Continuous bipolar membrane electrodialysis device and continuous bipolar membrane electrodialysis process

Abstract

The present invention relates to a continuous bipolar membrane electrodialysis device in which an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode are sequentially disposed and a plurality of unit cells are connected in series or in parallel, each unit cell comprising an acid room disposed between the first bipolar membrane and the anion-selective dialysis membrane, a salt room arranged between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and a base room arranged between the cation-selective dialysis membrane and the second bipolar membrane, and a cell at one end of the plurality of unit cells is defined as a first unit cell and a cell at the other end of the plurality of cells is defined as a second unit cell, the continuous bipolar membrane electrodialysis device comprising: a lithium salt inflow vessel into which a lithium salt aqueous solution is introduced; a first transfer pipe connected to the lithium salt inflow vessel to transfer a salt-flow solution to a desalted liquid inflow vessel through the salt tank of the second unit cell, wherein the salt-flow solution is formed as follows: when the lithium salt aqueous solution is put into the salt tank of the first unit cell, same is transferred back to the salt room of the first unit cell, and then transferred to the salt tank of the first unit cell; and a second transfer pipe connected to a lower portion of the desalted liquid inflow vessel to transfer a portion of the desalted liquid in the vessel to the lithium salt inflow vessel.

Description

Continuous bipolar membrane electrodialysis device and continuous bipolar membrane electrodialysis process

[0001] The present invention relates to a continuous bipolar membrane electrodialysis device and a continuous bipolar membrane electrodialysis process, and specifically, to a continuous bipolar membrane electrodialysis device and a continuous bipolar membrane electrodialysis process capable of self-circulation of the discharge solution of the continuous bipolar membrane electrodialysis process.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0145930 filed on October 23, 2024, the entire contents of said prior application incorporated herein by reference.

[0003] Lithium secondary batteries are seeing a diversification of applications, ranging from individual cell batteries used in IT devices such as smartphones and laptops to large modular batteries used in electric vehicles (EVs) and energy storage systems (ESS), and battery production is also on the rise globally.

[0004] Among them, the global electric vehicle market is projected to grow from 2.3 million units in 2019 to 21.9 million units in 2030, and battery performance is continuously improving with increased capacity and longer lifespan. In addition, the share of high-energy-density High-Ni batteries as cathode active materials for electric vehicles is projected to rise to 76% by 2030, and the demand for lithium hydroxide, a lithium raw material for High-Ni cathode active materials, is also expected to increase.

[0005] Lithium, a raw material for lithium-ion batteries, has traditionally been produced by extracting lithium carbonate from salt lakes, reacting it with lime to obtain a lithium hydroxide solution, and then crystallizing it. However, the lime process generates limestone as a byproduct, and the operation of kilns to recycle the limestone produces large amounts of carbon dioxide, posing a problem of being unenvironmentally friendly.

[0006] To address this, research is being conducted on a process for producing lithium hydroxide using an electrodialysis device with a bipolar membrane. However, since the method for producing lithium hydroxide using an electrodialysis device with a bipolar membrane requires the input of electrical energy to move lithium ion charges, it is necessary to improve electrical energy efficiency. Additionally, if a problem occurs during the upstream or downstream process of an electrodialysis device with a bipolar membrane and is not resolved within 10 hours, the operation of the device must be stopped. Furthermore, the lifespan of the dialysis membrane installed in the device may decrease as the shutdown becomes more frequent.

[0007] Accordingly, there is a need for research on a process that can minimize process downtime by maximizing retention time through the recirculation of a portion of the discharged solution during the operation of an electrodialysis device using a bipolar membrane.

[0008] One objective of the present invention is to provide a continuous bipolar membrane electrodialysis device and a continuous bipolar membrane electrodialysis process that can simultaneously obtain lithium hydroxide and acid by using a continuous bipolar membrane electrodialysis device, and can minimize process downtime by maximizing the retention time through the recirculation of a portion of the discharge solution from the electrodialysis device.

[0009] A continuous bipolar membrane electrodialysis device according to one embodiment of the present invention is a continuous bipolar membrane electrodialysis device in which an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode are arranged in sequence, wherein a plurality of unit cells are connected in series or parallel, and wherein a cell at one end of the plurality of unit cells is defined as a first unit cell and a cell at the other end of the plurality of cells is defined as a second unit cell, and a lithium salt inlet tank into which a lithium salt aqueous solution is introduced; It includes: a first transfer pipe connected to the lithium salt inlet tank, wherein when the lithium salt aqueous solution is introduced into the salt tank of the first unit cell, it is transferred to the salt room of the first unit cell and then transferred again to the salt tank of the first unit cell to form a salt flow solution, and the salt flow solution is transferred through the salt tank of the second unit cell to the desalination liquid inlet tank; and a second transfer pipe connected to the lower part of the desalination liquid inlet tank to transfer a portion of the desalination liquid in the tank to the lithium salt inlet tank.

[0010] It may include: a water and / or basic aqueous solution inlet tank into which water and / or basic aqueous solution is introduced; a third transfer pipe connected to the water and / or basic aqueous solution inlet tank, wherein when the water and / or basic aqueous solution is introduced into the base tank of the second unit cell, it is transferred to the base room of the second unit cell and then transferred again to the base tank of the second unit cell to form a basic fluid solution, and the basic fluid solution is transferred through the base tank of the first unit cell to a lithium hydroxide aqueous solution inlet tank; and a fourth transfer pipe connected to the third transfer pipe at the point where the solution is transferred through the base tank of the first unit cell to the lithium hydroxide aqueous solution inlet tank, which recirculates a portion of the lithium hydroxide aqueous solution to the base tank within each unit cell.

