A method for cleaning and recycling of a lithium bisfluorosulfonylimide separation filtrate

Abstract

The present application relates to a kind of bifluorosulfonylimide lithium separation filtrate resourceization clean processing method, comprising the following steps: step 1, intermediate conversion: lithium hydroxide is added to bifluorosulfonylimide lithium separation filtrate, and reaction generates bifluorosulfonylimide lithium and water, thionyl chloride reacts with the water generated, and is decomposed into sulfur dioxide and hydrogen chloride gas, gas enters waste gas treatment system, and reaction liquid is reserved;Step 2, lithium salt recovery: the reaction liquid of step 1 is filtered, and bifluorosulfonylimide lithium crude product is recovered;Filtrate is reserved;Step 3, solvent fractionation: the filtrate is transferred to solvent fractionation column, at 40~50 ℃ temperature, realize the separation of dichloromethane and thionyl chloride, and recover dichloromethane crude product and thionyl chloride crude product.The present application can realize the recovery and resource utilization of organic solvent and lithium salt, and cost is low, processing efficiency is high, only a small amount of waste gas is produced, almost no waste water and hazardous waste are produced, and the unity of environmental and economic benefits is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of filtrate treatment, and particularly relates to a method for cleaning and recycling of lithium bisfluorosulfonylimide separation filtrate. BACKGROUND

[0002] Lithium bisfluorosulfonylimide is a new type of lithium salt, which is widely used in the field of lithium batteries because it can overcome the shortcomings of traditional lithium hexafluorophosphate lithium salt, such as sensitivity to water and easy decomposition under high temperature and high pressure, and has the advantages of high thermal stability, hydrolysis resistance, high temperature resistance, high conductivity and inhibition of battery swelling. Lithium bisfluorosulfonylimide is usually synthesized by taking chlorosulfonic acid, dichlorosulfoxide, chlorosulfonyl isocyanate, sulfamic acid, hydrogen fluoride, lithium hydroxide monohydrate and dichloromethane as raw materials. During the separation process after salification, salt-containing and solvent filtrate, i.e. lithium bisfluorosulfonylimide separation filtrate, is produced. The filtrate contains 0.3-0.4% lithium bisfluorosulfonylimide, 92-93% dichloromethane, 0.5-0.8% bisfluorosulfonylimide acid, 5.5-6.5% dichlorosulfoxide and 0.1-0.3% impurities.

[0003] For the lithium bisfluorosulfonylimide separation filtrate produced in the production process of lithium bisfluorosulfonylimide, the lithium bisfluorosulfonylimide production enterprises currently generally adopt the recycling and treatment method as shown in the formula (I), i.e. the lithium bisfluorosulfonylimide separation filtrate is first washed with water to remove dichlorosulfoxide, then the bisfluorosulfonylimide acid is converted into sodium bisfluorosulfonylimide by sodium hydroxide alkaline washing, and then the dichloromethane crude product is separated from the salt-containing wastewater by using the layer separation technology; the dichloromethane crude product is dried, rectified and then dichloromethane is obtained after drying, which is recycled to the production process of lithium bisfluorosulfonylimide, and the salt-containing wastewater needs to be further treated before being discharged. Figure 1

[0004] The recycling and treatment method has the following problems:

[0005] 1) In the water washing process, the dichlorosulfoxide is completely decomposed into sulfur dioxide and hydrogen chloride due to the addition of water, and a large amount of waste gas is generated. Moreover, the waste gas is also mixed with dichloromethane gas when it is discharged, so the waste gas treatment is difficult and the cost is high.

[0006] ​2) Due to the addition of a large amount of water in the water washing process, the content of water in the lithium bisfluorosulfonylimide separation filtrate is high, so that the sulfur dioxide and hydrogen chloride generated by the decomposition of thionyl chloride are partially dissolved in water; After the alkali washing process, sodium chloride and sodium sulfite mixed salt will be generated, in addition, in the alkali washing process, lithium bisfluorosulfonylimide reacts with sodium hydroxide to generate sodium bisfluorosulfonylimide, therefore, there are at least sodium chloride, sodium sulfite, lithium bisfluorosulfonylimide, sodium bisfluorosulfonylimide and sodium hydroxide in the salt-containing wastewater separated after the alkali washing, due to the large number of mixed salt types, it brings great difficulty to the subsequent solid waste treatment, greatly increases the cost of solid waste treatment, and does not conform to the principle of resource recycling.

[0007] 3) In the alkali washing process, the dichloromethane crude product separated by layering still contains water, sodium hydroxide and other impurities, which cannot be directly used and still needs a series of operations such as drying, rectification and drying again to remove impurities, which increases the post-treatment cost of dichloromethane, and also easily causes secondary pollution problems such as waste gas and still residue.

