Drying method for reducing agglomeration of ultrafine powder during drying

Abstract

A drying method for relieving agglomeration of superfine powder during drying comprises the steps that slurry is placed in a pressure container, and the temperature and the air pressure are controlled; adding CO2 into the slurry to fully dissolve CO2 in the slurry, and carrying out spray drying to obtain dried ultrafine powder; the slurry comprises a dispersing agent and a dispersoid; the dispersoid comprises one or two of undissolved ultrafine particles and soluble solid substances dissolved in a dispersing agent. Under the action of sudden pressure drop and temperature rise at the moment of atomization, CO2 dissolved in the slurry is quickly gasified and expanded in liquid beads to generate a micro-blasting effect, the liquid drops are further micronized, and the drying time is shortened; compared with a conventional drying mode, the specific surface area of the superfine powder dried through the method is obviously increased and is closer to the original granularity of the superfine powder in a liquid phase.

Description

Technical Field

[0001] This invention relates to the field of powder dispersion, and more specifically to a drying method for reducing the agglomeration of ultrafine powders. Background Technology

[0002] Ultrafine powders refer to tiny solid particles with a scale between molecules, atoms, and bulk materials. They include particles of various materials such as metals, non-metals, organics, inorganics, and biological materials. Ultrafine powders typically refer to powders at the micrometer or nanometer scale.

[0003] The preparation methods of ultrafine powders can be summarized into two categories: chemical synthesis and physical pulverization. They can usually be prepared by ball milling, mechanical pulverization, spraying, explosion, chemical deposition and other methods. As the material becomes ultrafine, its surface electronic structure and crystal structure change, producing surface effects, small size effects, quantum effects and macroscopic quantum tunneling effects that are not present in bulk materials. As a result, ultrafine powders have a series of excellent physical and chemical properties compared with conventional particulate materials. Ultrafine powders have many unique properties, mainly as follows: (1) large specific surface area; (2) low melting point; (3) superparamagnetism or high coercivity; (4) good chemical reactivity; (5) good light absorption, low reflectivity, and blue shift of light absorption band; (6) good thermal conductivity, ultrafine powders have almost no thermal resistance at low temperatures; (7) the conductivity of metal micro powders drops sharply, and the conductivity of non-metal powders increases sharply. 10-15nm silver powder becomes non-conductive, and 15-20nm SiO2 becomes conductive; (8) mechanical properties are multiplied. It has shown promising application prospects in catalysis, electronics, information, optical flux, medicine, and new magnetic media materials, expanding many scientific research fields.

[0004] Generally, the narrower the particle size distribution of ultrafine powders, the more stable their performance. However, ultrafine powders are prone to agglomeration, causing changes in particle size, which is a major challenge in the application of ultrafine powders. The aggregation of multiple small particles into a larger agglomerate is called agglomeration; ultrafine powders are more prone to agglomeration during the drying process than ordinary powders. As the particle size decreases, its specific surface area (total surface area per unit mass) increases; as the total number of atoms per particle decreases, the number of atoms on the particle surface increases rapidly; the chemical environment of surface atoms or molecules differs from that of internal atoms, resulting in an imbalance of forces and an unstable state; ultrafine powders have a huge specific surface area, thus possessing high surface energy. High surface energy means the system is in a thermodynamically unstable state, and particles have a strong spontaneous tendency to reduce surface area to lower surface energy. Agglomeration is one of the most effective ways to reduce the total surface area.

[0005] Van der Waals forces are a universal attraction between all molecules and particles, originating from the interaction of instantaneous dipole moments. The magnitude of the van der Waals force is inversely proportional to the sixth power of the interparticle distance and directly proportional to the particle size. Therefore, when particles are extremely small, they are more likely to come close together during drying, causing the van der Waals force to increase dramatically. For ultrafine powders, the strong van der Waals forces at close range are sufficient to overcome forces such as gravity that would separate them.

[0006] Furthermore, liquid bridging forces (capillary forces) are also a significant factor contributing to the agglomeration of ultrafine particles during drying. In the initial stages of drying or when residual solvent is present, liquid capillary bridges form between particles. The menisci formed by the liquid between the particles generate strong capillary pressure (negative pressure), tightly binding the particles together. As drying progresses, the liquid bridges gradually shrink, but even with a small liquid volume, the capillary force generated by the extremely small menisci formed near evaporation can reach very high orders of magnitude (inversely proportional to the volume of the liquid bridge). The liquid bridges formed between ultrafine particles are even smaller, thus generating even greater capillary forces.

