Method for producing lithium sulfide in a circulating bed reactor

Abstract

The present invention relates to a process for preparing lithium sulfide (LiS) from lithium hydroxide (LiOH) and hydrogen sulfide (HS), characterized in that the lithium hydroxide is sulfided in a reaction zone (9) comprising at least one moving-bed tubular reactor (9a) with an ascending oscillating spiral configuration, in which the lithium hydroxide (4) circulates countercurrently to an anhydrous gas mixture (10) containing hydrogen sulfide and at least one inert gas.

Description

[Technical Field]

[0001] The subject of the present invention is the preparation of lithium sulfide from lithium hydroxide and hydrogen sulfide by a continuous process using a moving bed (or circulating bed). [Background technology]

[0002] Lithium sulfide (Li2S) is a critical raw material for the production of solid electrolytes used in next-generation batteries, which are less flammable and potentially more efficient and lighter than liquid electrolytes. Several methods for synthesizing lithium sulfide are known, but all of them face the extremely hydrophilic nature of this compound. Specifically, at ambient temperatures, lithium sulfide is highly reactive with moisture, and upon contact with water, it spontaneously reacts to form lithium hydroxide (LiOH) and release hydrogen sulfide (HS). Therefore, reaction conditions must be perfectly controlled to avoid decomposition during lithium sulfide formation. Once lithium sulfide is formed, it is essential to strictly control its residual moisture content, especially by storing it in a dry, inert atmosphere. Furthermore, it is desirable to be able to produce lithium sulfide in the form of solid particles with as high a purity as possible and with an average particle size of less than 1 mm, as these properties result in good electrolyte stability and good capacitance. One known method for synthesizing lithium sulfide is to react lithium hydroxide with hydrogen sulfide according to the following reaction: 2LiOH + H2S → Li2S + 2H2O This route is often used because the starting material LiOH is available and inexpensive, and the reaction is endothermic and can be carried out at moderate temperatures, typically between 130 and 450°C. However, industrial processes using this synthetic route face several drawbacks, including the need to completely remove the large amount of water evolved in the reaction to avoid reconversion of Li2S to LiO. Furthermore, the starting LiOH material is generally present in the hydrated form LiOH·H2O, which requires a thorough drying step to allow the sulfidation to properly begin. This is because the sulfidity of the hydrated form, LiOH·H2O, is too low. Furthermore, the presence of this hydrated form in the sulfurization reactor leads to the formation of lithium sulfide blocks, i.e., larger lithium sulfide particles consisting of aggregates of Li2S surrounding an inner core of unsulfurized LiOH·H2O. This results in a significant decrease in the quality of the resulting lithium sulfide, not only in its purity but also in its average particle size.

[0003] Various methods have been described in the prior art, including, in particular, discontinuous processes (or "batch" processes) using reactors in which the solid particles can be stirred or placed in a fluidized bed. Such batch processes are described, for example, in EP 0802159, JP 2020-033259, JP 2015-137183, and WO 2018 / 141919. These processes often require very large quantities of sulfiding agent (H2S). They also face the problem of maintaining the reactor temperature (because the reaction is endothermic) and removing the water produced during the reaction. Finally, processes operated batchwise require periodic interruptions of production and significant logistical management associated with charging and unloading the reactor, making them less productive on an industrial scale. Therefore, these methods are not economical and often result in poor quality and purity of the lithium sulfide, which contains residual LiOH and large particles due to the presence of aggregates of Li2S and LiOH·H2O. Due to the significant limitations of the LiOH sulfurization reaction, few continuous processes exist.

