Continuous production method for large-scale battery-grade iron phosphate

Abstract

This invention discloses a continuous production system for large-scale battery-grade iron phosphate. Specifically, it includes the following sections: (1) a continuous impurity removal system for ferrous sulfate, a byproduct of titanium dioxide production; (2) a continuous production system for mixed phosphate salts; (3) a continuous synthesis and washing system for iron phosphate; and (4) a continuous flash drying and calcination system for iron phosphate. Each section is connected by pumps and pipelines, and key control points within each section are monitored by a process monitoring device. The process is automatically controlled by a DCS automatic control system. This invention employs a continuous production process throughout the entire preparation process, from iron and phosphorus raw materials to finished iron phosphate, successfully solving the problem of large-scale, batch-free, and continuous preparation methods. The iron phosphate prepared in this way has advantages of high quality and high consistency. The products produced after continuous and stable operation of the equipment fully meet the product specifications of downstream customers.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of lithium-ion battery material precursor iron phosphate, specifically relating to a continuous production system for large-scale battery-grade iron phosphate. Background Technology

[0002] Lithium-ion batteries have garnered significant attention due to their high specific energy, excellent cycle performance, and environmental friendliness, and are currently widely used in smartphones, laptops, energy storage power stations, and electric vehicles. Among the many battery types, lithium iron phosphate (LFP) batteries have surpassed ternary lithium batteries in market share due to their high safety performance, long cycle life, low pollution, and low cost, becoming the preferred choice for power and energy storage batteries. The explosive growth in demand for power and energy storage batteries has also driven the development of LFP materials. The solid-phase synthesis method—carbothermic reduction method—is the preparation method adopted by over 90% of companies due to its relatively simple process and high maturity. LFP produced using this method accounts for nearly 80% of total shipments. Iron phosphate is the main raw material for solid-phase LFP preparation. Combining relevant process and market demand analysis, the development of solid-phase LFP has a promising market prospect.

[0003] In an increasingly competitive landscape, production costs and consistency of products are receiving growing attention. Currently, manufacturers of ferric phosphate mainly employ ammonia and sodium processes, which, limited by process conditions and equipment, are primarily based on batch production methods, such as batch single-reactor batch preparation of raw materials. This production method suffers from the following problems: ① Single-reactor feeding leads to low production efficiency and high labor costs; ② Batch variations in raw materials during preparation, insufficiently precise control of preparation conditions, cumbersome operation, and difficulty in automation result in poor consistency of the finished ferric phosphate product; ③ Numerous reaction vessels and large floor space required, leading to significant equipment investment. In contrast, continuous processes are particularly suitable for large-scale, economical production. They offer advantages such as simplified processes, ease of automation, low production costs, large production capacity, and good product consistency. Therefore, developing a continuous preparation technology for ferric phosphate precursors has become the future direction of this industry.

[0004] Currently, continuous production of ferric phosphate precursors is not common in practical applications. For example, patent CN107337189A discloses a continuous production system and method for ferric phosphate, but this patent does not mention the preparation process of the raw material and the pressure filtration and washing system, which are likely to have intermittent production issues. Furthermore, in actual two-step ammonia production processes, continuous preparation of the iron source, continuous and stable preparation of phosphate salts, and stable synthesis and crystallization reactions have not been fully achieved. Summary of the Invention

[0005] This invention addresses the problems of insufficient precision and control, cumbersome operation, difficulty in automation, poor product consistency, small production capacity, and high cost in the existing batch-based preparation process of iron phosphate precursors. It proposes a continuous production system and method for large-scale battery-grade iron phosphate, specifically including the following steps: The present invention discloses a continuous production system for large-scale battery-grade iron phosphate, comprising: (1) Used in a continuous purification system for ferrous sulfate byproduct of titanium dioxide; (2) Used in a continuous batching system for mixed phosphate salts; (3) Used in a continuous synthesis and washing system for ferric phosphate; (4) Used in a continuous flash drying and calcination system for ferric phosphate.

[0006] The continuous titanium dioxide ferrous sulfate production system consists of several parts, including a ferrous sulfate dissolving tank, a multi-stage reaction tank, a plate and frame filter press, and a storage tank. The reaction tanks, filtration devices, and storage tanks are connected by pumps and pipelines, and the materials are heated by steam.

[0007] The ferrous sulfate dissolving tank is mainly used for dissolving ferrous sulfate and conducting the initial reaction. The tank includes an inlet and an outlet. A conveyor belt is installed at the front end of the inlet to transport ferrous sulfate crystals. Water and ferrous sulfate, a byproduct of titanium dioxide production, are continuously added to the inlet. The ferrous sulfate crystals are dissolved by heating with hot water and steam. The outlet uses a diaphragm pump to transport the dissolved saturated ferrous sulfate solution from the top to the inlet at the bottom of the primary reaction tank.

