A method for photocatalytic preparation of metal sulfides

Abstract

The application provides a method for photocatalytic preparation of metal sulfide, comprising: performing photocatalytic reaction on solid metal hydroxide and hydrogen sulfide gas under the condition of ultraviolet light irradiation to obtain solid metal sulfide. The method can be combined with a fluidized bed reactor to reduce the reaction activation energy, improve the interface reaction rate and realize continuous production. The method provided by the application has high efficiency, low energy consumption and high purity of the prepared product. Compared with the existing hot sulfuration method, the reaction time can be greatly shortened, the efficiency can be improved by more than 50%, high temperature does not need to be maintained for a long time, the overall energy consumption can be reduced by more than 40%, the by-products are few, the water content in the tail gas can be stably controlled to be less than 100 ppm, and the prepared metal sulfide meets the requirements of battery-grade materials.

Description

Technical Field

[0001] This invention belongs to the field of sulfide preparation technology, specifically relating to a method for photocatalytic preparation of metal sulfides. Background Technology

[0002] Metal sulfides are key functional materials in the fields of new energy batteries, photoelectric conversion, and catalytic materials. Lithium sulfide is a core raw material for the cathode and sulfide solid electrolyte of lithium-sulfur batteries, while sodium sulfide and potassium sulfide are widely used in sodium-sulfur batteries, potassium-ion batteries, and high-temperature ceramics. Existing methods for preparing metal sulfides have some drawbacks. Taking lithium sulfide as an example, existing methods mainly include carbothermic reduction, the traditional hydrogen sulfide-lithium hydroxide method, metathesis, hydrazine hydrate-assisted sulfidation, and direct reaction of lithium metal with sulfur. The carbothermic reduction method requires temperatures above 700℃ and an excess carbon source; the byproducts CO / CO2 are difficult to separate, easily introducing impurities, and has high energy consumption. The traditional hydrogen sulfide-lithium hydroxide method is usually carried out in a closed reactor, with a slow reaction rate requiring several hours to tens of hours, poor mass transfer, and a tendency to form localized oversulfidation byproducts (such as Li2S2), making continuous operation difficult. The metathesis method (e.g., using LiCO3 and Na2S for metathesis reaction) requires multiple steps, resulting in high raw material costs and limited yield. The hydrazine hydrate-assisted sulfidation method requires the use of toxic and flammable hydrazine reagents, posing significant safety risks and severe environmental pollution. The direct reaction of lithium metal with sulfur produces intense exothermic reactions, is difficult to control, and carries an explosion hazard, limiting its application to small-scale laboratory synthesis. Therefore, the aforementioned existing methods generally suffer from common drawbacks such as high energy consumption, low reaction efficiency, poor safety, inability to be continuous, and unstable product purity.

[0003] Therefore, there is an urgent need to develop a method for preparing metal sulfides that is efficient, energy-saving, allows for continuous operation, and is environmentally friendly. Summary of the Invention

[0004] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions: The main objective of this invention is to provide a method for photocatalytic preparation of metal sulfides, comprising: subjecting solid metal hydroxide and hydrogen sulfide gas to a photocatalytic reaction under ultraviolet light irradiation to obtain solid metal sulfides.

[0005] The method for preparing metal sulfides based on ultraviolet photocatalysis provided by this invention is highly efficient, low in energy consumption, and produces high-purity products that meet battery-grade standards.

[0006] In some embodiments, the wavelength of the ultraviolet light is 250-365 nm.

[0007] In some embodiments, the luminous flux of the ultraviolet light is 30-120 mW / cm², preferably 50-90 mW / cm².

[0008] In some embodiments, the water content in the exhaust gas is monitored during the reaction process, and the reaction is terminated when the water content in the exhaust gas drops below 100 ppm. For example, an online mass spectrometer or infrared analyzer can be used to monitor the water content in the exhaust gas.

