Device and method for preparing spherical alpha-aluminum oxide nano powder

Abstract

The invention discloses a device and a method for preparing spherical alpha-alumina nano powder. The device comprises an impinging stream-rotating packed bed, structured packing is arranged in the impinging stream-rotating packed bed, the structured packing is axially formed by arranging and combining a plurality of single-layer packing in a staggered manner in the horizontal direction, and each single-layer packing is composed of a plurality of concentric rings with different diameters; a liquid feeding impact structure is arranged in the center of the interior of the structured packing, the impact structure is Y-shaped and is composed of an upper V-shaped liquid inlet and a lower vertical liquid inlet, the upper V-shaped liquid inlet divides one strand of raw materials into a V-shaped structure, the other strand of raw materials is vertically and upwards sprayed out through the lower vertical liquid inlet, and when the two strands of materials with large concentration difference impact, the two strands of raw materials are separated from each other to form a V-shaped structure. According to the impact structure, high-concentration materials are divided into two strands to be fed, so that the impact strength is enhanced, and the mixing effect is improved. The device and the method provided by the invention have the advantages of continuity, uniform reaction, strong controllability, high dispersion degree, easiness in industrialization and the like.

Description

Technical Field

[0001] The invention relates to a device and a method for preparing spherical alpha-alumina nano powder, belonging to the technical field of ceramic powder preparation. Background Art

[0002] Spherical alumina powder has the advantages of good fluidity, high specific surface area and large bulk density, and exhibits corrosion resistance, high temperature resistance, high hardness and other properties, making it widely used in integrated circuit chips, aerospace, catalysts and catalyst carriers and sensors. Studies have shown that its excellent performance in many fields is largely related to the morphology, size and dispersibility of its powder particles. 2 O 3 Nanopowders have shown good application prospects in more and more key technology fields. In recent years, the demand for high-end alumina products has continued to grow, and most of them rely on imports. 2 O 3 There are still many problems to be solved in the preparation process of nanopowders, such as the difficulty in controlling the morphology of the powder, the tendency to agglomerate, the wide range of particle size distribution, and the high process cost. In addition, due to the high activation energy barrier, it usually requires high-temperature calcination above 1200°C. Long-term high-temperature calcination can easily cause sintering and agglomeration between the alumina particles in contact with each other, forming a worm-like structure, losing the advantages of the spherical morphology, and the preparation process conditions are harsh. High-end alumina products require alumina powders to be high in purity, spherical in shape, small in size, uniform in particle size, and good in particle dispersion. Therefore, the preparation of spherical α-Al2O3 that meets the requirements of high-end alumina is a process that requires high purity, spherical in shape, small in size, uniform in particle size, and good in particle dispersion. 2 O 3 Nanopowders have important academic and commercial significance.

[0003] Chinese patent CN108658107A discloses a method for preparing nano-scale monodisperse spherical α-alumina, which combines a coprecipitation method, a high-temperature hydrothermal method and other methods to solve the problem of incomplete phase change and sintering of particles, and prepares nano-scale, monodisperse spherical α-Al 2 O 3 particles, but the use of its iron salt introduces impurities. Chinese patent CN114751435A discloses a method for preparing original crystal quasi-spherical α-alumina powder, which uses industrial alumina as raw material and adopts composite mineralizers such as fluoride and chloride to obtain quasi-spherical alumina with a median particle size (20 μm~30 μm). The proportion of fluorine-containing mineralizer added is higher than 5%, which pollutes the environment, consumes a lot of energy, and has a complicated preparation process. In the disclosed spherical / quasi-spherical α-alumina powder production process, there are problems such as wide powder particle size distribution range, easy agglomeration, long time consumption, high energy consumption and production cost. In 2017, Shuai Wei reported the preparation of α-Al by ball milling co-precipitation method. 2O 3 The effect of aluminum salt concentration on the final product aluminum oxide during the generation of precursors from aluminum salt nitrate and precipitant ammonium bicarbonate was studied. When the aluminum ion concentration was low, the reaction rate was slow and the reaction could not proceed well. As the concentration of aluminum nitrate solution increased, the number of crystal collisions increased, resulting in the precursor Al(OH) 3 The reaction formed is accelerated accordingly. Secondly, when the concentration is too high, the viscosity of the solution also increases, and the fluidity of the crystalline component is significantly reduced, which will lead to larger particle size and wider particle size distribution (Journal of Materials Science: Materials in Electronics. 2017, 28: 16254-16261). In 2016, Lili Zhang reported a study on the coprecipitation synthesis of aluminum oxide, in which the precipitant NH 4 HCO 3 and aluminum salt NH 4 Al(SO 4 ) 2 The concentrations are 2 mol / L and 0.2 mol / L respectively, and the concentration ratio is as high as 10 times (Vacuum.2016,133:1-6). In the industrial production of alumina powder, the precipitation method has the advantages of simpler preparation process, convenient operation, and good repeatability compared to other methods. However, it has strict requirements on the concentration ratio of the precipitant and the aluminum salt. When the concentration ratio is too low, the ions cannot be completely precipitated, affecting the product effect; when the concentration ratio is appropriately excessive, it can promote the formation of precipitation; and when the concentration ratio is greatly excessive, it will lead to unnecessary cost increases and may have an impact on the environment. Therefore, appropriate concentrations and full contact and mixing of the two materials are necessary prerequisites.

