Method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide nmp solution

Abstract

The application relates to the technical field of lithium sulfide production, and discloses a method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution, which comprises the following steps: continuously dissolving lithium hydroxide raw materials in N-methyl-2-pyrrolidone solvent; continuously pumping the lithium hydroxide-NMP solution into a first-stage bubble column of a reaction system composed of at least three-stage series connection bubble columns; continuously carrying out solid-liquid separation on the slurry containing lithium sulfide solids to obtain lithium sulfide solids; continuously drying the lithium sulfide solids obtained after the leaching; and high-temperature calcining the dried lithium sulfide powder at a temperature of 430-480 DEG C under an inert gas atmosphere. According to the application, the reaction water and high-boiling-point solvent are efficiently removed through in-situ dehydration of the NaA film and acetone replacement leaching, the balance limitation is broken, the conversion rate is improved, and high-purity lithium sulfide without carbonization residue is prepared.

Description

Technical Field

[0001] This invention relates to the field of lithium sulfide production technology, specifically a method for producing lithium sulfide by reacting hydrogen sulfide gas with lithium hydroxide NMP solution. Background Technology

[0002] Lithium sulfide is a cathode material for lithium-sulfur batteries with high theoretical specific capacity, and also a key precursor for the preparation of sulfide solid electrolytes. With the increasing demands for energy density and safety in new energy battery technologies, the need for high-purity lithium sulfide with low impurity content is becoming increasingly urgent. In existing preparation processes, the liquid-phase reaction of lithium hydroxide with hydrogen sulfide in an organic solvent is the mainstream route for industrial production. Compared to the high-temperature carbothermal reduction method or the direct sulfidation method of metallic lithium, this route has the advantages of lower raw material costs and relatively milder reaction conditions. However, in the actual production process of lithium sulfide synthesis via the liquid phase method, technical bottlenecks still exist, limiting product quality and production efficiency. This reaction is a typical reversible reaction; if the water generated during the reaction is not removed in time, it will accumulate in the reaction system. The presence of water not only inhibits the forward reaction, leading to a decrease in raw material conversion rate, but also easily causes lithium sulfide to hydrolyze or form difficult-to-remove crystalline hydrates. Existing dehydration processes mostly employ azeotropic distillation or high-temperature evaporation, which not only consumes a large amount of heat energy, but also easily triggers side reactions due to prolonged heating at high temperatures, and is difficult to deeply remove the trace amounts of water generated in the reaction. Furthermore, the selection and removal of the solvent are another key factor affecting the purity of the final product. N-methyl-2-pyrrolidone (NMP) is often used as a reaction medium due to its good solubility for lithium hydroxide. However, NMP is a high-boiling-point polar solvent with a boiling point as high as 202℃, and it has a strong adsorption effect on lithium sulfide particles. In the solid-liquid separation and drying stage after the reaction, conventional vacuum drying or heating drying alone is insufficient to completely remove the NMP solvent adsorbed on the crystal surface and pores. When the lithium sulfide precursor containing residual NMP enters the subsequent high-temperature calcination process, the residual organic solvent will undergo cracking and carbonization under high temperature and inert atmosphere, resulting in excessive total carbon content in the final product, a grayish-black appearance, and severely affecting the electrochemical performance of lithium sulfide. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution. This method solves the problems in existing liquid-phase lithium sulfide production processes, such as limited chemical equilibrium, low raw material conversion rate, and difficulty in removing high-boiling-point reaction solvent residues in the solid, which leads to carbonization and decreased purity of the product during subsequent high-temperature calcination. To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for producing lithium sulfide by reacting hydrogen sulfide gas with lithium hydroxide NMP solution, the method comprising the following steps: S1. Lithium hydroxide raw material is continuously dissolved in N-methyl-2-pyrrolidone solvent to obtain a lithium hydroxide-NMP solution with a mass fraction of 5-10%; S2. The lithium hydroxide-NMP solution is continuously pumped into the first stage bubble column of a reaction system consisting of at least three bubble columns connected in series. Simultaneously, gas containing hydrogen sulfide is introduced from the last stage bubble column of the reaction system, causing the solution and gas to undergo a continuous countercurrent reaction in the reaction system to generate a slurry containing lithium sulfide solids. A tube made of NaA-type inorganic pervaporation membrane is installed in the center of the bubble column. The pervaporation membrane tube is arranged vertically. The reaction temperature of the bubble column is 60-80 degrees Celsius, and the internal negative pressure of the pervaporation tube is 10-50 kPa. The water generated in the reaction is removed by the pervaporation membrane in real time. A portion of the hydrogen sulfide also enters the pervaporation membrane tube. The pervaporation membrane is connected to a gas-liquid separator. The water is discharged by gravity, and the hydrogen sulfide is pumped back into the bubble column for circulation. S3. The slurry containing lithium sulfide solid is subjected to continuous solid-liquid separation to obtain lithium sulfide solid, and the lithium sulfide solid is washed. S4. The lithium sulfide solid obtained after rinsing is continuously dried to obtain dry lithium sulfide powder. S5. The dried lithium sulfide powder is calcined at a temperature of 430-480°C in an inert gas atmosphere to obtain the final lithium sulfide product. In one specific embodiment, the step of continuously dissolving lithium hydroxide raw material in N-methyl-2-pyrrolidone solvent is carried out in a continuous dissolution vessel equipped with jacket heating and mechanical stirring. The solvent temperature inside the vessel is maintained at 80-100°C by the jacket heating. The N-methyl-2-pyrrolidone solvent is pumped into the continuous dissolution vessel at a stable flow rate. Simultaneously, the lithium hydroxide raw material is added to the vessel at a precisely controlled rate using a loss-in-weight feeder, and the material inside the vessel is mechanically stirred at a stirring speed of 100-300 rpm. In one specific implementation, the lithium hydroxide-NMP solution is continuously injected from the top of the first-stage bubble column. Under gravity, the solution flows sequentially through subsequent bubble columns, and is finally continuously discharged from the bottom of the final-stage bubble column. The total residence time of the solution in the reaction system is set to 30-120 minutes. As one specific implementation, the step of performing a continuous countercurrent reaction includes a structure for controlling the reaction process: Hydrogen sulfide gas is independently supplied to the first-stage bubbling tower; a monitoring device is installed to monitor the conductivity or pH value of the solution at the outlet of the first-stage bubbling tower. The monitoring signal is used to control the flow rate of the independently supplied hydrogen sulfide gas. Furthermore, the exhaust gas discharged from the top of the first-stage bubble column is collected, pressurized, and then reinjected into the second or third-stage bubble column of the reaction system. In one specific implementation, the step of rinsing the lithium sulfide solid is carried out on a PTFE filter belt conveyor with a filtration function. The reaction solution falls onto the PTFE filter belt conveyor, and the solvent is filtered away. Li2S particles remain on the filter belt conveyor. A rinsing zone is set on the PTFE filter belt conveyor, and the lithium sulfide solid is rinsed in a multi-stage spray process using N-methyl-2-pyrrolidone solvent at the front end and acetone at the rear end. In one specific implementation, the step of continuously drying the lithium sulfide solid obtained after rinsing is carried out in a fluidized bed or rake vacuum dryer. The drying temperature is 140-180℃, and the vacuum degree is -0.08 to -0.098 MPa. The residence time of the lithium sulfide solid in the fluidized bed or rake vacuum dryer is 2-4 hours. In one specific implementation, the step of high-temperature calcination in an inert gas atmosphere is carried out in a rotary tube furnace. The inert gas is nitrogen or argon, and it is introduced into the rotary tube furnace at a flow rate of 5-20 L / min to maintain a positive pressure inside the furnace. The residence time of the dried lithium sulfide powder in the rotary tube furnace is 1-3 hours. As one specific implementation, the step of obtaining the final lithium sulfide product further includes: continuously cooling the final lithium sulfide product to room temperature in a closed device; and automatically packaging the cooled final lithium sulfide product in an inert gas atmosphere. This invention provides a method for producing lithium sulfide by reacting hydrogen sulfide gas with lithium hydroxide NMP solution. It has the following advantages: 1. This invention uses N-methyl-2-pyrrolidone (NMP) as the reaction medium and introduces acetone for secondary displacement rinsing during the solid-liquid separation stage. Due to the high boiling point of NMP, conventional drying alone is insufficient to completely remove it from the intercrystalline spaces. Residual NMP undergoes pyrolysis and carbonization during subsequent high-temperature calcination, resulting in a blackened product and increased carbon impurities. This invention utilizes the physical properties of acetone being miscible with NMP and having a low boiling point. A downstream spray effectively replaces the NMP solvent adsorbed in the lithium sulfide filter cake, while residual acetone is easily volatilized and removed during the drying stage. This solvent displacement strategy reduces organic residues in the final product and avoids the impact of calcination carbonization on product quality, thereby producing high-purity lithium sulfide with low impurity content. 2. This invention integrates a NaA-type inorganic pervaporation membrane tube within the bubbling tower reaction system, achieving in-situ efficient dehydration during the reaction process. The reaction between lithium hydroxide and hydrogen sulfide is a reversible reaction, and the accumulation of water in the system directly limits the forward reaction. By utilizing the selective permeation of water molecules through the NaA membrane under negative pressure, the product water generated at the reaction interface can be removed in real time, thereby disrupting the chemical equilibrium and forcibly pushing the reaction towards the formation of lithium sulfide. This technical approach avoids the high energy consumption and solvent loss problems associated with traditional azeotropic distillation or high-temperature evaporation for water removal, achieving extremely high raw material conversion rates at relatively low reaction temperatures. 3. This invention designs a multi-stage series bubble column reaction system and a gas-liquid countercurrent contact process, achieving continuous production and efficient gas utilization. By counter-currently transporting lithium hydroxide solution and hydrogen sulfide gas within the multi-stage column, a high concentration gradient and mass transfer driving force are maintained throughout the reaction path, ensuring complete reaction. Simultaneously, combined with the gas-liquid separation function of the membrane separation system, unreacted hydrogen sulfide and trace amounts of gas dissolved in the permeate are separated, repressurized, and recycled back to the bubble column. This closed-loop design significantly improves the utilization rate of expensive and toxic hydrogen sulfide gas, reduces the tail gas treatment load, and the continuous and stable process operation ensures consistent product quality across different batches. Attached Figure Description Figure 1 This is a schematic diagram of the continuous lithium sulfide production process of the present invention; Figure 2 This is a graph showing the change in the proportion of water removed by the membrane and the total utilization rate of H2S during 12 hours of continuous operation in Example 1 of the present invention. Figure 3 This is a comparison chart of the purity of Li2S, residual NMP, and moisture content of Examples 1-4 and Comparative Examples 1-5 of the present invention. Detailed Implementation The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products. Anhydrous Lithium Hydroxide: CAS No.: 1310-66-3; Battery grade, purity ≥99.0%. N-Methyl-2-pyrrolidone: CAS No.: 872-50-4; anhydrous grade, purity ≥99.5%. Hydrogen sulfide: CAS No.: 7783-06-4; high purity, purity ≥99.5%. Nitrogen: CAS No.: 7727-37-9; High purity, ≥99.999%. Argon: CAS No.: 7440-37-1; high purity, purity ≥99.999%. Acetone: CAS No.: 67-64-1, analytical grade (AR), purity ≥99.5%. Examples 1-4: Reference Figure 1 Example 1: This embodiment provides a method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution, including the following steps: In a continuous dissolution vessel equipped with jacketed heating and mechanical stirring, N-methyl-2-pyrrolidone (NMP) solvent was pumped in at a stable flow rate, while lithium hydroxide feedstock was added to the vessel at a precisely controlled rate using a loss-in-weight feeder. The solvent temperature inside the vessel was maintained at 80°C, and the mechanical stirring