[0009] The method provided by this invention is highly efficient, reducing the reaction time by more than 50% compared to a control method without ultraviolet light irradiation, thus enabling the rapid preparation of metal sulfides. In some preferred embodiments, the photocatalytic reaction time is 30-240 minutes.

[0010] In some embodiments, the reaction temperature of the photocatalytic reaction is 50°C to 350°C.

[0011] In some embodiments, the photocatalyst used in the photocatalytic reaction includes one or more of titanium dioxide, zinc oxide, tin oxide, tungsten oxide, cerium oxide, cadmium sulfide, zinc sulfide, copper sulfide, molybdenum sulfide, and tungsten sulfide, but is not limited thereto.

[0012] In some embodiments, a mixed gas containing hydrogen sulfide gas and a carrier gas is brought into full contact with the metal hydroxide to carry out the photocatalytic reaction, wherein the volume concentration of hydrogen sulfide gas in the mixed gas is 1% to 10%. The carrier gas includes, for example, nitrogen, argon, etc.

[0013] In some embodiments, the concentration of hydrogen sulfide gas in the mixed gas adopts any one of a constant mode, a decreasing mode, or an increasing mode.

[0014] In some embodiments, in the constant mode, the volume concentration of hydrogen sulfide gas in the mixed gas is 1% to 10% and remains constant during the reaction.

[0015] In some embodiments, in the decreasing mode, the volume concentration of lithium sulfide gas in the mixed gas is 8%-10% in the first reaction stage and 2%-4% in the second reaction stage. When the water content in the exhaust gas drops to 50% of the initial water content, the volume concentration is switched from the first reaction stage to the second reaction stage.

[0016] In some embodiments, in the incremental mode, the volume concentration of lithium sulfide gas in the mixed gas is 1%-2% in the first reaction stage and 6%-8% in the second reaction stage. When the water content in the exhaust gas drops to 50% of the initial water content, the volume concentration changes from the first reaction stage to the second reaction stage.

[0017] The preferred mode for controlling the concentration of hydrogen sulfide gas is the decreasing mode. In this mode, the initial reaction rate is faster, thus requiring a shorter reaction time (i.e., a shorter time is required for the water content in the tail gas to decrease to below 100 ppm); and it can suppress side reactions, thereby further improving the purity of the product.

[0018] In some embodiments, the photocatalytic reaction involves an excess of hydrogen sulfide gas relative to metal hydroxide, on a stoichiometric basis, and the excess is no more than 10%.

[0019] In some embodiments, the metal hydroxide includes one or a combination of lithium hydroxide, sodium hydroxide, and potassium hydroxide. For example, lithium sulfide is prepared using lithium hydroxide, sodium sulfide is prepared using sodium hydroxide, and potassium sulfide is prepared using potassium hydroxide.

[0020] In some embodiments, the particle size D50 of the metal hydroxide is 380 μm to 420 μm. Using raw materials within this range ensures good fluidization performance and mass transfer efficiency.

[0021] In some embodiments, the method employs a fluidized bed reactor, which includes a fluidized bed body and an ultraviolet lamp source; the fluidized bed body has a material channel inside, and a photocatalyst layer is disposed on the inner wall of the fluidized bed body; the ultraviolet lamp source is disposed on the inner side wall of the fluidized bed body, and the ultraviolet light emitted by it can irradiate into the material channel.

[0022] The above-mentioned photocatalytic preparation of metal sulfides using a fluidized bed reactor can significantly reduce the reaction activation energy, increase the interfacial reaction rate, and achieve continuous operation, making it suitable for industrial scale-up. The inner wall of the fluidized bed has a uniform and dense photocatalyst layer, which increases the density of surface active sites and promotes the efficient conduction of the photocatalytic reaction.

