JP2015071139A - System and method for separation of liquid organic material and water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve separation performance of a liquid organic material and water.SOLUTION: There is provided a separation system 1 including pervaporation membrane modules 3, 4. Each of the pervaporation membrane modules is supplied with a mixture of water and a liquid organic material having a point higher than that of water, and separates the supplied mixture into concentrated liquid in which concentration of the liquid organic material is higher than that in the supplied mixture, and thin vapor in which concentration of water is higher than that in the supplied mixture, and each of the pervaporation modules except for the second pervaporation membrane module 4 supplies the separated concentrated liquid to the pervaporation membrane module in a next stage, as mixture to be supplied. The separation system 1 further includes: a storage tank 2 for storing the mixture supplied to the first pervaporation membrane module; thin vapor discharge means 34 for discharging the thin vapor V1 generated in the first pervaporation membrane module 3 to outside; recirculation means 44 for returning the thin vapor V2 generated in the second pervaporation membrane module 4 to the storage tank 2 or a piping 58; and recovery means 50 for recovering the concentrated liquid generated in the second pervaporation membrane module 4.

Description

  The present invention relates to a separation system and separation method for liquid organic matter and water, and more particularly to a separation system and separation method using an osmotic vaporization method.

  2. Description of the Related Art Conventionally, as a method for separating a liquid mixture of liquid organic material and water into liquid organic material and water, a method of distillation under reduced pressure (vacuum distillation method) is known. However, this method requires a lot of energy for distillation. As a technique excellent in energy saving performance, a pervaporation method (PV method) is known.

  Patent Document 1 describes a method for separating NMP by a PV method from a mixed solution of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) and water. In the PV method, a separation membrane (permeation vaporization membrane) having an affinity for components to be separated is used. By supplying the liquid mixture to the inlet side of the pervaporation membrane and reducing the pressure on the permeate side, a driving force for moving the liquid mixture from the inlet side to the permeate side is obtained, and separation is performed by the difference in the permeation speed between NMP and water. . The pervaporation membrane is composed of a zeolite membrane. Due to the high hydrophilicity of zeolite, water permeates the pervaporation membrane and NMP remains on the inlet side of the pervaporation membrane. The permeated water that has permeated the pervaporation membrane is released to the environment.

JP 2013-18747 A

  In the method described in Patent Document 1, the entire amount of permeated water that has permeated the pervaporation membrane is discharged to the outside. However, since a part of the liquid organic substance is accompanied to the permeation side together with water, the permeated water contains the liquid organic substance. Since the liquid organic substance contained in the permeated water is released to the environment and cannot be recovered, there is a restriction in improving the recovery efficiency of the liquid organic substance.

  An object of the present invention is to provide a separation system and a separation method for a liquid organic material and water in which the separation performance of the liquid organic material and water is improved.

  The separation system for liquid organic matter and water of the present invention is connected in series, and includes a plurality of permeation membrane modules including a first pervaporation membrane module located at the uppermost stream and a second pervaporation membrane module located at the most downstream side. It has a vaporization membrane module. Each pervaporation membrane module is supplied with a mixed liquid of water and a liquid organic substance having a boiling point higher than water, and supplied with the mixed liquid and a concentrated liquid having a higher concentration of the liquid organic substance than the supplied mixed liquid. And dilute vapor having a higher water concentration than the mixed liquid. Each pervaporation membrane module except the second pervaporation membrane module supplies the separated concentrated liquid to the next-stage pervaporation membrane module as a mixed liquid to be supplied. The separation system further includes a storage tank for storing the mixed liquid supplied to the first pervaporation membrane module, a lean steam discharge means for releasing the lean steam generated by the first pervaporation membrane module to the outside, A recirculation means for returning the dilute vapor generated by the second pervaporation membrane module to the storage tank or the pipe connecting the storage tank and the first pervaporation membrane module; and the concentrated liquid generated by the second pervaporation membrane module Recovery means.

  The separation method of the liquid organic substance and water of the present invention is connected in series, and includes a plurality of permeation units including a first pervaporation membrane module located at the uppermost stream and a second pervaporation membrane module located at the most downstream side. This is a method for separating liquid organic matter from water using a vaporized membrane module. In this method, in each pervaporation membrane module, a liquid mixture of liquid organic substance and water to be supplied is concentrated with a higher concentration of liquid organic substance than the liquid mixture supplied, and the water concentration is higher than the liquid mixture to be supplied. The separated pervaporation membrane module excluding the second pervaporation membrane module and supplying the separated concentrated liquid to the next-stage pervaporation membrane module as a mixed solution supplied to each of the pervaporation membrane modules except the second pervaporation membrane module And a step of releasing the lean steam generated by the first pervaporation membrane module to the outside, and a mixture for supplying the lean steam generated by the second pervaporation membrane module to the first pervaporation membrane module A step of returning to a storage tank for storing the liquid or a pipe connecting the storage tank and the first pervaporation membrane module, and a step of recovering the concentrated liquid generated by the second pervaporation membrane module. .

