Reverse electrodialysis system using rectifying ion exchange membrane

Abstract

The reverse electrodialysis system using a rectifying ion exchange membrane according to an embodiment of the present invention comprises: a power supply unit: an electrode unit in which a positive electrode plate and a negative electrode plate electrically connected to the power supply unit are arranged to face each other at a predetermined interval; a rectifying ion exchange membrane stack provided between the positive electrode plate and the negative electrode plate of the electrode unit and having at least one positive ion rectifying ion exchange membrane and at least one negative ion rectifying ion exchange membrane which are alternately arranged at a predetermined interval; a supply fluid channel unit for supplying raw water to the rectifying ion exchange membrane stack; and a discharge fluid channel unit for separating and discharging diluted water and concentrated water generated by processing the raw water in the rectifying ion exchange membrane stack.

Description

Reverse electrodialysis system using a rectifying ion exchange membrane

[0001] The present invention relates to a reverse electrodialysis system using a rectifying ion exchange membrane, and more specifically, to a reverse electrodialysis system using a rectifying ion exchange membrane having both ion selectivity and rectifying characteristics, so that when the direction of the electrode is changed for scale removal, the bidirectional movement of ions is suppressed, thereby eliminating the need to change the discharge paths of diluted water and concentrated water, and also enabling effective removal of scale attached to the rectifying ion exchange membrane without damaging the membrane, and further minimizing dialysis loss caused by mixing of the concentrated solution and the diluted solution when the direction of the electrode is changed, thereby significantly improving the dialysis performance compared to the prior art.

[0002] The origin of ion exchange membranes began in 1890 when Oswald first discovered a separation membrane with ion selectivity, and in 1930 when Donnan understood the Donnan exclusion phenomenon, which is the selective permeation of counter ions due to the ionic bonding of fixed ions inside an ion exchange membrane in an electrolyte solution.

[0003] Ion exchange membranes primarily utilize specific polymeric synthetic resins known as ion exchange resins. The water and ion channels formed by hydrophilic functional groups with internal charges are extremely small, on the order of a few nanometers in size, and these ion channels are intricately connected in a three-dimensional network structure. Furthermore, due to the extremely small size of these ion channels, typical commercial ion exchange membranes typically have ion selectivities of over 90%.

[0004] Meanwhile, ion exchange membranes are classified into cation exchange membranes and anion exchange membranes according to the functional groups of the membrane. Cation exchange membranes have -SO3 on their surface. - , -COO - , -PO3 2- , -PO3H - , -C6H4O -Because it has a negatively charged functional group, it excludes anions and selectively passes cations. On the other hand, anion exchange membranes are -NH3 + , -NRH2 + , -NR2H + , -NR3 + , -PR3 + , -SR 2+ It has a positively charged functional group, so it selectively transmits anions.

[0005] The above ion exchange membrane has been traditionally applied in various industrial fields such as electrical desalination technology, acid / alkali production, removal of heavy metals from industrial wastewater, desalination of seawater, production of ultrapure water in the semiconductor industry, production of salt from seawater, and recovery of organic acids and amino acids in the fermentation industry. However, recently, as the field of application has expanded beyond these existing fields of application, ion exchange membranes with new functions and characteristics are in demand.

[0006] As described above, ion exchange membranes are used as key materials that determine performance and cost in fields such as membrane-capacitor seawater desalination, reverse electrodialysis power generation, fuel cells, and new and renewable energy sources such as redox flow batteries, which have recently attracted much attention. However, commercialization in related industries is hindered due to high price, membrane resistance, and low mechanical, chemical, and thermal durability.

[0007] Typically, ion exchange membranes are manufactured through phase separation of polymer electrolytes. At the molecular level, hydrophilic regions and hydrophobic regions, composed of negatively or positively charged functional groups, exist in a state of microscopic phase separation. In the presence of water, the hydrophobic portion serves as the framework of the ion exchange membrane, and ion exchange is known to occur through hydrophilic portions called ion domains, which are connected by channels of about 1 nm in size where the hydrophilic groups of the ion exchange membrane are gathered. At this time, the more channels that serve as ion passages and the shorter their length, the smoother ion exchange and transfer can occur, thereby increasing ion conductivity.

[0008] However, since conventional ion exchange membranes basically have bidirectional ion conductivity that allows ions to move from left to right or from right to left around the membrane, there was a problem in that when such ion exchange membranes were applied as they were to seawater desalination facilities, the sodium ions that moved in the reverse direction in the reverse electrode state where the plus and minus electrodes were switched would stick to the electrodes and precipitate, causing scale.

[0009] In this case, the efficiency of the seawater desalination facility is reduced due to the above-mentioned scale, so the facility must be stopped and the scale must be removed periodically, or in severe cases, the ion exchange membrane itself must be replaced. This not only reduces the ion exchange efficiency, but also causes various problems such as increased maintenance costs.

[0010] Specifically, the scale is Ca dissolved in a substance that causes fouling. 2+ , MG 2+ divalent cations such as SO4 2- , CO3 2- It is created when divalent anions such as ions are combined and attached to the membrane surface in excessive concentration, and although it can lower membrane function and allow chemical cleaning, it generally causes damage to the membrane and a decrease in performance.

[0011] In order to prevent the reverse movement of ions that causes the scale described above, a functional membrane specialized in the ion rectification phenomenon (hereinafter referred to as an "ion rectification membrane") that allows ions to flow in only one direction, like a semiconductor diode element, has been developed and attempted in the past (see Korean Patent Registration No. 1896266). However, the ion rectification membrane must go through a complex process of changing the geometric size of the ion channel or the charge distribution inside the ion channel, and in addition, as described above, in the process of applying structural changes such as the geometric size of the ion channel or the charge distribution, the ion selectivity that the ion exchange membrane must fundamentally have is relatively significantly reduced in performance, which is a contradictory problem.

[0012] Meanwhile, a system utilizing electrodialysis to separate ionic species in a solution using such ion exchange membranes is known (see U.S. Patent No. 4,539,091). The known electrodialysis method for separating ionic species in a solution essentially comprises an alternating arrangement of cation exchange membranes that selectively pass cations and anion exchange membranes that selectively pass anions between a pair of electrodes. A direct current passing between the electrodes causes cations to migrate toward the cathode and anions to migrate toward the anode. The ions selectively pass through the ion exchange membranes, and dilution tanks and concentrate tanks are arranged to obtain separated ionic solution fractions.

[0013] The electrodialysis (ED) method has been commercially known since the early 1960s. Known electrodialysis methods rely on the general principles that (1) most salts dissolved in water are ionic (positively or negatively charged) (cations or anions), (2) such ions are attracted to an electrode with an opposite charge, and (3) the membrane can be designed to selectively allow the passage of either anions or cations.

[0014] For example, dissolved ionic components in ionic solutions, i.e. Na+, Ca 2+ and CO3 2- are dispersed in water and effectively neutralize individual charges. When an electrode connected to an external direct current source, such as a battery, is placed in a circuit containing salt water, current passes through the salt water and the ions tend to migrate to the electrode with the opposite charge.

[0015] An example of such an electrodialysis system (10) including a cathode (12) and an anode (24) is disclosed in the attached FIG. 1. Specifically, referring to FIG. 1, the system (10) includes a first cation-transport membrane (14), an anion-transport membrane (18), a second cation-transport membrane (22), and a direct current source (26). When the circuit including the source (26), the cathode (12), and the anode (24) is closed, sodium ions (Na+) migrate toward the cathode (12). This migration separates the input single impaired water stream into a demineralized product stream (16) and a concentrate stream (20).

[0016] Meanwhile, the electrodialysis reverse (EDR) technique has been known since the early 1970s. The electrodialysis reverse system operates under the same general principle as the electrodialysis (ED) system of FIG. 1 described above, except that the electrical polarity is frequently reversed. The electrodialysis reverse system typically involves repeated polarity reversals of the EDR several times per hour, and simultaneously the flow is reversed so that the saline channel becomes the product water channel and vice versa.

[0017] This reversal process alternates between the concentrate channel (containing salt water) and the dilution channel (containing fresh water) over time. This reversal process is useful for removing and flushing scale, slime, and other deposits in the concentrate or dilution treatment area before they accumulate and cause problems. This flushing allows the system to operate with fewer pretreatment chemicals, minimizing fouling of the ion exchange membranes.