[0008] After dissolution, the saturated ferrous sulfate solution enters a multi-stage reaction tank, which can be 3-6 stages. In some embodiments, the multi-stage reaction tank is divided into 4 stages according to process requirements, and the reaction tanks are arranged in series. The overflow trough at the top of the first-stage reaction tank is connected to the bottom of the second-stage reaction tank via a pump. The overflow trough at the top of the second-stage reaction tank is connected to the bottom of the third-stage reaction tank via a pump. The overflow trough at the top of the third-stage reaction tank is connected to the bottom of the fourth-stage reaction tank via a pump. The overflow trough at the top of the fourth-stage reaction tank is connected to a filter press via a pump for filtration. The solution temperature at the outlet of each stage of the reaction tank is monitored by a temperature sensor. A controller is connected to the temperature sensor and a steam heating pneumatic valve to control the opening of the pneumatic valve and adjust the steam flow in real time, thereby ensuring that the temperature in the reaction tank is stable to the set value. Specifically, the first-stage reaction tank contains ferrous sulfate solution and excess iron filings; the second-stage reaction tank contains ferrous sulfate solution and excess reduced iron powder; the third-stage reaction tank contains ferrous sulfate solution and excess reduced iron powder; and the fourth-stage reaction tank contains ferrous sulfate solution and ammonium phosphate solution.

[0009] The (2) continuous phosphate production system includes: raw material storage tanks (specifically, phosphate storage tanks, liquid ammonia storage tanks, and pure water storage tanks connected in parallel), tubular mixing reactors, and phosphate storage tanks. Materials are transported between the various parts through pumps and pipelines.

[0010] The tubular mixing reactor primarily provides a homogeneous mixing and reaction environment for materials. Using a tubular mixing reactor in conjunction with automated control technology enables the continuous and stable preparation of phosphates, eliminating the need for large-scale batching reactors. Furthermore, it provides heat exchange to ensure the required reaction temperature for the materials. This process is crucial for achieving and stabilizing the product's specifications. The tubular mixing reactor ensures consistent specifications, meeting the requirements for downstream product preparation, and allows the unit to operate stably for at least 30 days, more preferably 50 days, and even more preferably 6 months or more.

[0011] The tubular mixing reactor consists of three stages. The first-stage tubular mixing reactor provides the reaction site and also plays a role in coarsely adjusting the pH and density of the phosphate solution. The second-stage tubular mixing reactor is responsible for finely adjusting the pH and temperature of the solution, and the third-stage tubular mixing reactor is responsible for correcting the pH and temperature of the solution and stabilizing the phosphate.

[0012] In some industrial production processes, the degree of mixing of a mixed solution is extremely difficult to control due to specific process requirements. This may be because there are many reactants, making it difficult for stirring equipment to achieve proper mixing, or because the different contact processes and reaction degrees of the various raw materials result in different mixing outcomes, making the mixing process difficult to achieve. This application employs a three-stage tubular mixing reactor, and analyzes the degree and effectiveness of mixing uniformity by adjusting pH, density, phosphorus content, and temperature.

[0013] The single-stage tubular mixing reactor has a double-helix structure inside. The blades distributed at both ends of the axis are rotated and twisted so that the blades on both sides are arranged in a spiral on the axis. The rotating blades are spaced inside the tube, and the tube contains a spacer chamber for fluid flow to achieve the effect of dispersing the fluid. The inner tube is designed with a jacket structure with heat exchange function. A phosphate density monitor and a pH monitor are connected between the primary tubular mixing reactor and the secondary tubular mixing reactor. The phosphate density controller is connected to the density monitor and the deionized water feed pneumatic valve, and the pH controller is connected to the pH monitor and the ammonia feed pneumatic valve. The interior of the two-stage tubular mixing reactor is filled with a cylindrical structure assembled from corrugated plates. The corrugations of the plates are at a certain torsional angle to the tube axis. The corrugated plates of adjacent mixing units are arranged in parallel to form a cross-shaped and three-dimensional flow channel. A pH monitor is connected between the two-stage tubular mixing reactor and the three-stage tubular mixing reactor. The pH controller is connected to the pH monitor and the pneumatic valve for feeding high-concentration ammonia water. The interior of the three-stage tubular mixing reactor consists of X-shaped unit modules formed by intersecting grids arranged in a regular pattern, at an angle of 30-60° to the axis. The inner tubes are designed with a jacket structure with heat exchange function on the outside. The outlet of the tertiary reactor is connected to a pH monitor, a phosphate density monitor, and a temperature monitor. The phosphate density controller is connected to the density monitor and the deionized water feed pneumatic valve; the pH controller is connected to the pH monitor and the saturated ammonia feed pneumatic valve; and the temperature monitor is connected to the jacket inlet steam valve. The continuous synthesis and washing section of ferric phosphate includes: a feed mixing tank, a slurry grinding reactor, ferric phosphate washing system one (amorphous ferric phosphate horizontal washing centrifuge), a heated crystallization reactor, and ferric phosphate washing system two (i.e., aqueous ferric phosphate horizontal washing centrifuge). The reaction equipment is connected to each other by pumps and pipe fittings.

[0014] The aforementioned feed mixing tank is mainly used for the initial mixing of ferric phosphate materials. The feed system automatically adjusts the feed rate of each material by monitoring the pH of the synthesis reaction, and the slurry D50 is controlled at approximately 3-5 μm.