[0011] It may include: a water and / or acidic solution inlet tank into which water and / or acidic solution is introduced; a fifth transfer pipe connected to the water and / or acidic solution inlet tank, into which the water and / or acidic solution is introduced into the acid tank of the second unit cell, and which forms an acidic fluid solution by passing through the acid room and then through the acid tank of the second unit cell, and which transfers the acidic fluid solution to the acid solution inlet tank by passing through the acid tank of the first unit cell; and a sixth transfer pipe connected to the fifth transfer pipe at the point where the acid solution is transferred to the acid solution inlet tank by passing through the acid tank of the first unit cell, which recirculates a portion of the acidic solution to the acid tank within each unit cell.

[0012] The above unit cell may be stacked in multiple pairs, each consisting of a triplet of an acid room, a salt room, and a base room.

[0013] Each of the plurality of unit cells connected in series or parallel above may further include an acid tank connected to the acid room, a salt tank connected to the salt room, and a base tank connected to the base room.

[0014] The number of unit cells connected in series of the above-mentioned bipolar membrane electrodialysis device may be 2 to 10.

[0015] A continuous bipolar membrane electrodialysis process according to another embodiment of the present invention comprises the step of preparing a bipolar membrane electrodialysis device in which a plurality of unit cells are connected in series, each unit cell comprising an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode arranged in order, and an acid room disposed between the first bipolar membrane and the anion-selective dialysis membrane, a salt room disposed between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and a base room disposed between the cation-selective dialysis membrane and the second bipolar membrane. The method includes the step of, when a cell at one end of the plurality of unit cells is defined as a first unit cell and a cell at the other end of the plurality of cells is defined as a second unit cell, introducing a lithium salt aqueous solution into the salt tank of the first unit cell, passing through a salt room, and passing through the salt tank of the first unit cell again to form a salt flow solution, wherein the salt flow solution finally passes through the salt tank of the second unit cell, where a portion is obtained as a desalted solution, and a portion of the desalted solution is mixed with the lithium salt aqueous solution and introduced into the salt tank of the first unit cell for recirculation.

[0016] The flow rate (linear velocity) of the above salt flow solution may be 0.5 to 100 cm / sec.

[0017] The method may further include the step of introducing water or a basic aqueous solution into the base tank of the second unit cell, passing through the base room and then through the base tank of the second unit cell again to form a basic fluid solution, wherein the basic fluid solution finally passes through the base tank of the first unit cell, where a portion is obtained as a lithium hydroxide aqueous solution, and the remainder of the basic fluid solution not obtained as a lithium hydroxide aqueous solution is introduced into the base tanks of the plurality of unit cells for recirculation.

[0018] The flow rate (linear velocity) of the above basic fluid solution may be 0.5 to 100 cm / sec.

[0019] The method may further include the step of introducing water or an acidic aqueous solution into the acid tank of the second unit cell, passing through the acid room, and then passing through the acid tank of the second unit cell again to form an acidic fluid solution, wherein the acidic fluid solution is finally obtained as an acidic solution by passing through the acid room of the first unit cell, and the remainder of the acidic fluid solution that is not obtained as an acidic solution is introduced into the acid tanks of the plurality of unit cells for recirculation.

[0020] The flow rate (linear velocity) of the above acidic fluid solution may be 0.5 to 100 cm / sec.

[0021] After the step of preparing the above-mentioned bipolar membrane electrodialysis device, the method may further include the step of introducing a lithium salt aqueous solution into the salt tank of the first unit cell to form a salt flow solution, introducing water or a basic aqueous solution into the base tank of the second unit cell to form a basic flow solution, introducing water or an acidic aqueous solution into the acid tank of the second unit cell to form an acidic flow solution; and the step of applying an electric current to the above-mentioned bipolar membrane electrodialysis device to obtain a lithium hydroxide aqueous solution and an acidic solution.

[0022] The above salt flow solution and the above basic flow solution may flow in opposite directions to each other, and the above salt flow solution and the above acid flow solution may flow in opposite directions to each other.

[0023] The above lithium salt aqueous solution may be an aqueous Li2SO4 solution or an aqueous LiCl solution.

[0024] The above lithium salt aqueous solution may have impurity content of Ca, Mg, Al, and P of 10 ppm or less each.

[0025] In one embodiment of the present invention, a continuous bipolar electrodialysis process can produce lithium hydroxide and acid, and by recirculating a portion of the discharge solution to maximize retention time, process downtime can be minimized and the performance degradation of the ion exchange membrane can be prevented.

[0026] Figure 1 is a schematic diagram of a continuous bipolar membrane electrodialysis process according to the present invention.

[0027] FIG. 2 is a schematic diagram of a unit cell (unit stack) in which unit pairs are stacked according to the present invention.

[0028] Figure 3 is the result of a bipolar membrane electrodialysis process according to one comparative example of the present invention.

[0029] Figure 4 is the result of a continuous bipolar membrane electrodialysis process capable of solution recirculation operation according to one embodiment of the present invention.

[0030] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0031] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0032] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other part is interposed in between.

[0033] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0034] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0035] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0036] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0037] In this specification, “front end and rear end” are defined as the side the solution reaches first and the side the solution reaches later, based on the flow direction of a salt flow solution, a basic flow solution, or an acid flow solution.

[0038] In this specification, “effective area” is defined as the area through which current can substantially pass in a cation-selective dialysis membrane, anion-selective dialysis membrane, or bipolar membrane.