[0018] However, the conventional electrodialysis reverse reaction (EDR) system described above has a complex system design because it requires periodic switching between the concentrated water channel and the ionized water channel, and has also had problems such as rapid reduction in the life of the electrode due to the amount of scaling and contamination occurring within the membrane and corrosion caused by the Faraday reaction.

[0019] In addition, chlorine contained in brine rapidly corrodes ion exchange membranes, reducing their effective lifespan, which ultimately necessitates frequent replacement of ion exchange membranes between processes. This not only significantly reduces the dialysis efficiency of conventional reverse electrodialysis systems, but also significantly increases maintenance costs due to surface contamination and damage to ion exchange membranes and increased use of membrane cleaning chemicals.

[0020] In addition, referring to FIG. 2, the conventional electrodialysis reverser (EDR) system periodically changes the direction of the electrodes as described above, and in this process, treatment area 1 is switched from a concentration chamber to a dilution chamber, and treatment area 2 is switched from a dilution chamber to a concentration chamber, thereby having the principle of discharging scale or sediment without accumulating on the ion exchange membrane in a certain amount.

[0021] That is, when cation exchange membranes and anion exchange membranes are alternately arranged at regular intervals inside an electrodialysis system and direct current is supplied, a region where the concentration of ions increases (concentration chamber) and a region where the concentration of ions decreases (dilution chamber) are formed, and as electrodialysis proceeds thereafter, membrane contamination is formed and the current decreases.

[0022] Therefore, the conventional reverse electrodialysis system switches the electrode direction at regular intervals to remove membrane contaminants. As described above, immediately after switching the electrode direction, the current size is restored by the removal of membrane contaminants, but as membrane contamination progresses again, the current decreases, which is repeated infinitely.

[0023] That is, referring to the lower graph of Fig. 2, when the initial electrode direction is called the forward direction and the opposite direction is called the reverse direction, the area that was a concentration chamber in the forward direction is converted to a dilution chamber in the reverse direction, and the area that was a dilution chamber in the forward direction is converted to a concentration chamber in the reverse direction.

[0024] Accordingly, as the dilution chamber is converted to a concentration chamber and vice versa, there is a section (hereinafter referred to as a 'conversion period', see Fig. 2) in which the concentration changes as the concentrate and dilution are mixed. At this time, the electrodialysis effect is significantly reduced in the conversion period, resulting in a huge power loss, which causes the electrodialysis efficiency to decrease.

[0025] In short, these conventional reverse electrodialysis systems had the following problems due to the change in electrode direction.

[0026] First, since the positions of the concentrate and diluted solution also change according to the change in electrode direction as described above, a somewhat complex flow path configuration (e.g., a 3-way valve configuration) and control system are required, which not only increases the equipment size of the entire electrodialysis system but also increases the installation and maintenance costs.

[0027] Second, after each switching of the electrode direction, the concentrate and diluted solution remaining in the flow path before switching are mixed, resulting in a decrease in electrodialysis performance. In this case, when the rate of scale or sediment formation is fast, the cycle of the switching must also be shortened, so there is a problem that the diluted solution is mixed with the concentrate and re-contaminated by frequent switching, resulting in a decrease in dialysis performance and efficiency.

[0028] Accordingly, the present invention has been devised to solve the above problems, and by applying a rectifying ion exchange membrane having both ion selectivity and rectifying characteristics to a reverse electrodialysis system, when the direction of the electrode is changed to remove scale, the bidirectional movement of ions is suppressed, so that not only is there no need to change the discharge paths of diluted water and concentrated water, but also the scale attached to the rectifying ion exchange membrane can be effectively removed without damaging the membrane, and in addition, the dialysis loss that occurs when the concentrate and diluted solution are mixed when the direction of the electrode is changed is minimized, thereby providing a reverse electrodialysis system using a rectifying ion exchange membrane with significantly improved dialysis performance compared to the prior art.

[0029] In order to achieve the above object, the present invention, according to one embodiment, comprises: a power supply unit; an electrode unit in which positive and negative electrode plates electrically connected to the power supply unit are arranged oppositely with a predetermined interval; a rectifying ion exchange membrane stack provided between the positive and negative electrode plates of the electrode unit, in which at least one cation rectifying ion exchange membrane and an anion rectifying ion exchange membrane are alternately arranged with a predetermined interval; a supply channel unit for supplying raw water to the rectifying ion exchange membrane stack; and a discharge channel unit for separately discharging diluted water and concentrated water generated by treating raw water in the rectifying ion exchange membrane stack.

[0030] Also, according to one embodiment, the rectifying ion exchange membrane stack includes: a cation rectifying ion exchange membrane having a rectifying directionality of one direction or the other; an anion rectifying ion exchange membrane having a rectifying directionality opposite to that of the cation rectifying ion exchange membrane; a first treatment region formed between the cation rectifying ion exchange membrane and the anion rectifying ion exchange membrane having rectifying directions opposite to each other, and generating a concentrated water containing cations and anions; and a second treatment region formed between the cation rectifying ion exchange membrane and the anion rectifying ion exchange membrane having rectifying directions opposite to each other, and generating a diluted water from which cations and anions are removed.

[0031] In addition, according to one embodiment, the supply path section includes a supply tank for storing raw water to be electrodialyzed; a raw water supply pipe connecting the supply tank and the rectifying ion exchange membrane stack; and a flow rate control unit provided on one side of the supply pipe for selectively controlling the supply of raw water or controlling the flow rate.

[0032] In addition, according to one embodiment, the discharge path includes a concentration tank for storing the concentrated water discharged from the first treatment area; a dilution tank for storing the dilution water discharged from the second treatment area; and a discharge pipe extending the path so that the concentrated water of the first treatment area and the dilution water of the second treatment area are discharged to the concentration tank and the dilution tank, respectively, in a separated state without mixing.

[0033] In addition, according to one embodiment, a current measuring unit is further provided between the electrode unit and the rectifying ion exchange membrane stack to check for performance degradation of the rectifying ion exchange membrane due to scale attachment.

[0034] Additionally, according to one embodiment, the power supply unit includes a power supply for supplying direct current power; and an electrode direction controller for periodically switching the electrode direction of the power supply for removing scale.

[0035] In addition, according to one embodiment, the rectifying ion exchange membrane comprises: (a) forming a base layer having a plurality of ion channels inside an ion exchange resin including at least one of a fluorine-based polymer, a hydrocarbon-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer; (b) blending an ionomer including at least one of a fluorine-based polymer, a hydrocarbon-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer, and a mixture that suppresses the generation of ion channels inside the ionomer when mixed with the ionomer, together with a solvent, at a certain ratio to form a coating solution in which the ionomer and the mixture are uniformly dispersed in the solvent; (c) coating the coating solution of step b on the base layer of step a to form at least one coating layer; And (d) a step of providing a rectifying characteristic in which ions flow better in a specific direction from a large number of ion channels formed in the base layer toward a smaller number of ion channels formed in the coating layer by forming a smaller number of ion channels inside the coating layer than the number of ion channels in the base layer during the process of removing the solvent by heating and drying the coating layer of step c;

[0036] In addition, according to one embodiment, the base layer of step a is formed of an ion exchange resin including at least one of a fluorine-based polymer including perfluorosulfonic acid, perfluorocarboxylic acid, a polyphenylene-based polymer, a polyetheretherketone-based polymer, a polyarylene ether-based polymer, a polyimide-based polymer, a polystyrene-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer.

[0037] Also, according to one embodiment, the coating solution of step b is formed by blending 0 to 10 wt% of ionomer, 10 to 20 wt% of mixed material, and the remaining balance of solvent.

[0038] In addition, according to one embodiment, the coating solution of step b is formed by gradually reducing the content of the ionomer from an initial 10 wt% to approach 0, while gradually increasing the content of the mixture from an initial 10 wt% to converge to 20 wt% in proportion to the reduced content of the ionomer, and blending the remaining amount with a solvent.