[0015] The slurry grinding reactor is mainly used for fine grinding and re-reaction of primary iron phosphate particles. The feed mixing tank and the slurry grinding reactor are controlled by a one-way feeder.

[0016] The slurry grinding reactor comprises three grinding stages connected in series. A high-pressure feeder connects to the inlet, with multiple nozzles at its end. The reaction iron source, mixed phosphorus source, and oxidant are pressurized and injected into the reaction chamber. The lower end of the reaction chamber connects to the upper end of the first-stage grinding stage, the lower end of the first-stage grinding stage connects to the upper end of the second-stage grinding stage, and the lower end of the second-stage grinding stage connects to the upper end of the third-stage grinding stage. Each grinding stage reactor is equipped with different types and proportions of zirconia balls, resulting in different particle size distributions in the slurry after passing through each stage. The material exiting the lower end of the third-stage grinding stage enters a horizontal piston pusher washing centrifuge via a screw feeder, where it is washed until the conductivity of the wash water meets product requirements.

[0017] The aforementioned washing systems for amorphous ferric phosphate and aqueous ferric phosphate (ferric phosphate washing system one and ferric phosphate washing system two) are mainly used for washing impurity ions during the synthesis of ferric phosphate. They primarily consist of a slurry storage tank and a horizontal piston-driven washing centrifuge. The slurry storage tank is mainly used for temporary storage of the synthesized slurry, while the horizontal piston-driven washing centrifuge is mainly used for continuous washing of ferric phosphate. The conductivity of the washing water for amorphous ferric phosphate is controlled to be below 5 mS / cm, and the conductivity of the washing water for aqueous ferric phosphate is controlled to be below 0.5 μS / cm.

[0018] The aforementioned heated crystallization reactor is mainly used for the crystallization reaction of ferric phosphate. It primarily consists of a tubular mixing reactor and a heat exchange steam jacket. The tubular mixing reactor contains baffles to promote uniform material distribution. The temperature of the material in the tubular mixing reactor is controlled by a DCS automatic control system. The length of the tubular mixing reactor can be flexibly adjusted by adding or reducing modules according to process requirements. Before entering the tubular mixing reactor, the washed paste-like slurry needs to be dispersed in a high-temperature crystallization solution and continuously fed into the insulated tubular mixing reactor via a diaphragm pump for the crystallization reaction.

[0019] The continuous flash drying and calcination section for iron phosphate includes: a flash dryer, a rotary kiln, and a post-processing system.

[0020] The flash dryer is mainly used for drying ferric phosphate materials. The pressed hydrated ferric phosphate is fed into a rotating cutter head via a hinge, and after being dried by hot air and crushed by the cutter head, ferric phosphate dihydrate is collected. The rotary kiln is mainly used for calcining ferric phosphate dihydrate. After the material is sintered at high temperature in the rotary kiln, anhydrous ferric phosphate is obtained by completely removing the water of crystallization.

[0021] The aforementioned post-processing system is mainly used for grinding, sieving, and packaging ferric phosphate materials. The physicochemical properties of the materials processed by the post-processing system all meet the product requirements of downstream manufacturers.

[0022] The method for large-scale continuous preparation of battery-grade iron phosphate using the aforementioned continuous preparation system specifically includes the following steps: S1: Ferrous sulfate, a byproduct of titanium dioxide production, is used as a stable iron source after being purified by a continuous purification device. S2: Phosphoric acid, ammonia, concentrated ammonia water, saturated ammonia water and water are processed into a stable phosphate solution through a continuous phosphate production unit. S3: The iron source from step S1, the phosphate from step S2 and the hydrogen peroxide are added through the iron source pipeline inlet and the mixed phosphorus source pipeline inlet, respectively. After being reacted in the grinding reactor, washed in the washing equipment, and carried out in the insulated tubular mixing reactor for crystallization reaction, the final washed result is hydrated iron phosphate. S4: Anhydrous ferric phosphate is obtained by processing the washed hydrated ferric phosphate through a flash drying device, rotary kiln calcination and post-treatment system.

[0023] In step S1, the ferrous sulfate dissolution tank is mainly used for the dissolution and initial reaction of ferrous sulfate. During the dissolution process, the solution density is maintained between 1.15 and 1.25 g / cm³. 3 Between these temperatures, the temperature of the dissolving tank is controlled at 60~80 ℃, and the pH of the outlet reaction is controlled at 1.0~2.0; In the multi-stage reaction tank (A02), the temperature of the first reaction tank is controlled at 70~90 ℃, and the outlet pH is controlled at 2.0~2.5; the temperature of the second reaction tank is controlled at 70~90 ℃, and the outlet pH is controlled at approximately 2.5~3.0; the temperature of the third reaction tank is controlled at 60-70 ℃, the pH is controlled at approximately 3.2-3.6, and the solution density is controlled at 1.18-1.20 g / cm³. 3 After being filtered by a filter press, the solution in the third reaction tank is clear and transparent with a turbidity of less than 20 NTU. The temperature of the iron salts used in the final reaction is maintained at 20-50 ℃, and it can be used directly.