[0004] The impinging stream-rotating packed bed is suitable for rapid liquid-liquid chemical reactions. It has strong microscopic mixing and mass transfer capabilities in a supergravity environment, and has an extremely short residence time. It can provide the required supersaturated and uniformly concentrated nucleation environment for the preparation of nanopowders by precipitation, and has significant advantages in the preparation of inorganic nanomaterials. In addition, the high molar ratio and supersaturated conditions required for the preparation of precursors can be solved by changing the internal fillers and impact structures of the impinging stream-rotating packed bed. The fillers provided in the existing impinging stream-rotating packed bed are bulk fillers. Common bulk fillers used in rotating packed beds often have the disadvantages of being inconvenient to disassemble and assemble, poor rotation stability and dynamic balance, and having channel flow, wall flow and more dead zones inside the fillers, which are not suitable for precipitation reaction systems. Therefore, the present invention starts from the raw materials, concentration and reaction process in the production process of spherical alumina, and proposes a device and method for preparing spherical α-alumina nanopowders in supergravity. Summary of the invention

[0005] In view of the above problems, the present invention aims to provide a device and method for preparing spherical α-alumina nanopowder under ultra-gravity, which has the advantages of continuity, uniform reaction, strong controllability, high degree of dispersion, and easy industrialization.

[0006] The present invention combines structured packing with an impinging stream-rotating packing reactor for preparing high-end alumina products. The prepared alumina powder has the characteristics of high purity, spherical particles, fine particles, uniform particle size, and good particle dispersibility. Structured packing is easy to disassemble and has good dynamic balance. It can also provide a larger effective interphase contact area and better mass transfer performance. Based on the performance advantages of structured packing, the present invention specially develops a structured packing with fine structure channels for a supergravity rotating packing bed for preparing nano-spherical α-alumina by liquid-liquid precipitation reaction. The key component in the impingement flow-rotating packing reactor is the impingement flow structure, and its main parameters are the number of nozzles, structural layout, direction and angle. When the molar ratio and concentration ratio of the two reaction materials differ greatly, it is difficult to achieve the expected effect by using two nozzles for impingement flow. The increase in the number of nozzles can improve the uniformity of the impact intensity, and the multi-stream diversion of the material is more conducive to turbulent mixing in the reactor. However, if the number of nozzles increases too much, the multiple fluids will affect each other when they collide, and the flow field becomes complicated. Based on this, the present invention proposes a three-nozzle impingement structure, whose flow field is simpler than that of four nozzles, the mutual influence between the fluids is small, and the turbulence degree is better than that of two nozzles. When two materials with a large difference in reaction concentration collide, by dispersing the material with a much higher concentration into two feeds and colliding with another reactant, the local concentration can be reduced, thereby improving the mixing uniformity of the reactants.

[0007] The invention provides a device for preparing spherical alpha-alumina nano powder under supergravity, comprising a liquid storage tank I, a pump I, an impinging stream-rotating packed bed, a pump II, a liquid storage tank II and a liquid storage tank III, wherein the liquid storage tank I is connected to a liquid inlet I of the impinging stream-rotating packed bed through the pump I, a valve I and a liquid flow meter I, the liquid storage tank II is connected to a liquid inlet II of the impinging stream-rotating packed bed through the pump II, the valve II and the liquid flow meter II, and the discharge port of the impinging stream-rotating packed bed is connected to the liquid storage tank III.

[0008] In the present invention, a structured packing is arranged in an impinging flow-rotating packed bed, and the structured packing is axially composed of a plurality of single-layer packings staggered in the horizontal direction, wherein the single-layer packing is composed of a plurality of concentric circular rings of different diameters; further, the structured packing as a whole is composed of 3 to 12 layers of single-layer packings arranged in parallel, and adjacent layers are staggered at an angle of 10° to 60°; wherein the single-layer packing is composed of 4 to 7 circles of concentric circular rings of different diameters, and the structure of adjacent inner and outer circular rings is staggered at an angle of 5° to 30°; each circular ring is composed of a plurality of arc structures.

[0009] The performance of the structured packing provided by the present invention depends on the characteristics of its channel structure. If all the packings are oriented in the same direction, when the liquid falls, the residence time is short and a channel flow or a bias flow is formed. The upper and lower adjacent packing layers are staggered. The liquid will be disturbed and redistributed due to the change in flow direction when passing through the gap between the packing layers, which inhibits the occurrence of wall flow phenomenon, so that the liquid phase forms a liquid film or a mist film state many times, while increasing the residence time of the liquid phase and strengthening the mass transfer process. The structured packing can add or reduce the number of axial and radial layers as needed. On the one hand, by changing the degree of liquid tearing, the reaction can be fully generated. On the other hand, the concentric ring baffle plays a role in liquid redistribution in the axial and radial directions, strengthening liquid dispersion and thus improving the mass transfer effect.

[0010] Each basic unit of the circular ring (i.e., arc-shaped structure) includes a support structure and a filling structure. The support structure uses a wire mesh as a frame, and the internal filling structure is provided with curved blades. The surface of the filling structure is roughened using the potassium permanganate method. After the liquid is dispersed through the hydrophobic wire mesh, its liquid dispersion cone angle can be greatly improved. At the same time, the droplet size is smaller and the distribution is narrower, which can improve the mass transfer performance and strengthen the dispersion performance of the liquid.

