A method for directly synthesizing thionyl chloride using LiFSI byproducts

Abstract

This invention belongs to the field of lithium battery electrolyte technology, specifically relating to a method for directly synthesizing thionyl chloride from LiFSI byproducts. The method involves mixing sulfur, a passivating agent, a catalyst, and a dehydrating agent, pretreating the mixture at high temperature, and then introducing a byproduct gas containing sulfur dioxide and hydrogen chloride, along with oxygen. A one-step synthesis reaction occurs at high temperature. After the reaction, the solid is filtered off to obtain thionyl chloride. This invention directly utilizes the LiFSI byproduct mixed gas without further treatment, converting it into the core raw material SOCl2, which can then be recycled for LiFSI production, achieving high-value utilization of the byproducts. The reaction in this invention is a one-step synthesis in a single reactor, eliminating the need for a high-temperature oxidation reactor and Cl2 storage and transportation system. This significantly simplifies the process, makes operation convenient, and reduces costs considerably. The reaction temperature does not exceed 130°C, making it easy to control and resulting in low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery electrolyte technology, specifically relating to a method for directly synthesizing thionyl chloride using LiFSI byproducts. Background Technology

[0002] LiFSI (lithium bisfluorosulfonylimide, molecular formula F2NO4S2·Li or LiN(SO2F)2) is one of the important electrolytes in lithium batteries. It can be used in traditional liquid electrolytes and is also a major component of solid-state electrolytes. With the rapid development of solid-state batteries, the market demand for LiFSI is also increasing. LiFSI is generally produced by fluorination and lithiation of bischlorosulfonylimide. The production of bischlorosulfonylimide generates a large amount of SO2 and HCl mixed byproduct gas, and the reaction formula is shown below: NH₂SO₃H + ClSO₃H + 2SOCl₂→ ClSO₂NHSO₂Cl + 2SO₂↑ + 3HCl↑, labeled as formula (a).

[0003] Existing technologies for treating this type of exhaust gas involve separation and recovery followed by low-value utilization to produce hydrochloric acid and SO2, as shown in patents CN109205573A and CN112370942B. Alternatively, HCl can be oxidized to Cl2, which is then reacted with elemental sulfur and SO2 to produce SOCl2, as shown in patents CN106698364A and CN119349514B. While the latter method utilizes the byproducts, it requires two conversion steps, posing safety risks related to Cl2 storage and transportation. Furthermore, the HCl oxidation step involves high temperatures, typically above 300°C.

[0004] This application was developed to overcome the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and, in order to improve the utilization value of by-products and reduce safety risks, provide a method for directly synthesizing thionyl chloride from LiFSI by-products. This method directly utilizes the LiFSI by-product mixed gas without treatment, converting it into the core raw material SOCl2, which is then recycled for LiFSI production, achieving high-value utilization of the by-products.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This application provides a method for directly synthesizing thionyl chloride from LiFSI byproducts, which includes the following steps: Sulfur, passivating agent, catalyst, and dehydrating agent are mixed and pretreated at high temperature. Then, byproduct gases containing sulfur dioxide and hydrogen chloride, along with oxygen, are introduced to initiate a one-step synthesis reaction at high temperature. After the reaction, solid and liquid phases are separated (e.g., the solid can be removed by filtration) to obtain crude thionyl chloride. The crude thionyl chloride is then subjected to vacuum distillation at 75-80℃ and a vacuum degree of -0.09 to -0.095 MPa to obtain lithium-ion battery-grade high-purity thionyl chloride SOCl2.

[0007] Furthermore, the passivating agent may be selected from at least one of lithium chloride, zinc chloride, etc., the catalyst may be selected from at least two of ruthenium chloride, titanium chloride, aluminum chloride, etc., and the dehydrating agent may be calcium chloride, etc.

[0008] Furthermore, the amount of passivating agent is 0.1-0.8% of the sulfur mass, the amount of catalyst is 4%-10% of the sulfur mass, and the amount of dehydrating agent is 0.6-1 times the theoretical molar amount of water produced.

[0009] Furthermore, the high-temperature pretreatment is as follows: melting at 80-90℃ for 20-30 minutes under inert gas protection.

[0010] Furthermore, the byproduct gas containing sulfur dioxide and hydrogen chloride is a mixed tail gas of sulfur dioxide and hydrogen chloride generated by the LiFSI production line, wherein the molar ratio of sulfur dioxide to hydrogen chloride is approximately 2:3.

[0011] Furthermore, the equation for the one-step synthesis reaction described in this invention is as follows: S + SO2+ 4HCl + O2+ CaCl2→ 2SOCl2+ CaCl2·2H2O.