[0023] In some embodiments, a protective sleeve is provided around the ultraviolet lamp source, and a cooling chamber is provided between the ultraviolet lamp source and the protective sleeve. The cooling chamber is used to control the operating temperature of the ultraviolet lamp source. The cooling chamber can be connected to the inlet and outlet of external circulating gas to achieve cooling. Integrating the ultraviolet photocatalytic function into the inner wall of the fluidized bed reactor, and using a protective sleeve and circulating cooling gas heat dissipation structure, can ensure the long-term stable operation of the light source. The protective sleeve is, for example, a quartz protective sleeve. The quartz sleeve and circulating cooling design can extend the life of the ultraviolet lamp by more than three times.

[0024] In some embodiments, the thickness of the photocatalyst layer is 100 nm to 500 nm. For example, the photocatalyst layer contains anatase-type nanoscale titanium dioxide (TiO2) within this thickness range.

[0025] In some embodiments, the method for photocatalytic preparation of metal sulfides specifically includes: feeding metal hydroxide into the material channel of the fluidized bed body; turning on the ultraviolet light source, setting the ultraviolet wavelength to 250-365 nm and the light flux to 30-120 mW / cm²; simultaneously introducing a mixed gas containing hydrogen sulfide gas and a carrier gas, wherein the volume concentration of hydrogen sulfide in the mixed gas is 1%~10%; continuing the reaction for 30 min-240 min, monitoring the water content in the exhaust gas during the reaction, and stopping the gas supply when the water content drops below 100 ppm, thus ending the reaction.

[0026] In some embodiments, the feed rate of the metal hydroxide is 50~500 g / h.

[0027] In some embodiments, the flow rate of hydrogen sulfide gas is 0.5~2.0 m / s.

[0028] In some embodiments, the carrier gas flow rate is 1.5-2.0 m / s.

[0029] In some embodiments, when the metal hydroxide used has water of crystallization, the method further includes: feeding the metal hydroxide with water of crystallization into the material channel, heating it under an inert atmosphere to maintain its sulfidation state for dehydration and drying, and then carrying out a photocatalytic reaction. For example, lithium hydroxide monohydrate is fed into a fluidized bed and heated to 150°C under an inert gas atmosphere, maintaining the fluidized state for dehydration and drying. When the temperature inside the bed rises linearly from 150°C to above 200°C, dehydration is considered complete, the heating source for the drying stage is turned off, and hydrogen sulfide gas is introduced to initiate the reaction. The fluidized bed reactor may also include a temperature sensor and a gas flow control structure for real-time monitoring of the dehydration endpoint of the metal hydroxide and triggering the reaction start. This intelligent control mechanism, which determines the dehydration endpoint by temperature and initiates sulfidation by light, can avoid premature or delayed start-up.

[0030] Compared with existing technologies, the present invention has at least some or all of the following beneficial effects: The ultraviolet photocatalytic method for preparing metal sulfides provided by the present invention is highly efficient, energy-saving, and produces products with high purity; compared with existing thermal sulfidation methods, the method of the present invention can significantly reduce reaction time, increase efficiency by more than 50%, and eliminate the need to maintain high temperatures for extended periods, resulting in an overall energy consumption reduction of more than 40%; fewer byproducts are produced, and the water content in the exhaust gas can be stably controlled below 100 ppm, with the obtained metal sulfides meeting the requirements for battery-grade materials. Furthermore, the method of the present invention does not require the use of toxic reagents, does not produce harmful gas emissions, and the purified exhaust gas meets emission standards, making it a green and environmentally friendly method. Detailed Implementation

[0031] The invention will be more fully understood through the following detailed description of embodiments. The detailed embodiments disclosed herein are merely illustrative, and the invention may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims.

[0032] In addition, unless otherwise specified, all raw materials used in the following embodiments can be purchased from the market or other sources, and all production and testing equipment used are known in the art, as are the testing methods used.

[0033] Example 1 Example 1 provides a method for photocatalytic preparation of lithium metal sulfide based on a fluidized bed reactor.