[0011] The curved blades in the filling structure have a certain curvature, and according to the blade curvature calculation formula r=(u 2 ) / (g·tan(α)), where u represents the velocity of the fluid, g represents the acceleration of gravity, α represents the angle of the blade relative to the frame, and the blade curvature r is 0.7 ~ 1.1. The curved blade can collide and cross with the direction of the droplet to fully disperse it, and the use of the curved blade enhances the self-cleaning and anti-fouling capabilities of the packing; after the surface of the curved blade is roughened, it is beneficial for the liquid to disturb the liquid film at the surface of the packing, inhibit laminar flow, reduce the thickness of the laminar layer, and thus enhance the mass transfer rate.

[0012] Furthermore, in the packing structure, a hole with an outward-extending tongue is opened on the curved blade, one side of the window blade cut by the hole is connected to the blade mother body, and the other side is bent outward of the blade, and a protrusion is designed on the curved blade. The aperture of the curved blade in the structured packing is 2 mm~5 mm, the hole spacing is 4 mm~10 mm, and the inclination angle of the outward-extending tongue on the curved blade is 30°~70°. When the droplets pass through the window, some of the droplets collide again, and some of the droplets merge to fully mix the unreacted liquid phase; the opening of the curved blade and the outward-extending tongue in the structured packing can disturb the liquid film, change the flow direction of the liquid, and continuously generate small turbulence and eddy currents, which greatly reduce the laminar flow thickness and reduce the mass transfer resistance, greatly improving the mass transfer rate and mixing efficiency; the protrusion design on the curved blade makes the liquid have a more reasonable distribution in the longitudinal direction, and ensures that the liquid flows smoothly between the packing layers while increasing the disturbance, effectively reducing the resistance caused by the change of flow direction at the junction of the packing layers.

[0013] A liquid feed impact structure is provided at the center of the regular packing in the impinging flow-rotating packed bed. The impact structure is a "Y"-shaped impact structure, which consists of an upper "V"-shaped liquid inlet and a lower vertical liquid inlet. The upper "V"-shaped liquid inlet diverts one stream of raw material to form a "V" structure, and the other stream of raw material passes vertically upward through the lower vertical liquid inlet. When two streams of materials with a large concentration difference collide, there will be a local excessive concentration. The "Y"-shaped impact structure divides the high-concentration material into two streams, thereby strengthening the impact intensity, so that the precipitant concentration in the impact mist area is excessive compared to the precipitant concentration required for the reaction, achieving an oversaturation effect, and the reaction is more intense, thereby improving the mixing effect.

[0014] The angle β of the "V"-shaped incident tube of the "Y"-shaped impact structure in the impinging flow-rotating packed bed satisfies: 70°<β<100°. When the impact angle is too small, the liquid gathers and forms a chain structure downstream of the nozzle, and the dispersion is uneven; when the impact angle is too large, the dispersion degree is high, but the liquid near and below the nozzle outlet is unevenly dispersed. During the impact, not only the dispersion degree of the liquid should be considered, but also the uniformity of the liquid dispersion after the impact. It is not possible to only pursue a higher dispersion degree while ignoring the uniformity of the liquid dispersion, which will lead to an uneven liquid mixing environment and affect the mixing effect. Therefore, it is necessary to comprehensively consider the above two aspects to select the best impact angle.

[0015] The apertures of the end nozzles of the impact structure are 0.5 mm to 10 mm, and the aperture ratio of the end nozzles at the upper liquid inlet and the lower liquid inlet is 0.5 to 1. This structure enables the raw materials to quickly form a supersaturated zone, and the "Y"-shaped impact flow structure radiates radially around the impact zone during the reaction, with a better degree of liquid dispersion, which is more conducive to improving the dispersibility of the powder and reducing the particle size of the powder.

[0016] The above-mentioned device for continuously preparing spherical α-alumina nanopowder is a reaction system suitable for rapid preparation of spherical α-alumina nanopowder for industrial continuous production. The reaction system has the advantages of strong universality, fast mixing, strong controllability, easy scale-up, etc., and is a reaction system suitable for industrial production of spherical α-alumina nanopowder.

[0017] The present invention provides a method for preparing spherical α-alumina nanopowder, which is prepared by using the device for preparing spherical α-alumina nanopowder as described above, and comprises the following steps: (1) dissolving aluminum salt in deionized water to prepare aluminum salt solution A and pouring it into liquid storage tank II; dissolving precipitant in deionized water and adjusting the pH value of the resulting solution to prepare precipitant solution B and pouring it into liquid storage tank I; (2) Subsequently, the precipitant solution B and the aluminum salt solution A are pumped into the upper liquid inlet and the lower liquid inlet of the impinging flow-rotating packed bed to rapidly mix and react to generate a suspension C containing the precursor; wherein the feed concentration ratio of the precipitant to the aluminum salt is 6 to 13:1; Two streams of raw materials flow out of the liquid storage tank and enter the impinging flow-rotating packed bed after passing through the pump and liquid flow meter. The "Y" type three-nozzle impact structure diverts the material on the one hand, so that the concentration of the precipitant in the impact mist area is excessive compared to the concentration of the precipitant required for the reaction, achieving a supersaturated effect, thereby improving the mixing effect and enhancing the reaction rate. On the other hand, the impact intensity is increased, which is more conducive to turbulent mixing in the reaction area. The liquid entering the ultra-gravity rotor is affected by the rotating packing in the rotor, and the circumferential speed increases. The centrifugal force generated pushes the material liquid to the outer edge of the rotor; in this process, the staggered packing provides a tortuous flow channel, and the liquid is continuously dispersed, aggregated, and broken by the curved blades filled in the packing, so that the concentration distribution is uniform. That is, excellent mixing, mass transfer and reaction conditions are created inside the rotor. Finally, under the action of gravity, the suspension C flows from the outlet of the impinging flow-rotating packed bed into the liquid storage tank III.

