JP2014144939A - NMP purification system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system that can effectively carry out the purification of NMP.SOLUTION: Pervaporation separation means 18, in which a concentration chamber and a permeation chamber are separated by a separation membrane, selectively pervaporates moisture from NMP aqueous solution supplied to the concentration chamber from heating means, into the permeation chamber via the separation membrane, to yield water vapor as well as to yield dewatered NMP in the concentration chamber. Exhaust means 44, which is connected to the permeation chamber of the pervaporation separation means 18, exhausts from the permeation chamber. Cooling means 40a, 40b cool the exhaust from permeation chamber and remove condensed water from the exhausts in gas liquid separation means 42. Meanwhile, the cooling means 40a, 40b provide sufficient cooling to freeze the moisture in the exhaust discharged from the permeation chamber.

Description

  The present invention relates to an NMP purification system for purifying an NMP aqueous solution containing NMP (N-methyl-2-pyrrolidone).

  The main constituent materials of the positive electrode and the negative electrode in the lithium ion battery are an active material, a current collector, and a binder. The binder is generally obtained by dissolving polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP) as a dispersion medium. And an electrode is manufactured by apply | coating an active material and a binder mixed slurry to a collector. Here, NMP is gasified in the drying process after slurry application, but most of it is recovered due to environmental impact and cost issues. Recently, there are an increasing number of cases where the recovered NMP is reused in the manufacturing process.

The outline of the NMP recovery and reuse process is as follows.
(1) NMP in exhaust gas is recovered by an adsorbent or a water scrubber. By this step, NMP is concentrated to a state of about 70 to 90% of NMP and about 30 to 30% of water.
(2) The NMP / water mixture is purified by distillation. In this step, NMP is purified to 99% and moisture to 1% or less. Various impurities other than moisture are required to be removed at the same time.

  NMP purified in these steps is reused in the manufacturing process again. Further, distillation purification is performed both off-site and on-site.

  Thus, NMP recovery usually includes a distillation purification step. This distillation purification requires a lot of energy and has drawbacks such as an increase in the size of the apparatus.

  On the other hand, as a water separation technique, a technique utilizing pervaporation separation instead of distillation purification has been proposed. As the pervaporation membrane, a NaA-type zeolite membrane (inorganic porous support-zeolite membrane) or the like is used. Patent Document 1 discloses that an anhydrous alcohol is produced by using an osmotic vapor separation step. Patent Document 2 describes the purification of NMP by pervaporation separation (PV) method using a special framework type zeolite membrane that is not NaA type.

  The pervaporation separator removes moisture from the NMP aqueous solution as water vapor through a separation membrane. For this purpose, the NMP aqueous solution supplied to the pervaporation / separation device is heated to about 120 degrees, and the permeation chamber side of the permeation / vaporization device is evacuated. The water vapor obtained from the permeation chamber is cooled to remove condensed water. However, since the exhaust gas contains NMP, a device for removing this is required.

JP 2004-51617 A JP 2012-67090 A

  Here, it is required that the NMP purification system using the pervaporation / separation (PV) method be as efficient as possible. In particular, it is desirable to efficiently dispose of the exhaust gas obtained in the pervaporation / separation apparatus.

  The present invention is an NMP purification system for purifying an NMP aqueous solution containing NMP (N-methyl-2-pyrrolidone), wherein a concentration chamber and a permeation chamber are separated by a heating means for heating the NMP aqueous solution and a separation membrane, Permeation vapor separation means for selectively degassing moisture from the NMP aqueous solution supplied from the heating means to the permeation chamber through the separation membrane into the permeation chamber and obtaining dehydrated NMP in the concentration chamber; An exhaust means connected to the permeation chamber of the separation means and exhausting from the permeation chamber; a cooling means for cooling the exhaust from the permeation chamber; and a gas-liquid separation means for removing condensed water from the exhaust cooled by the cooling means; The cooling means performs sufficient cooling to freeze water in the exhaust discharged from the permeation chamber.

  In one embodiment, the cooling means has a plurality of heat exchangers, and when cooling in one heat exchanger increases the ventilation resistance due to freezing of water vapor in the exhaust gas, the exhaust gas is exchanged with another heat exchanger. And cooling in another heat exchanger.

  Moreover, in one form, it has a means to measure the pressure loss in the plurality of heat exchangers, and the ventilation resistance increases when the pressure loss becomes a predetermined value or more.

  According to the present invention, the exhaust from the gas-liquid separation means is cooled to a degree sufficient for its moisture to freeze. Therefore, efficient exhaust can be performed.

It is a block diagram which shows the whole structure of a system. It is a block diagram which shows the structure of a NMP dehydration purification system. It is a block diagram which shows the structure of the reference example of a NMP dehydration purification system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration of an NMP purification system according to an embodiment.

