Process for the preparation of lithium hydroxide

Abstract

The present invention relates to a method for producing lithium hydroxide. The method for producing lithium hydroxide according to the present invention comprises: step (a), preparing lithium sulfate and sodium hydroxide; step (b), preparing a mixed solution by adding a solvent containing an alcohol to the lithium sulfate and sodium hydroxide; step (c), separating sodium sulfate decahydrate precipitated in the mixed solution to obtain a remaining lithium hydroxide solution; and step (d), obtaining lithium hydroxide from the lithium hydroxide solution, whereby lithium hydroxide usable for an energy storage device can be produced with less energy and cost compared to the prior art.

Description

Technical Field

[0001] This invention relates to a method for preparing lithium hydroxide. Background Technology

[0002] Due to the dramatic increase in demand for electronic devices that utilize secondary batteries, the demand for lithium-ion batteries that are both lightweight and have high energy density and high capacity is also growing rapidly.

[0003] A lithium-ion battery is composed of a positive electrode material, a negative electrode material, a separator, and an electrolyte. The positive electrode material uses lithium oxide containing valuable metals such as nickel, cobalt, and manganese. In this positive electrode material, the lithium oxide serves as the active material, and the lithium ions in the lithium oxide store or release electrical energy during charging and discharging.

[0004] In recent years, the demand for lithium hydroxide and lithium carbonate used in lithium-ion batteries has increased dramatically.

[0005] Examine existing technologies for converting lithium sulfate into lithium hydroxide, which involve adding caustic soda (sodium hydroxide) to lithium sulfate to obtain lithium hydroxide.

[0006] This process requires separating a mixture of lithium hydroxide and sodium sulfate. The separation process involves cooling the mixture to a very low temperature to separate it into liquid lithium hydroxide and solid sodium sulfate decahydrate. In this process, solid sodium sulfate is produced as a byproduct.

[0007] The cooling process described above for separating the mixture of lithium hydroxide and sodium sulfate is carried out at a temperature of 0 to -15°C. The causticization process of lithium sulfate is an exothermic reaction. Therefore, if an additive (NaOH) is added to the lithium sulfate, the temperature of the mixture will rise to at least 70°C. Cooling this heated mixture to the aforementioned low temperature (0 to -15°C) requires considerable energy and incurs high costs. Furthermore, to evaporate and concentrate the cooled lithium hydroxide solution, the solution must be reheated to 60 to 80°C. This heating also requires considerable energy and incurs significant costs.

[0008] As mentioned above, existing methods for preparing lithium hydroxide have the disadvantages of consuming a large amount of energy and incurring high costs. Summary of the Invention

[0009] Technical issues The purpose of this invention is to provide a method for preparing lithium hydroxide that can be used in energy storage devices with less energy and cost.

[0010] Technical solution The method for preparing lithium hydroxide according to the present invention for solving the aforementioned technical problem includes: step (a) preparing lithium sulfate and sodium hydroxide; step (b) preparing a mixture by adding a solvent containing an alcohol to the lithium sulfate and sodium hydroxide; step (c) separating the sodium sulfate precipitated in the mixture due to the reaction to obtain the remaining lithium hydroxide solution; and step (d) obtaining lithium hydroxide from the lithium hydroxide solution.

[0011] The solvent containing alcohols may include one or more of methanol, ethanol and isopropyl alcohol (IPA), and the content of methanol may be from 10% to 90% by weight.

[0012] Furthermore, step (d) may include a process for recovering the alcohol-containing solvent remaining after obtaining lithium hydroxide from the lithium hydroxide solution.

[0013] Preferably, in step (d), the recovery process can generate a recovered alcohol stream by evaporating a solvent containing alcohols at 40–60°C and 100–300 mbar, and the recovered alcohol stream can be transferred to step (b).

[0014] More preferably, in step (d), a mixed stream can be generated that combines the remaining solution after obtaining lithium hydroxide with the recovered alcohol stream, and the mixed stream can be transferred to step (b).

[0015] Furthermore, the method for preparing lithium hydroxide of the present invention may further include step (e) after step (d), in which the obtained lithium hydroxide is dried.

