Preparation process of anhydrous iron phosphate

Abstract

The invention discloses a preparation process of anhydrous iron phosphate, and relates to the technical field of chemical engineering. The process comprises the following steps: mixing and stirring iron-containing and phosphorus-containing raw materials and deionized water, adding an oxidant solution and a catalyst, and adjusting the pH value of the mixed solution; after heating reaction, separating to obtain ferric phosphate polyhydrate; and aging in a phosphoric acid buffer solution, and calcining at high temperature after aging to obtain the anhydrous iron phosphate. The method disclosed by the invention is simple and convenient in process and low in cost, and the obtained anhydrous iron phosphate is high in purity, good in crystallinity and suitable for various application fields such as high-performance lithium ion battery positive electrode materials.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering technology, and in particular to a process for preparing anhydrous ferric phosphate. Background Technology

[0002] Anhydrous iron phosphate (FePO4) is an important inorganic functional material widely used in lithium-ion batteries, catalysts, pigments, adsorbents, and other fields. Especially in lithium-ion battery cathode materials, anhydrous iron phosphate has become a crucial precursor for lithium iron phosphate (LiFePO4) batteries due to its excellent thermal stability, environmental friendliness, and low cost. Furthermore, anhydrous iron phosphate is widely used in various catalytic reaction systems, such as organic waste gas purification and redox reactions, due to its high surface activity, stable physicochemical properties, and excellent corrosion resistance.

[0003] Existing methods for preparing anhydrous ferric phosphate mainly include high-temperature thermal decomposition, precipitation, and solvothermal methods. The high-temperature thermal decomposition method primarily involves heating iron-containing and phosphorus-containing compounds to generate anhydrous ferric phosphate through a high-temperature decomposition reaction. However, this method requires high-temperature conditions, consumes a large amount of energy, demands sophisticated equipment, and is complex, making it unsuitable for large-scale industrial production. For example, Chinese patent CN109179353A discloses a process for preparing anhydrous ferric phosphate. Iron oxide red is mixed with ammonium monohydrogen phosphate or ammonium dihydrogen phosphate, then pure water is added to form a slurry. The slurry is then milled in a sand mill until the particle size is 500-600 nm. After spray drying, the dried material is placed in a roller furnace or rotary kiln and calcined at 350-550℃ for 5-7 hours. The generated waste gas is absorbed by a phosphoric acid solution spray and then discharged. The calcined material is cooled, then subjected to air-jet pulverization, and finally screened to remove iron, yielding anhydrous ferric phosphate.

[0004] The precipitation method prepares ferric phosphate by co-precipitating iron-containing and phosphorus-containing solutions under certain conditions, followed by heating and drying or calcination to remove moisture and obtain anhydrous ferric phosphate. Although the precipitation method has lower energy consumption, the reaction process is difficult to control, resulting in lower purity and crystallinity of the product, and uneven particle size and morphology of the precipitate, leading to unstable performance of the final product. Furthermore, the precipitation method generates a large amount of wastewater and waste residue that requires treatment, placing a significant environmental burden on the plant.

[0005] The solvothermal method involves obtaining anhydrous ferric phosphate through a chemical reaction in a solvent environment at high temperature and pressure. This method produces ferric phosphate with good crystallinity, uniform particle size, and high purity. However, it requires equipment such as autoclaves, resulting in high investment costs. Furthermore, solvent recovery and treatment are difficult, hindering its widespread application in industrial production.

