Ceramic membrane reactor and method for the preparation of iron oxyhydroxide precursors

Abstract

The application provides a ceramic membrane reactor and method for preparing iron oxyhydroxide precursor, the reactor comprises a reactor shell, an upper hollow rotating shaft, an upper disc ceramic membrane installed at the lower end of the upper hollow rotating shaft, a lower hollow rotating shaft, a lower disc ceramic membrane installed at the upper end of the lower hollow rotating shaft, the membrane surfaces of the upper disc ceramic membrane and the lower disc ceramic membrane are oppositely arranged, a gap-adjustable micro-reaction channel is formed between the two opposite membrane surfaces, iron salt solution and alkali liquor are respectively ejected in the form of micro-scale jet flow from the membrane surface micro-holes to the micro-reaction channel through the upper and lower hollow rotating shafts, FeOOH particles are generated by opposite collision and mixing, and the differential shear force makes the reaction medium centrifugally throw out and continuously discharge. The three mechanisms of opposite micro-jet collision and mixing, double-shaft differential shear centrifugal throwing out and micro-reaction channel limitation can realize continuous production of FeOOH with narrow particle size distribution, and the particle size is accurately controllable in the range of 200-500 nm.

Description

Technical Field

[0001] This invention relates to the field of nanopowder preparation technology, and in particular to a ceramic membrane reactor and method for preparing iron hydroxyl oxide precursors. Background Technology

[0002] Spherical submicron-sized iron oxides, such as γ-Fe₂O₃ (maghemite), are important functional inorganic powder materials. Their magnetic properties, catalytic activity, and optical properties are highly dependent on the particle size, particle size distribution, and particle morphology. The preparation of spherical iron oxides typically employs a two-step route: precursor synthesis followed by calcination. First, a spherical FeOOH (ferric hydroxy oxide) precursor is prepared via liquid-phase co-precipitation, which is then calcined to convert it into the target iron oxide. Therefore, the particle size distribution and sphericity of the precursor directly determine the quality of the final product.

[0003] Currently, the main industrial method for preparing FeOOH precursors is the stirred tank co-precipitation method. This method involves adding iron salt solution and alkali solution to a stirred tank, mixing them by mechanical stirring, and generating FeOOH through a neutralization precipitation reaction. However, the stirred tank co-precipitation method has the following inherent technical defects: (1) The local supersaturation is extremely uneven. An extremely high pH is formed instantaneously near the alkali inlet, and the reactants nucleate after contact. The supersaturation is insufficient far from the inlet, resulting in a wide particle size distribution of the final product, which cannot meet the requirements of high-performance soft magnetic materials for a narrow distribution; (2) There are large differences in product quality between batches; (3) It is difficult to guarantee the sphericity of the precursor; (4) It is impossible to achieve continuous large-scale production.

[0004] In existing technologies, researchers use rotating disk reactors to promote mixing by utilizing the centrifugal and shear forces generated by the rotation of the disk. However, the traditional design uses free liquid surface flow, and the contact and mixing of reactants are still limited by macroscopic fluid dynamics, making it difficult to achieve molecular-level uniform mixing.

[0005] Therefore, there is still a need in the field for a FeOOH preparation method and apparatus that can simultaneously achieve continuous operation, narrow particle size distribution, precise particle size control, high sphericity products, and is suitable for industrial scale-up, in order to solve the above problems. Summary of the Invention

[0006] The first objective of this invention is to disclose an apparatus for preparing narrow-particle-size spherical iron hydroxyl oxide (FeOOH) precursors by using a double-hollow shaft differential-driven rotating disc ceramic membrane reactor and combining upper and lower opposing membrane surface micro-jet injection with differential shear centrifugation.

[0007] To achieve the above objectives, the present invention discloses a ceramic membrane reactor for preparing iron hydroxyl oxide precursor, comprising a reactor shell, and further comprising: an upper hollow rotating shaft, an upper circular ceramic membrane mounted on the lower end of the upper hollow rotating shaft with its membrane surface facing downward; and a lower hollow rotating shaft, a lower circular ceramic membrane mounted on the upper end of the lower hollow rotating shaft with its membrane surface facing upward; the membrane surfaces of the upper circular ceramic membrane and the lower circular ceramic membrane are arranged opposite to each other, and an adjustable gap micro-reaction channel is formed between the two opposite membrane surfaces;

[0008] The upper hollow rotating shaft has an iron salt feeding channel inside. The iron salt solution is transported to the upper circular ceramic membrane through the upper hollow rotating shaft and ejected into the micro-reaction channel from the micropores on the surface of the upper circular ceramic membrane in the form of a micro-scale jet.

