System and method for directly producing battery-grade ferrous oxalate using dimethyl oxalate

Abstract

The application discloses a system and method for directly producing battery-grade ferrous oxalate from dimethyl oxalate, which comprises a hydrolysis reactor, an adsorption stripping tower provided with adsorption fillers, which is used for stripping and removing impurities through countercurrent contact of oxalic acid solution and steam in the tower, and adsorption and removal of impurities, a precipitation reactor, which is used for mixing the oxalic acid solution and iron salt to perform a precipitation reaction and aging, so as to obtain a reaction product, and a product recovery unit, which is used for separating and recovering the reaction product to obtain the battery-grade ferrous oxalate, and recycling a synthesis mother liquor to an iron salt preparation unit. The application selectively removes DMO, MMO and methanol from the hydrolysis solution through steam stripping and removal of impurities, and the effect of removal of impurities is significantly better than that of conventional distillation. The adsorption removal of impurities is simultaneously performed in the stripping and removal of impurities, metal impurities are removed, the product has good crystallinity, regular crystal form and concentrated particle size distribution, and stable chemical purity, so that the requirements of battery-grade material precursors can be met, no additional energy consumption is increased, and the application has strong popularization.

Description

Technical Field

[0001] This application belongs to the field of battery-grade ferrous oxalate preparation technology, specifically relating to a system and method for directly producing battery-grade ferrous oxalate using dimethyl oxalate. Background Technology

[0002] Battery-grade ferrous oxalate is one of the main raw materials for producing lithium iron phosphate (LFP) cathode materials for lithium-ion batteries. Its purity, crystal form, particle size distribution, and other physicochemical properties directly determine the electrochemical performance of LFP materials. Therefore, the purity requirements for battery-grade ferrous oxalate are extremely stringent in industry. Current processes for preparing battery-grade ferrous oxalate use solid oxalic acid dissolved in water as a raw material. However, solid oxalic acid is generally obtained by crystallizing and drying an aqueous solution of oxalic acid. This leads to problems such as high energy consumption, long production processes, high costs, and low product yield in existing processes.

[0003] The direct production of ferrous oxalate from the bottom solution of a dimethyl oxalate hydrolysis tower is significant as it simplifies the process and reduces energy consumption. However, due to hydrolysis equilibrium and kinetic limitations, the crude oxalic acid solution produced from the hydrolysis tower inevitably contains unreacted dimethyl oxalate (DMO), the intermediate hydrolysis product monomethyl oxalate (MMO), the byproduct methanol, and metallic impurities. Directly using this impure oxalic acid solution for ferrous oxalate synthesis will inhibit crystal growth, reduce product purity, affect process stability, and lead to yield losses. Therefore, this limits the application of the process for directly preparing battery-grade ferrous oxalate from dimethyl oxalate hydrolysis. Summary of the Invention

[0004] The purpose of this application is to provide a system and method for directly producing battery-grade ferrous oxalate from dimethyl oxalate, in order to solve the technical problem that in the existing process of directly producing ferrous oxalate from the bottom solution of a dimethyl oxalate hydrolysis tower, impurities in the hydrolysate inhibit crystal growth, lead to a decrease in product purity, affect process stability, and cause yield loss, thus limiting the application of the process of directly preparing battery-grade ferrous oxalate from dimethyl oxalate hydrolysis.

[0005] To achieve the above objectives, the first aspect of this application provides a system for directly producing battery-grade ferrous oxalate using dimethyl oxalate, comprising:

[0006] A hydrolysis reactor is used to hydrolyze dimethyl oxalate to obtain an oxalic acid solution;

[0007] An adsorption stripping tower is connected to the hydrolysis reactor. The adsorption stripping tower is equipped with adsorption packing material. The adsorption stripping tower is used to strip and remove impurities from the oxalic acid solution by countercurrent contact with steam in the tower, and to adsorb and remove impurities from the oxalic acid solution through the adsorption packing material.

[0008] A precipitation reactor has a first inlet and a second inlet. The first inlet is connected to the adsorption stripping tower and is used to introduce the oxalic acid solution that has undergone stripping and adsorption purification into the precipitation reactor. The second inlet is used to introduce iron salt into the precipitation reactor. The precipitation reactor is used to mix the oxalic acid solution and the iron salt to carry out a precipitation reaction and aging to obtain the reaction product.

