Method for preparing nano material by taking supercritical carbon dioxide as medium through high-pressure convection method

Abstract

The invention discloses a method for preparing a nano material by using a high-pressure convection method by taking supercritical carbon dioxide as a medium, which can greatly save energy and greatly reduce the manufacturing cost of the nano material. On the basis of a high-pressure homogenizer, conventional liquid such as water or ethyl alcohol is not adopted as a working medium, supercritical CO2 fluid is adopted, materials form turbid liquid in the supercritical CO2 fluid, and the materials are separated from the turbid liquid in a collision or correlation mode above the critical pressure and temperature (the pressure is 7.4 Mpa and the temperature is 32 DEG C) of the supercritical CO2 fluid. The materials flow through a containing cavity (a high-pressure homogenizing cavity) with a special internal structure at a high speed, so that the materials have a series of changes in physical, chemical, structural properties and the like; and finally, the effect of preparing the nano powder is achieved.

Description

Technical Field

[0001] The invention relates to a method for preparing a nano material, in particular to a method for preparing the nano material by a high-pressure convection method based on a high-pressure homogenizer and taking supercritical carbon dioxide as a medium. Background Art

[0002] High-pressure homogenizers are widely used in the production of food (including milk, beverages, etc.), pigments (including organic pigments, inorganic pigments chrome yellow and carbon black), dyes (including disperse dyes, vat dyes and anthraquinone acid dyes) and ultrafine nanomaterials. The rapid development of ultrafine nano-scale pulverization technology has prompted major domestic dye, pigment and nanomaterial companies to switch to ultrafine process equipment.

[0003] There are two completely different types of high-pressure homogenizers in this technical field. The first and most common type of high-pressure homogenizer is also called a "high-pressure fluid nano-homogenizer". It can make materials in a suspended state flow through a cavity with a special internal structure (high-pressure homogenization cavity) at high speed by collision or counter-emission under ultra-high pressure (up to 414MPa), thereby causing a series of changes in physical, chemical, and structural properties, and ultimately achieving a homogenization effect. This type of high-pressure homogenizer generally uses conventional liquids such as water or ethanol as the working medium for preparing powder materials. This type of homogenizer not only works under high pressure, but also mixes the crushed material with water or other conventional liquids into a suspension, and then performs high-speed convection collision crushing, because water or ethanol must be present in the crushing process to maintain high-speed convection and take away a large amount of heat generated during the crushing. However, a large amount of water needs to be removed from the crushed material, which will consume a lot of energy and greatly increase the cost of nanomaterials. If solvents such as ethanol are used, their volatilization may emit organic gases, which is also a waste of solvents; the other is a high-pressure homogenizer, which has no high-speed collision or cross-shooting. It is mainly a pressure vessel and a jet pressure reduction device. The principle is to use supercritical fluid as the medium and use the change of the supercritical fluid state caused by sudden pressure reduction to prepare ultrafine powders. This process is a process in which a supercritical fluid solution rapidly expands through a fine nozzle. During the expansion process, the sudden change in pressure causes the solute supersaturation to increase suddenly. When the solution is sprayed out in a single phase, a large number of micronuclei are precipitated, and the micronuclei grow rapidly in a very short time to form submicron and even nanometer-level microparticles with uniform particle size, but there are problems of complex equipment structure and high production cost. Summary of the invention

[0004] The present invention provides a method for preparing nanometer materials by high pressure convection method with supercritical carbon dioxide as medium, which can greatly save energy and greatly reduce the production cost of nanometer materials.

[0005] The present invention solves the above technical problems through the following technical solutions: The overall concept of the present invention is: the present invention is based on a high-pressure homogenizer, and does not use conventional liquids such as water or ethanol as a working medium, but uses supercritical CO2 fluid. The pre-prepared micron material powder forms a suspension in the supercritical CO2 fluid, and above the critical pressure and temperature of the supercritical carbon dioxide fluid (pressure 7.4MPa and temperature 32°C), it flows at high speed through a cavity (high-pressure homogenization cavity) with a special internal structure in a collision or counter-emission manner, causing a series of changes in the physical, chemical, and structural properties of the material; ultimately, the effect of preparing nanopowders is achieved.