[0024] The aforementioned single-stage tubular mixing reactor features a double-helix structure. Blades at both ends of the axis rotate and twist, arranging the blades helically along the axis. This structure increases the gas-liquid contact area. The rotating blades are spaced apart within the tube, enabling continuous gas-liquid mixing multiple times in a short period. This system undergoes a vigorous reaction and releases a large amount of heat; therefore, the tube cavity is designed with compartments containing fluid flow to disperse the fluid. Furthermore, the closed-pipe mixing method prevents ammonia escape, achieving complete absorption of ammonia compared to a batch reactor structure (e.g., ...). Figure 1 (As shown).

[0025] The pH and density of the primary reaction solution are controlled by adjusting the concentration and flow rate of phosphoric acid and the flow rate of ammonia at the feed end of the primary tubular mixer. At the end of the primary tubular mixer, the pH of the solution is adjusted to 4.0–4.5, and the solution density is controlled to 1.28–1.30 g / cm³. 3 The reaction temperature of the solution is controlled at around 50~60 ℃. Within this range, the phosphate generated by the reaction of a large amount of phosphoric acid and ammonia is mainly composed of monoammonium phosphate and phosphoric acid. Its solubility is relatively high and it is not sensitive to the pH of the solution, so it is not easy to crystallize out. The two-stage tubular mixing reactor is filled with cylindrical structures assembled from corrugated plates. The corrugations of the plates are twisted at a certain angle to the tube axis. The corrugated plates of adjacent mixing units are arranged in parallel, forming intersecting and three-dimensional flow channels. The corrugated structure reduces dead angles within the pipes, making the liquid-liquid reaction contact more uniform, while also preventing the formation of fine crystal precipitates. The closed structural design further reduces ammonia loss (e.g., ...). Figure 2 (As shown).

[0026] By controlling the flow rate of high-concentration ammonia water at the feed end of the two-tube mixing reactor (i.e., selectively injecting ammonia water into the two-tube mixing reactor during equipment operation, with an ammonia water concentration of 30-40% being preferable), the pH of the secondary reaction is adjusted to 5.5-6.5. This reaction process, through the slow addition of high-concentration ammonia water, increases the proportion of monohydrogen phosphate, and the solution density is controlled at 1.24-1.26 g / cm³.3 Around 1000 phosphates were present during this process, but only some tiny crystal nuclei were formed. The three-stage tubular mixing reactor is internally composed of X-shaped unit modules formed by intersecting grids arranged at a 30-60° angle to the axis. This structure primarily promotes mixed flow of the reaction solution within, ensuring more thorough mixing. The outer casing of the inner tubes features a heat-exchange jacket structure to further increase the solution temperature and accelerate the dissolution of fine crystals (e.g., ...). Figure 3 (As shown).

[0027] The three-stage tubular mixing reactor is fed with saturated ammonia water (i.e., saturated ammonia water needs to be selectively injected into the reactor during operation). The pH of the secondary reaction is adjusted to 6.7-6.8, and the solution density is controlled at 1.25±0.05 g / cm³. 3 Around this point, the main function of this part is to fine-tune the pH and solution density. At this point, the main anion in the solution is monohydrogen phosphate. Under this pH condition, it is easy to maintain the synthesis reaction process in equilibrium, and the nucleation rate is faster during the reaction, resulting in smaller primary particles of iron phosphate.

[0028] The production system heats up through a heat exchange jacket outside the pipes. The heat exchange medium is steam. Steam enters from the jacket inlet and exits from the jacket outlet.

[0029] In step S3, the slurry has different particle size distributions after passing through various stages of slurry grinding reactors. The first-stage grinding stage controls the particle size to be around 1 μm, the second-stage grinding stage controls the particle size to be around 300-600 nm, and the third-stage grinding stage controls the particle size to be around 100-300 nm. In step S3, the material after the reaction is completed is washed until the conductivity of the wash water is below 5 mS / cm.

[0030] In step S3, the reaction temperature of the heated crystallization reactor is controlled at 94~98 ℃, the reaction time is controlled at 10-15 min, and the slurry changes from yellow to pink after the reaction is completed.

[0031] In step S4, the calcination temperature is set to 550-650 ℃ and the calcination time is 100-300 min. After calcination, battery-grade anhydrous iron phosphate can be obtained.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention, based on the requirements for phosphates in the synthesis of ferric phosphate and the characteristics of phosphates, employs a multi-stage pipeline mixer for the preparation of high-concentration ammonium phosphate solutions. This successfully solves the problem of large-scale, batch-free, continuous preparation of high-concentration phosphates. Simultaneously, the use of a multi-stage pipeline mixer replaces the investment in large equipment such as reaction kettles and reduces the floor space required, significantly improving production efficiency.

[0033] 2. This invention employs a continuous production process throughout the entire preparation process, from iron and phosphorus source raw materials to finished iron phosphate product. This allows the entire reaction to be connected in series, and all key indicators from raw material to finished product are monitored by an automated system, reducing errors caused by human intervention and resulting in higher product consistency. Simultaneously, this continuous process significantly reduces manual labor, lowering production costs.