[0008] Therefore, it is very important to develop a lithium bisfluorosulfonylimide separation filtrate resource clean treatment method, which can realize the recycling and resource utilization of organic solvents and lithium salts in lithium bisfluorosulfonylimide separation filtrate, effectively solve the problems of high cost, low efficiency, generation of a large amount of wastewater, waste gas and hazardous waste, poor environmental and economic benefits, and the like existing in the traditional technology. SUMMARY

[0009] The purpose of the present application is to overcome the defects in the prior art, and provide a lithium bisfluorosulfonylimide separation filtrate resource clean treatment method, which can realize the recycling and resource utilization of organic solvents and lithium salts in lithium bisfluorosulfonylimide separation filtrate, and has low cost, high treatment efficiency, only generates a small amount of waste gas, almost does not generate wastewater and hazardous waste, and realizes the unity of environment and economic efficiency.

[0010] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0011] A lithium bisfluorosulfonylimide separation filtrate resource clean treatment method, comprising the following steps:

[0012] Step 1, intermediate conversion: lithium hydroxide is added to the lithium bisfluorosulfonylimide separation filtrate, and lithium bisfluorosulfonylimide and water are generated by reaction, the thionyl chloride in the lithium bisfluorosulfonylimide separation filtrate reacts with the generated water to decompose into sulfur dioxide and hydrogen chloride gas, and the gas enters the waste treatment system, and the reaction liquid is reserved;

[0013] Step 2, lithium salt recovery: filtering the reaction liquid after the reaction in step 1, and recovering the filter residue, i.e. lithium bisfluorosulfonylimide crude product; the filtrate is reserved;

[0014] Step 3, solvent fractionation: the filtrate obtained in step 2 is transferred to a solvent fractionation column, and dichloromethane and dichlorosulfoxide are separated at a temperature of 40-50℃, and the crude dichloromethane is recovered from the top of the fractionation column; the bottom of the column is the crude dichlorosulfoxide.

[0015] As a further technical solution, after step 3, step 4, solvent rectification, is further included, wherein the solvent rectification includes dichloromethane rectification and dichlorosulfoxide rectification.

[0016] A, dichloromethane rectification: the crude dichloromethane obtained in step 3 is transferred to a dichloromethane rectification column, and rectified at a temperature of 42-44℃, and the dichloromethane is recovered from the top; the crude dichlorosulfoxide obtained from the bottom of the dichloromethane rectification column;

[0017] B, dichlorosulfoxide rectification: the crude dichlorosulfoxide obtained in step 3 is transferred to a dichlorosulfoxide rectification column, and rectified at a temperature of 45-50℃, and the crude dichloromethane is recovered from the top of the dichlorosulfoxide rectification column, and the dichlorosulfoxide is recovered from the bottom.

[0018] As a further technical solution, in step 4, the crude dichlorosulfoxide obtained from the bottom of the dichloromethane rectification column is combined with the crude dichlorosulfoxide obtained in step 3 for subsequent processing.

[0019] The crude dichloromethane recovered from the top of the dichlorosulfoxide rectification column is combined with the crude dichlorosulfoxide obtained in step 3 for subsequent processing.

[0020] As a further technical solution, the dichloromethane and dichlorosulfoxide prepared in step 4 are reused in the production system of lithium bisfluorosulfonylimide.

[0021] As a further technical solution, in step 4, the crude dichloromethane is preheated to 38-39℃ before being transferred to the dichloromethane rectification column.

[0022] The crude dichlorosulfoxide is preheated to 38-39℃ before being transferred to the dichlorosulfoxide rectification column.

[0023] The preheating is performed using a heat exchanger, and the heat source for the heating is steam or secondary steam generated in the lithium bisfluorosulfonylimide production system.

[0024] As a further technical solution, in step 1, the lithium bisfluorosulfonylimide separation filtrate contains lithium bisfluorosulfonylimide, bisfluorosulfonylimide acid, dichlorosulfoxide, dichloromethane, and impurities.

[0025] As a further technical solution, in the lithium bisfluorosulfonylimide separation filtrate, the content of lithium bisfluorosulfonylimide is 0.3-0.4%; the content of bisfluorosulfonylimide acid is 0.5-0.8%; the content of dichlorosulfoxide is 5.5-6.5%; the content of dichloromethane is 92-93%; and the content of impurities is 0.1-0.3%.

[0026] As a further technical solution, in step 1, the lithium hydroxide adopts lithium hydroxide monohydrate;

[0027] When the lithium hydroxide is added, the lithium hydroxide is added in a molar ratio of 1:(1.0-1.3) of lithium hydroxide to bisfluorosulfonylimide acid;

[0028] After adding lithium hydroxide, the reaction is carried out at 90-120 DEG C for 7-9h, and the reaction is completed.

[0029] As a further technical solution, the crude lithium bisfluorosulfonylimide recovered in step 2 is refined to obtain lithium bisfluorosulfonylimide.

[0030] As a further technical solution, when the crude lithium bisfluorosulfonylimide recovered in step 2 is refined, the refined unit of the lithium bisfluorosulfonylimide production system is combined for refining.