[0007] Although ultrafine powder particles with particle sizes of tens or hundreds of nanometers can be obtained in the liquid phase through liquid-phase reaction or wet ultrafine grinding, if drying agglomeration cannot be solved or effectively reduced during the drying process, severe agglomeration will occur in the ultrafine particles, causing the particle size to increase and the specific surface area to decrease, which seriously impairs the application performance and may even be inferior to products with ordinary fineness. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a drying method that can effectively reduce the agglomeration of ultrafine powders during drying.

[0009] The technical solution adopted by this invention to solve its technical problem is as follows: A drying method for reducing the agglomeration of ultrafine powders during drying, comprising: Slurry A is placed in a pressure vessel, and the temperature is controlled at 0℃~10℃ and the air pressure is controlled at 0.2MPa~1.2MPa; CO2 is added to slurry A and fully dissolved in slurry A to obtain slurry B; slurry B is spray dried to obtain dried ultrafine powder. The slurry A includes a dispersant and a dispersed phase; the dispersed phase includes one or two of the following: undissolved ultrafine particles and soluble solids dissolved in the dispersant. In the slurry B, the amount of CO2 dissolved is 1.5 to 10 times the volume of CO2; the volume of CO2 refers to the ratio of the volume of carbon dioxide dissolved in slurry B under standard conditions (20°C, 1 atmosphere) to the volume of slurry B.

[0010] Preferably, the solid content in the slurry A is 10wt%~60wt%.

[0011] Preferably, the dispersion of the slurry A includes one or more of nano-sized powders, micron-sized powders, and easily hardened agglomerated materials.

[0012] Preferably, the dispersant in the slurry A includes water.

[0013] Preferably, the spray drying temperature is 150℃~600℃.

[0014] Preferably, the temperature in the pressure vessel is 0℃~4℃ and the air pressure is 0.4MPa~1MPa.

[0015] Preferably, the CO2 is introduced into slurry A and then stirred for 1 to 10 minutes.

[0016] Preferably, the dried ultrafine powder is further deagglomerated.

[0017] Preferably, the temperature of slurry A is first controlled to a suitable range, and then the air pressure of the environment in which slurry A is located is controlled.

[0018] Preferably, the dispersion of the slurry A is obtained by chemical synthesis and / or physical pulverization.

[0019] The present invention has the following beneficial effects: This invention employs a spray drying method. When a slurry containing dissolved carbon dioxide is spray-dried, the sudden drop in pressure and rise in temperature during atomization cause the dissolved CO2 inside the slurry to rapidly vaporize and expand within the droplets, producing a micro-explosion effect. The droplets rapidly break down and disintegrate during the drying process, further refining the spray-generated droplets, reducing the volume of individual droplets, decreasing the contact opportunities between small particles, and reducing agglomeration caused by van der Waals forces. Simultaneously, the further refining of droplets creates a larger contact area with hot air, shortening the drying time and reducing agglomeration caused by capillary forces. Compared to conventional drying methods, the ultrafine powder dried using this invention has a significantly increased specific surface area, more closely resembling the original particle size of the ultrafine powder in the liquid phase.

[0020] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a cumulative particle size distribution diagram of the powder obtained in Example 1 of the present invention; Figure 2 These are electron microscope images of the powder obtained in Example 1 of this invention; Figure 3 This is an electron microscope image of the powder obtained in Comparative Example 1. Detailed Implementation

[0022] To make the objectives, solutions, and beneficial technologies of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be noted that the embodiments described in this specification are merely illustrative of the invention and are not intended to limit the invention.

[0023] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0024] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, "multiple" in "one or more" means two or more, and "more than" in "one or more" means two or more.

[0025] Embodiments of the present invention provide a drying method for reducing the agglomeration of ultrafine powders during drying, comprising: Slurry A is placed in a pressure vessel, and the temperature is controlled at 0℃~10℃ and the air pressure is controlled at 0.2MPa~1.2MPa; CO2 is added to slurry A and fully dissolved in slurry A to obtain slurry B; slurry B is spray dried to obtain dried ultrafine powder. The slurry A includes a dispersant and a dispersed phase; the dispersed phase includes one or two of the following: undissolved ultrafine particles and soluble solids dissolved in the dispersant. In the slurry B, the amount of CO2 dissolved is 1.5 to 10 times the volume of CO2; the volume of CO2 refers to the ratio of the volume of carbon dioxide dissolved in slurry B under standard conditions (20°C, 1 atmosphere) to the volume of slurry B.