[0039] In addition, according to one embodiment, the coating solution of step b includes an ionomer including at least one of a hydrocarbon polymer including a polyphenylene type, a polyetheretherketone type, a polyarylene ether type, a polyimide type, a polystyrene type, or a fluorine-substituted hydrocarbon polymer; and a mixture including at least one of a fluorine-substituted hydrocarbon polymer including a polyvinylidene fluoride (PVDF), a polytetrafluoroethylene (PTFE), or a hydrocarbon polymer including a polysulfone, a polyetheretherketone, a polyimide, a polystyrene, or a fluorine-substituted hydrocarbon polymer.

[0040] In addition, according to one embodiment, a crosslinking agent including at least one of PDA (polydiacetylene), MBA (N,N'-Methylene bisacrylamide), EGDA (Ethylene glycol diacrylate), DVA (Divinyl adipate), BAED (Bis(2-acryl amido ethyl)disulfide), BPO (Benzoyl Peroxide), MDI (Methylene diphenyl diisocyanate), and PEI (Polyethyleneimine) is further added to the coating solution of step b.

[0041] Additionally, according to one embodiment, the solvent comprises at least one of water, ethanol, methanol, propyl alcohol, acetone, DMF, DMAc, NMP.

[0042] In addition, according to one embodiment, as a result of step d, the ratio of the number of ion channels formed inside the base layer and the coating layer is within 10:1 to 100:1.

[0043] Additionally, according to one embodiment, the base layer of step a further comprises a film-forming binder comprising at least one of polyethylene, polypropylene, and polyvinyl chloride.

[0044] Additionally, according to one embodiment, the base layer of step a further comprises an inorganic additive comprising at least one of silica gel, carbon nanotubes, aluminum oxide, and glass fiber.

[0045] Additionally, according to one embodiment, the base layer of step a further comprises a support membrane composition material comprising at least one of polypropylene, polyethylene, PVC, PTFE, PVDF, and PET.

[0046] Additionally, according to one embodiment, the composite material comprises at least one of a fluorine-based polymer including polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a hydrocarbon-based polymer including polysulfone, polyetheretherketone, polyimide, polystyrene, or a fluorine-partially substituted hydrocarbon-based polymer.

[0047] Meanwhile, according to another embodiment, the present invention comprises: a power supply unit for supplying AC power; an electrode unit in which positive and negative electrode plates electrically connected to the power supply unit are arranged opposite each other at a predetermined interval; a rectifying ion exchange membrane stack provided between the positive and negative electrode plates of the electrode unit, in which at least one cation rectifying ion exchange membrane and an anion rectifying ion exchange membrane are alternately arranged at a predetermined interval; a supply channel unit for supplying raw water to the rectifying ion exchange membrane stack; and a discharge channel unit for separating and discharging diluted water and concentrated water generated in the rectifying ion exchange membrane stack.

[0048] As described above, the present invention applies a rectifying ion exchange membrane having both ion selectivity and rectifying properties to a reverse electrodialysis system, so that when the direction of the electrode is changed for scale removal, the two-way movement of ions is suppressed, thereby eliminating the need to switch the discharge paths of diluted water and concentrated water, and also has the effect of effectively removing scale attached to the rectifying ion exchange membrane without damaging the membrane.

[0049] In addition, the present invention has the effect of significantly improving dialysis performance compared to conventional methods by minimizing dialysis loss that occurs when the concentrate and diluted solution are mixed when the direction of the electrode is changed.

[0050] In addition, the rectifying ion exchange membrane of the present invention can achieve high ion exchange efficiency by preventing the occurrence of scale in a reverse electrode situation by integrally forming a coating layer designed to have a smaller number of ion channels on a substrate layer having a large number of ion channels, and since scale removal or ion exchange membrane replacement is not required, there is an effect of reducing various maintenance costs.

[0051] In addition, the rectifying ion exchange membrane of the present invention has the effect of effectively implementing ion selectivity and rectifying characteristics simultaneously by controlling the asymmetry of the density (number) of ion channels without going through a complex process of changing the geometric size of ion channels or the charge distribution inside the ion channels to impart rectifying characteristics to conventional commercial ion rectifying membranes.

[0052] FIG. 1 is a schematic diagram showing a conventional electrodialysis system. FIG. 1 is a schematic diagram showing a conventional electrodialysis system. FIG. 2 is a diagram showing a control method of a conventional reversal electrodialysis system. FIG. 2 is a diagram showing a control method of a conventional reversal electrodialysis system. FIG. 3 is a schematic diagram showing a reversal electrodialysis system using a rectifying ion exchange membrane of the present invention according to an embodiment. FIG. 3 is a schematic diagram showing a reversal electrodialysis system using a rectifying ion exchange membrane of the present invention according to an embodiment. FIG. 4 is a diagram showing a control method of the reversal electrodialysis system disclosed in FIG. 3. FIG. 4 is a diagram showing a control method of the reversal electrodialysis system disclosed in FIG. 3. FIG. 5 is a process flow diagram showing a method of manufacturing a rectifying ion exchange membrane used in the present invention according to an embodiment. FIG. 5 is a process flow diagram showing a method of manufacturing a rectifying ion exchange membrane used in the present invention according to an embodiment. FIG. 6 is a conceptual diagram showing an ion channel formed inside the rectifying ion exchange membrane of FIG. 5, wherein (a) a general ion exchange membrane, (b) Drawing showing a rectifying ion exchange membrane used in the present invention Drawing 6 is a conceptual diagram showing ion channels formed inside the rectifying ion exchange membrane of FIG. 5, (a) a general ion exchange membrane, (b) a drawing showing a rectifying ion exchange membrane used in the present invention Drawing 7 is a conceptual diagram showing a process in which the ratio of the number of ion channels inside the rectifying ion exchange membrane used in the present invention changes Drawing 7 is a conceptual diagram showing a process in which the ratio of the number of ion channels inside the rectifying ion exchange membrane used in the present invention changes Drawing 8 is a diagram showing the concentration distribution of ions moved along the ion channels at a ratio of 1:9 in FIG. 7, (a) an example of a cation rectifying ion exchange membrane, (b) an example of an anion rectifying ion exchange membrane Drawing 8 is a diagram showing the concentration distribution of ions moved along the ion channels at a ratio of 1:9 in FIG. 7, (a) an example of a cation rectifying ion exchange membrane,(b) Example of anion rectifying ion exchange membrane Figure 9 is a graph showing the current ratio according to the ion channel ratio of Figure 7 Figure 9 is a graph showing the current ratio according to the ion channel ratio of Figure 7 Figure 10 is a flow chart showing a method for manufacturing a rectifying ion exchange membrane used in the present invention step by step Figure 10 is a flow chart showing a method for manufacturing a rectifying ion exchange membrane used in the present invention step by step Figure 11 is a graph showing the results of evaluating the rectifying characteristics of a rectifying ion exchange membrane used in the present invention Figure 11 is a graph showing the results of evaluating the rectifying characteristics of a rectifying ion exchange membrane used in the present invention <Description of the main symbols in the drawings><Description of the main symbols in the drawings> 1000: Reverse electrodialysis system 1000: Reverse electrodialysis system 1100: Power supply 1100: Power supply 1110: Power supply 1120: Electrode direction controller 1120: Electrode section 1200: Electrode section 1300: Rectifying ion exchange membrane stack 1300: Rectifying ion exchange membrane stack 1310, 1320: Cation rectifying ion exchange membrane, anion rectifying ion exchange membrane 1310, 1320: Cation rectifying ion exchange membrane, anion rectifying ion exchange membrane 1330, 1340: First treatment area, second treatment area 1330, 1340: First treatment area, second treatment area 1400: Supply channel section 1400: Supply channel section 1500: Discharge channel section 1500: Discharge channel section BL: Base layer BL: Base layer CL: Coating layer CL: Coating layer C: Ion channel C: Ion channel 100: Coating bar 100: Coating bar 200: Coating solution Supply nozzle 200: Coating liquid supply nozzle 300: Hot plate 300: Hot plate,

[0053] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprises" or "has" or "has" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in this specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0054] Unless otherwise defined herein, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0055] Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0056] First, the 'rectifying ion exchange membrane' defined in the present invention means one that has a rectifying function while also having ion selectivity and ion conductivity at the level of a commercial ion exchange membrane.

