Bipolar electrodialysis device

Abstract

The present invention relates to a bipolar electrodialysis device for producing lithium hydroxide. According to an embodiment of the present invention, the bipolar electrodialysis device comprises an anode to which a positive voltage is applied, and a cathode to which a negative voltage is applied, and further comprises sequentially stacked bipolar membranes, acidic solution chambers, anion exchange chambers, salt solution chambers, cation exchange membranes, bipolar membranes, and basic solution chambers between the anode and the cathode, wherein: water is introduced into the acidic solution chambers to generate an acidic solution; water is introduced into the basic solution chambers to generate a basic solution; a lithium salt solution is introduced into the salt solution chambers to generate a desalinated lithium salt solution; and the thickness control ratio of at least one of the bipolar membranes, the anion exchange membranes, and the cation exchange membranes satisfies a predefined equation.

Description

bipolar electrodialysis device

[0001] The present invention relates to a bipolar electrodialysis device, and more specifically, to a bipolar electrodialysis device for producing lithium hydroxide.

[0002] The global electric vehicle market is projected to grow from 2.3 million units in 2019 to 21.9 million units in 2030. Battery performance is also continuously improving through increased capacity and longer lifespan. Regarding cathode active materials for secondary batteries, the market share of high-energy-density High-Ni batteries is also predicted to rise to 76% by 2030. Consequently, the demand for lithium hydroxide, a raw material for High-Ni cathode active materials, is also expected to increase.

[0003] Lithium, which serves as a raw material for lithium secondary batteries, has conventionally 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 the kiln to recycle the limestone produces a large amount of carbon dioxide, which is not environmentally friendly. Alternatively, an aqueous lithium hydroxide solution can be produced using the bipolar electrodialysis (BPED) method.

[0004] Such a bipolar electrodialysis device has a structure in which a bipolar membrane, an acid chamber, an anion exchange membrane (AEM), a salt chamber, a cation exchange membrane (CEM), and a basic chamber repeat between the anode and the cathode, and lithium ions (Li) of an aqueous lithium salt solution flowing through the salt chamber by an electric field + ) moves toward the cathode, and sulfate ions (SO4) 2- ) moves toward the anode. In addition, lithium ions (Li+) move toward hydroxide ions (OH) generated in the bipolar membrane. -It meets with ) in the basic solution and is converted into an aqueous lithium hydroxide (LiOH) solution, and sulfate ions (SO4 2- ) is hydrogen ions (H) generated in the bipolar membrane + It meets with ) in an acidic liquid chamber to become an aqueous solution of sulfuric acid (H2SO4).

[0005] However, if the concentration of the acidic fluid is excessively high, hydrogen ions (H₂) in the acidic fluid + ) could permeate the anion exchange membrane and move to the salt or basic solution chamber, and in this case, there was a problem of reduced current efficiency. In addition, sulfate ions (SO4) in the acidic solution chamber 2- ) could pass through the bipolar membrane and move to the basic liquid chamber, and in this case, there was a problem causing a deterioration in the quality of the basic liquid chamber (increase in impurity concentration).

[0006] In order to solve these problems, attempts were made to change the material of the ion exchange membrane or change the operating conditions of the bipolar electrodialysis device, but this required excessive effort and time.

[0007] The problem that the present invention aims to solve is to provide a bipolar electrodialysis device that improves current efficiency and the quality of the basic solution chamber through a simple change in specifications.

[0008] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0009] To achieve the above objective, a bipolar electrodialysis device according to an embodiment of the present invention comprises an anode to which a positive voltage is applied; and a cathode to which a negative voltage is applied, and further comprises a bipolar membrane that is sequentially and repeatedly disposed between the anode and the cathode; an acidic liquid chamber; an anion exchange membrane; a salt liquid chamber; a cation exchange membrane; a bipolar membrane; and a basic liquid chamber, wherein water is introduced into the acidic liquid chamber to produce an acidic aqueous solution, water is introduced into the basic liquid chamber to produce a basic aqueous solution, and a lithium salt aqueous solution is introduced into the salt liquid chamber to produce a desalinated lithium salt aqueous solution, and the thickness control ratio of at least one of the bipolar membrane, the anion exchange membrane, and the cation exchange membrane satisfies the following Equation 1.