[0004] The present invention aims to propose a method which makes it possible to prepare lithium sulfide continuously on an industrial scale. Another object of the present invention is to make it possible to prepare lithium sulfide in the form of small particles and with high chemical purity. Summary of the Invention

[0005] The applicant has now developed an innovative method that makes it possible to produce very high quality lithium sulfide from lithium hydroxide and hydrogen sulfide in a continuous process using a moving bed (or circulating bed) that circulates in at least one reactor having a specific design. The process according to the invention is characterized in that the key step of sulfurization of lithium hydroxide is carried out in a reaction zone comprising at least one tubular reactor of ascending vibrating spiral construction, in which the lithium hydroxide circulates countercurrently to a stream of anhydrous sulfurizing gas containing hydrogen sulfide and an inert gas. The subject of the present invention is therefore a process for preparing lithium sulfide (LiS) from lithium hydroxide (LiOH) and hydrogen sulfide (HS), characterized in that the sulfurization of lithium hydroxide is carried out in a reaction zone comprising at least one moving-bed tubular reactor with ascending oscillating spiral configuration, in which the lithium hydroxide circulates countercurrently against an anhydrous gas mixture containing hydrogen sulfide and at least one inert gas.

[0006] The process according to the invention makes it possible to prepare lithium sulfide in high yield, in particular in mass yields of more than 80%. Furthermore, the process of the present invention allows for the sulfurization of lithium hydroxide under controlled temperature conditions, particularly as it facilitates maintaining the temperature within the reactor in the desired operating range of 150-450°C, and the endothermic nature of the reaction is compensated for by the circulation of the bed of lithium hydroxide particles. Furthermore, in contrast to prior art processes, the lithium sulfide produced during its progression through the reactor does not remain in contact with water, which is removed by the counter-circulating gas stream. The process according to the invention therefore makes it possible to obtain lithium sulfide with a high purity of more than 99.0% by mass.

[0007] Furthermore, the lithium sulfide leaving the reactor is not contacted with anything other than the inflow of anhydrous sulfurizing gas based on hydrogen sulfide and an inert gas, which ensures that a product is obtained with a particularly low residual lithium hydroxide content of less than 1% by weight. According to the invention, the reaction zone comprises at least one tubular reactor of ascending oscillating spiral configuration, in which LiOH particles travel upward along an oscillating spiral coil against a descending anhydrous sulfurous gas. This structure has the added advantage of avoiding the formation of blocks of lithium sulfide in the form of aggregates of Li2S surrounding an inner core of LiOH·H2O. Specifically, the LiOH particles move with the bounce provided by the vibration of the helical coil, which ensures a high degree of particle mixing in the sulfurizing gas flow and improves contact between the LiOH particles and the sulfurizing gas, while avoiding the particles colliding with the reactor walls and forming agglomerates. Compared to the methods described in the prior art, this structure also allows for a reduction in the flow rate of sulfurizing gas and the amount of hydrogen sulfide used due to improved contact between the sulfurizing gas and lithium hydroxide, thereby accelerating the latter sulfurization reaction and efficiently removing water as it is produced. Other objects, features, aspects and advantages of the present invention will become more apparent upon review of this specification and the accompanying non-limiting drawings. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows an example of an apparatus for producing lithium sulfide according to the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the text below, unless otherwise indicated, in particular in the expressions "of between" and "ranging from ... to ...", the limits of ranges of values ​​are included within the range. Furthermore, as used herein, the terms "at least one" and "at least" are equivalent to the terms "one or more" and "greater than or equal to," respectively.

[0010] sulfur gas The present invention uses an anhydrous gas mixture comprising hydrogen sulfide and at least one inert gas. The gas mixture is anhydrous, ie, contains less than 1% water by volume. The gas mixture contains hydrogen sulfide (H2S), a sulfiding agent that reacts with lithium hydroxide to produce lithium sulfide, releasing water. The content of hydrogen sulfide in the gas mixture is advantageously in the range of 30% to 90% by volume, preferably 40% to 80%, more preferentially 50% to 70% and even better still 55% to 65% by volume relative to the total volume of said mixture. The gas mixture also contains at least one inert gas, i.e., a non-reactive gas. Inert gases are well known to those skilled in the art. The inert gas may be selected in particular from nitrogen (N2) and noble gases such as argon, helium, krypton, neon, and xenon, and mixtures thereof. Preferably, the inert gas is selected from argon, nitrogen and mixtures thereof, more preferentially the inert gas is nitrogen. The inert gas content is advantageously in the range of 10% to 70% by volume relative to the total volume of the gas mixture. Preferably, the gas mixture further comprises hydrogen (H2), in which case the content of hydrogen in the gas mixture is advantageously in the range of 5% to 30% by volume, preferably 10% to 20% by volume, relative to the total volume of the mixture.

