Method for simultaneously preparing lithium hydroxide and sulfuric acid

Abstract

The invention relates to a method for simultaneously preparing lithium hydroxide and sulfuric acid. The invention provides a method for simultaneously preparing lithium hydroxide and sulfuric acid, which comprises the following steps: preparing a bipolar membrane electrodialysis device which comprises a first bipolar membrane, an anion exchange membrane, a cation exchange membrane and a second bipolar membrane, and forming an acid chamber between the first bipolar membrane and the anion exchange membrane, a salt chamber is formed between the anion exchange membrane and the cation exchange membrane, and an alkali chamber is formed between the cation exchange membrane and the second bipolar membrane; a lithium sulfate aqueous solution is added into a salt chamber of the bipolar membrane electrodialysis device, a sulfuric acid aqueous solution is added into an acid chamber, and a lithium hydroxide aqueous solution is added into an alkali chamber; and discharging the desalted solution formed in the salt chamber of the bipolar membrane electrodialysis device, discharging the sulfuric acid aqueous solution formed in the acid chamber, and discharging the lithium hydroxide aqueous solution formed in the alkali chamber.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for simultaneously producing lithium hydroxide and sulfuric acid. In particular, the present invention relates to a method for simultaneously producing lithium hydroxide and sulfuric acid, which can prevent a decrease in current efficiency of a bipolar membrane electrodialysis process and reduce power consumption. BACKGROUND

[0002] In recent years, as the market for electric vehicles is rapidly growing, the market for lithium secondary batteries for electric vehicles is also experiencing explosive growth. For this reason, innovative technologies that can more efficiently produce lithium compounds, which are raw materials for lithium secondary batteries, are being developed.

[0003] Among various methods for producing battery-grade high-purity lithium hydroxide for electric vehicles, in particular, electrochemical membrane separation technology for producing lithium hydroxide from lithium salts is being actively developed.

[0004] Using a bipolar membrane electrodialysis method, lithium hydroxide (LiOH) and sulfuric acid (H2SO4) can be simultaneously produced from lithium salts. When a lithium sulfate (Li2SO4) aqueous solution is added to a bipolar membrane electrodialysis cell and a direct current is applied, lithium hydroxide (LiOH) and sulfuric acid (H2SO4) can be simultaneously produced. In this case, lithium ions (Li + ) and sulfate ions (SO4 2- ) dissociated from lithium sulfate move through a cation exchange membrane and an anion exchange membrane, respectively. On the other hand, the bipolar membrane dissociates water using the applied current to generate protons (H + ) and hydroxide ions (OH - ), the generated hydroxide ions move to the anode (+) side and meet lithium ions to form lithium hydroxide, and the generated protons move to the cathode (-) side and meet sulfate ions to form sulfuric acid.

[0005] Among the applied current, the proportion used to produce the target product can be expressed as current efficiency (Current Efficiency), which is calculated as follows:

[0006] Current Efficiency (%) = 100 × (Target ion production [mol]) × Faraday constant [C / mol] / (Current density [A / m 2 ] × Effective area of membrane [m 2 ] × Application time [sec])

[0007] There are many factors that affect current efficiency, among which the physical properties of the cation exchange membrane, the anion exchange membrane, and the bipolar membrane used are important.

[0008] On the other hand, current efficiency is directly linked to production costs, so there is a need to develop technologies for improving current efficiency. Summary of the Invention

[0009] (a) Technical problems to be solved

[0010] This invention provides a method for simultaneously and efficiently preparing lithium hydroxide and sulfuric acid while improving current efficiency. Specifically, this invention aims to provide a method for simultaneously preparing lithium hydroxide and sulfuric acid by utilizing bipolar membrane electrodialysis. By controlling the movement of water and lithium cations in the ion exchange membrane, current efficiency can be improved.

[0011] (II) Technical Solution

[0012] A method for simultaneously preparing lithium hydroxide and sulfuric acid according to an embodiment of the present invention may include the following steps: preparing a bipolar membrane electrodialysis device, the bipolar membrane electrodialysis device comprising a first bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a second bipolar membrane, wherein an acid chamber is formed between the first bipolar membrane and the anion exchange membrane, a salt chamber is formed between the anion exchange membrane and the cation exchange membrane, and a base chamber is formed between the cation exchange membrane and the second bipolar membrane; adding an aqueous solution of lithium sulfate to the salt chamber of the bipolar membrane electrodialysis device, adding an aqueous solution of sulfuric acid to the acid chamber, and adding an aqueous solution of lithium hydroxide to the base chamber; and discharging the desalination solution formed in the salt chamber of the bipolar membrane electrodialysis device, discharging the aqueous solution of sulfuric acid formed in the acid chamber, and discharging the aqueous solution of lithium hydroxide formed in the base chamber.

[0013] The cation exchange membrane of the bipolar membrane electrodialysis device contains water (H2O) and lithium cations (Li). + The ratio of movement to weight can be below 40.