[0012] Furthermore, the molar ratio of the reaction raw materials sulfur, sulfur dioxide, hydrogen chloride and oxygen is (0.7-0.75):2:3:(0.8-1), that is, the molar ratio of each raw material is: S:SO2:HCl:O2=(0.7-0.75):2:3:(0.8-1).

[0013] Furthermore, the synthesis reaction temperature is 90-130℃, the pressure is 0.08-0.12MPa, and the time is 2-3h.

[0014] Furthermore, the solid obtained from the solid-liquid separation is calcined at 200-250℃, under a negative pressure of -0.08 to -0.09 MPa and nitrogen protection for 2-3 hours to remove water, and then reused.

[0015] Compared with the prior art, the advantages and beneficial effects of the method of the present invention are as follows: 1) The method of this invention directly utilizes the mixed gas produced by LiFSI without treatment, converting it into the core raw material SOCl2, which is then recycled for LiFSI production, thus realizing the high-value utilization of by-products.

[0016] 2) The method of the present invention is a one-step synthesis in a single reactor, which eliminates the need to build a high-temperature oxidation reactor and a Cl2 storage and transportation device, greatly simplifying the process, making the operation convenient, and significantly reducing the cost.

[0017] 3) The reaction temperature of the method of the present invention does not exceed 130℃, which is easy to control and has low energy consumption.

[0018] 4) In the method of the present invention, the composite catalyst has high catalytic activity and good selectivity, with SOCl2 yield reaching up to 92%. The catalyst has better recycling and reuse properties than traditional FeCl3, making it more suitable for industrial continuous production.

[0019] 5) In the method of the present invention, the dehydrating agent can be calcined and regenerated, and recycled together with the catalyst and passivating agent, further reducing production costs. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. These embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention or the method of implementing the present invention.

[0021] This application provides a method for directly synthesizing thionyl chloride using LiFSI byproducts, as detailed below: Elemental sulfur, passivating agent, catalyst, and dehydrating agent are mixed and melted at 80-90℃ for 20-30 minutes under inert gas protection. Then, a mixture of sulfur dioxide and hydrogen chloride tail gas and oxygen generated from the LiFSI production line is introduced and reacted at 90-130℃ and 0.08-0.12MPa for 2-3 hours. The gas is then discharged, cooled to room temperature, and the solid is filtered off to obtain crude thionyl chloride. Further distillation yields lithium battery-grade thionyl chloride products.

[0022] Furthermore, the passivating agent is selected from lithium chloride or zinc chloride, or a mixture of the two, and is added in very small amounts, only 0.1-0.8% of the sulfur mass. When molten at 80-90℃, the chloride ions in the passivating agent form a monomolecular coordination adsorption layer with the highly active sites on the sulfur surface, completing the surface passivation of sulfur, so that sulfur hardly reacts with oxygen during subsequent synthesis reactions. At the same time, this coordination adsorption layer does not hinder the diffusion of HCl, chlorine-containing active intermediates, and SO2 to the sulfur surface reaction interface, allowing sulfur to preferentially participate in the chlorination reaction and directionally generate SOCl2.

[0023] The catalyst is selected from two or three of ruthenium chloride, titanium chloride, and aluminum chloride, preferably a combination of ruthenium chloride and aluminum chloride (mass ratio 1:3-5), or a combination of titanium chloride and aluminum chloride (mass ratio 1:1-2), and most preferably a combination of ruthenium chloride, titanium chloride, and aluminum chloride (1:1-2:3-5). The catalyst dosage is 4%-10% of the sulfur mass. The synergistic effect of the bimetallic or multimetallic components results in superior catalytic activity and selectivity compared to a single catalyst. Under slightly excess O2 conditions, it efficiently promotes HCl activation, ensuring complete sulfur conversion. The catalyst is in solid form and does not dissolve, volatilize, or enter the product system under reaction conditions, thus avoiding the entry of Fe impurities into the electrolyte compared to traditional Fe-based catalysts.

[0024] The preferred dehydrating agent is calcium chloride, used at a rate of 0.6-1 times the theoretical molar amount of water produced. Calcium chloride irreversibly combines with the water generated in the synthesis reaction to form a stable, non-volatile CaCl2·2H2O solid-phase crystalline hydrate that does not react with SOCl2, exhibiting high water-fixing efficiency. Excess dehydrating agent creates redundancy protection, controlling free water in the system to below 10 ppm and preventing SOCl2 hydrolysis.