[0034] 3. This invention designs the purification of ferrous sulfate, a byproduct of titanium dioxide, into a continuous purification method, which realizes the economical, continuous, and stable preparation of iron source and greatly improves production efficiency.

[0035] 4. This invention utilizes a slurry grinding reactor in the reaction stage, which can uniformly control the primary particle size of ferric phosphate particles. This allows sulfate, ammonium, and other metal impurity ions encapsulated in the product to be carried out by the wash water during a single washing process, thereby improving product purity and reducing wash water consumption. Simultaneously, the grinding process reduces the overall particle size, decreasing the time consumed in the crystallization process and improving production efficiency. Attached Figure Description

[0036] To more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 It is a single-stage tubular mixing reactor.

[0038] Figure 2 It is a two-stage tubular mixing reactor.

[0039] Figure 3 It is a three-stage tubular mixing reactor.

[0040] Figure 4 A simplified process flow diagram for the continuous production of battery-grade iron phosphate for large-scale applications provided by this invention.

[0041] Figure 5 A simplified flow chart of the continuous impurity removal section for ferrous sulfate, a byproduct of titanium dioxide, provided by this invention.

[0042] Figure 6 A simplified flow chart of the continuous phosphate production process provided by the present invention.

[0043] Figure 7 The image shows the XRD pattern of ferric phosphate in Example 1 of this invention.

[0044] Figure 8 This is a SEM image of ferric phosphate from Example 1 of the present invention.

[0045] Figure 9 This is a SEM image of lithium iron phosphate prepared from iron phosphate according to the present invention.

[0046] Figure 10 The figure shows the electrical properties of lithium iron phosphate prepared using this iron phosphate precursor. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0048] Example 1 Adopting attachment Figure 4 , 5 The simplified process flow diagram of continuous production of battery-grade iron phosphate, as shown in section 6, enables the following large-scale continuous production system: (1) Continuous purification system for ferrous sulfate byproduct of titanium dioxide; (2) Continuous batching system for mixed phosphate salts; (3) Continuous synthesis and washing system for ferric phosphate; (4) Continuous flash drying and calcination system for ferric phosphate.

[0049] The continuous titanium dioxide ferrous sulfate production system consists of several parts, including a ferrous sulfate dissolving tank (A01), a multi-stage reaction tank (A02), a plate and frame filter press (A03), and a storage tank (A04). Material is transported between the reaction tanks, filtration devices, and storage tanks via pumps and pipelines, and heated by steam. In this case, the multi-stage reaction tank (A02) is composed of three reaction tanks connected in series.

[0050] The ferrous sulfate dissolving tank (A01) is mainly used for dissolving ferrous sulfate and conducting the initial reaction. The reaction tank includes an inlet and an outlet. A conveyor belt is installed at the front end of the inlet to transport ferrous sulfate crystals. Water and ferrous sulfate, a byproduct of titanium dioxide production, are continuously added to the inlet. The ferrous sulfate crystals are dissolved by heating with hot water and steam. The outlet uses a diaphragm pump to transport the dissolved saturated ferrous sulfate solution from the top to the inlet at the bottom of the primary reaction tank.

[0051] After dissolution, the saturated ferrous sulfate solution enters a multi-stage reaction tank (A02). This multi-stage reaction tank is divided into three stages according to process requirements, and the tanks are arranged in series. The overflow tank at the top of the first-stage reaction tank is connected to the bottom of the second-stage reaction tank via a pump. The overflow tank at the top of the second-stage reaction tank is connected to the bottom of the third-stage reaction tank via a pump. The overflow tank at the top of the third-stage reaction tank is connected to a filter press for filtration. The solution temperature at the overflow outlet of each stage of the reaction tank is monitored by temperature sensors. A controller is connected to the temperature sensors and a steam-heating pneumatic valve to control the valve opening and adjust the steam flow rate in real time, thereby ensuring that the temperature in the reaction tank remains stable at the set value. Specifically, the first-stage reaction tank contains ferrous sulfate solution and excess iron filings; the second-stage reaction tank contains ferrous sulfate solution and excess reduced iron powder; and the third-stage reaction tank contains ferrous sulfate solution and ammonium phosphate solution.

[0052] The (2) continuous batching system for mixed phosphate salts consists of three parts: raw material storage tanks (specifically, a phosphate storage tank (B01), a liquid ammonia storage tank (B02), and a pure water storage tank (B03)), a tubular mixing reactor (B04), and a phosphate storage tank (B05). The materials are transported between the parts through pumps and pipelines.

[0053] The aforementioned phosphate storage tank (B05) is used for storing phosphate solutions.

[0054] The tubular mixing reactor (B04) mainly provides a uniform mixing and reaction environment for materials. By using the tubular mixing reactor in conjunction with automated control technology, the continuous and stable preparation of phosphates can be achieved, eliminating the need for large batching reactors. In addition, it can also provide heat exchange to ensure the required reaction temperature of the materials.