[0057] Here, rectification generally means in electrical engineering changing an alternating current with a reversed current direction into a direct current, and is implemented through a diode element that allows current to flow in the forward direction but not in the reverse direction.

[0058] Similarly, a 'rectifying ion exchange membrane' refers to an ion exchange membrane that exhibits the function of maintaining or increasing the current due to ion flow in one direction and decreasing it in the other direction.

[0059] Meanwhile, existing ion exchange membranes that selectively pass cations or anions have high selectivity, but are distinct from the 'rectifying ion exchange membrane' of the present invention in that they exhibit the same ion flow and current regardless of the direction of the electric field crossing the membrane.

[0060] On the other hand, although a membrane-type 'ion rectifying membrane' with an ion rectifying function has been developed in the past, its basic principle is to utilize an asymmetrical structure of ion channel size or a functional group with opposite charge, so there is a limit to high ion selectivity, and this is also significantly different from the 'rectifying ion exchange membrane' of the present invention.

[0061] Accordingly, since existing ion rectifying membranes have had difficulty replacing ion exchange membranes in technologies such as electrodialysis that require high ion selectivity, the applicant of the present invention developed a rectifying ion exchange membrane that has not only a rectifying function but also an ion selectivity at the level of a commercial ion exchange membrane so that it can be used in electrodialysis, as follows.

[0062] FIG. 3 is a schematic diagram showing a reverse electrodialysis system using a rectifying ion exchange membrane of the present invention according to one embodiment, and FIG. 4 is a diagram showing a control method of the reverse electrodialysis system disclosed in FIG. 3.

[0063] Referring to the above Figures 3 and 4, according to one embodiment, a reverse electrodialysis system (1000) using a rectifying ion exchange membrane of the present invention is largely configured to include a power supply unit (1100), an electrode unit (1200), a rectifying ion exchange membrane stack (1300), a supply path unit (1400), and a discharge path unit (1500).

[0064] First, the power supply unit (1100) supplies direct current power to the electrode unit (1200) described later.

[0065] According to one embodiment, the power supply unit (1100) comprises a power supply (1110) that supplies direct current power; and an electrode direction controller (1120) that periodically switches the electrode direction of the power supply to remove scale.

[0066] In addition, the electrode unit (1200) is configured such that the positive and negative plates, which are electrically connected to the power supply unit (1100), are positioned facing each other at a certain interval. That is, the electrode units (1200) shown on the left and right sides of Fig. 3 may be the positive and negative plates, respectively, that supply direct current power.

[0067] In addition, a rectifying ion exchange membrane stack (1300) is provided between the positive and negative electrode plates of the electrode unit (1200), and at least one cation rectifying ion exchange membrane (1310) and anion rectifying ion exchange membrane (1320) are alternately arranged at a certain interval.

[0068] More specifically, the rectifying ion exchange membrane stack (1300) comprises a cation rectifying ion exchange membrane (1310) having a rectifying directionality of one direction or the opposite direction; an anion rectifying ion exchange membrane (1320) having a rectifying directionality opposite to that of the cation rectifying ion exchange membrane; a first treatment region (1330) formed between the cation rectifying ion exchange membrane (1310) and the anion rectifying ion exchange membrane (1320) having rectifying directions opposite to each other and generating a concentrated water containing cations and anions; and a second treatment region (1340) formed between the cation rectifying ion exchange membrane (1310) and the anion rectifying ion exchange membrane (1320) having rectifying directions opposite to each other and generating a diluted water from which cations and anions are removed.

[0069] Accordingly, as the direction of current flow is switched by the electrode direction controller (1120), the positive and negative electrode plates connected thereto are also switched with each other at regular intervals. Therefore, the scale attached to the cation and anion rectification ion exchange membranes (1310)(1320) is separated from the cation and anion rectification ion exchange membranes (1310)(1320) by the reverse operation in which the positive and negative electrode plates are switched with each other. Thereafter, the separated scale is discharged to the outside of the rectification ion exchange membrane stack (1300) together with the concentrated water along the discharge path (1500) described below.

[0070] In addition, the supply path (1400) supplies raw water to the rectifying ion exchange membrane stack (1300). For example, the raw water may be seawater supplied to a seawater desalination facility.

[0071] According to one embodiment, the supply path section (1400) is composed of a supply tank (1410) for storing raw water to be electrodialyzed; a raw water supply pipe (1420) connecting the supply tank and a rectifying ion exchange membrane stack (1300); and a flow controller (1430) provided on one side of the raw water supply pipe to selectively control the supply of raw water or the flow rate of raw water.

[0072] In addition, the discharge path (1500) separates and discharges the diluted water and concentrated water generated in the rectifying ion exchange membrane stack (1300).

[0073] According to one embodiment, the discharge path (1500) includes a discharge pipe (1510)(1520) that extends the path so that the concentrated water of the first treatment area (1330) and the diluted water of the second treatment area (1340) are discharged to the concentration tank and the dilution tank, respectively, in a separated state without mixing; a concentration tank (1530) that stores the concentrated water discharged from the first treatment area; and a dilution tank (1540) that stores the diluted water discharged from the second treatment area.

[0074] More specifically, the discharge pipe (1510)(1520) is composed of a concentrated water discharge pipe (1510) connected to the first treatment area (1330) of the rectifying ion exchange membrane stack (1300) to discharge concentrated water generated in the first treatment area (1330); and a dilution water discharge pipe (1520) connected to the second treatment area (1340) to discharge dilution water generated in the second treatment area.

[0075] At this time, since the present invention uses cation and anion rectifying ion exchange membranes (1310) (1320), the concentrated water discharge path (1510) and the diluted water discharge path (1520) can be fixed without switching the paths, and accordingly, unlike in the conventional reverse electrodialysis system, there is no need to switch the concentrated water discharge path (1510) and the diluted water discharge path (1520), so the discharge path section (1500) does not need to be equipped with a separate control device (e.g., a 3-way valve) like in the conventional one, and thus has the advantage of greatly simplifying the configuration.

[0076] In addition, a current measuring unit (1600) is further provided between the electrode unit (1200) and the rectifying ion exchange membrane stack (1300) to check for performance degradation of the rectifying ion exchange membrane stack (1300) due to scale attachment.

[0077] According to one embodiment, referring to FIG. 3, the current measuring unit (1600) is provided in each electrode chamber (no symbol) provided inside the electrode unit (1200) to continuously measure current and thereby detect a deterioration in the performance of the rectifying ion exchange membrane stack (1300) due to scale attachment. Thereafter, when the current value at both ends of the rectifying ion exchange membrane stack (1300) measured by the current measuring unit falls below a preset constant value, the DC power is reversed to forcibly separate the scale attached to the cation and anion rectifying ion exchange membranes (1310)(1320).

[0078] The reverse electrodialysis system (1000) of the present invention configured as described above can be installed and operated as follows according to one embodiment. (See FIGS. 3 and 4)

[0079] Embodiment of installation and operation control of the reverse electrodialysis system of the present invention

[0080] Step (a): First, the cation rectifying ion exchange membranes (1310) and anion rectifying ion exchange membranes (1320) prepared in multiples are arranged alternately so that the rectifying directions are opposite to each other. (Arrangement of cation rectifying ion exchange membranes and anion rectifying ion exchange membranes)

[0081] Step (b): At this time, a first processing region (1330) for generating concentrated water is formed in the space between the cation rectification ion exchange membrane (1310) and the anion rectification ion exchange membrane (1320) whose rectification directions face each other in the above step 1, and a second processing region (1340) for generating diluted water is formed in the space between the cation rectification ion exchange membrane (1310) and the anion rectification ion exchange membrane (1320) whose rectification directions face each other. (Completion of rectification ion exchange membrane stack assembly)

[0082] Step (c): In addition, the raw water supply pipe (1420) of the supply path section (1400) is connected in parallel to one side of the first treatment area (1330) and the second treatment area (1340). Accordingly, the raw water is equally supplied or the supply is blocked to the first treatment area (1330) and the second treatment area (1340) through the raw water supply pipe (1420). (Connecting the supply path section to the rectifying ion exchange membrane stack)

[0083] Step (d): In addition, an electrode unit (1200) and a current measuring unit (1600) are installed on both sides of the rectifying ion exchange membrane stack (1300) assembled as described above, and a power supply unit (1100) is connected to the electrode unit. (Installation of electrical components)

[0084] Step (e): Next, the concentrated water discharge pipe (1510) of the discharge path (1500) is connected to the first treatment area (1330), and the concentrated water discharge pipe (1520) of the discharge path (1500) is connected to the second treatment area (1340). Accordingly, the concentrated water containing cations and anions generated in the first treatment area (1330) is discharged through the concentrated water discharge pipe (1510) and then stored in the concentration tank (1530), and the diluted water from which cations and anions have been removed generated in the second treatment area (1340) is discharged through the diluted water discharge pipe (1520) and then stored in the dilution tank (1540). (Connecting the discharge path to the rectifying ion exchange membrane stack)

[0085] Step (f): When the electrodialysis system of the present invention is installed as described above, the electrodialysis system (1000) is operated by supplying raw water into the rectifying ion exchange membrane (1300) through the supply path (1400) and turning on the power supply unit (1100) and the current measurement unit (1600).

