 226 provided on the return line L215. Cool with cooling water so that

The permeation chambers 202b, 203b, 204b of the first to third permeation vaporization membrane modules 202, 203, 204 are formed by the first to third permeation liquid discharge lines L206, L209, L212, respectively, to form the first to third permeation liquid tanks. It is connected to 214, 215, 216. A negative pressure can be applied to the permeation chambers 201b, 202b, 203b above the first to third permeation tanks 214, 215, 216, and the inside of the permeation chambers 201b, 202b, 203b can be maintained at a negative pressure. The first to third vacuum pumps 217, 218, 219 are provided. Gas phase water and a small amount of NMP are condensed by cooling water or brine to become permeable liquid and collected at the bottom of the first to third permeable liquid tanks 214, 215 and 216. The first to third permeate tanks 214, 215 and 216 can temporarily store the permeate. Specifically, the cooling water CW and the brines BR1 and BR2 flow through the cooling jackets (not shown) surrounding the first to third permeation tanks 214, 215 and 216, respectively, and the gas phase water and NMP. To the first to third heat exchangers 211, 212, 213 provided in the first to third permeate discharge lines L206, L209, L212 through the cooling lines L207, L210, L213. It is supplied to condense vapor phase water and NMP. The temperature of the brine BR1 and BR2 is preferably about 0 to -20 ° C.

The first to third heat exchangers 211, 212, and 213 have the first to third osmotic vaporization membrane modules 202, 203, and 204 via the first to third permeation liquid discharge lines L206, L209, and L212, respectively. It communicates with the transmission chambers 202b, 203b, 204b of the above. The first to third heat exchangers 211, 212, and 213 are coolers that cool the permeated vapor that has permeated through the permeation chambers 202b, 203b, and 204b and condense it to generate a permeated liquid. The permeation chambers 202b, 203b, 204b communicate with the first to third permeation liquid tanks 214, 215, 216 downstream of the first to third heat exchangers 211, 212, 213.

The first to third permeated water discharge lines L208, L211 and L214 are connected to the bottoms of the first to third permeated liquid tanks 214, 215 and 216, respectively. Inert gas supply lines L406A, 406B, and 406C branched from the inert gas supply main pipe L401, which will be described later, are connected to the upper portions of the first to third permeation tanks 214, 215, and 216, respectively. The condensed water and a small amount of NMP are temporarily stored in the first to third permeate tanks 214, 215 and 216, and the first is the inert gas supplied from the inert gas supply lines L406A, 406B and 406C. By pressurizing the inside of the third permeable liquid tanks 214, 215 and 216, the gas is discharged from the first to third permeable liquid tanks 214, 215 and 216. The permeated water discharged from the first permeation tank 214 is discharged to the waste liquid tank, and the permeated water discharged from the second to third permeation tanks 215 and 216 is reused as described later.

The gas phase water collected in the first permeate tank 214 and the cooling water CW in which a small amount of NMP is cooled are discharged to the first cooling water discharge line L220. A 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 heat provided in the second permeated water discharge line L211. The permeated water containing NMP supplied to the exchanger 220 and flowing through the second permeated water discharge line L211 is heated. The rest of the cooling water is supplied to the heat exchanger 221 provided in the third permeated water discharge line L214, and heats the permeated water containing NMP flowing through the third permeated water discharge line L214. Measuring instruments 222 and 223 for measuring water concentration, flow rate, etc. are provided downstream of the heat exchangers 220 and 221 of the second and third permeated water discharge lines L211 and L214.

