Preparation method of anhydrous lithium iodide

Abstract

The invention relates to the technical field of new energy battery electrolyte, in particular to a preparation method of anhydrous lithium iodide, which comprises the following steps: (1) disproportionation reaction: carrying out disproportionation reaction on elemental iodine and a lithium hydroxide solution; (2) dehydration pretreatment: carrying out dehydration treatment on a reaction product in the step (1) to obtain mixed solid powder of lithium iodate and lithium iodide; (3) hydrogen reduction: reacting the mixed solid powder of the lithium iodate and the lithium iodide in the step (2) with hydrogen to prepare lithium iodide solid powder; and (4) drying treatment: carrying out vacuum drying on the lithium iodide solid powder in the step (3) to prepare the anhydrous lithium iodide. According to the preparation method of the anhydrous lithium iodide, hydrogen is selected as a reducing agent, so that excessive impurities are not introduced, and the product purity is higher; dehydration pretreatment is carried out between disproportionation reaction and hydrogen reduction reaction, and the process is simple and efficient.

Description

Technical Field

[0001] The invention relates to the technical field of new energy battery electrolytes, and in particular to a method for preparing high-purity anhydrous lithium iodide. Background Art

[0002] Lithium iodide, chemical formula LiI, is an important chemical raw material. Due to its good solubility, ionic conductivity, high selectivity and chemical stability, it has broad application prospects in the fields of new energy batteries, medicine, chemical synthesis, optoelectronic devices, etc. In the field of batteries, anhydrous lithium iodide is mainly used in the production of battery electrolytes, especially in lithium-ion batteries. Anhydrous lithium iodide can improve the performance of batteries and improve the cycle stability of batteries. Lithium-ion batteries prepared with anhydrous lithium iodide have been widely used in new energy vehicles, electronic products and medical devices.

[0003] The preparation method of anhydrous lithium iodide mainly includes neutralization method, formic acid reduction method, acetone method, hydrazine method, liquid ammonia method, etc. at present. As the invention patent of publication number CN10426144A is prepared by neutralization method, specifically reacting with hydroiodic acid with lithium carbonate or lithium hydroxide as raw material, the method is produced without waste material, but the obtained product is lithium iodide trihydrate, the dehydration process of this method does not have solvent or gas protection, if air enters disperser at high temperature, product is easy to be oxidized and deteriorate, and the sealing and operation requirements of the dispersion process are high. The invention patent of publication number CN103137981A is to add lithium hydroxide after mixing water, elemental iodine particles and excess iron powder, solid-liquid separation, obtain the lithium iodide solid containing crystal water and dissolve in organic solvent again, carry out constant voltage electrolysis, obtain anhydrous lithium iodide solid. The formic acid reduction method used in the prior art is to react iodine and lithium hydroxide in an aqueous solution to prepare lithium iodide and lithium iodate, then add formic acid for reduction, and then dehydrate at high temperature to obtain anhydrous lithium iodide.

[0004] It can be seen that the above methods for preparing anhydrous lithium iodide all have the disadvantages of complex synthesis process, harsh reaction conditions, difficult operation, and high product cost. Especially in the latter two methods, the water content of the lithium iodide obtained is too high, and the problem of excessive free acid is prone to occur during the preparation process of formic acid reduction. The above problems make post-processing and product quality control too difficult. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing anhydrous lithium iodide with simple process, high product purity and easy post-treatment.

[0006] The present invention adopts the following technical solutions:

[0007] A method for preparing anhydrous lithium iodide, the method comprising:

[0008] (1) Disproportionation reaction: iodine element undergoes disproportionation reaction with lithium hydroxide solution;

[0009] (2) Dehydration pretreatment: dehydrating the reaction product of step (1) to obtain a mixed solid powder of lithium iodate and lithium iodide;

[0010] (3) Hydrogen reduction: reacting the solid powder of the mixture of lithium iodate and lithium iodide in step (2) with hydrogen to obtain a solid powder of lithium iodide;

[0011] (4) Drying treatment: vacuum drying the lithium iodide solid powder in step (3) to obtain anhydrous lithium iodide.

[0012] Specifically, the purity of the iodine element is ≥99.9%. High-purity iodine element reduces the amount of impurities introduced into the disproportionation reaction.