[0031] Compared with the prior art, the beneficial effects of the present application are:

[0032] 1. The present application directly recycles and recovers the lithium bisfluorosulfonylimide separation filtrate in anhydrous system, and the water introduced in the process is only because the added lithium hydroxide monohydrate contains crystal water, and water is produced in the reaction of lithium hydroxide and bisfluorosulfonylimide acid. Therefore, compared with the traditional technology, the water introduced in the recycling and recovery process is extremely limited, not only avoiding the generation of a large amount of sulfur dioxide and hydrogen chloride acid waste gas, saving the treatment cost of acid waste gas, but also avoiding the dissolution of sulfur dioxide and hydrogen chloride in water, resulting in the generation of mixed salt, thereby increasing the difficulty of recycling and recovery. In addition, the water introduced in the recycling and recovery process is extremely limited, so compared with the traditional technology, the drying process of dichloromethane is also saved, not only further reducing the cost, but also avoiding the generation of solid waste in the drying process of dichloromethane.

[0033] 2. The present application adds lithium hydroxide in a molar ratio of 1:(1.0-1.3) of lithium hydroxide to bisfluorosulfonylimide acid, not only realizes the quantitative conversion of organic acid in lithium bisfluorosulfonylimide separation filtrate, but also recovers lithium bisfluorosulfonylimide and returns it to the generation system. The present application not only realizes the recycling of useful components in lithium bisfluorosulfonylimide separation filtrate, but also avoids the generation of mixed salt compared with the traditional technology, so that the mixed salt originally disposed as hazardous waste in the traditional technology can be recycled and utilized.

[0034] 3、The application utilizes the different boiling points of dichloromethane and dichlorosulfoxide, and realizes the effective separation of the organic solvents dichloromethane and dichlorosulfoxide by adopting the mode of 'fractionation + rectification', and recycling them in the generation system; therefore, compared with the traditional technology, the application not only realizes the recycling of resources, but also reduces the emission of organic waste gas, and realizes the unity of economic and environmental benefits.

[0035] 4、In the whole process of the application, almost zero emission of waste water and solid waste is realized, and the process of the application is simple, easy to operate and low in cost.

[0036] 5、Most of the resources in the application are recycled, and the obtained lithium bisfluorosulfonylimide, dichloromethane and dichlorosulfoxide can be recycled in the production system, although a small amount of acid tail gas and dichloromethane and dichlorosulfoxide organic waste gas are generated in the resource recycling process, wherein the acid tail gas can be treated in the water absorption and alkali washing system in the production system, and the dichloromethane and dichlorosulfoxide organic waste gas can be treated in the resin adsorption and desorption solvent recovery system in the production system, and thus the production enterprises do not need to set up independent waste gas treatment facilities, which greatly reduces the treatment cost of the lithium bisfluorosulfonylimide separation filtrate, and the application does not produce waste water, solid waste and other secondary pollution in the treatment process of the lithium bisfluorosulfonylimide separation filtrate, and has good economic and environmental benefits.

[0037] In summary, the application realizes the recycling and resource utilization of the organic solvents and lithium salts in the lithium bisfluorosulfonylimide separation filtrate, the treatment effect of the lithium bisfluorosulfonylimide separation filtrate is good, and the problems of high cost, low efficiency, generation of a large amount of waste water, waste gas and hazardous waste, poor environmental and economic benefits in the traditional technology are effectively solved, the resource utilization of the lithium bisfluorosulfonylimide separation filtrate is realized, energy and water resources are saved, and the unity of environmental and economic benefits is realized. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 A flow chart of the resource utilization treatment of the lithium bisfluorosulfonylimide separation filtrate in the traditional technology;

[0039] Figure 2 A flow chart of the resource utilization treatment of the lithium bisfluorosulfonylimide separation filtrate in the application. DETAILED DESCRIPTION

[0040] In the present application, the method for obtaining the lithium bisfluorosulfonimide separation filtrate is as follows: mixing lithium hydroxide monohydrate and dichloromethane in a salt formation reactor, adding dropwise an equimolar amount of bisfluorosulfonimide acid, and performing salt formation reaction for 8 hours to generate lithium bisfluorosulfonimide; adding dropwise dichlorosulfoxide at 20-30℃ for dehydration; performing pressure filtration on the solid-liquid mixture after dehydration, and repeatedly washing with dichloromethane for 3 times; and the obtained filtrate is the lithium bisfluorosulfonimide separation filtrate, wherein the content of lithium bisfluorosulfonimide is 0.3-0.4% by weight; the content of bisfluorosulfonimide acid is 0.5-0.8%; the content of dichlorosulfoxide is 5.5-6.5%; the content of dichloromethane is 92-93%; and the content of impurities is 0.1-0.3%.

[0041] In order to better explain the present application, the present application will be further described below in combination with the drawings and specific examples.