[0009] The product recovery unit is connected to the precipitation reactor. The product recovery unit is used to separate and recover the reaction product to obtain battery-grade ferrous oxalate, and to recycle the separated and recovered synthesis mother liquor to the iron salt preparation unit.

[0010] In one or more embodiments, the hydrolysis reactor is a hydrolysis distillation column, having a feed inlet, a reflux outlet, and a liquid phase outlet at the bottom of the column. The feed inlet is used to introduce dimethyl oxalate and water, and the hydrolysis distillation column is used to hydrolyze dimethyl oxalate and discharge the oxalic acid solution through the liquid phase outlet.

[0011] In one or more embodiments, the adsorption stripping tower has a steam inlet and a solution outlet located at the bottom of the tower, and a solution inlet and a steam outlet located at the top of the tower. The solution inlet is connected to the liquid phase outlet to allow the oxalic acid solution to be input into the adsorption stripping tower and flow downwards. The steam inlet is used to input steam into the adsorption stripping tower and allow it to flow upwards to contact the oxalic acid solution countercurrently. The steam outlet is connected to the reflux port to allow the steam after stripping and impurity removal to be returned to the hydrolysis reactor. The solution outlet is connected to the first inlet to allow the oxalic acid solution after stripping and adsorption impurity removal to be input into the precipitation reactor.

[0012] In one or more embodiments, the adsorption filler is activated carbon.

[0013] In one or more embodiments, the product recovery unit includes a filter and a dryer, the filter being used to filter the reaction products and collect the filter cake and filtrate, and to convey the filter cake to the dryer for drying the filter cake to obtain battery-grade ferrous oxalate.

[0014] In one or more embodiments, a reactive distillation column is further included, which is connected to the product recovery unit and is used to distill the synthesis mother liquor obtained in the reaction product separation and recovery to remove impurities, and to recycle the distilled synthesis mother liquor to the iron salt preparation unit.

[0015] In one or more embodiments, the reactive distillation column includes a mother liquor inlet and a mother liquor outlet located in the bottom of the column. The mother liquor inlet is connected to the product recovery unit to introduce the synthetic mother liquor into the reactive distillation column, and the mother liquor outlet is connected to the iron salt preparation unit.

[0016] To achieve the above objectives, a second aspect of this application provides a method for directly producing battery-grade ferrous oxalate using dimethyl oxalate, comprising:

[0017] Dimethyl oxalate and water are passed into a hydrolysis reactor to carry out the hydrolysis reaction, and the oxalic acid solution is collected.

[0018] The oxalic acid solution and steam are fed into an adsorption stripping tower containing adsorption packing, so that the oxalic acid solution comes into countercurrent contact with the steam in the tower to achieve stripping and impurity removal, and adsorption and impurity removal are carried out simultaneously.

[0019] The oxalic acid solution, after stripping and adsorption to remove impurities, is transported to a precipitation reactor, and iron salt is added to the precipitation reactor. The mixture is then mixed to carry out a precipitation reaction. After the reaction is completed, the mixture is kept at a constant temperature and aged to obtain the reaction product.

[0020] The reaction product is separated and recovered to obtain battery-grade ferrous oxalate, and the mother liquor obtained from the separation and recovery is recycled to the iron salt preparation unit.

[0021] In one or more embodiments, in the step of feeding the oxalic acid solution and steam into an adsorption stripping tower in which adsorption packing is arranged, the steam is saturated steam of 0.1~1 MPaG, and the mass ratio of the steam to the oxalic acid solution is (0.05~0.3):1.

[0022] In one or more embodiments, the adsorption filler is activated carbon.

[0023] In one or more embodiments, the top pressure of the adsorption stripping tower is 0.01~0.02 MPaG, the top temperature is 90~120 ℃, and the bottom temperature is 110~140 ℃.

[0024] In one or more embodiments, the precipitation reaction is carried out at a temperature of 30-100 °C for 0.5-2 h.

[0025] In one or more embodiments, the precipitation reaction is carried out under an inert atmosphere.

[0026] In one or more embodiments, the iron salt is one or more combinations of ferrous sulfate, ferrous nitrate, and ferrous phosphate.

[0027] In one or more embodiments, the mass ratio of oxalic acid to the iron salt in the precipitation reactor is 1:(1~2).

[0028] In one or more embodiments, the aging time is 1 to 3 hours.