The most upstream osmotic vaporization membrane module, that is, the first osmotic vaporization membrane module 202 has an osmotic vaporization membrane 202c made of CHA-type, T-type, Y-type or MOR-type zeolite. The osmotic vaporization membrane modules other than the most upstream osmotic vaporization membrane module, that is, the second and third osmotic vaporization membrane modules 203 and 204 have osmotic vaporization membranes 203c and 204c made of A-type zeolite. A-type zeolite is relatively inexpensive and has high dehydration performance, but leaks and performance deterioration are likely to occur when treating an NMP aqueous solution having 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-mentioned environment. Therefore, the osmotic vaporization membrane 202c of the first osmotic vaporization membrane module 202 for treating the NMP aqueous solution containing 10 to 20% by weight of water uses CHA-type, T-type, Y-type or MOR-type zeolite and contains water. A-type zeolite is used for the osmotic vaporization membranes 203c and 204c of the second and third osmotic vaporization membrane modules 203 and 204 for treating a small amount of NMP aqueous solution. It is not necessary that all of the plurality of osmotic vaporization membranes constituting the first osmotic vaporization membrane module 202 are made of CHA-type, T-type, Y-type or MOR-type zeolite, and some of the membranes are A-type zeolites. It may consist of.

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

The permeated liquids of the second and third osmotic vaporization membrane modules 203 and 204 are collected on the upstream side of the osmotic vaporization membrane apparatus 201. Specifically, the second and third permeate discharge lines L211 and L214 are connected to the permeate recovery line L205, and the permeate recovery line L205 is connected to the primary treatment liquid tank 106. The permeate discharged from the second and third permeate discharge lines L211 and L214 has a higher NMP content than the permeate discharged from the first permeate discharge line L208, so by recovering this. , The recovery rate of NMP can be increased. The osmotic vaporization membrane module from which the permeable liquid is recovered is not limited to the second and third osmotic vaporization membrane modules 203 and 204, and at least the permeable liquid of the most downstream osmotic vaporization membrane module (third permeable vaporization membrane module 204) May be collected on the upstream side of the osmotic vaporization membrane device 201. The permeated liquid may be collected in the receiving unit 101, or may be selectively collected in the primary treatment liquid tank 106 and the receiving unit 101 by providing a branch line (not shown) in the permeated liquid collecting line L205. Good.

(Third subsystem 300)
Most of the water in the NMP concentrate produced by the second subsystem 200 has been removed. However, since the NMP concentrate contains a small amount of chromaticity components, fine particles of the osmotic vaporization membranes 202c, 203c, and 204c eluted from the osmotic vaporization membrane module and ionic components, a third osmotic vaporization membrane apparatus 201 is located further downstream. Distillation in subsystem 300 produces an NMP purified solution. The third subsystem 300 produces a purified NMP solution by distilling and condensing the NMP concentrate, and thus functions as a distillation purification device for the NMP concentrate. 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 because it consumes less energy, the size of the apparatus is small, and the operation is easy. Further, among the simple distillation methods, the reduced pressure 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 of the second subsystem 200, and for example, an operation such as temporarily stopping the operation of the third subsystem 300 while the second subsystem 200 is in operation is performed. May be done. Therefore, by providing the relay tank 301, the second subsystem 200 and the third subsystem 300 can be operated more flexibly while maintaining their independence from each other. The relay tank 301 is connected to the regenerator 302 via the first NMP concentrate supply line L301. The first NMP concentrate supply line L301 is provided with a pump 306 and a valve V301. The regenerator 302 is a heat exchanger, and exchanges heat with the NMP concentrate (hereinafter referred to as NMP purified gas) evaporated in the evaporation can 303 described later. Thereby, the heat load of the evaporation can 303 can be reduced. The regenerator 302 is connected to the evaporation can 303 via the second NMP concentrate supply line L302. The evaporation can 303 heats and evaporates the NMP concentrate with high-temperature steam supplied from an external steam source (not shown). The steam supply line of the evaporation can 303 is provided with a valve V302 for adjusting the steam supply amount. A high-temperature liquid-phase NMP concentrate stays at the bottom of the evaporation can 303, and a gas-phase NMP purified gas from which fine particles have been removed is formed at the top thereof. Since the chromaticity component contained in the liquid phase NMP concentrate is also difficult to evaporate, it is accumulated at the bottom of the evaporation can 303. The evaporation can 303 in the present embodiment will be described below by taking a liquid film flow-down type evaporation can as an example, but an evaporation can other than the liquid film flow-down type, for example, a flash type or a calandria type evaporation can. You may use it. A circulation line L303 is connected to the bottom and top of the evaporation can 303, and a circulation path including the evaporation can 303 is formed by the circulation line L303. On the circulation path, the cycle of taking out the liquid phase NMP concentrated liquid, returning it to the evaporation can 303, and heating it again under the liquid film flow is repeated. At the bottom of the steam take-out can 304 (described later), an NMP concentrate take-out line L306 that joins the circulation line L303 is provided. The NMP concentrate staying at the bottom of the steam take-out can 304 is also returned to the evaporation can 303 through the NMP concentrate take-out line L306 and the circulation line L303, and is heated again. The circulation line L303 is provided with a circulation pump 307 and a valve V303. From the circulation line L303, the impurity discharge line L309 of the NMP concentrate provided with the valve V304 is branched.