[0026] The ultrafine powder is micron-sized and / or nano-sized. Ultrafine particles refer to small particles located in the slurry, which form ultrafine powder after drying.

[0027] The dispersed phase in slurry A can be undissolved ultrafine particles or soluble solids dissolved in the dispersant. In the spray drying process of this scheme, undissolved ultrafine particles are removed from the dispersant to form dry ultrafine powder. For soluble solids dissolved in the dispersant, nucleation and precipitation occur simultaneously when the dispersant is removed, eventually forming dry ultrafine powder.

[0028] Among commonly used drying methods, those that can reduce agglomeration during the drying of ultrafine powder slurries include solvent displacement drying, freeze drying, supercritical drying, and spray drying. Spray drying is the most widely used industrial drying method, and it is less expensive than the other three. The core principle of spray drying is to highly disperse liquid materials into extremely fine droplets and complete the drying process in a very short time. Spray drying processes liquid materials, which can be solutions, suspensions, emulsions, etc. The first step involves using atomizers such as rotating discs, pressure nozzles, and airflow nozzles to rapidly disperse the liquid material into countless extremely small droplets, typically with a diameter of 10-500 micrometers. Each small droplet exists relatively independently within the drying tower, greatly reducing the chance of contact between them. The total surface area of ​​the micro-droplets increases dramatically, resulting in extremely high efficiency in heat and mass transfer (mainly water evaporation), and a very short drying time, completed within seconds or tens of seconds. The small droplets bring short water evaporation paths and drying times, making capillary forces during drying smaller, thus reducing agglomeration. A typical spray drying process involves: processing the raw material into an ultrafine slurry, then spray drying, deagglomeration treatment, and packaging. Compared to conventional drying, spray drying atomizes the slurry, resulting in shorter water evaporation time and lighter agglomeration. However, for many ultrafine materials, droplets of 10–500 micrometers are still quite large, and spray drying still results in significant agglomeration.

[0029] This invention is based on commonly used spray drying methods such as centrifugal spray, pressure spray, and airflow spray. Under low temperature and high pressure conditions, CO2 is introduced into an ultrafine powder slurry. When CO2 is introduced under pressure, the solution mainly consists of dissolved CO2 molecules (aq) and a small amount of HCO3. - It exists in liquid form. At this time, CO2 has high solubility in liquid, with a volume ratio of 1 to 6.

[0030] During spray drying, the CO2 dissolved inside the slurry rapidly vaporizes and expands within the droplets due to the sudden pressure drop and temperature increase at the moment of atomization, producing a micro-explosion effect. The droplets rapidly break down and disintegrate during the drying process, further refining the spray-generated droplets, reducing the volume of individual droplets, decreasing the contact opportunities between small particles, and reducing agglomeration caused by van der Waals forces. At the same time, the further refinement of the droplets creates a larger contact area with hot air, shortening the drying time and reducing agglomeration caused by capillary forces. This invention fundamentally reduces the agglomeration driving force. Compared with conventional drying methods, the specific surface area of ​​the ultrafine powder dried using this method is significantly increased, and it is closer to the original particle size of the ultrafine powder in the liquid phase.

[0031] The present invention has a significantly better effect on reducing agglomeration than air spray and other spray drying methods, especially for ultrafine powders or materials that are prone to hard agglomeration, such as SiO2 and Al2O3.

[0032] This invention is applicable to fields requiring extremely high powder dispersibility, such as electronic ceramics and catalyst supports, as well as special materials for which dispersants cannot be added, such as biopharmaceutical powders.

[0033] In some embodiments of the present invention, the amount of CO2 dissolved in slurry B is 2 to 8 times the volume of CO2.

[0034] In an embodiment of the present invention, the solid content in slurry A is 10wt%~60wt%.

[0035] In some embodiments of the present invention, the viscosity of slurry A is below 300 centipoise.

[0036] In some embodiments of the present invention, the viscosity of slurry A is below 100 centipoise.

[0037] In embodiments of the present invention, the dispersion of the slurry A includes one or more of nano-sized powders, micro-sized powders, and easily hardened agglomerated materials.

[0038] In an embodiment of the present invention, the dispersant of the slurry A includes water.