[0029] In one or more embodiments, it further includes:

[0030] The synthetic mother liquor obtained from the separation and recovery of the reaction products is fed into a reactive distillation column for distillation to remove impurities. The distilled synthetic mother liquor is then recycled to the iron salt preparation unit.

[0031] In one or more embodiments, the top pressure of the reactive distillation column is 0.01~0.02 MPaG, the top temperature is 65~75 ℃, and the bottom temperature is 110~140 ℃.

[0032] The advantages of this application, which differ from existing technologies, are:

[0033] This application addresses the volatility differences between DMO, MMO, and methanol and oxalic acid solutions by selectively removing DMO, MMO, and methanol from the hydrolysis solution using steam stripping. The removal efficiency is significantly better than conventional distillation. Simultaneously, adsorption removal is performed during stripping to remove metallic impurities. Furthermore, the inherent properties of the synthesis mother liquor are utilized for distillation to effectively remove residual impurities and convert them into useful raw materials, further improving product purity. Total impurities can be stably reduced to the 5 ppm level. The product exhibits good crystallinity, regular crystal form, concentrated particle size distribution, and stable chemical purity, meeting the requirements for battery-grade material precursors. This lays the foundation for the synthesis of battery-grade ferrous oxalate without increasing additional energy consumption, making it highly applicable. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of one embodiment of the system for directly producing battery-grade ferrous oxalate using dimethyl oxalate, as described in this application.

[0036] Figure 2 This is a schematic flowchart of one embodiment of the method for directly producing battery-grade ferrous oxalate using dimethyl oxalate according to this application.

[0037] Explanation of key figure labels:

[0038] Hydrolysis distillation column 100; feed inlet 101; reflux port 102; liquid phase outlet 103;

[0039] Adsorption stripping tower 200; adsorption packing 201; steam inlet 202; solution outlet 203; solution inlet 204; steam outlet 205;

[0040] Precipitation reactor 300; First inlet 301; Second inlet 302;

[0041] Product recovery unit 400; filter 401; dryer 402;

[0042] Reactive distillation column 500; Mother liquor inlet 501; Mother liquor outlet 502;

[0043] Iron salt configuration unit 600. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0045] Due to hydrolysis equilibrium and kinetic limitations, unreacted dimethyl oxalate (DMO), intermediate hydrolysis product monomethyl oxalate (MMO), byproduct methanol, and metallic impurities inevitably remain in the bottom solution of the dimethyl oxalate hydrolysis tower. The total content of these impurities is usually in the range of 100 ppm to 10,000 ppm.

[0046] Using dimethyl oxalate in oxalic acid solution directly to synthesize ferrous oxalate will affect product quality. The main problems are: 1. Surface-active substances such as DMO and MMO will adsorb onto the nuclei or faces of ferrous oxalate crystals, interfering with normal crystal growth and leading to poor crystallinity, irregular crystal form, and excessively wide particle size distribution in the ferrous oxalate product; 2. Ester and alcohol impurities may co-precipitate into the ferrous oxalate lattice, resulting in excessive carbon and hydrogen content and insufficient iron content in the final product, affecting its electrochemical consistency as a battery material; 3. The presence of methanol may change the dielectric constant and supersaturation of the reaction system, making the precipitation process difficult to control and affecting batch stability; 4. Residual effective oxalate and ferrous ions in the solution are difficult to completely precipitate and recover due to impurities, leading to yield loss.

[0047] To address the aforementioned issues, the applicant has developed a novel system for the direct production of battery-grade ferrous oxalate from dimethyl oxalate. This system effectively removes impurities from the dimethyl oxalate oxalic acid solution, ensuring the crystallinity, purity, and yield of the ferrous oxalate product. This facilitates the widespread adoption of the process for directly preparing battery-grade ferrous oxalate from dimethyl oxalate and effectively reduces the energy consumption and cost of ferrous oxalate preparation.

[0048] Specifically, please refer to Figure 1 , Figure 1 This is a schematic diagram of one embodiment of the system for directly producing battery-grade ferrous oxalate using dimethyl oxalate, as described in this application.

[0049] like Figure 1 As shown, the system includes a hydrolysis reactor, an adsorption stripping tower 200, a precipitation reactor 300, and a product recovery unit 400.

[0050] The hydrolysis reactor is used to hydrolyze dimethyl oxalate to obtain an oxalic acid solution.

