Method of preparing lithium hydroxide

Abstract

The present invention relates to a method of preparing a lithium hydroxide. The preparing method of the present invention may include operation (a) of preparing a lithium sulfate and a sodium hydroxide, operation (b) of preparing a mixed solution by adding a solvent containing alcohol to the lithium sulfate and the sodium hydroxide, operation (c) of separating precipitated sodium sulfate decahydrate in the mixed solution and obtaining the remaining lithium hydroxide solution, and operation (d) of obtaining a lithium hydroxide from the lithium hydroxide solution, and thus may prepare a lithium hydroxide that can be used for an energy storage system with less energy and cost than the related art.

Description

METHOD OF PREPARING LITHIUM HYDROXIDE

[0001] The present invention relates to a method of preparing a lithium hydroxide.

[0002]

[0003] The demand for electronic devices using secondary batteries is rapidly increasing, and the demand for lithium ion batteries that are lightweight and have a high energy density and high capacity is rapidly increasing.

[0004] The lithium ion battery is formed of a positive electrode material, a negative electrode material, a separator, an electrolyte, and the like. As the positive electrode material, a lithium oxide including valuable metals such as nickel, cobalt, and manganese is used. In the positive electrode material, the lithium oxide is used as an active material, and lithium ions in the lithium oxide serve to store or discharge electric energy upon charging and discharging.

[0005] Recently, the demand for lithium hydroxide and lithium carbonate applied to lithium ion batteries has increased rapidly.

[0006] Describing the related art that converts a lithium sulfate into a lithium hydroxide, the related art obtains a lithium hydroxide by adding caustic soda (sodium hydroxide) to the lithium sulfate.

[0007] Here, a mixture of a lithium hydroxide and sodium sulfate needs to be separated. A separation process cools the mixture to a very low temperature to separate a liquid lithium hydroxide and a solid sodium sulfate decahydrate. In this case, a solid sodium sulfate is generated as a byproduct in the above process.

[0008] The cooling process of the mixture for separating the lithium hydroxide from the sodium sulfate is carried out at 0 to -15 ℃. A causticization process of the lithium sulfate is an exothermic reaction. Accordingly, when an additive (NaOH) is added to the lithium sulfate, a temperature of the mixture rises to at least 70 ℃. To cool the heated mixture to the above-described low temperature (0 to -15 ℃), considerable and high cost are required. In addition, to evaporate and concentrate the cooled lithium hydroxide solution, the solution to be re-heated to 60 to 80 ℃. The energy and cost required for the heating are also considerable.

[0009] In this way, the conventional method of preparing a lithium hydroxide has a disadvantage of requiring much energy and cost.

[0010] The present invention is directed to providing a method of preparing a lithium hydroxide that may be used for an energy storage system with less energy and cost.

[0011]

[0012] A method of preparing a lithium hydroxide for achieving the object includes operation (a) of preparing a lithium sulfate and a sodium hydroxide, operation (b) of preparing a mixed solution by adding a solvent containing alcohol to the lithium sulfate and the sodium hydroxide, operation (c) of separating precipitated sodium sulfate decahydrate in the mixed solution and obtaining the remaining lithium hydroxide solution, and operation (d) of obtaining a lithium hydroxide from the lithium hydroxide solution.

[0013] Here, the solvent containing alcohol may include one or more of methanol, ethanol, and iso propyl alcohol (IPA), and the solvent containing alcohol may include 10 wt% to 90 wt% of the methanol.

[0014] In addition, operation (d) may include a recovering process of recovering a solvent containing alcohol left after obtaining the lithium hydroxide from the lithium hydroxide solution.

[0015] Preferably, the recovering process in operation (d) may include generating an alcohol stream recovered by evaporating the solvent containing alcohol at a temperature of 40 to 60 ℃ and a pressure of 100 to 300 mbar, and the recovered alcohol stream may move to operation (b).

[0016] More preferably, operation (d) may include generating a mixed solution stream that mixes the recovered alcohol stream with the solution left after obtaining the lithium hydroxide, and the mixed solution stream may move to operation (b).