[0011] Reaction Zone In the present invention, the sulfurization of lithium hydroxide is carried out in a reaction zone comprising at least one moving-bed tubular reactor having the form of an ascending oscillating spiral in which the lithium hydroxide circulates countercurrently to the sulfurizing gas. The term "moving bed reactor" means, in a manner known per se, a reactor in which solid particles circulate from the inlet to the outlet of the reactor. In the reactor in the form of an ascending oscillating spiral used in the present invention, the particles progress upward along the spiral. The progress of the particles is brought about by the vibration of the tubular reactor. A particular feature of the process of the present invention is that the conversion of lithium hydroxide to lithium sulfide is carried out in a tubular reactor into which lithium hydroxide particles are introduced at the inlet and circulated towards the outlet, while the sulfiding gas is introduced at the outlet of the reactor and circulated towards the inlet. As used herein, the terms "inlet" and "outlet" of the reactor are defined relative to the direction of upward circulation of the solid lithium hydroxide particles in the tubular reactor. Thus, inside the reactor, two streams circulate countercurrently, one solid and one gas: The solids stream consists of lithium hydroxide particles. As the solids stream progresses upward in the reactor, it becomes depleted in lithium hydroxide and enriched in lithium sulfide. The gas stream consists of a sulfurized gas, i.e., an anhydrous gas mixture containing hydrogen sulfide and at least one inert gas. As the gas stream progresses downward through the reactor, it becomes depleted in hydrogen sulfide and enriched in steam. According to a preferred embodiment, the anhydrous gas mixture is introduced into the reaction zone at at least two points: at the outlet of the reaction zone, and at least one point located between the outlet and the inlet of the reaction zone. More preferably, the anhydrous gas mixture is introduced at the outlet of the reaction zone and at least two different successive points located between the outlet and the inlet of the reaction zone. Introducing an anhydrous gas mixture at multiple successive points along the reaction zone provides the following advantages, among others: -A stoichiometric excess of H2S is allowed to act locally to ensure maximum conversion of LiOH to Li2S; The partial pressure of -H2O can be locally reduced, thereby limiting its inhibitory effect on the conversion of LiOH to Li2S. In this embodiment, the composition of the anhydrous gas mixture may vary between the individual injection points, in particular the H2S content may vary, for example being higher the closer the injection point of the mixture is to the outlet of the reaction zone.

[0012] The temperature inside the reactor is advantageously maintained in the range of from 150°C to 450°C, preferably from 300°C to 450°C, and better still from 350°C to 400°C. The temperature inside the reactor can be measured in a manner known per se using a thermocouple. Due to the endothermic nature of the reaction, it is important to be able to control the temperature in order to ensure as constant a temperature as possible within the reactor and to ensure that the reaction zone does not at any time fall below a temperature of 100° C. This is facilitated by the use of a countercurrent process and the possibility of multiple reactors within the reaction zone as described below. According to the present invention, the temperature at the inlet of the reaction zone is greater than or equal to 350°C and less than or equal to 450°C. At the outlet of the reaction zone, the temperature is generally below 450°C, or even below 350°C. The pressure inside the reactor is 3 x 10 5 Pa (3 bar), preferably less than 2 x 10 5 Pa (2 bar), and even more preferentially less than 1.3 × 10 5 The pressure is maintained at a value below 1.3 bar.

