Method for preparing nitrogen supercritical dispersion catalyst

Abstract

The invention discloses a method for preparing a nitrogen supercritical dispersion catalyst. The method comprises the following steps: S1, preparing a catalyst solution; s2, high-purity nitrogen is introduced into the reaction kettle, replacement is conducted 2-5 times, and the oxygen content < lt > is ensured; 5 ppm; s3, heating the reaction kettle to 200-250 DEG C, pressurizing to 10-15 MPa, and continuously introducing supercritical nitrogen to form a supercritical nitrogen environment; s4, the catalyst solution is injected into a net type nozzle through a high-pressure plunger pump for primary atomization, and micron-sized primary liquid drops are produced; and S5, spraying the primary liquid drops into the supercritical nitrogen environment of the reaction kettle for secondary atomization, carrying out explosive refining on the primary liquid drops by virtue of ultrasonic cooperation and an ultrasonic cavitation effect, and instantaneously extracting a solvent in the catalyst solution by virtue of supercritical nitrogen, so as to generate solid catalyst nanoparticles. According to the method for supercritical dispersion of the catalyst through nitrogen, agglomeration inhibition in the supercritical nitrogen environment and two-stage atomization are adopted to achieve nanocrystallization of the catalyst, the traditional catalyst dispersion bottleneck is broken through, and a solid foundation is provided for controllable preparation of high-performance SWCNT.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst dispersion, and particularly relates to a method for supercritical nitrogen dispersion of a catalyst. Background Art

[0002] Single-walled carbon nanotubes (SWCNTs) are seamless hollow cylinders formed by curling a single layer of graphene. Their carbon atoms are bonded by sp2 hybrid bonds, forming a nanomaterial with a unique electronic structure. They possess numerous excellent physical and chemical properties and show great potential for application in numerous fields, including: (1) Electrical properties: It has excellent electrical conductivity, which is superior to materials such as graphene and carbon black. Due to its one-dimensional structure, it can form a three-dimensional conductive network at a very low addition amount. For example, in lithium batteries, as a conductive agent, it can significantly improve the conductivity and cycle stability of the battery. In particular, in silicon negative electrode materials, it can alleviate the volume change of the silicon-based negative electrode during the charge and discharge process, thereby improving the cycle life of the battery.

[0003] (2) Thermal properties: It has extremely high thermal conductivity, which is twice that of diamond at room temperature. Its axial thermal conductivity is better than its radial one. It can synthesize anisotropic thermal conductive materials and can be used in the field of thermal management materials.

[0004] (3) Mechanical properties: It has extremely high elasticity and toughness, with a Young's modulus nearly 6 times that of steel and a tensile strength 100 times that of steel. Its strong carbon-carbon bond enables it to withstand greater mechanical stress. In the field of high-performance composite fibers, adding single-walled carbon nanotubes to fiber materials can significantly enhance the mechanical properties, thermal conductivity, and electrical conductivity of the fibers. For example, in the aerospace field, it can be used to manufacture aircraft structural components, reduce the weight of aircraft, and improve flight performance.

[0005] (4) Chemical stability: It has good chemical stability, acid resistance and alkali resistance. Adding single-walled carbon nanotubes to polymer composite materials can improve the acid and oxidation resistance of the material.

[0006] Catalysts play a key role in the preparation of single-walled carbon nanotubes. However, traditional catalysts have many problems that limit the preparation of high-quality single-walled carbon nanotubes. Specifically: (1) Difficulty in catalyst dispersion: Strong van der Waals forces exist between traditional catalyst particles, which causes the particles to aggregate with each other, making it difficult to achieve uniform dispersion. For example, in some traditional catalyst preparation processes, catalyst particles tend to agglomerate into larger particles, resulting in the inability to fully exert the catalytic effect during the reaction, affecting the growth quality and efficiency of single-walled carbon nanotubes.

[0007] (2) Large catalyst particle size: The particle size of traditional catalysts is usually in the tens or hundreds of nanometers. The finer the catalyst particle size, the smaller the diameter and wall thickness of the prepared carbon nanotubes will be, and the easier it will be to form carbon nanotubes with a large aspect ratio. Single-walled carbon nanotubes with a large aspect ratio have better performance and wider application prospects in many fields, but the large particle size of traditional catalysts cannot meet this demand.

[0008] (3) Limitations of pressurized airflow transport: The previous method of using pressurized airflow to transport catalysts may not achieve uniform dispersion and efficient transport of the catalyst. During the airflow transport process, the catalyst may deposit and agglomerate in the pipeline, resulting in uneven distribution of the catalyst entering the reaction system, affecting the growth quality and consistency of single-walled carbon nanotubes.