  Since the separation performance between the liquid organic substance and water depends on the moisture density difference between the inlet side and the permeate side of the pervaporation membrane module, the first pervaporation membrane module that processes a mixed solution having a high moisture concentration is a mixed solution. Efficiently separates water from The diluted vapor generated by the first pervaporation membrane module has a low concentration of liquid organic matter, and even if it is discharged out of the system as it is, it does not greatly affect the recovery efficiency of the liquid organic matter. On the other hand, since the second pervaporation membrane module processes a mixed solution having a reduced moisture concentration, the concentration of the liquid organic substance in the generated diluted vapor is relatively high. Therefore, the recovery efficiency of the liquid organic matter can be improved by returning the diluted steam generated in the second pervaporation membrane module to the storage tank or the pipe connecting the storage tank and the first pervaporation membrane module. As described above, in the present invention, the multi-stage pervaporation membrane module including the first and second pervaporation membrane modules is used, the diluted vapor generated in the first pervaporation membrane module is discharged, and the second permeation is performed. Since the dilute vapor generated in the vaporized membrane module is recirculated, the separation performance between the liquid organic substance and water can be enhanced.

1 is a schematic configuration diagram of a separation system according to an embodiment of the present invention. It is a schematic block diagram of a pervaporation membrane module. It is a schematic block diagram of the separation system in an Example. It is a schematic block diagram of the separation system in a comparative example.

  Next, some embodiments of the present invention will be described with reference to the drawings. In this embodiment, NMP is used as the liquid organic material, but the liquid organic material is not limited to this, and generally has a boiling point higher than that of water at 1 atm (1013 hPa), preferably a boiling point at 1 atm. A liquid organic substance having a general operating temperature of the pervaporation membrane module of 120 ° C. or higher can be used. Examples of such liquid organic substances are shown in Table 1.

  NMP is used in the manufacturing process of lithium ion batteries. The positive electrode and negative electrode of the lithium ion battery are mainly composed of an active material, a current collector, and a binder. In general, the binder can be a binder mixed slurry produced by dissolving polyvinylidene fluoride (PVDF) in NMP as a dispersion medium. An electrode is manufactured by apply | coating an active material and a binder mixed slurry to a collector. NMP is gasified in the drying process after slurry application, and most of it is recovered due to environmental impact and cost issues. Recently, the recovered NMP is often reused in the manufacturing process of a lithium ion battery.

  NMP is recovered by collecting NMP in exhaust gas with an adsorbent or a water scrubber. By this step, a mixed liquid of NMP and water having an NMP concentration of 70 to 90% is obtained. Thereafter, NMP is separated from the mixed solution. The liquid organic matter and water separation system and separation method of the present invention are used in the step of separating NMP from this mixed solution.

  With reference to FIG. 1, the structure of the separation system (henceforth the separation system 1) of the liquid organic substance and water which concerns on the 1st Embodiment of this invention is demonstrated.

  The separation system 1 has a storage tank 2 that stores a mixed liquid of water and NMP. The storage tank 2 stores the mixed solution S obtained in the recovery process described above. The storage tank 2 can also store a mixed solution of water and NMP supplied or manufactured by any other method.

  A plurality of pervaporation membrane modules 3 and 4 connected in series are provided downstream of the storage tank 2. In the present embodiment, the plurality of pervaporation membrane modules 3, 4 are a first pervaporation membrane module 3 located upstream and a second pervaporation membrane module 4 located downstream of the first pervaporation membrane module 3. It consists of. “Upstream” and “downstream” are defined along the direction in which the liquid mixture S flows.

  The first pervaporation membrane module 3 is supplied with the mixed liquid S from the storage tank 2, and is supplied with the first concentrated liquid C1 having a higher concentration of NMP than the mixed liquid S supplied with the supplied mixed liquid S. The first dilute vapor V1 having a higher water concentration than the mixed liquid S is separated. The first pervaporation membrane module 3 supplies the first concentrated liquid C1 to the second pervaporation membrane module 4 as a new mixed liquid C1.

  The second pervaporation membrane module 4 is supplied with the mixed liquid C1 from the first pervaporation membrane module 3, and the second concentrated liquid having a higher NMP concentration than the mixed liquid C1 supplied with the supplied mixed liquid C1. Separated into C2 and a second lean vapor V2 having a higher water concentration than the supplied mixed liquid C1. The second concentrated liquid C2 generated by the second pervaporation membrane module 4 is recovered by the recovery means 50 and reused in the manufacturing process in the lithium ion battery.

  The plurality of pervaporation membrane modules can also be composed of three or more pervaporation membrane modules connected in series. In that case, the permeation vaporization membrane module located in the uppermost stream corresponds to the first permeation vaporization membrane module 3 of the present embodiment, and the permeation vaporization membrane module located in the most downstream is the second permeation vaporization membrane module of the present embodiment. Corresponding to 4. Each pervaporation membrane module operates as follows.

  The first pervaporation membrane module 3 is supplied with the mixed liquid S from the storage tank 2, and is supplied with the first concentrated liquid C1 having a higher concentration of NMP than the mixed liquid S supplied with the supplied mixed liquid S. The first dilute vapor V1 having a higher water concentration than the mixed liquid S is separated. The first pervaporation membrane module 3 supplies the first concentrated liquid C1 to the next-stage pervaporation membrane module as a new mixed liquid C1.