[0055] The tubular mixing reactor consists of three stages. The first-stage tubular mixing reactor provides the main reaction site and also coarsely adjusts the pH and density of the solution. The second-stage tubular mixing reactor adjusts the pH and density of the solution. The third-stage tubular mixing reactor finely adjusts the pH, density, and temperature of the solution. After three stages of regulation, the various indicators of phosphate salts meet the requirements of the reaction raw materials.

[0056] The single-stage tubular mixing reactor (manufactured by Shanghai Anfit Chemical Equipment Co., Ltd.) has a double-helix structure inside. The blades distributed at both ends of the axis are rotated and twisted, so that the blades on both sides are arranged in a spiral on the axis. The rotating blades are spaced inside the tube, and the tube contains a spacer chamber for fluid flow, which achieves the function of dispersing the fluid. The inner tube is designed with a jacket structure with heat exchange function.

[0057] A density monitor and a pH monitor are connected between the primary tubular mixing reactor and the secondary tubular mixing reactor. The density controller is connected to the density monitor and the phosphoric acid feed pneumatic valve, and the pH controller is connected to the pH monitor and the ammonia feed pneumatic valve.

[0058] The two-stage tubular mixing reactor (manufactured by Shanghai Anfit Chemical Equipment Co., Ltd.) is filled with cylindrical bodies assembled from corrugated plates. The corrugations of the plates are at a certain torsional angle to the tube axis. The corrugated plates of adjacent mixing units are arranged in parallel to form a cross-shaped and three-dimensional flow channel.

[0059] A pH monitor is connected between the two-stage tubular mixing reactor and the three-stage tubular mixing reactor. The pH controller is connected to the pH monitor and the pneumatic valve for concentrated ammonia water feed.

[0060] The three-stage tubular mixing reactor (Shanghai Chongye Industrial Co., Ltd.) is composed of X-shaped unit modules formed by intersecting grids arranged in a regular pattern, at a 60° angle to the axis. The inner tubes are designed with a jacket structure for heat exchange.

[0061] A pH monitor is connected to the outlet of the three-stage reactor, and the pH controller is connected to the pH monitor and the pneumatic valve for saturated ammonia water feed.

[0062] The continuous synthesis and washing section of ferric phosphate consists of four parts: a feed mixing tank (C01), a slurry grinding reactor (C02), an amorphous ferric phosphate horizontal washing centrifuge (C03), a heated crystallization reactor (C04), and an aqueous ferric phosphate horizontal washing centrifuge (C05). The reaction equipment is connected by pumps and pipelines.

[0063] The feed mixing tank (C01) is mainly used for the initial mixing of ferric phosphate materials. The feed system automatically adjusts the feed rate of each material by monitoring the pH of the synthesis reaction, and the slurry D50 is controlled at about 3-5 μm.

[0064] The slurry grinding reactor (CO2) is mainly used for fine grinding and re-reaction of primary iron phosphate particles. The feed mixing tank and the slurry grinding reactor are controlled by a one-way feeder.

[0065] The slurry grinding reactor comprises three grinding stages connected in series. A high-pressure feeder connects to the inlet, with multiple nozzles at its end. The reaction iron source, mixed phosphorus source, and oxidant are pressurized and injected into the reaction chamber. The lower end of the reaction chamber connects to the upper end of the first-stage grinding stage, the lower end of the first-stage grinding stage connects to the upper end of the second-stage grinding stage, and the lower end of the second-stage grinding stage connects to the upper end of the third-stage grinding stage. Each grinding stage reactor is equipped with different types and proportions of zirconia balls, resulting in different particle size distributions in the slurry after passing through each stage. The material exiting the lower end of the third-stage grinding stage enters a horizontal piston pusher washing centrifuge via a screw feeder, where it is washed until the conductivity of the wash water meets product requirements.

[0066] The aforementioned heated crystallization reactor (CO3) is mainly used for the crystallization reaction of ferric phosphate. It primarily consists of a tubular mixing reactor (Qidong Yongda Petrochemical Equipment Co., Ltd., U-tube type) equipped with a heat exchange steam jacket. The tubular mixing reactor contains baffles to promote uniform material distribution. The temperature of the material in the tubular mixing reactor is controlled by a DCS automatic control system. The length of the tubular mixing reactor can be flexibly adjusted by adding or reducing modules according to process requirements. Before entering the tubular mixing reactor, the washed paste-like slurry needs to be dispersed in a high-temperature crystallization solution and continuously fed into the insulated tubular mixing reactor via a diaphragm pump for the crystallization reaction.

[0067] The aforementioned aqueous ferric phosphate washing system (CO4) is mainly used for washing impurity ions during the synthesis of ferric phosphate. It primarily consists of a slurry storage tank and a horizontal piston-driven washing centrifuge. The slurry storage tank is mainly used for the temporary storage of the synthesized slurry, while the horizontal piston-driven washing centrifuge is mainly used for the continuous washing of ferric phosphate, with the wash water conductivity controlled to be below 0.5 mS / cm.

[0068] The continuous flash drying and calcination section for iron phosphate includes: a flash dryer (D01), a rotary kiln (D02), and a post-treatment system (D03).

