Process for preparing lithium sulfide in circulating bed reactor

Abstract

The invention relates to a process for preparing lithium sulfide (Li2S) from lithium hydroxide (LiOH) and hydrogen sulfide (H2S), characterized in that the sulfuration of lithium hydroxide is carried out in a reaction zone (9) comprising at least one spiral moving bed tubular reactor (9a) having a vibratory lifting structure, lithium hydroxide (4) is circulated in countercurrent with 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 a circulating bed). Background Art

[0002] Lithium sulfide (Li2S) is an essential raw material for manufacturing solid electrolytes used in next-generation batteries. Solid electrolytes are less flammable than liquid electrolytes and may be more efficient and lighter.

[0003] Currently, there are several known methods for synthesizing lithium sulfide, and these methods all face the problem of the extremely strong hydrophilicity of this compound. Specifically, at room temperature, lithium sulfide reacts highly with moisture and will spontaneously react to form lithium hydroxide (LiOH) while releasing hydrogen sulfide (H2S) when in contact with water. Therefore, the reaction conditions must be perfectly controlled to avoid any degradation during the formation of lithium sulfide. Once lithium sulfide is formed, it is essential to strictly control its residual moisture content, especially by storing it in a dry inert atmosphere.

[0004] In addition, it is also desirable to be able to produce lithium sulfide with as high a purity as possible and in the form of solid particles with an average particle size of less than 1 mm. These characteristics make the electrolyte have good stability and good capacitance.

[0005] One known way to synthesize lithium sulfide is to react lithium hydroxide and hydrogen sulfide, and the reaction is as follows: 2 LiOH + H2S → Li2S + 2 H2O Since the initial raw material LiOH is accessible and inexpensive, and the reaction is endothermic and can be carried out at a moderate temperature, which is usually between 130 and 450 degrees Celsius, this method is often used.

[0006] However, there are some disadvantages in the industrial preparation process using this synthesis method. First of all, a large amount of water generated by the reaction must be completely removed to prevent the re-conversion of Li2S into LiOH.

[0007] In addition, the initial raw material LiOH usually exists in the hydrated form LiOH·H2O, and in order to be able to start the sulfidation process, it needs to be thoroughly dried.

[0008] The above is because the degree of sulfidation of the hydrated form LiOH·H2O is too low.

[0009] Furthermore, the presence of this hydrated form in the sulfurization reactor leads to the formation of lithium sulfide lumps, i.e., larger lithium sulfide particles, which consist of aggregates composed of an un-sulfurized LiOH·H2O core wrapped by Li2S. As a result, the quality of the obtained lithium sulfide is greatly reduced: not only is its purity lower, but its average particle size also increases.

[0010] Various preparation methods have been described in the prior art, especially discontinuous preparation methods (or "batch" mode preparation methods), where solid particles can be stirred or placed in a fluidized bed reactor. For example, such batch preparation methods are described in patent applications EP 0 802 159, JP2020033259A, JP2015137183, and WO2018 / 141919.

[0011] These preparation methods generally require a large amount of sulfurizing agent (Li2S). In addition, these preparation methods also face problems of maintaining the reactor temperature (since the reaction is endothermic) and removing the water formed during the reaction. Finally, the preparation methods operating in batch mode have low production efficiency on an industrial scale because they require regular production interruptions and a large amount of logistics for loading and unloading the reactor.

[0012] Therefore, the economics of these preparation methods are poor, and they generally result in lithium sulfide with both low quality and purity, containing residual LiOH and larger-sized particles due to aggregates of Li2S and LiOH·H2O.

[0013] Due to the significant constraints associated with the sulfurization reaction of LiOH, continuous preparation methods are rare.

[0014] The present invention aims to provide a method for continuously preparing lithium sulfide on an industrial scale.

[0015] The present invention also aims to be able to prepare lithium sulfide with high chemical purity and in the form of small-sized particles. Summary of the Invention

[0016] The applicant has now developed an innovative process that can produce high-quality lithium sulfide from lithium hydroxide and hydrogen sulfide through a continuous process by means of a mobile bed (or circulating bed) circulating in at least one reactor with a specific configuration.

[0017] The process of the present invention is characterized in that the key sulfurization step of lithium hydroxide is carried out in a reaction zone containing at least one tubular reactor configured as a vibrating-lifting spiral, in which lithium hydroxide circulates countercurrently with an anhydrous sulfurizing gas stream containing hydrogen sulfide and an inert gas.