[0039] Continuous bipolar membrane electrodialysis device

[0040] A continuous bipolar membrane electrodialysis device according to one embodiment of the present invention, wherein an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode are arranged in order, and an acid room (101 to 103) disposed between the first bipolar membrane and the anion-selective dialysis membrane; A plurality of unit cells (11 to 13) are connected in series or in parallel, each comprising: a salt room (201 to 203) disposed between the cation-selective dialysis membrane and the anion-selective dialysis membrane; and a base room (301 to 303) disposed between the cation-selective dialysis membrane and the second bipolar membrane; wherein a cell at one end of the plurality of unit cells is defined as a first unit cell (11) and a cell at the other end of the plurality of cells is defined as a second unit cell (13), and a lithium salt inlet tank (80) into which a lithium salt aqueous solution is introduced; It includes: a first transfer pipe (401) connected to the lithium salt inflow tank (80) and, when the lithium salt aqueous solution is introduced into the salt tank (41) of the first unit cell, transferred to the salt room (201) of the first unit cell and then transferred again to the salt tank (41) of the first unit cell to form a salt flow solution, and the salt flow solution is transferred to the desalination liquid inflow tank (81) by passing through the salt tank (43) of the second unit cell; and a second transfer pipe (402) connected to the lower part of the desalination liquid inflow tank (81) and transferred a portion of the desalination liquid in the tank to the lithium salt inflow tank (80).

[0041] A continuous bipolar membrane electrodialysis device according to one embodiment of the present invention, a water and / or basic aqueous solution inlet tank (71) into which water and / or basic aqueous solution is introduced; a third transfer pipe (403) connected to the water and / or basic aqueous solution inlet tank (71) and which, when the water and / or basic aqueous solution is introduced into the base tank (53) of the second unit cell (13), is transferred to the base room (303) of the second unit cell (13) and then transferred again to the base tank (53) of the second unit cell (13) to form a basic fluid solution, and which transfers the basic fluid solution through the base tank (51) of the first unit cell (11) to a lithium hydroxide aqueous solution inlet tank (70); and a fourth transfer pipe (404) connected to a third transfer pipe (403) at a point where the lithium hydroxide aqueous solution is transferred through the base tank (51) of the first unit cell (11) to the lithium hydroxide aqueous solution inflow tank (70), thereby recirculating a portion of the lithium hydroxide aqueous solution to the base tanks (51 to 53) within each unit cell (11 to 13); may be included.

[0042] In a continuous bipolar membrane electrodialysis device according to one embodiment of the present invention, a water and / or acidic aqueous solution inlet tank (91) into which water and / or acidic aqueous solution is introduced; It may include: a fifth transfer pipe (405) connected to the above water and / or acidic aqueous solution inflow tank, which introduces the above water and / or acidic aqueous solution into the acid tank (33) of the second unit cell (13), forms an acidic fluid solution by passing through the acid room (103) and then through the acid tank (31) of the second unit cell (13), and transfers the acidic fluid solution to the acid solution inflow tank (90) by passing through the acid tank (31) of the first unit cell (11); and a sixth transfer pipe (406) connected to the fifth transfer pipe (405) at the point where the acid solution is transferred to the acid solution inflow tank (90) by passing through the acid tank (31) of the first unit cell (11), and which recirculates a portion of the acidic solution to the acid tanks (31 to 33) within each unit cell (11 to 13). The salt flow solution and the basic flow solution may flow in opposite directions, and the salt flow solution and the acid flow solution may flow in opposite directions.

[0043] FIG. 1 is a schematic diagram of a continuous bipolar membrane electrodialysis apparatus according to the present invention. The lithium salt is lithium sulfate, and the meanings of the abbreviations are as follows: LS: Li2SO4, HS: H2SO4, LH: LiOH, DI: de-ionized, CWS: cooling water supply, CWR: cooling water return.

[0044] Referring to FIG. 1, the bipolar membrane electrodialysis device according to the present invention may have a plurality of unit cells connected in series.

[0045] In a continuous bipolar membrane electrodialysis device according to one embodiment of the present invention, the unit cells (11 to 13) may be stacked in multiple units, each unit pair consisting of three triplets: an acid room (101 to 103), a salt room (201 to 203), and a base room (301 to 303). If the number of unit pairs is small, productivity decreases, and if the number of unit pairs is too large, the voltage of the unit cells (unit stacks) becomes too high, making operation difficult. Typically, the number of unit pairs is preferably 10 to 200.

[0046] FIG. 2 is a schematic diagram of a unit cell (unit stack) in which unit pairs are stacked according to the present invention.

[0047] Referring to FIG. 2, the unit cell according to the present invention has a structure in which an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode are arranged in order. At this time, an acid room is arranged between the first bipolar membrane and the anion-selective dialysis membrane, a salt room is arranged between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and a base room is arranged between the cation-selective dialysis membrane and the second bipolar membrane. At this time, the unit cell may have a structure in which a plurality of unit pairs, each consisting of a triplet of an acid room, a salt room, and a base room, are stacked. Depending on the specifications or conditions of the three types of membranes—cation-selective dialysis membranes, anion-selective dialysis membranes, and bipolar membranes—the input ratio of lithium salt aqueous solution, water or basic aqueous solution and acidic aqueous solution, and the actual discharge flow rate of desalinated solution, basic flow solution, or acidic flow solution may vary.

[0048] In a continuous bipolar membrane electrodialysis device according to one embodiment of the present invention, each of the plurality of unit cells (11 to 13) connected in series or parallel may further include an acid tank (31 to 33) connected to an acid room (101 to 103), a salt tank (41 to 43) connected to a salt room (201 to 203), and a base tank (51 to 53) connected to a base room (301 to 303).