  Each of the pervaporation membrane modules located between the first pervaporation membrane module 3 and the second pervaporation membrane module 4 is supplied with the concentrated liquid generated by the previous pervaporation membrane module as a new mixed solution, The supplied mixed liquid is separated into a concentrated liquid having a higher NMP concentration than the supplied mixed liquid and a dilute vapor having a higher water concentration than the supplied mixed liquid. Each pervaporation membrane module supplies the concentrated liquid as a new mixed solution to the next-stage pervaporation membrane module.

  The second pervaporation membrane module 4 is supplied with the concentrated solution generated in the previous pervaporation membrane module as a new mixed solution, and the concentration of NMP is higher than that of the supplied mixed solution. The second concentrated liquid C2 and the second diluted vapor V2 having a higher concentration of water than the supplied mixed liquid. The second concentrated liquid C2 generated by the second pervaporation membrane module 4 is recovered by the recovery means 50 and reused in the manufacturing process in the lithium ion battery.

  The first pervaporation membrane module 3 includes a first pervaporation membrane 31. The first pervaporation membrane 31 partitions the first inlet-side space 32 of the first pervaporation membrane module 3 from the first permeation-side space 33 and is supplied to the first inlet-side space 32. Is separated into a first concentrated liquid C1 staying in the first inlet side space 32 and a first lean vapor V1 permeating through the first permeate side space 33.

  The second pervaporation membrane module 4 includes a second pervaporation membrane 41. The second pervaporation membrane 41 partitions the second inlet-side space 42 of the second pervaporation membrane module 4 from the second permeation-side space 43 and is supplied to the second inlet-side space 42. Is separated into a second concentrated liquid C2 staying in the second inlet side space 42 and a second lean vapor V2 permeating through the second permeate side space 43.

  FIG. 2 shows a schematic configuration of the pervaporation membrane module. The first and second pervaporation membrane modules 3 and 4 (and other pervaporation membrane modules) can have substantially the same configuration. As shown in the entire cross-sectional view of FIG. 2A, the pervaporation membrane modules 3 and 4 have a cylindrical casing 5 and a large number of tubes 6 arranged inside the casing 5. . FIG.2 (b) has shown sectional drawing of the pipe body 6 along the bb line in Fig.2 (a). Each tubular body 6 includes a base material 7 made of a cylindrical inorganic material and a zeolite membrane 8 provided on the outer peripheral surface of the base material 7. The substrate 7 is made of a porous ceramic material such as alumina or mullite. The configuration of the pervaporation membrane module is not limited to that shown in FIG. 2, and a module having an arbitrary shape and configuration can be used as long as the pervaporation membrane is used.

  The inside of the casing 5 is partitioned into an upper space 10 and a lower space 11 by a partition plate 9. The upper end 12 of the tube body 6 is opened, and the lower end 13 is closed. The upper space 10 accommodates the upper end 12 of the tubular body 6, and the lower space 11 accommodates most parts except the upper end 12 of the tubular body 6. The inside 6a of the tubular body 6 and the upper space 10 constitute a transmission side space (first and second transmission side spaces 33, 43), and the other internal spaces are inlet side spaces (first and second inlet side spaces 32, 42). The liquid mixture is supplied from the inlet 14 provided at the lower part of the casing 5 (arrow A1), and the lower space 11 is filled. The mixed liquid is dehydrated by contacting with the zeolite membrane 8 constituting the side wall of the tube body 6, mainly water permeates into the inside 6 a of the tube body 6 (arrow A 2), and the concentrated solution of NMP is outside the tube body 6. (Arrow A3). The concentrated liquid of NMP is discharged from the concentrated liquid outlet 15 provided in the upper part of the lower space 11 (arrow A4), and the vapor mainly composed of water that has permeated the inside 6a of the tubular body 6 passes through the upper end 12 of the tubular body 6. It flows into the upper space 10 (arrow A5), and is discharged from the steam outlet 16 opening in the upper space 10 (arrow A6).

  The zeolite membrane 8 can use zeolite of A type, Y type, T type, MOR type, CHA type or the like. These zeolites have different skeletal structures and ratios of Si and Al, and the higher the Si / Al ratio, the more hydrophobic, that is, the more difficult it is to permeate water. Type A is particularly excellent in dehydration efficiency and can be used preferably. In one preferred embodiment, the zeolite membrane 8 of the first and second pervaporation membranes 31 and 41 is composed of only A-type zeolite.

  For the zeolite membrane 8 of the first pervaporation membrane 31, it may be preferable to use a zeolite other than the A type, for example, a T type, Y type, or CHA type zeolite. A-type zeolite is likely to cause leaks and performance degradation when the water concentration is high or when impurities such as acids are contained in the mixed solution. On the other hand, zeolites other than the A type can maintain performance for a longer period in the above-described environment. As will be described later, the zeolite membrane 8 of the first pervaporation membrane 31 does not require higher dehydration performance than the zeolite membrane 8 of the second pervaporation membrane 41. Further, as will be described later, since the first lean vapor V1 generated from the first pervaporation membrane module 3 is released out of the system, it is necessary to prevent leakage of the zeolite membrane 8 of the first pervaporation membrane 31. The nature is particularly high. For this reason, in another preferred embodiment, the zeolite membrane 8 of the first pervaporation membrane 31 partially contains A-type zeolite. That is, the zeolite membrane 8 of the first pervaporation membrane 31 includes A-type zeolite and at least one type of zeolite selected from the other zeolites described above (for example, T-type, Y-type, MOR-type, CHA-type), Is included.