[0014] The ratio of the added lithium hydroxide aqueous solution flow rate to the lithium hydroxide aqueous solution flow rate discharged from the alkali chamber of the bipolar membrane electrodialysis device can be 0.3 to 0.6.

[0015] The ratio of the added sulfuric acid aqueous solution flow rate to the sulfuric acid aqueous solution flow rate discharged from the acid chamber of the bipolar membrane electrodialysis device can be from 0.9 to 1.2.

[0016] The current density passing through the cation exchange membrane and anion exchange membrane of the bipolar membrane electrodialysis device can be 20 mA / cm². 2 Up to 150mA / cm 2 .

[0017] The concentration of the lithium hydroxide aqueous solution added to the alkali chamber of the bipolar membrane electrodialysis device can be from 0 mol / L to 1 mol / L, and the concentration of the lithium hydroxide aqueous solution discharged from the alkali chamber of the bipolar membrane electrodialysis device can be from 1 mol / L to 5 mol / L.

[0018] The concentration of the sulfuric acid aqueous solution added to the acid chamber of the bipolar membrane electrodialysis device can be from 0 mol / L to 0.5 mol / L, and the concentration of the sulfuric acid aqueous solution discharged from the acid chamber of the bipolar membrane electrodialysis device can be from 0.5 mol / L to 3 mol / L.

[0019] The concentration of the lithium sulfate aqueous solution added to the salt chamber of the bipolar membrane electrodialysis device can be from 0.5 mol / L to 2.5 mol / L, and the concentration of the lithium sulfate aqueous solution discharged from the salt chamber of the bipolar membrane electrodialysis device can be from 0.1 mol / L to 2 mol / L.

[0020] The bipolar membrane electrodialysis device may be composed of two or more electrodialysis membrane stacks connected in series. The electrodialysis membrane stack includes a first bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a second bipolar membrane. An acid chamber is formed between the first bipolar membrane and the anion exchange membrane, a salt chamber is formed between the anion exchange membrane and the cation exchange membrane, and an alkali chamber is formed between the cation exchange membrane and the second bipolar membrane.

[0021] (III) Beneficial Effects

[0022] According to one embodiment of the present invention, in a bipolar membrane electrodialysis process, the current efficiency of the bipolar membrane electrodialysis process can be improved by controlling the amount of water and lithium cations moving in the ion exchange membrane. Attached Figure Description

[0023] Figure 1 A bipolar membrane electrodialysis (BPED) apparatus according to an embodiment of the present invention is illustrated schematically.

[0024] Figure 2 The bipolar membrane electrodialysis (BPED) system of the present invention is schematically shown for experiments on the preparation of lithium hydroxide and sulfuric acid. Best practice

[0025] The terms "first," "second," "third," etc., are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, and / or segment described below can also be described as a second part, component, region, layer, and / or segment.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used are intended to include the plural forms as well. It should also be understood that the term "comprising" as used in the specification can specifically refer to a particular feature, domain, integer, step, action, element, and / or component, and does not exclude the presence or addition of other features, domains, integers, steps, actions, elements, and / or components.

[0027] If one part is described as being on top of another part, then other parts can exist directly on top of or in between the other part. When one part is described as being directly on top of another part, there are no other parts in between.

[0028] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0029] Furthermore, unless otherwise specified, % means weight, 1 ppm means 0.0001 wt%.

[0030] In this specification, the term "combination" as used in the Markush form refers to a mixture or combination of one or more of the constituent elements described in the Markush form, which means including one or more of the constituent elements described above.

[0031] The embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0032] Figure 1 A bipolar membrane electrodialysis (BPED) apparatus according to an embodiment of the present invention is illustrated schematically.

[0033] Reference Figure 1According to one embodiment of the present invention, a bipolar membrane electrodialysis apparatus may include repeatedly stacked unit pairs located between an anode chamber and a cathode chamber. The unit pair may be a triplet structure in which a bipolar membrane, an anion exchange membrane, and a cation exchange membrane are sequentially positioned. Specifically, it may be a structure in which a bipolar membrane, a spacer gasket, an anion exchange membrane, a spacer gasket, a cation exchange membrane, and a spacer gasket are sequentially positioned. The unit pairs of the structure may be sequentially positioned adjacent to each other. In two adjacent unit pairs, the spacer gasket of the preceding unit pair located at the rear end of the cation exchange membrane may be positioned adjacent to the bipolar membrane of the adjacent unit pair located at the rear end.

[0034] Reference Figure 1 An acid chamber can be formed between the first bipolar membrane and the anion exchange membrane, and a salt chamber can be formed between the anion exchange membrane and the cation exchange membrane. Furthermore, a base chamber can be formed between the cation exchange membrane and the second bipolar membrane.

[0035] The following describes a method for simultaneously preparing lithium hydroxide and sulfuric acid according to an embodiment of the present invention.