[0013] The Applicant has surprisingly observed that the process of the present invention makes it possible to obtain a high conversion yield of LiOH to LiS using less H2S and at a lower flow rate than in the prior art. In the process of the present invention, the hourly space velocity of hydrogen sulfide is advantageously between 30 and 450 h -1 The range is. The particular reactor used in the present invention consists of an oscillating spiral of substantially tubular form helically surrounding a vertical axis and comprising at least two steps. The spiral cross section is preferentially circular, in which case the spiral is tubular. Generally, the diameter of the tube is 100-300 mm. The tube typically has a deployment length of up to 400 m. The tube is hollow, i.e., contains no elements in the inner portion. The total height of the spiral may be in the range of 5 to 40 m, preferably 10 to 20 m. The rising angle of the spiral may be in the range of 1 to 10 degrees, preferably 1 to 5 degrees, and even more preferentially 1 to 4 degrees. The reactor preferably has a number of turns ranging from 15 to 60, more preferentially from 25 to 40. Typically, the number of turns is such that the particle flow rate can range from 50 to 6000 kg / h, preferably from 50 to 500 kg / h, and the gas hourly space velocity (GHSV) is typically from 50 to 1500 h -1 , preferably 50 to 500 hours -1 The solid particles typically occupy 5% to 80% of the volume of the turn, preferably 10% to 50%. Said oscillating spiral is advantageously made of a metallic material, preferably a metal tube made of a metal alloy, more preferentially of steel. The oscillating spiral can be obtained, for example, by forming a metal tube in the form of a helix around a substantially vertical axis. According to an advantageous embodiment, a central pillar makes it possible to stiffen and support the helix formed by the spiral. The spiral can be electrically insulated from the central pillar by a fixing system.

[0014] According to a preferred embodiment, the transformer supplies the oscillating spiral with a low voltage current of less than 50 V in at least one step (i.e. at least one turn), which makes it possible to directly heat the metal mass of the tube to the temperature required in the reactor by Joule heating. In particular, one or more steps (one or more turns) are heated by Joule heating at temperatures between 150 and 450 °C, especially in the lower part of the reactor, in the inlet zone of the LiOH particles. The direct result of Joule heating is the generation of heat in the mass of the turns. This allows for greater flexibility in controlling the temperature in the core of the turns compared to indirect heating, for example, by a heat transfer fluid. The vibration of the spiral reactor can be generated by at least one system located at a suitable level, for example at the base or at the top of the column, or around the spiral. Suitable vibration systems include unbalanced motors, electromagnetic vibrators (excited by a variable cycle with pulse generation) and unbalanced excitation systems. Preferably, the vibration is generated by a table that serves as a support for the central column and is driven by two unbalanced motors. The reaction zone may consist of one or more moving bed reactors. Preferably, the reaction zone comprises at least two moving bed reactors. Thus, the reaction zone may be composed of a plurality of moving bed reactors, which may be arranged in series and / or in parallel. The moving bed reactors may be of the same construction (especially when arranged in parallel) or of different constructions. Thus, a plurality of moving bed reactors may be used, which may be entirely or partially composed of tubular reactors with oscillating spiral construction. When multiple oscillating spirals are used, they may be of different sizes.

[0015] Lithium sulfide Li 2 S At the outlet of the reaction zone, the lithium sulfide is recovered in the form of small solid particles, for example beads, or particles of roughly cylindrical or irregular shape. The number average particle size of the lithium sulfide particles corresponds to the diameter of the equivalent spherical volume and is preferably 4 mm or less, more preferably 1 mm or less. Here, the average particle size refers to the number average diameter of particles when the particles are considered to be spherical, and is defined, for example, by the d50 median diameter measured by laser diffraction particle size distribution measurement using a device known as a laser diffraction particle size analyzer, which allows the size distribution of a population of particles to be determined. If the particles are substantially spherical, the average particle size is equal to the average diameter. According to an advantageous embodiment, a portion of the particle stream leaving the reaction zone is recycled to said zone at its inlet or at an intermediate point thereof, particularly when the reaction zone comprises multiple reactors in series, e.g., when the recycled particles are introduced between two successive individual reactors, intermediate recycling is particularly facilitated. Such recycling of the particle stream exiting the reaction zone is advantageous when the conversion of LiOH to Li2S is not complete after one pass through the reaction zone.

[0016] Lithium hydroxide LiOH The lithium hydroxide introduced at the inlet to the reaction zone is present in the form of small solid particles, such as beads, or particles of roughly cylindrical or irregular shape. The number average particle size of the lithium hydroxide particles corresponds to the diameter of the equivalent spherical volume, and is preferably within the range of 10 μm to 4 mm. Here, the average particle size refers to the number average diameter of particles when the particles are considered to be spherical, and is defined, for example, by the d50 median diameter measured by laser diffraction particle size distribution measurement using a device known as a laser diffraction particle size analyzer, which allows the size distribution of a population of particles to be determined. If the particles are substantially spherical, the average particle size is equal to the average diameter. According to a preferred embodiment, the lithium hydroxide is introduced into the reaction zone with a water content of less than 10 mole percent.