  Even in this case, it is desirable that the zeolite membrane 8 of the second pervaporation membrane 41 is made of A-type zeolite. Since the liquid mixture supplied to the second pervaporation membrane 41 has already been dehydrated in a considerable amount and contains a small amount of water, the possibility that the water in the liquid mixture will adversely affect the membrane performance is low. Further, since the water content in the mixed solution is small, the driving force for dehydration is small, and a film other than the A type requires a larger film area than the A type. For this reason, apparatus scales and apparatus costs tend to increase with films other than A-type films.

  The separation system 1 has a lean vapor discharge means 34 that discharges the first lean vapor V1 generated by the first pervaporation membrane module 3 to the outside. The lean vapor discharge means 34 is connected to the first drain pot 35 connected to the first transmission side space 33 and to the first drain pot 35 (or indirectly to the first transmission side space 33. Connected) a first vacuum pump 36. The inlet pipe 37 of the first vacuum pump 36 opens into the upper space 35 a of the first drain pot 35. The first vacuum pump 36 creates a negative pressure in the first permeation side space 33 and gives a driving force for dehydration to the first pervaporation membrane 31. The lean vapor discharge means 34 further includes a first cooling means 38 that condenses the first lean vapor V1 between the first pervaporation membrane module 3 and the first drain pot 35. When the first lean vapor V1 is condensed by the first cooling means 38, VOC (volatile organic compound) is liquefied together with the vapor and taken into the first drain pot 35 together with the condensed vapor. That is, by providing the first drain pot 35 for recovering VOC, it is possible to prevent VOC from being discharged outside in the gas phase. This facilitates the management of VOC emissions and facilitates compliance with VOC emission regulations. The first cooling means 38 may cool the first lean vapor V1 to a temperature necessary for condensation, and for example, a cooling tower can be used. The first lean vapor V1 that has permeated the first permeation side space 33 is cooled and condensed by the first cooling means 38 before being released to the outside. The condensed water is collected in the first drain pot 35. The collected condensed water is discharged to the outside through a drain pipe 39 connected to the bottom of the first drain pot 35.

  The separation system 1 has recirculation means 44 for returning the second lean vapor V2 generated by the second pervaporation membrane module 4 to the storage tank 2. The recirculation means 44 is connected to the second drain pot 45 connected to the second transmission side space 43 and to the second drain pot 45 (or indirectly connected to the second transmission side space 43. And) a second vacuum pump 46. The inlet pipe 47 of the second vacuum pump 46 opens into the upper space 45 a of the second drain pot 45. The second vacuum pump 46 makes the second permeation side space 43 have a negative pressure and gives a driving force for dehydration to the second pervaporation membrane 41. The recirculation means 44 further includes a second cooling means 48 between the second pervaporation membrane module 4 and the second drain pot 45.

  The second cooling means 48 needs not only to condense the second lean vapor V2 but also to cool the second lean vapor V2 to the lowest possible temperature in order to increase the degree of vacuum of the second transmission side space 43. For this reason, it is preferable to use cold water or brine. The second lean vapor V2 that has passed through the second permeation side space 43 is cooled and condensed by the second cooling means 48 before being returned to the storage tank 2. The condensed water is collected in the second drain pot 45. The collected condensed water is returned to the storage tank 2 through a drain pipe 49 connected to the bottom of the second drain pot 45. The collected condensed water can be returned to the pipe 58 connecting the storage tank 2 and the first pervaporation membrane module 3. That is, the drain pipe 49 may merge with the pipe 58.

  The separation system 1 has a first ion exchange resin 51 between the storage tank 2 and the first pervaporation membrane module 3. In some cases, the mixed solution contains an acidic substance or a basic substance. Particularly, when a basic substance, particularly an amine, remains in NMP, PVDF constituting the binder causes a defluorination reaction. The PVDF that has undergone the defluorination reaction changes in viscosity and may affect the slurry application process. Therefore, it is desirable to remove the basic substance with the first ion exchange resin 51.

  The separation system 1 has a filter 52 between the storage tank 2 and the first pervaporation membrane module 3. There is a possibility that the dehydration performance of the zeolite membrane 8 is reduced due to adhesion (clogging) of fine particles contained in the mixed solution. It is desirable to remove the fine particles by the filter 52 immediately before the fine particles flow into the first pervaporation membrane module 3. As the filter 52, a microfiltration membrane (MF membrane) and an ultrafiltration membrane (UF membrane) can be suitably used. In this embodiment, the filter 52 is provided upstream of the first ion exchange resin 51, but may be provided downstream of the first ion exchange resin 51.

  The separation system 1 has a heating means 53 immediately before the first pervaporation membrane module 3, that is, between the filter 52 and the first ion exchange resin 51 and the first pervaporation membrane module 3. For example, the heating means 53 may be a ribbon heater or a belt heater attached to the outer periphery of the pipe. The heating means 53 can raise the temperature of the liquid mixture flowing in the pipe to at least 120 ° C. By heating the mixed liquid, the dewatering performance in the first and second pervaporation membrane modules 3 and 4 can be enhanced.

  The separation system 1 has a cooling means 54 connected to the second inlet side space 42 of the second pervaporation membrane module 4. The cooling unit 54 cools the high-temperature second concentrated liquid C2 before transferring it to the recovery unit 50.