[0006] Therefore, there is an urgent need for a method to prepare anhydrous iron phosphate at lower temperatures and through simple process steps, in order to reduce production energy consumption, simplify the process flow, improve the purity and performance of the product, and reduce environmental pollution. Summary of the Invention

[0007] To address at least one of the technical problems mentioned in the background section, this invention proposes a process for preparing anhydrous ferric phosphate. This process aims to generate anhydrous ferric phosphate by directly reacting iron-containing raw materials with phosphorus-containing raw materials under mild conditions. It has advantages such as simple operation, low cost, and low energy consumption, and is particularly suitable for the needs of industrial production.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A process for preparing anhydrous ferric phosphate, characterized by comprising the following steps:

[0010] A. According to the mass number, add 100-120 parts of iron-containing raw material and phosphorus-containing raw material and 80-120 parts of deionized water to the reactor, and stir evenly to obtain a mixed solution;

[0011] B. Add 600-1000 parts of oxidant solution and 1-5 parts of oxidation catalyst to the above mixed solution, and add pH adjuster to adjust the pH of the mixed solution to 2-4.

[0012] C. Heat the above mixture for 1-3 hours, and then perform liquid-solid separation to obtain solid iron phosphate polyhydrate.

[0013] D. The above-mentioned ferric phosphate polyhydrate was aged in phosphate buffer for 1-3 hours, and then calcined at high temperature for 2-4 hours to obtain anhydrous ferric phosphate product.

[0014] In this invention, the iron-containing raw material in step A is selected from at least one of ferrous sulfate, ferric chloride, or ferrous chloride.

[0015] In this invention, the phosphorus-containing raw material in step A is at least one of phosphoric acid, sodium dihydrogen phosphate, or potassium dihydrogen phosphate.

[0016] In this invention, the molar ratio of iron-containing raw material to phosphorus-containing raw material in step A is 1:1-5.

[0017] In this invention, the oxidant in step B is selected from at least one of hydrogen peroxide, potassium permanganate, sodium hypochlorite, and ammonium persulfate, and the concentration of the oxidant solution is 2-6%.

[0018] In this invention, the preparation method of the oxidation catalyst in step B is as follows:

[0019] S1: Take 100-120 parts by weight of iron-molybdenum oxide and place them on the transmission device of the plasma processing equipment. The container or carrier is placed within a specific distance of 2 cm below the nozzle of the atmospheric pressure / room temperature plasma jet device. The nanopowder is laid with a thickness of 2-5 mm. Under the premise of turning on the atmospheric pressure / room temperature plasma, the discharge power is 50W-120W and the processing time is 30s-90s to obtain surface amino-modified iron-molybdenum oxide.

[0020] S2: Take 50-100 parts of surface amino-modified iron-molybdenum oxide and add it to a reactor containing 1000-1200 parts of DMF. Stir evenly, add 0.005-0.05 parts of palladium methacrylate, 3-6 parts of potassium propylene trifluoroborate, and 2-5 parts of potassium ethoxide. Stir and react at 70-80℃ for 10-20 hours, filter under pressure, and dry to obtain the oxidation catalyst.

[0021] The reaction mechanism of the above oxidation catalysts:

[0022] In the catalytic process, the surface-amino-modified iron-molybdenum oxide first undergoes an amino-propylene addition reaction with palladium methacrylate and potassium allyl trifluoroborate to obtain an iron-molybdenum oxide supported on palladium complex and potassium trifluoroborate. This composite catalyst may promote the reaction in the catalytic oxidation of ferrous phosphite to ferric phosphate by forming active intermediates or providing specific reaction sites. The specific catalytic cycle may involve steps such as changes in oxidation state, electron transfer, and substrate adsorption and desorption.

[0023] In this invention, the pH adjuster in step B is ammonia, sodium hydroxide solution, or phosphoric acid solution.

[0024] In this invention, the heating reaction temperature in step C is 70-90℃.

[0025] In this invention, the pH value of the phosphate buffer in step D is 2-4.

[0026] In this invention, the high-temperature calcination temperature in step D is 400-600℃.

[0027] The method for preparing anhydrous ferric phosphate provided by this invention has the following technical advantages:

[0028] 1. High purity and crystallinity: The anhydrous iron phosphate obtained by this method has high purity, ensuring that the material has good cycle stability and conductivity in battery applications.