[0017] In addition, the method may further include operation (e) drying the obtained lithium hydroxide after operation (d).

[0018] The solubility of sodium sulfate varies greatly depending on a temperature. Conventionally, the mixture is cooled to a very low temperature to crystallize sodium sulfate in the mixture into sodium sulfate decahydrate and precipitate the crystallized sodium sulfate. Such a method is a good method for precipitating and separating the crystallized sodium sulfate in the mixture, but requires much energy and cost to cool the mixture. In addition, since the related art requires re-heating the cooled solution to prepare a lithium hydroxide, additional energy and cost are required.

[0019] According to the present invention, it is possible to more efficiently prepare a lithium hydroxide while reducing energy and cost unlike the related art by adopting a method of adding a solvent that can dissolve a lithium hydroxide while lowering the solubility of sodium sulfate.

[0020] FIG. 1 is a flowchart illustrating a series of operations of a method of preparing a lithium hydroxide according to one embodiment of the present invention.

[0021] FIG. 2 is a flowchart illustrating a series of operations of a method of preparing a lithium hydroxide according to another embodiment of the present invention.

[0022] FIG. 3 is a view illustrating the result of analyzing lithium hydroxides obtained from the embodiments of the present invention.

[0023]

[0024] The above-described objects, features, and advantages will be described below in detail, and thus those skilled in the art to which the present invention pertains will be able to easily carry out the technical spirit of the present invention. In describing the present invention, when it is determined that a detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted. Hereinafter, exemplary embodiments according to the present invention will be described in detail.

[0025] The present invention is not limited to embodiments to be disclosed below but may be implemented in various different forms, these embodiments are merely provided to make the disclosure of the present invention complete and fully inform those skilled in the art of the scope of the invention.

[0026] Hereinafter, a method of preparing a lithium hydroxide according to the present invention will be described in detail.

[0027]

[0028] <Method of preparing lithium hydroxide>

[0029] FIGS. 1 and 2 are flowcharts illustrating a series of operations of a method of preparing a lithium hydroxide according to the present invention. Referring to FIG. 1, the method of preparing a lithium hydroxide according to the present invention includes operation (a) of preparing a lithium sulfate and a sodium hydroxide (S100), operation (b) of preparing a mixture by adding a solvent including alcohol to the lithium sulfate and the sodium hydroxide (S200), operation (c) of separating sodium sulfate precipitated in the mixture and extracting the remaining lithium hydroxide solution (S300), and operation (d) of obtaining a lithium hydroxide from the lithium hydroxide solution (S400).

[0030] First, the method of preparing a lithium hydroxide according to the present invention includes operation (a) of preparing a lithium sulfate and a sodium hydroxide (S100).

[0031] First, the lithium sulfate may be obtained using a concentrate containing lithium and may also be obtained from a lithium carbonate. As a specific example, the lithium sulfate may be obtained by mixing sulfuric acid with lithium carbonate.

[0032] Here, since the present invention uses a solvent including alcohol, a high-concentration lithium sulfate with less water usage in comparison to the related art may be used. Accordingly, specific heat of the mixture of the lithium hydroxide and the sodium sulfate is reduced in comparison to the related art. Since the present invention uses a mixture with reduced specific heat, there is an advantage that cooling and heating processes may be performed using less energy than the related art in a process of separating a lithium hydroxide.

[0033] Next, the method of preparing a lithium hydroxide according to the present invention includes operation (b) of preparing a mixture by adding a solvent including alcohol to the lithium sulfate and the sodium hydroxide (S200).

[0034] The lithium sulfate and sodium hydroxide prepared in operation (a) may be used as a solid phase in operation (b) or may also be used as a liquid phase included in an aqueous solution. Here, when the lithium sulfate meets the sodium hydroxide, a sodium sulfate and a lithium hydroxide are generated by a reaction. In this regard, to prepare a lithium hydroxide, which is a final product, in an aqueous solution state, it is preferable to perform the process in an aqueous solution state in operation (a) to maintain an appropriate concentration.