speed was set to 200 rpm, allowing the lithium hydroxide feedstock to dissolve continuously, yielding an 8% (w / w) lithium hydroxide-NMP solution. A lithium hydroxide-NMP solution is continuously injected from the top of the first-stage bubble column in the reaction system, which consists of three bubble columns connected in series. The solution flows sequentially through each bubble column under gravity and is finally discharged continuously from the bottom of the last bubble column. The total residence time of the solution in the reaction system is controlled to be 60 minutes. Simultaneously, hydrogen sulfide gas is introduced from the last bubble column, and hydrogen sulfide gas is independently supplied to the first-stage bubble column (flow rate controlled by monitoring the conductivity of the first-stage outlet), allowing the solution and gas to undergo a continuous countercurrent reaction. The reaction temperature in each bubble column is maintained at 70°C. A vertically arranged NaA-type inorganic pervaporation membrane tube is installed in the center of each bubble column. The tube is evacuated to a negative pressure of 30 kPa, and the water generated in the reaction permeates through the membrane and is removed in real time. A small amount of hydrogen sulfide entering the membrane is separated by a gas-liquid separator and then pumped back into the bubble column for circulation. The exhaust gas from the first-stage bubble column is pressurized and reinjected into the second-stage bubble column. The reaction produces a slurry containing solid lithium sulfide. The slurry containing lithium sulfide solids is discharged onto a PTFE filter belt conveyor for continuous solid-liquid separation. After the solvent is filtered out, Li₂S particles remain on the filter belt. The PTFE filter belt operates at a speed of 0.5 m / min. In the rinsing zone, the lithium sulfide solids are first initially rinsed with 80°C NMP solvent through the front spray head, and then secondarily rinsed with room temperature acetone through the rear spray head. The washed lithium sulfide solid was fed into a rake-type vacuum dryer for continuous drying. The drying temperature was set to 180℃, the vacuum degree was -0.09MPa, and the residence time was 3 hours to obtain dried lithium sulfide powder. Dry lithium sulfide powder was fed into a rotary tube furnace and calcined at 450°C for 2 hours under a nitrogen atmosphere (flow rate 10 L / min). The calcined product was then cooled to room temperature in a sealed environment and automatically packaged under nitrogen protection to obtain the final lithium sulfide product. Example 2: This embodiment provides a method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution, including the following steps: In a continuous dissolution vessel, the temperature is controlled at 60℃ and the stirring speed is 100rpm. Lithium hydroxide raw material is continuously dissolved in NMP to obtain a lithium hydroxide-NMP solution with a mass fraction of 5%. The solution is pumped into the first stage of a three-stage tandem bubble column system, with a total residence time of 30 minutes. The reaction temperature in the bubble column is controlled at 60°C. A negative pressure of 10 kPa is applied inside the NaA pervaporation membrane tube to remove the water generated in real time. Hydrogen sulfide gas is introduced in countercurrent flow and recycled. The slurry is subjected to solid-liquid separation on a PTFE filter belt conveyor (running speed 0.1 m / min). The initial stage of the rinsing zone uses room temperature NMP for rinsing, and the subsequent stage uses room temperature acetone for rinsing. The solid was fed into a fluidized bed dryer and dried for 2 hours at 140°C and a vacuum of -0.08 MPa. The dried powder was calcined at 430°C for 1 hour in a rotary tube furnace under an argon atmosphere (flow rate 5 L / min). After cooling and packaging, lithium sulfide product was obtained. Example 3: This embodiment provides a method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution, including the following steps: In a continuous dissolving vessel, the temperature was controlled at 100℃ and the stirring speed at 300rpm to obtain a 10% lithium hydroxide-NMP solution. The solution was pumped into the reaction system, with a total residence time of 120 minutes. The reaction temperature in the bubbling tower was controlled at 80°C. The NaA pervaporation membrane tube was evacuated to a negative pressure of 50 kPa. The slurry is separated on a PTFE filter belt conveyor (running speed 1.0 m / min). The first section of the rinsing zone uses NMP rinsing at 110°C, and the second section uses acetone rinsing at room temperature. The solid was dried in a rake-type vacuum dryer at 250°C and a vacuum of -0.098 