[0018] (3) aging, filtering and washing the suspension C to obtain a filter cake D; (4) Drying the filter cake D to obtain a precursor powder; (5) The precursor powder is ball-milled and then calcined to obtain spherical α-alumina nanopowder.

[0019] The precipitant is one or more of ammonium bicarbonate, ammonium carbonate and urea.

[0020] The concentration of the aluminum salt solution A is 0.1 mol / L to 0.6 mol / L; the concentration of the precipitant solution B is 1.0 mol / L to 4.0 mol / L, and the initial pH value is 9.0 to 11.0.

[0021] The reaction temperature of the impinging stream-rotating packed bed reactor is 30°C to 60°C, the supergravity factor is 10 to 80, and the initial impact velocity is 5 m / s to 40 m / s.

[0022] The calcination temperature is 900°C to 1300°C, and the calcination time is 1 h to 4 h.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts an impinging stream-rotating packed bed that combines the advantages of impinging stream and rotating packed bed to better enhance the microscopic mixing of liquid-liquid two phases. By optimizing the packing structure and material, the effects of suppressing wall flow phenomenon, increasing disturbance, reducing laminar layer thickness, reducing mass transfer resistance, and increasing mass transfer rate and mixing efficiency are achieved; (2) The present invention invents a "Y" type impact structure based on the impact flow-rotating packed bed equipment. This structure is based on a system where the concentration ratio of the reaction materials is much greater than 1:1. The material with a higher concentration is divided into two streams and then collides with another raw material, thereby increasing the impact intensity, enhancing the degree of liquid dispersion and uniformity, and preparing nanomaterials with narrow size distribution, uniform morphology and small particle size, which has strong industrialization conditions and application prospects; (3) In the prior art, the preparation of α-alumina nanopowders is mainly carried out by precipitation method, hydrothermal method, sol-gel method, etc., and the particle size is large and unevenly distributed. The present invention uses supergravity technology to realize the preparation of spherical α-alumina nanopowders, and determines the influence of various control conditions on product performance, thereby preparing high-quality spherical α-alumina nanopowder materials suitable for industrial applications; the excellent micro-mixing of the supergravity reactor is used to effectively control the growth process of the precursor crystal nucleus, ensuring that the concentration is consistent and the particle size distribution is uniform at all locations during the crystal nucleus growth process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the structure of the device for preparing spherical α-alumina nanopowders under ultra-gravity according to the present invention; Figure 2 It is a schematic structural diagram of the impinging flow-rotating packed bed of the present invention; Figure 3 It is a schematic diagram of the "Y" type impact structure; Figure 4 A top view of a structured packing in an impinging flow-rotating packed bed of the present invention; Figure 5 for Figure 4 The enlarged view of point A in the middle; Figure 6 for Figure 4 The enlarged view of point B in the middle; Figure 7 It is a schematic diagram of the impact mist surface of the "Y" type impact structure of the impact flow-rotating packed bed of the present invention; In the figure: 1-liquid storage tank Ⅰ; 2-pump Ⅰ; 3-valve Ⅰ; 4-liquid flow meter Ⅰ; 5-impinging flow-rotating packed bed; 6-packing; 7-liquid inlet Ⅰ; 8-liquid inlet Ⅱ; 9-rotating shaft; 10-liquid flow meter Ⅱ; 11-valve Ⅱ; 12-liquid storage tank Ⅱ; 13-pump Ⅱ; 14-liquid storage tank Ⅲ; 15-discharge port; 6.1-curved blade; 6.2-hole; 6.3-protrusion; 6.4-extending tongue. DETAILED DESCRIPTION