[0035] In operation (b), a solvent containing alcohol is added to the lithium sulfate and the sodium hydroxide. When the lithium sulfate reacts with the sodium hydroxide, they are converted into a lithium hydroxide and a sodium sulfate. Accordingly, operation (b) also includes adding a solvent containing alcohol to a lithium hydroxide and a sodium sulfate.

[0036] The sodium sulfate and the lithium hydroxide have different solubilities. In this case, the sodium sulfate may be precipitated as a solid slurry state of sodium sulfate decahydrate (Na2SO4·10H2O) by the solvent containing alcohol. In addition, the lithium hydroxide is dissolved in the solvent containing alcohol. In this way, the present invention uses the solvent containing alcohol to separate the sodium sulfate and the lithium hydroxide.

[0037] As described above, conventionally, the mixture was cooled to a very low temperature to crystallize and precipitate the sodium sulfate in the mixture. Such a method is a good method for precipitating and separating the crystallized sodium sulfate in the mixture, but requires much energy and cost to cool the mixture. In addition, since the related art requires re-heating the cooled solution to prepare a lithium hydroxide, additional energy and cost are required.

[0038] According to the present invention, it is possible to more efficiently prepare a lithium hydroxide while reducing energy and cost unlike the related art by adopting a method of adding a solvent that can dissolve a lithium hydroxide while lowering the solubility of sodium sulfate.

[0039] The preparing method according to the present invention does not require cooling the mixture to a very low temperature (lower than 0 ℃) to precipitate the sodium sulfate decahydrate. In the present invention, the mixture may be cooled to a temperature lower than room temperature to quickly precipitate a large amount of the sodium sulfate decahydrate as needed. Preferably, the mixture may be cooled to 10 ℃ or lower.

[0040] The solvent containing alcohol may include at least one of methanol, ethanol, and iso propyl alcohol (IPA). Preferably, the closer the solvent containing alcohol is to 100% methanol, the better the separation effect of a lithium hydroxide and a sodium sulfate. However, considering the solubility of the lithium hydroxide and a solvent of which phase is not separated when mixed with water, the solvent containing alcohol may include 10 to 90 wt% of methanol, preferably, 30 to 85 wt% of methanol, and more preferably, 50 to 80 wt% of methanol. For example, the solvent containing alcohol may include 60 wt% of methanol and 40 wt% of water.

[0041] The amount of the added solvent containing alcohol is not particularly limited. The solvent containing alcohol may be used in an amount that may dissolve both the sodium hydroxide and the lithium hydroxide of operation (c). For example, the solvent containing alcohol may be used in the same amount as the aqueous solution containing the lithium sulfate and the sodium hydroxide.

[0042] Next, the method of preparing a lithium hydroxide according to the present invention includes separating the sodium sulfate precipitated in the mixed solution and obtaining the remaining lithium hydroxide solution (S300).

[0043] As described above, a sodium sulfate is precipitated as sodium sulfate decahydrate in a solid state by the solvent containing alcohol in the mixed solution. In operation (c), the precipitated sodium sulfate decahydrate is separated, and the remaining lithium hydroxide solution is obtained.

[0044] The present invention does not limit the method of separating the precipitated sodium sulfate, and known methods of separating a solid and a liquid may be used.

[0045] Next, the method of preparing a lithium hydroxide according to the present invention includes operation (d) of obtaining a lithium hydroxide from the lithium hydroxide solution (S400).

[0046] Here, to obtain a lithium hydroxide, operation (d) may include concentrating the lithium hydroxide solution and crystallizing the lithium hydroxide to obtain the lithium hydroxide.

[0047] Operation (d) may include heating the lithium hydroxide solution to a temperature of 40 to 60 ℃ to crystallize and obtain the lithium hydroxide.

[0048] Operation (d) may include a process of recovering a solvent containing alcohol left after obtaining the lithium hydroxide from the lithium hydroxide solution. In this case, the solvent containing the recovered alcohol may be re-used in operation (b).

[0049] Referring to FIG. 2, the recovering process in operation (d) may include generating an alcohol stream 10 recovered by evaporating the solvent containing alcohol at a temperature 40 to 60 ℃ and a pressure of 100 to 300 mbar.