[0086] Step (g): Referring to FIGS. 3 and 4, when the electrodialysis system (1000) of the present invention is operated, cations and anions contained in the raw water move across the membranes (1310)(1320) along the electrical potential of the electrode unit (1200) and the rectification direction of the cation and anion rectification ion exchange membranes (1310)(1320), and at this time, concentrated water containing cations and anions is generated (concentrator) in the first treatment area (1330), while diluted water from which cations and anions have been removed is generated (diluter) in the second treatment area (1340). The concentrated water and diluted water generated as described above are separated and discharged through the concentrated water discharge pipe (1510) and the diluted water discharge pipe (1520), and then stored in the concentrator (1530) and the diluter (1540), respectively.

[0087] Step (h): Meanwhile, when the current value measured by the current measuring unit (1600) falls below a preset reference current value due to the attachment of scale during operation of the electrodialysis system (1000) (e.g., a 20% decrease compared to the initial current value), an antifouling device (see FIG. 4) is implemented to separate the scale from the cation and anion rectification ion exchange membranes (1310) (1320) by instantaneously switching the positive and negative plates (no sign) of the electrode unit (1200) with each other by the electrode direction controller (1120).

[0088] That is, the anti-fouling device is controlled through an electrode direction controller (1120), and the electrode direction controller (1120) can be set to have a very short holding time in the reverse direction compared to the forward direction of the current for the sole purpose of separating the scale from the cation and anion rectifying ion exchange membrane (1310)(1320). (See Fig. 4)

[0089] Through this, as shown in FIG. 2, in the conventional reverse electrodialysis system, the holding time of the forward direction and the reverse direction of the current are set to be equal, and when the direction of the current is changed, a certain amount at the beginning of the change is mixed with each other when the flow path of the concentrated water and the diluted water is changed, so it is not stored in the dilution tank but is discarded at each change (a loss occurs by the amount indicated as 'Loss' in FIG. 2), whereas in the present invention, by using the cation and anion rectifying ion exchange membranes (1310)(1320), not only is the concentrated water and the diluted water not mixed with each other, but the reverse holding time of the antifouling device is very short, so the dialysis efficiency is greatly improved by minimizing the loss.

[0090] In order to control the operation of the above system (1000), the anti-fouling device can be controlled to control the flow rate controller (1430) to cut off the supply of raw water or reduce the supply flow rate. For example, the supply flow rate of the flow rate controller (1430) can be automatically controlled according to the current value measured by the current measuring unit (1600). Alternatively, the flow rate control of the flow rate controller (1430) can be set in advance to match the switching cycle of the electrode direction controller (1120), or the flow rate controller (1430) can be configured to be directly linked with the electrode direction controller (1120).

[0091] Specific examples

[0092] 1) Conditions of the rectifying ion exchange membrane

[0093] - The rectifying ion exchange membrane for the present invention must have an ion mobility (selectivity) of 85% or more and a rectification ratio in which the forward current size is more than twice the reverse current size.

[0094] - If the selectivity is less than 85%, the efficiency of electrodialysis may be significantly reduced, and if the rectification ratio is less than twice, excessive current may be generated in the membrane fouling remover (hereinafter referred to as the 'anti-fouling device'), making fast switching impossible. Therefore, it is advantageous if both the rectification ratio and selectivity are high.

[0095] - Any material can be used to form the rectifying ion exchange membrane, but a polymer compound including at least one of hydrocarbon polymers and fluorine-substituted polymers, including polyphenylene, phenylene oxide, phenylene sulfide, para-phenylene, polyetheretherketone, polyarylene ether, polyimide, and polystyrene, can be used.

[0096] - In one embodiment, the cation rectifying ion exchange membrane is composed of PFSA ionomer, and the anion rectifying ion exchange membrane is composed of FAA ionomer.

[0097] 2) DC current conversion conditions

[0098] - The condition for switching from the concentrate / diluter to the anti-fouling device can be set to switch when the current size (maximum current value) when there is no membrane contamination decreases below a certain ratio, and at this time, the ratio of the current value that serves as the reference for starting the anti-fouling device is controlled to turn on the anti-fouling device at a specific current value preset among the range of 60 to 90% of the maximum current value (hereinafter referred to as the 'start reference current value').

[0099] - That is, when the current value constantly monitored by the current measuring unit (1600) gradually decreases and reaches the starting reference current value within the range of 60 to 90% of the maximum current value, the anti-fouling device starts (turns on).

[0100] - At this time, if the setting range of the starting reference current value is set to exceed 90%, the number of switching times may increase excessively, in which case, loss due to switching may occur, and if it is set to less than 60%, the accumulated membrane contamination may be excessive and irreversible contamination may occur, and the dialysis efficiency may decrease due to excessive increase in the time of the anti-fouling device.

[0101] 3) Anti-fouling device maintenance time

[0102] - While membrane contamination is being removed in the anti-fouling device, the current changes according to the degree of membrane contamination. After membrane contamination removal is complete, the current remains within a certain range without change, so this can be used to set the end point of the anti-fouling device.

[0103] - According to one embodiment, the anti-fouling device is turned off when the rate of change in current after the anti-fouling device is maintained at ±5% or less (hereinafter referred to as the “termination criterion current change rate”).

[0104] - That is, the current value is constantly measured in the current measuring unit (1600) and the rate of change in current is calculated for each time (second), and when the calculated rate of change in current falls below the preset termination reference rate of change in current, the anti-fouling device is turned off.

[0105] - For example, the method for calculating the rate of change of the current can be calculated by the following formula [('current at time t(s)' - 'current at time t-1(s)') / 'current at time t(s)')*100]

[0106] - At this time, the anti-fouling device maintenance time can be set within the range of 1 second to 5 minutes. A time of less than 1 second may not be enough time to completely remove membrane contamination, and if it is longer than 5 minutes, membrane contamination may occur again, albeit in small amounts.

[0107] Meanwhile, although not shown in the drawing, the reverse electrodialysis system (1000) of the present invention can also be operated by supplying AC power to the electrode unit (1200) according to another embodiment.

[0108] That is, the present invention can replace the power supply unit (1100) that supplies direct current power to the electrode unit (1200) according to another embodiment with an AC power supply unit (not shown) that supplies alternating current power. In this case, since the AC power automatically switches the current direction, the electrode direction controller (1120) of the configuration of the embodiment discussed above in FIG. 3 becomes unnecessary, and has the advantage of enabling the configuration of a more compact electrodialysis system (1000) by the AC power supply unit (not shown).

[0109] In addition, a multilayer ion exchange membrane having rectifying properties used in the present invention (hereinafter referred to as a 'rectifying ion exchange membrane') can be manufactured according to the manufacturing method below.

[0110] That is, unlike the manufacturing process of a conventionally known ion rectifying membrane, the present invention provides a method for manufacturing a rectifying ion exchange membrane having an ion selectivity level equivalent to that of commercial ion exchange membranes currently used in various industrial fields, as well as an ion rectification characteristic, by effectively implementing the ion rectification phenomenon using a simple process.