  In the electrode manufacturing facility 10, an electrode manufacturing process of a lithium ion battery is performed using NMP. At the time of this electrode manufacture, an electrode is manufactured by apply | coating an active material and a binder mixed slurry to a collector. Here, a binder in which PVDF is dissolved in NMP is used as the binder, and NMP is gasified and exhausted in a drying step after slurry application.

  Exhaust gas from the electrode manufacturing facility 10 is introduced into a recovery device 12, where NMP is recovered. The recovery device 12 recovers NMP in the exhaust, and various methods can be used.

  For example, there is a method using a scrubber that sprays water, contacts with exhaust, and dissolves and recovers NMP in water. With this method, an aqueous solution of NMP having a relatively high water content can be obtained. On the other hand, the equipment itself is relatively simple, can be operated easily, can be processed at a low temperature, and can suppress the deterioration of NMP.

    If NMP contains 15% or more of moisture, the flash point disappears and it is treated as a non-hazardous material. Therefore, when NMP is purified off-site, it is common to keep the NMP concentration of the recovered aqueous solution at 85% or less (water content 15% or more) even if an adsorption method is used. For this reason, it is also preferable that the water content of the NMP aqueous solution recovered by the recovery device 12 is 15% or more. It is also suitable to replenish water if necessary.

  The NMP aqueous solution (recovered liquid) recovered in the recovery device 12 is supplied to the filtration device 14 to remove impurities. The filtration device 14 is a membrane filtration device using a UF (ultrafiltration) membrane or an MF (microfiltration) membrane, and removes solid matter contained in the recovered liquid.

  The filtrate obtained by the filtration device 14 is supplied to the ion exchange resin column 16 where excess ions are removed. In particular, acids such as nitric acid produced from formic acid, amines and amines contained in the NMP aqueous solution are removed.

  The filtrate obtained by the filtration device 14 is supplied to the ion exchange resin column 16 where excess ions are removed. In particular, acids such as nitric acid produced from formic acid, amines and amines are removed.

  The treatment liquid (NMP aqueous solution) that has been desalted by the ion exchange resin column 16 is supplied to the NMP dehydration purification unit 30 including the pervaporation separator (PV) 18 and the ion exchange resin column 20, where water is removed. The recovered NMP is obtained.

  The water content of the recovered NMP dehydrated and concentrated in the NMP dehydration purification unit 30 is 1% or less. Then, the recovered NMP is once again removed from the ion exchange resin column 20 by removing ions such as amines, and then the suspended solids are removed by the filtration device 22 to be recovered and used in the electrode manufacturing facility 10.

  FIG. 2 shows a configuration of an NMP dehydration purification unit 30 including an ion exchange resin column 16, a pervaporation / separation apparatus 18, and an ion exchange resin column 20 that constitute the NMP dehydration purification system. As described above, the NMP aqueous solution with a water content of about 30% to 5% recovered by the recovery device 12 is supplied to the ion exchange resin column 16 where ions are removed.

  The NMP aqueous solution from the ion exchange column 16 is supplied to a heat exchanger 36 by a pump or the like, and is heated by passing through the heat exchanger 36 and supplied to a permeation vapor separation (PV) apparatus 18 which is a permeation vapor separation means. . Here, another heat exchanger is provided in the effluent pipe of the ion exchange resin column 16, and the dehydrated NMP obtained by the pervaporation separation device 18 is supplied thereto, whereby the effluent of the ion exchange resin column 16 is dehydrated. It is good to move the heat of NMP. As a result, the effluent from the ion exchange resin column 16 can be heated and the dehydrated NMP can be cooled. Further, heating steam is supplied to the heat exchanger 36, and the heat of the heating steam raises the temperature of the NMP aqueous solution to an appropriate temperature, for example, 120 ° C., for supplying to the pervaporation separation device 18.

  The pervaporation / separation device 18 uses a separation membrane (permeation vaporization membrane) having an affinity for the component to be treated, flows the mixture to the supply side of the membrane, and depressurizes the permeation side. To separate.

  In the case of this embodiment, a zeolite membrane is used, and water is separated and concentrated on the permeate side and NMP on the supply side due to the hydrophilicity of the zeolite. At that time, the permeate water changes from a liquid to a gas (water vapor).