[0017] Pre-drying process According to a preferred embodiment, before being introduced into the reaction zone, the lithium hydroxide undergoes a drying step, which is typically carried out in a drying zone and has the purpose of producing lithium hydroxide in an anhydrous form according to the following process: LiOH HO → LiOH + HO The drying step is preferably carried out by subjecting the lithium hydroxide to a heat treatment at a temperature in the range of 150 to 350°C, preferably 175 to 250°C, and by circulating at least one inert gas through a drying zone to remove moisture. The inert gas may be selected in particular from nitrogen (N2) and noble gases such as argon, helium, krypton, neon, and xenon, and mixtures thereof. Preferably, the inert gas is selected from argon, nitrogen and mixtures thereof, more preferentially the inert gas is nitrogen. The pressure inside the drying zone is advantageously 3×10 5 Pa (3 bar), preferably less than 2 x 10 5 Pa (2 bar), or better still 1.3 x 10 5 Pa (1.3 bar) or less. The drying step is preferably carried out continuously, more preferentially in a drying zone comprising one or more moving bed reactors through which lithium hydroxide particles circulate, with an inert gas stream circulating through the drying zone either cocurrently or countercurrently to the flow of lithium hydroxide particles. Preferably, the inert gas stream circulates through the drying zone cocurrently to the flow of lithium hydroxide particles.

[0018] According to a first particularly preferred embodiment, at least one moving-bed reactor in the drying zone is a tubular reactor in the form of an ascending oscillating spiral, in which the particles travel upward along the spiral and are gradually converted into anhydrous LiOH with the removal of water. The tubular reactor in the form of an oscillating spiral has been described above. In this embodiment, the inert gas flow preferably circulates upward through the oscillating spiral (i.e., in cocurrent with the flow of solid particles). However, downward circulation of the inert gas flow through the oscillating spiral (i.e., countercurrent with the flow of solid particles) may also be carried out.

[0019] According to a second embodiment, at least one moving-bed reactor in the drying zone is a horizontal tubular reactor equipped with a thermal screw, i.e., an endless screw, or an Archimedes screw, in which the particles are transported and dried in a continuous flow with the removal of water. In such a reactor, the LiOH·HO particles advance along the screw flights and are gradually converted to anhydrous LiOH with the removal of water. The thermal screw can be heated electrically or by a heat transfer fluid, and heat exchange can occur through a trough, a central core, or a coil. A flow of inert gas is injected co-currently or counter-currently, preferably co-currently, to the flow of solid particles.

[0020] Pre-sulfurization process Preferably, during the drying step, presulfidation of the lithium hydroxide is also carried out. The term "presulfidation" refers to partial sulfidation of the lithium hydroxide such that at the end of the drying step the anhydrous lithium hydroxide contains between 5% and 40% by weight of lithium sulfide, LiS. This presulphurization is advantageously carried out by contacting the lithium hydroxide particles with an anhydrous gas mixture containing at least one inert gas and 5% to 30% by volume of hydrogen sulphide relative to the total volume of the mixture, while the lithium hydroxide particles are circulating in a drying zone. The gas mixture is anhydrous, ie, contains less than 1% water by volume. The content of hydrogen sulfide in the gas mixture used for presulfurization is more preferentially in the range of 10% to 15% by volume relative to the total volume of said mixture. The inert gas is selected from the gases listed above for the drying step, such as nitrogen (N), noble gases and mixtures thereof. Preferably, the inert gas is selected from argon, nitrogen and mixtures thereof, more preferentially the inert gas is nitrogen. According to a preferred embodiment, the inert gas present in the gas mixture used for the presulphurization of lithium hydroxide is the gas used for drying. Thus, for example, presulphurization may be carried out by adding hydrogen sulphide or a mixture comprising hydrogen sulphide, an inert gas and optionally hydrogen, as described below, directly to the gas stream circulating in the drying zone. Preferably, the gas mixture used for presulfurization further comprises hydrogen (H2), in which case the content of hydrogen in the gas mixture is advantageously in the range of 1% to 10% by volume, preferably 2% to 5% by volume, relative to the total volume of said mixture.