MPa for 4 hours. The dried powder was calcined at 480°C for 3 hours in a rotary tube furnace under a nitrogen atmosphere (flow rate 20 L / min). After cooling and packaging, lithium sulfide product was obtained. Example 4: This embodiment provides a method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution, including the following steps: Lithium hydroxide-NMP solution was continuously prepared according to the parameters of Example 1 (80°C, 8% concentration), and the system was continuously operated for 24 hours without interruption. The solution continuously enters a five-stage bubbling tower reaction system (belonging to the category of "at least three stages"), with a total residence time set at 90 min. The reaction temperature at each stage is 75℃, and the negative pressure in the pervaporation membrane tube is 40 kPa. The first stage independently replenishes H2S, and the gas flow rate is finely adjusted in real time according to the outlet pH value. The slurry is continuously separated on a PTFE filter belt (speed 0.6 m / min). The washing process is strictly followed: the mother liquor is removed by 90°C NMP at the front, and a large amount of room temperature acetone (flow rate 1.5 times that of the front) is used to replace the NMP in the back to ensure the lowest possible solvent residue in the filter cake during long-term operation. Continuously dried in a fluidized bed (200℃, -0.095MPa, 3.5 hours). The lithium sulfide product is continuously produced by calcining in a rotary tube furnace (460°C, nitrogen protection, 2.5 hours). Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that in step S3, acetone is not used for secondary displacement rinsing of lithium sulfide solid. That is, in the rinsing zone of the PTFE filter belt conveyor, both the front and rear spray heads use NMP solvent at 80°C for spraying. The remaining steps and parameters are the same. Comparative Example 2: Compared with Example 1, the difference is that in step S2, the NaA type inorganic pervaporation membrane tube is not set in the center of the bubbling tower, and no in-situ membrane separation and dehydration is performed during the reaction process. Only some water is carried out by the airflow. The other steps and parameters are the same. Comparative Example 3: Compared with Example 1, the difference is that in step S2, the reaction system consisting of three-stage series bubble towers is replaced with a single-stage large bubble tower reactor. The lithium hydroxide-NMP solution and hydrogen sulfide gas react in contact within the single-stage tower, and the residence time remains unchanged at 60 min. All other steps and parameters are the same. Comparative Example 4: Compared with Example 1, the difference is that step S5 is omitted. The lithium sulfide powder obtained after drying in step S4 by a rake vacuum dryer (180°C) is directly cooled and automatically packaged as the final product. The remaining steps and parameters are the same. Comparative Example 5: Compared with Example 1, the difference is that in step S3, the acetone used in the downstream spray head is replaced with anhydrous ethanol for secondary rinsing, while the other steps and parameters are the same. Test Case 1 - Test Case 2: Test Example 1: Experimental objective: Based on the process parameters and equipment configuration of Example 1, the dehydration efficiency of the reaction system and the recycling rate of hydrogen sulfide (H2S) gas were continuously monitored. The experiment aimed to verify the in-situ dehydration performance of the NaA-type inorganic pervaporation membrane in a three-stage series bubble column, and the effect of the countercurrent circulation system on improving gas utilization. Experimental steps: After the system started up and reached steady-state operation (Example 1 parameters: 80℃, 8% LiOH-NMP solution, residence time 60 min, membrane-side negative pressure 30 kPa), data recording began. The continuous monitoring duration was set to 12 hours. Water removal monitoring: Level and weight sensors are installed at the vacuum side condensate collection tank of the pervaporation membrane module (marked as point A) and the condensate separator for exhaust gas from the reaction system (marked as point B). The amount of condensate is recorded every 1 hour. Gas monitoring: Mass flow meters are installed at the fresh H2S injection port of the first-stage bubbling tower, the recirculated gas inlet of the last-stage bubbling tower, and the final exhaust port. The fresh gas supply and recirculated gas flow rates are recorded. Calculation index: Water removal rate (%) = (Water collection volume at point A / Theoretical water generation volume) × 100%; H2S total utilization rate (%) = [(total input - total discharge) / total input] × 100%.

