A method for the continuous synthesis of lithium fluoride

Abstract

The application provides a method for continuously synthesizing lithium fluoride, which comprises the following steps: (1) continuously reacting and crystallizing a lithium bicarbonate solution and a hydrofluoric acid solution in a tubular reactor to obtain a suspension; the lithium bicarbonate solution is fed in two streams, and the flow rate ratio of the first stream to the second stream is 1:0.25-1:1; (2) sequentially subjecting the suspension to solid-liquid separation, washing and vacuum drying to obtain a lithium fluoride product. The application precisely controls the particle size distribution of the generated lithium fluoride product by controlling the feeding mode of the lithium bicarbonate solution, and realizes the continuous synthesis of lithium fluoride, which is high in production efficiency and suitable for large-scale popularization and application.

Description

Technical Field

[0001] This invention relates to the field of lithium fluoride synthesis technology, and more particularly to a method for continuous synthesis of lithium fluoride. Background Technology

[0002] Lithium fluoride is a key raw material in the synthesis of lithium battery electrolyte materials. Currently, the mainstream process for synthesizing lithium fluoride involves reacting hydrofluoric acid solution with lithium bicarbonate solution, but the production process is intermittent and inefficient. To improve the production efficiency of lithium fluoride, the industry is actively developing new production processes.

[0003] CN117466314A discloses a preparation process for battery-grade lithium fluoride production, comprising the following raw material components: lithium carbonate, water, 48% hydrofluoric acid, carbon dioxide, and lithium hydroxide solution. Lithium fluoride is prepared using these raw materials through the following steps: S1. Carbonization process; S2. Three-stage continuous synthesis process, in which a quantitative amount of lithium bicarbonate solution is continuously added to a first-stage continuous flow reactor along with 48% hydrofluoric acid for reaction, and the reaction solution overflows into the second and third-stage continuous flow reactors for further reaction; S3. Continuous neutralization process, in which the reaction solution from the third-stage synthesis reactor overflows into a continuous flow neutralization reactor for neutralization; S4. Filtration and drying process. The continuous multiple synthesis and neutralization reactions between carbonization and centrifugal filtration improve the neutralization effect of lithium fluoride, ultimately improving the quality of the synthesized lithium fluoride. However, this preparation process still requires a three-stage reactor to achieve continuous process control, and the process cannot accurately control the particle size of the lithium fluoride product during the reaction, leaving room for further improvement.

[0004] CN101570337A discloses a method for producing battery-grade lithium fluoride, comprising the following steps: (1) first, the mother liquor is poured into the synthesis tank and stirred, anhydrous hydrofluoric acid is slowly added to the mother liquor and diluted to a certain concentration, and then the temperature is raised to 70-90℃; (2) within 20-40 minutes, the required solid lithium carbonate is added uniformly to the solution formed in step (1), after the addition is completed, the temperature is raised to 90-110℃, and the mixture is stirred at a constant temperature for 2-4 hours, and the discharged gas is absorbed by the mother liquor; (3) after the reaction is complete, the resulting slurry is filtered and washed, and the washing liquid and filtrate are returned to step (1) for use; (4) the filter cake is vacuum concentrated and dried for 4-6 hours, and finally packaged to obtain the finished product.

[0005] CN102030344A discloses a method for preparing lithium fluoride, comprising the following steps: (1) passing carbon dioxide into water, then adding lithium carbonate as raw material to obtain a lithium bicarbonate solution, then adding a precipitant, passing carbon dioxide into the solution until the pH is 8-9, filtering, and collecting the lithium bicarbonate solution; (2) adding hydrofluoric acid to the filtrate obtained in step (1) to carry out a fluorination reaction, then adding lithium hydroxide solution to adjust the pH of the system to 7-7.5, then filtering, collecting the filter cake, drying, and obtaining the product lithium fluoride.

[0006] However, none of the above-mentioned lithium fluoride production methods can directionally control the particle size distribution of lithium fluoride. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for continuous synthesis of lithium fluoride. By controlling the lithium bicarbonate solution to be fed in two streams and strictly controlling the flow ratio of the first stream to the second stream, the continuous production of lithium fluoride products can be achieved while accurately controlling the particle size. The method is simple to operate and has high lithium fluoride production efficiency.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for the continuous synthesis of lithium fluoride, the method comprising the following steps:

[0010] (1) A lithium bicarbonate solution and a hydrofluoric acid solution are continuously reacted and crystallized in a tubular reactor to obtain a suspension; the lithium bicarbonate solution is fed in two streams, and the flow rate ratio of the first stream to the second stream is 1:0.25 to 1:1.