[0018] Therefore, the subject of the present invention is a process for preparing lithium sulfide (Li2S) from lithium hydroxide (LiOH) and hydrogen sulfide (H2S), wherein the sulfidation of lithium hydroxide is carried out in the reaction zone of a moving bed tubular reactor with at least one helix having a vibration-lifting structure, in which lithium hydroxide is circulated countercurrently with an anhydrous gas mixture containing hydrogen sulfide and at least one inert gas.

[0019] The process of the present invention can prepare lithium sulfide in high yield, especially with a mass yield greater than 80%.

[0020] In addition, the process can sulfidate lithium hydroxide under controllable temperature conditions. In particular, the endothermic nature of the reaction is compensated for by the circulation of the lithium hydroxide particle bed, promoting the temperature in the reactor to remain within the desired operating range of 150 to 450 degrees Celsius.

[0021] In addition, compared with the processes of the prior art, the lithium sulfide formed in the process carried out in the reactor does not come into contact with water, which is removed with the counter-circulating gas stream.

[0022] Therefore, the process of the present invention can obtain lithium sulfide with high purity, with a mass fraction greater than 99.0%.

[0023] In addition, the lithium sulfide discharged from the reactor does not come into contact with other substances except being in contact with the feed of the anhydrous sulfiding gas based on hydrogen sulfide and inert gas, which ensures that the content of residual lithium hydroxide in the obtained product is particularly low, with a mass fraction less than 1%.

[0024] According to the present invention, the reaction zone includes at least one tubular reactor configured as a vibration-lifting helix. In this reactor, LiOH particles move upward along the vibrating helical tube, countercurrently to the descending anhydrous sulfiding gas stream.

[0025] This configuration also has the additional advantage of being able to avoid the formation of lithium sulfide lumps composed of aggregates with a LiOH·H2O core surrounded by Li2S. Specifically, due to the vibration of the helical tube, the LiOH particles make upward transitions, ensuring a high degree of mixing of the particles in the sulfiding gas stream and better contact between the LiOH particles and the sulfiding gas, while avoiding the formation of lumps due to particle collisions with the reactor wall.

[0026] Compared with the processes described in the prior art, due to the improved contact between the sulfiding gas and lithium hydroxide, this configuration can also reduce the flow rate of the sulfiding gas and the amount of hydrogen sulfide used. It can accelerate the sulfidation reaction of the latter and effectively remove the generated water.

[0027] Other subjects, features, aspects and advantages of the present invention will become clearer by reading the following description and the attached non-limiting drawings: Figure 1 ​shows an example of an apparatus for producing lithium sulfide according to the process of the present invention.

[0028] In the following description, unless otherwise specified, the limits of a range value are included within that range, especially in expressions such as "between... and..." and "from... to...".

[0029] In addition, as used in this specification, "at least one" and "at least" are respectively equivalent to the expressions "one or more" and "greater than or equal to". Detailed Description

[0030] Sulfide gas The present invention uses an anhydrous gas mixture containing hydrogen sulfide and at least one inert gas.

[0031] The gas mixture is anhydrous, that is, its water content is less than or equal to 1% by volume.

[0032] The gas mixture contains hydrogen sulfide (H2S), which is a sulfiding agent that reacts with lithium hydroxide to form lithium sulfide while releasing water.

[0033] The content of hydrogen sulfide in the gas mixture, relative to the total volume of the mixture, is advantageously between 30% and 90% by volume fraction, preferably between 40% and 80%, more preferably between 50% and 70%, and most preferably between 55% and 65% by volume fraction.

[0034] The gas mixture also includes at least one inert gas, that is, an inactive gas. Inert gases are well known to those skilled in the art.

[0035] The inert gas can be particularly selected from nitrogen (N2) and inert gases such as argon, helium, krypton, neon, and xenon and mixtures thereof.

[0036] Preferably, the inert gas is selected from argon, nitrogen, and mixtures thereof, and more preferably, the inert gas is nitrogen.

[0037] The content of the inert gas, relative to the total volume of the gas mixture, is advantageously between 10% and 70% by volume fraction.