[0029] 2. Larger specific surface area: The prepared anhydrous iron phosphate has a large specific surface area, which is beneficial for providing more active sites in battery applications, enhancing the electrochemical activity of the material, and improving the capacity and rate performance of the battery.

[0030] 3. Suitable particle size distribution: The obtained anhydrous iron phosphate has a uniform particle size distribution, making it suitable as a cathode material for high-rate lithium-ion batteries, reducing internal resistance and improving rate performance.

[0031] 4. Low cost and environmental protection: This method does not require high temperature and high pressure equipment, the process is simple, the operating conditions are mild, and the production cost is reduced; at the same time, it reduces the emission of waste gas and wastewater, reduces the pollution to the environment, and meets the requirements of green production.

[0032] 5. Technical benefits of oxidation catalysts:

[0033] Particle morphology optimization: By modifying with amino groups and supporting palladium complexes, the particle morphology of iron-molybdenum oxide can be improved, making it more uniform and dispersed, thereby increasing the active surface area and catalytic efficiency of the catalyst.

[0034] Enhancing Catalytic Activity: Palladium, as a noble metal catalyst, possesses excellent catalytic performance. Supporting it on iron-molybdenum oxide can further improve the catalyst's activity and selectivity, making it easier to oxidize iron phosphite to iron phosphate.

[0035] Enhanced stability: The addition of potassium trifluoroborate may help enhance the stability of the catalyst and prevent it from being deactivated or degraded during the reaction.

[0036] Environmentally friendly: Compared to traditional oxidation methods, using this supported catalyst may be more environmentally friendly, reducing the generation and emission of harmful byproducts. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] A process for preparing anhydrous ferric phosphate, characterized by comprising the following steps:

[0040] A. Add 100g of iron-containing raw material and 100g of phosphorus-containing raw material and 80g of deionized water to the reactor, and stir until a mixed solution is obtained;

[0041] B. Add 600g of oxidant solution and 1g of oxidation catalyst to the above mixed solution, and add pH adjuster to adjust the pH of the mixed solution to 2.

[0042] C. Heat the above mixture for 1 hour, and then perform liquid-solid separation to obtain solid iron phosphate polyhydrate.

[0043] D. The above-mentioned ferric phosphate polyhydrate was aged in phosphate buffer for 1 hour, and then calcined at high temperature for 2 hours to obtain anhydrous ferric phosphate product.

[0044] The iron-containing raw material in step A is selected from ferrous sulfate.

[0045] The phosphorus-containing raw material in step A is phosphoric acid.

[0046] In step A, the molar ratio of iron-containing raw material to phosphorus-containing raw material is 1:1.

[0047] In step B, the oxidant is selected from hydrogen peroxide, and the concentration of the oxidant solution is 2%.

[0048] The preparation method of the oxidation catalyst in step B is as follows:

[0049] S1: Take 100g of iron-molybdenum oxide and place it on the transmission device of the plasma processing equipment. The container or carrier is placed within a specific distance of 2 cm below the nozzle of the atmospheric pressure / room temperature plasma jet device. The nanopowder is laid with a thickness of 2 mm. Under the premise of turning on the atmospheric pressure / room temperature plasma, the discharge power is 50W and the processing time is 30s, to obtain iron-molybdenum oxide with surface amino modification.

[0050] S2: Take 50g of surface amino-modified iron-molybdenum oxide and add it to a reaction vessel containing 1000g of DMF. Stir well, add 0.005g of palladium methacrylate, 3g of potassium propenyl trifluoroborate, and 2g of potassium ethoxide. Stir and react at 70℃ for 10h, filter under pressure, and dry to obtain the oxidation catalyst.

[0051] In step B, the pH adjuster is ammonia.

[0052] The heating reaction temperature in step C is 70°C.

[0053] The pH value of the phosphate buffer in step D is 2.

[0054] The high-temperature calcination temperature in step D is 400℃.