[0025] In order to clearly illustrate the present invention, the present invention is further described below in conjunction with preferred examples. Those skilled in the art should understand that the content described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0026] like Figures 1 to 6 As shown, a device for preparing spherical α-alumina nanopowder under ultra-gravity, comprising a liquid storage tank Ⅰ, a pump Ⅰ, an impinging stream-rotating packed bed, a pump Ⅱ, a liquid storage tank Ⅱ and a liquid storage tank Ⅲ, wherein the liquid storage tank Ⅰ 1 is connected to the liquid inlet Ⅰ 7 of the impinging stream-rotating packed bed through a pump Ⅰ 2, a valve Ⅰ 3 and a liquid flow meter Ⅰ 4, the liquid storage tank Ⅱ 12 is connected to the liquid inlet Ⅱ 8 of the impinging stream-rotating packed bed through a pump Ⅱ 13, a valve Ⅱ 11 and a liquid flow meter Ⅱ 10, and the discharge port 15 of the impinging stream-rotating packed bed is connected to the liquid storage tank Ⅲ 14. Two streams of raw materials flow out of the liquid storage tank and enter the impinging flow-rotating packed bed through the pump and liquid flow meter. The "Y" type three-nozzle impact structure diverts the material on the one hand, making it partially supersaturated and enhancing the reaction rate. On the other hand, it increases the impact intensity, which is more conducive to turbulent mixing in the reactor. The liquid entering the ultra-gravity rotor is affected by the rotation of the packing in the rotor, and the circumferential speed increases. The centrifugal force generated pushes the reaction liquid to the outer edge of the rotor; in this process, the liquid is continuously dispersed, aggregated, and broken by the packing, and the tortuous flow channel makes the concentration distribution uniform. In this way, excellent mixing, mass transfer and reaction conditions are created inside the rotor. Finally, under the action of gravity, the suspension C flows from the outlet of the impinging flow-rotating packed bed into the liquid storage tank III.

[0027] Press the above devices Figure 1 When connected together as shown, a reaction system for preparing spherical α-alumina nanopowder under ultra-gravity is formed.

[0028] In the present invention, a structured packing is arranged in the impinging flow-rotating packed bed, such as Figures 4 to 6 The structured packing is composed of multiple single-layer packings arranged alternately in the horizontal direction in the axial direction, wherein the single-layer packing is composed of multiple concentric rings of different diameters; further, the structured packing as a whole is composed of 3 to 12 layers of single-layer packings arranged in parallel, and adjacent layers are staggered at an angle of 10° to 60°; wherein the single-layer packing is composed of 4 to 7 circles of concentric rings of different diameters, and the structure of adjacent inner and outer rings is staggered at an angle of 5° to 30°; each ring is composed of a combination of multiple arc structures.

[0029] The performance of the structured packing provided by the present invention depends on the characteristics of its channel structure. If all the packings are oriented in the same direction, when the liquid falls, the residence time is short and a channel flow or a bias flow is formed. The upper and lower adjacent packing layers are staggered. The liquid will be disturbed and redistributed due to the change in flow direction when passing through the gap between the packing layers, which inhibits the occurrence of wall flow phenomenon, so that the liquid phase forms a liquid film or a mist film state many times, while increasing the residence time of the liquid phase and strengthening the mass transfer process. The structured packing can add or reduce the number of axial and radial layers as needed. On the one hand, by changing the degree of liquid tearing, the reaction can be fully generated. On the other hand, the concentric ring baffle plays a role in liquid redistribution in the axial and radial directions, strengthening liquid dispersion and thus improving the mass transfer effect.

[0030] Each basic ring unit (i.e., arc-shaped structure) includes a support structure and a filling structure. The support structure uses a wire mesh as a frame, and the internal filling structure is provided with curved blades 6.1, and the surface of the filling structure is roughened using potassium permanganate method. After the liquid is dispersed by the hydrophobic wire mesh, its liquid dispersion cone angle can be greatly improved, and at the same time, the droplet size is smaller and the distribution is narrower, which can improve the mass transfer performance and strengthen the dispersion performance of the liquid.

[0031] The curved blade 6.1 in the filling structure has a certain curvature, and according to the blade curvature calculation formula r=(u 2 ) / (g·tan(α)), where u represents the velocity of the fluid, g represents the acceleration of gravity, and α represents the angle between the blade and the frame (see Figure 5 ), the blade curvature r is 0.7 ~ 1.1. The curved blade can collide and cross with the direction of the droplet to fully disperse, and the use of the curved blade enhances the self-cleaning and anti-fouling ability of the filler; after the surface of the curved blade is roughened, it is beneficial for the liquid to disturb the liquid film at the surface of the filler, inhibit laminar flow, reduce the thickness of the laminar layer, and thus enhance the mass transfer rate.

[0032] Furthermore, in the packing structure, a hole 6.2 with an outwardly extending tongue is opened on the curved blade, one side of the window blade cut by the hole is connected to the blade mother body, and the other side is bent outward of the blade, and a protrusion 6.3 is designed on the curved blade. The aperture of the curved blade 6.1 in the structured packing is 2 mm~5 mm, the hole spacing is 4 mm~10 mm, and the inclination angle of the outwardly extending tongue on the curved blade is 30°~70°. When the droplets pass through the window, some of the droplets collide again, and some of the droplets merge, and the unreacted liquid phase is fully mixed; the opening of the curved blade and the outwardly extending tongue in the structured packing can cause disturbance to the liquid film, change the flow direction of the liquid, and continuously generate small turbulence and eddy currents, which greatly reduce the laminar flow thickness and reduce the mass transfer resistance, greatly improving the mass transfer rate and mixing efficiency; the protrusion design on the curved blade makes the liquid have a more reasonable distribution in the longitudinal direction, and ensures that the liquid flows smoothly between the packing layers while increasing the disturbance, effectively reducing the resistance caused by the change of flow direction at the junction of the packing layers.