[0010] <Formula 1>

[0011]

[0012] Specific details of other embodiments are included in the detailed description and drawings.

[0013] According to the bipolar electrodialysis device of the present invention, one or more of the following effects are present.

[0014] First, by appropriately adjusting the thickness of the anion exchange membrane, while preventing a decrease in power efficiency due to increased electrical resistance, hydrogen ions (H + It has the advantage of preventing reverse diffusion of ) and increasing current efficiency.

[0015] Second, by appropriately adjusting the thickness of the bipolar film, while preventing a decrease in power efficiency due to increased electrical resistance, sulfate ions (SO4 2- It also has the advantage of preventing back diffusion of ) and improving the quality of the basic solution.

[0016] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims.

[0017] FIG. 1 is a schematic structural diagram of a bipolar electrodialysis device according to one embodiment of the present invention.

[0018] Figure 2 shows the experimental results regarding the quality and current efficiency of the basic solution chamber according to the thickness control of the anion exchange membrane or bipolar membrane.

[0019] Figure 3 is a graph showing the relationship between the thickness of the ion exchange membrane and the electrical resistance.

[0020] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0021] Although terms such as first, second, etc. are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used merely to distinguish one component from another, and unless specifically stated otherwise, the first component may also be the second component.

[0022] Throughout the specification, unless specifically stated otherwise, each component may be singular or plural.

[0023] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0024] In addition, where it is stated that one component is "connected," "combined," or "connected" to another component, it should be understood that while the components may be directly connected or connected to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "connected" through another component.

[0025] Singular expressions used in this specification include plural expressions unless the context clearly indicates otherwise. In this application, terms such as "composed of" or "comprising" should not be interpreted as necessarily including all of the various components or steps described in the specification, and should be interpreted as meaning that some of the components or steps may be omitted or additional components or steps may be included.

[0026] Throughout the specification, "A and / or B" means A, B, or A and B unless specifically stated otherwise, and "C to D" means C or more and D or less unless specifically stated otherwise.

[0027] Hereinafter, the present invention will be described with reference to the drawings for explaining a bipolar electrodialysis device according to embodiments of the present invention.

[0028] A bipolar electrodialysis device according to one embodiment of the present invention includes an anode (1) to which a positive voltage is applied and a cathode (2) to which a negative voltage is applied, and further includes a first bipolar membrane (3), an acidic liquid chamber (11), an anion exchange membrane (4), a salt liquid chamber (13), a cation exchange membrane (5), a basic liquid chamber (12), and a second bipolar membrane (6) that are sequentially and repeatedly arranged between the anode (1) and the cathode (2).

[0029] The acidic liquid chamber (11) is formed between the first bipolar membrane (3) and the anion exchange membrane (4). Water (90) is introduced into the acidic liquid chamber (11) to produce and discharge an acidic aqueous solution (20).

[0030] The basic liquid chamber (12) is formed between the second bipolar membrane (6) and the cation exchange membrane (5). Water (90) is introduced into the basic liquid chamber (12) to produce and discharge a basic aqueous solution (30).

[0031] The salt solution chamber (13) is formed between the anion exchange membrane (4) and the cation exchange membrane (5). A lithium salt aqueous solution (10) can be introduced into the salt solution chamber (13). In this embodiment, the lithium salt aqueous solution (10) may be a lithium sulfate (Li2SO4) aqueous solution.

[0032] When a lithium salt aqueous solution (10) is introduced into the salt solution chamber (13), lithium ions (Li) in the lithium salt aqueous solution (10) + ) passes through the cation exchange membrane (5), and sulfate ions (SO4) 2- Anions such as ) pass through the anion exchange membrane (4), and the salt solution chamber (13) produces and discharges a desalinated aqueous solution (10').

[0033] When voltage is applied to the positive electrode (1) and the negative electrode (2), water is converted into hydrogen ions (H) by electrodialysis in the first bipolar membrane (3) and the second bipolar membrane (6). + ) and hydroxide ions (OH - It is decomposed into ) and hydrogen ions (H) into the acidic liquid chamber (11) by electric force. + ) moves, and hydroxide ions (OH) move to the basic liquid chamber (12). -) will move.