[0042] Example 1

[0043] A lithium bisfluorosulfonimide separation filtrate resource clean treatment method, comprising the following steps:

[0044] Step 1, intermediate conversion: converting bisfluorosulfonimide acid in lithium bisfluorosulfonimide separation filtrate into lithium bisfluorosulfonimide;

[0045] The lithium bisfluorosulfonimide separation filtrate (dichloromethane filtrate) used in this example is derived from a lithium bisfluorosulfonimide pilot test. On October 2, 2022, about 10 kg of dichloromethane filtrate was generated, containing 35 g of lithium bisfluorosulfonimide, 9290 g of dichloromethane, 55 g of bisfluorosulfonimide acid, 598 g of dichlorosulfoxide, and 22 g of impurities.

[0046] The specific method for intermediate conversion includes:

[0047] After sampling and analyzing the content of bisfluorosulfonimide acid in the generated dichloromethane filtrate, 15 g of lithium hydroxide monohydrate was added to the dichloromethane filtrate while stirring; in the reaction kettle, lithium hydroxide monohydrate and bisfluorosulfonimide acid were reacted at 100-110℃ for 8 hours to obtain a reaction liquid (i.e., a mixed solution containing lithium salt and organic solvent) 9932 g;

[0048] In the reaction, the reaction of the bisfluorosulfonylimide acid and lithium hydroxide monohydrate generates lithium bisfluorosulfonylimide 56.8g and water 10.9g. Since the dichloromethane filtrate contains 598g of dichlorosulfoxide, and a small amount of water is generated in the conversion of the bisfluorosulfonylimide acid, a small amount of dichlorosulfoxide is decomposed by water to generate sulfur dioxide 38.8g and hydrogen chloride 44.2g; since the original dichloromethane filtrate is water-free, the sulfur dioxide and hydrogen chloride generated by the decomposition of dichlorosulfoxide are not dissolved in the system, but are in the gas phase and are further treated in the waste gas treatment system (water absorption and alkali absorption system) of the lithium bisfluorosulfonylimide production workshop to generate by-products 147g of 30% hydrochloric acid and 77g of sodium sulfite;

[0049] Step 2, lithium salt recovery: filter the reaction solution after the reaction in step 1 to recover the filter residue, i.e. the crude lithium bisfluorosulfonylimide and the mixed solvent of dichloromethane and dichlorosulfoxide, for standby use;

[0050] The reaction solution (i.e. the mixed solution containing lithium salt and organic solvent) after the reaction in step 1, 9932g, is pumped at a rate of 500g / h by a diaphragm pump to a fully-closed pneumatic residue discharge filter (processing capacity 1L / h) for filtration. The filter residue, i.e. the crude lithium bisfluorosulfonylimide, is 98g, and the filtrate, i.e. the mixed solvent of dichloromethane and dichlorosulfoxide, is 9821.5g;

[0051] The recovered filter residue, i.e. the crude lithium bisfluorosulfonylimide, is transferred to the refining unit in the lithium bisfluorosulfonylimide production system for refining. After refining, lithium bisfluorosulfonylimide product 93g is obtained.

[0052] The method for refining the crude lithium bisfluorosulfonylimide is as follows: the crude lithium bisfluorosulfonylimide is put into a desolventization crystallization reactor, and diethyl ether and dichloromethane are added. The temperature in the reactor is controlled to be ≤30℃, and the pressure is controlled to be ≤-0.095MPa, for desolventization crystallization. The solid-liquid mixed phase (crude product and dichloroethane) obtained by desolventization crystallization is transferred to a filter. The gaseous organic solvent (including diethyl ether and a part of dichloroethane) evaporated in the desolventization is collected by condensation. The uncondensed gas is pressurized by a compressor and then collected by condensation. The uncondensed gas is sent to a resin adsorption tower for adsorption and then discharged after reaching the standard. The mother liquor filtered by the filter is sent to a filtrate desolventization reactor for vacuum distillation, while dichloroethane is recovered by condensation. The uncondensed gas is pressurized by a compressor and then collected by condensation. The solid obtained by the filter is dried to obtain the solid finished product, lithium bisfluorosulfonylimide.

[0053] Step 3, solvent fractionation: fractionate and separate dichloromethane and dichlorosulfoxide;

[0054] The filtrate obtained in step 2, i.e. the mixed solvent of dichloromethane and dichlorosulfoxide, 9821.5g, is pumped at a rate of 500g / h by a diaphragm pump to a solvent fractionation tower. During the pumping process, a heat exchanger (1m 2The mixed solvent of dichloromethane and dichlorosulfoxide is preheated to about 38℃ by using secondary steam or steam condensate water in the production system as heat source, and then pumped into the fractionating column. By using the boiling point difference between dichloromethane and dichlorosulfoxide (boiling point of dichloromethane is 39.8℃, and boiling point of dichlorosulfoxide is 78.8℃), the temperature of the fractionating column is controlled between 40-50℃, and then the crude dichloromethane 9104g is recovered from the top of the fractionating column, and the crude dichlorosulfoxide 716g is recovered from the bottom of the fractionating column;

