Preparation method of lithium citrate tetrahydrate

Abstract

The invention belongs to the technical field of lithium citrate, and provides a preparation method of lithium citrate tetrahydrate. The preparation method comprises the following steps: dropwise adding a lithium hydroxide solution into a citric acid solution for reaction to obtain a reaction solution; adding an adsorbent into the reaction liquid for adsorption and impurity removal to obtain clear liquid; performing vacuum concentration on the clear liquid to obtain a supersaturated solution; adding low alcohol into the supersaturated solution for gradient cooling, and then stirring for crystallization to obtain crystal mush; and carrying out solid-liquid separation on the crystal slurry, and washing the solid. The lithium hydroxide solution is dripped controllably, activated carbon is added for adsorption and impurity removal, local excessive alkali is avoided, and side reactions and introduction of impurities are reduced; in the concentration and crystallization process, low alcohol is added, the precipitation rate of the lithium citrate tetrahydrate is increased, crystals are washed with the low alcohol, mother liquor attached to the surfaces of the crystals is effectively removed, the yield and purity of the lithium citrate tetrahydrate are improved, the purity reaches 99.5% or above, and the yield is improved by 5% or above compared with a traditional method.

Description

Technical Field

[0001] This invention relates to the field of lithium citrate technology, and more particularly to a method for preparing lithium citrate tetrahydrate. Background Technology

[0002] Lithium citrate tetrahydrate is an important chemical raw material with wide applications in pharmaceuticals, food, and battery electrolytes. Currently, lithium citrate tetrahydrate is mainly obtained by neutralizing citric acid with a lithium source (such as lithium carbonate or lithium hydroxide) in an aqueous solution, followed by direct concentration and crystallization.

[0003] However, existing preparation methods have several problems: adding a solid lithium source to a citric acid solution in a single step can easily lead to localized over-alkaliness in the reaction system, causing side reactions. It may also cause some lithium ions to form insoluble impurities, affecting the purity and yield of the final product. Traditional crystallization processes typically employ atmospheric pressure evaporation and rapid cooling, resulting in a high residual lithium ion content in the mother liquor and unsatisfactory product yields. Furthermore, it is difficult to control crystal nucleation and growth rates, easily leading to impurities such as lithium citrate dihydrate and anhydrous lithium citrate, affecting the product's purity, flowability, and subsequent processing performance.

[0004] Therefore, developing new methods for preparing lithium citrate tetrahydrate, improving product purity, yield, and crystal quality, and obtaining lithium citrate tetrahydrate with regular crystal form are technical problems that urgently need to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing lithium citrate tetrahydrate, addressing the shortcomings of existing technologies.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing lithium citrate tetrahydrate, comprising the following steps: 1) Lithium hydroxide solution is added dropwise to citric acid solution to carry out the reaction and obtain the reaction solution; 2) Add an adsorbent to the reaction solution to remove impurities through adsorption, and obtain a clear solution; 3) The clarified liquid is concentrated under reduced pressure to obtain a supersaturated solution; 4) Add a lower alcohol to the supersaturated solution and gradually cool it down, then stir to induce crystallization and obtain a crystal slurry; 5) Separate the solid and liquid phases of the crystal slurry, and wash the solid to obtain lithium citrate tetrahydrate.

[0007] Preferably, the lithium hydroxide solution has a mass fraction of 10-20%, the citric acid solution has a mass fraction of 20-30%, and the molar ratio of lithium hydroxide in the lithium hydroxide solution to citric acid in the citric acid solution is 3:1.

[0008] Preferably, the dropping rate in step 1) is 1~5 mL / min; The reaction temperature is 30~50℃, the pH value is 7~9, and the reaction time is 1~2h.

[0009] Preferably, the adsorbent in step 2) is activated carbon, and the mass of the adsorbent is 0.1-2% of the mass of the reaction solution. Step 2) The adsorption and impurity removal time is 30~60 min.