The NMP refined gas of the evaporation can 303 is taken out from the gas phase portion of the evaporation can 303, and is taken out to the steam take-out can 304 by the first NMP purification gas take-out line L304. The steam take-out can 304 is connected to the regenerator 302 via a second NMP refined gas take-out line L305. The heat of the NMP purified gas is heat-exchanged with the liquid phase NMP concentrate in the regenerator 302. The NMP purified gas that has left the regenerator 302 is further introduced into the condenser 305 by the third NMP purified gas take-out line L307, and is condensed by the cooling water CW to become an NMP purified liquid. Inside the condenser 305, an NMP purified liquid is stored at the bottom, and above that is a gas phase portion composed of NMP purified gas. The gas phase portion of the condenser 305 communicates with the vacuum pump 309 by the negative pressure line L310, and the gas phase portion of the condenser 305 is made negative pressure by the vacuum pump 309. The gas phase portion of the third subsystem 300 including the evaporation can 303 is also made negative pressure by the vacuum pump 309, and evaporation under reduced pressure is performed in the evaporation can 303. This promotes the 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, and the gas containing the NMP purified gas discharged from the condenser 305 to the vacuum pump 309 is cooled. 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 drainage line L311, and the NMP concentrate flowing through the impurity discharge line L309 is cooled by the heat exchanger 311 before being discharged.

The NMP purification liquid take-out pipe L308 is connected to the outlet of the condenser 305. The NMP purified liquid is sent to the payout unit 311 by a pump 308 provided in the NMP purified liquid take-out pipe L308. Like the receiving unit 101, the dispensing unit 311 has a plurality of containers (first to third containers 311a, 311b, 311c), and these containers 311a, 311b, 311c are the NMP purified liquids discharged from the purification system 1. It can be switched according to the purpose of acceptance, analysis, transfer, etc. If there is no problem as a result of the analysis, the NMP purified liquid is transferred to the manufacturing system of the lithium ion secondary battery 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 liquid 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 the inert gas. As described above, various containers for storing the NMP aqueous solution, the NMP concentrate, or the NMP purified solution are provided upstream and downstream of the osmotic vaporization membrane device 201. In some of these containers, an interface between the NMP aqueous solution, the NMP concentrate or the NMP purified solution and the gas phase portion is formed inside. The following are examples of containers that satisfy this condition.

(1) First to third containers 101a, 101b, 101c of the receiving portion 101 of the NMP aqueous solution
(2) Primary treatment liquid tank 106
(3) Relay tank 301
(4) Regenerator 302
(5) Evaporation can 303
(6) Steam take-out can 304
(7) Capacitor 305
(8) First to third containers 311a, 311b, 311c of the NMP purified liquid dispensing unit 311
The gas phase portion of the conventional container (in the following description regarding the inert gas supply means, the container means the container 101a, 101b, 101c, 106, 301 to 305, 311a, 311b, 311c) was formed of air. .. However, the inventor found that when these containers were filled with air, NMP combined with the air in the gas phase to combine NMP peroxides (NMP-O-OH; 5-hydroperoxo-1). It was found that −methyl-2-pyrrolidone) was produced. Peroxides in NMP can explode if accumulated. Therefore, in the present embodiment, the inert gas supply means is provided in these containers. Nitrogen gas is preferable as the inert gas, and argon gas can also be used. The inert gas supply means are installed on the inert gas supply mother pipe L401 described below, the inert gas supply line that branches from the mother pipe L401 and supplies the inert gas to each container, and each inert gas supply line. It consists of a gas seal unit and.