[0055] Example 2

[0056] A process for preparing anhydrous ferric phosphate, characterized by comprising the following steps:

[0057] A. Add 110g of iron-containing raw material and 100g of phosphorus-containing raw material and 100g of deionized water to the reactor, and stir until a mixed solution is obtained;

[0058] B. Add 800g of oxidant solution and 2.5g of oxidation catalyst to the above mixed solution, and add pH adjuster to adjust the pH of the mixed solution to 3.

[0059] C. Heat the above mixture for 2 hours, and then perform liquid-solid separation to obtain solid iron phosphate polyhydrate.

[0060] D. The above-mentioned ferric phosphate polyhydrate was aged in phosphate buffer for 2 hours, and then calcined at high temperature for 3 hours to obtain anhydrous ferric phosphate product.

[0061] The iron-containing raw material in step A is selected from ferrous sulfate.

[0062] The phosphorus-containing raw material in step A is sodium dihydrogen phosphate.

[0063] In step A, the molar ratio of iron-containing raw material to phosphorus-containing raw material is 1:2.5.

[0064] In step B, the oxidant is selected from potassium permanganate, and the concentration of the oxidant solution is 4%.

[0065] The preparation method of the oxidation catalyst in step B is as follows:

[0066] S1: Take 110g of iron-molybdenum oxide and place it on the transmission device of the plasma processing equipment. The container or carrier is placed within a specific distance of 2 cm below the nozzle of the atmospheric pressure / room temperature plasma jet device. The nanopowder is laid with a thickness of 3 mm. Under the premise of turning on the atmospheric pressure / room temperature plasma, the discharge power is 80W and the processing time is 60s, and surface amino-modified iron-molybdenum oxide is obtained.

[0067] S2: Take out 70g of surface amino-modified iron-molybdenum oxide and add it to a reaction vessel containing 1100g of DMF. Stir well, add 0.02g of palladium methacrylate, 4g of potassium propenyl trifluoroborate, and 3g of potassium ethoxide. Stir and react at 75℃ for 15h, filter under pressure, and dry to obtain the oxidation catalyst.

[0068] In step B, the pH adjuster is a sodium hydroxide solution.

[0069] The heating reaction temperature in step C is 80°C.

[0070] In step D, the pH value of the phosphate buffer is 3.

[0071] The high-temperature calcination temperature in step D is 500℃.

[0072] Example 3

[0073] A process for preparing anhydrous ferric phosphate, characterized by comprising the following steps:

[0074] A. Add 110g of iron-containing raw material and 100g of phosphorus-containing raw material and 100g of deionized water to the reactor, and stir until a mixed solution is obtained;

[0075] B. Add 800g of oxidant solution and 4g of oxidation catalyst to the above mixed solution, and add pH adjuster to adjust the pH of the mixed solution to 3.

[0076] C. Heat the above mixture for 2 hours, and then perform liquid-solid separation to obtain solid iron phosphate polyhydrate.

[0077] D. The above-mentioned ferric phosphate polyhydrate was aged in phosphate buffer for 2 hours, and then calcined at high temperature for 3 hours to obtain anhydrous ferric phosphate product.

[0078] The iron-containing raw material in step A is selected from ferric chloride.

[0079] The phosphorus-containing raw material in step A is sodium dihydrogen phosphate.

[0080] In step A, the molar ratio of iron-containing raw material to phosphorus-containing raw material is 1:4.

[0081] In step B, the oxidant is selected from sodium hypochlorite, and the concentration of the oxidant solution is 5%.

[0082] The preparation method of the oxidation catalyst in step B is as follows:

[0083] S1: Take 110g of iron-molybdenum oxide and place it on the transmission device of the plasma processing equipment. The container or carrier is placed within a specific distance of 2 cm below the nozzle of the atmospheric pressure / room temperature plasma jet device. The nanopowder is laid with a thickness of 4 mm. Under the premise of turning on the atmospheric pressure / room temperature plasma, the discharge power is 100W and the processing time is 60s, and surface amino-modified iron-molybdenum oxide is obtained.