[0036] First, an aqueous solution of lithium salt (specifically, an aqueous solution of lithium sulfate) can be added to the salt chamber of the unit pair, a low-concentration aqueous solution of sulfuric acid (containing a sulfuric acid concentration of 0) can be added to the acid chamber as the reaction solution of the acid chamber, and a low-concentration aqueous solution of lithium hydroxide (containing a lithium hydroxide concentration of 0) can be added to the alkali chamber as the reaction solution of the alkali chamber, so as to perform bipolar electrodialysis.

[0037] At this time, when a DC voltage is applied to the bipolar membrane electrodialysis device to make the current flow, an aqueous solution of sulfuric acid (H2SO4) is formed in the acid chamber between the first bipolar membrane and the anion exchange membrane, an aqueous solution of lithium hydroxide (LiOH) is formed in the alkali chamber between the cation exchange membrane and the second bipolar membrane, and a desalination solution containing residual lithium salt that has not moved in the aqueous solution of the added lithium salt is formed in the salt chamber between the cation exchange membrane and the anion exchange membrane.

[0038] Specifically, the formation process of the sulfuric acid (H2SO4) and lithium hydroxide (LiOH) is as follows.

[0039] When the first bipolar membrane is energized, water entering the membrane from the acid and alkali chambers is dissociated into hydrogen ions (H+). + ) and hydroxide ions (OH-) - At this point, hydroxide ions (OH-) are generated from the decomposition of water. -The hydrogen ions (H+) migrate to the base chamber on the anode (+) side, generating hydrogen ions (H+). + The hydrogen ions migrate to the acid chamber between the first bipolar membrane and the anion exchange membrane. Meanwhile, anions from the lithium salt aqueous solution added between the anion exchange membrane and the cation exchange membrane migrate through the anion exchange membrane to the space between the first bipolar membrane and the anion exchange membrane. Additionally, the hydrogen ions (H+)... + The sulfuric acid (H2SO4) and the anions are concentrated between the first bipolar membrane and the anion exchange membrane, thereby forming a high-concentration aqueous solution of sulfuric acid (H2SO4). In this invention, the acid chamber reaction solution may specifically be a mixture of aqueous solution of sulfuric acid (H2SO4) and deionized water (DIwater).

[0040] Next, the formation process of the lithium hydroxide (LiOH) aqueous solution is as follows. The second bipolar membrane decomposes the water entering from the alkali chamber and acid chamber into hydrogen ions (H+). + ) and hydroxide ions (OH-) - At this point, hydrogen ions (H+) are generated from the decomposition of water. + The acid cells move to the cathode (-) side of the acid chamber, where they decompose into hydroxide ions (OH-). - The lithium ions (Li) move to the alkaline chamber between the second bipolar membrane and the anion exchange membrane. Meanwhile, lithium ions (Li) in the lithium salt aqueous solution added between the anion exchange membrane and the cation exchange membrane are... + The hydroxide ions (OH-) migrate through the cation exchange membrane to the alkaline chamber. - ) and the lithium ion (Li + The solution is concentrated in the alkali chamber to form a high-concentration aqueous solution of lithium hydroxide (LiOH). In this invention, the alkali chamber solution may specifically be an aqueous solution of lithium hydroxide (LiOH) and / or deionized water (DI water).

[0041] More specifically, sulfate anion (SO4) 2- At the bipolar membrane on the anode side, hydrogen ions (H+) are formed by the decomposition of water. + When they meet, they are converted into acid (H2SO4), and lithium ions (Li) move through the cation exchange membrane to the cathode. + ) and the hydroxyl groups (OH) generated at the bipolar membrane - It reacts to form lithium hydroxide (LiOH).

[0042] In one embodiment of the present invention, the lithium salt may specifically be a sulfate (Li₂SO₄), and the acid may be sulfuric acid (H₂SO₄). Alternatively, the acid chamber reaction solution may be a low-concentration sulfuric acid (H₂SO₄) or water (deionized water), and the alkali chamber reaction solution may be a low-concentration aqueous solution of lithium hydroxide or water (deionized water).

[0043] At this point, the overall reaction formula may be as follows:

[0044] Li2SO4(aq) 2Li + (Moves to the alkali chamber) + SO4 2- (Move to the acid chamber)

[0045] H2O H + (Moves to the acid chamber) + OH- - (Move to the alkali chamber)

[0046] Li2SO4(aq) + 2H2O 2LiOH (aq, base compartment) + H₂SO₄ (aq, acid compartment)

[0047] At this point, for the high-concentration lithium salt aqueous solution added to the salt chamber, lithium ions and acid groups are removed, and a portion is used to generate the remaining low-concentration lithium salt aqueous solution (i.e., desalination solution), which can be discharged outside the electrodialysis device.

[0048] In addition, the lithium salt aqueous solution formed in the salt chamber can be added to the adjacent rear-end unit pair to perform the same electrodialysis as the front-end unit pair.