[0011] (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying in sequence to obtain lithium fluoride product.

[0012] The method for continuous synthesis of lithium fluoride described in this invention achieves accurate control of the particle size of the lithium fluoride product by controlling the simultaneous feeding of lithium bicarbonate solution in two streams at a specific flow ratio and regulating the material ratio of lithium bicarbonate solution with hydrofluoric acid at different stages in a tubular reactor. Moreover, the method has high production efficiency and the particle size index of the obtained lithium fluoride product can meet the needs of different applications.

[0013] The lithium bicarbonate solution described in this invention is fed in two streams. The flow rate ratio of the first stream to the second stream is 1:0.25 to 1:1, for example, it can be 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.5, 1:0.7 or 1:1, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] The particle size D50 of the lithium fluoride product described in this invention is 30 to 150 μm, for example, it can be 30 μm, 50 μm, 80 μm, 100 μm, 120 μm or 150 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the concentration of the lithium bicarbonate solution in step (1) is 6 to 9 wt%, for example, it can be 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, or 9 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the concentration of the hydrofluoric acid solution in step (1) is 40 to 50 wt%, for example, it can be 40 wt%, 42 wt%, 44 wt%, 45 wt%, 47 wt%, 49 wt%, or 50 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Preferably, the molar ratio of the solute in the lithium bicarbonate solution to the hydrofluoric acid solution in step (1) is 1:1 to 1:1.1, for example, it can be 1:1, 1:1.01, 1:1.03, 1:1.05, 1:1.07, 1:1.09 or 1:1.1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the pressure of the tubular reactor in step (1) is 0.05 to 0.15 MPaG, for example, it can be 0.05 MPaG, 0.07 MPaG, 0.1 MPaG, 0.12 MPaG, 0.14 MPaG or 0.15 MPaG, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the temperature of the continuous reaction in step (1) is 10 to 40°C, for example, it can be 10°C, 15°C, 20°C, 25°C, 30°C or 40°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, in step (1), the distance between the feed position of the first feed stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second feed stream and the feed position of the first feed stream is 1 / 3L to 1 / 2L, for example, it can be 1 / 3L, 7 / 20L, 5 / 12L, 9 / 20L or 1 / 2L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In this invention, the distance between the feed position of the second feed stream and the feed position of the first feed stream is preferably 1 / 3L to 1 / 2L. This better matches the reaction kinetics of lithium bicarbonate and hydrofluoric acid, as well as the crystal precipitation kinetics of lithium fluoride, allowing for better control of the reaction and crystallization within an optimal range. If the feed position of the second feed stream is too close to the feed position of the first feed stream, the hydrofluoric acid and an equivalent amount of lithium bicarbonate will react rapidly and completely in a short time, leading to explosive precipitation of lithium fluoride crystals in the system, resulting in smaller lithium fluoride particle sizes and reduced product yield. If the feed position of the second feed stream is too far from the feed position of the first feed stream, the lithium fluoride crystals will continue to grow, easily causing the reaction product to have larger and less uniform particle sizes.

[0022] Preferably, the vacuum drying temperature in step (2) is 90 to 110°C, for example, it can be 90°C, 92°C, 95°C, 100°C, 105°C or 110°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the vacuum degree of the vacuum drying in step (2) is 0.03 to 0.07 MPa, for example, it can be 0.03 MPa, 0.035 MPa, 0.04 MPa, 0.05 MPa, 0.06 MPa or 0.07 MPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] The solid-liquid separation described in this invention is not limited, and any method known to those skilled in the art for solid-liquid separation can be used, such as filtration, sedimentation, or centrifugation.