[0111] In addition, the cation and anion rectifying ion exchange membrane (1310)(1320) used in the present invention does not use a complex process of changing the geometric size of the ion channel or the charge distribution inside the ion channel, compared to the conventional ion rectifying membrane, but forms one or more coating layers integrally on a base layer made of ion exchange resin and having a number of ion channels, and has a smaller number of ion channels than the base layer, thereby asymmetrically controlling the density (number) of ion channels inside the base layer and the coating layer, so that ion rectifying characteristics are expressed, and thus has the characteristic that ion selectivity is not reduced.

[0112] To this end, by controlling the content ratio of the ion exchange resin that forms an ion channel as the main component of the base layer and the coating layer and the mixed material that has the function of preventing and suppressing the formation of an ion channel in the ion exchange resin, an ion channel having an asymmetrical rectifying characteristic can be simply added to the coating layer.

[0113] Here, the mixture included in the coating layer has the characteristic of a material that, in contrast to the ion exchange resin, does not function as an ion channel-forming agent. As this mixture is mixed within the coating layer, a region where ion channels do not exist is formed in proportion to the ratio.

[0114] That is, it performs the function of inhibiting and suppressing the formation of ion channels in the coating layer by reducing the proportion of the area where ion channels exist by the ion exchange resin in proportion to the proportion of the mixture added to the coating layer. Therefore, by utilizing this characteristic, it is possible to control the number of ion channels depending on the relative proportion of the ion exchange resin and the mixture. In this way, the manufacturing method of the present invention enables the realization of a high degree of rectification characteristics through precise control of the formation of ion channels.

[0115] Hereinafter, with reference to the attached drawings, a method for manufacturing a rectifying ion exchange membrane used in the present invention will be specifically examined as follows.

[0116] FIG. 5 is a process flow chart showing a method for manufacturing a rectifying ion exchange membrane used in the present invention according to one embodiment, and FIG. 6 is a conceptual diagram showing ion channels formed inside the rectifying ion exchange membrane of FIG. 5, and is a diagram showing (a) a general ion exchange membrane and (b) a rectifying ion exchange membrane used in the present invention, and FIG. 7 is a conceptual diagram showing a process in which the ratio of the number of ion channels inside the rectifying ion exchange membrane used in the present invention changes, and FIG. 8 is a diagram showing the concentration distribution of ions moved along the ion channels of 1:9 ratio in FIG. 7, and is (a) an example of a cation rectifying ion exchange membrane and (b) an example of an anion rectifying ion exchange membrane, and FIG. 9 is a graph showing the current ratio according to the ion channel ratio of FIG. 7, and FIG. 10 is a flow chart showing a method for manufacturing a rectifying ion exchange membrane used in the present invention step by step, and FIG. 11 is a diagram showing the results of evaluating the rectifying characteristics of the rectifying ion exchange membrane used in the present invention. It's a graph.

[0117] First, referring to FIGS. 5 to 11, a method for manufacturing a rectifying ion exchange membrane according to an embodiment of the present invention can be performed according to the following steps.

[0118] Step (a): Forming a base layer (BL) having n ion channels (C) inside an ion exchange resin comprising at least one of a fluorine-based polymer, a hydrocarbon-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer. (S100)

[0119] According to one embodiment, the base layer (BL) of the present step may be formed of an ion exchange resin including at least one of a fluorine-based polymer including a perfluorosulfonic acid, a perfluorocarboxylic acid, a polyphenylene-based polymer (e.g., phenylene oxide, phenylene sulfide, para-phenylene), a polyetheretherketone-based polymer, a polyarylene ether-based polymer, a polyimide-based polymer, a polystyrene-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer.

[0120] For reference, the above fluorine-substituted hydrocarbon polymer refers to a hydrocarbon polymer in which a portion is substituted with fluorine, and is distinct from the general hydrocarbon polymer described above.

[0121] The above phenylene oxide, phenylene sulfide, and para-phenylene are types of carbon-hydrogen polymers, each classified as a group based on the repeating units that make up the polymer. Therefore, polymers composed of phenylene oxide, phenylene sulfide, and para-phenylene can be collectively referred to as polyphenylenes because they all have linked phenylene units.

[0122] Additionally, the base layer (BL) may further include a film-forming binder including at least one of polyethylene, polypropylene, and polyvinyl chloride.

[0123] Additionally, the base layer (BL) may further include an inorganic additive including at least one of silica gel, carbon nanotubes, aluminum oxide, and glass fiber.

[0124] Additionally, the base layer (BL) may further include a support membrane composition material including at least one of polypropylene, polyethylene, PVC, PTFE, PVDF, and PET.

[0125] Step (b): An ionomer comprising at least one of a fluorine-based polymer, a hydrocarbon-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer, and a mixture that suppresses the generation of ion channels (C) within the ionomer when mixed with the ionomer are blended together with a solvent at a certain ratio to form a coating solution in which the ionomer and the mixture are uniformly dispersed in the solvent. (S200)

[0126] According to one embodiment, the coating solution of the present step is formed by blending 0 to 10 wt% of ionomer, 10 to 20 wt% of mixed material, and the remaining balance of solvent.

[0127] More specifically, the coating solution of the present step is formed by gradually reducing the content of the ionomer from an initial 10 wt% to approach 0, while gradually increasing the content of the mixed material from an initial 10 wt% to converge to 20 wt% in proportion to the reduced content of the ionomer, and blending the remaining amount with a solvent.

[0128] According to one embodiment, the ionomer may be a polymer compound including at least one of a hydrocarbon polymer including polyphenylene (e.g., phenylene oxide, phenylene sulfide, para-phenylene), polyetheretherketone, polyarylene ether, polyimide, and polystyrene, or a fluorine-partially substituted hydrocarbon polymer.

[0129] Meanwhile, the mixed material may be a polymer compound including at least one of a fluorine-based polymer including polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), a hydrocarbon-based polymer including polysulfone, polyetheretherketone, polyimide, and polystyrene, or a fluorine-partially substituted hydrocarbon-based polymer.

[0130] In addition, according to one embodiment, the coating solution of step b may further include a crosslinking agent including at least one of PDA (polydiacetylene), MBA (N,N'-Methylene bisacrylamide), EGDA (Ethylene glycol diacrylate), DVA (Divinyl adipate), BAED (Bis(2-acryl amido ethyl)disulfide), BPO (Benzoyl Peroxide), MDI (Methylene diphenyl diisocyanate), and PEI (Polyethyleneimine).

[0131] Additionally, according to one embodiment, the solvent may be at least one of water, ethanol, methanol, propyl alcohol, acetone, DMF, DMAc, NMP, or a mixture thereof.

[0132] Step (c): Coating the coating solution of step b on the base layer (BL) of step a to form at least one coating layer (Coating layer; CL). (S300)

[0133] First, the manufacturing device for a multilayer ion exchange membrane having rectifying properties for performing this step and the next step may be largely composed of a coating section and a drying section. Referring to FIG. 10, according to one embodiment, the coating section may be a coating bar (100) in the shape of a circular rod and a coating solution supply nozzle (200), and the drying section may be a hot plate (300).

[0134] Continuing, in this step, the coating liquid is first coated on the surface of a circular coating bar (100) using a coating liquid supply nozzle (200), and then, in this state, the coating bar (100) is brought into contact with the upper surface of the base layer (BL), so that the coating liquid is transferred from the surface of the coating bar (100) to the upper surface of the base layer (BL).

[0135] In addition, the coating bar (100) is moved at a speed of, for example, 20 mm per second while in contact with the upper surface of the base layer (BL).

[0136] In one embodiment, an ion exchange resin of the same material as the base layer (BL) may be applied to the ionomer, and a coating solution blended with a mixture and a solvent is coated on the base layer (BL) to additionally form a coating layer (CL). Accordingly, the rectification characteristics of the ion exchange membrane of the present invention can be controlled by adjusting the ratio of the number of ion channels (C) formed within the base layer (BL) and the coating layer (CL).