[0049] In a continuous bipolar membrane electrodialysis device according to one embodiment of the present invention, the number of unit cells (11 to 13) connected in series or in parallel of the bipolar membrane electrodialysis device may be 2 to 10, specifically 3 to 9, and more specifically 4 to 8. The unit cells may also be connected in parallel depending on the process configuration. When the number of unit cells connected in series of the bipolar membrane electrodialysis device satisfies the above range, the current efficiency increases, thereby improving electrical energy efficiency and the concentration of the lithium hydroxide aqueous solution and sulfuric acid solution produced may be high. On the other hand, if the number of unit cells is less than 2, the current efficiency may decrease because the change in ion concentration within the unit cell becomes too large compared to when there are multiple units, and the concentration of the lithium hydroxide aqueous solution and sulfuric acid solution produced may be low. In addition, if the number of unit cells exceeds 10, there may be a problem of reduced economic feasibility due to increased initial investment costs.

[0050] In a continuous bipolar membrane electrodialysis device according to one embodiment of the present invention, in each of the plurality of unit cells, the effective area of ​​the anion-selective dialysis membrane is equal to the effective area of ​​the cation-selective dialysis membrane, and the effective area of ​​the first bipolar membrane and the second bipolar membrane may be less than or equal to the effective area of ​​the anion-selective dialysis membrane or the cation-selective dialysis membrane. Typically, the operating current density (current value / membrane area) of the bipolar electrodialysis unit cell is greater than or equal to the limiting current density of the bipolar membrane, but may be less than or equal to the limiting current density of the cation-selective dialysis membrane and the anion-selective dialysis membrane. However, as the operating current density of the unit cell increases, the amount of ions moving through the cation-selective dialysis membrane and the anion-selective dialysis membrane to maintain electrical neutrality also increases, approaching the limiting current density of these membranes and eventually exceeding it, which may cause a problem of excessive resistance. Accordingly, by making the effective area of ​​the bipolar membrane less than or equal to the effective area of ​​the anion-selective dialysis membrane or the cation-selective dialysis membrane, the aforementioned problem of excessive resistance generation can be mitigated, and thus electrical energy efficiency can be improved.

[0051]

[0052] Continuous bipolar membrane electrodialysis process

[0053] A continuous bipolar membrane electrodialysis process according to another embodiment of the present invention comprises the step of preparing a bipolar membrane electrodialysis device in which a plurality of unit cells are connected in series, each unit cell comprising an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode arranged in order, and an acid room (101) disposed between the first bipolar membrane and the anion-selective dialysis membrane, a salt room (201) disposed between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and a base room (301) disposed between the cation-selective dialysis membrane and the second bipolar membrane. A continuous bipolar membrane electrodialysis process is provided, comprising the step of: defining a cell at one end of the plurality of unit cells as a first unit cell (11) and a cell at the other end of the plurality of cells as a second unit cell (13); introducing a lithium salt solution (LS Solution) into a salt tank (41) of the first unit cell (11), passing through a salt room (201), and passing through the salt tank (41) of the first unit cell again to form a salt flow solution; and finally passing through the salt tank (43) of the second unit cell, a portion of which is obtained as a desalted solution, and a portion of which is mixed with the lithium salt solution (LS Solution) and introduced into the salt tank (41) of the first unit cell for recirculation.

[0054] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, the flow rate (linear velocity) of the salt flow solution may be 0.5 to 100 cm / sec, specifically 0.7 to 80 cm / sec, and more specifically 0.9 to 60 cm / sec. When the flow rate (linear velocity) of the salt flow solution satisfies the above range, it may be advantageous for ion movement through the membrane. On the other hand, if the flow rate (linear velocity) of the salt flow solution is less than 0.5 cm / sec, ion polarization may occur between the cation- and anion-selective dialysis membranes, increasing electrical resistance and potentially reducing electrical energy efficiency. Furthermore, if the flow rate (linear velocity) of the salt flow solution exceeds 100 cm / sec, the pressure between the cation- and anion-selective dialysis membranes increases, which may cause leakage of the solution or rupture of the membrane. The control of such flow rates can be controlled by the volume of the empty space in each liquid chamber inside the unit cell and by controlling the pumping speed in the salt tank, base tank, or acid tank.

[0055] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, water or a basic aqueous solution is introduced into the base tank (53) of the second unit cell (13) to form a basic fluid solution by passing through the base room (303) and then through the base tank (53) of the second unit cell (13), and the basic fluid solution finally passes through the base tank (51) of the first unit cell (11), where a portion is obtained as a lithium hydroxide aqueous solution (LH Solution), and the remainder of the basic fluid solution not obtained as a lithium hydroxide aqueous solution is introduced into the base tanks (51 to 53) of the plurality of unit cells and recirculated. As the basic fluid solution is recirculated within the plurality of unit cells (11 to 13), there is an advantage that the basic fluid solution comes into contact with the electrodialysis membrane, thereby increasing the time of movement. In addition, the method of moving the above basic fluid solution to the base tanks (51 to 53) of adjacent unit cells (11 to 13) may preferably be an overflow. The overflow method may refer to a flow method in which an amount exceeding a certain amount within the tank naturally flows out, and may have the advantage of easily controlling the amount retained within the tank to a certain level without using energy.

[0056] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, the flow rate (linear velocity) of the basic fluid solution may be 0.5 to 100 cm / sec, specifically 0.7 to 80 cm / sec, and more specifically 0.9 to 60 cm / sec. When the flow rate (linear velocity) of the basic fluid solution satisfies the above range, ion movement is active and the appropriate lifespan of the membrane can be maintained. On the other hand, if the flow rate (linear velocity) of the basic fluid solution is less than 0.5 cm / sec, ion polarization occurs between the cation- and anion-selective dialysis membranes, increasing electrical resistance and potentially reducing electrical energy efficiency. Additionally, if the flow rate (linear velocity) of the basic fluid solution exceeds 100 cm / sec, the pressure between the cation- and anion-selective dialysis membranes increases, which may cause leakage of the solution or rupture of the membrane. The control of such flow rates can be controlled by the volume of the empty space in each liquid chamber inside the unit cell and by controlling the pumping speed in the salt tank, base tank, or acid tank.