Specifically, the inert gas supply mother pipe L401 is connected to the inert gas supply source (not shown), and the inert gas supply mother pipe L401 and the receiving unit 101, the primary treatment liquid tank 106, the relay tank 301, The payout unit 311 is connected by the inert gas supply lines L402, L403, L404, and L407, respectively. The inert gas supply lines L402, L403, L404, L407 are connected to the top of the container. Gas seal units U402, U403, U404, and U405 are provided on the inert gas supply lines L402, L403, L404, and L407, respectively. Further, an inert gas supply line L405 for sweeping is connected to a negative pressure line L310 between the condenser 305 (more accurately, the gas cooler 310) and the vacuum pump 309. The inert gas is supplied from the inert gas supply line L405 to the condenser 305, and further, the inert gas is also supplied to the regenerator 302, the evaporation can 303 and the steam extraction can 304 through the lines L307, L302, L304 and L305. .. Although not shown, the regenerator 302, the evaporation can 303, and the steam take-out can 304 can be provided with a similar vacuum pump and an inert gas supply line for sweeping.

The inert gas is filled in the container when the NMP aqueous solution purification system 1 is first operated. 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, and the air inside the container is forcibly replaced with the inert gas. The gas seal units U402, U403, U404, and U405 are automatically opened when the pressure of the container on the downstream side drops, and the container is filled with the inert gas. Therefore, when the amounts of the NMP aqueous solution, the NMP concentrated solution, and the NMP purified solution in the container decrease, the pressure in the container decreases, and the inert gas is replenished in the container via 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 reduces 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 osmotic vaporization membrane module can be reduced. Further, since almost no oxygen is present in the container, the effect of preventing the oxidation of the NMP aqueous solution, the NMP concentrated solution and the NMP purified solution can be obtained.

(Dehydrator 600)
Next, the dehydrator of the NMP aqueous solution purification system will be described. FIG. 2 is a schematic configuration diagram of the dehydrator 600. The dehydrator 600 includes the first to third osmotic vaporization membrane modules 202 to 204 and ancillary equipment thereof in the second subsystem 200. Heaters 220 and 221 for heating the permeate are provided downstream of the second and third permeation tanks 215 and 216. The configuration of the heaters 220 and 221 is not limited as long as the permeated liquid can be heated, and may be, for example, an electric heater. In the present embodiment, the heaters 220 and 221 are heat exchangers 220 and 221 in order to use the cooling drainage of the first heat exchanger 211 as the heat source. Therefore, the heat exchangers 220 and 221 are connected to the first cooling water discharge line L220 that discharges the cooling drainage of the first heat exchanger 211. As described above, the first heat exchanger 211 is connected to the first permeation chamber 202b of the first permeation vaporization membrane module 202, and the permeated steam permeated through the first permeation chamber 202b is heated with the cooling water CW. Cool by replacement. The heaters 220 and 221 heat the permeated liquid generated by the second and third osmotic vaporization membrane modules 203 and 204 by heat exchange with the cooling drainage flowing through the first cooling water discharge line L220 and the cooling water discharge line L221. To do. The permeate heated by the heat exchangers 220 and 221 is recovered by the permeate recovery line L205, which is a return line for returning the permeate to the inlet side of the first permeation vaporization membrane module 202.