[0049] At this point, as mentioned above, when preparing lithium hydroxide aqueous solution and sulfuric acid aqueous solution from lithium salt aqueous solution, in order to improve current efficiency, it is necessary to appropriately adjust the rate of water (pure water) dissociation at the bipolar membrane and the migration rate of lithium ions and anions contained in the lithium-containing aqueous solution. If these rates are not properly adjusted, for example, if the dissociation rate of pure water (or deionized water) is faster than the migration rate of lithium ions and anions contained in the lithium-containing aqueous solution, the decomposed hydrogen ions and hydroxide ions will not encounter their corresponding ions. Therefore, ion migration will occur in order to maintain electroneutrality. On the other hand, the direction of ion migration should take into account both the direction of electromigration and the direction of diffusion caused by the concentration difference. For example, when the hydroxyl ions (OH-) in the alkaline chamber of the cation exchange membrane... - The concentration of hydroxyl radicals (OH-) in the salt chamber is higher than that in the salt chamber. -At a certain concentration, hydroxyl ions diffuse from the alkali chamber to the acid chamber due to diffusion. Since this diffusion is opposite to the direction of electrophoresis, it reduces current efficiency. For cation exchange membranes, the Donnan repulsion of the internally fixed anions can, to some extent, suppress the back diffusion of anion hydroxyl ions (also known as back diffusion because it is opposite to the direction of electrophoresis). However, as the hydroxyl concentration in the alkali chamber gradually increases, the back diffusion to the acid chamber also gradually increases, potentially leading to a gradual decrease in current efficiency.

[0050] Therefore, in order to improve the current efficiency of lithium hydroxide production, it is important to adjust the physical properties of the anion exchange membrane, bipolar membrane, and cation exchange membrane, and to regulate the water decomposition rate and the movement rate of lithium ions and anions in the bipolar membrane, so as to maintain an appropriate balance between the movement rate of the moving ions and the movement rate of water (H2O) in the exchange membrane.

[0051] Lithium cation (OH) - When cation exchangers move through a cation exchange membrane, water also moves with them. If the amount of water (H₂O) moving with them is too large, the expansion of the cation exchange membrane will lead to a decrease in the fixed anion density of the cation exchange membrane, thus affecting the concentration of hydroxide ions (OH⁻). - The reduced repulsive force of the anions leads to an increase in the back migration of the anions, resulting in a decrease in current efficiency.

[0052] In one embodiment of the present invention, the cation exchange membrane may be one or more selected from Astom's CM2, CMB, CSE, W-Scocpe's CD100, CH100, Shandong Tianwei's TWEDC1S, Hangzhou Lanran's CT-4, CTG-10.

[0053] Water (H2O) and lithium cations (Li) in the cation exchange membrane of an electrodialysis device + The proportion of weight of the amount of movement (ω) C It can be below 40, specifically below 35, or more specifically between 20 and 35.

[0054] In the cation exchange membrane, the weight ratio of water to lithium cations moving per unit time (ω) C ) can be represented by the following formula.

[0055] ω C =H2O transport amount (g) / Li + Quantity moved (g) (1)

[0056] When water (H2O) and lithium cations (Li) are exchanged in the cation exchange membrane... + The proportion of weight of the amount of movement (ω) C When the value is 40, it can prevent a significant decrease in the efficiency of the current applied during the production of lithium hydroxide and reduce the amount of electrical energy consumed.

[0057] In this invention, ωc can be adjusted according to the type of polymer constituting the cation exchange membrane, the type of fixed ion groups, the ion exchange capacity, and the membrane thickness. Even if the polymer constituting the membrane, the type of fixed ions, and the membrane thickness are the same, ωc will change when the proportion of the amount (moles) of fixed ion groups in the dry weight of the membrane, i.e., the ion exchange capacity (milli-equivalent / g-dry polymer), changes. Furthermore, ωc will also change with the process conditions of the bipolar membrane electrodialysis device (i.e., temperature, concentration, etc.).

[0058] In another embodiment of the present invention, the supply flow rate of the low-concentration lithium hydroxide (LiOH) aqueous solution added as a raw material is relative to the discharge flow rate of the high-concentration lithium hydroxide (LiOH) aqueous solution generated in the alkali chamber of the bipolar membrane electrodialysis device (Q). LH加入(in) / Q LH排出(out) The value can be between 0.3 and 0.6. If the stated ratio (Q) LH加入 / Q LH排出 If the ratio (Q) is less than 0.3, the concentration of the lithium hydroxide aqueous solution increases, leading to increased reverse migration of hydroxide ions (OH-) through the cation exchange membrane, which may decrease the current efficiency. LH加入 / Q LH排出 If the concentration of the lithium hydroxide solution is greater than 0.6, the amount of water that needs to be removed in the downstream crystalline lithium hydroxide preparation process increases, leading to a decrease in overall productivity. On the other hand, in this invention, the concentration of the high-concentration lithium hydroxide (LiOH) aqueous solution generated in the alkali chamber can be in the range of 1 mol / L to 5 mol / L, and the concentration of the low-concentration lithium hydroxide (LiOH) aqueous solution added as a raw material can be in the range of 0 mol / L to 1 mol / L. If the concentration of the generated lithium hydroxide (LiOH) aqueous solution is less than 1 mol / L, the economic efficiency is poor; if the concentration of the generated lithium hydroxide is greater than 5 mol / L, the back diffusion through the cation exchange membrane increases excessively, resulting in a decrease in current efficiency. The lithium hydroxide (LiOH) aqueous solution added as a raw material can be pure water (lithium hydroxide concentration 0 mol / L). If the concentration exceeds 1 mol / L, excessive consumption of lithium hydroxide occurs, leading to a decrease in economic efficiency.