[0057] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, water or an acidic aqueous solution is introduced into an acid tank (33) of the second unit cell (13) to form an acidic fluid solution by passing through an acid room (103) and then passing through the acid tank (33) of the second unit cell (13) again, and the acidic fluid solution is finally obtained as an acidic solution by passing through the acid room (31) of the first unit cell (11), and the remainder of the acidic fluid solution that is not obtained as an acidic solution is introduced into the acid tanks (31 to 33) of the plurality of unit cells (11 to 13) for recirculation; the process may further include the step of recirculating the acidic fluid solution. As the acidic fluid solution is recirculated within the plurality of unit cells, there is an advantage that the time the acidic fluid solution comes into contact with the electrodialysis membrane and moves through it can be increased. In addition, the method of moving the above acidic fluid solution to an acid tank (31 to 33) within adjacent unit cells (11 to 13) may preferably involve an overflow.

[0058] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, the flow rate (linear velocity) of the acidic flow solution may be 0.5 to 100 cm / sec, specifically 0.7 to 80 cm / sec, and more specifically 0.9 to 60 cm / sec. When the flow rate (linear velocity) of the acidic flow solution satisfies the above range, ion movement is facilitated and the appropriate membrane life can be maintained. On the other hand, if the flow rate (linear velocity) of the acidic flow solution is less than 0.5 cm / sec, ion polarization occurs between the cation- and anion-selective dialysis membranes, increasing electrical resistance and potentially reducing electrical energy efficiency. Additionally, if the flow rate (linear velocity) of the acidic flow solution exceeds 100 cm / sec, the pressure between the cation- and anion-selective dialysis membranes increases, which may cause leakage of the solution or rupture of the membrane. The control of such flow rates can be controlled by the volume of the empty space in each liquid chamber inside the unit cell and by controlling the pumping speed in the salt tank, base tank, or acid tank.

[0059] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, after the step of preparing the bipolar membrane electrodialysis device, the process may further include the step of introducing a lithium salt aqueous solution into the salt tank (41) of the first unit cell (11) to form a salt flow solution, introducing water or a basic aqueous solution into the base tank (53) of the second unit cell (13) to form a basic flow solution, introducing water or an acidic aqueous solution into the acid tank (33) of the second unit cell (13) to form an acidic flow solution; and the step of applying an electric current to the bipolar membrane electrodialysis device to obtain a lithium hydroxide aqueous solution and an acidic solution.

[0060] That is, the lithium salt aqueous solution is introduced into the salt tank (41) of the first unit cell (11), passes through the salt room (201), and is introduced back into the salt tank (41) to form a salt flow solution, thereby forming a continuous flow of the salt flow solution in the continuous bipolar membrane electrodialysis process according to the present invention. The salt flow solution can pass through the salt tank (41) of the first unit cell (11), sequentially through the salt tanks (42) of adjacent unit cells, and finally pass through the salt tank (43) of the second unit cell (13) to be discharged as a desalinated solution, and the remainder of the salt flow solution that is not converted into the desalinated solution can be mixed again with the lithium salt aqueous solution and introduced into the salt tank (41) of the first unit cell (11) for recirculation.

[0061] In addition, water or a basic aqueous solution is introduced into the base tank (53) of the second unit cell (13), passes through the base room (303), and is introduced back into the base tank (53) to form a basic fluid solution, thereby forming a continuous flow of the basic fluid solution in the continuous bipolar membrane electrodialysis process according to the present invention. The basic fluid solution can pass through the base tank (53) of the second unit cell (13), pass through the base tanks (52) of sequentially adjacent unit cells, and finally pass through the base tank (51) of the first unit cell (11) to be discharged as a lithium hydroxide aqueous solution, and the remainder of the basic fluid solution that is not converted into the lithium hydroxide aqueous solution can be introduced back into the base tanks (51 to 53) of a plurality of unit cells (11 to 13) connected in series and recirculated.

[0062] Additionally, water or an acidic aqueous solution is introduced into the acid tank (33) of the second unit cell (13), passes through the acid room (103), and is introduced back into the acid tank (33) to form an acidic fluid solution, thereby forming a continuous flow of acidic fluid solution in the continuous bipolar membrane electrodialysis process according to the present invention. The acidic fluid solution can pass through the acid tank (33) of the second unit cell (13), pass through the acid tanks (32) of sequentially adjacent unit cells, and finally pass through the acid tank (31) of the first unit cell (11) to be discharged as an acidic solution, and the remainder of the acidic fluid solution that is not converted into an acidic solution can be introduced back into the acid tanks (31 to 33) of a plurality of unit cells (11 to 13) connected in series and recirculated.

[0063] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, the salt flow solution and the basic flow solution may flow in opposite directions to each other, and the salt flow solution and the acid flow solution may flow in opposite directions to each other. As the flow directions of the salt flow solution and the basic flow solution or the acid flow solution are opposite to each other, the salt concentration of the salt flow solution may decrease as it moves from the first unit cell (11) to the second unit cell (13), the basic concentration of the basic flow solution may decrease as it moves from the first unit cell (11) to the second unit cell (13), and the acid concentration of the acid flow solution may decrease as it moves from the first unit cell (11) to the second unit cell (13). That is, the concentrations of salt, basic, and acid in the salt flow solution, basic flow solution, and acid flow solution may decrease sequentially as they move from the first unit cell (11) to the second unit cell (13).