[0009] The lower hollow rotating shaft has an alkali feed channel inside. The alkali is transported to the lower disc ceramic membrane through the lower hollow rotating shaft and ejected into the micro-reaction channel in the form of a micro-scale jet from the micropores on the surface of the lower disc ceramic membrane.

[0010] The reactive fluids collide and mix in opposite directions within the microreaction channel and react.

[0011] In some embodiments, there is a speed difference between the upper hollow shaft and the lower hollow shaft, thereby generating a differential shear flow between the two opposing membrane surfaces.

[0012] In some embodiments, the upper hollow shaft and the lower hollow shaft are driven to rotate around their respective axes by independent upper drive motors and lower drive motors, and the speeds of the upper drive motors and lower drive motors are independently adjustable.

[0013] In some embodiments, the height of the microreaction channel is 1 to 5 mm.

[0014] In some embodiments, the pore size of the upper and lower circular ceramic membranes is 0.1-1 μm.

[0015] In some embodiments, the reactor shell is provided with an inlet and an outlet; inside the reactor shell, along the outer periphery of the disc ceramic membrane, there is a ring plate for product collection, used to collect the hydroxyl oxide slurry suspension centrifuged from the microreaction channel.

[0016] In some embodiments, the ring plate is an annular collection trough plate arranged along the outer periphery of the disc ceramic membrane, with its inner edge adjacent to the outer periphery of the disc ceramic membrane, for receiving and collecting the ferric hydroxide slurry suspension centrifuged from the microreaction channel.

[0017] In some embodiments, a temperature control system is also included, disposed on the inner or outer wall of the reactor shell, for controlling the temperature within the microreaction channel.

[0018] In some embodiments, an online pH monitoring and feedback control system is also included, which is located at the microreaction channel to monitor the pH value in real time and adjust the alkali feed flow rate accordingly.

[0019] In some embodiments, the speed difference between the upper hollow shaft and the lower hollow shaft is 200~1500 rpm.

[0020] To achieve the above objectives, the present invention also discloses a method for preparing an iron hydroxyl oxide precursor, using the aforementioned ceramic membrane reactor for preparing the iron hydroxyl oxide precursor, comprising the following steps:

[0021] S1: Preparation of iron salt precursor solution: Dissolve iron salt in water to prepare iron salt solution;

[0022] S2: Preparation of alkaline solution;

[0023] S3: Control reaction conditions: Inject liquid medium into the reactor so that the upper and lower circular ceramic membranes are immersed in the liquid phase. Control the reaction pH value by adjusting the injection ratio of iron salt solution and alkali solution, and control the reaction temperature in the reactor.

[0024] S4: Coprecipitation reaction: The iron salt solution of S1 is introduced into the iron salt feed channel of the upper hollow rotating shaft, and the alkali solution of S2 is introduced into the alkali feed channel of the lower hollow rotating shaft. Driven by the transmembrane pressure difference, the iron salt solution and the alkali solution are ejected from the micropores of the upper and lower circular ceramic membranes respectively into the micro-reaction channel in the form of micro-scale jets and then collide and mix in opposite directions. A coprecipitation reaction occurs in the micro-reaction channel to generate FeOOH particles, which are continuously discharged from the micro-reaction channel with the shear flow.

[0025] S5: Product collection and post-processing: The FeOOH slurry suspension ejected by centrifugation is continuously collected from the reactor outlet, and after solid-liquid separation, washing and drying, spherical FeOOH powder is obtained.

[0026] In some embodiments, the concentration of the iron salt solution is 0.05~0.5 mol / L, and the concentration of the alkali solution is 0.1~2 mol / L.

[0027] In some embodiments, in step S3, the reaction temperature is 15~80°C, and the reaction pH is controlled to be 8~10 by adjusting the ratio of the amount of iron salt solution and alkali solution injected.

[0028] In some embodiments, the iron salt is a mixture of FeCl3 and FeCl2, wherein the molar ratio of FeCl3 to FeCl2 is 1.5:1 to 3:1.

[0029] In some embodiments, the alkaline solution is a NaOH solution or a KOH solution.

[0030] In some embodiments, the drying is performed under vacuum drying or spray drying at a temperature of 60-100°C.

[0031] In some embodiments, the average particle size of the spherical FeOOH powder is 200~500 nm, and the particle size distribution variation coefficient (CV) is less than 10%.