The temperature of the permeate in the first to third permeate tanks 214, 215 and 216 decreases in the order of the first permeate tank 214, the second permeate tank 215, and the third permeate tank 216. There is. This is because the osmotic vaporization membrane module in the subsequent stage reduces the amount of water in the NMP aqueous solution and increases the NMP concentration. In order to dehydrate the NMP aqueous solution having a small amount of water, it is necessary to increase the pressure difference between the inlet side and the permeation side of the osmotic vaporization membrane module. Since the pressure on the permeation side is equal to the saturated vapor pressure of water, it is necessary to lower the temperature on the permeation side and lower the saturated vapor pressure of water in order to increase the pressure difference between the inlet side and the permeation side. Therefore, although normal temperature water can be used as cooling water in the first heat exchanger 211, the brine BR1 which is a lower temperature refrigerant is used in the second heat exchanger 212, and the brine BR1 is used in the third heat exchanger 213. Brine BR2, which is a lower temperature refrigerant, is used. As a result, in one example, the temperature of the permeated water is about 40 ° C. in the first permeate tank 214, about 2 ° C. in the second permeate tank 215, and about −10 ° C. in the third permeate tank 216. Further, in one example, the temperature of the cooling drainage flowing through the first cooling water discharge line L220 and the cooling water discharge line L221 is about 37 ° C. Therefore, the cooling drainage 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 of the second and third permeation liquid tanks 215 and 216. The permeated water is preferably heated to a temperature above 20 ° C. Since the cooling drainage flowing through the first cooling water discharge line L220 is cooled to around room temperature and discarded, ancillary equipment such as a cooling tower for cooling the cooling drainage is not required or can be miniaturized.

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 taken from the second and third permeated water discharge lines L211 and L214 to the upstream side of the first permeated vaporization membrane module 202 (the primary treatment liquid in this embodiment). When returning to the tank 106), the permeated water is pushed out by the pressure of the inert gas, as will be described later. As a result, the negative pressures of the second and third permeable liquid tanks 215 and 216 and the negative pressures of the second and third permeable chambers 203b and 204b are released, and the second and third osmotic vaporization membrane modules 203, The performance of 204 is reduced. 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. If a pump is used instead of the inert gas, the permeated water may be drained continuously, but in order to secure the suction head of the pump, the second and third permeation tanks 215 and 216 and the pump are used. It is not realistic because it is necessary to provide a large height difference between them. For this reason, the permeated water stored in the second and third permeation tanks 215 and 216 is intermittently returned to the primary treatment 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 treatment liquid tank 106 and stored in the primary treatment liquid tank 106. The temperature of the NMP aqueous solution will decrease. The NMP aqueous solution is heated by the first heater 205 and the waste heat recovery heat exchanger 206, and 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 osmotic vaporization membrane module 202 temporarily falls below 120 ° C., and the temperature of the dehydration membrane and the temperature on the permeation side of the first osmotic vaporization membrane module 202 fluctuate, resulting in dehydration. Performance becomes unstable. In the present embodiment, since the permeated water in the second and third permeation liquid tanks 215 and 216 is heated, the temperature change of the NMP aqueous solution supplied to the first permeation vaporization membrane module 202 is suppressed, and more stable dehydration is performed. Performance can be obtained.