[0013] Specifically, the mass percentage concentration of the lithium hydroxide solution is 5% to 12%.

[0014] Specifically, the molar ratio of the lithium hydroxide to the iodine element is 2:1.

[0015] Specifically, the temperature of the disproportionation reaction in step (1) is 50-70° C., the reaction time is 5 h, and the pH value of the reaction system is 6-7.

[0016] Specifically, the dehydration pretreatment in step (2) adopts a reduced pressure drying treatment.

[0017] Specifically, both step (3) and step (4) are carried out under the protection of an inert gas.

[0018] Specifically, the inert gas is at least one of nitrogen, argon and helium.

[0019] Preferably, the inert gas is nitrogen, the purity of the nitrogen is 99.99%, and the water content is ≤3ppm.

[0020] Preferably, the molar ratio of hydrogen in the step (3) to the iodine in the step (1) is (1-2):1. Specifically: 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1 or a range consisting of any two of these values. The molar ratio of hydrogen to iodine is controlled to be (1-2):1 to avoid the problem of incomplete reaction due to insufficient hydrogen consumption and waste of raw hydrogen due to excessive consumption.

[0021] More preferably, the molar ratio of the hydrogen to the iodine element is (1.2-1.3):1.

[0022] Specifically, in the step (3), the reaction temperature of the lithium iodate and lithium iodide mixed solid powder and hydrogen is 100-200°C, the reaction time is 0.5-2 hours, and the lithium iodate and lithium iodide mixed solid powder reacts with hydrogen until no gas is generated, and then heated for 0.5-2 hours. If the temperature is lower than 100°C and the reaction time is less than 0.5 hours, the reaction cannot occur or the yield is reduced. If the temperature is higher than 200°C or the reaction time is more than 2 hours, the produced lithium iodide tends to decompose, which reduces the yield.

[0023] Preferably, in step (3), the reaction temperature of the reaction of the mixed solid powder of lithium iodate and lithium iodide with hydrogen is 145-155° C., and the reaction time is 1 hour.

[0024] Specifically, the vacuum drying temperature in step (4) is 120-180°C.

[0025] Preferably, the drying temperature is 150°C.

[0026] The present invention uses iodine and lithium hydroxide to generate 6LiOH+3I 2 →5LiI+LiIO 3 +3H 2 O disproportionation reaction, after the reaction is complete, the above solution is subjected to a one-step decompression drying treatment to obtain a mixed solid powder of lithium iodide and lithium iodate as an intermediate product. This process removes the solvent, increases the contact area between hydrogen and lithium iodate during the reduction process, making the reaction easier to proceed, and reduces the pressure to reduce the drying temperature to prevent lithium iodide from contacting with the solvent and air at high temperature and deteriorating, thereby affecting the product quality; then, in an inert gas protected environment, hydrogen is used as a reducing agent to reduce lithium iodate, and the reaction LiIO 3 +3H 2 →LiI++3H 2 O↑. Compared with formic acid, carbon powder and other reducing agents, hydrogen as a reducing agent does not need to introduce too many impurities, making the product purer, avoiding excessive free acid and post-treatment water washing acid process, simplifying the process flow and making the process less difficult. At the same time, a one-step dehydration pretreatment is carried out between the disproportionation reaction and the hydrogen reduction reaction, and the final product does not need to undergo subsequent multiple complex dehydration steps, further simplifying the process flow. The high-temperature drying process is carried out under the protection of an inert gas, so that the anhydrous lithium iodide obtained will not be secondary oxidized or decomposed.

[0027] Compared with the preparation methods in the prior art, this method has the advantages of high product purity, low industrial difficulty, low cost, good benefits, etc. The purity of the prepared anhydrous lithium iodide can reach more than 99.95%, and the yield is more than 99%. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0029] The hydrogen volume given in each embodiment and comparative example is the volume at 0°C and 1 standard atmospheric pressure.

[0030] Example 1

[0031] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0032] (1) 0.96 g (0.04 mol) of lithium hydroxide was prepared into a 10% lithium hydroxide solution, and 5.08 g (0.02 mol) of elemental iodine was poured into the lithium hydroxide solution. The reaction temperature was controlled to be 55° C. and the pH value was 6. The iodine particles were stirred until they disappeared and the reaction was continued for 5 h to generate a purple-brown solution.