[0033] The impinging flow-rotating packed bed has a liquid feed impingement structure at the center of the structured packing, such as Figure 3 and Figure 7 As shown, the impact structure is a "Y"-shaped impact structure, which consists of an upper "V"-shaped liquid inlet 7 and a lower vertical liquid inlet 8. The upper "V"-shaped liquid inlet diverts one stream of raw material to form a "V" structure, and the other stream of raw material passes vertically upward through the lower vertical liquid inlet. When two streams of materials with a large difference in concentration collide, this impact structure strengthens the impact intensity by dividing the high-concentration material into two streams, so that the precipitant concentration in the impact mist area is excessive compared to the precipitant concentration required for the reaction, achieving an oversaturation effect, making the reaction more intense, thereby improving the mixing effect.

[0034] The angle β of the "V"-shaped incident tube of the "Y"-shaped impact structure in the impinging stream-rotating packed bed (see Figure 3 ) satisfies: 70°<β<100°. When the impact angle is too small, the liquid gathers and forms a chain structure at the downstream of the nozzle, and the dispersion is uneven. When the impact angle is too large, the dispersion degree is high, but the liquid near and below the nozzle outlet is unevenly dispersed. During the impact, not only the dispersion degree of the liquid should be considered, but also the uniformity of the liquid dispersion after the impact. We cannot only pursue a higher dispersion degree while ignoring the uniformity of the liquid dispersion, which will lead to an uneven liquid mixing environment and affect the mixing effect. Therefore, we need to comprehensively consider the above two aspects to select the best impact angle.

[0035] The end nozzle apertures of the impact structure are 0.5 mm to 10 mm, and the ratio of the end nozzle apertures at the upper liquid inlet to the lower liquid inlet is 0.5 to 1. This structure allows the raw material to quickly form a supersaturated zone, and the "Y"-shaped impact flow structure radiates radially around the impact zone during the reaction (see Figure 7), has a better liquid dispersion degree, which is more conducive to improving the dispersibility of powders and reducing the particle size of powders.

[0036] The above-mentioned device for continuously preparing spherical α-alumina nanopowder is a reaction system suitable for continuous and rapid preparation of spherical α-alumina nanopowder in industrial production. The reaction system has the advantages of strong universality, fast mixing, strong controllability, easy amplification, etc., and is a reaction system suitable for industrial production of spherical α-alumina nanopowder.

[0037] The present invention provides a method for preparing spherical α-alumina nanopowder, which is prepared by using the device for preparing spherical α-alumina nanopowder as described above, and comprises the following steps: (1) dissolving aluminum salt in deionized water to prepare aluminum salt solution A and pouring it into liquid storage tank II; dissolving precipitant in deionized water and adjusting the pH value of the resulting solution to prepare precipitant solution B and pouring it into liquid storage tank I; (2) Subsequently, the precipitant solution B and the aluminum salt solution A are pumped into the upper liquid inlet and the lower liquid inlet of the impinging flow-rotating packed bed to rapidly mix and react to generate a suspension C containing the precursor; wherein the feed concentration ratio of the precipitant to the aluminum salt is 6 to 13:1; Two streams of raw materials flow out of the liquid storage tank through the pump and liquid flow meter and enter the impinging flow-rotating packed bed. The "Y" type three-nozzle impact structure diverts the material on the one hand, so that the concentration of the precipitant in the impact mist area is excessive compared to the concentration of the precipitant required for the reaction, achieving a supersaturated effect, thereby improving the mixing effect and enhancing the reaction rate. On the other hand, the impact intensity is increased, which is more conducive to turbulent mixing in the reactor. The liquid entering the ultra-gravity rotor is affected by the rotating packing in the rotor, and the circumferential speed increases. The centrifugal force generated pushes the reaction liquid to the outer edge of the rotor; in this process, the staggered packing provides a tortuous flow channel, and the liquid is continuously dispersed, aggregated, and broken by the curved blades filled in the packing, so that the concentration distribution is uniform. In this way, excellent mixing, mass transfer and reaction conditions are created inside the rotor. Finally, under the action of gravity, the suspension C flows from the outlet of the impinging flow-rotating packed bed into the liquid storage tank III.

[0038] (3) aging, filtering and washing the suspension C to obtain a filter cake D; (4) Drying the filter cake D to obtain a precursor powder; (5) The precursor powder is ball-milled and then calcined to obtain spherical α-alumina nanopowder.

[0039] The precipitant is one or more of ammonium bicarbonate, ammonium carbonate and urea.

[0040] The concentration of the aluminum salt solution A is 0.1 mol / L to 0.6 mol / L; the concentration of the precipitant solution B is 1.0 mol / L to 4.0 mol / L, and the initial pH value is 9.0 to 11.0.

[0041] The reaction temperature of the impinging stream-rotating packed bed reactor is 30°C to 60°C, the supergravity factor is 10 to 80, and the initial impact velocity is 5 m / s to 40 m / s.

[0042] The calcination temperature is 900°C to 1300°C, and the calcination time is 1 h to 4 h.

[0043] The following is a method for preparing spherical α-alumina nanopowder using the above device by using a specific embodiment: Example 1

[0044] This embodiment 1 provides a method for preparing spherical α-alumina nanopowder under ultra-gravity, which is prepared by using the device for preparing spherical α-alumina nanopowder as described above, and comprises the following steps: Weigh 52.173 g of ammonium aluminum sulfate and dissolve it in 1000 mL of deionized water, and heat it in a water bath to 40 °C to obtain aluminum salt solution A; weigh 134.394 g of ammonium carbonate solution and dissolve it in 1000 mL of deionized water, adjust its pH to 9 with ammonia water, and heat it in a water bath to 40 °C to obtain precipitant solution B.