[0084] S2: Take out 90g of surface amino-modified iron-molybdenum oxide and add it to a reaction vessel containing 1100g of DMF. Stir well, add 0.04g of palladium methacrylate, 5g of potassium propylene trifluoroborate, and 4g of potassium ethoxide. Stir and react at 75℃ for 15h, filter under pressure, and dry to obtain the oxidation catalyst.

[0085] In step B, the pH adjuster is a sodium hydroxide solution.

[0086] The heating reaction temperature in step C is 80°C.

[0087] In step D, the pH value of the phosphate buffer is 3.

[0088] The high-temperature calcination temperature in step D is 500℃.

[0089] Example 4

[0090] A process for preparing anhydrous ferric phosphate, characterized by comprising the following steps:

[0091] A. Add 120g of iron-containing raw material and 120g of phosphorus-containing raw material and 120g of deionized water to the reactor, and stir until a mixed solution is obtained;

[0092] B. Add 1000g of oxidant solution and 5g of oxidation catalyst to the above mixed solution, and add pH adjuster to adjust the pH of the mixed solution to 4.

[0093] C. Heat the above mixture for 3 hours, and then perform liquid-solid separation to obtain solid iron phosphate polyhydrate.

[0094] D. The above-mentioned ferric phosphate polyhydrate was aged in phosphate buffer for 3 hours, and then calcined at high temperature for 4 hours to obtain anhydrous ferric phosphate product.

[0095] The iron-containing raw material in step A is selected from ferrous chloride.

[0096] The phosphorus-containing raw material in step A is potassium dihydrogen phosphate.

[0097] In step A, the molar ratio of iron-containing raw material to phosphorus-containing raw material is 1:5.

[0098] In step B, the oxidant is selected from ammonium persulfate, and the concentration of the oxidant solution is 6%.

[0099] The preparation method of the oxidation catalyst in step B is as follows:

[0100] S1: Take 120g of iron-molybdenum oxide and place it on the transmission device of the plasma processing equipment. The container or carrier is placed within a specific distance of 2 cm below the nozzle of the atmospheric pressure / room temperature plasma jet device. The nanopowder is laid with a thickness of 5 mm. Under the premise of turning on the atmospheric pressure / room temperature plasma, the discharge power is 120W and the processing time is 90s, and surface amino-modified iron-molybdenum oxide is obtained.

[0101] S2: Take 100g of surface amino-modified iron-molybdenum oxide and add it to a reaction vessel containing 1200g of DMF. Stir well, add 0.05g of palladium methacrylate, 6g of potassium propenyl trifluoroborate, and 5g of potassium ethoxide. Stir and react at 80℃ for 20h, filter under pressure, and dry to obtain the oxidation catalyst.

[0102] In step B, the pH adjuster is ammonia.

[0103] The heating reaction temperature in step C is 90°C.

[0104] The pH value of the phosphate buffer in step D is 4.

[0105] The high-temperature calcination temperature in step D is 600℃.

[0106] Comparative Example 1

[0107] In this example, no oxidation catalyst was added in step B as a comparison; the remaining steps were completely consistent with those in Example 1.

[0108] Comparative Example 2

[0109] In this example, palladium methacrylate was not added during the preparation of the oxidation catalyst as a comparison; the remaining steps were completely consistent with those in Example 1.

[0110] Comparative Example 3

[0111] In this example, potassium propylene trifluoroborate was not added during the preparation of the oxidation catalyst as a comparison; the remaining steps were completely consistent with those in Example 1.

[0112] To verify the performance of the anhydrous ferric phosphate prepared by the method of this invention, we conducted the following tests on the sample, including purity analysis, specific surface area testing, and particle size distribution testing. The test methods and corresponding results are as follows:

[0113] Test method:

[0114] 1. Purity: The elemental composition of the sample was analyzed using X-ray fluorescence spectrometry (XRF) to determine the purity of anhydrous iron phosphate.