[0010] Preferably, the temperature of the vacuum concentration in step 3) is 40~60℃, and the vacuum degree of the vacuum concentration is -0.1~-0.08MPa.

[0011] Preferably, the mass fraction of the supersaturated solution in step 3) is 60-65%.

[0012] Preferably, the gradient cooling rate in step 4) is 3~10℃ / h, and the gradient cooling to the temperature of the supersaturated solution is 10~20℃.

[0013] Preferably, the volume of the lower alcohol in step 4) is 10-25% of the volume of the supersaturated solution; The stirring speed for crystallization is 300~500 r / min, and the stirring time for crystallization is 2~4 h.

[0014] Preferably, the washing agent used in step 5) is a lower alcohol.

[0015] Preferably, the lower alcohol has 1 to 4 carbon atoms.

[0016] The beneficial effects of this invention are: 1) This invention effectively avoids localized over-alkaliness and reduces side reactions and the introduction of impurities by controlling the dropping rate of the lithium hydroxide solution and adding activated carbon for adsorption and impurity removal. During the concentration and crystallization process, the addition of a lower alcohol increases the precipitation rate of lithium citrate tetrahydrate. Washing the crystals with the lower alcohol effectively removes the mother liquor adhering to the crystal surface, reducing product loss due to dissolution and improving the yield and purity of lithium citrate tetrahydrate, achieving a purity of over 99.5% and a yield increase of over 5% compared to traditional methods. The induced crystallization process, combining reduced pressure concentration with gradient cooling and supplemented with a lower alcohol, ensures uniform and slow crystal growth, resulting in lithium citrate tetrahydrate crystals with uniform particle size, regular morphology, good flowability, and no agglomeration.

[0017] 2) The preparation method of the present invention is stable, easy to industrialize, simple and easy to control; vacuum concentration reduces the operating temperature and energy consumption, and the lower alcohol can be recycled, which meets the requirements of green chemistry. Detailed Implementation

[0018] This invention provides a method for preparing lithium citrate tetrahydrate, comprising the following steps: 1) Lithium hydroxide solution is added dropwise to citric acid solution to carry out the reaction and obtain the reaction solution; 2) Add an adsorbent to the reaction solution to remove impurities through adsorption, and obtain a clear solution; 3) The clarified liquid is concentrated under reduced pressure to obtain a supersaturated solution; 4) Add a lower alcohol to the supersaturated solution and gradually cool it down, then stir to induce crystallization and obtain a crystal slurry; 5) Separate the solid and liquid phases of the crystal slurry, and wash the solid to obtain lithium citrate tetrahydrate.

[0019] In this invention, the mass fraction of the lithium hydroxide solution is preferably 10-20%, more preferably 12-18%, and even more preferably 15%; the mass fraction of the citric acid solution is preferably 20-30%, more preferably 22-28%, and even more preferably 25%; the molar ratio of lithium hydroxide in the lithium hydroxide solution to citric acid in the citric acid solution is preferably 3:1.

[0020] In this invention, the dripping rate in step 1) is preferably 1~5 mL / min, more preferably 2~4 mL / min, and even more preferably 3 mL / min; The reaction temperature is preferably 30~50℃, more preferably 35~45℃, and even more preferably 40℃; the reaction pH is preferably 7~9, more preferably 7.5~8.5, and even more preferably 8; the reaction time is preferably 1~2h, more preferably 1.2~1.8h, and even more preferably 1.5h.

[0021] In this invention, during the dropwise addition process in step 1), the citric acid solution is preferably stirred, and the stirring speed is preferably 200~300 r / min, more preferably 250 r / min.

[0022] In this invention, the adsorbent in step 2) is preferably activated carbon, and the mass of the adsorbent is preferably 0.1-2% of the mass of the reaction solution, more preferably 0.5-1.5%, and even more preferably 1%. Step 2) The adsorption and impurity removal time is preferably 30-60 min, more preferably 35-55 min, and even more preferably 40-50 min.