[0038] Preferably, the gas mixture also includes hydrogen (H2). In this case, the content of hydrogen in the gas mixture, relative to the total volume of the mixture, is advantageously between 5% and 30% by volume fraction, preferably between 10% and 20%.

[0039] Reaction zone In the present invention, the sulfidation of lithium hydroxide is carried out in the reaction zone of at least one helical moving bed tubular reactor having a vibration lifting structure, in which the lithium hydroxide and the sulfiding gas are circulated in countercurrent.

[0040] The term "moving bed reactor" is well known to refer to any reactor in which solid particles are circulated from the reactor inlet to the outlet. In the vibrating lifting helical reactor used in the present invention, the particles move upward along the helix. The movement of the particles is brought about by the vibration of the tubular reactor.

[0041] One 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 of the reactor and circulated towards the outlet. Conversely, the sulfiding gas is introduced at the outlet of the reactor and circulated towards the inlet.

[0042] In the present specification, the two terms "inlet" and "outlet" of the reactor are defined according to the upward circulation direction of the solid lithium hydroxide particles in the tubular reactor.

[0043] Therefore, there are two fluid streams circulating in countercurrent in the reactor, one of which is a solid stream and the other is a gas stream: The solid stream includes lithium hydroxide particles. As the particles move upward in the reactor, the lithium hydroxide in the solid stream gradually decreases, while the lithium sulfide gradually increases; The gas stream includes the sulfiding gas, that is, an anhydrous gas mixture containing hydrogen sulfide and at least one inert gas. As the gas moves downward in the reactor, the hydrogen sulfide in the gas stream gradually decreases, while the water vapor gradually increases.

[0044] According to a preferred embodiment, the anhydrous gas mixture is introduced into the reaction zone at at least two positions in the reaction zone: namely, at the outlet of the reaction zone and at at least one position between the outlet and the inlet of the reaction zone.

[0045] More preferably, the anhydrous gas mixture is introduced at the outlet of the reaction zone and at at least two different consecutive positions between the outlet and the inlet of the reaction zone.

[0046] The introduction of the anhydrous gas mixture at multiple consecutive positions along the reaction zone has the following advantages: The stoichiometric excess of H2S can be locally achieved to ensure the maximum conversion rate 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.

[0047] In this embodiment, the composition of the anhydrous gas mixture may vary between the respective introduction positions. In particular, the content of H2S may vary. For example, the closer the introduction position of the mixture is to the outlet of the reaction zone, the higher the content of H2S.

[0048] The temperature inside the reactor is advantageously maintained between 150 °C and 450 °C, preferably between 300 °C and 450 °C, and most preferably between 350 °C and 400 °C.

[0049] The temperature inside the reactor can be determined in a known manner, for example, using a thermocouple.

[0050] Due to the endothermic nature of the reaction, it is important to be able to control the temperature to ensure as constant a temperature as possible inside the reactor. In any case, there should be at least no reaction zone with a temperature lower than or equal to 100 °C. This can be achieved by using a countercurrent process and multiple reactors that may be present in the reaction zone, as described below.

[0051] 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.

[0052] At the outlet of the reaction zone, the temperature is generally less than or equal to 450 °C, and even less than or equal to 350 °C.

[0053] The pressure inside the reactor is maintained at a value less than 3 bar (3×10 5 Pa), preferably less than 2 bar (2×10 5 Pa), and more preferably less than 1.5 bar (1.5×10 5 Pa).

[0054] The applicant has surprisingly found that the process of the present invention can achieve the conversion rate of LiOH to Li2S using a smaller amount of H2S and a lower flow rate than the prior art. In the process of the present invention, advantageously, the space velocity of hydrogen sulfide is in the range of 30 - 450 h -1 .

[0055] The specific reactor used in the present invention consists of a vibrating screw, which is generally tubular, helically wound around a vertical axis, and includes at least two steps.

[0056] The cross-section of the screw is preferably circular. In this case, the screw is a pipe fitting. Generally, the diameter of the pipe fitting is between 100 and 300 mm. Usually, the pipe fitting has an unfolded length of up to 400 meters.

[0057] The pipe fitting is hollow, that is, its interior does not contain any elements.

[0058] The total height of the helix may be between 5 - 40 meters, preferably between 10 - 20 meters.

[0059] The climbing angle of the helix may be between 1 degree and 10 degrees, preferably between 1 - 5 degrees, more preferably between 1 - 4 degrees.