[0069] The flash dryer (D01) is mainly used for drying ferric phosphate materials. The pressed hydrated ferric phosphate is fed into the rotating cutter head position through a hinge, and after being dried by hot air and crushed by the cutter head, ferric phosphate dihydrate is collected. The rotary kiln (DO2) is mainly used for calcining ferric phosphate dihydrate. After the material is sintered at high temperature in the rotary kiln, anhydrous ferric phosphate is obtained by completely removing the water of crystallization.

[0070] The post-processing system (D03) is mainly used for grinding, sieving, and packaging of ferric phosphate materials. The physicochemical properties of the materials processed by the post-processing system meet the product requirements of downstream manufacturers.

[0071] Example 2 The continuous production system of Example 1 was used to prepare battery-grade iron phosphate on a large scale. The method includes the following steps: S1: Dissolve 1 ton of ferrous sulfate, a byproduct of titanium dioxide production, in a dissolving tank (A01). This dissolution mainly involves the initial reaction and dissolution of ferrous sulfate. Throughout the dissolution process, maintain the solution density between 1.20 and 1.25 g / cm³. 3 Between these stages, the temperature of the dissolving tank (A01) is controlled at 60~80 ℃, and the pH of the outlet reaction is controlled at 1.0~2.0; after dissolution, it enters the multi-stage reaction tank (A02). In the multi-stage reaction tank (A02), the temperature of the first reaction tank is controlled at 70~90 ℃, and the outlet pH is controlled at 2.0~2.5; the temperature of the second reaction tank is controlled at 70~90 ℃, and the outlet pH is controlled at approximately 2.5~3.0; the temperature of the third reaction tank is controlled at 60-70 ℃, the pH is controlled at approximately 3.5-3.6, and the solution density is controlled at 1.18-1.20 g / cm³. 3 The solution in the third reaction tank is clear and transparent after being filtered by a filter press, with a turbidity of 10 NTU. The temperature of the iron salt used in the final reaction is maintained at 40-50℃, and it can be used directly as a stable iron source.

[0072] S2: 85% food-grade phosphoric acid, ammonia, ammonia solution, and pure water are separately introduced into a multi-stage tubular reactor B04. The multi-stage tubular mixing reactor consists of three stages. At the end of the first-stage tubular mixing reactor, the pH is adjusted to 4.0-4.5, and the density is controlled at 1.28-1.30 g / cm³. 3 The solution reaction temperature is controlled at approximately 50-60 °C; the two-stage tubular mixing reactor is supplemented with high-concentration ammonia water (approximately 38%) at a flow rate of 1-2 L / min, with the final pH adjusted to 5.5-6.5 and the density controlled at 1.24-1.26 g / cm³. 3 A three-stage tubular mixing reactor is used, supplemented with saturated ammonia water at a flow rate of 0.5~1.5 L / min, with the final pH adjusted to 6.7~6.8 and the temperature controlled at 65~70 ℃. A stable phosphate solution with a pH of 6.75±0.05, an overall feed molar ratio of ammonia to phosphoric acid controlled between 1:1 and 10:1, and a phosphorus content of approximately 9.5% (wt%) is prepared through a continuous phosphate production unit.

[0073] S3: The iron source from step S1, the phosphate salt from step S2, and hydrogen peroxide are added to the feed mixing tank CO1 through the iron source inlet, the phosphate source inlet, and the oxidant inlet, respectively, in a molar ratio of 1:1:0.8. After mixing, the mixture enters the slurry grinding reactor CO2 for reaction. The slurry grinding reactor CO2 is a three-stage reactor. The first-stage grinding section controls the particle size to be 900nm-1μm, the second-stage grinding section controls the particle size to be 500-600nm, and the third-stage grinding section controls the particle size to be 100-200nm. After reaction in the grinding reactor, the mixture is washed in a horizontal piston pusher washing centrifuge until the conductivity of the wash water is lower than 5 mS / cm. Then, the mixture enters the heated crystallization reactor (CO3), which is a heat-insulated tubular reactor where the crystallization reaction is carried out at 98℃. After 10 minutes, hydrated ferric phosphate is finally obtained. S4: After washing the hydrated ferric phosphate, it is dehydrated by flash drying equipment and then calcined in a rotary kiln at 700 ℃ for 2 h to obtain anhydrous ferric phosphate, which is then packaged through a post-processing system.

[0074] Table 1. Product and Device Operation Status in Example 2

[0075] With stable equipment operation, the finished iron phosphate product indicators (iron-phosphorus ratio) are consistent and the electrical properties fluctuate little. The products produced by this equipment fully meet the downstream manufacturers' requirements for high product consistency.

[0076] Example 3 Example 3 only changed the positions of the primary and secondary tubular reactors, and the rest of the methods and steps were the same as in Example 2. Iron phosphate products were prepared by running the continuous equipment in this way.

[0077] Example 4 Example 4 only changes the positions of the secondary and tertiary tubular reactors in step S2; the rest of the methods and steps are the same as in Example 2. Ferric phosphate products are prepared by operating a continuous process device in this way.