[0033] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0034] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen until the gas overflows; then introducing 0.54 L (0.024 mol) of hydrogen into the reactor, heating to 155° C. for 0.5 hour, and heating for another 0.5 hour after no gas is generated, to obtain a white powder;

[0035] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor and stopped. Under the protection of nitrogen, the white powder was vacuum dried at 150° C. for 24 hours. The heating was stopped and the mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product.

[0036] (5) The obtained white solid powder was tested for its composition.

[0037] The yield of the anhydrous lithium iodide product prepared in Example 1 is 99.85% and the purity is 99.98%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide is white solid / 99.98% / 120ppm.

[0038] Example 2

[0039] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0040] (1) 2.4 g (0.10 mol) of lithium hydroxide was prepared into a 12% lithium hydroxide solution, 12.7 g (0.05 mol) of elemental iodine was poured into the lithium hydroxide solution, the reaction temperature was controlled to 70° C., the pH value was 6.5, and the mixture was stirred until the iodine particles disappeared. The reaction was continued for 5 h to generate a purple-brown solution;

[0041] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0042] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen until the gas overflows; then introducing 1.46 L (0.065 mol) of hydrogen into the reactor, heating to 200° C. for 1.5 hours, and heating for another 1.5 hours after no gas is generated, to obtain a white powder;

[0043] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor and stopped. Under the protection of nitrogen, the white powder was vacuum dried at 180° C. for 24 hours. The heating was stopped and the mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product.

[0044] (5) The obtained white solid powder was tested for its composition.

[0045] The yield of the anhydrous lithium iodide product obtained in Example 2 was 99.82% and the purity was 99.96%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.96% / 300ppm.

[0046] Example 3

[0047] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0048] (1) 0.96 g (0.04 mol) of lithium hydroxide was prepared into a lithium hydroxide solution with a concentration of 8%, and 5.08 g (0.02 mol) of elemental iodine was poured into the lithium hydroxide solution. The reaction temperature was controlled to be 50° C. and the pH value was 7. The mixture was stirred until the iodine particles disappeared and the reaction was continued for 5 h to generate a purple-brown solution.

[0049] (2) drying the purple-brown solution under reduced pressure for 60 minutes to obtain a solid mixture of lithium iodate and lithium iodide in the form of a powder;

[0050] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen until the gas overflows; then introducing 0.90 L (0.04 mol) of hydrogen into the reactor, heating to 145° C. for 0.5 hour, and heating for another 2 hours after no gas is generated, to obtain a white powder;

[0051] (4) nitrogen was charged into the reactor again until gas overflowed from the reactor and stopped. The white powder was vacuum dried under the protection of nitrogen at a temperature of 120° C. for 24 hours. The heating was stopped and the mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product.

[0052] (5) The obtained white solid powder was subjected to component detection.

[0053] The yield of the anhydrous lithium iodide product obtained in Example 3 was 99.84% and the purity was 99.97%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.97% / 200ppm.

[0054] Example 4

[0055] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0056] (1) 1.92 g (0.08 mol) of lithium hydroxide was prepared into a 5% lithium hydroxide solution, 10.16 g (0.04 mol) of elemental iodine was poured into the lithium hydroxide solution, the reaction temperature was controlled to be 60° C., the pH value was 7, the iodine particles were stirred until they disappeared, and the reaction was continued for 5 h to generate a purple-brown solution;

[0057] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0058] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen until the gas overflows; then introducing 0.90 L (0.04 mol) of hydrogen into the reactor, heating to 100° C. for 1 hour, and heating for another 1.5 hours after no gas is generated, to obtain a white powder;

[0059] (4) nitrogen was charged into the reactor again until gas overflowed from the reactor, and the white powder was vacuum dried under the protection of nitrogen at a temperature of 140° C. for 24 hours, and the heating was stopped. The mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product;

[0060] (5) The obtained white solid powder was tested for its composition.

[0061] The yield of the anhydrous lithium iodide product obtained in Example 4 was 99.84% and the purity was 99.96%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.96% / 260ppm.

[0062] Example 5

[0063] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0064] (1) 1.92 g (0.08 mol) of lithium hydroxide was prepared into a 10% lithium hydroxide solution, and 10.16 g (0.04 mol) of elemental iodine was poured into the lithium hydroxide solution. The reaction temperature was controlled to be 65° C. and the pH value was 6. The mixture was stirred until the iodine particles disappeared and the reaction was continued for 5 h to generate a purple-brown solution.