[0025] As a preferred technical solution of the present invention, the method includes the following steps:

[0026] (1) A lithium bicarbonate solution with a concentration of 6-9 wt% and a hydrofluoric acid solution with a concentration of 40-50 wt% are subjected to a continuous reaction and crystallization at a temperature of 10-40℃ in a tubular reactor with a total residence time of 5-30 min, according to a solute molar ratio of 1:1 to 1:1.1, to obtain a suspension; the lithium bicarbonate solution is fed in two streams, with a flow rate ratio of 1:0.25 to 1:1 between the first and second streams; the distance between the feed position of the first stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second stream and the feed position of the first stream is 1 / 3L to 1 / 2L; the pressure of the tubular reactor is 0.05-0.15 MPaG;

[0027] (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying at a temperature of 90-110℃ and a vacuum degree of 0.03-0.07MPa to obtain lithium fluoride products with a particle size D50 of 30-150μm.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] (1) The method for continuous synthesis of lithium fluoride provided by the present invention achieves directional control of the particle size of lithium fluoride products by controlling the ratio of the two feeds of lithium bicarbonate solution, which can meet different application requirements.

[0030] (2) The method for continuous synthesis of lithium fluoride provided by the present invention uses a tubular reactor to realize the continuous synthesis of lithium fluoride, which can reduce the number of reactor equipment sets and significantly reduce equipment investment. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the tubular reactor used in a method for continuous synthesis of lithium fluoride provided by the present invention.

[0032] In the diagram: 1-First lithium bicarbonate solution feed pipe; 2-Second lithium bicarbonate solution feed pipe; 3-Hydrofluoric acid solution feed pipe; 4-Suspension discharge pipe; 5-Carbon dioxide outlet pipe; 6-Tube reactor. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] This invention provides a method for the continuous synthesis of lithium fluoride, the method comprising the following steps:

[0035] (1) A lithium bicarbonate solution and a hydrofluoric acid solution are continuously reacted and crystallized in a tubular reactor to obtain a suspension; the lithium bicarbonate solution is fed in two streams, and the flow rate ratio of the first stream to the second stream is 1:0.25 to 1:1.

[0036] (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying in sequence to obtain lithium fluoride product.

[0037] A schematic diagram of the tubular reactor used in the continuous synthesis method of lithium fluoride described in this invention is shown below. Figure 1 As shown.

[0038] The tubular reactor 6 includes a lithium bicarbonate solution feed pipe and a hydrofluoric acid solution feed pipe 3; the lithium bicarbonate solution feed pipe includes a first feed pipe 1 and a second feed pipe 2; the distance between the feed position of the first feed pipe 1 and the liquid phase outlet of the tubular reactor 6 is L, and the distance between the feed position of the second feed pipe 2 and the feed position of the first feed pipe 1 is 1 / 3L to 1 / 2L.

[0039] The tubular reactor 6 is equipped with a suspension discharge pipe 4 at the bottom and a carbon dioxide gas discharge pipe 5 at the top.

[0040] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0041] It should be understood that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0042] Unless otherwise specified, all raw materials and reagents used in the following examples and comparative examples are commercially available.

[0043] Hydrofluoric acid (HF concentration of 50%; Sigma-Aldirch) can be used to prepare hydrofluoric acid solutions of other desired concentrations, and lithium bicarbonate solution (prepared by reacting battery-grade lithium carbonate with carbon dioxide).

[0044] Example 1

[0045] This embodiment provides a method for the continuous synthesis of lithium fluoride, the method comprising the following steps:

[0046] (1) A lithium bicarbonate solution with a flow rate of 20 g / min and a concentration of 6 wt% and a hydrofluoric acid solution with a flow rate of 71.5 g / min and a concentration of 40 wt% are reacted in a tubular reactor at a total residence time of 20 min, with a solute molar ratio of 1:1, to obtain a suspension. The lithium bicarbonate solution is fed in two streams with a flow rate ratio of 1:1 between the first and second streams. The distance between the feed position of the first stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second stream and the feed position of the first stream is 1 / 2 L. The pressure of the tubular reactor is 0.15 MPaG.

[0047] (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying at 100°C and 0.05MPa to obtain lithium fluoride product.

[0048] Example 2

[0049] This embodiment provides a method for the continuous synthesis of lithium fluoride, the method comprising the following steps:

[0050] (1) A lithium bicarbonate solution with a flow rate of 15 g / min and a concentration of 7 wt% and a hydrofluoric acid solution with a flow rate of 56.7 g / min and a concentration of 45 wt% are subjected to a continuous reaction and crystallization at a temperature of 10 °C in a tubular reactor with a solute molar ratio of 1:1.02 and a total residence time of 10 min, to obtain a suspension; the lithium bicarbonate solution is fed in two streams with a flow rate ratio of 1:0.8 between the first stream and the second stream; the distance between the feed position of the first stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second stream and the feed position of the first stream is 1 / 3 L; the pressure of the tubular reactor is 0.10 MPaG;

[0051] (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying at 100°C and 0.05MPa to obtain lithium fluoride product.