[0021] According to a preferred embodiment, the gas mixture used for the presulfurization of lithium hydroxide consists entirely or partly of the gas mixture recovered at the outlet of the reaction zone, previously dried to remove water therefrom, and, if necessary, may be diluted with an inert gas to adjust the hydrogen sulfide content of the gas mixture to the concentration required for the presulfurization. The gas mixture used for presulphurization may be introduced at one or more points in the drying zone, preferably at a point located downstream of the inlet zone of the lithium hydroxide particles. In particular, the presulphurization step is advantageously initiated at a point in the drying zone where the water content of the lithium hydroxide is sufficiently low. The gas mixture used for presulfiding is therefore preferentially brought into contact with the lithium hydroxide circulating through the drying zone at one or more points of entry located downstream, i.e. later, relative to the injection point of the solids. Preferably, the gas mixture used for presulfiding is circulated through the drying zone cocurrently with the flow of lithium hydroxide particles. When the drying zone is in the form of an ascending oscillating spiral, the gas mixture used for presulfiding is typically introduced at one, two or three points preferably located in the upper half of the spiral. The gas mixture advantageously circulates upwardly in co-current with the ascending flow of the solid particles. The step of presulphurization of lithium hydroxide is advantageously carried out at a temperature ranging from 150 to 350°C, preferably from 175 to 250°C. This pre-sulfiding step improves the dryness of the lithium hydroxide and makes it possible to increase the sulfidation rate in the downstream reaction zone.

[0022] A non-limiting example of an apparatus for producing lithium sulfide is shown in attached Figure 1. According to the invention, lithium hydroxide (LiOH) is converted to lithium sulfide (LiS) in a reaction zone 9 comprising a moving-bed tubular reactor consisting of an ascending oscillating spiral 9a. Lithium hydroxide particles are introduced into the lower part of the reaction zone 9 via line 4. The particles progress upwardly in the spiral 9a, this progress being effected by the vibration of the spiral. An anhydrous gas mixture containing a stoichiometric excess of hydrogen sulfide and nitrogen is introduced into the upper portion of the reaction zone 9. This mixture is conveyed via line 10 and injected into the reactor at two successive injection points 10a and 10b located in the upper portion of the spiral reactor 9a. The mixture circulates downward through the spiral reactor 9a countercurrent to the upward flow of the particles. At the outlet of the reaction zone 9, lithium sulfide particles are collected and discharged via line 11. In the lower part of the reaction zone 9, a gas mixture containing nitrogen, water and hydrogen sulfide residues is discharged at two successive points 12a and 12b and sent via line 12 to a treatment device 13. In unit 13, the mixture obtained from line 12 is treated to remove water from the mixture, which is separated via line 14. Dust removal of the gas mixture (not shown) can also be carried out to remove any entrained particulate dust from the gas mixture. The mixture of nitrogen and residual hydrogen sulfide is then discharged via line 15. Before being introduced into the reaction zone, the lithium hydroxide undergoes a drying step carried out in a drying zone 2, which comprises a moving-bed tubular reactor, in this example constituted by an ascending oscillating spiral 2a. Particles of hydrated lithium hydroxide (LiOH·H2O) are introduced into the lower part of the drying zone 2 via line 1. The particles travel upwards in the spiral 2a, this travel being brought about by the vibration of the spiral. An inert gas consisting of nitrogen conveyed via line 3 is also introduced into the lower part of drying zone 2 and injected into spiral 2a at injection points 3a and 3b. The nitrogen travels upwards within spiral reactor 2a, cocurrent with the particle flow. At the upper portion of drying zone 2, dried lithium hydroxide particles are discharged via line 4 and transferred to reaction zone 9. At the upper portion of drying zone 2, a mixture of water and nitrogen is discharged at successive points 5a and 5b and transferred via line 5 to treatment unit 6. In the device 6, the mixture obtained from line 5 is treated to remove water from the mixture, which is separated via line 7. It is also possible to carry out a dedusting of the gas mixture (not shown) in order to remove any entrained particulate dust from the gas mixture. The nitrogen is then discharged via line 8. According to an advantageous embodiment (not shown), the nitrogen recovered at the outlet of the drying zone is recycled to the device at the level of the drying zone 2 or at the level of the reaction zone 9.