[0016] Invention Effects The solubility of sodium sulfate varies significantly with temperature. Traditionally, the mixture has been cooled to very low temperatures to crystallize and precipitate sodium sulfate as sodium sulfate decahydrate. While this method is advantageous for precipitating and separating sodium sulfate crystals from the mixture, it requires substantial energy and is costly to cool the mixture. Furthermore, existing techniques necessitate reheating the cooled solution to prepare lithium hydroxide, thus incurring additional energy and cost.

[0017] This invention employs a method of adding a solvent that can both reduce the solubility of sodium sulfate and dissolve lithium hydroxide. Therefore, unlike existing technologies, it can prepare lithium hydroxide more efficiently while reducing energy and cost. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating a series of steps in a method for preparing lithium hydroxide according to an embodiment of the present invention.

[0019] Figure 2 The flowchart illustrates a series of steps in a method for preparing lithium hydroxide according to another embodiment of the present invention.

[0020] Figure 3 The results of analyzing lithium hydroxide obtained from embodiments of the present invention are shown. Detailed Implementation

[0021] The foregoing objectives, features, and advantages will be described in detail below, enabling those skilled in the art to readily implement the technical concept of this invention. In describing this invention, detailed descriptions of previously known technologies related to this invention will be omitted where it is deemed that such technologies might unnecessarily obscure the essence of the invention. Preferred embodiments of the invention will now be described in detail.

[0022] This invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. This embodiment is provided only to make the disclosure of this invention complete and to fully inform those skilled in the art of the scope of this invention.

[0023] The preparation method of lithium hydroxide according to the present invention will be described in detail below.

[0024] Preparation method of lithium hydroxide Figure 1 and Figure 2 A flowchart illustrating a series of steps in the preparation method of lithium hydroxide according to the present invention. (See reference...) Figure 1 The method for preparing lithium hydroxide according to the present invention includes: step (a), preparing lithium sulfate and sodium hydroxide (S100); step (b), preparing a mixture by adding a solvent containing an alcohol to the lithium sulfate and sodium hydroxide (S200); step (c), separating the sodium sulfate precipitated in the mixture and extracting the remaining lithium hydroxide solution (S300); and step (d), obtaining lithium hydroxide from the lithium hydroxide solution (S400).

[0025] First, the method for preparing lithium hydroxide according to the present invention includes step (a), preparing lithium sulfate and sodium hydroxide (S100).

[0026] First, the lithium sulfate can be obtained from lithium-containing concentrates or from lithium carbonate. As a specific example, the lithium sulfate can be obtained by mixing lithium carbonate and sulfuric acid.

[0027] In this invention, because a solvent containing alcohols is used, a high concentration of lithium sulfate with a lower water content can be used compared to existing technologies. Consequently, the specific heat of the lithium hydroxide and sodium sulfate mixture is reduced compared to existing technologies. Because this invention utilizes a mixture with reduced specific heat, it has the advantage of using less energy for cooling and heating processes in the lithium hydroxide separation process compared to existing technologies.

[0028] Secondly, the method for preparing lithium hydroxide according to the present invention includes step (b), which involves adding a solvent containing an alcohol to the lithium sulfate and sodium hydroxide to prepare a mixture (S200).

[0029] The lithium sulfate and sodium hydroxide prepared in step (a) can be used directly in solid form in step (b) or in liquid form contained in an aqueous solution. If lithium sulfate comes into contact with sodium hydroxide, a reaction will produce sodium sulfate and lithium hydroxide. In this regard, to prepare lithium hydroxide as the final product in an aqueous solution state, it is preferable to process it in aqueous solution form in step (a) to maintain an appropriate concentration.

[0030] In step (b), a solvent containing an alcohol is added to the lithium sulfate and sodium hydroxide. If the lithium sulfate reacts with the sodium hydroxide, it will be converted into lithium hydroxide and sodium sulfate. Therefore, it can be said that step (b) also includes adding a solvent containing an alcohol to the lithium hydroxide and sodium sulfate.