[0025] The byproduct gas containing sulfur dioxide and hydrogen chloride is a mixed tail gas of sulfur dioxide and hydrogen chloride generated from the LiFSI production line. The molar ratio of the two components conforms to the molar ratio of reaction formula (a), which is 2:3. Besides sulfur dioxide and hydrogen chloride, this tail gas contains very few other impurities and is almost water-free, making it suitable for direct use in the synthesis reaction.

[0026] The equation for the one-step synthesis reaction is: S + SO2 + 4HCl + O2 + CaCl2 → 2SOCl2 + CaCl2·2H2O, denoted as equation (b).

[0027] Furthermore, the reaction raw materials are used in proportion based on the tail gas, with a molar ratio of S:SO2:HCl:O2=(0.7-0.75):2:3:(0.8-1). Under this ratio, sulfur can react completely, and the remaining raw materials are discharged in gaseous form after the reaction. The reaction product SOCl2 is in liquid form and can be easily separated from the solid dehydrating agent, catalyst, and passivating agent.

[0028] Further purification of crude SOCl2 can be achieved using conventional techniques, such as vacuum distillation at 75-80℃ and a vacuum of -0.09 to -0.095 MPa, to obtain lithium-ion battery-grade high-purity SOCl2.

[0029] Furthermore, the solid obtained from the above solid-liquid separation can be reused after being calcined at 200-250℃, under negative pressure of -0.08 to -0.09 MPa and nitrogen protection for 2-3 hours to remove water.

[0030] Furthermore, the remaining mixed gas after the above synthesis reaction is mainly SO2, containing a small amount of O2 and HCl. It can be condensed to below -10℃ to condense and separate SO2, and then the remaining O2 and HCl gas can be reused in the synthesis reaction.

[0031] In the following examples, all raw materials used are common commercially available products that can be purchased directly, or can be prepared using conventional techniques in the art. Example 1

[0032] Catalyst: Ruthenium chloride + aluminum chloride.

[0033] 1. Raw material preparation: 6.0 kg of elemental sulfur, 0.03 kg of anhydrous LiCl (0.5% of sulfur mass) as passivating agent, 0.42 kg of RuCl3 + AlCl3 catalyst (7% of sulfur mass, mass ratio 1:4), 29.1 kg of anhydrous CaCl2 dehydrating agent (0.7 times the theoretical molar number of water produced); 61.85 kg of mixed SO2 + HCl tail gas (molar ratio 2:3) from the LiFSI production line, and 7.5 kg of industrial pure O2.

[0034] 2. Solid pretreatment: Add elemental sulfur, passivating agent, catalyst and dehydrating agent to the premixing tank, melt and premix at 85°C for 25 min under nitrogen protection, and maintain the system temperature at 85°C for later use.

[0035] 3. One-step synthesis reaction: The pretreated solid mixture is fed into a fixed-bed reactor, heated to 100℃, and the reaction pressure is controlled at 0.1MPa. The molar ratio of S:SO2:HCl:O2 = 0.72:2:3:0.9 is used to continuously introduce SO2+HCl mixed tail gas and O2. The reaction time is 2.5h.

[0036] 4. Product separation and purification: After the reaction is completed, the remaining gaseous impurities are removed, the material in the reactor is cooled to room temperature, the solid is filtered off, and the crude SOCl2 is distilled under reduced pressure at 78℃ and a vacuum degree of -0.092MPa to obtain 38.2kg of lithium-ion battery grade thionyl chloride.

[0037] 5. Test results: SOCl2 yield 85.7%, purity 99.95%, moisture 7ppm, metal impurities ≤0.8ppm, sulfate impurities ≤0.08%.

[0038] 6. Solid reuse: The filtered solids are calcined at 220℃, under negative pressure of -0.085MPa and nitrogen protection for 2.5h to remove water, and then kept for later use. Example 2

[0039] Catalyst: Titanium chloride + aluminum chloride.

[0040] 1. Raw material preparation: 6.0 kg of elemental sulfur, 0.048 kg of anhydrous ZnCl2 passivating agent (0.8% of sulfur mass), 0.48 kg of TiCl4 + AlC3 catalyst (8% of sulfur mass, mass ratio 1:2), 27.1 kg of anhydrous CaCl2 dehydrating agent (0.65 times the theoretical molar number of water produced); 61.85 kg of SO2 + HCl mixed tail gas (molar ratio 2:3) by-product of LiFSI production line, and 8.3 kg of industrial pure O2.

[0041] 2. Solid pretreatment: Add the above-mentioned solid raw materials, elemental sulfur, passivating agent, catalyst and dehydrating agent to the premixing kettle, and melt and premix at 85°C for 25 minutes under nitrogen protection, and maintain the system temperature at 85°C for later use.