[0065] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0066] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen when the gas overflows; then introducing 1.34 L (0.06 mol) of hydrogen into the reactor, heating to 175° C. for 1 hour, and heating for another 1 hour after no gas is generated, to obtain a white powder;

[0067] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor, and the white powder was vacuum dried under the protection of nitrogen at a temperature of 150° C. for 24 hours, and the heating was stopped. The mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product;

[0068] (5) The obtained white solid powder was tested for its composition.

[0069] The yield of the anhydrous lithium iodide product obtained in Example 5 was 99.83% and the purity was 99.95%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.95% / 310ppm.

[0070] Example 6

[0071] (1) 0.96 g (0.04 mol) of lithium hydroxide was prepared into a 10% lithium hydroxide solution, and 5.08 g (0.02 mol) of elemental iodine was poured into the lithium hydroxide solution. The reaction temperature was controlled to be 55° C. and the pH value was 6. The mixture was stirred until the iodine particles disappeared and the reaction was continued for 5 h to generate a purple-brown solution.

[0072] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0073] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen until the gas overflows; then introducing 0.99 L (0.044 mol) of hydrogen into the reactor, heating to 155° C. for 0.5 hour, and heating for another 0.5 hour after no gas is generated, to obtain a white powder;

[0074] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor and stopped. Under the protection of nitrogen, the white powder was vacuum dried at 150° C. for 24 hours. The heating was stopped and the mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product.

[0075] (5) The obtained white solid powder was tested for its composition.

[0076] The yield of the anhydrous lithium iodide product obtained in Example 6 was 99.84% and the purity was 99.97%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.97% / 220ppm.

[0077] Example 7

[0078] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0079] (1) Take 2.4 g (0.10 mol) of lithium hydroxide to prepare a lithium hydroxide solution with a concentration of 12%. Pour 12.7 g (0.05 mol) of elemental iodine into the lithium hydroxide solution, control the reaction temperature to 70°C and the pH value to 6.5, stir until the iodine particles disappear, react for 5 hours, and generate a purple-brown solution;

[0080] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0081] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen when the gas overflows; then introducing 1.46 L (0.065 mol) of hydrogen into the reactor, heating to 250° C. for 1.5 hours, and heating for another 1.5 hours after no gas is generated, to obtain a white powder;

[0082] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor and stopped. Under the protection of nitrogen, the white powder was vacuum dried at 180° C. for 24 hours. The heating was stopped and the mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product.

[0083] (5) The obtained white solid powder was tested for its composition.

[0084] The yield of the anhydrous lithium iodide product obtained in Example 7 was 99.81% and the purity was 99.92%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was light yellow solid / 99.92% / 330ppm.

[0085] Example 8

[0086] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0087] (1) Take 2.4 g (0.10 mol) of lithium hydroxide to prepare a lithium hydroxide solution with a concentration of 12%, pour 12.7 g (0.05 mol) of elemental iodine into the lithium hydroxide solution, control the reaction temperature to 70°C and the pH value to 6.5, stir until the iodine particles disappear, react for 5 hours, and generate a purple-brown solution;

[0088] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0089] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen when the gas overflows; then introducing 1.46 L (0.065 mol) of hydrogen into the reactor, heating to 70° C. for 1.5 hours, and heating for another 1.5 hours after no gas is generated, to obtain a white powder;

[0090] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor and stopped. Under the protection of nitrogen, the white powder was vacuum dried at 180° C. for 24 hours. The heating was stopped and the mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product.

[0091] (5) The obtained white solid powder was tested for its composition.

[0092] The yield of the anhydrous lithium iodide product obtained in Example 8 was 99.80% and the purity was 99.91%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was light yellow solid / 99.91% / 400ppm.

[0093] Example 9

[0094] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0095] (1) 0.96 g (0.04 mol) of lithium hydroxide was prepared into a 10% lithium hydroxide solution, and 5.08 g (0.02 mol) of elemental iodine was poured into the lithium hydroxide solution. The reaction temperature was controlled to be 55° C. and the pH value was 6. The mixture was stirred until the iodine particles disappeared and the reaction was continued for 5 h to generate a purple-brown solution.