[0059] In another embodiment of the present invention, the supply flow rate of the low-concentration sulfuric acid (H2SO4) aqueous solution added as a raw material is relative to the discharge flow rate of the high-concentration sulfuric acid (H2SO4) aqueous solution generated in the acid chamber of the bipolar membrane electrodialysis device (Q) HS加入 / Q HS排出 The ratio (Q) can be from 0.9 to 1.2. HS加入 / Q HS排出 If the ratio (Q) is less than 0.9, the concentration of sulfuric acid (H2SO4) produced becomes too high, increasing the reverse migration of hydrogen ions (protons) through the anion exchange membrane, which may reduce the current efficiency. Furthermore, if the ratio (Q) is less than 0.9, the concentration of sulfuric acid (H2SO4) produced becomes too high, increasing the reverse migration of hydrogen ions (protons) through the anion exchange membrane, potentially reducing the current efficiency. HS加入 / Q HS排出 If the concentration of sulfuric acid (H₂SO₄) exceeds 1.2, the concentration of the produced sulfuric acid (H₂SO₄) becomes too dilute, resulting in a decrease in the utilization rate of the prepared sulfuric acid as a product. On the other hand, in this invention, the concentration of the high-concentration sulfuric acid (H₂SO₄) aqueous solution generated in the acid chamber can be in the range of 0.5 mol / L to 3 mol / L, and the concentration of the low-concentration sulfuric acid (H₂SO₄) aqueous solution added as a raw material can be in the range of 0 mol / L to 0.5 mol / L. If the concentration of the generated sulfuric acid aqueous solution is below 0.5 mol / L, the economic efficiency decreases; if the concentration is above 3 mol / L, excessive back diffusion of hydrogen ions (H⁺) through the anion exchange membrane occurs, reducing the current efficiency. The sulfuric acid (H₂SO₄) aqueous solution added as a raw material can be pure water (sulfuric acid concentration 0 mol / L); if it exceeds 0.5 mol / L, excessive sulfuric acid consumption occurs, reducing the economic efficiency.

[0060] On the other hand, in this invention, the concentration of the lithium sulfate aqueous solution added to the salt chamber of the bipolar membrane electrodialysis device can be from 0.5 mol / L to 2.5 mol / L, and the concentration of the lithium sulfate aqueous solution discharged from the salt chamber of the electrodialysis device can be from 0.1 mol / L to 2 mol / L. If the concentration of the added lithium sulfate aqueous solution is less than 0.5 mol / L, the resistance of the brine solution becomes high, making operation difficult; while if the concentration is above 2.5 mol / L, the solubility in water approaches its limit, also making operation difficult. Furthermore, if the concentration of the lithium sulfate aqueous solution (desalination solution) discharged from the salt chamber of the electrodialysis device is less than 0.1 mol / L, the resistance of the brine solution becomes too high, making it difficult to operate at high current densities; while if the concentration exceeds 2 mol / L, the required device size becomes too large, reducing economic efficiency.

[0061] In another embodiment of the invention, the current density through the membranes (cation exchange membrane and anion exchange membrane) can be 20 mA / cm². 2 Up to 150mA / cm 2 (Based on the effective area of ​​the membrane), specifically 50 mA / cm².2 Up to 100mA / cm 2 If the current density is less than 20 mA / cm² 2 The yield of lithium hydroxide (LiOH) or sulfuric acid (H2SO4) per unit effective membrane area (kg / m²) 2 -hr) is too low, while if the current density exceeds 150mA / cm 2 If the resistance becomes too high, it can lead to the deterioration of ion exchange membranes, especially bipolar membranes (bubbles, delamination, aging, etc.).

[0062] In this invention, given the effective membrane area, the membrane current density can be provided by a rectifier. At this point, the current density should be within a range that does not cause temperature rises or membrane degradation due to various resistances that may occur in bipolar membrane electrodialysis devices.

[0063] Figure 2 The bipolar membrane electrodialysis (BPED) system of the present invention is schematically shown for experiments on the preparation of lithium hydroxide and sulfuric acid.

[0064] In one embodiment of the present invention, the bipolar membrane electrodialysis (BPED) system may include an electrodialysis membrane stack comprising one or more pairs of cation exchange membrane C, anion exchange membrane A and bipolar membrane BP arranged sequentially.

[0065] Furthermore, two or more of the aforementioned membrane stacks can be connected in series. In this case, the membrane current density of the series-connected membrane stacks will gradually decrease.