  Next, an operation example of the separation system 1 described above will be described.

  First, a mixed liquid of used NMP and water used for manufacturing a lithium ion battery is supplied to the storage tank 2. Impurities such as insoluble fine particles are removed from the mixed solution S by the filter 52, and then soluble impurities, particularly amines, are removed by the first ion exchange resin 51. Next, the mixed solution is heated to a temperature of 70 ° C. or higher, preferably 100 ° C. or higher, more preferably 120 ° C. or higher by the heating means 53, and is supplied to the first pervaporation membrane module 3. In addition, it is desirable that the supply temperature of the mixed liquid is less than 200 ° C. from the viewpoint of heat resistance such as a joint between the membrane and the module.

  The first pervaporation membrane module 3 is separated by the first pervaporation membrane 31 into a first inlet side space 32 and a first permeation side space 33. The mixed liquid S is heated, and the first permeate side space 33 is set to a negative pressure by the first vacuum pump 36, so that the mixed liquid S is added to the first pervaporation film 31. A driving force to be transmitted through one transmission side space 33 is given. The first pervaporation membrane 31 having the zeolite membrane 8 mainly allows water to pass therethrough, and the first concentrated water C1 with an increased NMP concentration is generated in the first inlet-side space 32, and the first permeation-side space is generated. A first lean vapor V1 containing a small amount of NMP in 33 is generated.

  Next, the concentrated water C1 of NMP is supplied to the second pervaporation membrane module 4, and the second concentrated water C2 having a further increased NMP concentration is generated in the second inlet-side space 42 by the same principle. Then, the second lean vapor V2 containing a small amount of NMP is generated in the second transmission side space 43. The second concentrated water C2 is cooled by the cooling means 54, transferred to the recovery means 50, and used in the manufacturing process of the lithium ion battery.

  The first lean vapor V1 generated in the first transmission side space 33 is cooled by the first cooling means 38 and condensed. The condensed water is collected in the first drain pot 35 and discharged outside. The second lean vapor V2 generated in the second transmission side space 43 is cooled by the second cooling means 48 and condensed. The condensed water is collected in the second drain pot 45, returned to the storage tank 2, and the above-described steps are repeated again. Therefore, the NMP returned to the storage tank 2 can be recovered in the process after the next cycle.

  The dewatering performance of the pervaporation membrane module depends on the moisture density difference between both sides of the pervaporation membrane, that is, the inlet side space and the permeation side space, and the degree of vacuum on the permeation side. Specifically, the higher the moisture density in the inlet side space or the higher the degree of vacuum on the permeate side (the lower the absolute pressure), the better the dehydration performance. The liquid mixture supplied to the first pervaporation membrane module 3 has a water concentration of usually 10 to 30%, and the first pervaporation membrane module 3 can separate a large amount of water due to a large water density difference. it can. In contrast, since the second pervaporation membrane module 4 processes the mixed liquid that has already been dehydrated, the amount of water to be separated is small. On the other hand, the permeation amount of NMP does not greatly depend on the moisture density difference. For this reason, the NMP concentration of water vapor generated in the first pervaporation membrane module 3 is extremely low, and the NMP concentration of water vapor generated in the second pervaporation membrane module 4 is higher than this.

  In the present embodiment, the first lean vapor V1 (condensed water) having a low NMP concentration generated by the first pervaporation membrane module 3 is discharged to the outside and is generated by the second pervaporation membrane module 4. The second lean vapor V2 (condensed water) having a high NMP concentration is returned to the storage tank 2. Thereby, the NMP recovery efficiency of the entire system can be increased. The condensed water returned to the storage tank 2 is a small amount compared to the water separated by the first pervaporation membrane module 3, and the reduction of the dewatering efficiency due to returning the water is limited.

  The dewatering performance of the pervaporation membrane module has a positive correlation with the permeate vaporization membrane channel area per unit flow rate of the supplied liquid mixture (the value obtained by dividing the permeation vaporization membrane channel area by the flow rate of the liquid mixture). It is in. Therefore, in order to obtain the required dewatering performance with a single pervaporation membrane module, it is necessary to increase the permeate vaporization membrane channel area. On the other hand, since the permeation amount of NMP is also positively correlated with the permeate vaporization membrane channel area, when a single pervaporation membrane module with a large channel area is used to improve the dewatering performance, the permeation rate of NMP is also increased. It increases accordingly. On the other hand, in the present embodiment, the first pervaporation membrane module 3 only needs to dehydrate a part of the necessary dehydration amount, and does not need to excessively increase the channel area. In the second pervaporation membrane module 4, the permeated NMP is collected in the storage tank 2, so there is no problem even if the flow path area is increased in order to improve the dewatering performance. In other words, the first pervaporation membrane module 3 considers the balance between the amount of dehydration and the NMP permeation amount, but the second pervaporation membrane module 4 need not consider such a balance. In this way, two pervaporation membrane modules are provided in series, and NMP that permeates the second pervaporation membrane module 4 is collected, thereby obtaining the necessary dehydration performance and reducing the amount of NMP released outside the system. Can do. As is apparent from the above, the second pervaporation membrane module 4 (more generally, the pervaporation membrane module from which condensed water is recovered) is the first pervaporation membrane module 3 (more generally). Compared with a pervaporation membrane module in which condensed water is discharged out of the system, it is possible to increase the flow passage area of the pervaporation membrane (or the flow passage area per unit flow rate of the mixed liquid).