By heating the permeated water in the second and third permeated liquid tanks 215 and 216, it becomes easy to maintain the performance of the measuring instruments 222 and 223. The type of the measuring instrument 222 is not limited, but in the present 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 water concentration meter 223B provided on the water discharge line L214. These measuring instruments 222 and 223 are often not guaranteed to operate for liquids below 0 ° C., and their use for cold liquids is disadvantageous in terms of reliability. In the present 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 of discharging the permeate from the first to third permeation tanks 214, 215 and 216 will be described. As described above, the inert gas supply means, that is, the inert gas supply lines L406A and 406B branched from the inert gas supply main pipe L401, are located above the first to third permeation tanks 214, 215 and 216. The 406C is connected. Further, the first to third permeation liquid discharge lines L206, L209, and L212 are provided with first to third shutoff valves V207, V208, and V209, respectively. The first to third shutoff valves V207, V208, and V209 are the first to third permeation liquid tanks 214, 215, 216 and the permeation chambers 202b of the first to third permeation vaporization membrane modules 202, 203, 204, respectively. This is an example of means for blocking communication with 203b and 204b. For example, when the permeate is discharged from the second permeate tank 215, the second shutoff valve V208 is first closed to shut off the communication between the second permeate tank 215 and the permeation chamber 203b. At the same time, the second vacuum pump 218 is stopped. Next, the inert gas is supplied from the inert gas supply line 406B. The inert gas supply line 406B can apply a pressure to the second permeate tank 215 so that the permeate stored inside the second permeate tank 215 can be discharged to the permeate recovery line L205. As a result, the permeated liquid from the second permeated liquid tank 215 is returned to the primary treatment liquid tank 106. There is a possibility that a part of the inert gas may flow into the primary treatment liquid tank 106, but 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 shown by the broken line in FIG. 2, a pump for discharging the permeate between the second permeate tank 215 and the heat exchanger 220 and between the third permeate 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 permeation tanks 214, 215 and 216, and does not require a pressurizing capacity for discharge. Therefore, when the pressure of the inert gas cannot be sufficiently secured, the installation of the pump P is effective. However, since the permeate at a low temperature of about -10 ° C is transferred, the pump P may be damaged due to freezing of the permeate, and the installation cost of the pump P itself is high. Therefore, the permeate is used with an inert gas. It is preferable to transfer.

In this embodiment, three osmotic vaporization membrane modules 202 to 204 are used, but the number of osmotic vaporization membrane modules is not limited. Therefore, more generally, at least downstream of the second osmotic vaporization membrane module 203 is arranged in series with the first and second osmotic vaporization membrane modules 202, 203 to further remove water from the concentrated liquid of the organic solvent. One other osmotic vaporization membrane module can be placed. At least one other cooler that communicates with the permeation chamber of the other permeation vaporization membrane module is provided, and the other cooler cools and condenses the permeated vapor that has permeated the permeation chamber of the other permeation vaporization membrane module. To generate a permeate. Further, at least one other permeation tank communicating with the other cooler is provided downstream of the other cooler. The inside of the other permeate tank can be maintained at a negative pressure, and the permeate can be stored. At least one other heater for heating the permeate is provided downstream of each of the other permeation tanks. The cooling drainage discharge line has a branch line connected to each of the other heaters, and the other heater heats the permeated liquid by heat exchange with the cooling drainage flowing through the branch line.

1 NMP aqueous solution purification system 100 1st subsystem 101 Receiving section 101a, 101b, 101c 1st to 3rd containers of receiving section 102 1st microfiltration membrane device 103 Membrane degassing device 104 Ion exchange device 105 2nd Microfiltration membrane device 106 Primary treatment liquid tank 107 Pump 108 Heater L101 to L106 1st to 6th NMP aqueous solution supply line L107 Return line V101, V102 Valve 200 2nd subsystem 201 Osmotic vaporization membrane device 202 to 204 1st to 3rd osmotic vaporization membrane modules 202a, 203a, 204a Concentration chamber 202b, 203b, 204b Permeation chamber 202c, 203c, 204c Separation membrane (osmotic vaporization membrane)
205 1st heater 206 Regenerative heat exchanger 207 2nd heater 208 3rd heater 209 Cooler 210 Mechanical booster pump 211,212,213 1st to 3rd heat exchangers 214,215,216 1st to 1st 3rd permeate tank 217, 218, 219 1st to 3rd vacuum pumps 220, 221 4th and 5th heat exchangers 223 Temperature alarm indicator 224 Pump 225 Flow alarm indicator 226 Cooler L201 7th NMP aqueous solution supply line L202, L203 1st and 2nd connection lines L204 NMP concentrate discharge line L205 Permeate recovery line L206, L209, L212 1st to 3rd permeate discharge lines L207, L210, L213 Cooling line L208, L211 and L214 First to third permeated water 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 Evaporation can 304 Steam removal Can 305 Condenser 306 Pump 307 Circulation pump 308 Pump 309 Vacuum pump 310 Gas cooler 311 Dispensing section 311a, 311b, 311c 1st to 3rd containers of dispensing section L301 1st NMP concentrate supply line L302 2nd NMP concentrate supply Line L303 Circulation line L304 First NMP refined gas take-out line L305 Second NMP refined gas take-out line L306 NMP concentrate take-out line L307 Third NMP refined gas take-out line L308 NMP refined liquid take-out pipe L309 NMP concentrate impurity discharge Line L310 Negative pressure line L311 Cooling water drainage line V301 to V304 Valve L401 Inactive gas supply mother pipe L402 to L407 Inactive gas supply line U402, U403, U404, U405 Gas seal unit 600 Dehydrator V207, V208, V209 No. 1 Third shutoff valve