[0051] In this embodiment, the hydrolysis reactor is specifically a hydrolysis distillation column 100, which has a raw material inlet 101, a reflux port 102, and a liquid phase outlet 103 located at the bottom of the column. The raw material inlet 101 is used to introduce dimethyl oxalate and water, and the hydrolysis distillation column 100 is used to perform a hydrolysis reaction on dimethyl oxalate and discharge the oxalic acid solution through the liquid phase outlet 103.

[0052] The adsorption stripping tower 200 is connected to the hydrolysis reactor, and the adsorption stripping tower 200 is equipped with adsorption packing 201 inside the tower. The adsorption stripping tower 200 is used for stripping and removing impurities from oxalic acid solution by countercurrent contact with steam inside the tower, and for adsorbing and removing impurities from oxalic acid solution through the adsorption packing 201.

[0053] In this embodiment, the adsorption filler 201 is activated carbon. In other embodiments, the adsorption filler 201 can also be any adsorption material commonly used in the art, such as molecular sieves.

[0054] By combining steam stripping and adsorption for impurity removal, on the one hand, the difference in boiling points between dimethyl oxalate, monomethyl oxalate, and methanol compared to oxalic acid and water is utilized. Using steam as a carrier and heat source, these impurity components can be selectively separated from the oxalic acid solution, effectively removing dimethyl oxalate, monomethyl oxalate, and methanol from the oxalic acid solution. On the other hand, when the oxalic acid solution flows through the adsorption packing 201 in the tower, activated carbon can effectively adsorb the metallic impurities in the oxalic acid solution, achieving the removal of metallic impurities.

[0055] Specifically, in this embodiment, the adsorption stripping tower 200 has a steam inlet 202 and a solution outlet 203 located at the bottom of the tower, and a solution inlet 204 and a steam outlet 205 located at the top of the tower.

[0056] The solution inlet 204 is connected to the liquid phase outlet 103 to input the oxalic acid solution into the adsorption stripping tower 200 and allow it to flow downwards; the steam inlet 202 is used to input steam into the adsorption stripping tower 200 and allow it to flow upwards to contact the oxalic acid solution countercurrently; the steam outlet 205 is connected to the reflux port 102 to return the steam after stripping and impurity removal to the hydrolysis reactor; and the solution outlet 203 is connected to the precipitation reactor 300 to input the oxalic acid solution after stripping and adsorption impurity removal into the precipitation reactor 300.

[0057] Based on the above scheme, the steam used for stripping and impurity removal can be returned to the hydrolysis reactor as a heat source and water source, thereby achieving efficient impurity removal of dimethyl oxalate oxalic acid solution without increasing energy consumption.

[0058] The precipitation reactor 300 has a first inlet 301 and a second inlet 302. The first inlet 301 is connected to the adsorption stripping tower 200 and is used to introduce oxalic acid solution that has undergone stripping and adsorption purification into the precipitation reactor 300. The second inlet 302 is used to introduce iron salt into the precipitation reactor 300. The precipitation reactor 300 is used to mix the oxalic acid solution and iron salt for precipitation reaction and aging to obtain the reaction product.

[0059] The product recovery unit 400 is connected to the precipitation reactor 300 to separate and recover the reaction products, obtain battery-grade ferrous oxalate, and recycle the separated and recovered synthesis mother liquor to the iron salt preparation unit 600.

[0060] Specifically, in this embodiment, the product recovery unit 400 includes a filter 401 and a dryer 402. The filter 401 is used to filter the reaction products and collect the filter cake and filtrate. The filter cake is transported to the dryer 402, and the filtrate is transported to the iron salt preparation unit 600. The dryer 402 is used to dry the filter cake to obtain battery-grade ferrous oxalate.

[0061] Understandably, in order to make full use of the unreacted iron salts, the filtrate can be transported to the iron salt preparation unit 600.

[0062] Furthermore, in this embodiment, the system also includes a reactive distillation column 500, which is connected to the product recovery unit 400400 and is used to distill the synthetic mother liquor obtained in the reaction product separation and recovery to remove impurities, and to recycle the distilled synthetic mother liquor to the iron salt preparation unit 600.

[0063] Since trace amounts of DMO and MMO inevitably remain in the synthesis mother liquor obtained after solid-liquid separation of the precipitation reaction products, if it is used directly to prepare iron salts, impurities will be introduced after subsequent addition to the precipitation reactor 300, affecting product quality. In this embodiment, the system also includes a reactive distillation column 500 for rectifying the synthesis mother liquor to achieve further impurity removal.