[0034] The fluidized bed reactor used in this embodiment is a vertical cylindrical fluidized bed with a diameter of Φ300 mm and a height of 2.5 m. It has six ultraviolet lamps, each 800 mm long, laterally distributed on the inner wall of the fluidized bed body. Each lamp is encased in a transparent quartz sleeve (3 mm thick), with an aluminum reflective film coated on the inner side of the sleeve. An annular cooling chamber is provided between the ultraviolet lamps and the sleeve, connecting the external circulating gas inlet and outlet to control the lamp operating temperature. During operation, cooling gas (nitrogen) enters from the annular chamber and flows upwards, carrying away heat, with the outlet temperature controlled at 40-60℃. The stainless steel inner wall of the fluidized bed is coated with a 200 nm thick photocatalyst coating; the photocatalyst is anatase-type nano-sized titanium dioxide. A platinum resistance temperature probe is also installed in the middle of the fluidized bed, sampling at a frequency of 10 times / minute.

[0035] The specific methods for photocatalytic preparation of lithium metal sulfide in this embodiment include: (1) Add lithium hydroxide monohydrate (particle size D50 = 400 μm) continuously to the fluidized bed at a rate of 300 g / h; turn on the nitrogen flow and heat to 150 °C to keep the lithium hydroxide in a fluidized state and start dehydration. Observe the temperature change curve. When the temperature shows a steep upward trend from 150 °C to 200 °C (duration < 5 minutes), the dehydration is completed.

[0036] (2) A mixture of hydrogen sulfide gas and nitrogen gas is introduced at a flow rate of 1.75 m / s, wherein the volume concentration of hydrogen sulfide gas is kept constant at 5%, and the total amount of hydrogen sulfide gas is controlled to be 8% in excess based on the stoichiometric ratio; at the same time, the ultraviolet lamp is turned on with an ultraviolet light wavelength of 300 nm and an average light flux of 80 mW / cm²; during the reaction, the water content in the tail gas is monitored in real time using an online mass spectrometer. When the water content is lower than 100 ppm, the gas supply is stopped, the ultraviolet lamp is turned off, and the reaction is terminated.

[0037] (3) Collect the obtained lithium sulfide product, grind and crush it to a particle size of less than 50 μm to form a battery-grade lithium sulfide product.

[0038] Example 2 Example 2 is basically the same as Example 1, except that in step (2), the volume concentration of hydrogen sulfide gas in the mixed gas is in a decreasing mode. In the first reaction stage, the volume concentration of hydrogen sulfide gas in the mixed gas is 8%. When the reaction proceeds to the point where the water content in the tail gas drops to 50% of the initial water content, the volume concentration of hydrogen sulfide gas in the mixed gas is adjusted to 3%, that is, the second reaction stage is carried out.

[0039] The rest is the same as in Example 1, and will not be described again here.

[0040] Example 3 Example 3 is basically the same as Example 1, except that in step (2), the volume concentration of hydrogen sulfide gas in the mixed gas is in an increasing mode. In the first reaction stage, the volume concentration of hydrogen sulfide gas in the mixed gas is 2%. When the reaction proceeds to the point where the water content in the tail gas drops to 50% of the initial water content, the volume concentration of hydrogen sulfide gas in the mixed gas is adjusted to 8%, that is, the second reaction stage is carried out.

[0041] The rest is the same as in Example 1, and will not be described again here.

[0042] Example 4 Example 4 is essentially the same as Example 2, except that lithium hydroxide is replaced with sodium hydroxide to prepare sodium sulfide. The water content in the exhaust gas is less than 100 ppm, the reaction time is 4 hours, and the purity of the obtained sodium sulfide product is over 99%. The rest of the process is the same as in Example 1 and will not be repeated here.

[0043] Example 5 Example 4 is basically the same as Example 2, except that lithium hydroxide is replaced with potassium hydroxide to obtain potassium sulfide product. The rest is the same as Example 1, and will not be described again here.

[0044] Comparative Example 1 Comparative Example 1 is basically the same as Example 2, except that the UV lamp is turned off during the reaction. The rest is the same as in Example 1, and will not be described again here.