[0055] Step 4, solvent distillation: the crude dichloromethane and the crude dichlorosulfoxide are respectively subjected to distillation;

[0056] A, distillation of dichloromethane: the crude dichloromethane 9104g recovered in step 3 is pumped into the dichloromethane distillation column at a rate of 500g / h by using a diaphragm pump, and in the process of pumping, the crude dichloromethane is preheated to about 38℃ by using a heat exchanger (5m 2 ) with secondary steam or steam condensate water in the production system as heat source, and after the crude dichloromethane is pumped into the dichloromethane distillation column, the temperature of the dichloromethane distillation column is controlled between 42-44℃, and then the dichloromethane 8912g is recovered from the top of the dichloromethane distillation column and reused in the production system, and the crude dichlorosulfoxide 183g is recovered from the bottom of the dichloromethane distillation column and combined with the crude dichlorosulfoxide obtained in step 3;

[0057] B, distillation of dichlorosulfoxide: the crude dichlorosulfoxide 716g recovered in step 3 is pumped into the dichlorosulfoxide distillation column at a rate of 50g / h by using a diaphragm pump, and in the process of pumping, the crude dichlorosulfoxide is preheated to about 38℃ by using a heat exchanger (1m 2 , with secondary steam or steam condensate water in the production system as heat source), and after the crude dichlorosulfoxide is pumped into the dichlorosulfoxide distillation column, the temperature of the dichlorosulfoxide distillation column is controlled between 45-50℃, and then the dichloromethane 190g is recovered from the top of the dichlorosulfoxide distillation column and combined with the crude dichloromethane obtained in step 3, and the dichlorosulfoxide 525g is recovered from the bottom of the dichlorosulfoxide distillation column and reused in the production system.

[0058] The waste gas (mainly dichloromethane and dichlorosulfoxide) in the fractionation and distillation processes of steps 3 and 4 in this example enters the waste gas treatment system (condensation + resin adsorption system) of the lithium bisfluorosulfonylimide production workshop for further treatment and reaches the discharge standard after treatment.

[0059] Example 2

[0060] A method for cleaning and recycling the filtrate of lithium bisfluorosulfonylimide, comprising the following steps:

[0061] Step 1, conversion of intermediates: converting the lithium bisfluorosulfonylimide acid in the filtrate of lithium bisfluorosulfonylimide into lithium bisfluorosulfonylimide;

[0062] The dichloromethane filtrate used in this embodiment is the filtrate of lithium bisfluorosulfonimide separation, which is derived from the small-scale experiment of lithium bisfluorosulfonimide. On August 17, 2022, about 10 kg of dichloromethane filtrate was generated, containing 30 g of lithium bisfluorosulfonimide, 9250 g of dichloromethane, 60 g of bisfluorosulfonimide acid, 630 g of dichlorosulfoxide, and 30 g of impurities.

[0063] The specific method of intermediate conversion includes:

[0064] After sampling and analyzing the content of bisfluorosulfonimide acid in the generated dichloromethane filtrate, 16 g of lithium hydroxide monohydrate was added to the dichloromethane filtrate while stirring. In the reaction kettle, lithium hydroxide monohydrate and bisfluorosulfonimide acid were reacted at 100-110°C for 8 hours. After the reaction was completed, 9902 g of reaction liquid (i.e. mixed solution containing lithium salt and organic solvent) was obtained.

[0065] In this step, bisfluorosulfonimide acid reacts with lithium hydroxide monohydrate to produce 62 g of lithium bisfluorosulfonimide and 12.8 g of water. Since the dichloromethane filtrate contains 630 g of dichlorosulfoxide, and a small amount of water is generated during the conversion of bisfluorosulfonimide acid, a small part of dichlorosulfoxide decomposes in water to produce 45.6 g of sulfur dioxide and 52 g of hydrogen chloride. Since the original dichloromethane filtrate does not contain water, the sulfur dioxide and hydrogen chloride generated by the decomposition of dichlorosulfoxide do not dissolve in the system, but enter the waste gas treatment system (water absorption and alkali absorption system) of the lithium bisfluorosulfonimide production workshop in the gas phase for further treatment, generating 173 g of by-product 30% hydrochloric acid and 90 g of by-product sodium sulfite.

[0066] Step 2, lithium salt recovery: filter the reaction liquid after the reaction in step 1 to recover the filter residue, which is the mixture of lithium bisfluorosulfonimide crude product, dichloromethane and dichlorosulfoxide, for standby use.