[0032] Compared with the prior art, the beneficial effects of the present invention are: (1) The iron salt solution and the alkaline solution are ejected from the micropores of the upper and lower membrane surfaces in the form of micron-level jets, and collide in opposite directions in the narrow gap, achieving molecular-level uniform mixing in a very short time, effectively reducing the local concentration gradient; (2) The narrow gap between the upper and lower membrane surfaces constitutes a micro-reaction channel, which restricts the spatial range of nucleation and growth, so that all particles nucleate and grow under the same spatial conditions, further improving the uniformity of particle size distribution; (3) By adjusting the membrane pore size, precursor concentration, rotation speed difference and membrane gap, the average particle size can be precisely controlled within the range of 200~500 nm; (4) Under the conditions of spatial uniform supersaturation, FeOOH grows along each crystal plane at a nearly the same rate, naturally forming a spherical or near-spherical morphology with better sphericity. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the ceramic membrane reactor structure shown in Embodiment 1 of the present invention;

[0034] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0035] Explanation of reference numerals in the attached diagram: 1. Reactor shell; 2. Inlet; 3. Ring plate; 4. Outlet; 51. Upper hollow rotating shaft; 52. Upper drive motor; 53. Upper circular ceramic membrane; 531. Upper circular ceramic membrane pores; 61. Lower hollow rotating shaft; 62. Lower drive motor; 63. Lower circular ceramic membrane; 631. Lower circular ceramic membrane pores; 7. Microreaction channel. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Any equivalent substitutions or replacements in function, method, or structure made by those skilled in the art based on these embodiments are within the scope of protection of the present invention.

[0037] Example 1

[0038] like Figure 1-2As shown, a ceramic membrane reactor for preparing iron hydroxyl oxide precursor includes a reactor shell 1, and further includes:

[0039] The upper hollow rotating shaft 51 has an upper circular ceramic membrane 53 installed at the lower end of the upper hollow rotating shaft 51 with its membrane surface facing downwards.

[0040] A lower hollow rotating shaft 61, and a lower circular ceramic membrane 63 installed at the upper end of the lower hollow rotating shaft 61 with the membrane surface facing upward;

[0041] The upper circular ceramic membrane 53 and the lower circular ceramic membrane 63 are arranged opposite each other, and an adjustable micro-reaction channel 7 is formed between the two opposite membrane surfaces. The height of the micro-reaction channel 7 is 1~5 mm and is adjustable.

[0042] There is a speed difference between the upper hollow shaft 51 and the lower hollow shaft 61, thereby generating a differential shear flow between the two opposite membrane surfaces. The speed difference between the upper hollow shaft 51 and the lower hollow shaft 61 is 200~1500 rpm.

[0043] One of the upper hollow rotating shaft 51 and the lower hollow rotating shaft 61 is set to a fixed state, and the other hollow rotating shaft is set to a rotating state, forming a differential shear flow between the two membrane surfaces.

[0044] Another approach is that the upper hollow shaft 51 and the lower hollow shaft 61 are driven to rotate around their respective axes by independent upper drive motors 52 and lower drive motors 62, and the speeds of the upper drive motors 52 and lower drive motors 62 are independently adjustable.

[0045] The upper hollow rotating shaft 51 has an internal iron salt feeding channel. The iron salt solution is transported through the upper hollow rotating shaft 51 to the upper circular ceramic membrane 53, and then exits through the micropores on the surface of the upper circular ceramic membrane 53 (i.e., Figure 2 In the middle, the upper circular ceramic membrane pores 531 are ejected into the micro-reaction channel 7 in the form of micro-scale jets; the interior of the lower hollow rotating shaft 61 is an alkali feed channel, through which the alkali is transported to the lower circular ceramic membrane 63, and exits from the micropores on the surface of the lower circular ceramic membrane 63 (i.e., Figure 2 The reaction fluid is ejected into the micro-reaction channel 7 in the form of a micro-scale jet through the lower circular ceramic membrane hole 631; the reaction fluid collides and mixes with each other in the micro-reaction channel 7, and a co-precipitation reaction occurs to generate hydroxyl iron oxide particles.

[0046] Of course, the interior of the upper hollow shaft 51 can also be an alkaline feed channel, while the interior of the lower hollow shaft 61 is an iron salt feed channel. In one or more embodiments of the present invention, the hollow shaft is used only as a material distribution channel for the reaction fluid.

[0047] The reactor shell 1 is provided with an inlet 2 and an outlet 4; a product collection ring plate 3 is provided inside the reactor shell 1 along the outer periphery of the disc ceramic membrane, which is used to collect the hydroxyl oxide slurry suspension centrifuged from the micro-reaction channel 7.

[0048] Specifically, the ring plate 3 is an annular collection trough plate arranged along the outer periphery of the disc ceramic membrane, with its inner edge adjacent to the outer periphery of the disc ceramic membrane, used to receive and collect the hydroxyl oxide slurry suspension centrifuged out from the micro-reaction channel 7.

[0049] The ceramic membrane reactor also includes a temperature control system, located on the inner or outer wall of the reactor shell 1, for controlling the temperature within the microreaction channel 7. Additionally, it includes an online pH monitoring and feedback control system, located at the microreaction channel 7, for real-time monitoring of the pH value and feedback adjustment of the alkali feed flow rate.