[0050] In this case, more preferably, the recovered alcohol may be applied to the precipitated sodium sulfate decahydrate (Na2SO4·10H2O(s)). Accordingly, an extraction stream 11 may be generated by extracting a small amount of lithium hydroxide contained in the precipitated sodium sulfate decahydrate, and the extraction stream 11 may be used in operation (b).

[0051] As described above, in the related art, to precipitate a sodium sulfate, after the mixed solution is cooled to a temperature of lower than 0 ℃ to -15 ℃, the mixed solution is re-heated to a temperature exceeding 100 ℃ in order to recover a lithium hydroxide. In this process, the related art requires much energy and cost. However, the present invention does not need to cool the mixed solution to a low temperature in the process of precipitating a sodium sulfate. Accordingly, the mixed solution may be easily heated with less energy in the process of recovering the lithium hydroxide unlike the related art.

[0052] In addition, the method of preparing a lithium hydroxide according to the present invention may further include operation (e) of drying the obtained lithium hydroxide (S500) after operation (d).

[0053] Operation (e) may be performed in a manner of drying the recovered lithium hydroxide crystals in a vacuum oven.

[0054] Hereinafter, the present invention will be described in more detail through exemplary examples. These examples are merely provided as examples for describing the present invention in more detail. Accordingly, the present invention is not limited to these examples.

[0055]

[0056] <Example>

[0057] 1. Preparing lithium sulfate and sodium hydroxide

[0058] In the examples and comparative examples, 26.20 g of a lithium sulfate obtained from a lithium carbonate was used. (95% content) In addition, 19.4 g of a sodium hydroxide was used in the production of lithium hydroxide.(50% aqueous solution and 97% or more solid content were used)

[0059]

[0060] 2. Preparing mixed solution

[0061] Tables 1 to 4 below describe materials, total amount of solvents, total amount of mixtures, and the like used in the examples and comparative examples.

[0062] As 26.20 g of a lithium sulfate, a material obtained by reacting a lithium carbonate and a sulfuric acid(95% content) was used, and in this case, the concentration of the lithium sulfate ranged from 9.80 to 27.23 wt%.

[0063] A 9% concentration was prepared by mixing a 50% aqueous sodium hydroxide solution containing 19.4 g of a sodium hydroxide or solid sodium hydroxide with methanol.

[0064] A mixture of 306.59 g was prepared by reacting 25.09 g (9.80 to 27.23 wt%) of a lithium sulfate and 19.4 g (9 to 50 wt%) of a sodium hydroxide, and the lithium hydroxide obtained during the mixing was prepared as 11.4 g and 34.53 g of a sodium sulfate. In this case, the total amount of solvent included in the mixture of 306.59 g was prepared as 260.65 g in the same manner.

[0065] As shown in Table 1 below, the composition of the solvent containing alcohol was changed to prepare mixed solutions according to Examples 1 to 4 and Comparative Example 1.

[0066]

[0067] Composition ratio of solvent containing alcoholMeOHgExample 1Water:methanol=1:0.8114.10Example 2Water:methanol=1:1.4152.20Example 3Water:methanol=1:1.9171.20Example 4Water:methanol=1:2.7190.60Comparative Example 1Water 100%0

[0068]

[0069] Li2CO3H2OH2SO4(95%)Li2SO4ggggwt%Example 117.63122.0025.0926.2017.09Example 217.6383.0025.0926.2022.74Example 317.6367.0025.0926.2027.23Example 417.6367.0025.0926.2027.23Comparative Example 117.63236.0025.0926.209.80

[0070]

[0071] NaOHgConcentration wt%Preparing methodExample 119.4050.00NaOH 50% aqueous solutionExample 219.4050.00NaOH 50% aqueous solutionExample 319.4050.00NaOH 50% aqueous solutionExample 419.409.00190.6 g dilution of NaOH 100% methanolComparative Example 119.4050.00NaOH 50% aqueous solution

[0072]

[0073] Total amount of solventLiOHNa2SO4Total amount of mixtureggggExample 1260.6511.4134.53306.59Example 2260.6511.4134.53306.59Example 3260.6511.4134.53306.59Example 4260.6511.4134.53306.59Comparative Example 1260.6511.4134.53306.59

[0074]

[0075] 3. Obtaining lithium hydroxide

[0076] The mixed solutions according to Examples 1 to 4 were cooled to 0℃ to precipitate sodium sulfate decahydrate, and a solution containing lithium hydroxide was extracted. after the solvent containing alcohol was added to the mixed solutions according to Examples 1 to 4, the precipitation reaction of the sodium sulfate was almost ended.