[0039] The solubility of CO2 gas in water is greatly affected by temperature and pressure. At normal temperature and pressure, the volume ratio of CO2 is close to zero, while at low temperature and high pressure it can reach 3 to 4 or even higher. The amount of CO2 dissolved in water (by mass or moles) at low temperature and high pressure is more than 200 times higher than at normal temperature and pressure (such as water in an open container exposed to air).

[0040] In embodiments of the present invention, the spray drying temperature is 150℃~600℃. Testing has shown that pressure spraying, centrifugal spraying, and airflow spraying are all suitable for the method of the present invention and exhibit good results under these temperature conditions.

[0041] In some embodiments of the present invention, the spray drying temperature is 200°C to 300°C.

[0042] In an embodiment of the present invention, the temperature in the pressure vessel is 0°C to 4°C and the air pressure is 0.4 MPa to 1 MPa.

[0043] In an embodiment of the present invention, the CO2 is introduced into slurry A and then stirred for 1 to 10 minutes. Stirring promotes the uniform dispersion of CO2 in the slurry.

[0044] In some embodiments of the present invention, the dried ultrafine powder is further deagglomerated. The dried ultrafine powder can be further deagglomerated using conventional methods.

[0045] In some embodiments of the present invention, a powder deagglomeration and dispersing machine is used to deagglomerate the obtained dried ultrafine powder.

[0046] In some embodiments of the present invention, high-pressure CO2 is used.

[0047] In some embodiments of the present invention, the temperature of slurry A is first controlled to a suitable range, and then the air pressure of the environment in which slurry A is located is controlled.

[0048] In some embodiments of the present invention, the dispersion of slurry A is obtained by chemical synthesis and / or physical pulverization. The present invention mainly relates to the drying of the slurry, and there are no strict requirements regarding the method of obtaining the dispersion of slurry A; existing processes for preparing ultrafine powders can generally be used.

[0049] Physical pulverization and chemical synthesis are the two main methods for preparing ultrafine powders. Physical pulverization involves breaking down larger blocks of material into powders. Commonly used pulverizing equipment includes planetary ball mills, vibratory mills, stirred mills, and mechanical impact mills, as well as newer technologies such as ultrasonic pulverization. Chemical synthesis involves chemical reactions or phase transformations, producing powders through the formation of crystal nuclei and growth of ions, atoms, or molecules. Examples include precipitation methods, hydrothermal methods, microemulsion methods, and sol-gel methods.

[0050] Precipitation is a common method for preparing powders through liquid-phase reactions. The morphology of the powder depends on the feeding method. It involves the synthesis of ultrafine metal oxide powders in liquid-phase chemical reactions. The process involves reacting substances dissolved in water to form insoluble compounds, which are then decomposed by heating or without heating to obtain the final desired compound product. Various methods exist for preparing nanoparticles using precipitation, including direct precipitation, co-precipitation, and homogeneous precipitation.

[0051] The hydrothermal method synthesizes powders under high temperature and pressure in a closed system of water, resulting in products with high purity and dispersibility. As an emerging technology for preparing ultrafine powders, the hydrothermal method directly generates ultrafine powders through a chemical reaction in a closed system using high temperature and pressure water or an aqueous solution. This method offers numerous advantages, such as small particle size, high purity, and good dispersibility, and it overcomes certain challenges encountered in high-temperature preparation processes.

[0052] Microemulsions are transparent or translucent, isotropic, thermodynamically stable systems carefully composed of water, oil, surfactants, and co-surfactants. Among the many types, W / O microemulsions are ideal for preparing ultrafine powder particles due to their unique properties. They not only provide excellent reaction media but also restrict particle growth at the microscale, thus making the preparation of ultrafine powders simpler and more efficient.

[0053] The sol-gel method is a process for preparing oxides or other solid compounds by passing them through solution, sol, and gel processes, followed by heat treatment. Based on the mechanisms of sol and gel formation, this method can be classified into three categories: traditional colloidal type, inorganic polymer type, and complex type.

[0054] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0055] Example 1 Preparation of slurry A: 1 kg of coal-series kaolin ore was coarsely ground into 325 mesh powder, and water was added to make a slurry with a solid content of 40 wt%. An appropriate amount of dispersant was added, and the mixture was ground in a sand mill for 1 hour to make the -2µm particle size 88 wt%. Water was added to dilute the slurry to a solid content of 20 wt%. The mixture was centrifuged to make the -2µm particle size 95 wt%, resulting in slurry A weighing 4.5 kg with a solid content of 16.7 wt%.