[0023] According to a preferred optional embodiment, the gas mixture of nitrogen and residual hydrogen sulfide obtained from reaction zone 9, dried and recovered via line 15, is recycled via line 16 to drying zone 2, where it is introduced into the upper second half of spiral reactor 2a. The hydrogen sulfide content of this recycled gas mixture is lower than that of the gas mixture introduced into reaction zone 9. This recycling allows a pre-sulfiding treatment of lithium hydroxide particles upstream of reaction zone 9 in the upper second half of drying zone 2.

Claims

1. Lithium hydroxide (LiOH) and hydrogen sulfide (H 2 S) and lithium sulfide (Li 2 1. A process for preparing lithium hydroxide (S), characterized in that the sulfurization of lithium hydroxide is carried out in a reaction zone (9) comprising at least one moving-bed tubular reactor (9a) having the structure of an ascending oscillating spiral, and in that the lithium hydroxide (4) circulates countercurrently to an anhydrous gas mixture (10) containing hydrogen sulfide and at least one inert gas.

2. 2. The method according to claim 1, characterized in that the content of hydrogen sulfide in the gas mixture (10) is in the range of 30% to 90% by volume, preferably 40% to 80%, more preferentially 50% to 70%, and even better still 55% to 65% by volume relative to the total volume of the mixture.

3. 3. The method according to claim 1 or 2, characterized in that the inert gas is selected from nitrogen, noble gases and mixtures thereof, preferably from argon, nitrogen and mixtures thereof, more preferentially the inert gas is nitrogen.

4. 4. The method according to claim 1, wherein the gas mixture (10) additionally comprises hydrogen in a content ranging from 5% to 30% by volume, preferably from 10% to 20%, relative to the total volume of the mixture.

5. 5. The method according to claim 1, wherein the anhydrous gas mixture (10) is introduced into the reaction zone (9) at at least two points (10a, 10b): at the outlet (10a) of the reaction zone (9) and at least one point (10b) located between the outlet and the inlet of the reaction zone.

6. 6. The process according to any one of claims 1 to 5, characterized in that the reaction zone (9) comprises at least two moving bed reactors arranged in series and / or in parallel.

7. 7. Process according to any one of claims 1 to 6, characterized in that the reaction zone (9) comprises a plurality of moving bed reactors, all or part of which may be constituted by oscillating spirals.

8. 8. The process according to claim 1, wherein, before being introduced into the reaction zone (9), the lithium hydroxide (1) is subjected to a drying step in a drying zone (2), which step is preferably carried out continuously.

9. 9. The process according to claim 8, characterized in that the drying zone (2) comprises one or more moving bed reactors (2a) through which the lithium hydroxide particles circulate.

10. 10. The process according to claim 9, characterized in that at least one moving bed reactor of the drying zone (2) is a tubular reactor in the form of an ascending oscillating spiral (2a).

11. 11. The method according to claim 9 or 10, characterized in that the presulfurization of the lithium hydroxide is carried out in the drying step by contacting the lithium hydroxide (1) particles with an anhydrous gas mixture containing at least one inert gas and 5% to 30% by volume of hydrogen sulfide relative to the total volume of the mixture, while the lithium hydroxide (1) particles are circulating in the drying zone (2).

12. 12. The method according to claim 11, wherein the content of hydrogen sulfide in the gas mixture used for presulfiding is in the range of 10% to 15% by volume relative to the total volume of the mixture.

13. 13. A method according to claim 11 or 12, characterized in that the gas mixture used for the presulphurization of the lithium hydroxide (1) consists entirely or partly of the gas mixture (16) recovered at the outlet of the reaction zone (9), having been previously dried to remove water from said gas mixture.

14. 14. The method according to any one of claims 11 to 13, characterized in that the gas mixture used for the presulphurization circulates in the drying zone (2) in cocurrent with the flow of lithium hydroxide particles (1).

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