[0066] For convenience, Figure 2 The diagram illustrates that material discharged from the front-end membrane stack flows directly into the back-end membrane stack. However, a portion of the material discharged from the front-end membrane stack can be separated and supplied only to the back-end membrane stack. Furthermore, the material discharged from the front-end membrane stack can be supplied to the back-end membrane stack after being mixed with additional feedstock. There are no particular limitations as long as the desired objectives of the invention are achieved.

[0067] (Experiment on the preparation of lithium hydroxide and sulfuric acid)

[0068] A pair (effective membrane area 0.5 m²) is formed by sequentially configuring cation exchange membrane C, anion exchange membrane A, and bipolar membrane BP. 2 The 40 layers of membranes are stacked together to form three membrane stacks connected in series, thus forming a BPED system.

[0069] Figure 2 The BPED system used in the lithium hydroxide and sulfuric acid preparation experiments of the present invention is shown schematically.

[0070] The cation exchange membrane C can be selected from one or more of the following: CM2, CMB, CSE from AsiaStone, CD100 and CH100 from W-Scocpe, TWEDC1S from Shandong Tianwei, and CT-4 and CTG-10 from Hangzhou Lanran. The cation exchange membranes used for membrane stacks 1 to 3 can be the same or different.

[0071] The anion exchange membrane A can be selected from one or more of the following: ASE, AID, ACD from AsiaStone, AD100 from W-Scocpe, TWEDA1R from Shandong Tianwei, and ATD from Hangzhou Lanran. The anion exchange membranes used for membrane stacks 1 to 3 can be the same or different.

[0072] The bipolar membrane BP can be selected from one or more of the following: BP-1 from Aston Biotech, BPU from Aston Biotech, FBM from Fumatech Biotech, TRJBM from Beijing Tingrun Biotech, and BP-2 from Hangzhou Lanran Biotech. The bipolar membranes used for membrane stacks 1 to 3 can be the same or different.

[0073] For the flow of solution in the membrane stack, refer to Figure 2 Detailed description.

[0074] A lithium sulfate (Li₂SO₄) aqueous solution with a Li concentration of 10 g / L is supplied between anion exchange membrane A and cation exchange membrane C (lithium sulfate supply: Q). LS加入 (kg / hour (hr))), a mixture of water (deionized water (DIW)) or lithium hydroxide aqueous solution and water (DIW) is supplied between the cation exchange membrane C and the bipolar membrane BP (supply rate: Q). LH加入 (kg / hour)), water (DIW) or a mixture of water and sulfuric acid solution is supplied between the bipolar membrane BP and the anion exchange membrane A (supply rate: Q). HS加入 (kg / hour)). Based on the salt chamber supplying lithium sulfate, an anodic (+) direct current is applied to the electrode at the end of the membrane stack on the A side of the anion exchange membrane, and a cathodic (-) direct current is applied to the electrode at the end of the membrane stack on the C side of the cation exchange membrane.

[0075] Specifically, the ion exchange membrane current density of 77 mA / cm² was measured when applied to membrane stack 1. 2 The current applied to membrane stack 2 is 73 mA / cm². 2 A current of 60 mA / cm² was applied to membrane stack 3 as the ion exchange membrane current density. 2 The amount of lithium hydroxide (LiOH) produced and discharged by the current (Q) LH排出 (kg / hour) and the amount of sulfuric acid (H2SO4) (Q) HS排出 (kg / hour)).

[0076] The lithium ions (Li) in the produced lithium hydroxide were measured by ICP (ion-coupled chromatography). + The amount of sulfur and the sulfur content in sulfuric acid.

[0077] The lithium content in lithium hydroxide can be largely considered as lithium ions (Li) that move through the cation exchange membrane. + The value of (Q) Li+ C (kg / hour)), and the S value in sulfuric acid can mostly be considered as sulfate ions (SO4) moving through the anion exchange membrane. 2- The value of (Q) SO4(2-) A (kg / hour)). The amount of sulfate ion movement is calculated from the amount of sulfur movement.

[0078] The amount of water (Q) that moves with lithium ions through the cation exchange membrane H2O C (kg / hour) can be calculated as follows.

[0079] (Q H2O C )=(Q LH排出 )-(Q LH加入 )-(Q Li+ C (2)

[0080] However, the amount of water (H2O) flowing from the alkali chamber into the bipolar membrane is different from the amount of hydroxide ions (OH-) produced by hydrolysis in the bipolar membrane and supplied to the alkali chamber. - The amounts of these two components cancel each other out under normal conditions and can be considered negligible.

[0081] The weight ratio of water to lithium ions moving through the cation exchange membrane (parameter, ω) C The following calculation can be performed.

[0082] ω C =(Q H2O C ) / (Q Li+ C (3)

[0083] The amount of water (Q) that moves with sulfate ions through the anion exchange membrane H2O A (kg / hour) can be calculated as follows.

[0084] (Q H2O A )=(Q HS排出 )-(Q HS加入 )-(Q SO4(2-) A (4)

[0085] However, the amount of water flowing from the acid chamber into the bipolar membrane is related to the amount of hydrogen ions (H+) produced by hydrolysis in the bipolar membrane and supplied to the acid chamber. + The amounts of these two components cancel each other out under normal conditions and can be considered negligible.