  Thus, the NMP aqueous solution is heated to about 120 ° C. by heat exchange by the heat exchanger 36 and supplied to the pervaporation separation device 18. As the separation membrane of the pervaporation separator 18, for example, a cylindrical membrane module using a NaA type zeolite membrane is used. An NMP aqueous solution is supplied to the stock solution chamber (supply liquid side) of the osmosis vapor separation device 18, while the permeation chamber (permeation side) is supplied with a vacuum pump via heat exchangers 40 a and 40 b and a gas-liquid separator 42. 44 is connected and the inside is decompressed. Therefore, water in the NMP aqueous solution is vaporized while penetrating the separation membrane, and is obtained as water vapor in the permeation chamber (permeation side). The water vapor obtained in the permeation chamber is cooled in the heat exchangers 40a and 40b to which the cooling liquid is supplied via the valves 38a and 38b, and then introduced into the gas-liquid separator 42, where condensed water flows downward. Stay. Further, a pressure gauge 46 for measuring the pressure is provided in the permeation chamber of the pervaporation separator 18.

  Here, in the present embodiment, brine of about −10 ° C. is used as the coolant supplied to the heat exchangers 40a and 40b. As a result, the water vapor obtained in the permeation chamber of the pervaporation separator 18 is not only liquefied but also partially frozen. In the gas-liquid separator 42, when the purpose is to remove condensed water, freezing of water in the heat exchanger 40 should be avoided. However, in this embodiment, the temperature of the brine supplied to the heat exchanger 40 is set to be sufficiently low, the temperature of the gas flowing therethrough is set to 0 ° C. or less, and heat exchange is performed so that freezing always occurs. The temperature of the coolant is preferably about −5 ° C. to −15 ° C., particularly about −10 ° C. as described above, although it depends on the ability of the heat exchanger 40.

  For example, the valve 38a is opened and the valve 38b is closed, and the exhaust gas from the permeation chamber of the pervaporation separator 18 is introduced into the gas-liquid separator 42 through the heat exchanger 40a. In this state, most of the exhaust gas is water vapor, which freezes in the internal passage of the heat exchanger 40a to become ice and reaches the gas-liquid separator 42, but part of it adheres to the inner surface of the internal passage. Therefore, the passage becomes smaller according to use, and the pressure loss in the heat exchanger 40a increases. In the present embodiment, an increase in pressure loss in the heat exchanger 40a is detected based on the detected value of the pressure gauge 46, as the pressure in the permeation chamber has increased.

  When the pressure loss becomes a predetermined value or more, the valve 38a is closed and the valve 38b is opened, and the exhaust of the permeation chamber is introduced into the gas-liquid separator 42 through the heat exchanger 40b, and the process is continued. On the other hand, with respect to the heat exchanger 40a, the valve 38c is closed and disconnected, and water is discharged by thawing by means of circulating high temperature water or the like.

  When starting to use the heat exchangers 40a and 40b, first, the downstream valves 38c and 38d are opened, the inside is evacuated, and then the upstream valves 38a and 38b are opened to start use. .

  In this way, by sequentially switching and using the two heat exchangers 40a and 40b, even if ice adheres to the internal passages of the heat exchangers 40a and 40b, the pervaporation separator can be used continuously. Can do. It is also preferable to provide a pressure gauge for detecting the pressure downstream of the heat exchangers 40a and 40b and measure the pressure loss from the pressure before and after the heat exchangers 40a and 40b.

  Thus, according to this embodiment, the temperature of the target gas exhausted by the vacuum pump 44 is lower than that of the conventional gas. Therefore, NMP is difficult to vaporize, and the NMP concentration in the exhaust of the vacuum pump 44 is lowered. In some cases, an abatement device for the exhaust of the vacuum pump 44 is unnecessary, or even if necessary, the capacity can be reduced. Moreover, since the temperature in the gas-liquid separator 44 is also low, the amount of volatilization from the liquid in the gas-liquid separator 42 is small.

  When the temperature is high and the amount of volatilization in the gas-liquid separator 42 is large, the degree of vacuum decreases accordingly, so that the operation time of the vacuum pump 44 becomes long and energy consumption increases. Therefore, when the temperature is high, it is necessary to discharge condensed water frequently. However, if this condensed water is discharged frequently, the operating time of the vacuum pump 44 increases accordingly, and energy consumption increases. In the pervaporation method, the water pressure difference between the primary side (raw solution chamber) and the secondary side (permeation chamber) of the pervaporation membrane is the driving force for water separation. Therefore, when the degree of vacuum drops, the water concentration in the concentrate cannot be kept stable and low.

  As in the present embodiment, by reducing the temperature of the exhaust system, the occurrence of the above problems can be suppressed and efficient operation can be performed.