[0050] The upper disc ceramic membrane 53 and the lower disc ceramic membrane 63 of the ceramic membrane reactor have a pore size of 0.1-1 μm.

[0051] The working mechanism of this ceramic membrane reactor:

[0052] (1) The iron salt solution and the alkaline solution are ejected from the micropores on the upper and lower membrane surfaces in the form of micron-sized jets. They collide in opposite directions in the narrow gap, achieving molecular-level uniform mixing in a very short time, thus fundamentally eliminating the local concentration gradient.

[0053] (2) The two hollow shafts are driven independently. The shear force generated by the difference in their rotation speed further enhances the micro-mixing of reactants in the micro-reaction channel. On the other hand, the centrifugal force quickly throws the reaction products outward, avoiding excessive residence and aggregation of particles in the reaction zone, and ensuring the dispersibility of the product.

[0054] (3) The narrow gap between the upper and lower membrane surfaces forms a micro-reaction channel, which restricts the space range for nucleation and growth, allowing all particles to nucleate and grow under the same spatial conditions, further improving the uniformity of particle size distribution.

[0055] Example 2

[0056] A method for preparing an iron hydroxyl oxide precursor includes the following steps:

[0057] S1: Preparation of iron salt precursor solution: Dissolve iron salt in water to prepare an iron salt solution of a certain concentration;

[0058] S2: Preparation of alkaline solution: Preparation of alkaline solution of a certain concentration;

[0059] S3: Control reaction conditions: Inject liquid medium into the reactor so that the upper circular ceramic membrane 53 and the lower circular ceramic membrane 63 are immersed in the liquid phase. Control the reaction pH value by adjusting the injection ratio of iron salt solution and alkali solution, and control the reaction temperature in the reactor.

[0060] S4: Coprecipitation reaction: The iron salt solution of S1 is introduced into the iron salt feed channel of the upper hollow rotating shaft 51, and the alkali solution of S2 is introduced into the alkali feed channel of the lower hollow rotating shaft 61. The iron salt solution and the alkali solution are injected into the micro-reaction channel 7 from the micropores of the upper and lower circular ceramic membranes 53 and 63 respectively in the form of micro-scale jets, and then collide and mix in opposite directions. A coprecipitation reaction occurs in the micro-reaction channel 7 to generate FeOOH particles, which are continuously discharged from the micro-reaction channel 7 with the shear flow.

[0061] S5: Product collection and post-processing: FeOOH slurry suspension ejected by centrifugation is continuously collected from reactor outlet 4, and after solid-liquid separation, washing and drying, spherical FeOOH powder is obtained.

[0062] The concentration of the iron salt solution is 0.05~0.5 mol / L, and the concentration of the alkali solution is 0.1~2 mol / L. In step S3, the reaction temperature is 15~80℃, and the reaction pH is controlled to be 8~10 by adjusting the ratio of the iron salt solution and the alkali solution injected.

[0063] The iron salt is a mixture of FeCl3 and FeCl2, wherein the molar ratio of FeCl3 to FeCl2 is 1.5:1 to 3:1. The alkaline solution is a NaOH solution or a KOH solution.

[0064] The drying process is performed under vacuum or spray drying at a temperature of 60-100°C.

[0065] The spherical FeOOH powder prepared in this embodiment has an average particle size of 200~500 nm and a particle size distribution variation coefficient (CV) of less than 10%.

[0066] Example 3

[0067] S1: Preparation of iron salt solution: Weigh 0.3 mol of FeCl3 and 0.2 mol of FeCl2, dissolve them in deionized water, and bring the volume to 1 L to obtain Fe... 3+ Concentration 0.3 mol / L, Fe 2+ A mixed solution with a concentration of 0.2 mol / L.

[0068] S2: Preparation of alkaline solution: Prepare a NaOH solution with a concentration of 1 mol / L.

[0069] S3: Controlled reaction conditions: two sets of Al2O3 disk ceramic membranes, with a pore size of 0.2 μm and a membrane gap (i.e., Figure 2 The distance H of the microreaction channels shown is set to 2.5 mm. The upper hollow rotating shaft 51 is driven by the upper drive motor 52, and the lower hollow rotating shaft 61 is driven by the lower drive motor 62. The upper speed is set to 600 rpm, and the lower speed is set to 400 rpm, with a speed difference of 200 rpm. The reactor shell 1 is provided with a liquid inlet 2. Before start-up, deionized water is injected to fill the inner cavity of the shell, so that the disc membrane assembly is immersed in water.