[0064] Specifically, the reactive distillation column 500 includes a mother liquor inlet 501 and a mother liquor outlet 502 located in the column bottom. The mother liquor inlet 501 is connected to the product recovery unit 400 to introduce the synthetic mother liquor into the reactive distillation column 500. The mother liquor outlet 502 is connected to the first inlet 301 of the precipitation reactor 300 to return the distilled synthetic mother liquor to the precipitation reactor 300.

[0065] Since the synthesis mother liquor is an acidic solution and contains excessive ferrous ions, this embodiment uses distillation heating to remove impurities from the synthesis mother liquor. Under heating conditions, ferrous ions can act as Lewis acid catalysts to accelerate the hydrolysis reaction of residual trace amounts of DMO and MMO in the synthesis mother liquor, converting them into oxalic acid and methanol. Methanol is distilled off from the top of the column, and then the synthesis mother liquor is refluxed to the precipitation reaction vessel 300 to further reduce the impurity content in the reaction solution of the precipitation reaction.

[0066] By reactive distilling the synthesis mother liquor, the acidic environment of the mother liquor and the catalytic properties of ferrous ions are creatively utilized to couple the purification process with the chemical reaction. This not only eliminates the final residual impurities but also converts harmful impurities DMO and MMO into useful raw material oxalic acid. The content of DMO, MMO and methanol in the reaction system can be controlled within 5 ppm, achieving process intensification and resource recovery, and significantly improving the overall economic efficiency of the process.

[0067] Based on the systems described above, on the one hand, taking advantage of the volatility differences between DMO, MMO, and methanol and oxalic acid solutions, steam stripping is used to selectively remove DMO, MMO, and methanol from the hydrolysis solution. The removal effect is significantly better than conventional distillation. Simultaneously, adsorption removal is carried out during the stripping process to remove metallic impurities. On the other hand, the characteristics of the synthesis mother liquor itself are utilized for distillation to effectively remove the final residual impurities and convert them into useful raw materials, which helps to further improve product purity. The total impurities can be stably reduced to the 5 ppm level. The product has good crystallinity, regular crystal form, concentrated particle size distribution, and stable chemical purity, which can meet the requirements of battery-grade material precursors. This lays the foundation for the synthesis of battery-grade ferrous oxalate without increasing additional energy consumption and has strong applicability.

[0068] It should be noted that the apparatus in this embodiment includes an adsorption stripping tower 200 and a reactive distillation tower 500. In other embodiments, the number of adsorption stripping tower 200 and reactive distillation tower 500 can be adjusted according to actual needs. Alternatively, it may include only the adsorption stripping tower 200 or only the reactive distillation tower 500. All of these can achieve the purpose of impurity removal to a certain extent and optimize product quality.

[0069] This application also provides a method for directly producing battery-grade ferrous oxalate using dimethyl oxalate. Please refer to [link to relevant documentation]. Figure 2 , Figure 2 This is a schematic flowchart of one embodiment of the method for directly producing battery-grade ferrous oxalate using dimethyl oxalate according to this application.

[0070] like Figure 2 As shown, the method includes:

[0071] S101. Dimethyl oxalate and water are passed into a hydrolysis reactor to carry out the hydrolysis reaction, and the oxalic acid solution is collected.

[0072] S102. Oxalic acid solution and steam are fed into an adsorption stripping tower equipped with adsorption packing, so that the oxalic acid solution comes into countercurrent contact with the steam in the tower to achieve stripping and impurity removal, and adsorption and impurity removal are carried out simultaneously.

[0073] In one embodiment, the steam may specifically be saturated steam with a concentration of 0.1 to 1 MPaG.

[0074] To ensure the effectiveness of stripping and impurity removal, in one embodiment, the mass ratio of steam to oxalic acid solution is (0.05~0.3):1.

[0075] In one embodiment, the top pressure of the adsorption stripping tower can be 0.01~0.02 MPaG, the top temperature can be 90~120 ℃, and the bottom temperature can be 110~140 ℃.

[0076] S103. The oxalic acid solution that has undergone stripping and adsorption to remove impurities is transported to a precipitation reactor, and iron salt is added to the precipitation reactor. The mixture is then mixed to carry out the precipitation reaction. After the reaction is completed, the mixture is kept at a constant temperature and aged to obtain the reaction product.