  Since the NMP concentration of the condensed water to be discharged is low, processing at the time of discharge becomes easy. As described above, NMP emissions may be subject to VOC emission regulations, but condensed water having a low NMP concentration is likely to be discharged as it is or after dilution. However, since the condensed water to be released contains nitrogen and carbon components derived from NMP in high concentrations, it may be desirable to remove them. In order to remove high-concentration carbon, anaerobic treatment such as fluid carrier type anaerobic treatment or anaerobic MBR method can be applied. Many biological nitrogen removal methods have been proposed as methods for removing high concentrations of nitrogen. For example, a method using granules may be applicable (Japanese Patent Laid-Open No. 2006-289310). In this method, a granule mainly composed of anaerobic bacteria is used as the nucleus of the nitrifying bacteria granule, and a stable nitrification treatment is performed. The granule is formed in a reaction apparatus represented by UASB (Upflow Anaerobic Sludge Blanket).

  Since the first pervaporation membrane module 3 has high dehydration performance due to a large moisture density difference, it is less necessary to increase the degree of vacuum in order to further increase the dewatering performance. The negative pressure acting on the permeate-side spaces 33 and 43 of the pervaporation membrane modules 3 and 4 is determined by the water vapor pressure of the space portions 35a and 45a of the drain pots 35 and 45. When the water vapor pressure is lowered, the degree of vacuum is increased and the dehydration performance is improved. On the other hand, since the water vapor pressure decreases as the temperature of the condensed water decreases, it is necessary to cool the condensed water at a low temperature in order to improve the dewatering performance. However, it is sufficient to cool the first lean vapor V1 generated in the first pervaporation membrane module 3 to about 30 to 40 ° C., and cooling means 38 having a low operating cost such as a cooling tower using outside air is used. be able to.

  On the other hand, the second pervaporation membrane module 4 is the last-stage pervaporation membrane module, and a high degree of vacuum is required to achieve the required NMP concentration. In one example, a vacuum level of 1.0 kPA or less is required. In order to realize such a high degree of vacuum, it is necessary to use a cooling means having a high operating cost such as a refrigerator. However, as described above, the second lean vapor V2 generated by the second pervaporation membrane module 4 is a small amount, and the increase in operating cost is limited.

  As described above, the first lean vapor V1 generated in the first pervaporation membrane module 3 is discharged after condensation, and the second lean vapor V2 generated in the second pervaporation membrane module 4 is condensed. By returning to the post-storage tank 2, it is possible to improve NMP recovery efficiency and reduce power costs.

  When the separation system 1 includes three or more permeation vapor membrane modules arranged in series, the separation system 1 is generated from an intermediate pervaporation membrane module between the first pervaporation membrane module 3 and the second pervaporation membrane module 4. The lean steam can be discharged to the outside in the same manner as the first lean steam V1, or can be returned to the storage tank 2 in the same manner as the second lean steam V2. However, the lean steam discharged to the outside is desirably cooled by a cooling means such as a cooling tower, and the lean steam returned to the storage tank 2 is desirably cooled by a cooling means such as a refrigerator.

  Advantages of the present invention over a single-stage pervaporation membrane module as described in Patent Document 1 are as follows.

  (1) First, NMP recovery efficiency is improved. In a single-stage pervaporation membrane module, it is necessary to obtain a desired NMP concentration with a single pervaporation membrane module. In particular, in the production process of a lithium ion battery, it is necessary to reduce the water concentration to 0.1% or less, preferably 0.05% or less, more preferably 0.02% or less. In order to realize such a moisture concentration, it is necessary to maintain the permeate-side vapor transmission membrane at a high degree of vacuum. The pervaporation membrane module can separate a large amount of water due to a large difference in water density, but if the flow path area is increased in order to improve the dewatering performance, the amount of NMP that permeates into the permeate side space increases. As a result, the NMP concentration of the permeate side vapor increases. Therefore, it is difficult to increase the recovery efficiency of NMP while ensuring the necessary dehydration performance. On the other hand, in the present invention, a large amount of water can be separated by the first pervaporation membrane module 3, and the amount of NMP that permeates into the permeation side space is limited. Therefore, it is possible to increase the recovery efficiency of NMP. Since the NMP concentration of the permeate side steam is low, the burden of wastewater treatment is also small.

  (2) Next, the operating cost is improved. In a single-stage pervaporation membrane module, it is necessary to cool a large amount of discharged steam at a low temperature (for example, 0 ° C.) in order to maintain the permeate vaporization membrane space on the permeation side at a high degree of vacuum. For this reason, the operating cost of the refrigerator or the like increases. On the other hand, in the present invention, it is not necessary to cool a large amount of steam generated in the first pervaporation membrane module 3 at a low temperature (for example, 30 to 40 ° C. is sufficient), and the operation cost of the cooling tower or the like is reduced. Low means can be adopted. The steam generated in the second pervaporation membrane module 4 needs to be cooled by a refrigerator or the like, but since the amount of steam to be cooled is limited, the total operating cost is greatly reduced.