[0042] 3. One-step synthesis reaction: The pretreated solid mixture is fed into a fixed-bed reactor, heated to 105℃, and the reaction pressure is controlled at 0.1MPa. The molar ratio of S:SO2:HCl:O2 = 0.72:2:3:1.0 is used to continuously introduce SO2+HCl mixed tail gas and O2. The reaction time is 2.3h.

[0043] 4. Product separation and purification: Same as in Example 1, the crude product was subjected to vacuum distillation to obtain 38.5 kg of lithium-ion battery grade thionyl chloride.

[0044] 5. Test results: SOCl2 yield 86.3%, purity 99.94%, moisture 6ppm, metal impurities ≤0.7ppm, sulfate impurities ≤0.07%. Example 3

[0045] Catalyst: Ruthenium chloride + Titanium chloride.

[0046] 1. Raw material preparation: 6.0 kg of elemental sulfur, 0.024 kg of anhydrous LiCl (0.4% of sulfur by mass) as passivating agent, 0.54 kg of RuCl3 + TiCl4 catalyst (9% of sulfur by mass, mass ratio 1:3), 33.3 kg of anhydrous CaCl2 dehydrating agent (0.8 times the theoretical molar number of water produced); 61.85 kg of SO2 + HCl mixed tail gas (molar ratio 2:3) by-product of LiFSI production line, and 6.7 kg of industrial pure O2.

[0047] 2. Solid pretreatment: Add the above solid raw materials to a premixing kettle, and melt-premix at 88°C for 22 minutes under inert nitrogen protection. Maintain the system temperature at 88°C for later use.

[0048] 3. One-step synthesis reaction: The pretreated solid mixture is fed into a fixed-bed reactor, heated to 110℃, and the reaction pressure is controlled at 0.11MPa. The molar ratio of S:SO2:HCl:O2 = 0.72:2:3:0.8 is used to continuously introduce SO2+HCl mixed tail gas and O2. The reaction time is 2.2h.

[0049] 4. Product separation and purification: Same as in Example 1, the crude product was subjected to vacuum distillation to obtain 35.9 kg of lithium-ion battery grade thionyl chloride.

[0050] 5. Test results: SOCl2 yield 80.5%, purity 99.95%, moisture 8ppm, metal impurities ≤0.9ppm, sulfate impurities ≤0.09%. Example 4

[0051] Catalyst: Ruthenium chloride + Titanium chloride + Aluminum chloride.

[0052] 1. Raw material preparation: 6.0 kg of elemental sulfur, 0.036 kg of anhydrous LiCl (0.6% of sulfur mass) as passivating agent, 0.6 kg of RuCl3+TiCl4+AlCl3 catalyst (10% of sulfur mass, mass ratio 1:2:4), 41.6 kg of anhydrous CaCl2 dehydrating agent (1.0 times the theoretical molar number of water produced); 61.85 kg of mixed SO2+HCl tail gas (molar ratio 2:3) from the LiFSI production line, and 7.5 kg of industrial pure O2.

[0053] 2. Solid pretreatment: Add the above solid raw materials to a premixing kettle, and melt-premix at 86°C for 24 minutes under inert nitrogen protection to complete the surface passivation of sulfur. Maintain the system temperature at 86°C for later use.

[0054] 3. One-step synthesis reaction: The pretreated solid mixture is fed into a fixed-bed reactor, heated to 108℃, and the reaction pressure is controlled at 0.12MPa. The molar ratio of S:SO2:HCl:O2 = 0.72:2:3:0.9 is used to continuously introduce SO2+HCl mixed tail gas and O2. The reaction time is 2.4h.

[0055] 4. Product separation and purification: Same as in Example 1, the crude product was subjected to vacuum distillation to obtain 41.2 kg of lithium-ion battery grade thionyl chloride.

[0056] 5. Test results: SOCl2 yield 92.3%, purity 99.97%, moisture 5ppm, metal impurities ≤0.7ppm, sulfate impurities ≤0.06%. Example 5

[0057] The catalyst, dehydrating agent, and passivating agent are a mixture regenerated using Example 1.

[0058] 1. Raw material preparation: 6.0 kg of elemental sulfur, 29.5 kg of catalyst, dehydrating agent and passivating agent (using the mixture regenerated in Example 1), 61.85 kg of SO2+HCl mixed tail gas (molar ratio 2:3) by-product of LiFSI production line, and 7.5 kg of industrial pure O2.