[0077] The oxalic acid solution, after stripping and adsorption purification, is directly mixed with iron salts for precipitation, yielding a reaction product containing ferrous oxalate. Since the oxalic acid solution is maintained at a constant temperature during this process, secondary heating is unnecessary; simply keeping the solution at this temperature during the reaction is sufficient.

[0078] In one embodiment, the precipitation reaction temperature can be 30~100 ℃, and the reaction time can be 0.5~2 h.

[0079] In one embodiment, the iron salt may be one or more combinations of ferrous sulfate, ferrous nitrate, and ferrous phosphate.

[0080] To ensure a complete reaction, in one embodiment, the mass ratio of oxalic acid to iron salt in the oxalic acid solution can be 1:(1~2).

[0081] In one implementation, the aging time can be 1 to 3 hours.

[0082] S104. The reaction product is separated and recovered to obtain battery-grade ferrous oxalate, and the synthesis mother liquor obtained from the separation and recovery is recycled to the iron salt preparation unit.

[0083] In one embodiment, the step of separating and recovering the reaction products can be specifically as follows:

[0084] The reaction product was filtered and the filter cake was collected. The filter cake was washed with solvent and dried after washing to obtain battery-grade ferrous oxalate.

[0085] The solvent can be one or a combination of water, ethanol, and ethylene glycol.

[0086] In one embodiment, the drying temperature can be 100~150 ℃, and the drying time can be 3~6 h.

[0087] S105. The synthesis mother liquor obtained in the reaction product separation and recovery process is fed into the reactive distillation column for distillation to remove impurities. The distilled synthesis mother liquor is then recycled to the iron salt preparation unit.

[0088] The synthesis mother liquor is distilled through a reactive distillation column to further remove residual impurities and convert it into oxalic acid. Then, an iron salt solution is prepared using the synthesis mother liquor to make full use of the raw materials. The prepared iron salt solution is added to a precipitation reactor for precipitation reaction.

[0089] In one embodiment, the pressure at the top of the reactive distillation column is 0.01~0.02 MPaG, the temperature at the top of the column is 65~75℃, and the temperature at the bottom of the column is 110~140℃.

[0090] Based on the methods described above, which utilize stripping, adsorption, and distillation to remove impurities, the impurity content in oxalic acid solutions is significantly reduced. This helps optimize the purity, crystallinity, stability, and yield of the product. Since no additional energy is consumed, this method facilitates the widespread adoption of the process for directly preparing ferrous oxalate from dimethyl oxalate.

[0091] The beneficial effects of the technical solution of this application will be further explained in detail below with reference to specific embodiments.

[0092] Example 1:

[0093] A process for directly preparing ferrous oxalate using dimethyl oxalate is as follows:

[0094] Dimethyl oxalate and water are fed into a hydrolysis distillation column for hydrolysis. The oxalic acid solution is collected at the bottom of the column and then pumped into the solution inlet of the adsorption stripping column at a flow rate of 10 L / h. At the same time, 0.5 MPaG saturated steam is introduced from the bottom of the adsorption stripping column at a flow rate of 2 L / h. The oxalic acid solution descending in the column is contacted with activated carbon to remove trace metal elements and is in countercurrent contact with the rising steam. The steam carries away the light components, organic solvents DMO, MMO, and methanol, and is discharged from the top of the column and refluxed back to the bottom of the hydrolysis distillation column.

[0095] The oxalic acid solution discharged from the bottom of the adsorption stripping tower was pumped into the precipitation reactor, and nitrogen gas was introduced at the same time. Stirring was started, and ferrous sulfate solution was introduced into the precipitation reactor at a flow rate of 9.5 L / h to carry out the precipitation reaction. The temperature was maintained at 65~68℃. After the reaction was completed, the reaction slurry was filtered, and the filter cake was washed three times with deionized water at 60℃, and then washed once with anhydrous ethanol. The filter cake was placed in a desiccator and dried at 100℃ under a nitrogen atmosphere for 4 hours to obtain a light yellow powdered ferrous oxalate product.

[0096] The filtrate obtained from filtration is pumped into a reactive distillation column for distillation. The pressure at the top of the reactive distillation column is controlled at 0.01~0.02 MPaG, and the temperature at the top of the column is controlled at 65~75 ℃. The temperature at the bottom of the column is controlled at 110~140 ℃. Methanol is obtained at the top of the column. The mother liquor from the bottom of the column is recycled to the ferrous sulfate preparation process to prepare ferrous sulfate solution, which is then pumped into the precipitation reactor.