[0060] The number of turns of the reactor is preferably between 15 and 60, more preferably between 25 and 40.

[0061] Generally, this number of turns can achieve a particle flow rate between 50 and 6000 kg / h, preferably between 50 and 500 kg / h, and the gas hourly space velocity (GHSV) is generally in the range of 50 - 1500 h -1 within the range, preferably within the range of 50 - 500 h -1 within the range. The solid particles generally occupy 5% to 80% of the pipe fitting volume, preferably 10% to 50%.

[0062] The vibrating helix is advantageously made of a metallic material. Preferably, it consists of a metal tube made of a metal alloy, more preferably, a metal tube made of steel.

[0063] For example, the vibrating helix can be obtained by bending a metal tube around a substantially vertical axis into a spiral body. According to an advantageous embodiment, a central cylinder can be used to reinforce and support the spiral body formed by the helix. The helix can be electrically insulated from the central cylinder by a fixing system.

[0064] According to a preferred embodiment, a transformer supplies a low - voltage current, less than 50 V, to at least one step (i.e., at least one turn) of the vibrating helix, which enables the metal mass of the tube to be directly heated to the required temperature of the reactor by Joule heating.

[0065] In particular, one or more steps (one turn or more) are heated by Joule heating at a temperature of 150 - 450 °C, especially in the lower part of the reactor, in the inlet area of the LiOH particles. The direct result of Joule heating is the generation of heat in the mass of the turns. Compared with indirect heating, for example, by a heat - transfer fluid, it enables greater flexibility in controlling the temperature of the core of the turns.

[0066] The vibration of the helical reactor can be generated by at least one system placed at any appropriate horizontal position, such as at the bottom or top of the central cylinder, or other positions around the helix. In a suitable vibration system, the following systems can be involved: unbalanced motors, electromagnetic vibrators (generating pulsed excitation through variable periods), and unbalanced excitation. Preferably, the vibration is generated by a platform supported by the central cylinder and driven by two unbalanced motors.

[0067] The reaction zone may consist of one or more moving bed reactors.

[0068] Preferably, the reaction zone includes at least two moving bed reactors. Thus, the reaction zone may consist of multiple moving bed reactors, which may be arranged in series and / or in parallel. The moving bed reactors may have the same configuration (especially when arranged in parallel), or may have different configurations. Thus, multiple moving bed reactors may be used, all of which, or a part of which, may consist of tubular reactors with a vibrating screw configuration. When multiple vibrating screws are used, they may have different sizes.

[0069] Lithium sulfide (Li 2 S） At the outlet of the reaction zone, lithium sulfide is recovered in the form of small-sized solid particles, such as beads, or particles more or less cylindrical or irregular in shape.

[0070] The number-average size of the lithium sulfide particles, i.e., the diameter corresponding to a sphere of equal volume, is preferably less than or equal to 4 mm, more preferably less than or equal to 1 mm.

[0071] Here, the number-average size refers to the average value of the diameters when the particles are regarded as spheres, and the number-average value is defined by the d50 median diameter, which is measured by laser diffraction particle size analysis, for example, using a device known as a laser diffraction particle size analyzer, which can determine the particle size distribution of a particle population.

[0072] If the particles are indeed spherical, the number-average size is equal to the average diameter.

[0073] According to a preferred embodiment, a part of the particle stream leaving the reaction zone is recycled to the reaction zone, either at the inlet or at an intermediate position. When the reaction zone contains multiple reactors in series, it is particularly convenient to recycle at an intermediate position, and the recycled particles are introduced, for example, between two consecutive independent reactors.

[0074] When the conversion from LiOH to Li2S is not yet complete after a single pass through the reaction zone, it is beneficial to recycle the particle stream leaving the reaction zone.

[0075] Lithium hydroxide (LiOH) The lithium hydroxide introduced at the inlet of the reaction zone exists in the form of small-sized solid particles, such as beads, or particles more or less cylindrical or irregular in shape.

[0076] The number-average size of the lithium hydroxide particles, i.e., the diameter corresponding to a sphere of equal volume, is preferably between 10 microns and 4 mm.

[0077] The number average size here refers to the number average diameter of the particles when considered as spheres, which is defined by the d50 median diameter measured by laser diffraction particle size analysis, for example using a device known as a laser diffraction particle size analyzer that can determine the particle size distribution of a particle population.