[0067] The reaction liquid (i.e. mixed solution containing lithium salt and organic solvent) after the reaction in step 1, 9902 g, is delivered to a fully enclosed pneumatic residue discharge filter (processing capacity 1 m 3 / h) at a rate of 500 g / h by a diaphragm pump, filtered, and the filter residue, i.e. lithium bisfluorosulfonimide crude product, is 93 g, and the filtrate, i.e. the mixed solution of dichloromethane and dichlorosulfoxide, is 9800 g.

[0068] The recovered filter residue, lithium bisfluorosulfonimide crude product, is transferred to the refining unit in the lithium bisfluorosulfonimide production system for refining. After refining, 89 g of lithium bisfluorosulfonimide product is obtained.

[0069] The method for refining the crude lithium bisfluorosulfonimide is as follows: the crude lithium bisfluorosulfonimide is put into a desolventization crystallization reactor, and diethyl ether and dichloromethane are added, the temperature in the reactor is controlled to be less than or equal to 30 ℃, and the pressure is controlled to be less than or equal to -0.095 MPa, and desolventization crystallization is carried out. The solid-liquid mixed phase (crude product and dichloroethane) obtained by desolventization crystallization is transferred to a filter, the gaseous organic solvent (including diethyl ether and part of dichloroethane) evaporated by desolventization is collected by condensation, the uncondensed gas phase is pressurized by a compressor and then collected by condensation, the non-condensable gas is sent to a resin adsorption tower for adsorption and then discharged after reaching the standard. The mother liquor filtered out by the filter is fed into a filtrate desolventization reactor for vacuum distillation, while dichloroethane is recovered by condensation, the uncondensed gas phase is pressurized by a compressor and then collected by condensation; the solid obtained from the filter is dried to obtain solid finished product lithium bisfluorosulfonimide.

[0070] Step 3, solvent fractionation: fractionate and separate dichloromethane and dichlorosulfoxide;

[0071] The 9800 g of the filtrate obtained in step 2, i.e., the mixed solvent of dichloromethane and dichlorosulfoxide, is pumped at a rate of 500 g / h to a solvent fractionation tower by a diaphragm pump, in the process of pumping, the mixed solvent of dichloromethane and dichlorosulfoxide is preheated to about 38 ℃ by a heat exchanger (5 m 2 , the heat source is secondary steam or steam condensate water in the production system), after the mixed solvent of dichloromethane and dichlorosulfoxide is pumped into the fractionation tower, the temperature in the fractionation tower is controlled to be between 40 and 50 ℃, the crude dichloromethane 9040 g is recovered from the top of the fractionation tower, and the crude dichlorosulfoxide 750 g is recovered from the bottom of the fractionation tower, by taking advantage of the difference in boiling points of dichloromethane and dichlorosulfoxide (the boiling point of dichloromethane is 39.8 ℃, and the boiling point of dichlorosulfoxide is 78.8 ℃);

[0072] Step 4, solvent rectification: rectification of the crude dichloromethane and the crude dichlorosulfoxide is carried out respectively;

[0073] A, rectification of dichloromethane: the crude dichloromethane 9040 g recovered in step 3 is pumped into a dichloromethane rectification tower at a rate of 500 g / h by a diaphragm pump, in the process of pumping, the crude dichloromethane is preheated to about 38 ℃ by a heat exchanger (5 m 2 , the heat source is secondary steam or steam condensate water in the production system), after the crude dichloromethane is pumped into the dichloromethane rectification tower, the temperature in the dichloromethane rectification tower is controlled to be between 42 and 44 ℃, the dichloromethane 8845 g is recovered from the top of the dichloromethane rectification tower and is reused in the production system, and the crude dichlorosulfoxide 185 g is recovered from the bottom of the dichloromethane rectification tower and is added to the crude dichlorosulfoxide obtained in step 3;

[0074] B, rectification of dichlorosulfoxide: the crude dichlorosulfoxide 750 g recovered in step 3 is pumped into a dichlorosulfoxide rectification tower at a rate of 50 g / h by a diaphragm pump, in the process of pumping, the crude dichlorosulfoxide is preheated to about 38 ℃ by a heat exchanger (1 m 2The crude thionyl chloride product is preheated to about 38°C using a heat source (secondary steam or steam condensate water from production), the thionyl chloride is pumped into the thionyl chloride rectification tower, and the temperature of the thionyl chloride rectification tower is controlled at 45-50°C. 330 g of dichloromethane is recovered from the top of the thionyl chloride rectification tower and is added to the crude dichloromethane obtained in step 3. 419 g of thionyl chloride is recovered from the bottom of the thionyl chloride rectification tower and is returned to the production system.