[0031] The sodium sulfate and lithium hydroxide have different solubilities. In this case, the sodium sulfate can precipitate as a solid slurry of sodium sulfate decahydrate (Na₂SO₄·10H₂O) using a solvent containing an alcohol. Furthermore, the lithium hydroxide dissolves directly in the alcohol-containing solvent. As described above, the present invention uses an alcohol-containing solvent to separate the sodium sulfate and lithium hydroxide.

[0032] As mentioned above, conventional methods involve cooling the mixture to very low temperatures to crystallize and precipitate sodium sulfate from the mixture. While this method is advantageous for precipitating and separating sodium sulfate crystals from the mixture, cooling the mixture requires significant energy and is costly. Furthermore, existing techniques require reheating the cooled solution to prepare lithium hydroxide, thus incurring additional energy and cost.

[0033] This invention employs a method of adding a solvent that can both reduce the solubility of sodium sulfate and dissolve lithium hydroxide. Therefore, unlike existing technologies, it can prepare lithium hydroxide more efficiently while reducing energy and cost.

[0034] The preparation method of the present invention does not require cooling the mixture to a very low temperature (below 0°C) to precipitate the sodium sulfate decahydrate. In the present invention, the mixture can be cooled to a temperature below room temperature as needed to rapidly and extensively precipitate the sodium sulfate decahydrate. Preferably, the mixture can be cooled to below 10°C.

[0035] The alcohol-containing solvent may contain one or more of methanol, ethanol, and isopropyl alcohol (IPA). Preferably, the closer the methanol content in the alcohol-containing solvent is to 100%, the better the separation effect of lithium hydroxide and sodium sulfate. However, considering the solubility of lithium hydroxide and solvents that do not undergo phase separation when mixed with water, the methanol content in the alcohol-containing solvent may be from 10% to 90% by weight. Preferably, the methanol content may be 30% to 85% by weight, and more preferably, the methanol content may be 50% to 80% by weight. For example, the alcohol-containing solvent may contain 60% by weight methanol and 40% by weight water.

[0036] The amount of the alcohol-containing solvent added is not particularly limited. The alcohol-containing solvent can be an amount sufficient to simultaneously dissolve the sodium hydroxide and the lithium hydroxide from step (c). As an example, the alcohol-containing solvent can be the same amount as the aqueous solution containing the lithium sulfate and sodium hydroxide.

[0037] Secondly, the method for preparing lithium hydroxide according to the present invention includes step (c), separating the sodium sulfate precipitated in the mixture to obtain the remaining lithium hydroxide solution (S300).

[0038] As described above, in the mixture, sodium sulfate precipitates as solid sodium sulfate decahydrate using a solvent containing alcohols. In step (c), the precipitated sodium sulfate decahydrate is separated to obtain the remaining lithium hydroxide solution.

[0039] This invention does not limit the method for separating the precipitated sodium sulfate; known methods for solid-liquid separation can be used.

[0040] Secondly, the method for preparing lithium hydroxide according to the present invention includes step (d), obtaining lithium hydroxide from the lithium hydroxide solution (S400).

[0041] In step (d), to obtain lithium hydroxide, the lithium hydroxide solution can be concentrated to crystallize lithium hydroxide.

[0042] In step (d), the lithium hydroxide solution can be heated to a temperature of 40-60°C to crystallize the lithium hydroxide and obtain it.

[0043] Step (d) may include a process for recovering the alcohol-containing solvent remaining after obtaining lithium hydroxide from the lithium hydroxide solution. In this case, the recovered alcohol-containing solvent can be reused in step (b).

[0044] refer to Figure 2 In step (d), the recovery process can generate a recovered alcohol stream 10 by evaporating a solvent containing alcohols at 40–60°C and 100–300 mbar.

[0045] In this case, more preferably, the recovered alcohol can be applied to the precipitated sodium sulfate decahydrate (Na2SO4·10H2O(s)). This allows the extraction of trace amounts of lithium hydroxide contained in the precipitated sodium sulfate decahydrate to generate an extraction stream 11, which can then be used in step (b).