[0006] A method for preparing nanomaterials by high-pressure convection method using supercritical carbon dioxide as a medium is based on a high-pressure homogenizer. Supercritical CO2 fluid is used as the working medium. Pre-prepared nanomaterials form a suspension in the supercritical CO2 fluid. Above the critical pressure and temperature of the supercritical carbon dioxide fluid, that is, the pressure is above 7.4MPa and the temperature is above 32°C. The suspension flows through a high-pressure homogenization cavity at a high speed in a collision or counter-emission manner to prepare nanopowders.

[0007] A method for preparing nanomaterials by high pressure convection method using supercritical carbon dioxide as a medium, selecting the prepared nanomaterial, comprising the following steps: The first step is to suck the pre-prepared nanomaterial micron-sized powder and CO2 gas into the pump chamber of the high-pressure homogenizer at a speed of 2 meters per second or more; The second step is to move the plunger in the pump chamber of the equipment in the opposite direction to reduce the volume of the pump chamber of the equipment to form high pressure, so that the pressure in the pump chamber of the equipment is maintained at 7.4-20MPa, and the temperature in the pump chamber of the equipment is maintained at 32-40℃, and the carbon dioxide in the pump chamber of the equipment enters and is in a supercritical liquid state; The third step is that after the micron-sized powder of the prepared nanomaterial in the pump cavity of the equipment is fully mixed with the supercritical CO2, the mixture is ejected out of the pump cavity of the equipment at a speed of at least 400 meters per second and enters the material cavity of the supercritical carbon dioxide equipment. The pressure in the material cavity of the supercritical carbon dioxide equipment is 7.4MPa or above, and the temperature in the material cavity of the supercritical carbon dioxide equipment is 32°C or above. The mixture becomes nano-level ultrafine powder under the impact of high-speed convection collision and the shear or stretching effect of high-speed flow.

[0008] The high-pressure homogenizer is operated in a high-pressure container at 7.4MPa or above, where liquid CO2 is mixed with pre-prepared nanomaterial powder to form a suspension, and then high-speed convection collision and crushing are performed.

[0009] The density of supercritical CO2 fluid is higher than that of liquid water, but its surface tension is low, its viscosity is close to that of gas, and its diffusion coefficient is 100 times that of conventional liquid.

[0010] The supercritical CO2 fluid is mixed with the pre-prepared nano-material powder in the form of a continuous phase. The supercritical CO2 can enter between the interlayers of the powder material, reduce the interaction force between the powder materials, and completely wrap the powder material.

[0011] By releasing the supercritical CO2 pressure and gasifying the supercritical CO2, dry nanomaterial powder can be obtained, which saves the energy consumption of evaporating the solvent and reduces the cost of nanomaterials.

[0012] The supercritical CO2 homogenizer of the present invention is operated in a high-pressure container of 7.4MPa (more than 74 atmospheres), and liquid CO2 is used instead of water to mix with the material into a suspension, and then high-speed convection collision and crushing are carried out; the present invention adds a supercritical fluid chamber and a metering pump to convert the corresponding gas into a supercritical fluid, and then pump it into the mixing chamber to mix with the material; the density of supercritical CO2 is higher than that of liquid water, but the surface tension is low, the viscosity is close to that of gas, and the diffusion coefficient is 100 times that of conventional liquids. It has stronger permeability and stronger dissolution and dispersion ability for powder materials. Supercritical CO2 liquid can be mixed with material powder in the form of a continuous phase. Supercritical CO2 can enter between the interlayers of the powder material, reduce the force between the powder materials, and completely wrap the powder material; the supercritical CO2 powder material mixed slurry achieves nano-level ultrafine crushing under the impact effect of high-speed convection collision and the shear or stretching effect of high-speed flow, thereby forming a homogeneous nano-dispersion; the crushed material does not need to remove a large amount of water, which reduces the pressure of the container, and Carbon dioxide is gasified to obtain dry nano powder materials, which can save 80%-90% of energy and reduce the cost of nano materials by 70%-80%; similar to the non-collision high-pressure homogenizer, when the crushing process is over, the valve of the pressure vessel is suddenly opened, and the supercritical CO2 will be quickly converted into gas and enter the interlayer gaps of the powder material, forming the CO2 intercalation structure of the powder material. The CO2 liquid will suddenly expand and further crush the powder material to obtain a smaller nano powder material, which is equivalent to the second non-collision high-pressure homogenizer. The supercritical fluid is only used to produce phase change and volume expansion, not for collision, so as to reduce the size of the material. Liquid medium; carbon dioxide is non-toxic and harmless, with stable chemical properties. At room temperature, it will not react with most substances. The powder materials for crushing and preparing nano materials can be biomass materials (wood powder, biochar powder), pharmaceutical materials, metal materials (gold, silver, copper, titanium, aluminum, iron powder, etc.), inorganic materials (carbon, silicon, aluminum oxide, zirconium oxide, other ceramic powders, etc.), other organic materials, etc.