[0064] In other words, the concentration difference between the salt flow solution, basic flow solution, and acid flow solution within each unit cell is reduced, thereby preventing membrane degradation or performance reduction and increasing current efficiency, which ultimately improves electrical energy efficiency. This may be because the concentration difference between the salt flow solution, basic flow solution, and acid flow solution is highly correlated with the swelling ratio and transport number of the ion exchange membrane.

[0065] Figure 3 is the result of a bipolar membrane electrodialysis process according to one comparative example of the present invention.

[0066] Figure 4 is the result of a continuous bipolar membrane electrodialysis process capable of solution circulation operation according to one embodiment of the present invention.

[0067] Referring to Figures 3 and 4, it can be seen that in Figure 4, water, a basic aqueous solution, or an acidic aqueous solution is introduced, and the produced desalinated solution, acidic fluidized solution, and basic fluidized solution are recirculated back into the circulation tank within the process, thereby reducing the actual flow rate of the final solution to nearly half compared to Figure 3. At this time, during the solution circulation operation in Figure 4, operational know-how may be required, such as gradually lowering the applied voltage in addition to changing the solution flow rate and operating the recirculation pump. This is because the concentration of the lithium salt aqueous solution introduced may gradually decrease due to the recirculated desalinated solution. The above solution circulation operation may be an operating mode designed to minimize shun-down by utilizing multiple buffer tanks between processes in the event of a problem occurring in the upstream or downstream process of the bipolar membrane electrodialysis device in the actual overall process. In addition, as the flow rates of the lithium salt aqueous solution introduced in Fig. 4, the basic fluid solution, the acidic fluid solution, and the desalinated solution produced are all reduced to nearly half the level of conventional operation, the bipolar membrane electrodialysis process can be operated as much as possible to maximize the retention time until the problems of the upstream and downstream processes are resolved. Due to the characteristics of the bipolar membrane electrodialysis process, it may be advantageous to minimize shun-downs to prevent negative effects such as shortened membrane lifespan and the production of a dilute solution during restart. On the other hand, in the bipolar membrane electrodialysis process of Fig. 3, the lithium salt aqueous solution, water, basic aqueous solution, or acidic aqueous solution are always separated except when they come into contact through the membrane; therefore, the overall water balance of the process may vary depending on how much water passes through which membrane, how many water molecules pass along with ions when they move through the membrane, or the amount of hydrogen back-diffusion.

[0068] In a continuous bipolar membrane electrodialysis process according to another embodiment of the present invention, the lithium salt aqueous solution may be an aqueous Li2SO4 solution or an aqueous LiCl solution, but is not limited thereto. The lithium salt aqueous solution is not particularly limited as long as the lithium salt does not precipitate, but preferably, a lithium salt with high solubility in water may be suitable.

[0069] At this time, the concentration of Li in the above lithium salt aqueous solution may be 1 g / L or the solubility of the lithium salt. If the concentration of Li is too low, the resistance of the electrolyte becomes too high, which may reduce electrical energy efficiency. In addition, if the concentration of Li is too high and exceeds the solubility of the lithium salt, precipitation of the lithium salt may occur. For example, if the lithium salt is lithium sulfate, it may be preferable for the concentration of Li to be 37.8 g / L (at 25°C) or less, which is the solubility of lithium sulfate.

[0070] In a continuous bipolar membrane electrodialysis process according to one embodiment of the present invention, the lithium salt aqueous solution may have an impurity content of Ca, Mg, Al, and P of 10 ppm or less each. If the content of the impurities is too high, salts of these substances (Ca(OH)2, Mg(OH)2, Al(OH)3, Li2PO4, etc.) may precipitate on the surface or inside the ion exchange membrane, thereby degrading the electrodialysis performance of the membrane and reducing its mechanical strength, which may cause membrane degradation.

[0071] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0072] Example 1: Continuous bipolar membrane electrodialysis process

[0073] A bipolar electrodialysis device consisting of three unit cells (unit stacks) connected in series was prepared, and the device was put into operation. Depending on the process configuration, they may also be connected in parallel. Each unit cell is composed of six presses, and each press is composed of eight stacks; the effective area inside each unit cell is 0.5 m² 2 Forty pairs of first bipolar membranes, anion-selective dialysis membranes, cation-selective dialysis membranes, and second bipolar membranes are arranged sequentially. An acid room is provided between the first bipolar membrane and the anion-selective dialysis membrane, a salt room is provided between the anion-selective dialysis membrane and the cation-selective dialysis membrane, and a base room is provided between the cation-selective dialysis membrane and the second bipolar membrane. An acid tank is connected to the acid room, a salt tank to the salt room, and a base tank to the base room within each unit cell. In addition, heat exchangers are installed downstream of the acid tank, salt tank, and base tank within each unit cell to control the temperature of the fluid passing through them to 40°C or lower.

[0074] In addition, heat exchangers are installed at the front of the salt tank in the first unit cell (the unit cell on which the lithium salt solution is supplied) and at the front of the base tank and acid tank in the second unit cell (the unit cell on which water is supplied) so that the temperature of the fluid solution passing through them is controlled to 15 to 40°C.

[0075] Subsequently, an aqueous Li2SO4 solution (LS Solution) containing approximately 10 g / L of Li was introduced into the salt chamber of the first unit cell at a flow rate of approximately 18 ton / hr, and pure water (Dionized Water) was introduced into the acid tank and base tank of the second unit cell at flow rates of approximately 0.56 ton / hr and 0.33 ton / hr, respectively. In other words, the flow directions of the salt solution, the basic solution, and the acid solution were made opposite to each other.