[0078] If the particles are truly spherical, the number average size is equal to the average diameter.

[0079] According to a preferred embodiment, the water content of lithium hydroxide introduced into the reaction zone is less than 10 mol%.

[0080] Pre-drying step According to a preferred embodiment, before being introduced into the reaction zone, lithium hydroxide undergoes a drying step. This step is typically carried out in a drying zone with the aim of producing anhydrous lithium hydroxide through the following process: LiOH·H2O → LiOH + H2O The drying step is preferably completed by heat-treating lithium hydroxide in the temperature range of 150 - 350 °C, more preferably in the range of 175 - 250 °C, and circulating at least one inert gas in the drying zone to remove moisture.

[0081] The inert gas can be particularly selected from nitrogen (N2) and inert gases such as argon, helium, krypton, neon, and xenon and their mixtures.

[0082] Preferably, the inert gas is selected from argon, nitrogen, and their mixtures, and more preferably, the inert gas is nitrogen.

[0083] The pressure in the drying zone is advantageously maintained at a value less than 3 bar (3×10 5 Pa), preferably less than 2 bar (2×10 5 Pa), and more preferably less than 1.5 bar (1.5×10 5 Pa).

[0084] The drying step is preferably carried out continuously, more preferably in a drying zone containing one or more moving bed reactors where lithium hydroxide particles are circulated. Then, the gas flow of the inert gas can be circulated in the same or opposite direction as the solid flow of lithium hydroxide particles in the drying zone. Preferably, the gas flow of the inert gas is circulated in the same direction as the solid flow of lithium hydroxide particles in the drying zone.

[0085] 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 a vibrating lift screw. In such a reactor, the particles move upward along the screw, during which the particles are gradually converted into anhydrous LiOH while releasing moisture.

[0086] A tubular reactor in a vibrating spiral form has been described above. In this embodiment, the gas flow of the inert gas preferably circulates upward in the vibrating spiral (i.e., in the same direction as the solid flow of the solid particles). However, it is also possible to implement the gas flow of the inert gas to circulate downward in the vibrating spiral (i.e., in the opposite direction to the solid flow of the solid particles).

[0087] According to the second embodiment, at least one moving bed reactor in the drying zone is a horizontal tubular reactor with a hot screw, that is to say, the hot screw is an endless screw, or an Archimedes screw, in which the particles are conveyed and dried in a continuous flow manner while releasing moisture. In such a reactor, the LiOH·H2O particles move along the blades of the screw, during which process, they are gradually converted into anhydrous LiOH while releasing moisture.

[0088] The hot screw can be heated by electric heating or by a heat transfer fluid, and the heat exchange can occur through grooves, an intermediate core or coils. The gas flow of the inert gas can be injected in the same direction or in the opposite direction to the solid flow of the solid particles, preferably in the same direction.

[0089] Pre-sulfidation step Preferably, lithium hydroxide is also pre-sulfurized during the above-mentioned drying step. The term "pre-sulfurization" means partial sulfurization of lithium hydroxide such that the anhydrous lithium hydroxide contains 5% to 40% by mass of lithium sulfide (Li2S) at the end of the drying step.

[0090] Pre-sulfurization is preferably achieved by contacting the lithium hydroxide particles with an anhydrous gas mixture during the circulation in the drying zone, and the gas mixture contains at least one inert gas and 5% to 30% by volume of hydrogen sulfide relative to the total volume of the mixture.

[0091] The gas mixture is anhydrous, that is to say, its moisture content is less than or equal to 1% by volume.

[0092] The content of hydrogen sulfide in the gas mixture for pre-sulfurization is more preferably within the volume fraction of 10% to 15% relative to the total volume of the mixture.

[0093] The inert gas is selected from the gases used in the above-mentioned drying step, including nitrogen (N2), inert gases and their mixtures. Preferably, the inert gas is selected from argon, nitrogen and their mixtures, and more preferably, the inert gas is nitrogen.

[0094] According to a preferred embodiment, the inert gas present in the gas mixture for the pre-sulfurization of lithium hydroxide is the inert gas for drying. Thus, for example, the pre-sulfurization can be achieved by directly adding hydrogen sulfide to the gas stream circulating in the drying zone, or by adding a mixture containing hydrogen sulfide, an inert gas, and optionally hydrogen as described below.