[0045] The prepared aluminum salt solution A and precipitant solution B were placed in the liquid storage tank II and liquid storage tank I of the supergravity reactor respectively, the supergravity factor was 30, the initial impact velocity was 15 m / s, and the suspension C of the precursor ammonium aluminum carbonate was prepared. The suspension C was aged and washed with deionized water, and the filter cake D was obtained after filtration.

[0046] The filter cake D was dried at 80 °C for 12 h, and then calcined in a muffle furnace at 1200 °C for 2 h to obtain nano-α-alumina powder. The nano-α-alumina powder was spherical and had a uniform particle size of 90 nm and good particle dispersibility. Example 2

[0047] This embodiment includes the following steps: Weigh 48.356 g of aluminum sulfate and dissolve it in 1000 mL of deionized water, and heat it in a water bath to 45 °C to obtain aluminum salt solution A; weigh 101.676 g of urea solution and dissolve it in 1000 mL of deionized water, adjust its pH to 10 with ammonia water, and heat it in a water bath to 45 °C to obtain precipitant solution B.

[0048] The prepared aluminum salt solution A and precipitant solution B were placed in the liquid storage tank II and liquid storage tank I of the supergravity reactor respectively, the supergravity factor was 20, the initial impact velocity was 20 m / s, and the suspension C of the precursor ammonium aluminum carbonate was prepared. The suspension C was aged and washed with deionized water, and the filter cake D was obtained after filtration.

[0049] The filter cake D was dried at 80 °C for 12 h, and then calcined in a muffle furnace at 1100 °C for 2 h to obtain nano-α-alumina powder. The nano-α-alumina powder was spherical and had a uniform particle size of 60 nm and good particle dispersibility. Example 3

[0050] This embodiment includes the following steps: Weigh 68.156 g of ammonium aluminum sulfate and dissolve it in 1000 mL of deionized water, and heat it in a water bath to 40 °C to obtain aluminum salt solution A; weigh 134.394 g of ammonium bicarbonate solution and dissolve it in 1000 mL of deionized water, adjust its pH to 11 with ammonia water, and heat it in a water bath to 40 °C to obtain precipitant solution B.

[0051] The prepared aluminum salt solution A and precipitant solution B were placed in the liquid storage tank II and liquid storage tank I of the supergravity reactor respectively, the supergravity factor was 15, the initial impact velocity was 10 m / s, and the suspension C of the precursor ammonium aluminum carbonate was prepared. The suspension C was aged and washed with deionized water, and the filter cake D was obtained after filtration.

[0052] The filter cake D was dried at 80 °C for 12 h and then calcined in a muffle furnace at 1300 °C for 1.5 h to obtain nano-α-alumina powder. The nano-α-alumina powder was spherical and had a uniform particle size of 76 nm and good particle dispersibility. Example 4

[0053] This embodiment includes the following steps: Weigh 39.482 g of ammonium aluminum sulfate and dissolve it in 1000 mL of deionized water, and heat it in a water bath to 30 °C to obtain aluminum salt solution A; weigh 110.825 g of ammonium carbonate solution and dissolve it in 1000 mL of deionized water, adjust its pH to 9 with ammonia water, and heat it in a water bath to 30 °C to obtain precipitant solution B.

[0054] The prepared aluminum salt solution A and precipitant solution B were placed in the liquid storage tank II and liquid storage tank I of the supergravity reactor respectively, the supergravity factor was 40, the initial impact velocity was 30 m / s, and the suspension C of the precursor ammonium aluminum carbonate was prepared. The suspension C was aged and washed with deionized water, and the filter cake D was obtained after filtration.

[0055] The filter cake D was dried at 80 °C for 12 h, and then calcined in a muffle furnace at 1200 °C for 2.5 h to obtain nano-α-alumina powder. The nano-α-alumina powder was spherical and had a uniform particle size of 95 nm and good particle dispersibility.

Claims

1. A device for preparing spherical α-alumina nanopowder, characterized in that: It comprises a liquid storage tank I, a pump I, an impinging stream-rotating packed bed, a pump II, a liquid storage tank II and a liquid storage tank III, wherein the liquid storage tank I is connected to a liquid inlet I of the impinging stream-rotating packed bed through a pump I, a valve I and a liquid flow meter I, the liquid storage tank II is connected to a liquid inlet II of the impinging stream-rotating packed bed through a pump II, a valve II and a liquid flow meter II, and the discharge port of the impinging stream-rotating packed bed is connected to the liquid storage tank III; A structured packing is arranged in the impinging flow-rotating packed bed, wherein the structured packing is composed of a plurality of single-layer packings arranged alternately in the horizontal direction in the axial direction, wherein the single-layer packings are composed of a plurality of concentric rings of different diameters; A liquid feed impact structure is arranged at the center of the structured packing. The impact structure is "Y"-shaped and consists of an upper "V"-shaped liquid inlet and a lower vertical liquid inlet. The upper "V"-shaped liquid inlet diverts one stream of raw material to form a "V" structure, and the other stream of raw material is ejected vertically upward through the lower vertical liquid inlet. When two streams of materials with a large difference in concentration collide, this impact structure divides the high-concentration material into two feeds, thereby enhancing the impact intensity and improving the mixing effect.