[0023] In this invention, the temperature of the vacuum concentration in step 3) is preferably 40~60℃, more preferably 45~55℃, and even more preferably 50℃; the vacuum degree of the vacuum concentration is preferably -0.1~-0.08MPa, and even more preferably -0.09MPa.

[0024] In this invention, the mass fraction of the supersaturated solution in step 3) is preferably 60-65%, more preferably 61-64%, and even more preferably 62-63%.

[0025] In this invention, the gradient cooling rate in step 4) is preferably 3~10℃ / h, more preferably 4~8℃ / h, and even more preferably 5~7℃ / h; the gradient cooling to the temperature of the supersaturated solution is preferably 10~20℃, more preferably 12~18℃, and even more preferably 15℃.

[0026] In this invention, the volume of the lower alcohol in step 4) is preferably 10-25% of the volume of the supersaturated solution, more preferably 15-22%, and even more preferably 18-21%. The stirring speed for crystallization is preferably 300~500 r / min, more preferably 360~450 r / min, and even more preferably 400 r / min; the stirring time for crystallization is preferably 2~4 h, more preferably 2.5~3.5 h, and even more preferably 3 h.

[0027] In this invention, step 4) preferably involves first lowering the temperature of the supersaturated solution to room temperature, and then adding a lower alcohol for gradient cooling.

[0028] In this invention, the temperature of the lower alcohol in step 4) is preferably the same as the temperature of the supersaturated solution.

[0029] In this invention, the reagent used for washing in step 5) is preferably a lower alcohol.

[0030] In this invention, the lower alcohol preferably has 1 to 4 carbon atoms, and more preferably 2 or 3.

[0031] In this invention, the lower alcohol is preferably methanol, anhydrous ethanol, propanol, isopropanol, n-butanol, or tert-butanol.

[0032] In this invention, the washing method in step 5) is preferably to first wash with deionized water and then wash with a lower alcohol, or to directly wash with an aqueous solution of a lower alcohol.

[0033] In this invention, after the washing in step 5), drying is preferably performed to obtain lithium citrate tetrahydrate; The drying temperature is preferably 60~80℃, more preferably 65~75℃, and even more preferably 70℃; the drying time is preferably 4~6h, more preferably 4.5~5.5h, and even more preferably 5h.

[0034] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0035] Example 1

[0036] 192 g (1 mol) of citric acid was dissolved in 800 mL of deionized water to obtain a citric acid solution. 126 g (3 mol) of lithium hydroxide monohydrate was dissolved in 1050 mL of deionized water to obtain a lithium hydroxide solution. The citric acid solution was placed in a reaction vessel, the temperature was controlled at 30℃, and stirring was started at 200 r / min. The lithium hydroxide solution was added dropwise to the reaction vessel at a rate of 1 mL / min using a peristaltic pump. After the addition was complete, the pH of the reaction system was adjusted to 8 using 25% citric acid, and the reaction was continued with stirring at the same temperature for 2 h. After the reaction was completed, 5 g of activated carbon was added to the reaction vessel, and adsorption and impurity removal were continued at 200 r / min for 30 min. The solution was filtered to obtain a clear liquid. The clear liquid was concentrated under reduced pressure at 40℃ and -0.08 MPa to a solute mass fraction of 60% to obtain a supersaturated solution. 480 mL of supersaturated solution was placed in a crystallization vessel and cooled to 25 °C. 100 mL of anhydrous ethanol at 25 °C was added, and the solution was cooled to 10 °C at a rate of 5 °C / h. The mixture was then stirred at 360 r / min at 10 °C for 3 h to induce crystallization, yielding a slurry. The slurry was centrifuged to separate the crystals. The crystals were first washed with 20 mL of ice water, then washed twice with 50 mL of 95% ethanol. The washed crystals were dried at 60 °C for 6 h to obtain white crystals, which were lithium citrate tetrahydrate.