[0137] At this time, the weight composition ratio of the solute (ionomer + mixture) forming the coating layer (CL) among the blended coating solutions can generally be mixed up to 30 wt% or less based on 100 wt% of the total coating solution, and in particular, in the coating solution excluding the solvent (the coating layer in which the solvent has evaporated and dried), when the weight composition ratio of the ionomer and the mixture is 40 wt% or less for the ionomer and 60% or more for the mixture, that is, when the content of the mixture is higher than that of the ionomer, the expression of the rectifying characteristic is more prominent.

[0138] According to one embodiment, the coating of the coating liquid in this step is performed by transfer coating using a coating bar (100), and the transfer coating process of the coating bar is described below with reference to FIG. 10.

[0139] First, a circular coating bar (100) is placed on the base layer (BL), and then the surface of the coating bar (100) is coated with a blended coating solution.

[0140] Next, a coating bar (100) to which a coating liquid has been applied is moved at a constant speed in a horizontal direction (in the direction of the red arrow in the drawing) while in contact with the upper surface of the base layer (BL), thereby forming a coating layer (CL) of uniform thickness on the base layer (BL).

[0141] At this time, the thickness of the coating layer (CL) formed as described above can be controlled by adjusting the viscosity (concentration) of the blended coating liquid, the surface pattern of the coating bar (100) (see FIG. 10), the moving speed of the coating bar (100) (20 to 100 mm / sec), and the weight of the coating bar (100).

[0142] The moving speed of the coating bar should be adjusted within an appropriate range to ensure uniform thickness control of the coating layer. If the moving speed of the coating bar is slow, such as 20 mm / sec or less, the solution may dry at the beginning of the coating process, resulting in thickness variation. If the moving speed is fast, such as 100 mm / sec or more, there may not be sufficient time for the coating solution to flow across the coating surface to achieve uniform thickness.

[0143] Step (d): The coating layer of step c is heated and dried to remove the solvent. (See Fig. 10) In this process, a smaller number of ion channels (C) than the number of ion channels (C) of the base layer (BL), that is, m ion channels (C), are formed inside the coating layer (CL), thereby imparting a rectifying characteristic in which ions flow better in a specific direction from the large number of ion channels (C), that is, n ion channels (C) formed in the base layer toward the smaller number (m) of ion channels formed in the coating layer (CL). (S400)

[0144] For example, in this step, the base layer (BL) coated with the coating liquid can be slowly heated and dried on a hot plate (300, see FIG. 10) at a temperature of 15 to 300 degrees for up to 24 hours.

[0145] According to one embodiment, the process of creating an ion channel is described as follows, assuming that perfluorosulfonic acid (PFSA) is applied as the ionomer.

[0146] Perfluorosulfonic acid (PFSA) is a representative ion exchange resin component of cation exchange membranes and is sold under the product name Nafion. Perfluorosulfonic acid has a backbone structure of a perfluoroalkyl group and a side chain structure containing a sulfonic acid group.

[0147] The main chain above serves as a skeleton that forms the shape of the polymer, and the sulfonic acid group in the side chain is ionized in water to exhibit anionic properties and performs an ion exchange reaction with cations or plays a role in transferring ions.

[0148] The perfluorinated compound of the main chain above is hydrophobic, and the side chain is hydrophilic due to the sulfonic acid group. Accordingly, when dried, the hydrophilic portion forms an ionic region.

[0149] At this time, as water (solvent) is absorbed into the polymer compound, the water content increases, and the ion region expands and connects, forming a network-type ion channel. (The water content of the ion exchange membrane is in the range of 20-50% while maintaining the membrane form.)

[0150] In addition, the network-type ion channel is formed by nano-sized micro-phase separation of hydrophobic and hydrophilic regions, and the crystalline array spacing of the hydrophobic region and the array spacing of the hydrophilic region are on the order of several nanometers.

[0151] The structure of the ion channel created in this way is cylindrical and has a very small diameter. At this time, since the ion channel is surrounded by anion functional groups, a very large electric force acts inside the channel, and only positive ions can selectively pass through due to this electric force.

[0152] Therefore, as a result of this step, the ratio (n:m) of the number of ion channels (C) formed inside the base layer (BL) and the coating layer (CL) is formed within 10:1 to 100:1.

[0153] That is, the ratio of the number of ion channels (C) is controlled according to the content ratio between the two substances, which are the ionomer, which is the raw material of the ion exchange membrane, and the organic / inorganic mixture that can be dissolved and dispersed in the same solvent.

[0154] Referring to Fig. 8, the results of theoretical numerical analysis in a generalized model having a structure with two layers consisting of a base layer (BL) and a coating layer (CL) are shown, and when the asymmetry of the ratio of the number of ion channels (C) changes from 9:9 to 1:9, the ratio of the current at 2 V to the current at -2 V (ion rectification phenomenon) increases, and the cation current (i K + ) versus negative ion current (i Cl - ) maintained a low value (high ion selectivity).

[0155] Referring to the experimental examples below, it was confirmed that as the difference in the ratio (n:m) of the number of ion channels (C) formed inside the base layer (BL) and the coating layer (CL) increases, the ion rectification characteristics also increase proportionally.

[0156] Experimental Example: Evaluation Results of Rectification Characteristics of the Rectification Ion Exchange Membrane According to the Present Invention

[0157] The rectifying ion exchange membrane used in this experiment was manufactured under the following conditions.

[0158] 1) Structural design of the rectifying ion exchange membrane

[0159] - Ion channel (C) number ratio: Variable

[0160] - Number of coating layers (CL): 1

[0161] - Base layer (BL) thickness: 25㎛

[0162] - Coating layer (CL) thickness: approximately 1㎛

[0163] 2) Formation of the base layer of the rectifying ion exchange membrane

[0164] - Nafion NR211 (Material name: PFSA (perfluorosulfoinic acid) / Type: Ionomer (fluorine-based polymer) / Use: Base layer (BL) formation / State: Film form with a thickness of 25.4 ㎛)

[0165] 3) Control of the ratio of ion channels (C) (content ratio of ionomer and mixture during blending)

[0166] - Ionomer: PFSA (perfluorosulfoinic acid) / Type: Ionomer (fluorine-based polymer) / Use: Role in forming ion channels (C) in the coating layer

[0167] - Mixed material: PVDF-TrFE((Poly(vinylidene fluoride-co-tri fluoroethylene) / Type: Mixed material (fluorine-based polymer) / Use: Role in reducing the ratio of ion channels (C) in the coating layer (CL)

[0168] - Solvent: DMF (N N-Dimethylformamide) / Use: Mixed solvent for blending

[0169] - Solute (ionomer + mixture) content in the blended coating solution: 20 wt%

[0170] - Content ratio of solute (PFSA: PVDF-TrFE): 50:50, 40:60, 30:70, 20:80, 10:90, 1:99

[0171] 4) Results of ion rectification characteristics evaluation

[0172] - For detailed composition conditions and ion rectification characteristic evaluation results of the examples (compositions 1 to 6) used in the experiment, see Table 1 and Figure 10 below.

[0173] Comparison of the composition of the coating solution, solute weight, and ionic rectification characteristics (PFSA / PVDF-TrFE / DMF) (PFSA: PVDF-TrFE) (+2V current / -2V current) Base layer (no coating layer) -1.02 Composition 110g / 10g / 80g 50: 500.07 Composition 28g / 12g / 80g 40: 601.57 Composition 36g / 14g / 80g 30: 702.98 Composition 44g / 16g / 80g 20: 804.61 Composition 52g / 18g / 80g 10: 907.47 Composition 60.2g / 19.8g / 80g 1: 9912.36

[0174] - The ion current flowing through the rectifying ion exchange membrane according to the present invention was measured in a potassium chloride (KCl) electrolyte solution having a concentration of 100 mol / L.

[0175] - The ion rectification characteristics were evaluated by calculating the ratio of the forward current size to the reverse current size.

[0176] - As a result, it was confirmed that the value of the ion rectification characteristic in the case where there is no coating layer (CL) (comparative example) is close to 1, and the value of the ion rectification characteristic (difference between forward current and reverse current) proportionally increases as the difference in the weight ratio of the solute increases.

[0177] - That is, since composition 2 showed an ionic rectification phenomenon in which the forward current was 1.5 times higher than the reverse current, it showed rectification characteristics that are effective for commercialization at the solute weight ratio (40:60) or higher.