[0097] Example 2:

[0098] A process for directly preparing ferrous oxalate using dimethyl oxalate is basically the same as that in Example 1, except that:

[0099] The inlet flow rate of oxalic acid solution in the adsorption stripping tower is 50 L / h, and the steam flow rate is 10 L / h; the inlet flow rate of ferrous sulfate solution in the precipitation reactor is 45 L / h.

[0100] Example 3:

[0101] A process for directly preparing ferrous oxalate using dimethyl oxalate is basically the same as that in Example 1, except that:

[0102] The inlet flow rate of oxalic acid solution in the adsorption stripping tower is 80 L / h, and the steam flow rate is 15 L / h; the inlet flow rate of ferrous sulfate solution in the precipitation reactor is 75 L / h.

[0103] Comparative Example 1:

[0104] A process for directly preparing ferrous oxalate using dimethyl oxalate is as follows:

[0105] Dimethyl oxalate and water were fed into a hydrolysis distillation column for hydrolysis. The oxalic acid solution was collected in the bottom of the column and then pumped into a precipitation reactor at a flow rate of 50 L / h. Nitrogen gas was introduced simultaneously, and stirring was started. Ferrous sulfate solution was introduced into the precipitation reactor at a flow rate of 45 L / h to carry out the precipitation reaction. The temperature was maintained at 65-68 °C. After the reaction was completed, the reaction slurry was filtered. The filter cake was washed three times with deionized water at 60 °C and then washed once with anhydrous ethanol. The filter cake was placed in a desiccator and dried at 100 °C under a nitrogen atmosphere for 4 hours to obtain a light yellow powdered ferrous oxalate product.

[0106] The filtrate obtained from filtration is recycled to the ferrous sulfate preparation process to prepare ferrous sulfate solution, and then pumped into the precipitation reactor.

[0107] Example of results:

[0108] The oxalic acid solution in the bottom of the hydrolysis distillation column and the mother liquor in the bottom of the reactive distillation column in Examples 1 to 3 were tested. The test items and test methods are shown in the table below.

[0109]

[0110] Specifically, the test results are shown in the table below.

[0111]

[0112] As shown in the table above, after stripping, adsorption, and distillation, the impurity content in the mother liquor at the bottom of the reaction distillation column is much lower than that in the oxalic acid solution at the bottom of the hydrolysis distillation column. The impurity content of DMO, methanol, and MMO can be as low as 5-10 ppm, and the content of metal impurities can be as low as 25 ppm.

[0113] Furthermore, the ferrous oxalate products prepared in Examples 1 to 3 and Comparative Example 1 were tested. The specific test items and test methods are shown in the table below.

[0114]

[0115] Specifically, the test results are shown in the table below.

[0116]

[0117] As shown in the table above, the ferrous oxalate in Examples 1 to 3 has a more uniform particle size, higher tap density, and lower water content and metal impurity content than Comparative Example 1, and its purity is significantly better than Comparative Example 1.

[0118] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0119] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A system for directly producing battery-grade ferrous oxalate using dimethyl oxalate, characterized in that, include: A hydrolysis reactor is used to hydrolyze dimethyl oxalate to obtain an oxalic acid solution; An adsorption stripping tower is connected to the hydrolysis reactor. The adsorption stripping tower is equipped with adsorption packing material. The adsorption stripping tower is used to strip and remove impurities from the oxalic acid solution by countercurrent contact with steam in the tower, and to adsorb and remove impurities from the oxalic acid solution through the adsorption packing material. A precipitation reactor has a first inlet and a second inlet. The first inlet is connected to the adsorption stripping tower and is used to introduce the oxalic acid solution that has undergone stripping and adsorption purification into the precipitation reactor. The second inlet is used to introduce iron salt into the precipitation reactor. The precipitation reactor is used to mix the oxalic acid solution and the iron salt to carry out a precipitation reaction and aging to obtain the reaction product. The product recovery unit is connected to the precipitation reactor. The product recovery unit is used to separate and recover the reaction product to obtain battery-grade ferrous oxalate, and to recycle the separated and recovered synthesis mother liquor to the iron salt preparation unit.