[0095] Preferably, the gas mixture for pre-sulfurization further contains hydrogen (H2). In this case, the content of hydrogen in the gas mixture is preferably within a volume fraction of 1% to 10% relative to the total volume of the mixture, more preferably within a volume fraction of 2% to 5%.

[0096] According to a preferred embodiment, the gas mixture for the pre-sulfurization of lithium hydroxide consists entirely or in part of the gas mixture recovered at the outlet of the reaction zone, which has been previously dried to remove the moisture therein. If necessary, the gas mixture can be diluted by adding an inert gas to adjust the content of hydrogen sulfide therein to the concentration required for pre-sulfurization.

[0097] The gas mixture for pre-sulfurization can be introduced at one or more positions in the drying zone, which are preferably located downstream of the lithium hydroxide particle inlet region. Specifically, the pre-sulfurization step preferably starts at a position in the drying zone where the water content of the lithium hydroxide is already low enough.

[0098] Therefore, the gas mixture for pre-sulfurization preferentially contacts the lithium hydroxide circulating in the drying zone at a part downstream of the solid injection position, i.e., the latter half.

[0099] Preferably, the gas mixture for pre-sulfurization circulates in the same direction as the solid stream of lithium hydroxide particles in the drying zone.

[0100] In the case of a vibrating lifting spiral in the drying zone, the gas mixture for pre-sulfurization is usually introduced at one, two, or three positions, which are preferably located in the upper half of the spiral.

[0101] The gas mixture advantageously circulates upward in the same direction as the solid stream of the rising solid particles.

[0102] The pre-sulfurization step of lithium hydroxide is preferably carried out in the temperature range of 150 - 350 °C, more preferably in the range of 175 - 250 °C.

[0103] The pre-sulfurization step can improve the drying degree of lithium hydroxide and increase the sulfidation rate in the downstream reaction zone.

[0104] Figure 1Shows a non - limiting example of an apparatus for producing lithium sulfide. According to the present invention, lithium hydroxide (LiOH) is converted to lithium sulfide (Li₂S) in reaction zone 9, which comprises a moving - bed tubular reactor formed by a helix 9a with a vibrating lifting structure.

[0105] Lithium hydroxide particles are introduced into the lower part of reaction zone 9 through pipeline 4. The particles move upward in helix 9a, and this movement is caused by the vibration of the helix.

[0106] An anhydrous gas mixture containing a stoichiometric excess of hydrogen sulfide and nitrogen is introduced into the upper part of reaction zone 9. This mixture is conveyed through pipeline 10 and introduced into helix reactor 9a at two consecutive injection positions 10a and 10b in the upper part of the reactor. The mixture circulates downward in helix reactor 9a, in counter - current circulation with the upward - flowing particulate solid stream.

[0107] At the outlet of reaction zone 9, lithium sulfide particles are recovered and discharged via pipeline 11.

[0108] In the lower part of reaction zone 9, a gas mixture containing nitrogen, water, and hydrogen sulfide residues is discharged at two consecutive positions 12a and 12b and conveyed through pipeline 12 to treatment unit 13.

[0109] In treatment unit 13, the mixture from pipeline 12 is treated to remove the water therein, and the water is separated through pipeline 14. Dust removal (not shown) can also be carried out on the gas mixture to remove entrained particulate dust. Subsequently, the mixture of nitrogen and residual hydrogen sulfide is discharged through pipeline 15.

[0110] Before being introduced into the reaction zone, lithium hydroxide undergoes a drying step in drying zone 2, which comprises a moving - bed tubular reactor. In this example, the tubular reactor is formed by a helix 2a with a vibrating lifting structure.

[0111] Hydrous lithium hydroxide (LiOH·H₂O) particles are introduced into the lower part of drying zone 2 through pipeline 1. The particles move upward in helix 2a, and this movement is caused by the vibration of the helix.

[0112] An inert gas containing nitrogen, conveyed through pipeline 3, is also introduced into the lower part of drying zone 2 and injected into helix 2a at injection positions 3a and 3b. The nitrogen moves upward in helix reactor 2a, in the same - direction flow as the particulate solid stream.