[0075] The waste gas (mainly dichloromethane and thionyl chloride) in the fractionation and rectification processes of steps 3 and 4 of the present example is further treated in the waste gas treatment system (condensation + resin adsorption system) of the lithium bisfluorosulfonylimide production workshop to meet the emission standards;

[0076] Comparative Example 1 (traditional process)

[0077] A method for cleaning and recycling the lithium bisfluorosulfonylimide separation filtrate, comprising the following steps:

[0078] Step 1: water washing: removing thionyl chloride from the lithium bisfluorosulfonylimide separation filtrate by reaction with water;

[0079] The lithium bisfluorosulfonylimide separation filtrate used in the present example, i.e. the dichloromethane filtrate, is derived from a lithium bisfluorosulfonylimide pilot experiment. On September 15, 2022, about 10 kg of dichloromethane filtrate was produced, containing 38 g of lithium bisfluorosulfonylimide, 9250 g of dichloromethane, 71 g of bisfluorosulfonylimide acid, 630 g of thionyl chloride, and 11 g of impurities.

[0080] The dichloromethane filtrate is added dropwise into a water washing reactor, and 630 g of thionyl chloride is removed therefrom. The generated hydrogen chloride 300 g and sulfur dioxide 300 g are sent to the tail gas treatment system. The by-product 30% hydrochloric acid 1000 g and the by-product sodium sulfite 600 g are prepared. After standing and layering, 9500 g of organic phase solvent (mainly 9200 g of dichloromethane, with 298.7 g of water, 1.8 g of sulfur dioxide, and 3.5 g of hydrogen chloride remaining) and 10300 g of aqueous solution (containing 10000 g of water, 38 g of lithium bisfluorosulfonylimide, 71 g of bisfluorosulfonylimide acid, 47.4 g of sulfurous acid, 83 g of hydrogen chloride, and 50 g of dichloromethane) are obtained and are ready for use.

[0081] During the reaction, thionyl chloride reacts with water to release sulfur dioxide and hydrogen chloride gas. Since a large amount of water is added to the reaction system, part of the generated sulfur dioxide and hydrogen chloride gas dissolves in the reaction system, and part is in the gas phase, which is discharged into the waste gas treatment system for further treatment.

[0082] Step 2, alkali washing: removing acidic substances in the organic phase solvent by alkali washing;

[0083] To the organic phase solvent obtained in step 1, add 24 ml of 30% sodium hydroxide solution (containing 7.2 g of sodium hydroxide); after stirring for 1 hour, separate the layers to obtain 9,300 g of crude dichloromethane and 224 g of aqueous solution (213.8 g of water, 5.6 g of sodium chloride, 3.5 g of sodium sulfite, and 1.1 g of sodium hydroxide);

[0084] During the reaction, because sulfur dioxide and hydrogen chloride remain in the organic phase solution, after adding the lye, sodium sulfite, sodium chloride, unreacted sodium hydroxide, and residual dichloromethane are generated, so the aqueous salt solution contains at least six substances: lithium bisfluorosulfonylimide, sodium bisfluorosulfonylimide, sodium sulfite, sodium chloride, sodium hydroxide, and dichloromethane; in addition, because of the residual sulfur dioxide and hydrogen chloride, trace amounts of sulfur dioxide and hydrogen chloride waste gas are discharged during the lye washing process and the separation process, and are further treated in the waste gas treatment system;

[0085] Step 3: stripping and neutralization of the aqueous solution

[0086] After combining the aqueous solution A of step 1 and the aqueous solution B of step B, the dichloromethane is stripped by steam at 45°C to obtain 53 g of crude dichloromethane and 10,500 g of waste water; the waste water is acidic, and according to the total amount of acidic substances in the waste water, 500 ml of 30% sodium hydroxide solution (containing 150 g of sodium hydroxide) is added; after stirring for 1 hour, the acidic waste water is converted into salt-containing waste water 11,000 g (containing 38 g of lithium bisfluorosulfonylimide, 80 g of sodium bisfluorosulfonylimide, 133 g of sodium chloride, 73 g of sodium sulfite, 13 g of sodium hydroxide, etc.) which enters the waste water treatment system;

[0087] Step 4: purification of the crude dichloromethane

[0088] After combining the crude dichloromethane obtained in steps 2 and 3, drying with a drying agent, and entering the rectification column, the temperature of the rectification column is controlled at 44°C, and the dichloromethane is discharged from the top of the column and then dried again with a drying agent, obtaining 9,350 g of dichloromethane which is recycled to the production system;

[0089] During the purification of dichloromethane, 10 g of solid waste is generated in each of the two drying processes, and 15 g of still residue waste and acidic waste gas are generated in the rectification process, wherein the acidic waste gas enters the waste gas treatment system for further treatment.

[0090] In this comparative example, all the waste gas is treated in the waste gas treatment system, and 1,000 g of 30% hydrochloric acid and 600 g of sodium sulfite are obtained as by-products.

[0091] Effect example: comprehensive benefit analysis

[0092] Comparing the present application with the conventional process, the consumption of the data example 2 of the present application is based on, the comprehensive benefits are analyzed, and the results are shown in Table 1.