[0086] The weight ratio of water to sulfate ions moving through the anion exchange membrane (parameter, ω) A The following calculation can be performed.

[0087] ω A =(Q H2O A ) / (Q SO4(2-) A (5)

[0088] When operating in a rectifier mode with the total voltage adjusted to a similar level, the current efficiency is calculated based on the amount of lithium produced.

[0089] Current efficiency (%) = 100 × {Li yield (mol) × Faraday constant (C / mol)} / {current density (A / m³)} 2 ) × membrane area (m 2 (6) × Time (seconds) Detailed Implementation

[0090] (Example 1)

[0091] In Example 1, W-Scocpe's CH100 membrane was used as the cation exchange membrane, W-Scocpe's A100 membrane as the anion exchange membrane, and Aston's BPU membrane as the bipolar membrane to prepare lithium hydroxide and sulfuric acid. Conversely, the same cation exchange membrane, anion exchange membrane, and bipolar membrane were used in membrane stacks 1 to 3.

[0092] On the other hand, the flow rate of the supplied lithium hydroxide aqueous solution relative to the flow rate of the lithium hydroxide aqueous solution discharged from the membrane stack (Q) LH加入 / Q LH排出 The ratio of the supplied sulfuric acid solution flow rate to the discharged sulfuric acid solution flow rate is 0.36. HS加入 / Q HS排出 The value is 1.03.

[0093] (Example 2)

[0094] In Example 2, W-Scocpe's CD100 was used as the cation exchange membrane, W-Scocpe's AD100 as the anion exchange membrane, and Fumatech's FBM as the bipolar membrane to prepare lithium hydroxide and sulfuric acid. Conversely, the same cation exchange membrane, anion exchange membrane, and bipolar membrane were used in membrane stacks 1 to 3.

[0095] On the other hand, the flow rate of the supplied lithium hydroxide aqueous solution relative to the flow rate of the lithium hydroxide aqueous solution discharged from the membrane stack (Q) LH加入 / Q LH排出The ratio of the supplied sulfuric acid solution flow rate to the discharged sulfuric acid solution flow rate is 0.43, which is the ratio of the supplied sulfuric acid solution flow rate to the discharged sulfuric acid solution flow rate (Q). HS加入 / Q HS排出 The value is 1.05.

[0096] (Example 3)

[0097] In Example 3, W-Scocpe's CH100 was used as the cation exchange membrane, W-Scocpe's AD100 as the anion exchange membrane, and Fumatech's FBM as the bipolar membrane to prepare lithium hydroxide and sulfuric acid. Conversely, the same cation exchange membrane, anion exchange membrane, and bipolar membrane were used in membrane stacks 1 to 3.

[0098] On the other hand, the flow rate of the supplied lithium hydroxide aqueous solution relative to the flow rate of the lithium hydroxide aqueous solution discharged from the membrane stack (Q) LH加入 / Q LH排出 The ratio of the supplied sulfuric acid solution flow rate to the discharged sulfuric acid solution flow rate is 0.53, which is the ratio of the supplied sulfuric acid solution flow rate to the discharged sulfuric acid solution flow rate (Q). HS加入 / Q HS排出 The value is 0.95.

[0099] (Comparative Example 1)

[0100] In Comparative Example 1, a W-Scocpe membrane with modified ion exchange capacity (CH100') was used as the cation exchange membrane, a W-Scocpe AD100 membrane was used as the anion exchange membrane, and a Fumatech FBM was used as the bipolar membrane to prepare lithium hydroxide and sulfuric acid. On the other hand, the same cation exchange membrane, anion exchange membrane, and bipolar membrane were used in membrane stacks 1 to 3.

[0101] On the other hand, the flow rate of the supplied lithium hydroxide aqueous solution relative to the flow rate of the lithium hydroxide aqueous solution discharged from the membrane stack (Q) LH加入 / Q LH排出 The ratio of the supplied sulfuric acid solution flow rate to the discharged sulfuric acid solution flow rate is 0.28. HS加入 / Q HS排出 The value is 1.27.

[0102] Flow rates and parameters (ω) measured in Examples 1 to 3 and Comparative Example 1 C ω A The calculation results are shown in Table 1 below.

[0103] Table 1

[0104]

[0105] Referring to Table 1 above, for ω CComparative Example 1, with a value of 44.8, used a CH100' cation exchange membrane and had a current efficiency of 41.7%, significantly lower than Examples 1 to 3. The cation exchange membrane exhibits the so-called Donnan Exclusion Effect, where the movement of anions is repelled and blocked by the fixed anions (co-ions) within the membrane. It is known that the higher the density of fixed anions, the stronger the Donnan Exclusion Effect. However, if ω... C A value of 44.8 indicates that the cation exchange membrane is over-expanded due to water, resulting in a decrease in the density of fixed anions inside the membrane. This suggests that the final concentration of anions (OH-) is reduced. - The rejection effect of Tang Nan was significantly reduced.