  (3) Furthermore, the burden of wastewater treatment is improved. In the single-stage pervaporation membrane module, since the NMP concentration of the permeate side vapor is high (for example, about 10%), the burden of wastewater treatment is also large. On the other hand, in the present invention, since the NMP concentration of the discharged steam is low (for example, about 2%), the burden of wastewater treatment is small.

  In addition, as shown in a comparative example described later, when the entire amount of permeated water is returned to the storage tank 2, a large amount of water is returned to the storage tank 2, so that the dehydration load in the pervaporation membrane module increases as the number of cycles increases. To do. In this embodiment, a part of the water contained in the permeate is returned to the storage tank 2, but the concentration of the water supplied to the pervaporation membrane module increases and the dehydration driving force increases. Offset.

  In the present embodiment, the liquid phase mixture is supplied to the pervaporation membrane module. However, it is not preferable to supply steam to the pervaporation membrane module as in the conventional vapor permeation method for the following reasons. That is, it is necessary to return the condensed water to the pervaporation membrane module in the vapor phase, and an evaporator is required separately. Further, in the mixed liquid of high boiling point liquid organic material such as NMP and water, water is first evaporated, so that water vapor is easily supplied to the pervaporation membrane module. In order to control the concentration of water and the high-boiling-point liquid organic substance to an appropriate range for the pervaporation membrane module, a facility for dehydrating part of the water is newly required.

  In the separation system 1 of the present invention, the following modified embodiments are possible.

  First, the lean vapor discharge means 34 may have a sensor 55 that detects the concentration of NMP contained in the first lean vapor V1. As described above, since a large amount of water is separated in the first pervaporation membrane module 3, the concentration of NMP contained in the condensate is extremely low. Therefore, when a leak occurs in the first pervaporation membrane 31 and NMP enters the first permeation side space 33, the concentration of NMP increases rapidly and can be easily detected by the sensor 55. As a result, the separation system 1 can be stopped immediately, and a large amount of NMP can be prevented from being released into the environment. Moreover, since the upstream pervaporation membrane processes a large amount of water, it is more likely to deteriorate than the downstream pervaporation membrane. By monitoring the concentration of NMP with the sensor 55, it is possible to grasp the state of the first pervaporation membrane 31 that is most likely to deteriorate. It should be noted that the above effect can be obtained by adopting a series configuration of the first pervaporation membrane module 3 and the second pervaporation membrane module 4.

  Further, the recirculation means 44 may have a second ion exchange resin 56. The water separated by the pervaporation membrane module is mixed with soluble impurities derived from inorganic components or pipes separated from the base material 7 of the pervaporation membrane. Therefore, in this embodiment, in addition to the first ion exchange resin 51 described above, the second ion exchange resin 56 is provided. The ion removal efficiency of the ion exchange resin has a positive correlation with the water concentration of the liquid to be processed, and the higher the water concentration, the more efficiently the ions are removed. The condensed water generated in the second pervaporation membrane module 4 often has a higher water content than the mixed liquid flowing between the storage tank 2 and the first pervaporation membrane module 3, and in such cases Is easy to remove. For this reason, the ion removal efficiency of the whole system can be improved by removing ions before returning the condensed water to the storage tank 2. In addition, it is possible to reduce the load of the first ion exchange resin 51, save the ion resin to be used, and extend the water passage time. When the drain pipe 49 is joined to the pipe 58, it is preferable to connect the outlet side pipe of the second ion exchange resin 56 to the pipe 58.

(Example)
In the examples, NMP recovery efficiency and the like were measured by the separation system having the configuration shown in FIG. As the zeolite membrane 8, an A-type zeolite membrane was used. As the ion exchange resin, Dow Chemical Company MR type mixed bed resin EG290 was used. As the MF membrane, a polyethylene filter having a thickness of 0.1 μm was used. The mixed liquid was treated with the MF membrane 52 and the ion exchange resin 51, heated to 120 ° C. with steam (heating means 53), and sequentially supplied to the first and second pervaporation membrane modules 3 and 4. The first lean vapor V1 generated by the first pervaporation membrane module 3 was cooled with cooling water (first cooling means 38) and discharged. The second lean vapor V2 generated by the second pervaporation membrane module 4 was cooled with brine (second cooling means 48) and returned to the tank 57 provided at the junction with the storage tank 2.

(Comparative example)
In the comparative example, NMP recovery efficiency and the like were measured with the separation system having the configuration shown in FIG. The dilute vapors generated in the first and second pervaporation membrane modules 3 and 4 were merged, cooled with brine (second cooling means 48), and discharged. Other conditions were the same as in the example.

  Table 2 shows the operation data of the example, and Table 3 shows the operation data of the comparative example. The recovery rate of NMP in the example is 99.50%, which is better than 98% of the comparative example. In the examples, the amount of NMP in the permeate was reduced to ¼ that of the comparative example. Therefore, the unrecovered NMP rate was also reduced to ¼. Since the 1st diluted vapor V1 produced | generated by the 1st pervaporation membrane module 3 was cooled with the normal temperature cooling water, the negative pressure concerning the 1st pervaporation membrane module 3 of an Example was 6 kPaA. On the other hand, the negative pressure applied to the second pervaporation membrane module 4 in both the examples and the comparative examples was 1 kPaA. For this reason, in the Example, the cooling energy of the brine also decreased.