[0034] The first bipolar membrane (3) and the second bipolar membrane (6) are composed of a cation layer that selectively passes only cations, including a negatively charged fixed ion group, and an anion layer that selectively passes only anions, including a positively charged fixed ion group.

[0035] The basic solution chamber (12) contains lithium ions (Li) that have passed through the cation exchange membrane (5) from the salt solution chamber (13). + ) and hydroxide ions (OH) formed from water by electrolysis in the second bipolar membrane (6) - An aqueous solution (30) of lithium hydroxide (LiOH) formed from ) is produced and discharged.

[0036] The lithium hydroxide (LiOH) aqueous solution (30) discharged from the basic liquid chamber (12) can be recirculated by being reintroduced into the basic liquid chamber (12).

[0037] The acidic liquid chamber (11) contains sulfate ions (SO4) that have passed through the anion exchange membrane (4) from the salt liquid chamber (13). 2- Anions such as ) and hydrogen ions (H) formed from water by electrolysis in the first bipolar membrane (3) + An acidic aqueous solution (20) formed from ) is discharged. For example, if the lithium salt aqueous solution (10) is a lithium sulfate (Li2SO4) aqueous solution, the acidic aqueous solution (20) may be a sulfuric acid (H2SO4) aqueous solution (20).

[0038] The aqueous sulfuric acid (H2SO4) solution (20) discharged from the acidic liquid chamber (11) can be recirculated by being reintroduced into the acidic liquid chamber (11).

[0039] The reaction in the bipolar electrodialysis device can be represented by the following chemical formula 1. That is, in the bipolar electrodialysis device, an aqueous solution of lithium hydroxide (LiOH) is produced together with an aqueous solution of sulfuric acid (H2SO4) according to the following chemical formula 1.

[0040] <Chemical Formula 1>

[0041] Li2SO4 + 2H2O → H2SO4 + 2LiOH

[0042]

[0043] In this embodiment, the bipolar electrodialysis device has a structure in which a plurality of stacks are repeated, with the acidic liquid chamber (11), salt liquid chamber (13), and basic liquid chamber (12) formed by the first bipolar membrane (3), an anion exchange membrane (4), a cation exchange membrane (5), and the second bipolar membrane (6) serving as a single stack unit.

[0044] A bipolar electrodialysis device may include at least two stacks, for example, 2 to 100, for example, 2 to 50, for example, 2 to 20, for example, 2 to 10 stacks.

[0045] The bipolar membrane (3, 6) is named 'first' or 'second' for convenience of explanation, but the bipolar membrane (3, 6) is a hydrogen ion (H) generated from water by electrolysis. + ) and hydroxide ions (OH - In a structure where multiple stacks are repeated and perform the same function of moving according to the direction of voltage application, there is no need to distinguish.

[0046] The starting point of a structure in which multiple stacks are repeated may be a bipolar membrane (3 / 6) or a cation exchange membrane (5), and it is preferable to use the same membrane as the starting membrane for the last one. For example, it may be repeated as bipolar membrane (3 / 6) - anion exchange membrane (4) - cation exchange membrane (5) - bipolar membrane (3 / 6) - anion exchange membrane (4) - cation exchange membrane (5) - … - bipolar membrane (3 / 6).

[0047] In this case, if the bipolar electrodialysis device includes n stacks, it may include n anion exchange membranes (4), n cation exchange membranes (5), and n+1 bipolar membranes (3 / 6).

[0048] Additionally, the sequence can be repeated as cation exchange membrane (5) - bipolar membrane (3 / 6) - anion exchange membrane (4) - cation exchange membrane (5) - bipolar membrane (3 / 6) - anion exchange membrane (4) - … - cation exchange membrane (5), in which case it may include n anion exchange membranes (4), n+1 cation exchange membranes (5), and n bipolar membranes (3 / 6).

[0049] Figure 2 shows the experimental results regarding the quality and current efficiency of the basic solution chamber according to the thickness control of the anion exchange membrane or bipolar membrane.