[0106] Therefore, the OH in the produced lithium hydroxide aqueous solution - The anions overcome the Donnan repulsion effect caused by the expanded cation exchange membrane, resulting in a significant increase in back migration towards the lithium sulfate aqueous solution side. This is due to the consumption of OH- ions during back migration. - When the amount of anions is equivalent to the applied current, the current efficiency decreases.

[0107] The ratio of water to sulfate ions moving through the anion exchange membrane (ω) in Table 1 above. A The symbol () is represented as a negative number (-). This is because, although it is shown that the amount of water (H2O) assuming to flow from the acid chamber into the bipolar membrane is related to the amount of hydrogen ions (H+) decomposed in the bipolar membrane, the equation is not directly related to the amount of water (H2O) flowing into the bipolar membrane. + The production figures can be calculated to offset each other, but in reality, the inflow of water is greater than the outflow of hydrogen ions.

[0108] This invention can take various forms and is not limited to the embodiments described above. Those skilled in the art will understand that other specific forms can be used without altering the technical concept or essential features of the invention. Therefore, the above embodiments are exemplary in all respects and are not restrictive.

Claims

1. A method for simultaneously preparing lithium hydroxide and sulfuric acid, comprising the following steps: Prepare a bipolar membrane electrodialysis device, which includes a first bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a second bipolar membrane. An acid chamber is formed between the first bipolar membrane and the anion exchange membrane, a salt chamber is formed between the anion exchange membrane and the cation exchange membrane, and an alkali chamber is formed between the cation exchange membrane and the second bipolar membrane. Lithium sulfate aqueous solution is added to the salt chamber of the bipolar membrane electrodialysis device, sulfuric acid aqueous solution is added to the acid chamber, and lithium hydroxide aqueous solution is added to the alkali chamber; and The desalination solution formed in the salt chamber of the bipolar membrane electrodialysis device is discharged, the sulfuric acid aqueous solution formed in the acid chamber is discharged, and the lithium hydroxide aqueous solution formed in the alkali chamber is discharged. The cation exchange membrane of the bipolar membrane electrodialysis device contains water (H2O) and lithium cations (Li). + The ratio of movement to weight is less than 40.

2. The method for simultaneously preparing lithium hydroxide and sulfuric acid according to claim 1, wherein, The flow rate of the added lithium hydroxide aqueous solution is in the ratio of 0.3 to 0.6 to the flow rate of the lithium hydroxide aqueous solution discharged from the alkali chamber of the bipolar membrane electrodialysis device.

3. The method for simultaneously preparing lithium hydroxide and sulfuric acid according to claim 1, wherein, The flow rate of the added sulfuric acid aqueous solution is in the ratio of 0.9 to 1.2 to the flow rate of the sulfuric acid aqueous solution discharged from the acid chamber of the bipolar membrane electrodialysis device.

4. The method for simultaneously preparing lithium hydroxide and sulfuric acid according to claim 1, wherein, The current density passing through the cation exchange membrane and anion exchange membrane of the bipolar membrane electrodialysis device is 20 mA / cm². 2 Up to 150mA / cm 2 .

5. The method for simultaneously preparing lithium hydroxide and sulfuric acid according to claim 1, wherein, The concentration of the lithium hydroxide aqueous solution added to the alkali chamber of the bipolar membrane electrodialysis device is 0 mol / L to 1 mol / L. The concentration of the lithium hydroxide aqueous solution discharged from the alkali chamber of the bipolar membrane electrodialysis device is from 1 mol / L to 5 mol / L.

6. The method for simultaneously preparing lithium hydroxide and sulfuric acid according to claim 1, wherein, The concentration of the sulfuric acid aqueous solution added to the acid chamber of the bipolar membrane electrodialysis device is 0 mol / L to 0.5 mol / L. The concentration of the sulfuric acid aqueous solution discharged from the acid chamber of the bipolar membrane electrodialysis device is from 0.5 mol / L to 3 mol / L.

7. The method for simultaneously preparing lithium hydroxide and sulfuric acid according to claim 1, wherein, The concentration of the lithium sulfate aqueous solution added to the salt chamber of the bipolar membrane electrodialysis device is from 0.5 mol / L to 2.5 mol / L. The concentration of the lithium sulfate aqueous solution discharged from the salt chamber of the bipolar membrane electrodialysis device is from 0.1 mol / L to 2 mol / L.

8. The method for simultaneously preparing lithium hydroxide and sulfuric acid according to claim 1, wherein, The bipolar membrane electrodialysis device consists of two or more electrodialysis membrane stacks connected in series. Each electrodialysis membrane stack includes a first bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a second bipolar membrane. An acid chamber is formed between the first bipolar membrane and the anion exchange membrane, a salt chamber is formed between the anion exchange membrane and the cation exchange membrane, and an alkali chamber is formed between the cation exchange membrane and the second bipolar membrane.

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