[0076] The voltage of all rectifiers is applied such that the conductivity of the final basic solution is 320 to 350 mS / cm. The flow rate of the LiOH aqueous solution obtained by passing through the base tank in the first unit cell is about 9.8 ton / hr and the concentration of Li is 18 to 20.0 g / L, and the flow rate of the sulfuric acid aqueous solution obtained by passing through the acid tank in the first unit cell (the unit cell on the side where the lithium salt aqueous solution is supplied) is about 15.7 ton / hr. At this time, the concentration of sulfuric acid is 10 to 12%. The Li2SO4 aqueous solution introduced in the opposite direction to the base tank and acid tank in the first unit cell (the unit cell on the side where the lithium salt aqueous solution is supplied) passes through the salt tank in the second unit cell (the unit cell on the side where water is supplied) to obtain a desalinated solution, and the flow rate of the obtained desalinated solution is about 15.9 ton / h, and the concentration of Li is 0.5 to 4 g / L.

[0077] At this time, a portion of the basic fluid solution obtained in the base tank within the first unit cell is recovered back into the base circulation tank within the process, and ultimately, only about 8.8 tons / hr of basic fluid solution is supplied to the next process. This is nearly half the amount compared to conventional operation.

[0078] In addition, a portion of the acid flow solution obtained in the acid tank within the first unit cell is recovered back into the acid circulation tank within the process, and ultimately only about 8.7 tons / hr of acid flow solution is supplied to the next process. This is nearly half the amount compared to conventional operation.

[0079] In addition, a portion of the desalinated liquid obtained in the salt tank within the second unit cell is recovered into the Li2SO4 aqueous solution input tank, mixed with a new Li2SO4 aqueous solution, and fed into the BPED process, and finally, only 1.5 ton / hr of the desalinated liquid solution is supplied to the next process.

[0080]

[0081] Comparative Example 1: Bipolar membrane electrodialysis process

[0082] A bipolar electrodialysis device consisting of three unit cells (unit stacks) connected in series was prepared, and the commercial device was put into operation. Depending on the process configuration, they may also be connected in parallel. Each unit cell is composed of 6 presses, and each press is composed of 8 stacks; the effective area inside each unit cell is 0.5 m² 2 Forty pairs of first bipolar membranes, anion-selective dialysis membranes, cation-selective dialysis membranes, and second bipolar membranes are arranged sequentially. An acid room is provided between the first bipolar membrane and the anion-selective dialysis membrane, a salt room is provided between the anion-selective dialysis membrane and the cation-selective dialysis membrane, and a base room is provided between the cation-selective dialysis membrane and the second bipolar membrane. In addition, an acid tank is connected to the acid room, a salt tank to the salt room, and a base tank to the base room within each unit cell. Furthermore, heat exchangers are installed downstream of the acid tank, salt tank, and base tank within each unit cell to control the temperature of the fluid passing through them to 40°C or lower. In addition, heat exchangers are installed at the front of the salt tank in the first unit cell (the unit cell on which the lithium salt solution is supplied) and at the front of the base tank and acid tank in the second unit cell (the unit cell on which water is supplied) so that the temperature of the fluid solution passing through them is controlled to 15 to 40°C.

[0083] Subsequently, an aqueous Li2SO4 solution containing approximately 10 g / L of Li was introduced into the salt tank within the first unit cell (the unit cell on which the lithium salt solution is supplied) at a flow rate of 36 ton / hr, and deionized water was introduced into the acid tank and base tank within the second unit cell (the unit cell on which water is supplied) at flow rates of 16 ton / hr and 9.5 ton / hr, respectively. That is, the flow directions of the salt solution, the basic solution, and the acid solution were made opposite to each other.

[0084] The voltage of all rectifiers is applied such that the conductivity of the final basic solution is 320 to 350 mS / cm. The flow rate of the aqueous LiOH solution obtained by passing through the base tank in the first unit cell is 16 ton / hr, and the concentration of Li is 18 to 20 g / L. Additionally, the flow rate of the aqueous sulfuric acid solution obtained by passing through the acid tank in the first unit cell is 17.4 ton / hr, and the concentration of sulfuric acid is 10 to 12%. The aqueous Li2SO4 solution introduced in the opposite direction to the base tank and acid tank in the first unit cell passes through the salt tank in the second unit cell to obtain a desalinated solution, and the flow rate of the obtained desalinated solution is 28.6 ton / hr, and the concentration of Li is 0.5 to 4 g / L. At this time, the concentration of Li is high during the initial operation, but it may converge to a lower concentration as operation progresses.

[0085] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0086] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

1. A continuous bipolar membrane electrodialysis device comprising an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode arranged in sequence, An acid room disposed between the first bipolar membrane and the anion-selective dialysis membrane; A salt room disposed between the cation-selective dialysis membrane and the anion-selective dialysis membrane; and A plurality of unit cells, each comprising a base room disposed between the cation-selective dialysis membrane and the second bipolar membrane, are connected in series or in parallel. When a cell at one end of the plurality of unit cells is defined as the first unit cell, and a cell at the other end of the plurality of cells is defined as the second unit cell, A lithium salt inlet tank into which a lithium salt aqueous solution is introduced; A first transfer pipe connected to the lithium salt inlet tank, wherein when the lithium salt aqueous solution is introduced into the salt tank of the first unit cell, it is transferred to the salt room of the first unit cell and then transferred again to the salt tank of the first unit cell to form a salt flow solution, and the salt flow solution is transferred to the desalination liquid inlet tank by passing through the salt tank of the second unit cell; and A continuous bipolar membrane electrodialysis device comprising: a second transfer pipe connected to the lower part of the desalination solution inlet tank to transfer a portion of the desalination solution in the tank to the lithium salt inlet tank.