[0050] The inventors of the present invention, in order to improve current efficiency and the quality of the basic solution chamber through a simple change in specifications, have hydrogen ions (H + Backdiffusion of ) and sulfate ions (SO4 2- A method was studied to control the thickness of the ion exchange membrane (4, 5) and the bipolar membrane (3, 6) to prevent back diffusion of ).

[0051] It is known that the increase in membrane resistance resulting from controlling membrane thickness inhibits ion migration and adversely affects current efficiency. However, below a certain thickness, controlling membrane thickness can increase ion selectivity, which can actually lead to higher current efficiency and improved impurity control capabilities.

[0052] Comparative Example 1 is an experimental result regarding the quality and current efficiency of a basic liquid chamber (12) in a conventional bipolar electrodialysis device that includes an anion exchange membrane (4) with a thickness of 100 μm, a cation exchange membrane (5) with a thickness of 100 μm, and a bipolar membrane (3, 6) with a thickness of 150 μm (hereinafter referred to as 'standard ion exchange membrane'), which are commonly used ion exchange membranes. The standard ion exchange membrane has an operating voltage of 18 V to 19 V and a current efficiency of 40% to 42%, and in this embodiment, the operating voltage is 18.8 V and the current efficiency is 41.5%.

[0053] Example 1 is a comparative example in which the thickness of the anion exchange membrane (4) is increased to 50 μm compared to Comparative Example 1. Although the operating voltage is increased to 20 V due to the increase in membrane resistance, resistance occurs to the movement of ions from the acidic liquid chamber (11) to the salt liquid chamber (13), so hydrogen ions (H + It was confirmed that the current efficiency increased compared to Comparative Example 1 as the back diffusion of ) was reduced. At the same time, the decrease in the impurity concentration of the basic liquid chamber (12) was due to the hydrogen ions (H) remaining in the acidic liquid chamber (11). + To achieve charge neutrality with ) sulfate ions (SO4 2- It is believed that the spread of ) has been inhibited.

[0054] Example 2 is a comparative example in which the thickness of the anion layer of the bipolar membrane (3, 6) is increased by 50 μm from Comparative Example 1, and sulfate ions (SO4) from the acidic liquid chamber (11) to the basic liquid chamber (12) 2- As the movement resistance of ) increases, the impurity concentration decreases compared to Comparative Example 1, and additional hydrogen ions (H) flowing in from the basic liquid chamber (12) + It was confirmed that the current efficiency increased compared to Comparative Example 1 as the impurity concentration decreased. In addition, the impurity concentration decreased and the current efficiency increased compared to Example 1.

[0055] Example 3 is a comparative example in which the thickness of the anion layer of the bipolar film (3, 6) is increased by 20 μm compared to Comparative Example 1. It was confirmed that the impurity concentration is lower than that of Comparative Example 1 but higher than that of Example 2, and the current efficiency is higher than that of Comparative Example 1 but lower than that of Example 2. At the same time, the operating voltage is 19.4 V, which is lower than that of Example 2's 20.5 V, and it was confirmed that the film resistance is lower. This indicates that within the thickness range of this example, the increase in film resistance is not directly related to the current efficiency.

[0056] Example 4 is a comparative example in which the thickness of the anion layer of the bipolar membrane (3, 6) is increased by 20 μm, and the starting volume of the acidic liquid chamber (11) and basic liquid chamber (12) is increased by 2 times (400 ml). Compared to Example 3, the current efficiency increases, but there is no significant difference in the impurity concentration.

[0057] Example 5 is a comparative example in which the thickness of the anion exchange membrane (4) is increased by 50 μm, the thickness of the anion layer of the bipolar membrane (3, 6) is increased by 20 μm, and the starting volume of the acidic liquid chamber (11) and basic liquid chamber (12) is increased by 2 times (400 ml). It was confirmed that the impurity concentration is higher than Example 2 and lower than Example 4, and the current efficiency is higher than Example 4.

[0058] Example 6 is a modified version of Comparative Example 1 in which the thickness of the cation layer of the bipolar membrane (3, 6) is increased by 50 μm and the starting volume of the acidic liquid chamber (11) and basic liquid chamber (12) is increased by twofold (400 ml), showing effects of reduced impurity concentration and increased current efficiency similar to Example 4.