[0077] The mixed solution of Comparative Example 1 was cooled to 0 ℃, but the precipitation reaction of the sodium sulfate hardly progressed in the mixed solution of Comparative Example 1. As the result of cooling the mixed solution of Comparative Example 1 to -10 ℃ and maintaining the cooling temperature for 1 to 2 hours, the precipitation reaction of the sodium sulfate was ended in the mixed solution of Comparative Example 1.

[0078] The temperature-specific mixed solutions of the comparative example and the examples were separated into solid and liquid, and the separated liquids were quantitatively and qualitatively analyzed for Li and Na using ICP-OES to analyze the contents of LiOH and Na2SO4. The content of LiOH of the total sum of LiOH and Na2SO4before cooling crystallization was about 25%, and the content (42%) of LiOH increased after cooling crystallization or the content (79%) of LiOH increased when methanol was added.

[0079]

[0080] Content wt% of temperature-specific lithium hydroxide in solution after crystallization

[0081] LiOH wt%=LiOH / (LiOH+Na2SO4)

[0082]

[0083] ItemsContent wt% of temperature-specific lithium hydroxide after crystallizationLiOH wt%=LiOH / (LiOH+ Na2SO4)TemperatureLi (ppm)Na (ppm)LiOH (ppm)Na2SO4(ppm)Content of LiOH (wt%)Comparative Example 125 ℃10780.0236469.7737195.63112625.7125%-5 ℃12832.1927776.7344276.4885779.9034%-10 ℃14316.2521814.1749397.1267366.3942%Example 125 ℃9671.9110876.1233372.1833587.5750%0 ℃13336.255290.9846015.7116339.5874%Example 225 ℃8265.195279.7928518.4116305.0164%0 ℃13752.225326.0347450.9616447.8174%Example 325 ℃9848.985403.5933983.1616687.3467%0 ℃13696.954110.7747260.2612694.8579%Example 425 ℃9124.305228.0031482.7016145.0766%0 ℃13392.663890.8946210.3512015.8379%

[0084]

[0085] Through the above process, lithium hydroxide solutions of Examples 1 to 4 and Comparative Example 1 were obtained. The contents of LiOH and Na2SO4were calculated using the amount of the obtained LiOH filtrate and ICP-OES analysis.

[0086]

[0087] ItemsYield after cooling crystallization solid-liquid separationYield of filtrateLiNaLiOHNa2SO4LiOHNa2SO4gppmppmppmppmggComparative Example 1202.7114316.2521814.1749397.1267366.3910.01313.656Example 1230.9613336.255290.9846015.7116339.5810.6283.774Example 2229.1013752.225326.0347450.9616447.8110.8713.768Example 3225.5413696.954110.7747260.2612694.8510.6592.863Example 4228.0513392.663890.8946210.3512015.8310.5382.740

[0088]

[0089] 4. Concentration and crystallization of lithium hydroxide

[0090] The concentration and crystallization process of a lithium hydroxide is described based on Example 4 of the present invention.

[0091] From 228.05 g of the lithium hydroxide solution obtained through the above-described operations, only the solvent containing alcohol was evaporated (40 to 60 ℃ and 100 to 300 mbar) and separated, and the recovered methanol was added to the sodium sulfate separated into solid and liquid phases after cooling crystallization to extract a small amount of lithium hydroxide.