[0059] 2. Solid pretreatment: Add elemental sulfur and the regenerated mixture to a premixing reactor, and melt-premix at 85°C for 25 minutes under nitrogen protection. Maintain the system temperature at 85°C for later use.

[0060] 3. One-step synthesis reaction: The pretreated solid mixture is fed into a fixed-bed reactor, heated to 100℃, and the reaction pressure is controlled at 0.1MPa. The molar ratio of S:SO2:HCl:O2 = 0.72:2:3:0.9 is used to continuously introduce SO2+HCl mixed tail gas and O2. The reaction time is 2.5h.

[0061] 4. Product separation and purification: After the reaction is completed, the remaining gaseous impurities are removed, the material in the reactor is cooled to room temperature, the solid is filtered out, and the crude SOCl2 is distilled under reduced pressure at 78℃ and a vacuum degree of -0.092MPa to obtain 38.0 kg of lithium-ion battery grade thionyl chloride.

[0062] 5. Test results: SOCl2 yield 85.1%, purity 99.90%, moisture 7ppm, metal impurities ≤0.8ppm, sulfate impurities ≤0.08%.

[0063] Comparative Example 1 No passivating agent is used.

[0064] 1. Experimental conditions: Except for the absence of any passivating agent, all other raw materials, process parameters, and raw material molar ratios were completely consistent with those in Example 1.

[0065] 2. Experimental results: The SOCl2 yield was 10.3%, and slight coking occurred on the inner wall of the equipment. This is because a large amount of elemental sulfur underwent an oxidation side reaction with O2 during the reaction, generating SO3 and sulfate impurities.

[0066] Comparative Example 2 No catalyst is used.

[0067] 1. Experimental conditions: Except for the absence of any catalyst, all other raw materials, process parameters, and raw material molar ratios were completely consistent with those in Example 1.

[0068] 2. Experimental results: The yield of SOCl2 was 0%. The reason is that without a catalyst, HCl cannot be activated, and the synthesis reaction cannot proceed.

[0069] Comparative Example 3 Do not use dehydrating agents.

[0070] 1. Experimental conditions: Except for the absence of anhydrous CaCl2, all other raw materials, process parameters, and raw material molar ratios were completely consistent with those in Example 1.

[0071] 2. Experimental results: The yield of SOCl2 was 0%. This is because the synthesis reaction cannot proceed in a non-dry environment.

Claims

1. A method for directly synthesizing thionyl chloride using LiFSI byproducts, characterized in that, Includes the following steps: Sulfur, passivating agent, catalyst, and dehydrating agent are mixed and pretreated at high temperature. Then, byproduct gas containing sulfur dioxide and hydrogen chloride and oxygen are introduced to carry out a one-step synthesis reaction at high temperature. After the reaction is completed, solid and liquid are separated to obtain thionyl chloride.

2. The method according to claim 1, characterized in that, The passivating agent is selected from at least one of lithium chloride and zinc chloride; the amount of the passivating agent used is 0.1-0.8% of the mass of sulfur.

3. The method according to claim 1, characterized in that, The catalyst is selected from at least two of ruthenium chloride, titanium chloride, and aluminum chloride, and the dehydrating agent is calcium chloride.

4. The method according to claim 1, characterized in that, The catalyst is used at a rate of 4%-10% of the sulfur mass, and the dehydrating agent is used at a rate of 0.6-1 times the theoretical molar amount of water produced.

5. The method according to claim 1, characterized in that, The high-temperature pretreatment is as follows: melting at 80-90℃ for 20-30 minutes under inert gas protection.

6. The method according to claim 1, characterized in that, The byproduct gas containing sulfur dioxide and hydrogen chloride is a mixed tail gas of sulfur dioxide and hydrogen chloride generated by the LiFSI production line.

7. The method according to claim 1, characterized in that, The molar ratio of the reactants sulfur, sulfur dioxide, hydrogen chloride, and oxygen is (0.7-0.75):2:3:(0.8-1).

8. The method according to claim 1, characterized in that, The synthesis reaction is carried out at a temperature of 90-130℃, a pressure of 0.08-0.12MPa, and a time of 2-3h.

9. The method according to claim 1, characterized in that, The solid obtained from the solid-liquid separation is calcined at 200-250℃, under a negative pressure of -0.08 to -0.09 MPa and nitrogen protection for 2-3 hours to remove water before being reused.

10. The method according to claim 1, characterized in that, The obtained thionyl chloride was subjected to vacuum distillation at 75-80℃ and a vacuum degree of -0.09 to -0.095 MPa to obtain lithium-ion battery grade thionyl chloride.