[0056] Slurry A is cooled to 4°C, pressurized to 0.8 MPa in a pressure vessel, and then high-pressure CO2 gas is added, with the amount of CO2 gas being 4 times the volume ratio. The mixture is stirred for 5 minutes to fully dissolve the CO2 gas, resulting in slurry B. Slurry B is then spray-dried to obtain dried ultrafine powder at a temperature of 260°C.

[0057] Comparative Example 1 Spray drying was performed using the same slurry A as in Example 1 to obtain dried ultrafine powder. The spray drying temperature was 260°C.

[0058] The particle size of the powders obtained in Example 1 and Comparative Example 1, as well as the particle size of the particles in slurry A, were measured using a Sedigragh 5100 sedimentation particle size analyzer. When the sample was slurry A, the measurement was performed directly. When the sample was the powder obtained in Example 1 or Comparative Example 1, water was added first to prepare a slurry before measurement. The results are shown in Table 1.

[0059] The specific surface area of ​​the powders obtained in Example 1 and Comparative Example 1 was determined by the BET liquid nitrogen adsorption method, and the results are shown in Table 1.

[0060] The cumulative particle size distribution diagram of the powder obtained in Example 1 is shown below. Figure 1 .

[0061] Table 1. Particle size and specific surface area of ​​each sample in Example 1 and Comparative Example 1 As shown in Table 1, the particle size of the powder obtained in Example 1 is basically the same as that of the particles in slurry A, indicating that the powder in Example 1 does not agglomerate during the drying process. The overall particle size of the powder obtained in Comparative Example 1 is significantly increased compared to that in slurry A, indicating that agglomeration occurred during its drying process; BET specific surface area detection shows that the specific surface area of ​​the powder obtained in Example 1 is more than 30% higher than that of Comparative Example 1.

[0062] Electron micrographs of the powder obtained in Example 1 are shown below. Figure 2 Electron micrographs of the powder obtained in Comparative Example 1 are shown below. Figure 3 . Figure 2 There are basically no aggregated particles with clearly defined outlines in the middle, while Figure 3 The clearly defined blocky aggregated particles can be seen, indicating that the agglomeration in Example 1 is significantly reduced compared to Comparative Example 1, which is consistent with the particle size test results.

[0063] Example 2 Preparation of slurry A: Dissolve analytical grade aluminum sulfate in distilled water to prepare Al 3+ An aluminum sulfate solution with a concentration of 0.8 mol / L was prepared; under stirring conditions, dilute ammonia water (3 mol / L) was slowly added until the pH value reached 5.5; the slurry was filtered and washed to obtain an ultrafine aluminum hydroxide filter cake. The filter cake was hydrated to make slurry A with a solid content of 15 wt%.

[0064] Slurry A was cooled to 0°C and added to a high-pressure container, pressurized to 1 MPa, and then high-pressure CO2 gas was added at a volume ratio of 5. The mixture was stirred for 5 minutes to fully dissolve the CO2 gas, yielding slurry B. Slurry B was then pumped into a centrifugal spray dryer for spray drying at 250°C to obtain dried ultrafine powder. The agglomerated particles were then broken up using a powder deagglomeration and dispersion machine to obtain the final sample.

[0065] Comparative Example 2 Using the same slurry A as in Example 2, the powder was pumped into a centrifugal spray dryer via a high-pressure pump for spray drying to obtain dried ultrafine powder. The spray drying temperature was 250°C. The agglomerated particles were then broken up using a powder deagglomeration and dispersion machine to obtain the final sample.

[0066] The particle size of the powders obtained in Example 2 and Comparative Example 2, as well as the particle size of the particles in slurry A, were measured using a Sedigragh 5100 sedimentation particle size analyzer. When the sample was slurry A, the measurement was performed directly. When the sample was the powder obtained in Example 2 or Comparative Example 2, water was added first to prepare a slurry before measurement. The results are shown in Table 2.

[0067] The specific surface area of ​​the powders obtained in Example 2 and Comparative Example 2 was determined by the BET liquid nitrogen adsorption method, and the results are shown in Table 2.

[0068] Table 2. Particle size and specific surface area of ​​each sample in Example 2 and Comparative Example 2 The ultrafine aluminum hydroxide in slurry A of Example 2 and Comparative Example 2 was directly generated by a chemical reaction, resulting in extremely fine particles. As shown in Table 2, the overall particle size of the powder obtained in Comparative Example 2 increased several times compared to slurry A, indicating significant agglomeration during the drying process. The particle size increase of the powder obtained in Example 2 was less, closer to the original particle size, and the agglomeration was significantly reduced. BET surface area analysis showed that the specific surface area of ​​the powder obtained in Example 2 was more than 50% higher than that in Comparative Example 2.