[0013] The beneficial effects of the present invention are as follows: ① Compared with the existing method for preparing nanomaterials by a homogenizer, the present invention not only has a simpler structure, but also fully mixes the powder material and CO2 through convection, and has a more significant refining effect, which can reach the nanometer level, and the prepared nano powder material has a very high specific surface area; ② The present invention can simultaneously and continuously inhale and discharge the material, thereby improving production efficiency; ③ By releasing the supercritical CO2 pressure and gasifying the supercritical CO2, dry nano material powder is obtained, which greatly saves the energy consumption of evaporating the solvent and reduces the cost of the nano material; ④ Using supercritical CO2 as a dispersant, the preparation process is safe and environmentally friendly. DETAILED DESCRIPTION

[0014] The present invention is described in detail below in conjunction with embodiments: Example

[0015] The equipment pump chamber plunger is moved to increase the volume of the equipment pump chamber to form a low pressure. The pre-prepared biochar powder (50μm) and CO2 gas are sucked into the equipment pump chamber at a low speed of 2 meters per second. The plunger moves in the opposite direction, and the volume of the equipment pump chamber is reduced to form a high pressure. The equipment pump chamber pressure is adjusted and maintained at 7.4MPa and the temperature is 32°C. The carbon dioxide gas enters a supercritical state, so that the biochar powder material and supercritical CO2 are fully mixed. Then, the powder material is ejected from the equipment pump chamber at a high speed of 400 meters per second. A zigzag transitional flow channel is set at the nozzle of the equipment pump chamber to crush and mix the powder material evenly. The powder material passes through Two corresponding nozzles spray into the material chamber of the supercritical carbon dioxide equipment at high speed. The holding pressure of the material chamber of the supercritical carbon dioxide equipment is above 7.4MPa and the temperature is above 32°C. The powder material is ultra-finely crushed at the nanometer level under the impact of high-speed convection collision and the shear or stretching effect of high-speed flow. The powder material suspension after the collision can be re-entered into the crushing process of convection collision until the refinement goal is achieved. The pump chamber corresponding to another pair of plungers can be used to discharge the nanometer powder, so that the nanometer material can be continuously inhaled and discharged, thereby improving production efficiency. The particle size of the prepared nanometer biocarbon powder is 36-60 nanometers through testing. Example

[0016] The equipment pump chamber plunger is moved to increase the volume of the equipment pump chamber to form a low pressure. The pre-prepared micron-grade wood powder (15μm) and CO2 gas are sucked into the equipment pump chamber at a low speed of 2 meters per second. The plunger moves in the opposite direction, and the volume of the equipment pump chamber is reduced to form a high pressure. The equipment pump chamber pressure is adjusted and maintained at 10MPa and the temperature is 35 oC, carbon dioxide gas enters a supercritical state, so that the powder material and supercritical CO2 are fully mixed, and then the powder material is ejected out of the equipment pump chamber at a high speed of 400 meters per second. The nozzle of the equipment pump chamber is provided with a zigzag transition deflection channel to crush and mix the powder material evenly; the powder material is ejected into the material chamber of the supercritical carbon dioxide equipment at a high speed through two corresponding nozzles. The holding pressure of the material chamber of the supercritical carbon dioxide equipment is above 10MPa, and the temperature is above 35°C. The powder material is ultra-finely crushed at the nanometer level under the impact effect of high-speed convection collision and the shear or stretching effect of high-speed flow; the powder material suspension after collision can be re-entered into the crushing process of convection collision until the refinement target is achieved; the pump chamber corresponding to another pair of plungers can be used to discharge nano powders, so that the nano materials can be continuously inhaled and discharged, thereby improving production efficiency; the particle size of the prepared nano powder is 25-50 nanometers through detection. Example