[0070] S4: Coprecipitation reaction: Iron salt solution is introduced into the upper circular ceramic membrane 53 via the upper hollow shaft 51 at a flow rate of 0.5 L / min, and alkali solution is introduced into the lower circular ceramic membrane 63 via the lower hollow shaft 61 at a flow rate of 1.0 L / min. The operating pressure difference across the membrane is 0.15 MPa. The temperature inside the reactor shell is 35℃, and the pH value is 9. The reaction liquid is ejected from the micropores on the membrane surface into the microreaction channel 7 in the form of a micro-scale jet, where it collides and mixes with each other. A coprecipitation reaction occurs in the microreaction channel 7 to generate FeOOH particles, which are continuously discharged from the microreaction channel 7 with the shear flow.

[0071] S5: Product collection and post-processing: FeOOH slurry suspension ejected by centrifugation is continuously collected from reactor outlet 4, centrifuged at 4000 rpm for 10 min, then washed 3 times with deionized water, and then vacuum dried at 60℃ for 12 h to obtain spherical FeOOH powder.

[0072] Example 4

[0073] The difference from Example 3 is that the lower hollow shaft 61 and the lower disc ceramic membrane 63 remain fixed, while only the upper hollow shaft 51 and the upper disc ceramic membrane 53 are driven by the upper drive motor 52 and rotate at a speed of 600 rpm. When the lower hollow shaft 61 is fixed, the fluid on the surface of the lower disc ceramic membrane 63 lacks the centrifugal force and shear force generated by rotation, and the alkali solution is only driven to be ejected from the membrane holes by the transmembrane pressure difference. In order to maintain the jet velocity and opposing collision intensity equivalent to the rotation of the two membranes, the operating pressure difference needs to be increased from 0.15 MPa to 0.50 MPa to ensure that the microjets on the lower membrane surface have sufficient penetration capability.

[0074] Example 5

[0075] The difference from Example 3 is that the iron salt solution concentration was adjusted to 0.1 mol / L FeCl3 + 0.05 mol / L FeCl2, the upper rotation speed was reduced to 400 rpm and the lower rotation speed to 300 rpm, and the operating pressure difference across the membrane was adjusted to 0.5 MPa.

[0076] Example 6

[0077] The difference from Example 3 is that the iron salt solution concentration was adjusted to 0.09 mol / L FeCl3 + 0.03 mol / L FeCl2, the upper rotation speed was increased to 1000 rpm and the lower rotation speed to 200 rpm, the rotation speed difference was 800 rpm, and the operating pressure difference across the membrane was adjusted to 0.1 MPa.

[0078] Example 7

[0079] The difference from Example 3 is that the iron salt solution concentration was adjusted to 0.03 mol / L FeCl3 + 0.02 mol / L FeCl2, the upper rotation speed was increased to 2000 rpm and the lower rotation speed to 500 rpm, the rotation speed difference was 1500 rpm, and the operating pressure difference across the membrane was adjusted to 0.1 MPa.

[0080] Example 8

[0081] The difference from Example 3 is that only the distance of the micro-reaction channel 7 is changed, and it is set to 0.5 mm, 1 mm, 2.5 mm, 5 mm and 8 mm respectively. The effect of the distance of the micro-reaction channel 7 on the size of FeOOH particles is analyzed.

[0082] Example 9

[0083] The difference from Example 4 is that only the rotation speed was changed, set to 200 rpm, 600 rpm, 1000 rpm, and 1500 rpm respectively, while keeping the other parameters the same, and the effect of the rotation speed difference on the size of FeOOH particles was analyzed.

[0084] Example 10

[0085] The difference from Example 3 is that only the pore size of the disc ceramic membrane was changed, set to 0.1 μm, 0.2 μm, 0.5 μm, and 1 μm respectively, while keeping the other parameters the same, and the influence of the membrane pore size on the size of FeOOH particles was analyzed.

[0086] Comparative Example 1

[0087] This comparative example used a stirred tank reactor and employed the same iron salt solution and alkali solution formulation as in Example 3. In a 2L stirred tank reactor, the iron salt solution and alkali solution were added dropwise simultaneously under mechanical stirring, with the pH controlled at 9 and the reaction temperature at 35°C. After the addition was complete, the mixture was stirred and aged for 20 minutes. The average particle size was measured to be 380 nm.

[0088] Comparative Example 2

[0089] This comparative example uses a rotating disc reactor. A solid stainless steel disc of the same size as the ceramic disc in Example 3 is used instead of the ceramic disc. The gap between the upper and lower discs is 2.5 mm. The upper disc rotates at 600 rpm, while the lower disc is fixed. Iron salt solution and alkali solution are injected into the central area of ​​the disc through the central feed inlets of the upper and lower hollow rotating shafts, respectively. Under the action of centrifugal force, they flow outward along the disc surface and react in the gap. All other conditions are the same.