[0037] The mass of lithium citrate tetrahydrate prepared in this embodiment is 285g, the purity is 99.7%, and the yield based on lithium is 95%.

[0038] Example 2

[0039] 288 g (1.5 mol) of citric acid was dissolved in 864 mL of deionized water to obtain a citric acid solution. 189 g (4.5 mol) of lithium hydroxide monohydrate was dissolved in 945 mL of deionized water to obtain a lithium hydroxide solution. The citric acid solution was placed in a reaction vessel, the temperature was controlled at 40℃, and stirring was started at 250 r / min. The lithium hydroxide solution was added dropwise to the reaction vessel at a rate of 3 mL / min using a peristaltic pump. After the addition was complete, the pH of the reaction system was adjusted to 8 using 24% citric acid, and the reaction was continued with stirring for 1.5 h. After the reaction was completed, 8 g of activated carbon was added to the reaction vessel, and adsorption and impurity removal were continued at 250 r / min for 45 min. The solution was filtered to obtain a clear liquid. The clear liquid was concentrated under reduced pressure at 50℃ and -0.09 MPa to a solute mass fraction of 65% to obtain a supersaturated solution. 705 mL of supersaturated solution was placed in a crystallization vessel and cooled to 25 °C. 150 mL of anhydrous ethanol at 25 °C was added, and the solution was cooled to 10 °C at a rate of 5 °C / h. The mixture was then stirred at 360 r / min at 10 °C for 3 h to induce crystallization, yielding a slurry. The slurry was centrifuged to separate the crystals, which were then washed twice with 100 mL of 95% ethanol. The washed crystals were dried at 70 °C for 5 h to obtain white crystals, which was lithium citrate tetrahydrate.

[0040] The mass of lithium citrate tetrahydrate prepared in this embodiment is 430g, the purity is 99.8%, and the yield based on lithium is 96.1%.

[0041] Example 3

[0042] 384 g (2 mol) of citric acid was dissolved in 960 mL of deionized water to obtain a citric acid solution. 252 g (6 mol) of lithium hydroxide monohydrate was dissolved in 1008 mL of deionized water to obtain a lithium hydroxide solution. The citric acid solution was placed in a reaction vessel, the temperature was controlled at 50℃, and stirring was started at 250 r / min. The lithium hydroxide solution was added dropwise to the reaction vessel using a peristaltic pump at a rate of 5 mL / min. After the addition was complete, the pH of the reaction system was adjusted to 8 using 26% citric acid, and the reaction was continued with stirring for 1 h. After the reaction was completed, 10 g of activated carbon was added to the reaction vessel, and adsorption and impurity removal were performed at 280 r / min for 30 min. The solution was filtered to obtain a clear liquid. The clear liquid was concentrated under reduced pressure at 60℃ and -0.1 MPa to a solute mass fraction of 63%, obtaining a supersaturated solution. 935 mL of supersaturated solution was placed in a crystallization vessel and cooled to 25 °C. 200 mL of anhydrous ethanol (at 25 °C) was added, and the solution was cooled to 10 °C at a rate of 10 °C / h. The mixture was then stirred at 360 r / min at 10 °C for 3 h to induce crystallization, yielding a slurry. The slurry was centrifuged to separate the crystals. The crystals were first washed with 30 mL of ice water, then washed twice with 60 mL of anhydrous ethanol. The washed crystals were dried at 80 °C for 4 h to obtain white crystals, which were lithium citrate tetrahydrate.

[0043] The mass of lithium citrate tetrahydrate prepared in this embodiment is 570g, the purity is 99.9%, and the yield based on lithium is 95.2%.

[0044] Comparative Example 1

[0045] The difference from Example 1 is that the crystal slurry was centrifuged to separate the crystals, the crystals were washed with 150 mL of ice water, and the washed crystals were dried at 60°C for 6 hours to obtain white crystals. The surface of the crystals was slightly sticky, and clumping occurred during the drying process.