[0069] Example 3 In this embodiment, slurry A is a nano-calcium carbonate slurry produced by a calcium carbonate manufacturer. It is prepared by carbonation, which involves calcining limestone to generate calcium oxide, adding water to form a calcium hydroxide suspension, and then introducing carbon dioxide for carbonation. A crystal form regulator is also used. The calcium carbonate is in the form of uniform cubic particles, and the solid content is 20wt%.

[0070] Slurry A was cooled to 4°C and added to a high-pressure container, pressurized to 0.9 MPa, and then high-pressure CO2 gas was introduced at a volume ratio of 6. The CO2 gas was fully dissolved to obtain slurry B. Slurry B was then pumped into a centrifugal spray dryer for spray drying at a temperature of 260°C to obtain dried ultrafine powder. The agglomerated particles were then broken up using a powder deagglomeration and dispersion machine to obtain the final sample.

[0071] Comparative Example 3 Using the same slurry A as in Example 3, the powder was pumped into a centrifugal spray dryer via a high-pressure pump for spray drying to obtain dried ultrafine powder. The spray drying temperature was 260°C. The agglomerated particles were then broken up using a powder deagglomeration and dispersion machine to obtain the final sample.

[0072] The particle size of the powders obtained in Example 3 and Comparative Example 3, as well as the particle size of the particles in slurry A, were measured using a Sedigragh 5100 sedimentation particle size analyzer. When the sample was slurry A, the measurement was performed directly. When the sample was the powder obtained in Example 3 or Comparative Example 3, water was added first to prepare a slurry before measurement. The results are shown in Table 3.

[0073] The specific surface area of ​​the powders obtained in Example 3 and Comparative Example 3 was determined by the BET liquid nitrogen adsorption method, and the results are shown in Table 3.

[0074] Table 3. Particle size and specific surface area of ​​each sample in Example 3 and Comparative Example 3 In Example 3 and Comparative Example 3, the nano-calcium carbonate in slurry A was directly generated by a chemical reaction, resulting in extremely fine particles. As shown in Table 3, the overall particle size of the powder obtained in Comparative Example 3 increased several times compared to slurry A, indicating significant agglomeration during the drying process. The particle size increase of the powder obtained in Example 3 was less, indicating a lower degree of agglomeration. BET surface area analysis showed that the specific surface area of ​​the powder obtained in Example 3 was more than 30% higher than that in Comparative Example 3.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A drying method for reducing the agglomeration of ultrafine powders during drying, characterized in that, include: Slurry A is placed in a pressure vessel, and the temperature is controlled at 0℃~10℃ and the air pressure is controlled at 0.2MPa~1.2MPa; CO2 is added to slurry A and fully dissolved in slurry A to obtain slurry B; slurry B is spray dried to obtain dried ultrafine powder. The slurry A includes a dispersant and a dispersed phase; the dispersed phase includes one or two of the following: undissolved ultrafine particles and soluble solids dissolved in the dispersant. In the slurry B, the amount of CO2 dissolved is 1.5 to 10 times the volume of CO2; the volume of CO2 refers to the ratio of the volume of carbon dioxide dissolved in slurry B at 20°C and 1 atmosphere to the volume of slurry B.

2. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, The solid content in the slurry A is 10wt%~60wt%.

3. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, The dispersion of the slurry A includes one or more of the following: nano-sized powder, micron-sized powder, and easily hardened agglomerated materials.

4. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, The dispersant for slurry A includes water.

5. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, The spray drying temperature is 150℃~600℃.

6. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, The temperature in the pressure vessel is 0℃~4℃ and the air pressure is 0.4MPa~1MPa.

7. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, The CO2 is introduced into slurry A and then stirred for 1 to 10 minutes.

8. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, The dried ultrafine powder was also deagglomerated.

9. The drying method for reducing the agglomeration of ultrafine powders during drying according to claim 1, characterized in that, First, control the temperature of slurry A to a suitable range, and then control the air pressure of the environment in which slurry A is located.

10. The drying method for reducing the agglomeration of ultrafine powders during drying according to any one of claims 1 to 9, characterized in that, The dispersion of the slurry A is obtained by chemical synthesis and / or physical pulverization.

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