[0096] (2) drying the purple-brown solution under reduced pressure for 60 minutes to obtain a solid mixture of lithium iodate and lithium iodide in the form of a powder;

[0097] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen when the gas overflows; then introducing 0.54 L (0.024 mol) of hydrogen into the reactor, heating to 155° C. for 0.3 hour, and heating for another 0.5 hour after no gas is generated, to obtain a white powder;

[0098] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor, and the white powder was vacuum dried under the protection of nitrogen at a temperature of 150° C. for 24 hours, and the heating was stopped. The mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product;

[0099] (5) The obtained white solid powder was subjected to component detection.

[0100] The yield of the anhydrous lithium iodide product obtained in Example 9 was 99.82% and the purity was 99.93%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.93% / 380ppm.

[0101] Example 10

[0102] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0103] (1) 0.96 g (0.04 mol) of lithium hydroxide was prepared into a lithium hydroxide solution with a concentration of 8%, and 5.08 g (0.02 mol) of elemental iodine was poured into the lithium hydroxide solution. The reaction temperature was controlled to be 55° C. and the pH value was 6. The mixture was stirred until the iodine particles disappeared and the reaction was continued for 5 h to generate a purple-brown solution.

[0104] (2) drying the purple-brown solution under reduced pressure for 60 minutes to obtain a solid mixture of lithium iodate and lithium iodide in the form of a powder;

[0105] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen when the gas overflows; then introducing 0.54 L (0.024 mol) of hydrogen into the reactor, heating to 155° C. for 2.2 hours, and heating for another 0.5 hour after no gas is generated, to obtain a white powder;

[0106] (4) nitrogen was again charged into the reactor until gas overflowed from the reactor, and the white powder was vacuum dried under the protection of nitrogen at a temperature of 150° C. for 24 hours, and the heating was stopped. The mixture was cooled to room temperature under the protection of nitrogen. The obtained white solid powder was stored under the protection of nitrogen to obtain an anhydrous lithium iodide product;

[0107] (5) The obtained white solid powder was subjected to component detection.

[0108] The yield of the anhydrous lithium iodide product obtained in Example 10 was 99.83% and the purity was 99.94%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.94% / 300ppm.

[0109] Embodiment 11

[0110] The preparation method of anhydrous lithium iodide in this embodiment comprises the following steps:

[0111] (1) 0.96 g (0.04 mol) of lithium hydroxide was prepared into a 10% lithium hydroxide solution, and 5.08 g (0.02 mol) of elemental iodine was poured into the lithium hydroxide solution. The reaction temperature was controlled to be 70° C. and the pH value was 6.5. The mixture was stirred until the iodine particles disappeared and the reaction was continued for 5 h to generate a purple-brown solution.

[0112] (2) drying the purple-brown solution under reduced pressure for 60 min to obtain a solid mixture of lithium iodate and lithium iodide in powder form;

[0113] (3) placing a powdered solid mixture of lithium iodate and lithium iodide into a reactor, introducing nitrogen into the reactor, and stopping the introduction of nitrogen until the gas overflows; then introducing 0.58 L (0.026 mol) of hydrogen into the reactor, heating to 155° C. for 1.5 hours, and heating for another 1.5 hours after no gas is generated, to obtain a white powder;

[0114] (4) nitrogen is again charged into the reactor until gas overflows from the reactor, and the white powder is vacuum dried under the protection of nitrogen at a temperature of 180° C. for 24 hours, and heating is stopped. The mixture is cooled to room temperature under the protection of nitrogen, and the obtained white solid powder is stored under the protection of nitrogen to obtain an anhydrous lithium iodide product;

[0115] (5) The obtained white solid powder was tested for its composition.

[0116] The yield of the anhydrous lithium iodide product obtained in Example 11 was 99.97% and the purity was 99.97%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was white solid / 99.97% / 220ppm.

[0117] Comparative Example 1

[0118] Comparative Example 1 is anhydrous lithium iodide prepared by neutralization method, and the specific method is as follows:

[0119] Add 121.4 g (476.64 mmol) of 57% aqueous solution of hydroiodic acid to the reaction flask, then add 22.72 g (476.64 mmol) of lithium hydroxide, react at room temperature for 0.5 h, and use an oil pump to evaporate at 80° C. under reduced pressure in the dark to obtain white crude lithium iodide (needle-shaped crystals). Dry under vacuum at 150° C. for 36 hours to remove the remaining crystal water to obtain anhydrous lithium iodide.