[0017] The equipment pump chamber plunger is moved to increase the volume of the equipment pump chamber to form a low pressure. The pre-prepared copper powder (35μm) and CO2 gas are sucked into the equipment pump chamber at a low speed of 2 meters per second. The plunger moves in the opposite direction, and the volume of the equipment pump chamber is reduced to form a high pressure. The equipment pump chamber pressure is adjusted and maintained at 20MPa and the temperature is 40°C. The carbon dioxide gas enters a supercritical state to fully mix the copper powder material and supercritical CO2. Then, the powder material is ejected from the equipment pump chamber at a high speed of 400 meters per second. A zigzag transition deflector is set at the nozzle of the equipment pump chamber to crush and mix the powder material evenly. The powder material passes through two The corresponding nozzle sprays into the material cavity of the supercritical carbon dioxide equipment at a high speed. The holding pressure of the material cavity of the supercritical carbon dioxide equipment is above 20MPa and the temperature is above 40°C. The powder material is ultra-finely crushed at the nanometer level under the impact effect of high-speed convection collision and the shear or stretching effect of high-speed flow. The powder material suspension after the collision can be re-entered into the crushing process of convection collision until the refinement goal is achieved. The pump cavity corresponding to another pair of plungers can be used to discharge the nanometer powder, so that the nanometer material can be continuously inhaled and discharged, thereby improving production efficiency. The particle size of the prepared nanometer powder is 12-20 nanometers through testing.

Claims

1. A method for preparing nanomaterials by high pressure convection method using supercritical carbon dioxide as a medium, which is based on a high pressure homogenizer and is characterized in that: Supercritical CO2 fluid is used as the working medium, and the pre-prepared nanomaterial forms a suspension in the supercritical CO2 fluid. Above the critical pressure and temperature of the supercritical carbon dioxide fluid, that is, the pressure is above 7.4MPa and the temperature is above 32°C, it flows through the high-pressure homogenization cavity at a high speed in a collision or counter-injection manner to prepare nanopowders.

2. The method for preparing nanomaterials by high pressure convection method using supercritical carbon dioxide as a medium according to claim 1, characterized by the following steps: The first step is to suck the pre-prepared nanomaterial micron-sized powder and CO2 gas into the pump chamber of the high-pressure homogenizer at a speed of 2 meters per second or more; The second step is to move the plunger in the pump chamber of the equipment in the opposite direction to reduce the volume of the pump chamber of the equipment to form high pressure, so that the pressure in the pump chamber of the equipment is maintained at 7.4-20MPa, and the temperature in the pump chamber of the equipment is maintained at 32-40℃, and the carbon dioxide in the pump chamber of the equipment enters and is in a supercritical liquid state; The third step is that after the micron-sized powder of the prepared nanomaterial in the pump cavity of the equipment is fully mixed with the supercritical CO2, the mixture is ejected out of the pump cavity of the equipment at a speed of at least 400 meters per second and enters the material cavity of the supercritical carbon dioxide equipment. The pressure in the material cavity of the supercritical carbon dioxide equipment is 7.4MPa or above, and the temperature in the material cavity of the supercritical carbon dioxide equipment is 32°C or above. The mixture becomes nano-level ultrafine powder under the impact of high-speed convection collision and the shear or stretching effect of high-speed flow.

3. The method for preparing nanomaterials by high pressure convection method using supercritical carbon dioxide as a medium according to claim 2, characterized in that: The high-pressure homogenizer is operated in a high-pressure container at 7.4MPa or above, where liquid CO2 is mixed with pre-prepared nanomaterial powder to form a suspension, and then high-speed convection collision and crushing are performed.

4. A method for preparing nanomaterials by high pressure convection method using supercritical carbon dioxide as a medium according to claim 1, 2 or 3, characterized in that: The density of supercritical CO2 fluid is higher than that of liquid water, but its surface tension is low, its viscosity is close to that of gas, and its diffusion coefficient is 100 times that of conventional liquid.

5. A method for preparing nanomaterials by high pressure convection method using supercritical carbon dioxide as a medium according to claim 1, 2 or 3, characterized in that: The supercritical CO2 fluid is mixed with the pre-prepared nano-material powder in the form of a continuous phase. The supercritical CO2 can enter between the interlayers of the powder material, reduce the interaction force between the powder materials, and completely wrap the powder material.

6. A method for preparing nanomaterials by high pressure convection method using supercritical carbon dioxide as a medium according to claim 1, 2 or 3, characterized in that: By releasing the supercritical CO2 pressure and gasifying the supercritical CO2, dry nanomaterial powder can be obtained, which saves the energy consumption of evaporating the solvent and reduces the cost of nanomaterials.