2. In Paragraph 1, Water and / or basic aqueous solution inlet tank into which water and / or basic aqueous solution are introduced; A third transfer pipe connected to the above water and / or basic aqueous solution inlet tank, wherein when the water and / or basic aqueous solution is introduced into the base tank of the second unit cell, it is transferred to the base room of the second unit cell and then transferred again to the base tank of the second unit cell to form a basic fluid solution, and the basic fluid solution is transferred through the base tank of the first unit cell to the lithium hydroxide aqueous solution inlet tank; and A continuous bipolar membrane electrodialysis device comprising: a fourth transfer pipe connected to a third transfer pipe at a point where the lithium hydroxide aqueous solution is transferred through the base tank of the first unit cell to the lithium hydroxide aqueous solution inflow tank, for recirculating a portion of the lithium hydroxide aqueous solution to the base tank within each unit cell.

3. In Paragraph 1, A water and / or acidic aqueous solution inlet tank into which water and / or acidic aqueous solution are introduced; A fifth transfer pipe connected to the above water and / or acidic aqueous solution inlet tank, which introduces the water and / or acidic aqueous solution into the acid tank of the second unit cell, forms an acidic fluid solution by passing through the acid room and then through the acid tank of the second unit cell, and transfers the acidic fluid solution to the acid solution inlet tank by passing through the acid tank of the first unit cell; and A continuous bipolar membrane electrodialysis device comprising: a sixth transfer pipe connected to a fifth transfer pipe at a point where the acid solution is transferred from the acid tank of the first unit cell to an acid solution inflow tank, and which recirculates a portion of the acid solution to the acid tank within each unit cell.

4. In Paragraph 1, A continuous bipolar membrane electrodialysis device in which the above unit cell is a plurality of unit pairs, each consisting of a triplet of an acid room, a salt room, and a base room, are stacked.

5. In Paragraph 1, A continuous bipolar membrane electrodialysis device, wherein each of the plurality of unit cells connected in series or parallel further comprises an acid tank connected to the acid room, a salt tank connected to the salt room, and a base tank connected to the base room.

6. In Paragraph 1, A continuous bipolar membrane electrodialysis device having 2 to 10 unit cells connected in series.

7. A step of preparing a bipolar membrane electrodialysis device in which a plurality of unit cells are connected in series or parallel, each unit cell comprising an anode, a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, a second bipolar membrane, and a cathode arranged in order, and an acid room disposed between the first bipolar membrane and the anion-selective dialysis membrane, a salt room disposed between the cation-selective dialysis membrane and the anion-selective dialysis membrane, and a base room disposed between the cation-selective dialysis membrane and the second bipolar membrane; and A continuous bipolar membrane electrodialysis process comprising the step of: defining a cell at one end of the plurality of unit cells as a first unit cell and a cell at the other end of the plurality of cells as a second unit cell, wherein a lithium salt aqueous solution is introduced into a salt tank of the first unit cell, passes through a salt room, and passes back through the salt tank of the first unit cell to form a salt flow solution, wherein the salt flow solution finally passes through the salt tank of the second unit cell, where a portion is obtained as a desalted solution, and a portion of the desalted solution is mixed with the lithium salt aqueous solution and introduced into the salt tank of the first unit cell for recirculation.

8. In Paragraph 7, A continuous bipolar membrane electrodialysis process in which the flow rate (linear velocity) of the above salt flow solution is 0.5 to 100 cm / sec.

9. In Paragraph 7, A continuous bipolar membrane electrodialysis process further comprising the step of introducing water or a basic aqueous solution into the base tank of the second unit cell, passing through the base room and then through the base tank of the second unit cell again to form a basic fluid solution, wherein the basic fluid solution finally passes through the base tank of the first unit cell, where a portion is obtained as a lithium hydroxide aqueous solution, and the remainder of the basic fluid solution not obtained as a lithium hydroxide aqueous solution is introduced into the base tanks of the plurality of unit cells for recirculation.

10. In Paragraph 9, A continuous bipolar membrane electrodialysis process in which the flow rate (linear velocity) of the above basic fluid solution is 0.5 to 100 cm / sec.

11. In Paragraph 7, A continuous bipolar membrane electrodialysis process further comprising the step of introducing water or an acidic aqueous solution into the acid tank of the second unit cell, passing through an acid room, and passing through the acid tank of the second unit cell again to form an acidic fluid solution, wherein the acidic fluid solution finally passes through the acid tank of the first unit cell to obtain an acidic solution, and the remainder of the acidic fluid solution not obtained as an acidic solution is introduced into the acid tanks of the plurality of unit cells for recirculation.

12. In Paragraph 11, A continuous bipolar membrane electrodialysis process in which the flow rate (linear velocity) of the above acidic flow solution is 0.5 to 100 cm / sec.

13. In Paragraph 7, After the step of preparing the above-mentioned bipolar membrane electrodialysis device, A step of forming a salt flow solution by introducing a lithium salt aqueous solution into the salt tank of the first unit cell, forming a basic flow solution by introducing water or a basic aqueous solution into the base tank of the second unit cell, and forming an acid flow solution by introducing water or an acidic aqueous solution into the acid tank of the second unit cell; and A continuous bipolar membrane electrodialysis process further comprising the step of applying an electric current to the above-mentioned bipolar membrane electrodialysis device to obtain an aqueous lithium hydroxide solution and an acidic solution.

14. In Paragraph 13, A continuous bipolar membrane electrodialysis process comprising the above salt flow solution and the above basic flow solution flowing in opposite directions, and the above salt flow solution and the above acid flow solution flowing in opposite directions.

15. In Paragraph 7, A continuous bipolar membrane electrodialysis process in which the above lithium salt aqueous solution is an aqueous Li2SO4 solution or an aqueous LiCl solution.

16. In Paragraph 7, The above lithium salt aqueous solution is a continuous bipolar membrane electrodialysis process in which the content of impurities Ca, Mg, Al, and P is 10 ppm or less each.

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