[0046] As described above, in order to precipitate sodium sulfate, the prior art involves cooling the mixture to a temperature below 0°C to -15°C, and then reheating it to a temperature above 100°C to recover lithium hydroxide. This process consumes a significant amount of energy and is costly. However, the present invention eliminates the need to cool the mixture to low temperatures during the sodium sulfate precipitation process. Therefore, unlike the prior art, the present invention can easily heat the mixture with less energy during the lithium hydroxide recovery process.

[0047] Furthermore, the method for preparing lithium hydroxide of the present invention may further include step (e) after step (d), in which the obtained lithium hydroxide is dried (S500).

[0048] Step (e) can be performed by drying the recovered lithium hydroxide crystals in a vacuum baking oven.

[0049] The present invention will now be described in more detail through preferred embodiments. These embodiments are merely illustrative examples provided to illustrate the invention in greater detail. Therefore, the invention is not limited to these embodiments.

[0050] Example 1. Preparation steps for lithium sulfate and sodium hydroxide In the examples and comparative examples, 26.20 g of lithium sulfate (95% purity) obtained from lithium carbonate was used. Furthermore, 19.4 g of sodium hydroxide (using a 50% aqueous solution and a solid with a purity of 97% or higher) was used in the preparation of lithium hydroxide. 2. Preparation steps of the mixture Tables 1 to 4 below record the substances, total amount of solvent, total amount of mixture, etc. used in the examples and comparative examples.

[0051] 26.20 g of lithium sulfate was prepared by reacting lithium carbonate with sulfuric acid (95% content), and the concentration of lithium sulfate was prepared to be 9.80–27.23 wt%.

[0052] Prepare a 9% concentration by mixing a 50% aqueous solution of sodium hydroxide containing 19.4g of sodium hydroxide or solid sodium hydroxide with methanol.

[0053] 25.09 g (9.80–27.23 wt%) of lithium sulfate was reacted with 19.4 g (9–50 wt%) of sodium hydroxide to prepare a mixture of 306.59 g. The resulting mixture contained 11.4 g of lithium hydroxide and 34.53 g of sodium sulfate. Under these conditions, the total amount of solvent in the 306.59 g mixture was also prepared to be 260.65 g.

[0054] As shown in Table 1 below, mixtures according to Examples 1 to 4 and Comparative Example 1 were prepared by changing the composition of the solvent containing alcohols.

[0055] Table 1

[0056] Table 2

[0057] Table 3

[0058] Table 4

[0059] 3. Steps to obtain lithium hydroxide The mixtures from Examples 1 to 4 were cooled to 0°C, causing sodium sulfate decahydrate to precipitate. The solution containing dissolved lithium hydroxide was then extracted. Upon addition of a solvent containing alcohols, the precipitation of sodium sulfate in the mixtures from Examples 1 to 4 was largely completed immediately.

[0060] The mixture of Comparative Example 1 was cooled to 0°C, but almost no sodium sulfate precipitation reaction occurred in the mixture of Comparative Example 1. The mixture of Comparative Example 1 was cooled to -10°C and kept at the cooling temperature for 1 to 2 hours. As a result, the sodium sulfate precipitation reaction was completed in the mixture of Comparative Example 1.

[0061] Solid-liquid separation was performed on the mixtures of the comparative examples and the embodiment at different temperatures. The separated liquids were analyzed quantitatively and qualitatively for Li and Na using ICP-OES (inductively coupled plasma atomic emission spectrometry), and the contents of LiOH and Na₂SO₄ were analyzed. Before cooling and crystallization, the total LiOH and Na₂SO₄ content was approximately 25%. After cooling and crystallization (42%) or with the addition of methanol (79%), the LiOH content increased.

[0062] Lithium hydroxide content (wt%) in solution at different temperatures after crystallization LiOH wt%=LiOH / (LiOH+Na2SO4) Table 5

[0063] Through the above process, lithium hydroxide solutions of Examples 1 to 4 and Comparative Example 1 were obtained. The contents of LiOH and Na₂SO₄ were calculated using the amount of the obtained LiOH filtrate and ICP-OES analysis.

[0064] Table 6

[0065] 4. Concentration and crystallization of lithium hydroxide Example 4 of the present invention illustrates the concentration and crystallization process of lithium hydroxide.