[0113] In the upper part of drying zone 2, the dried lithium hydroxide particles are discharged through pipeline 4 and transferred to reaction zone 9. Also in the upper part of drying zone 2, a mixture of water and nitrogen is discharged at consecutive positions 5a and 5b and conveyed through pipeline 5 to treatment unit 6.

[0114] In processing unit 6, the mixture from pipeline 5 is processed to remove the moisture therein, and the moisture is separated through pipeline 7. Dust removal (not shown) can also be performed on the gas mixture to remove the entrained particulate dust therein. Subsequently, nitrogen is discharged through pipeline 8. According to an advantageous embodiment (not shown), the nitrogen recovered at the outlet of the drying zone is recycled back to the processing unit, either at the level of the drying zone 2 or at the level of the reaction zone 9.

[0115] According to a preferred alternative embodiment, after the gas mixture of nitrogen and residual hydrogen sulfide from reaction zone 9 is dried and recovered through pipeline 15, it is recycled back to drying zone 2 through pipeline 16. In the drying zone, the gas mixture is introduced into the second half of the upper part of the spiral reactor 2a. This recycled gas mixture contains a lower hydrogen sulfide content than the gas mixture introduced into reaction zone 9. This recycling enables pre-sulfurization of the lithium hydroxide particles upstream of reaction zone 9 in the second half of the upper part of drying zone 2.

Claims

1. A process for preparing lithium sulfide (Li2S) from lithium hydroxide (LiOH) and hydrogen sulfide (H2S), characterized in that, The sulfidation of lithium hydroxide is carried out in a reaction zone (9) which comprises at least one moving bed tubular reactor (9a) with a helical vibration enhancing structure, in which lithium hydroxide (4) is circulated countercurrently to an anhydrous gas mixture (10) containing hydrogen sulfide and at least one inert gas.

2. The process according to the preceding claim, characterized in that, The content of hydrogen sulfide in the anhydrous gas mixture (10), relative to the total volume of the mixture, is in the range of 30% to 90% by volume, preferably between 40% and 80%, more preferably between 50% and 70%, and most preferably between 55% and 65% by volume.

3. The process according to any one of the preceding claims, characterized in that, The inert gas is selected from nitrogen, noble gases and mixtures thereof, preferably from argon, nitrogen and mixtures thereof, and more preferably, the inert gas is nitrogen.

4. The process according to any one of the preceding claims, characterized in that, The anhydrous gas mixture (10) further comprises hydrogen, the content of hydrogen being in the range of 5% to 30% by volume relative to the total volume of the mixture, preferably between 10% and 20%.

5. The process according to any one of the preceding claims, characterized in that, The anhydrous gas mixture (10) is introduced into the reaction zone (9) at at least two positions (10a, 10b) of the reaction zone: namely, at the outlet (10a) of the reaction zone and at at least one position between the outlet and the inlet (10b) of the reaction zone.

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

7. The process according to any one of the preceding claims, characterized in that, The reaction zone (9) comprises a plurality of moving bed reactors, all or some of which comprise a helix with a vibration structure.

8. The process according to any one of the preceding claims, characterized in that, Before being introduced into the reaction zone (9), lithium hydroxide (1) is subjected to a drying step in a drying zone (2), and the drying step is preferably carried out continuously.

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

10. The process according to claim 9, characterized in that, At least one moving bed reactor in the drying zone (2) is a tubular reactor in the form of a helix (2a) with a vibration enhancing structure.

11. The process according to claim 9 or 10, characterized in that, The pre-sulfidation of lithium hydroxide is carried out during the drying step by bringing the lithium hydroxide (1) particles into contact 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 during the circulation of lithium hydroxide in the drying zone (2).

12. The process according to claim 11, characterized in that, The content of hydrogen sulfide in the anhydrous gas mixture for pre-sulfidation is in the range of 10% to 15% by volume relative to the total volume of the mixture.

13. The process according to claim 11 or 12, characterized in that, The anhydrous gas mixture for pre-sulfidation of lithium hydroxide (1) consists entirely or in part of the gas mixture (16) recovered at the outlet (9) of the reaction zone, which has been previously dried to remove the moisture therein.

14. The process according to any one of claims 11 - 13, characterized in that, The gas mixture for pre-sulfidation is circulated in the same direction as the solid stream (1) of lithium hydroxide particles in the drying zone (2).

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