DESCRIPTION OF SYMBOLS 1 Separation system of liquid organic matter and water 2 Reservoir 3 First pervaporation membrane module 31 First pervaporation membrane 32 First inlet side space 33 First permeate side space 34 Dilute vapor discharge means 35 First drain Pot 36 First vacuum pump 4 Second pervaporation membrane module 41 Second pervaporation membrane 42 Second inlet side space 43 Second permeation side space 44 Recirculation means 45 Second drain pot 46 Second Vacuum pump 5 Casing 6 Tubing body 7 Base material 8 Zeolite membrane 50 Recovery means 51 First ion exchange resin 52 Filter 53 Heating means 54 Cooling means 55 Sensor 56 Second ion exchange resin C1 First concentrated liquid C2 Second Concentrate S Mixture V1 First lean steam V2 Second lean steam

Claims (12)

A plurality of pervaporation membrane modules including a first pervaporation membrane module connected in series and located at the most upstream, and a second pervaporation membrane module located at the most downstream, each pervaporation membrane module Is supplied with a mixed liquid of water and a liquid organic substance having a boiling point higher than water, and the supplied mixed liquid is supplied with a concentrated liquid having a higher concentration of the liquid organic substance than the supplied mixed liquid. Each of the pervaporation membrane modules excluding the second pervaporation membrane module is separated into a dilute vapor having a higher water concentration than the liquid mixture, and the separated liquid is used as the supplied liquid mixture. A plurality of pervaporation membrane modules to be supplied to the next-stage pervaporation membrane module;
A storage tank for storing the mixed liquid supplied to the first pervaporation membrane module;
Lean vapor discharge means for releasing the lean vapor generated by the first pervaporation membrane module to the outside;
Recirculation means for returning the lean vapor generated by the second pervaporation membrane module to the storage tank or a pipe connecting the storage tank and the first pervaporation membrane module;
Means for collecting the concentrate produced by the second pervaporation membrane module;
Liquid organic matter and water separation system. The first pervaporation membrane module includes a first pervaporation membrane, and the first pervaporation membrane moves the first inlet side space of the first pervaporation membrane module from the first permeation side space. A first dilute solution that partitions and supplies the mixed liquid supplied to the first inlet-side space and permeates the first permeate-side space, and a first dilute liquid that stays in the first inlet-side space. Separated into steam,
The second pervaporation membrane module includes a second pervaporation membrane, and the second pervaporation membrane moves the second inlet side space of the second pervaporation membrane module from the second permeation side space. A second concentrated liquid that partitions and supplies the mixed liquid supplied to the second inlet-side space to the second inlet-side space and a second lean liquid that permeates the second permeate-side space. Separated into steam,
The lean vapor discharge means has a first vacuum pump connected to the first permeation side space, and a cooling means for cooling and condensing the first lean vapor before releasing it to the outside. ,
The recirculation means includes a second vacuum pump connected to the second permeation side space, a cooling means for cooling and condensing the second lean steam before returning to the storage tank or the pipe, The separation system of claim 1, comprising:   The separation system according to claim 2, wherein the first and second pervaporation membranes include a base material made of an inorganic material and a zeolite membrane that is provided on the base material and contains A-type zeolite.   The separation system according to claim 3, wherein the zeolite membrane is made of the A-type zeolite.   The separation according to claim 3, wherein the zeolite membrane of the first pervaporation membrane partially includes the A-type zeolite, and the zeolite membrane of the second pervaporation membrane is composed of the A-type zeolite. system.   The separation system according to any one of claims 1 to 5, wherein the plurality of pervaporation membrane modules include the first pervaporation membrane module and the second pervaporation membrane module.   The separation system according to any one of claims 1 to 6, wherein the liquid organic substance is N-methyl-2-pyrrolidone.   The separation system according to any one of claims 1 to 7, further comprising a first ion exchange resin between the storage tank and the first pervaporation membrane module.   The separation system according to any one of claims 1 to 8, further comprising a filter between the storage tank and the first pervaporation membrane module.   The separation system according to any one of claims 1 to 9, wherein the recirculation means includes a second ion exchange resin.   The separation system according to any one of claims 1 to 10, wherein the lean vapor discharge means includes a sensor that detects a concentration of the liquid organic substance contained in the first lean vapor. Liquid organic matter and water using a plurality of pervaporation membrane modules connected in series and including a first pervaporation membrane module located at the most upstream and a second pervaporation membrane module located at the most downstream A separation method,
In each pervaporation membrane module, a liquid mixture of liquid organic substance and water to be supplied, a concentrated liquid having a higher concentration of the liquid organic substance than the liquid mixture supplied, and a concentration of the water higher than the liquid mixture supplied In each pervaporation membrane module excluding the second pervaporation membrane module, the separated concentrated solution is used as the supplied mixed solution in the next permeation vaporization membrane module. Supplying, and
Releasing the lean vapor generated by the first pervaporation membrane module to the outside;
A storage tank for storing the mixed liquid supplied to the first pervaporation membrane module or the storage tank and the first pervaporation membrane module for the dilute vapor generated by the second pervaporation membrane module Returning the pipe to the connecting pipe,
Recovering the concentrate produced by the second pervaporation membrane module;
A separation method.

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