[0066] In 228.05 g of the lithium hydroxide solution obtained through the above steps, only the solvent containing alcohols was evaporated (40–60 °C, 100–300 mbar) for separation. The recovered methanol was added to the sodium sulfate after solid-liquid separation by cooling and crystallization to extract trace amounts of lithium hydroxide.

[0067] After removing methanol in the evaporation and concentration step, the slurry-state lithium hydroxide solution (containing both crystalline lithium hydroxide and a lithium hydroxide solution) underwent solid-liquid separation. Crystalline lithium hydroxide monohydrate and 32.81 g of filtrate were obtained through solid-liquid separation. The obtained lithium hydroxide monohydrate was dried and its purity and structure were analyzed by ICP-OES and XRD (X-ray diffraction). (Refer to Tables 7 to 9, for further information...) Figure 3 ) The yield of LiOH was 8.72 g, or 76.39%. Using the recovered methanol (186.5 g), the recovery rates of lithium hydroxide (0.565 g) contained in the solid-liquid separation of sodium sulfate decahydrate and lithium hydroxide (2.06 g) contained in the filtrate separated after evaporation and concentration were 23.04% (total recovery 2.63 g). The recovered methanol (containing lithium hydroxide) can be reused in the sodium hydroxide preparation step.

[0068] Therefore, when using the preparation method of the present invention, compared with the existing preparation methods, lithium hydroxide with a purity of 99.72% can be obtained more economically and effectively, with a yield of up to 99%.

[0069] Table 7

[0070] Table 8

[0071] Table 9

[0072] 5. Conclusion Existing methods for preparing lithium hydroxide require a cooling process that consumes a large amount of energy and is costly in order to precipitate sodium sulfate.

[0073] However, the method for preparing lithium hydroxide of the present invention can obtain lithium hydroxide with lower energy and cost by using a solvent containing alcohols, and can also recover unrecovered lithium hydroxide by using recycled methanol.

[0074] As described above, the present invention has been illustrated, but it is obvious that the present invention is not limited to the embodiments disclosed in this specification, and various modifications can be made by those skilled in the art within the scope of the technical concept of the present invention. Furthermore, although the effects resulting from the configuration according to the present invention are not explicitly described in the above description of the embodiments, the effects foreseeable from this configuration should be readily acknowledged.

Claims

1. A method for preparing lithium hydroxide, characterized in that, include: Step (a): Prepare lithium sulfate and sodium hydroxide; Step (b) involves preparing a mixture by adding an alcohol-containing solvent to the lithium sulfate and sodium hydroxide. Step (c): Separate the sodium sulfate decahydrate precipitated in the mixture to obtain the remaining lithium hydroxide solution; as well as Step (d): Obtain lithium hydroxide from the lithium hydroxide solution.

2. The method for preparing lithium hydroxide according to claim 1, characterized in that, The solvent containing alcohols includes one or more of methanol, ethanol, and isopropanol.

3. The method for preparing lithium hydroxide according to claim 2, characterized in that, In the solvent containing alcohols, the methanol content is from 10% to 90% by weight.

4. The method for preparing lithium hydroxide according to claim 1, characterized in that, Step (d) includes a recycling process for recovering the alcohol-containing solvent remaining after obtaining lithium hydroxide from the lithium hydroxide solution.

5. The method for preparing lithium hydroxide according to claim 4, characterized in that, In step (d), the recovery process generates a recovered alcohol stream by evaporating a solvent containing alcohols at 40–60°C and 100–300 mbar.

6. The method for preparing lithium hydroxide according to claim 4, characterized in that, The recovered alcohol stream is transferred to step (b).

7. The method for preparing lithium hydroxide according to claim 6, characterized in that, In step (d), a mixed stream is generated that combines the remaining solution after obtaining lithium hydroxide with the recovered alcohol stream. The mixed liquid stream is transferred to step (b).

8. The method for preparing lithium hydroxide according to claim 1, characterized in that, In step (a), the lithium sulfate is obtained by mixing lithium carbonate and sulfuric acid.

9. The method for preparing lithium hydroxide according to claim 1, characterized in that, Following step (d), step (e) is included, in which the obtained lithium hydroxide is dried.

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