  The condensed water in the gas-liquid separator 42 is discharged in the following procedure. First, when the pressure in the evacuated space is a predetermined vacuum, the valve between the gas-liquid separator 42 and the vacuum pump 44 is closed and disconnected. In this state, when a certain amount of condensed water has accumulated in the gas-liquid separator 42, the valve between the pervaporation separator 18 and the gas-liquid separator 42 is closed, and the condensed water drain valve of the gas-liquid separator 42 and A vent valve that opens the upper space of the gas-liquid separator 42 to the atmosphere is opened, and condensed water is discharged. Next, the valve between the vacuum pump 44 and the gas-liquid separator 42 is opened, and after ensuring the degree of vacuum, the valve between the pervaporation separator 18 and the gas-liquid separator 42 is opened, and after ensuring the degree of vacuum as a whole, The valve between the vacuum pump 44 and the gas-liquid separator 42 is closed. This completes the discharge of condensed water.

  In addition, it is suitable to utilize the waste heat of the heat exchanger 50 for the defrosting of the heat exchangers 40a and 40b. That is, the heat exchangers 40a and 40b separated by freezing a high-temperature heat medium (cooling water whose temperature has been increased) after heat exchange in the heat exchanger 50 that cools the dehydrated NMP from the pervaporation separator 18 are brined. By introducing instead of, the internal ice can be thawed. Accordingly, the heat exchanger 40a, 40b can be defrosted using the waste heat of the heat exchanger 50, and the waste heat can be effectively used without using another heat source.

  The thawed water obtained by the heat exchangers 40a and 40b may be biologically treated together with the condensed water from the gas-liquid separator 42.

  Here, PVDF mainly used as a binder is known to cause a defluorination reaction by coexisting with a basic substance. Since the viscosity of the binder solution that has undergone the defluorination reaction changes before the reaction, it causes a failure in the slurry application process. For this reason, it is preferable to remove basic substances, particularly amines, from NMP.

  The ion exchange resin column 20 is filled with a mixed bed ion exchange resin and removes the amine concentration in the liquid. Then, purified NMP from which amines have been removed is obtained at the outlet of the ion exchange resin column 20.

<Reference example>
In the system shown in FIG. 3, the NMP aqueous solution was dehydrated by the pervaporation separator 18 and the water content of the supply liquid and the concentrated liquid was measured. The temperature of the brine was preliminarily operated at 0 ° C. for a while and then changed to −10 ° C. (this time was 0 minute after operation). The results are shown in Table 1.

  30 minutes after the start of operation, the permeation chamber pressure decreased due to the temperature decrease, and the water content in the concentrate decreased. Thereafter, the heat exchanger 40 was gradually frozen, the permeation chamber pressure increased due to pressure loss due to freezing, and the water content in the concentrate increased.

<Example>
In the system shown in FIG. 2, the NMP aqueous solution was dehydrated by the pervaporation separator 18, and the water content of the supply liquid and the concentrated liquid was measured. The temperature of the brine was preliminarily operated at 0 ° C. for a while and then changed to −10 ° C. (this time was 0 minute after operation). When the ventilation resistance increased, the heat exchanger was switched and used, and the unused heat exchanger was thawed. The results are shown in Table 2.

  Thus, there was no increase in the water concentration due to freezing, and the water concentration of the concentrate was stably kept low.

  DESCRIPTION OF SYMBOLS 10 Electrode manufacturing equipment, 12 Collection | recovery apparatus, 14,22 Filtration apparatus, 16,20 Ion exchange resin column, 18 Permeation vaporization separation apparatus, 30 NMP dehydration purification part, 36 Heat exchanger, 38a-38d valve | bulb, 40, 40a, 40b Heat exchanger, 42 gas-liquid separator, 44 vacuum pump, 46 pressure gauge.

Claims (3)

An NMP purification system for purifying an NMP aqueous solution containing NMP (N-methyl-2-pyrrolidone),
A heating means for heating the NMP aqueous solution;
The concentration chamber and the permeation chamber are separated by the separation membrane, moisture is selectively permeated into the permeation chamber through the separation membrane from the NMP aqueous solution supplied from the heating means to the concentration chamber, and water vapor is obtained. Pervaporation means for obtaining dehydrated NMP;
Exhaust means connected to the permeation chamber of the pervaporation separation means and exhausting from the permeation chamber;
Cooling means for cooling the exhaust from the permeation chamber;
A gas-liquid separation means for removing condensed water from the exhaust gas cooled by the cooling means;
Including
The NMP purification system, wherein the cooling means performs sufficient cooling to freeze water in the exhaust discharged from the permeation chamber. The NMP purification system according to claim 1,
The cooling means has a plurality of heat exchangers, and when cooling in one heat exchanger increases ventilation resistance due to freezing of water vapor in the exhaust, the exhaust is switched to another heat exchanger, NMP purification system that cools in the exchanger. The NMP purification system according to claim 2,
An NMP refining system, comprising means for measuring pressure loss in the plurality of heat exchangers, wherein the ventilation resistance is increased when the pressure loss exceeds a predetermined value.

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