[0178] In addition, the present invention is not limited to the above-described embodiment, and the same effect can be created even when the detailed configuration, number, and arrangement structure of the device are changed. Therefore, it is stated that a person having ordinary skill in the art can add, delete, and modify various configurations within the scope of the technical idea of ​​the present invention.

Claims

1. Power supply; An electrode section in which a positive electrode plate and a negative electrode plate, which are electrically connected to the power supply, are arranged facing each other at a certain interval; A rectifying ion exchange membrane stack provided between the positive and negative electrode plates of the electrode unit, wherein at least one cation rectifying ion exchange membrane and an anion rectifying ion exchange membrane are alternately arranged at a set interval; A supply path for supplying raw water to the above rectifying ion exchange membrane stack; and A discharge path section for separating and discharging diluted water and concentrated water generated by treating raw water in the above rectified ion exchange membrane stack; Reverse electrodialysis system using a rectifying ion exchange membrane.

2. In paragraph 1, The above rectifying ion exchange membrane stack, A cation rectifying ion exchange membrane having a unidirectional or reverse rectifying direction; An anion rectifying ion exchange membrane having a rectifying direction opposite to that of the above cation rectifying ion exchange membrane; A first treatment area formed between a cation rectifying ion exchange membrane and an anion rectifying ion exchange membrane having opposite rectifying directions, and generating a concentrated water containing cations and anions; and A second treatment area formed between a cation rectifying ion exchange membrane and an anion rectifying ion exchange membrane having opposite rectification directions and generating diluted water from which cations and anions are removed; Reverse electrodialysis system using a rectifying ion exchange membrane.

3. In paragraph 1, The above supply part is, A supply tank for storing raw water to be electrodialyzed; A raw water supply pipe connecting the above supply tank and the rectifying ion exchange membrane stack; and A flow control unit provided on one side of the above supply pipe to selectively control the supply of raw water or control the flow rate; Reverse electrodialysis system using a rectifying ion exchange membrane.

4. In paragraph 2, The above discharge path is, A concentration tank for storing the concentrated water discharged from the first treatment area; A dilution tank storing dilution water discharged from the second treatment area; and A discharge pipe extending the path so that the concentrated water of the first treatment area and the diluted water of the second treatment area are discharged to the concentration tank and the dilution tank respectively in a separated state without mixing with each other; including; Reverse electrodialysis system using a rectifying ion exchange membrane.

5. In paragraph 1, A current measuring unit is further provided between the electrode unit and the rectifying ion exchange membrane stack to check for performance degradation of the rectifying ion exchange membrane due to scale attachment. Reverse electrodialysis system using a rectifying ion exchange membrane.

6. In paragraph 1, The above power supply unit, A power supply that supplies direct current power; and An electrode direction controller that periodically switches the electrode direction of the power supply to remove scale; Reverse electrodialysis system using a rectifying ion exchange membrane.

7. In paragraph 1, The above rectifying ion exchange membrane is, (a) a step of forming a base layer having a plurality of ion channels inside an ion exchange resin comprising at least one of a fluorine-based polymer, a hydrocarbon-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer; (b) a step of blending an ionomer comprising at least one of a fluorine-based polymer, a hydrocarbon-based polymer, or a fluorine-partially substituted hydrocarbon-based polymer, and a mixture that suppresses the generation of ion channels within the ionomer when mixed with the ionomer, together with a solvent at a certain ratio, to form a coating solution in which the ionomer and the mixture are uniformly dispersed in the solvent; (c) a step of coating the coating solution of step b on the base layer of step a to form at least one coating layer; and (d) a step of providing a rectifying characteristic in which ions flow better in a specific direction from a large number of ion channels formed in the base layer toward a smaller number of ion channels formed in the coating layer by forming a smaller number of ion channels inside the coating layer than the number of ion channels in the base layer during the process of removing the solvent by heating and drying the coating layer of the step c above; characterized in that it is manufactured by; Reverse electrodialysis system using a rectifying ion exchange membrane.

8. In paragraph 7, The base layer of the above step a is, Formed by an ion exchange resin containing at least one of a fluorine-based polymer including perfluorosulfonic acid, perfluorocarboxylic acid, a hydrocarbon-based polymer including polyphenylene, polyetheretherketone, polyarylene ether, polyimide, and polystyrene, or a fluorine-partially substituted hydrocarbon-based polymer, Reverse electrodialysis system using a rectifying ion exchange membrane.

9. In paragraph 7, The coating solution of step b above is Formed by blending 0 to 10 wt% of ionomer, 10 to 20 wt% of mixed material, and the remaining balance of solvent. Reverse electrodialysis system using a rectifying ion exchange membrane.

10. In paragraph 9, The coating solution of step b above is The ionomer content is gradually reduced from the initial 10 wt% to approach 0, while the blend is gradually increased in proportion to the reduced content of the ionomer from the initial 10 wt% to converge to 20 wt%, and the remaining balance is formed by blending a solvent. Reverse electrodialysis system using a rectifying ion exchange membrane.

11. In paragraph 7, The coating solution of step b above is An ionomer comprising at least one of a hydrocarbon polymer including polyphenylene, polyetheretherketone, polyarylene ether, polyimide, and polystyrene, or a fluorine-substituted hydrocarbon polymer; and A mixture comprising at least one of a fluorine-based polymer including polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a hydrocarbon-based polymer including polysulfone, polyetheretherketone, polyimide, polystyrene, or a fluorine-partially substituted hydrocarbon-based polymer; Reverse electrodialysis system using a rectifying ion exchange membrane.

12. In paragraph 7, In the coating solution of step b, a crosslinking agent including at least one of PDA (polydiacetylene), MBA (N,N'-Methylene bisacrylamide), EGDA (Ethylene glycol diacrylate), DVA (Divinyl adipate), BAED (Bis(2-acryl amido ethyl)disulfide), BPO (Benzoyl Peroxide), MDI (Methylene diphenyl diisocyanate), and PEI (Polyethyleneimine) is further added. Reverse electrodialysis system using a rectifying ion exchange membrane.

13. In paragraph 7, The solvent comprises at least one of water, ethanol, methanol, propyl alcohol, acetone, DMF, DMAc, and NMP. Reverse electrodialysis system using a rectifying ion exchange membrane.

14. In paragraph 7, As a result of the above step d, The ratio of the number of ion channels formed within the base layer and the coating layer is characterized in that it is within 10:1 to 100:

1. Reverse electrodialysis system using a rectifying ion exchange membrane.

15. In paragraph 7, The base layer of the above step a further comprises a film-forming binder comprising at least one of polyethylene, polypropylene, and polyvinyl chloride. Reverse electrodialysis system using a rectifying ion exchange membrane.

16. In paragraph 7, The base layer of the above step a further comprises an inorganic additive including at least one of silica gel, carbon nanotubes, aluminum oxide, and glass fiber. Reverse electrodialysis system using a rectifying ion exchange membrane.

17. In paragraph 7, The base layer of the above step a further comprises a support membrane composition material comprising at least one of polypropylene, polyethylene, PVC, PTFE, PVDF, and PET. Reverse electrodialysis system using a rectifying ion exchange membrane.

18. In paragraph 7, The above mixture is, Comprising at least one of a fluorine-based polymer including polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a hydrocarbon-based polymer including polysulfone, polyetheretherketone, polyimide, polystyrene, or a fluorine-partially substituted hydrocarbon-based polymer. Reverse electrodialysis system using a rectifying ion exchange membrane.

19. Power supply unit that supplies AC power; An electrode section in which a positive electrode plate and a negative electrode plate, which are electrically connected to the power supply, are arranged facing each other at a certain interval; A rectifying ion exchange membrane stack provided between the positive and negative electrode plates of the electrode unit, wherein at least one cation rectifying ion exchange membrane and an anion rectifying ion exchange membrane are alternately arranged at a set interval; A supply path for supplying raw water to the above rectifying ion exchange membrane stack; and A discharge path section for separating and discharging diluted water and concentrated water generated in the above rectified ion exchange membrane stack; Reverse electrodialysis system using a rectifying ion exchange membrane.

Images