[0045] Table 1 shows the reaction time, tail gas water content, and energy consumption of Examples 1-5 and Comparative Example 1, as well as the product purity and conversion rate; wherein, the tail gas water content refers to the tail gas water content when the reaction time shown in Table 1 is reached.

[0046] Table 1. Reaction times and energy consumption of Examples 1-3 and Comparative Example 1

[0047] As shown in Table 1, compared to Comparative Example 1, Examples 1-3 significantly shortened the reaction time, obtained products with higher purity and conversion rate. Comparative Example 1, lacking photocatalytic activation, exhibited slow reaction kinetics and hindered mass transfer. Comparing Examples 1-3, compared to Examples 1 and 3, Example 2, using a decreasing hydrogen sulfide gas introduction mode, required a shorter reaction time and lower energy consumption. This is because, by exciting the photocatalyst (such as nano-TiO2) to generate photogenerated electron-hole pairs, photogenerated holes can effectively reduce the activation energy of the main reaction (the reaction of metal hydroxide with H2S to form metal sulfides), thereby significantly increasing the reaction rate. However, if the H2S concentration remains too high during the reaction, the active sulfur atoms generated by photolysis will further react with the already formed metal sulfides to form polysulfides (such as Li2S2, Li2S4, etc.). Simultaneously, photogenerated holes may also... 2- Excessive oxidation to byproducts such as elemental sulfur or sulfites leads to a decrease in product purity. Example 2 employs a decreasing reaction mode to achieve an optimal match between reaction kinetics and side reaction suppression: In the initial stage of the reaction, the metal hydroxide surface has abundant active sites, and the main reaction is controlled by chemical kinetics. Using a high concentration of 8%-10% hydrogen sulfide gas provides a large driving force for the reaction, rapidly advancing the main reaction process. At this time, the main reaction is absolutely dominant, and the risk of side reactions is low. In the middle and late stages of the reaction, as most of the metal hydroxide is converted into metal sulfides, the product layer thickens, and the reaction becomes diffusion-controlled. At the same time, free sulfur gradually accumulates in the system, and the risk of side reactions increases significantly. At this time, reducing the concentration of hydrogen sulfide gas to 2%-4% not only reduces the rate of free sulfur generation by photolysis and suppresses over-sulfidation, but also avoids excessive consumption of photogenerated holes in the deep oxidation of H2S. Thus, while ensuring rapid completion of the reaction, the generation of byproducts is minimized, ultimately achieving the best overall effect of shorter reaction time, lower energy consumption, higher product purity, and higher conversion rate.

[0048] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments. For example, they used ultraviolet light with wavelengths of 250nm and 365nm, and set the luminous flux to 50mW / cm² and 90 mW / cm², and kept the volume concentration of hydrogen sulfide gas in the mixed gas constant at 1% and 10%, and obtained relatively ideal results in all cases.

[0049] All aspects, embodiments, features, and examples of this invention should be considered illustrative and used to explain and illustrate the invention, but not to limit it. The scope of the invention is defined only by the claims.

[0050] In summary, the method for preparing metal sulfides based on ultraviolet photocatalysis provided by this invention has the advantages of high efficiency, low energy consumption, and high product purity. It can also achieve clean and continuous preparation, and has good prospects for large-scale industrial production applications.

[0051] Although the invention has been described with reference to the above embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that substantially equivalents can be substituted for elements in the described embodiments. Therefore, the invention is not intended to be limited to the specific embodiments disclosed, but rather to encompass all embodiments falling within the scope defined by the claims.

Claims

1. A method for photocatalytic preparation of metal sulfides, characterized in that, include: Solid metal sulfides are prepared by photocatalytic reaction of solid metal hydroxides and hydrogen sulfide gas under ultraviolet light irradiation.