[0078] Example 5 Example 5 only changed the phosphorus content of the phosphate salt in step S2 to 8% (wt%), and the rest of the methods and steps were the same as in Example 2. The ferric phosphate product was prepared by running the continuous process in this way.

[0079] Example 6 Example 6 only changed the phosphorus content of the phosphate salt in step S2 to 7% (wt%), and the rest of the methods and steps were the same as in Example 2. The ferric phosphate product was prepared by running the continuous process in this way.

[0080] Comparative Example 1 The comparative method and steps are the same as in Example 2, except that the tubular reactor in step S2 is reduced from a three-stage tubular reactor to a single-stage and two-stage tubular reactor. The rest of the methods and steps are the same as in Example 2. Iron phosphate products are prepared by running a continuous process device in this way.

[0081] Comparative Example 2 The comparative method and steps are the same as in Example 2, except that the tubular reactor in step S2 is replaced with a conventional batch reactor. The rest of the methods and steps are the same as in Example 2. Iron phosphate products are prepared by running a continuous process device in this way. .

Claims

1. A continuous method for large-scale preparation of battery-grade iron phosphate, characterized in that, Includes the following steps: S1: Ferrous sulfate, a byproduct of titanium dioxide production, is used as a stable iron source after being purified by a continuous purification device. S2: Phosphate is obtained by reacting phosphoric acid, ammonia, high-concentration ammonia water or saturated ammonia water in a multi-stage tubular mixing reactor, wherein the multi-stage tubular mixing reactor is a three-stage tubular reactor connected in series. The internal structure of the single-stage tubular mixing reactor is a double helix structure. The blades distributed at both ends of the axis are rotated and twisted so that the blades on both sides are arranged in a helical pattern on the axis. The rotating blades are spaced inside the tube, and the tube contains a spacer chamber for fluid flow, which achieves the effect of dispersing the fluid. The outer side of the inner tube is designed with a jacket structure with heat exchange function. The interior of the two-stage tubular mixing reactor is filled with a cylindrical structure assembled from corrugated plates. The corrugations of the plates are at a certain torsional angle to the tube axis. The corrugated plates of adjacent mixing units are arranged in parallel to form a cross-shaped and three-dimensional flow channel. The interior of the three-stage tubular mixing reactor consists of X-shaped unit modules formed by intersecting grids arranged in a regular pattern, at an angle of 30-60° to the axis. The inner tubes are designed with a jacket structure with heat exchange function on the outside. The pH of the solution at the end of the primary pipeline mixer is adjusted to 4.0-4.5, and the solution density is controlled to 1.28-1.30 g / cm³. 3 The solution reaction temperature is controlled at 50~60℃; In the two-stage tubular mixing reactor, the feed rates of ammonia gas, high-concentration ammonia solution, or saturated ammonia solution are controlled to adjust the pH of the secondary reaction to 5.5–6.5 and the solution density to 1.24–1.26 g / cm³. 3 ; The three-stage tubular mixer is fed with saturated ammonia water, and the pH of the three reactions is adjusted to 6.7-6.8, with the solution density controlled at 1.25±0.05 g / cm³. 3 ; S3: The iron source from step S1, the phosphate from step S2, and hydrogen peroxide are mixed, stirred, ground, washed, and the slurry is prepared. After a crystallization reaction at a higher temperature, the mixture is washed again to obtain hydrated ferric phosphate. The molar ratio of phosphate, iron source, and hydrogen peroxide is controlled at 0.8~1.2:1:0.5~1.5, and the phosphorus content of the phosphate is controlled at 8~12% by mass. S4: Anhydrous ferric phosphate is obtained by flash drying and calcining the washed hydrated ferric phosphate in a rotary kiln.

2. The method for large-scale continuous preparation of battery-grade iron phosphate according to claim 1, characterized in that, In step S1, the final pH value of ferrous sulfate is adjusted to between 2.5 and 4.5, and the solution density is controlled between 1.18 and 1.20 g / cm³. 3 Between these values, the turbidity is less than 20 NTU, and the temperature at which the iron salt reaction finally takes place is maintained at 20-50 °C.

3. The method for large-scale continuous preparation of battery-grade iron phosphate according to claim 1, characterized in that, In step S3, the iron source concentration is 0.5~1.5 mol / L.

4. The method for large-scale continuous preparation of battery-grade iron phosphate according to claim 3, characterized in that, The grinding reaction controls the particle size to be 50-100 nm; the slurry is washed until the conductivity is below 5 mS / cm. -1 the following.

5. The method for large-scale continuous preparation of battery-grade iron phosphate according to claim 3, characterized in that, The temperature for crystallization is controlled at 94~98℃.

6. The method for large-scale continuous preparation of battery-grade iron phosphate according to claim 1, characterized in that, In step S4, the flash drying inlet air temperature is controlled between 200 and 300 ℃, the outlet air temperature is controlled between 80 and 100 ℃, the rotary kiln calcination temperature is controlled between 550 ℃ and 650 ℃, and the calcination time is controlled between 3 and 5 h.

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