[0004] Experimental data (see Table 1): Table 1 in conclusion: In-situ membrane separation verifies the mechanism of disrupting chemical equilibrium. The reaction of LiOH with H2S to generate Li2S is a reversible reaction. Table 1 shows that during 12 hours of continuous operation, the water removal rate by the membrane remained consistently above 95% (average 96.19%). This indicates that the NaA-type pervaporation membrane tube arranged in the center of the bubble column has extremely high selective permeability to water molecules in the reaction system under negative pressure. Once water molecules are generated, they are removed from the reaction interface, keeping the water concentration in the reaction system at an extremely low level for a long period. According to Le Chatelier's principle, the removal of product water forces the chemical equilibrium to shift to the forward direction (the direction of Li2S generation), thereby achieving a high conversion rate at a relatively low reaction temperature (70℃), avoiding the increased energy consumption and side reactions caused by the high-temperature evaporation required for water removal in traditional processes.

[0005] Gas utilization efficiency of the countercurrent contact and internal circulation system. Monitoring data shows that the fresh H2S replenishment rate (approximately 12.5 L / min) is much lower than the internal circulation flow rate (approximately 35.1 L / min), and the total gas utilization rate remains stable at around 98%. This confirms the effectiveness of the three-stage series countercurrent reaction structure combined with the gas-liquid separation and reuse design. H2S gas is introduced from the final stage and flows sequentially to the first stage, countercurrently contacting the gradually decreasing concentration of LiOH solution. This ensures that the high concentration of hydrogen sulfide in the later stage of the reaction (final stage tower) drives the reaction to proceed completely, while the unreacted tail gas in the early stage of the reaction (first stage tower) is pressurized and reinjected into the middle stage, significantly reducing the escape loss of raw material gas.