2. The method for photocatalytic preparation of metal sulfides according to claim 1, characterized in that, The wavelength of the ultraviolet light is 250-365 nm, and / or the luminous flux of the ultraviolet light is 50-90 mW / cm². And / or, monitor the water content in the exhaust gas during the reaction process, and terminate the reaction when the water content in the exhaust gas drops below 100 ppm; And / or, the photocatalytic reaction is carried out at a temperature of 50°C to 350°C and for a reaction time of 30 min to 240 min; And / or, the photocatalyst used in the photocatalytic reaction includes one or more of the following: titanium dioxide, zinc oxide, tin oxide, tungsten oxide, cerium oxide, cadmium sulfide, zinc sulfide, copper sulfide, molybdenum sulfide, and tungsten sulfide.

3. The method for photocatalytic preparation of metal sulfides according to claim 1, characterized in that, The photocatalytic reaction is carried out by fully contacting the metal hydroxide with a mixed gas containing hydrogen sulfide gas and a carrier gas, wherein the volume concentration of hydrogen sulfide gas in the mixed gas is 1% to 10%.

4. The method for photocatalytic preparation of metal sulfides according to claim 3, characterized in that, The concentration of hydrogen sulfide gas in the mixed gas is adopted in any one of the following modes: constant mode, decreasing mode, or increasing mode. And / or, on a stoichiometric basis, the photocatalytic reaction process involves an excess of hydrogen sulfide gas relative to the metal hydroxide, with the excess not exceeding 10%.

5. The method for photocatalytic preparation of metal sulfides according to claim 4, characterized in that, In the constant mode, the volume concentration of hydrogen sulfide gas in the mixed gas is 1% to 10% and remains constant during the reaction. And / or, in the decreasing mode, in the first reaction stage, the volume concentration of lithium sulfide gas in the mixed gas is 8%-10%, and in the second reaction stage, the volume concentration of lithium sulfide gas in the mixed gas is 2%-4%; And / or, in the incremental mode, in the first reaction stage, the volume concentration of lithium sulfide gas in the mixed gas is 1%-2%, and in the second reaction stage, the volume concentration of lithium sulfide gas in the mixed gas is 6%-8%.

6. The method for photocatalytic preparation of metal sulfides according to claim 1, characterized in that, The metal hydroxide includes one or more of lithium hydroxide, sodium hydroxide, and potassium hydroxide; And / or, the particle size D50 of the metal hydroxide is 160 μm to 240 μm.

7. The method for photocatalytic preparation of metal sulfides according to any one of claims 1-6, characterized in that, The method employs a fluidized bed reactor, which includes a fluidized bed body and an ultraviolet lamp source. The fluidized bed body has a material channel inside, and a photocatalyst layer is provided on the inner wall of the fluidized bed body. The ultraviolet lamp source is located on the inner side wall of the fluidized bed body, and the ultraviolet light emitted by it can irradiate into the material channel.

8. The method for photocatalytic preparation of metal sulfides according to claim 7, characterized in that, The ultraviolet lamp source is provided with a protective sleeve, and a cooling cavity is provided between the ultraviolet lamp source and the protective sleeve. The cooling cavity is used to control the working temperature of the ultraviolet lamp source.

9. The method for photocatalytic preparation of metal sulfides according to claim 7, characterized in that, Specifically, it includes: The metal hydroxide is fed into the material channel of the fluidized bed body; the ultraviolet light source is turned on, and the ultraviolet wavelength is set to 250-365 nm with a light flux of 50-90 mW / cm²; at the same time, a mixed gas containing hydrogen sulfide and a carrier gas is introduced, wherein the volume concentration of hydrogen sulfide in the mixed gas is 1%~10%; the water content in the tail gas is monitored during the reaction, and when the water content in the tail gas drops below 100 ppm, the gas supply is stopped and the reaction ends.

10. The method for photocatalytic preparation of metal sulfides according to claim 9, characterized in that, When the metal hydroxide used has water of crystallization, the process further includes: feeding the metal hydroxide with water of crystallization into the material channel, heating it under an inert atmosphere to maintain its sulfidation state for dehydration and drying, and then carrying out a photocatalytic reaction.

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