[0092] After removing methanol in the evaporation and concentration operation, the slurried lithium hydroxide solution(crystallized lithium hydroxide and lithium hydroxide solution coexisted) was subjected to solid-liquid separation. The crystallized lithium hydroxide monohydrate was obtained through solid-liquid separation, and 32.81 g of the filtrate was obtained. The obtained lithium hydroxide monohydrate was dried and then subjected to purity and structural analysis using ICP-OES and XRD (see Tables 7 to 9 and FIG. 3)

[0093] The yield of LiOH was 8.72 g and the yield was 76.39%. Using the recovered methanol (186.5 g), a recovery rate of a lithium hydroxide (0.565 g) contained in sodium sulfate decahydrate separated into solid and liquid phases and a lithium hydroxide (2.06 g) contained in the separated filtrate after evaporation and concentration was 23.04%(total recovery 2.63g), and the methanol(containing a lithium hydroxide) used for recovery may be reused in the preparing of the sodium hydroxide.

[0094] Accordingly, using the preparing method of the present invention, a lithium hydroxide with a purity of 99.72% may be obtained up to 99% more economically and efficiently in comparison to the conventional preparing methods.

[0095]

[0096] ItemsEvaporation and concentration, and slurry separationSolid-liquid filtrate componentRecovery of lithium in sodium sulfate (adding 186.5 g of methanol)Recovery of MeOHYield of LiOHSolid-liquid separation filtrateLiNaLiOHNa2SO4YieldLiLiOHgggppmppmgggppmgExample 4186.58.7232.8118240.3219650.572.061.991801053.230.565

[0097]

[0098] Yield and recovery rate of LiOH in Example 4Theoretical valueYieldRecoverableYieldRecovery rateSumggg%%%11.418.722.6376.39%23.04%99.43%

[0099]

[0100] Purity (ppm) of lithium hydroxide obtained in Example 4LiNaCaMgAlFeNiMnCoCuZnCrB282037.182757.78<13.8310.22<1<1<1<1<1<1<1<1

[0101]

[0102] 5. Conclusion

[0103] The conventional methods of preparing a lithium hydroxide essentially require a cooling process that requires much energy and cost to precipitate a sodium sulfate.

[0104] However, the method of preparing a lithium hydroxide according to the present invention may obtain a lithium hydroxide with less energy and cost using a solvent containing alcohol and may also recover an unrecovered lithium hydroxide using recovered methanol.

[0105] Although the present invention has been described above, the present invention is not limited by the embodiments disclosed herein, and it is apparent that various modifications can be made by those skilled in the art within the scope of the technical spirit of the present invention. In addition, even when the operational effects according to the configuration of the present invention have not been explicitly described in the description of the embodiments of the present invention, it goes without saying that the effects predictable by the corresponding configuration should also be recognized.

Claims

1.A method of preparing a lithium hydroxide, comprising:operation (a) of preparing a lithium sulfate and a sodium hydroxide;operation (b) of preparing a mixed solution by adding a solvent containing alcohol to the lithium sulfate and the sodium hydroxide;operation (c) of separating precipitated sodium sulfate decahydrate in the mixed solution and obtaining the remaining lithium hydroxide solution; andoperation (d) of obtaining a lithium hydroxide from the lithium hydroxide solution.2.The method of claim 1, wherein the solvent containing alcohol includes one or more of methanol, ethanol, and iso propyl alcohol (IPA).3.The method of claim 2, wherein the solvent containing alcohol includes 10 wt% to 90 wt% of the methanol.4.The method of claim 1, wherein the operation (d) includes a recovering process of recovering a solvent containing alcohol left after obtaining the lithium hydroxide from the lithium hydroxide solution.5.The method of claim 4, wherein the recovering process in operation (d) includes generating an alcohol stream recovered by evaporating the solvent containing alcohol at a temperature of 40 to 60 ℃ and a pressure of 100 to 300 mbar.6.The method of claim 4, wherein the recovered alcohol stream moves to operation (b).7.The method of claim 6, wherein operation (d) includes generating a mixed solution stream that mixes the recovered alcohol stream with the solution left after obtaining the lithium hydroxide, andthe mixed solution stream moves to operation (b).8.The method of claim 1, wherein, in operation (a), the lithium sulfate is obtained by mixing a lithium carbonate with a sulfuric acid.9.The method of claim 1, further comprising operation (e) drying the obtained lithium hydroxide after operation (d).

Images