[0120] The yield of the anhydrous lithium iodide product prepared in Comparative Example 1 was 99.78% and the purity was 99.83%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was light yellow solid / 99.79% / 865ppm.

[0121] Comparative Example 2

[0122] Comparative Example 2 is a formic acid reduction method for preparing anhydrous lithium iodide, and the specific method is as follows:

[0123] (1) Dissolution and reaction: 22.72 g (476.64 mmol) of lithium hydroxide monohydrate was prepared into an 8% aqueous solution, iodine (238.32 mmol) was slowly added under stirring to generate lithium iodide and lithium iodate, and the mixture was stirred until the reaction was complete, at which point the solution was brown; formic acid was added under stirring until the brown color of the solution completely faded, the solution was boiled to remove the carbon dioxide generated by the reaction, and the pH was adjusted.

[0124] (2) Purification and separation: Add activated carbon, the mass of which is 0.296-0.893% of the mass of iodine, stir, filter, heat and concentrate the filtrate until lithium iodide crystals appear, and stop heating immediately. The temperature of the electric furnace during heating and concentration is 450-550°C, cool naturally, stand, centrifuge and dehydrate to obtain lithium iodide trihydrate. Vacuum dry at 150°C to obtain anhydrous lithium iodide product.

[0125] The yield of the anhydrous lithium iodide product obtained in Comparative Example 2 was 85.40% and the purity was 99.80%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was light yellow solid / 99.75% / 912ppm.

[0126] Comparative Example 3

[0127] The preparation method of anhydrous lithium iodide in this comparative example comprises the following steps:

[0128] (1) Take 1.92 g (0.08 mol) of lithium hydroxide to prepare a 5% lithium hydroxide solution, pour 10.16 g (0.04 mol) of elemental iodine into the lithium hydroxide solution, control the reaction temperature to 55°C and the pH value to 6, stir until the iodine particles disappear, react for 5 hours, and generate a purple-brown solution.

[0129] (2) The purple-brown solution was placed in a reactor, and nitrogen was introduced into the reactor. When the gas overflowed, the introduction of hydrogen (1.08 L (0.048 mol)) was stopped. The reactor was heated to 155° C., and when no gas was generated, the reactor was heated for another 0.5 hour to obtain a lithium iodide solution.

[0130] (4) Filter, evaporate, cool and crystallize the lithium iodide solution to separate the lithium iodide.

[0131] (5) Maintain the prepared lithium iodide under a nitrogen environment.

[0132] (6) The obtained white solid powder was tested for its composition.

[0133] The yield of the anhydrous lithium iodide product obtained in Comparative Example 3 was 81.51% and the purity was 99.55%. After being stored away from light for 6 months, the appearance / purity / water content of the anhydrous lithium iodide was light yellow solid / 99.00% / 952ppm.

[0134] The anhydrous lithium iodide prepared in Example 1-11 and Comparative Example 1-3 was measured using the detection method specified in the non-ferrous metal industry standard YS / T1244-2018 Anhydrous Lithium Iodide of the People's Republic of China, and the moisture content was determined by Karl Fischer point titration.

[0135] Analyze Examples 1-11 and Comparative Examples 1-3. The purity of anhydrous lithium iodide prepared by the method of the present invention in Examples 1-11 all reached 99.95% or more, and the finished product yield all reached 99.82% or more. The purity and yield of anhydrous lithium iodide prepared by neutralization or formic acid reduction are both low. It can be seen that the preparation method of the present invention has high product purity and good benefits compared with the neutralization method and formic acid reduction method. The present invention uses hydrogen as a reducing agent to reduce lithium iodate to lithium iodide. Before the reduction reaction, a dehydration and drying step is performed. The hydrogen reduction process is carried out in a non-liquid environment, so that the reaction is more complete, and the product is not easily reoxidized, so the yield is high; and hydrogen is a clean gas, and only water vapor is generated during the reaction, and other impurity elements will not be introduced, so the purity is high and the environment will not be polluted. At the same time, by comparing Examples 1-5 with the comparative examples, it can be seen that the process of the present invention is simple, and only one dehydration and drying and one drying and purification process are required in the two-step reaction, while in Comparative Example 2, it is also necessary to separate and remove the product in a variety of ways, and the process is more complicated than the present invention. The reaction conditions of the present invention are not as harsh as those of Comparative Example 1, which needs to be carried out under high temperature conditions to remove crystallization water, while the present invention does not require excessively high drying temperatures and excessively long drying times because the reduction reaction is carried out in a non-liquid environment. Therefore, the process of the present invention is simple, the equipment used is simple, the investment cost is low, and it is more conducive to industrialization.