[0006] Process stability. Within 12 hours, no sustained drift or abrupt changes were observed in any of the monitored indicators (water removal rate, gas flow rate, utilization rate), and the standard deviation was small. This indicates that the pervaporation membrane did not fail due to slurry erosion, and there was no phenomenon of membrane pore blockage leading to a decrease in flux, verifying the long-term operational stability of the reaction system when treating solid-containing slurries.

[0007] Test Example 2: Experimental objective: Lithium sulfide prepared in Examples 1-4 and Comparative Examples 1-5 ( The product was comprehensively tested for purity, solvent residue, moisture content, and appearance using standardized analytical methods. The specific testing methods are as follows.

[0008] Experimental steps: Purity test: A certain amount of sample was weighed and dissolved in deionized water, and the sulfur ion content was determined by potentiometric titration.

[0009] Solvent residue determination: Headspace gas chromatography was used to determine the residual amount of volatile organic compounds in the product, with N-methyl-2-pyrrolidone (NMP) and acetone as the detection targets.

[0010] Moisture determination: The trace moisture in the sample was determined using a Karl Fischer moisture analyzer (coulometric method) in a glove box protected by inert gas.

[0011] Appearance and color: Visually observe the color and state of the powder under a standard light source.

[0012] Experimental data (see Table 2):

[0013] in conclusion: Acetone displacement rinsing plays a crucial role in reducing solvent residue. Comparing the data from Example 1 and Comparative Example 1, it is evident that the NMP residue in the product of Comparative Example 1, which did not undergo acetone rinsing, was as high as 3250 ppm, and its appearance was grayish-yellow. This is because NMP has a high boiling point (202°C), making it difficult to remove by subsequent drying alone. Complete removal from intercrystalline interstitial spaces. Residual NMP undergoes thermal decomposition and carbonization during subsequent high-temperature calcination (450°C), generating amorphous carbon that deposits on the product surface, leading to decreased purity and deteriorated color. Example 1 introduced low-boiling-point (56°C) acetone as a displacement solvent, utilizing the miscibility of acetone and NMP to displace the high-boiling-point mother liquor from the filter cake. Acetone itself is highly volatile during the drying stage, thus controlling organic residues below 50 ppm. Although Comparative Example 5 used ethanol for rinsing, the NMP residue (120 ppm) was still higher than in Example 1, and the purity was slightly lower, indicating that acetone's displacement efficiency for NMP is superior to ethanol, and that ethanol may cause… Trace dissolution or side reactions.

[0014] The decisive influence of pervaporation membrane dehydration on the reaction conversion rate. Comparative Example 2 eliminated the NaA-type pervaporation membrane tube; its product purity was only 88.60%, and the moisture content was extremely high. Based on the reaction mechanism, and The reaction is limited by chemical equilibrium; the accumulation of water significantly inhibits the forward reaction. In the membrane-free system, water is carried away solely by gas flow, resulting in a dehydration rate far lower than the formation rate, leading to [unclear - possibly referring to a specific reaction process or process]. Increased concentration results in a large amount of unconverted raw materials remaining as crystalline hydrates, severely impacting product quality. Examples 1-4 utilize membrane separation technology to remove product water in real time, disrupting thermodynamic equilibrium and ensuring the reaction proceeds towards the product phase. Proceeding in the direction and depth.

[0015] The necessity of multi-stage countercurrent and high-temperature calcination processes. Comparative Example 3, using a single-stage reaction, had a purity (95.20%) significantly lower than that of the three-stage countercurrent process in Example 1, indicating insufficient gas-liquid contact and the existence of reaction dead zones or short-circuit phenomena in the single-stage mixed flow mode. Comparative Example 4 omitted the high-temperature calcination step of 430-480℃, resulting in incomplete removal of bound water and adsorbed solvent in the product (water 1240 ppm, NMP 850 ppm), confirming that high-temperature calcination is a necessary step for constructing a final crystal phase with high crystallinity and low impurity content.

Claims

1. A method for producing lithium sulfide by reacting hydrogen sulfide gas with lithium hydroxide NMP solution, characterized in that, Includes the following steps: S1. Lithium hydroxide raw material is continuously dissolved in N-methyl-2-pyrrolidone solvent to obtain a lithium hydroxide-NMP solution with a mass fraction of 5-10%; S2. The lithium hydroxide-NMP solution is continuously pumped into the first stage bubble column of a reaction system consisting of at least three bubble columns connected in series. Simultaneously, gas containing hydrogen sulfide is introduced from the last stage bubble column of the reaction system, causing the solution and gas to undergo a continuous countercurrent reaction in the reaction system to generate a slurry containing lithium sulfide solids. A tube made of NaA-type inorganic pervaporation membrane is installed in the center of the bubble column. The pervaporation membrane tube is arranged vertically. The reaction temperature of the bubble column is 60-80 degrees Celsius, and the internal negative pressure of the pervaporation tube is 10-50 kPa. The water generated in the reaction is removed by the pervaporation membrane in real time. A portion of the hydrogen sulfide also enters the pervaporation membrane tube. The pervaporation membrane is connected to a gas-liquid separator. The water is discharged by gravity, and the hydrogen sulfide is pumped back into the bubble column for circulation. S3. The slurry containing lithium sulfide solid is subjected to continuous solid-liquid separation to obtain lithium sulfide solid, and the lithium sulfide solid is washed. S4. The lithium sulfide solid obtained after rinsing is continuously dried to obtain dry lithium sulfide powder. S5. The dried lithium sulfide powder is calcined at a temperature of 430-480°C in an inert gas atmosphere to obtain the final lithium sulfide product.

2. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 1, characterized in that, In step S1, the continuous dissolution of lithium hydroxide raw material in N-methyl-2-pyrrolidone solvent specifically includes: The process is carried out in a continuous dissolving vessel equipped with jacketed heating and mechanical stirring, and the temperature of the solvent inside the vessel is maintained at 60-100°C by the jacketed heating. The N-methyl-2-pyrrolidone solvent is pumped into the continuous dissolution vessel at a stable flow rate, while the lithium hydroxide raw material is added to the vessel at a precisely controlled rate using a loss-in-weight feeder. The material inside the vessel is mechanically stirred at a speed of 100-300 rpm.

3. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 1, characterized in that, In step S2, the first-stage bubble column of the reaction system, which consists of at least three stages of bubble columns connected in series, specifically includes: The lithium hydroxide-NMP solution is continuously injected from the top of the first-stage bubbling tower; Under the influence of gravity, the solution flows sequentially through each stage of the subsequent bubble column and is finally discharged continuously from the bottom of the last bubble column. The total residence time of the solution in the reaction system is 30-120 min.

4. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 1, characterized in that, In step S2, the continuous countercurrent reaction specifically includes: Hydrogen sulfide gas is independently supplied to the first-stage bubbling tower; The conductivity or pH value of the solution at the outlet of the first-stage bubbling tower is monitored, and the flow rate of the independently supplemented hydrogen sulfide gas is controlled based on the monitoring signal feedback. The exhaust gas discharged from the top of the first-stage bubble column is collected, pressurized, and then re-injected into the second or third-stage bubble column of the reaction system.

5. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 1, characterized in that, In step S3, the rinsing of the lithium sulfide solid specifically includes: The rinsing is performed on a PTFE filter belt conveyor with filtration function; The reaction solution falls onto the PTFE filter belt conveyor, and the solvent will be filtered away; Li2S particles remain on the filter belt conveyor. A rinsing zone is set on the PTFE filter belt conveyor, and the lithium sulfide solid is rinsed in multiple stages by N-methyl-2-pyrrolidone solvent at the front end of the spray head and acetone at the rear end.

6. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 5, characterized in that, The temperature of the N-methyl-2-pyrrolidone solvent is room temperature - 110°C; the acetone is room temperature. The operating speed of the PTFE filter belt conveyor is 0.1-1.0 m / min.

7. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 1, characterized in that, In step S4, the continuous drying of the lithium sulfide solid obtained after rinsing specifically includes: Continuous drying is carried out in a fluidized bed or rake-type vacuum dryer; The drying temperature is 140-250℃, and the vacuum degree is -0.08 to -0.098MPa.

8. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 7, characterized in that, The residence time of the lithium sulfide solid in the fluidized bed or rake vacuum dryer is 2-4 hours.

9. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 1, characterized in that, In step S5, the high-temperature calcination at 430-480°C in an inert gas atmosphere includes: The high-temperature calcination is carried out in a rotary tube furnace; The inert gas is nitrogen or argon, and it is introduced into the rotary tube furnace at a flow rate of 5-20 L / min to maintain a positive pressure inside the furnace. The residence time of the dried lithium sulfide powder in the rotary tube furnace is 1-3 hours.

10. The method for producing lithium sulfide by reacting hydrogen sulfide gas and lithium hydroxide NMP solution according to claim 1, characterized in that, The final lithium sulfide product obtained further includes: The final lithium sulfide product is continuously cooled to room temperature in a closed device; The cooled final lithium sulfide product is then automatically packaged in an inert gas atmosphere.

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