Claims (6)

A first osmotic vaporization membrane module that removes a part of water from a mixed solution containing an organic solvent and water to generate a concentrated solution of the organic solvent.
A second osmotic vaporization membrane module located downstream of the first osmotic vaporization membrane module and further removing water from the concentrated solution of the organic solvent.
A cooler that communicates with the permeation chamber of the second permeation vaporization membrane module to cool and condense the permeated vapor that has permeated through the permeation chamber to generate a permeated liquid.
A permeation tank that communicates with the cooler downstream of the cooler, can maintain a negative pressure inside, and can store the permeate.
A heater located downstream of the permeate tank and heating the permeate,
A dehydrator having a return line for returning the permeated liquid heated by the heater to the inlet side of the first osmotic vaporization membrane module. It is connected to the permeation chamber of the first permeation vaporization film module, and the permeated vapor permeated into the permeation chamber of the first permeation vaporization film module is cooled by heat exchange with the cooling water and discharged from the permeate tank. A heat exchanger that discharges cooling wastewater that is hotter than the permeate,
It has a cooling drainage discharge line and
The dehydrator according to claim 1, wherein the heater heats the permeated liquid by heat exchange with the cooling drainage flowing through the discharge line. With at least one other osmotic vaporization membrane module, which is arranged in series with the first and second osmotic vaporization membrane modules downstream of the second osmotic vaporization membrane module and further removes water from the concentrated solution of the organic solvent. ,
At least one other cooler that communicates with the permeation chamber of the other permeation vaporization membrane module and cools and condenses the permeation vapor that has permeated into the permeation chamber of the other permeation vaporization membrane module to generate a permeated liquid.
At least one other permeate tank that communicates with the other cooler downstream of the other cooler, can maintain a negative pressure inside, and can store the permeate.
Each is located downstream of the other permeate tank and has at least one other heater that heats the permeate.
The cooling drainage discharge line has a branch line connected to each of the other heaters, and the other heater heats the permeated liquid by heat exchange with the cooling drainage flowing through the branch line. The dehydrator according to 1 or 2. A means for blocking communication between the permeate tank and the permeation chamber of the second permeation vaporization membrane module.
It has a means for supplying an inert gas connected to the permeate tank.
The means for supplying the inert gas exerts a pressure at which the permeate stored inside the permeate tank can be discharged to the return line when the communication between the permeate tank and the permeation chamber is cut off. The dehydrator according to any one of claims 1 to 3, which can be applied to the permeate tank. The dehydrator according to any one of claims 1 to 4, wherein the organic solvent is NMP. The first osmotic vaporization membrane module removes a part of water from the mixed solution containing the organic solvent and water to generate a concentrated solution of the organic solvent.
Further removing water from the concentrated solution of the organic solvent by the second osmotic vaporization membrane module located downstream of the first osmotic vaporization membrane module, and
A cooler communicating with the permeation chamber of the second permeation vaporization membrane module cools and condenses the permeated vapor permeated through the permeation chamber to generate a permeated liquid.
Transferring the permeate to a permeate tank that communicates with the cooler downstream of the cooler and maintains a negative pressure inside.
By heating the permeate discharged from the permeate tank,
A method for dehydrating a mixed liquid containing an organic solvent and water using the osmotic vaporization membrane module, which comprises returning the heated permeate to the inlet side of the first osmotic vaporization membrane module.

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