[0052] Example 3

[0053] This embodiment provides a method for the continuous synthesis of lithium fluoride, the method comprising the following steps:

[0054] (1) A lithium bicarbonate solution with a flow rate of 10 g / min and a concentration of 8 wt% and a hydrofluoric acid solution with a flow rate of 41.7 g / min and a concentration of 48 wt% are continuously reacted and crystallized in a tubular reactor at a temperature of 30°C, with a solute molar ratio of 1:1.05 and a total residence time of 5 min, to obtain a suspension. The lithium bicarbonate solution is fed in two streams, with a flow rate ratio of 1:0.5 between the first stream and the second stream. The distance between the feed position of the first stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second stream and the feed position of the first stream is 5 / 12 L. The pressure of the tubular reactor is 0.08 MPaG.

[0055] (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying at 100°C and 0.05MPa to obtain lithium fluoride product.

[0056] Example 4

[0057] This embodiment provides a method for the continuous synthesis of lithium fluoride, the method comprising the following steps:

[0058] (1) A lithium bicarbonate solution with a flow rate of 20 g / min and a concentration of 9 wt% and a hydrofluoric acid solution with a flow rate of 94.3 g / min and a concentration of 50 wt% are continuously reacted and crystallized in a tubular reactor at a temperature of 40 °C, with a solute molar ratio of 1:1.1 and a total residence time of 30 min, to obtain a suspension. The lithium bicarbonate solution is fed in two streams, with a flow rate ratio of 1:0.3 between the first stream and the second stream. The distance between the feed position of the first stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second stream and the feed position of the first stream is 1 / 2 L. The pressure of the tubular reactor is 0.05 MPaG.

[0059] (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying at 100°C and 0.05MPa to obtain lithium fluoride product.

[0060] Example 5

[0061] This embodiment provides a method for continuous synthesis of lithium fluoride. Except for step (1), in which the distance between the feed position of the second feed and the feed position of the first feed is 1 / 5L, the method is the same as in embodiment 1.

[0062] Example 6

[0063] This embodiment provides a method for continuous synthesis of lithium fluoride. Except for step (1), in which the distance between the feed position of the second feed and the feed position of the first feed is 2 / 3L, the method is the same as in embodiment 1.

[0064] Comparative Example 1

[0065] This comparative example provides a method for continuous synthesis of lithium fluoride. Except for step (1), in which the lithium bicarbonate solution is fed in one stream, i.e., all feeds are fed from the first feed position, the method is the same as in Example 1.

[0066] Comparative Example 2

[0067] This comparative example provides a method for continuous synthesis of lithium fluoride. Except for the flow ratio of the first feed to the second feed in step (1) being 1:0.1, the method is the same as that in Example 1.

[0068] Comparative Example 3

[0069] This comparative example provides a method for continuous synthesis of lithium fluoride. Except for the flow ratio of the first feed to the second feed in step (1) being 1:1.5, the method is the same as that in Example 1.

[0070] The yield and particle size D50 of the lithium fluoride products obtained in the above examples and comparative examples were determined, and the results are shown in Table 1.

[0071] Table 1

[0072]

[0073]

[0074] As can be seen from Table 1:

[0075] (1) As can be seen from Examples 1 to 4, the method for continuous synthesis of lithium fluoride provided by the present invention achieves directional control of the particle size of lithium fluoride product by controlling the ratio of the two feeds of lithium bicarbonate solution. The particle size D50 of the obtained lithium fluoride product is 30 to 150 μm, and the yield of lithium fluoride product is more than 90.3%.

[0076] (2) It can be seen from the combined examples 1 and 5-6 that in example 5, the distance between the feed position of the second feed and the feed position of the first feed is relatively close, which will cause hydrofluoric acid and the equivalent amount of lithium bicarbonate to react completely in a short time, resulting in the explosive precipitation of lithium fluoride crystals in the system, and the lithium fluoride particle size is relatively small, with a particle size D50 of 12 μm. At the same time, the yield of lithium fluoride product is reduced to 89.3%. In example 6, the distance between the feed position of the second feed and the feed position of the first feed is relatively far, which will cause the lithium fluoride crystal product to continue to grow crystals, which will easily cause the reaction product to have a larger and uneven particle size, with a particle size D50 of 180 μm. The yield of lithium fluoride product is also greatly reduced to 85.2%.