2. The system according to claim 1, characterized in that, The hydrolysis reactor is a hydrolysis distillation column, which has a raw material inlet, a reflux outlet and a liquid phase outlet located at the bottom of the column. The raw material inlet is used to introduce dimethyl oxalate and water. The hydrolysis distillation column is used to hydrolyze dimethyl oxalate and discharge the oxalic acid solution through the liquid phase outlet.

3. The system according to claim 2, characterized in that, The adsorption stripping tower has a steam inlet and a solution outlet located at the bottom of the tower, and a solution inlet and a steam outlet located at the top of the tower. The solution inlet is connected to the liquid phase outlet to allow the oxalic acid solution to be input into the adsorption stripping tower and flow downwards. The steam inlet is used to input steam into the adsorption stripping tower and allow it to flow upwards and contact the oxalic acid solution countercurrently. The steam outlet is connected to the reflux port to allow the steam after stripping and impurity removal to be returned to the hydrolysis reactor. The solution outlet is connected to the first inlet to allow the oxalic acid solution after stripping and adsorption impurity removal to be input into the precipitation reactor. And / or, The adsorption filler is activated carbon.

4. The system according to claim 1, characterized in that, The product recovery unit includes a filter and a dryer. The filter is used to filter the reaction products and collect the filter cake and filtrate, and to convey the filter cake to the dryer, which is used to dry the filter cake to obtain battery-grade ferrous oxalate.

5. The system according to claim 1, characterized in that, It also includes a reactive distillation column, which is connected to the product recovery unit and is used to distill the synthesis mother liquor obtained in the separation and recovery of the reaction products to remove impurities, and to recycle the distilled synthesis mother liquor to the iron salt preparation unit.

6. The system according to claim 5, characterized in that, The reactive distillation column includes a mother liquor inlet and a mother liquor outlet located in the bottom of the column. The mother liquor inlet is connected to the product recovery unit to introduce the synthetic mother liquor into the reactive distillation column, and the mother liquor outlet is connected to the iron salt preparation unit.

7. A method for directly producing battery-grade ferrous oxalate using dimethyl oxalate, characterized in that, include: Dimethyl oxalate and water are passed into a hydrolysis reactor to carry out the hydrolysis reaction, and the oxalic acid solution is collected. The oxalic acid solution and steam are fed into an adsorption stripping tower containing adsorption packing, so that the oxalic acid solution comes into countercurrent contact with the steam in the tower to achieve stripping and impurity removal, and adsorption and impurity removal are carried out simultaneously. The oxalic acid solution, after stripping and adsorption to remove impurities, is transported to a precipitation reactor, and iron salt is added to the precipitation reactor. The mixture is then mixed to carry out a precipitation reaction. After the reaction is completed, the mixture is kept at a constant temperature and aged to obtain the reaction product. The reaction product is separated and recovered to obtain battery-grade ferrous oxalate, and the mother liquor obtained from the separation and recovery is recycled to the iron salt preparation unit.

8. The method according to claim 7, characterized in that, In the step of feeding the oxalic acid solution and steam into an adsorption stripping tower equipped with adsorption packing, the steam is saturated steam with a concentration of 0.1~1 MPaG, and the mass ratio of the steam to the oxalic acid solution is (0.05~0.3):1; and / or, The adsorption packing material is activated carbon; and / or, The adsorption stripping column has a top pressure of 0.01~0.02 MPaG, a top temperature of 90~120 ℃, and a bottom temperature of 110~140 ℃; and / or, The precipitation reaction is carried out at a temperature of 30–100 °C for a time of 0.5–2 h; and / or, The precipitation reaction is carried out under an inert atmosphere; and / or, The iron salt is one or more combinations of ferrous sulfate, ferrous nitrate, and ferrous phosphate; and / or, The mass ratio of oxalic acid to the iron salt in the precipitation reactor is 1:(1~2); and / or, The aging time is 1 to 3 hours.

9. The method according to claim 7, characterized in that, Also includes: The synthetic mother liquor obtained from the separation and recovery of the reaction products is fed into a reactive distillation column for distillation to remove impurities. The distilled synthetic mother liquor is then recycled to the iron salt preparation unit.

10. The method according to claim 9, characterized in that, The reactive distillation column has a top pressure of 0.01~0.02 MPaG and a top temperature of 65~75 ℃; the bottom temperature is 110~140 ℃.

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