[0115] 2. Specific surface area: The specific surface area of ​​the sample was determined by the BET (Brunauer–Emmett–Teller) nitrogen adsorption method.

[0116] 3. Use a laser particle size analyzer to test the particle size distribution of the sample, focusing on measuring the average particle size and distribution uniformity.

[0117] Test results:

[0118] Table 1. Test results for examples and comparative examples.

[0119]

[0120]

[0121] The test results above show that the anhydrous iron phosphate prepared by the method of the present invention has high purity, large specific surface area, and uniform particle size distribution, making it suitable for high-performance material applications such as lithium-ion batteries and catalysis.

[0122] While the invention has been described and illustrated with reference to specific embodiments thereof, such description and illustration are not intended to limit the invention. It will be readily understood by those skilled in the art that various changes may be made to suit particular circumstances, materials, compositions, substances, methods, or processes to the objectives, spirit, and scope of this application without departing from the true spirit and scope of the invention as defined by the appended claims. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a particular order, it should be understood that these operations may be combined, subdivided, or reordered to form equivalent methods without departing from the teachings of the invention. Therefore, unless specifically indicated herein, the order and grouping of operations are not a limitation of this application.

Claims

1. A process for preparing anhydrous ferric phosphate, characterized in that, Includes the following steps: A. According to the mass number, add 100-120 parts of iron-containing raw material and phosphorus-containing raw material and 80-120 parts of deionized water to the reactor, and stir evenly to obtain a mixed solution; B. Add 600-1000 parts of oxidant solution and 1-5 parts of oxidation catalyst to the above mixed solution, and add pH adjuster to adjust the pH of the mixed solution to 2-4. C. Heat the above mixture for 1-3 hours, and then perform liquid-solid separation to obtain solid iron phosphate polyhydrate. D. The above-mentioned ferric phosphate polyhydrate was aged in phosphate buffer for 1-3 hours, and then calcined at high temperature for 2-4 hours to obtain anhydrous ferric phosphate product.

2. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: In step A, the iron-containing raw material is selected from at least one of ferrous sulfate, ferric chloride, or ferrous chloride.

3. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: The phosphorus-containing raw material in step A is at least one of phosphoric acid, sodium dihydrogen phosphate, or potassium dihydrogen phosphate.

4. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: In step A, the molar ratio of iron-containing raw material to phosphorus-containing raw material is 1:1-5.

5. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: In step B, the oxidant is selected from at least one of hydrogen peroxide, potassium permanganate, sodium hypochlorite, and ammonium persulfate, and the concentration of the oxidant solution is 2-6%.

6. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: The preparation method of the oxidation catalyst in step B: S1: Take 100-120 parts by weight of iron-molybdenum oxide and place them on the transmission device of the plasma processing equipment. The container or carrier is placed within a specific distance of 2 cm below the nozzle of the atmospheric pressure / room temperature plasma jet device. The nanopowder is laid with a thickness of 2-5 mm. Under the premise of turning on the atmospheric pressure / room temperature plasma, the discharge power is 50W-120W and the processing time is 30s-90s to obtain surface amino-modified iron-molybdenum oxide. S2: Take 50-100 parts of surface amino-modified iron-molybdenum oxide and add it to a reactor containing 1000-1200 parts of DMF. Stir evenly, add 0.005-0.05 parts of palladium methacrylate, 3-6 parts of potassium propylene trifluoroborate, and 2-5 parts of potassium ethoxide. Stir and react at 70-80℃ for 10-20 hours, filter under pressure, and dry to obtain the oxidation catalyst.

7. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: In step B, the pH adjuster is ammonia, sodium hydroxide solution, or phosphoric acid solution.

8. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: The heating reaction temperature in step C is 70-90℃.

9. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: In step D, the pH value of the phosphate buffer solution is 2-4.

10. The preparation process of anhydrous ferric phosphate according to claim 1, characterized in that: The high-temperature calcination temperature in step D is 400-600℃.

Images