[0090] The particle size distribution was determined using a Malvern Mastersizer 3000 laser particle size analyzer. Before testing, the FeOOH powder was ultrasonically dispersed in deionized water. The particle size of FeOOH in the above examples and comparative examples was measured, and the results are as follows:

[0091] Table 1 Test results of Examples 3-7 and Comparative Examples 1-2

[0092] Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Average particle size d (nm) 325 358 475 225 208 380 425 Particle size distribution CV (%) 7.2 8.8 9.5 6.5 8.2 18.5 22.3 sphericity 0.93 0.89 0.86 0.94 0.91 0.76 0.72

[0093] As can be seen from the data in Table 1, the present invention can achieve precise control of the average particle size of FeOOH powder by adjusting the iron salt concentration, rotation speed difference, and operating pressure difference.

[0094] Comparing Examples 3, 5, 6, and 7, the average particle size decreased from 475 nm to 208 nm as the iron salt concentration decreased, exhibiting a monotonically decreasing relationship. This is because the number of nuclei decreases under lower supersaturation conditions, the growth space of individual nuclei increases but the growth rate decreases, and the strong shear force generated by the high rotational speed difference restricts particle aggregation, ultimately forming particles with smaller diameters.

[0095] Compared with Examples 3, 6, and 7, the increased rotational speed difference resulted in a smaller particle size and a lower CV. This is because the higher rotational speed difference generates a stronger shear flow, which on the one hand enhances micromixing efficiency, making nucleation more uniform, and on the other hand accelerates product discharge, inhibiting excessive particle growth and agglomeration in the reaction zone.

[0096] Comparing Examples 3 and 4, the mixing effect of dual-membrane differential drive is better than that of single-membrane rotation. With dual-membrane differential drive, the upper and lower membrane surfaces rotate simultaneously, generating relative motion, resulting in a more uniform shear flow field and more thorough micro-scale jet collisions.

[0097] Comparative Example 1: FeOOH had an average particle size of 380 nm, a CV as high as 18.5%, and a sphericity of only 0.76. This was mainly because an extremely high pH was instantly formed near the alkali inlet in the stirred tank, resulting in local supersaturation, while the supersaturation was insufficient far from the inlet, leading to uneven nucleation, wide particle size distribution, and poor sphericity.

[0098] Comparative Example 2 used a rotating disk reactor, where the CV of FeOOH reached as high as 22.3%, and the sphericity was only 0.72. Because the solid stainless steel disk has no porous structure, the iron salt solution and alkali solution are only injected from the feed port at the center of the rotating shaft. After flowing radially along the disk surface, they are mixed in the gaps by macroscopic fluid dynamics, which cannot achieve microscale jet collisions. The mixing efficiency is much lower than that of ceramic membrane microporous jets.

[0099] Table 2. Effect of different microchannel gaps on FeOOH particle size in Example 8

[0100] Microchannel gap (mm) Average particle size d (nm) Particle size distribution CV (%) sphericity 0.5 468 13.5 0.82 1.0 295 8.6 0.91 2.5 325 7.2 0.93 5.0 365 9.8 0.88 8.0 520 16.2 0.78

[0101] As shown in Table 2, when the gap is in the range of 1-5 mm, the CV is below 10% and the sphericity is ≥0.88, indicating excellent product performance. The optimal gap is 2.5 mm, with the lowest CV at 7.2% and the highest sphericity at 0.93. When the gap is 0.5 mm, the CV increases to 13.5%, indicating insufficient jet collision space, partial membrane pore blockage, and uneven flow distribution due to the excessively narrow gap. When the gap is 8 mm, the CV increases to 16.2%, indicating that the excessively narrow gap leads to the loss of the microreactor effect, causing reactants to mix in the macroscopic space and negating the core technological advantages of this invention.

[0102] Table 3. Effect of different rotational speed differences on FeOOH particle size

[0103] Speed ​​difference (rpm) Average particle size (nm) CV (%) sphericity 200 380 9.5 0.82 600 358 8.8 0.89 1000 290 7.2 0.92 1500 255 6.5 0.95

[0104] As shown in Table 3, as the rotation speed increased from 200 rpm to 1500 rpm, the particle size gradually decreased from 380 nm to 255 nm, and the coefficient of variation improved from 9.5% to 6.5%.

[0105] Table 4. Effect of different membrane pore sizes on FeOOH particle size

[0106] Membrane pore size (μm) Average particle size (nm) CV (%) sphericity 0.1 210 6.8 0.94 0.2 325 7.2 0.93 0.5 450 8.2 0.89 1.0 495 9.5 0.85

[0107] As shown in Table 4, membrane pore size is an effective parameter for controlling the particle size of FeOOH. Smaller membrane pore sizes produce finer microjets, resulting in more uniform collisional mixing and a narrower particle size distribution; larger membrane pore sizes result in slightly coarser microjets, with slightly larger particle sizes and a slightly wider distribution, but still within the range described in this invention. Precise control of FeOOH particle size was achieved within the membrane pore size range of 0.1–1 μm.