[0077] (3) It can be seen from the combined example 1 and comparative example 1 that in comparative example 1, the lithium bicarbonate solution is fed in one stream. At this time, the lithium bicarbonate reacts rapidly with hydrofluoric acid. The local lithium fluoride concentration is too high, which causes the lithium fluoride crystals to explode and precipitate. As a result, the obtained lithium fluoride particles are smaller and the yield of lithium fluoride products is reduced.

[0078] (4) It can be seen from the combined examples 1 and 2-3 that in Comparative Example 2, the flow rates of the first and second feed streams are relatively high, which will result in most of the lithium bicarbonate reacting completely during the first feed stream, producing small-particle lithium fluoride products. However, due to the smaller flow rate of the second feed stream, the lithium fluoride produced is insufficient to grow the lithium fluoride crystals produced by the first reaction stream to the target particle size range, resulting in smaller lithium fluoride particle size and a lower yield of lithium fluoride products. In Comparative Example 3, the flow rates of the first and second feed streams are relatively low, which will result in only a small amount of lithium fluoride crystals being produced during the first feed stream. The lithium fluoride produced during the second feed stream, in addition to being used for the growth of lithium fluoride crystals produced by the first stream, will still be in a highly supersaturated state. This will also cause a large amount of lithium fluoride products to explode, resulting in uneven lithium fluoride particle size and a smaller overall particle size, thus reducing the yield of lithium fluoride products.

[0079] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for continuous synthesis of lithium fluoride, characterized in that, The method includes the following steps: (1) A lithium bicarbonate solution and a hydrofluoric acid solution are continuously reacted and crystallized in a tubular reactor to obtain a suspension; the lithium bicarbonate solution is fed in two streams, and the flow rate ratio of the first stream to the second stream is 1:0.25~1:

1. (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying in sequence to obtain lithium fluoride product; The distance between the feed position of the first feed stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second feed stream and the feed position of the first feed stream is 1 / 3L to 1 / 2L.

2. The method according to claim 1, characterized in that, The concentration of the lithium bicarbonate solution in step (1) is 6~9 wt%.

3. The method according to claim 1, characterized in that, The concentration of the hydrofluoric acid solution is 40~50wt%.

4. The method according to claim 1, characterized in that, The molar ratio of the solute in the lithium bicarbonate solution and the hydrofluoric acid solution in step (1) is 1:1 to 1:1.

1.

5. The method according to claim 1, characterized in that, The total residence time of the lithium bicarbonate solution and hydrofluoric acid solution in the tubular reactor in step (1) is 5~30 min.

6. The method according to claim 1, characterized in that, The pressure of the tubular reactor in step (1) is 0.05~0.15 MPaG.

7. The method according to claim 1, characterized in that, The temperature of the continuous reaction in step (1) is 10~40℃.

8. The method according to claim 1, characterized in that, The vacuum drying temperature in step (2) is 90~110℃.

9. The method according to claim 1, characterized in that, The vacuum degree of the vacuum drying is 0.03~0.07MPa.

10. The method according to claim 1, characterized in that, The particle size D50 of the lithium fluoride product in step (2) is 30~150μm.

11. The method according to claim 1, characterized in that, The method includes the following steps: (1) A lithium bicarbonate solution with a concentration of 6~9wt% and a hydrofluoric acid solution with a concentration of 40~50wt% are subjected to continuous reaction crystallization at a temperature of 10~40℃ in a tubular reactor with a total residence time of 5~30min, according to the molar ratio of the solutes in the solution being 1:1~1:1.1, to obtain a suspension; the lithium bicarbonate solution is fed in two streams, with the flow rate ratio of the first stream to the second stream being 1:0.25~1:

1. The distance between the feed position of the first feed stream and the liquid phase outlet of the tubular reactor is L, and the distance between the feed position of the second feed stream and the feed position of the first feed stream is 1 / 3L to 1 / 2L; the pressure of the tubular reactor is 0.05 to 0.15 MPaG; (2) The suspension is subjected to solid-liquid separation, washing and vacuum drying at a temperature of 90~110℃ and a vacuum degree of 0.03~0.07MPa to obtain lithium fluoride products with a particle size D50 of 30~150μm.

Images