[0093] Table 1 Comprehensive benefit analysis (converted according to ton of filtrate)

[0094]

[0095]

[0096] According to the analysis results obtained from Table 1, according to ton of filtrate, the present application process can save 214.9 yuan / ton compared with the conventional treatment method, realizes the resource utilization of organic solvents and lithium salts in filtrate, no waste water and solid waste are produced, a small amount of waste gas is produced, and no independent waste gas treatment facility is needed, can effectively treat and recover hydrochloric acid and sodium sulfite by-products. The value of the recovered by-products can be increased by 506.5 yuan / ton of filtrate compared with the original conventional process, which greatly saves raw materials, energy and water resources.

[0097] The above-described embodiments are only preferred embodiments of the present application, and are not an exhaustive list of the feasible implementations of the present application. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present application should be considered to be included in the protection scope of the claims of the present application.

Claims

1. A method for cleaning and recycling of a lithium bisfluorosulfonylimide separation filtrate, characterized in that, Comprising the following steps: Step 1, intermediate conversion: lithium bisfluorosulfonimide is separated from the filtrate, and lithium hydroxide is added to the filtrate, and lithium bisfluorosulfonimide and water are generated by reaction, and the dichlorosulfoxide in the lithium bisfluorosulfonimide separation filtrate reacts with the generated water to decompose into sulfur dioxide and hydrogen chloride gas, and the gas enters the waste gas treatment system, and the reaction liquid is ready for use; When lithium hydroxide is added, the molar ratio of lithium hydroxide to bisfluorosulfonimide acid is 1: (1.0-1.3); Step 2, lithium salt recovery: filter the reaction liquid after the reaction in step 1 is completed, and recover the filter residue, which is lithium bisfluorosulfonimide crude product; the filtrate is ready for use; Step 3, solvent fractionation: transfer the filtrate obtained in step 2 to a solvent fractionation column, separate dichloromethane and dichlorosulfoxide at a temperature of 40-50°C, and recover dichloromethane crude product from the top of the fractionation column; the bottom of the column is dichlorosulfoxide crude product.

2. The method according to claim 1, wherein the method is characterized by, After step 3, step 4, solvent rectification, is also included, which includes dichloromethane rectification and dichlorosulfoxide rectification; A, dichloromethane rectification: transfer the dichloromethane crude product prepared in step 3 to a dichloromethane rectification column, and rectify at 42-44°C, recover dichloromethane from the top, and obtain dichlorosulfoxide crude product from the bottom of the dichloromethane rectification column; B, dichlorosulfoxide rectification: transfer the dichlorosulfoxide crude product prepared in step 3 to a dichlorosulfoxide rectification column, and rectify at 45-50°C, recover dichloromethane crude product from the top of the dichlorosulfoxide rectification column, and recover dichlorosulfoxide from the bottom.

3. The method according to claim 2, wherein the method is characterized by, In step 4, the dichlorosulfoxide crude product obtained from the bottom of the dichloromethane rectification column is combined with the dichlorosulfoxide crude product obtained in step 3 for subsequent processing; The dichloromethane crude product recovered from the top of the dichlorosulfoxide rectification column is combined with the dichlorosulfoxide crude product obtained in step 3 for subsequent processing.

4. The method according to claim 2, wherein the method is characterized by, The dichloromethane and dichlorosulfoxide prepared in step 4 are recycled to the lithium bisfluorosulfonimide production system.

5. The method according to claim 2, wherein the method is characterized by, In step 4, the dichloromethane crude product is preheated to 38-39°C before being transferred to the dichloromethane rectification column; The dichlorosulfoxide crude product is preheated to 38-39°C before being transferred to the dichlorosulfoxide rectification column; The preheating is carried out using a heat exchanger, and the heat source for the heating is steam or secondary steam generated in the lithium bisfluorosulfonimide production system.

6. The method according to claim 1, wherein the method is characterized by, In step 1, the lithium bisfluorosulfonimide separation filtrate contains lithium bisfluorosulfonimide, bisfluorosulfonimide acid, dichlorosulfoxide, dichloromethane and impurities.

7. The method according to claim 6, wherein the method is characterized by, In the lithium bisfluorosulfonimide separation filtrate, the content of lithium bisfluorosulfonimide is 0.3-0.4%, the content of bisfluorosulfonimide acid is 0.5-0.8%, the content of dichlorosulfoxide is 5.5-6.5%, the content of dichloromethane is 92-93%, and the content of impurities is 0.1-0.3%.

8. The method according to claim 1, wherein the method is characterized by, In step 1, the lithium hydroxide is single-water lithium hydroxide; After adding lithium hydroxide, the reaction is carried out at 90-120°C for 7-9h to complete the reaction.

9. The method according to claim 1, wherein the method is characterized by, The lithium bisfluorosulfonimide crude product recovered in step 2 is refined to obtain lithium bisfluorosulfonimide.

10. The method according to claim 9, wherein the method is characterized by, When the lithium bisfluorosulfonimide crude product recovered in step 2 is refined, it is combined into the refining unit of the lithium bisfluorosulfonimide production system for refining.

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