2. The device for preparing spherical α-alumina nanopowder according to claim 1, characterized in that: The structured packing as a whole is composed of 3 to 12 layers of single-layer packing arranged in parallel, and adjacent layers are staggered at an angle of 10° to 60°; the single-layer packing is composed of 4 to 7 circles of concentric rings of different diameters, and the structure of adjacent inner and outer rings is staggered at an angle of 5° to 30°; each ring is composed of a combination of multiple arc structures.

3. The device for preparing spherical α-alumina nanopowder according to claim 2, characterized in that: Each arc-shaped structural unit of the single-layer filler includes a supporting structure and a filling structure. The supporting structure uses a wire mesh as a frame, and the internal filling structure is provided with curved blades. The surface of the filling structure is roughened using a potassium permanganate method.

4. The device for preparing spherical α-alumina nanopowder according to claim 3, characterized in that: The curved blades in the filling structure have a certain curvature, and according to the blade curvature calculation formula r=(u 2 ) / (g·tan(α)), where u represents the velocity of the fluid, g represents the acceleration of gravity, α represents the angle of the blade relative to the frame, and the blade curvature r is 0.7 ~ 1.1; the curved blade can collide and cross with the direction of the droplet to fully disperse it.

5. The device for preparing spherical α-alumina nanopowder according to claim 4, characterized in that: In the filling structure, a hole for an outwardly extending tongue is opened on the curved blade, one side of the window blade cut by the hole is connected to the blade mother body, and the other side is bent outward of the blade, and a protrusion is designed on the curved blade; the hole diameter of the curved blade is 2 mm~5 mm, the hole spacing is 4 mm~10 mm, and the inclination angle of the outwardly extending tongue on the curved blade is 30°~70°.

6. The device for preparing spherical α-alumina nanopowder according to claim 1, characterized in that: The angle β of the "V"-shaped incident tube of the "Y"-shaped impact structure satisfies: 70°<β<100°. When the impact angle is too small, the liquid gathers and forms a chain structure downstream of the nozzle, and the dispersion is uneven; when the impact angle is too large, the dispersion degree is high, and the liquid near and below the nozzle outlet is unevenly dispersed.

7. The device for preparing spherical α-alumina nanopowder according to claim 6, characterized in that: The apertures of the end nozzles of the impact structure are 0.5 mm to 10 mm, and the aperture ratio of the end nozzles at the upper liquid inlet and the lower liquid inlet is 0.5 to 1.

8. A method for preparing spherical α-alumina nanopowder, using the spherical α-alumina nanopowder preparation device according to any one of claims 1 to 7, characterized in that The following steps are involved: (1) Dissolve aluminum salt in deionized water to prepare aluminum salt solution A and pour it into storage tank II; The precipitant is dissolved in deionized water, and the pH value of the resulting solution is adjusted to prepare a precipitant solution B, which is then placed in the liquid storage tank I; (2) Subsequently, the precipitant solution B and the aluminum salt solution A are pumped into the upper liquid inlet and the lower liquid inlet of the impinging flow-rotating packed bed to rapidly mix and react to generate a suspension C containing the precursor; wherein the feed concentration ratio of the precipitant to the aluminum salt is 6 to 13:1; Two streams of raw materials flow out of the liquid storage tank through the pump and liquid flow meter and enter the impinging flow-rotating packed bed. The "Y"-shaped three-nozzle impact structure diverts the material on the one hand, so that the concentration of the precipitant in the impact mist area is excessive compared to the concentration of the precipitant required for the reaction, achieving a supersaturated effect, thereby improving the mixing effect and enhancing the reaction rate. On the other hand, the impact intensity is increased, which is more conducive to turbulent mixing in the reactor. The liquid entering the ultra-gravity rotor is affected by the rotating packing in the rotor, and the circumferential speed increases. The centrifugal force generated pushes the reaction liquid to the outer edge of the rotor; in this process, the staggered packing provides a tortuous flow channel, and the liquid is continuously dispersed, aggregated, and broken by the curved blades filled in the packing, so that the concentration distribution is uniform; excellent mixing, mass transfer and reaction conditions are created inside the rotor, and finally, under the action of gravity, the suspension C flows from the outlet of the impinging flow-rotating packed bed into the liquid storage tank III; (3) aging, filtering and washing the suspension C to obtain a filter cake D; (4) Drying the filter cake D to obtain a precursor powder; (5) The precursor powder is ball-milled and then calcined to obtain spherical α-alumina nanopowder.

9. The method for preparing spherical α-alumina nanopowder according to claim 8, characterized in that: The concentration of the aluminum salt solution A is 0.1 mol / L-0.6 mol / L; the concentration of the precipitant solution B is 1.0 mol / L-4.0 mol / L, and the initial pH value is 9.0-11.0; the precipitant is one or more of ammonium bicarbonate, ammonium carbonate, and urea.

10. The method for preparing spherical α-alumina nanopowder according to claim 8, characterized in that: The reaction temperature of the impinging stream-rotating packed bed reactor is 30°C to 60°C, the supergravity factor is 10 to 80, and the initial impact velocity is 5 m / s to 40 m / s; the calcination temperature is 900°C to 1300°C, and the calcination time is 1 h to 4 h.

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