[0108] Meanwhile, the FeOOH precursor described in this invention can be further used to prepare functional powder materials such as γ-Fe2O3 soft magnetic materials, α-Fe2O3 pigments or catalysts.

[0109] This invention discloses a reaction field coupled with membrane dispersion micromixing and differential shear centrifugal mass transfer. Microjet collision mixing involves iron salt solution and alkali solution being transported to the back surfaces of opposing circular ceramic membranes via two independent hollow rotating shafts. Driven by the transmembrane pressure difference, the two fluid streams permeate through the micropores of the ceramic membrane and are ejected from the membrane surface as micron-sized jets. Due to the extremely small interfacial distance, the two jets collide head-on within the microreaction channel, achieving uniform mixing at the molecular scale within microseconds, instantly reaching extremely high supersaturation and inducing homogeneous nucleation. Simultaneously, the upper and lower rotating shafts are driven by independent motors with a specific speed difference. This relative motion generates a strong shear flow field within the narrow gap, preventing particle agglomeration and, through fluid dynamics control, forcing particles to undergo uniform crystal growth within the confined space. Furthermore, the shear flow field simultaneously generates centrifugal force, horizontally ejecting the generated FeOOH slurry radially out of the microreaction channel, achieving continuous and clogging-free discharge. The entire process realizes an integrated continuous operation of mixing-nucleation-growth-separation.

[0110] In this invention, the hollow rotating shaft serves as both a rotation axis and an independent feed channel; the ceramic membrane acts as both a dispersion medium and a reaction interface. Utilizing the uniform dispersion characteristics of the membrane microjets and the confinement effect of the microchannels, the local concentration gradients of traditional batch reactors are eliminated, resulting in a product particle size distribution coefficient of variation (CV) of less than 10%. This invention overcomes the bottlenecks of microchannel reactors, such as easy clogging and low throughput. By adjusting the membrane pore size, rotation speed difference, gap, and concentration, this invention allows for precise control of particle size within the range of 200–500 nm.

[0111] It should be noted that this invention uses a mixed iron salt of FeCl3 and FeCl2 as a precursor raw material. The introduction of Fe... 2+ The purpose is to: (1) Fe 2+ In the co-precipitation process, it plays a role in crystal growth modification, which can regulate the nucleation rate and growth direction of FeOOH, and is conducive to the formation of isotropic spherical particle morphology; (2) the mixed valence state precursor is more likely to generate the target iron oxide phase γ-Fe2O3 in the subsequent calcination conversion process, which can improve the phase conversion efficiency.

[0112] The main processes of the coprecipitation reaction include:

[0113] Fe 3+ +3OH-→Fe(OH)3→FeOOH + H2O;

[0114] Fe 2+ +2OH-→Fe(OH)2;

[0115] 4Fe(OH)2 + O2 → 4FeOOH + 2H2O.

[0116] When the reaction system is exposed to air, Fe 2+ Partially oxidized to Fe 3+ The final product is dominated by α-FeOOH, with possible trace amounts of Fe3O4. The presence of these trace amounts of Fe3O4 does not affect the product's performance as an iron oxide precursor, and it can be completely converted into the target iron oxide phase through subsequent calcination.

[0117] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0118] 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 ceramic membrane reactor for preparing iron hydroxyl oxide precursor, comprising a reactor shell (1), characterized in that, Also includes: The upper hollow rotating shaft (51) is fitted with an upper circular ceramic membrane (53) at the lower end of the upper hollow rotating shaft (51), with the membrane surface facing downwards; The lower hollow rotating shaft (61) is mounted on the upper end of the lower hollow rotating shaft (61) with the lower disc ceramic membrane (63) facing upward; the upper disc ceramic membrane (53) and the lower disc ceramic membrane (63) are arranged opposite to each other, and an adjustable gap micro-reaction channel (7) is formed between the two opposite membrane surfaces. The upper hollow rotating shaft (51) has an iron salt feeding channel inside. The iron salt solution is transported to the upper disc ceramic membrane (53) through the upper hollow rotating shaft (51) and ejected into the micro-reaction channel (7) from the micropores on the surface of the upper disc ceramic membrane (53) in the form of a micro-scale jet. The lower hollow rotating shaft (61) has an alkali feed channel inside. The alkali is transported to the lower disc ceramic membrane (63) through the lower hollow rotating shaft (61) and ejected into the micro-reaction channel (7) from the micropores on the surface of the lower disc ceramic membrane (63) in the form of a micro-scale jet. The reactive fluids collide and mix in opposite directions within the microreaction channel (7) and react.

2. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 1, characterized in that, The upper hollow shaft (51) and the lower hollow shaft (61) have a speed difference, thereby generating a differential shear flow between the two opposite membrane surfaces.

3. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 2, characterized in that, The upper hollow shaft (51) and the lower hollow shaft (61) are driven to rotate around their respective axes by independent upper drive motors (52) and lower drive motors (62), and the speeds of the upper drive motors (52) and lower drive motors (62) are independently adjustable.

4. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 1, characterized in that, The height of the micro-reaction channel (7) is 1~5 mm.

5. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 1, characterized in that, The pore size of the upper circular ceramic membrane (53) and the lower circular ceramic membrane (63) is 0.1-1 μm.

6. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 1, characterized in that, The reactor shell (1) is provided with an inlet (2) and an outlet (4); a ring plate (3) for product collection is provided inside the reactor shell (1) along the outer periphery of the disc ceramic membrane, for collecting the hydroxyl iron oxide slurry suspension centrifuged from the micro-reaction channel (7).

7. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 6, characterized in that, The ring plate (3) is an annular collection trough plate arranged along the outer periphery of the disc ceramic membrane. Its inner edge is adjacent to the outer periphery of the disc ceramic membrane and is used to receive and collect the hydroxyl oxide slurry suspension centrifuged from the micro-reaction channel (7).

8. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 1, characterized in that, It also includes a temperature control system, which is installed on the inner or outer wall of the reactor shell (1) to control the temperature in the micro-reaction channel (7).

9. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 1, characterized in that, It also includes a pH online monitoring and feedback control system, which is set at the micro-reaction channel (7) to monitor the pH value in real time and adjust the alkali feed flow rate accordingly.

10. The ceramic membrane reactor for preparing iron hydroxyl oxide precursor according to claim 2, characterized in that, The speed difference between the upper hollow shaft (51) and the lower hollow shaft (61) is 200~1500 rpm.

11. A method for preparing an iron hydroxyl oxide precursor, using the ceramic membrane reactor for preparing an iron hydroxyl oxide precursor as described in any one of claims 1 to 10, characterized in that, Includes the following steps: S1: Preparation of iron salt precursor solution: Dissolve iron salt in water to prepare iron salt solution; S2: Preparation of alkaline solution; S3: Control reaction conditions: Inject liquid medium into the reactor so that the upper disc ceramic membrane (53) and the lower disc ceramic membrane (63) are immersed in the liquid phase. Control the reaction pH value by adjusting the injection ratio of iron salt solution and alkali solution, and control the reaction temperature in the reactor. S4: Coprecipitation reaction: The iron salt solution of S1 is introduced into the iron salt feed channel of the upper hollow rotating shaft (51), and the alkali solution of S2 is introduced into the alkali feed channel of the lower hollow rotating shaft (61). Driven by the transmembrane pressure difference, the iron salt solution and the alkali solution are ejected into the micro-reaction channel (7) in the form of micro-scale jets from the micropores of the upper and lower circular ceramic membranes (53) respectively. They then collide and mix in opposite directions, and a coprecipitation reaction occurs in the micro-reaction channel (7) to generate FeOOH particles, which are continuously discharged from the micro-reaction channel (7) with the shear flow. S5: Product collection and post-processing: The FeOOH slurry suspension ejected by centrifugation is continuously collected from the reactor outlet (4), and after solid-liquid separation, washing and drying, spherical FeOOH powder is obtained.

12. The method for preparing the ferric hydroxide precursor according to claim 11, characterized in that, The concentration of the iron salt solution is 0.05~0.5 mol / L, and the concentration of the alkali solution is 0.1~2 mol / L.

13. The method for preparing the iron hydroxyl oxide precursor according to claim 11, characterized in that, In step S3, the reaction temperature is 15~80℃, and the reaction pH is controlled to be 8~10 by adjusting the ratio of the amount of iron salt solution and alkali solution injected.

14. The method for preparing the ferric hydroxide precursor according to claim 11, characterized in that, The iron salt is a mixture of FeCl3 and FeCl2, wherein the molar ratio of FeCl3 to FeCl2 is 1.5:1 to 3:

1.

15. The method for preparing the iron hydroxyl oxide precursor according to claim 11, characterized in that, The alkaline solution is either NaOH or KOH.

16. The method for preparing the iron hydroxyl oxide precursor according to claim 13, characterized in that, The drying process is performed under vacuum or spray drying at a temperature of 60-100°C.

17. The method for preparing the iron hydroxyl oxide precursor according to claim 11, characterized in that, The average particle size of the spherical FeOOH powder is 200~500 nm, and the particle size distribution variation coefficient (CV) is less than 10%.

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