[0059] When the above factors are taken into account, it appears that there is no significant effect in controlling the starting volumes of the acidic liquid chamber (11) and the basic liquid chamber (12). Additionally, increasing the thickness of the anion layer of the bipolar membrane (3, 6) has a greater effect in reducing impurity concentration and increasing current efficiency than increasing the thickness of the cation layer of the bipolar membrane (3, 6). Furthermore, it appears that increasing the thickness of the anion layer of the anion exchange membrane (4) and the bipolar membrane (3, 6) has the greatest effect in reducing impurity concentration and increasing current efficiency.

[0060] Figure 3 is a graph showing the relationship between the thickness of the ion exchange membrane and the electrical resistance.

[0061] Ion exchange membranes operate on the principle that ion channels are formed by micropores created by polymer chains, and functional groups at the chain ends form fixed ion groups, thereby excluding copper ions (co-ions) and allowing counter-ions to pass through. If the membrane thickness is too thin, the reduced copper ion permeability resistance leads to weakened ion selectivity, resulting in decreased current efficiency and increased impurity concentration. If the membrane thickness is too thick, the copper ion permeability resistance increases, which improves ion selectivity; however, since electrical resistance also increases, power efficiency decreases, making it necessary to limit the upper thickness.

[0062] In ion exchange membranes with a thickness of 400 µm or more, a decrease in power efficiency due to the relationship between thickness and electrical resistance may occur to some extent, but below that, a relationship is not formed due to the influence of copper ion permeation.

[0063] As shown in Figure 3, the relationship between the thickness and electrical resistance of a commercial ion exchange membrane was examined, and a trend was observed in which the sheet resistance was 5 Ω / cm² at a membrane thickness of 250 µm. If the sheet resistance exceeds 5 Ω / cm², the bipolar electrodialysis device does not operate, or no increase in current efficiency is observed. Therefore, it is desirable to increase the membrane thickness up to a maximum of 250 µm.

[0064] Based on the combined experimental results of Figures 2 and 3, the thickness control ratio of the ion exchange membrane, which is the amount of thickness control relative to the thickness of the standard ion exchange membrane, was derived as shown in Equation 1 below. (Thickness control amount = (Thickness of controlled ion exchange membrane - Thickness of standard ion exchange membrane))

[0065] <Formula 1>

[0066]

[0067] As described above, increasing the thickness of the anion layer of the bipolar membrane (3, 6) is highly effective, but even if the thickness of the anion layer of the bipolar membrane (3, 6) is adjusted, it is desirable that the maximum thickness of the entire bipolar membrane (3, 6) does not exceed 250㎛.

[0068] Therefore, the thickness control amount of the anion layer of the bipolar membrane (3, 6) is derived as shown in Equation 2 below.

[0069] <Equation 2>

[0070]

[0071] The thickness control amount of the anion exchange membrane (4) is given by Formula 3 below.

[0072] <Equation 3>

[0073]

[0074] Although preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above. Various modifications are possible by those skilled in the art without departing from the essence of the invention as claimed in the patent claims, and such modifications should not be understood individually from the technical spirit or perspective of the present invention.

Claims

1. A positive electrode to which a positive voltage is applied; and a negative electrode to which a negative voltage is applied, comprising A bipolar membrane sequentially and repeatedly disposed between the anode and the cathode; an acidic liquid chamber; an anion exchange membrane; a salt liquid chamber; a cation exchange membrane; a bipolar membrane; and a basic liquid chamber are further included. In the above acidic liquid chamber, water is introduced to produce an acidic aqueous solution, and Water is introduced into the above basic liquid chamber to produce a basic aqueous solution, and In the above salt solution chamber, a lithium salt aqueous solution is introduced to produce a desalinated lithium salt aqueous solution, and A bipolar electrodialysis device in which the thickness control ratio of at least one of the above bipolar membrane, the above anion exchange membrane, and the above cation exchange membrane satisfies the following Formula 1. <Formula 1> 2. In Paragraph 1, A bipolar electrodialysis device in which the thickness control amount of the anion layer of the above bipolar membrane satisfies the following Equation 2. <Equation 2> 3. In Paragraph 1, A bipolar electrodialysis device in which the thickness control amount of the above anion exchange membrane satisfies the following Equation 3. <Equation 3>

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