[0136] By comparing Example 1 with Example 6, the molar ratio of the amount of hydrogen used as a reducing agent to the iodine element is (1-2): 1 is the optimal range. If it is not within this range, the yield and purity of lithium iodide will be reduced. When the molar ratio is too small, the lithium iodate reduction is not complete, resulting in the doping of lithium iodate impurities in the product LiI, and the yield and purity are reduced; when the molar ratio is too large, the reducing agent hydrogen is excessive, which not only reduces the lithium iodide yield, but also the presence of hydrogen leads to a low content of inert gas, thereby affecting the storage time of lithium iodide.

[0137] By comparing Example 2, Example 7-8 and Example 11, the suitable reaction temperature for the hydrogen reduction reaction is 100-200°C. Temperatures exceeding or below this range will result in reduced yield and purity of lithium iodide, because lithium iodide will decompose if the temperature is too high, and the reaction will not be complete if the temperature is too low. The effect is better within the range of 145-155°C.

[0138] By comparing Example 1 with Examples 9-10, the reaction time adapted to the hydrogen reduction reaction is between 0.5-2h, and the reaction efficiency is higher and more sufficient. If the time exceeds or is less than this range, the yield and purity of lithium iodide will be reduced. This is because if the reaction time is too short, the reaction cannot be fully achieved, and if the reaction time is too long, the reaction product is easy to decompose.

[0139] By comparing Example 1 with Comparative Example 3, the process of performing dehydration treatment before hydrogen reduction greatly improves the product yield and reduces the water content of the product compared to the process of drying the finished product after the reaction. This is because hydrogen is poorly soluble in water, and the reaction in a solution environment makes the hydrogen reduction reaction of lithium iodate incomplete, thereby greatly reducing the yield. In addition, since Comparative Example 3 lacks a pre-dehydration treatment step, higher temperature and longer time are required for drying the finished product.

[0140] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description here should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in the field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A method for preparing anhydrous lithium iodide, characterized in that: The following steps are involved: (1) Disproportionation reaction: iodine element undergoes disproportionation reaction with lithium hydroxide solution; (2) Dehydration pretreatment: dehydrating the reaction product of step (1) to obtain a mixed solid powder of lithium iodate and lithium iodide; (3) Hydrogen reduction: reacting the solid powder of the mixture of lithium iodate and lithium iodide in step (2) with hydrogen to obtain a solid powder of lithium iodide; (4) Drying treatment: vacuum drying the lithium iodide solid powder in step (3) to obtain anhydrous lithium iodide.

2. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: The mass percentage concentration of the lithium hydroxide solution in step (1) is 5% to 12%.

3. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: In the step (1), the molar ratio of lithium hydroxide to the iodine element is 2:

1.

4. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: The reaction temperature of the disproportionation reaction in step (1) is 50-70° C., the reaction time is 5 h, and the pH value of the reaction system is 6-7.

5. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: The dehydration pretreatment in step (2) adopts reduced pressure drying treatment.

6. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: Both step (3) and step (4) are carried out under the protection of inert gas.

7. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: The molar ratio of hydrogen in the step (3) to the iodine element in the step (1) is (1-2):

1.

8. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: In the step (3), the reaction temperature of the mixed solid powder of lithium iodate and lithium iodide and hydrogen is 100-200°C.

9. The method for preparing anhydrous lithium iodide according to claim 8, characterized in that: The reaction time of the lithium iodate and lithium iodide mixed solid powder and hydrogen is 0.5 to 2 hours.

10. The method for preparing anhydrous lithium iodide according to claim 1, characterized in that: The vacuum drying temperature in step (4) is 120-180°C.