[0046] The mass of lithium citrate tetrahydrate prepared in this comparative example was 275 g, the purity was 99.4%, and the yield based on lithium was 90.5%.

[0047] Comparative Example 2

[0048] The difference from Example 1 is that the lithium hydroxide solution was poured into the reaction vessel all at once, and the reaction was carried out at a speed of 300 r / min with stirring for 2 hours.

[0049] The mass of lithium citrate tetrahydrate prepared in this comparative example was 263 g, the purity was 98.15%, and the yield based on lithium was 86.79%.

[0050] Comparative Example 3

[0051] The difference from Example 1 is that the clarified liquid was concentrated at 160°C under normal pressure to a solute mass fraction of 65%, resulting in a supersaturated solution. The supersaturated solution was placed in a crystallization vessel and stirred at 360 r / min for 3 hours to crystallize, yielding a crystal slurry.

[0052] The mass of lithium citrate tetrahydrate prepared in this comparative example was 273 g, the purity was 99.1%, and the yield based on lithium was 90.09%.

[0053] As shown in the above embodiments, this invention provides a method for preparing lithium citrate tetrahydrate. The lithium hydroxide solution is controllably added dropwise to a citric acid solution to avoid side reactions caused by localized over-alkaliness. An adsorbent is added to remove impurities and improve product purity. Reduced pressure concentration and gradient cooling are used to assist crystallization, and a lower alcohol is added during the crystallization process to improve crystallization efficiency. The crude product is washed with a lower alcohol to remove the mother liquor and reduce dissolution losses. The lithium citrate tetrahydrate prepared by the method of this invention achieves a purity of over 99.5% and a yield of over 95%, which is 5% higher than that of traditional methods.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing lithium citrate tetrahydrate, characterized by, The method comprises the following steps: 1) adding lithium hydroxide solution into citric acid solution to react, to obtain a reaction solution; 2) adding an adsorbent into the reaction solution to remove impurities by adsorption, to obtain a clear solution; 3) concentrating the clear solution under reduced pressure to obtain a supersaturated solution; 4) adding a lower alcohol into the supersaturated solution to perform gradient cooling, and then stirring to crystallize, to obtain a crystal slurry; 5) separating the crystal slurry into solid and liquid, and washing the solid, to obtain lithium citrate tetrahydrate.

2. The production method according to claim 1, characterized by, The mass fraction of the lithium hydroxide solution is 10-20%, the mass fraction of the citric acid solution is 20-30%, and the molar ratio of lithium hydroxide in the lithium hydroxide solution to citric acid in the citric acid solution is 3:

1.

3. The preparation method according to claim 1, characterized in that, The dropping speed in step 1) is 1-5 mL / min. The reaction temperature is 30-50℃, the reaction pH value is 7-9, and the reaction time is 1-2 h.

4. The production method according to any one of claims 1 to 3, characterized by, The adsorbent in step 2) is activated carbon, and the mass of the adsorbent is 0.1-2% of the mass of the reaction solution. The time for removing impurities by adsorption in step 2) is 30-60 min.

5. The preparation method according to claim 4, characterized in that, The concentration temperature under reduced pressure in step 3) is 40-60℃, and the vacuum degree under reduced pressure is-0.1--0.08 MPa.

6. The preparation method according to claim 5, characterized in that, The mass fraction of the supersaturated solution in step 3) is 60-65%.

7. The production method according to claim 5 or 6, characterized by, The gradient cooling rate in step 4) is 3-10℃ / h, and the temperature of the gradient cooling is 10-20℃.

8. The preparation method according to claim 7, characterized in that, The volume of the lower alcohol in step 4) is 10-25% of the volume of the supersaturated solution. The stirring speed for crystallization in step 4) is 300-500 r / min, and the stirring time for crystallization is 2-4 h.

9. The production method according to claim 8, characterized by, The reagent for washing in step 5) is a lower alcohol.

10. The production method according to claim 1 or 9, characterized by, The number of carbon atoms of the lower alcohol is independently 1-4.