[0009] In summary, it is particularly urgent to develop a new technology that can effectively solve the catalyst dispersion problem, reduce the catalyst particle size, and improve the preparation process efficiency and product quality. The method of supercritical nitrogen dispersion catalyst of the present invention came into being in this context. Summary of the Invention

[0010] Purpose of the invention: In order to overcome the above shortcomings, the purpose of the present invention is to provide a method for supercritical nitrogen dispersion of catalysts. Through the synergistic effect of supercritical nitrogen environment and two-stage atomization, the van der Waals force constraints are broken at the molecular scale, the catalyst is monodispersed and nanosized, and the underlying support is provided for the controllable growth of high-quality SWCNTs.

[0011] The purpose of the present invention is achieved through the following technical solutions: A method for supercritical nitrogen dispersion of a catalyst comprises the following steps: S1: dissolving the catalyst in a solvent to prepare a catalyst solution; S2: Introduce high-purity nitrogen into the reactor and replace it 2 to 5 times to ensure that the oxygen content is <5 ppm; S3: The reactor is heated to 200-250°C and pressurized to 10-15 MPa, and supercritical nitrogen is continuously introduced to form a supercritical nitrogen environment; S4: The catalyst solution is first injected into the mesh nozzle through a high-pressure plunger pump for primary atomization to produce micron-sized primary droplets; S5: The primary droplets are then sprayed into the supercritical nitrogen environment of the reactor for secondary atomization. At the same time, ultrasound synergizes and the ultrasonic cavitation effect causes the primary droplets to be explosively refined. The supercritical nitrogen instantly extracts the solvent in the catalyst solution to generate solid catalyst nanoparticles.

[0012] The method of supercritical nitrogen dispersion catalyst described in the present invention solves the problem of difficulty in dispersing traditional catalysts through the synergistic effect of secondary atomization and supercritical nitrogen. The secondary atomization technology breaks the aggregation tendency caused by van der Waals forces between particles, and significantly improves the dispersion uniformity of the catalyst. In the preparation of traditional catalysts, particles tend to agglomerate into large particles, affecting the catalytic effect, while this method can make the catalyst evenly distributed in the reaction system, ensuring that the reaction is more sufficient and stable. The catalyst particle size is reduced from the micron level of traditional processes to the submicron level. The smaller particle size means that the catalyst has a larger specific surface area and can provide more active sites, thereby improving the efficiency of the catalytic reaction.

[0013] Furthermore, the catalyst dispersed using this method provides excellent catalytic conditions for the controlled growth of single-walled carbon nanotubes (SWCNTs), breaking through the bottleneck of traditional catalyst preparation technology and achieving the controlled growth of single, high-aspect-ratio SWCNTs. While traditional preparation methods struggle to precisely control the growth morphology and aspect ratio of SWCNTs, this method, by optimizing catalyst dispersion and particle size, allows for precise control of the carbon nanotube growth process.

[0014] Furthermore, in the above-mentioned method of supercritical nitrogen dispersion catalyst, in S2, the purity of the high-purity nitrogen is 99.999%.

[0015] High-purity nitrogen effectively displaces other gases within the reactor, ensuring an oxygen content of <5 ppm and providing a pure supercritical nitrogen environment for catalyst preparation. Using 99.999% pure nitrogen minimizes this interference and ensures the stability and reliability of catalyst preparation.

[0016] Furthermore, in the above-mentioned method of supercritical nitrogen dispersion of catalyst, in S3, the flow rate of the supercritical nitrogen is 5-10 L / min.

[0017] An appropriate flow rate ensures a stable supercritical nitrogen environment is continuously formed in the reactor. If the flow rate is too fast, it may cause excessive pressure fluctuations in the reactor, affecting catalyst preparation; if the flow rate is too slow, an effective supercritical environment may not be formed in time, reducing catalyst preparation efficiency.

[0018] Furthermore, in the above-mentioned method of supercritical nitrogen dispersion of catalyst, in said S4, the pressure of the high-pressure plunger pump is 10-30 MPa, and the aperture of the mesh nozzle is 1-20 μm.

[0019] Preferably, the pressure of the high-pressure plunger pump is 20 MPa, and the aperture of the mesh nozzle is 10 μm. The pressure provided by the high-pressure plunger pump smoothly injects the catalyst solution into the mesh nozzle, initially atomizing it into micron-sized droplets. Appropriate pressure ensures that the droplet size and distribution meet the requirements of subsequent secondary atomization. The mesh nozzle's aperture determines the size and quality of the primary droplets. A suitable aperture disperses the catalyst solution into micron-sized droplets of appropriate size, providing an excellent foundation for subsequent ultrasonic secondary atomization, allowing the droplets to be further refined under the action of ultrasound.

[0020] Furthermore, in the above-mentioned method of supercritical nitrogen dispersion of catalyst, in S5, the frequency of ultrasound is 10-30 kHz, and the power density is 50-200 W / cm².

[0021] Preferably, the frequency of ultrasound is 20 kHz and the power density is 100 W / cm².

[0022] Appropriate ultrasonic frequency and power density can fully leverage the acoustic cavitation effect, creating a localized high-temperature and high-pressure environment in the liquid, explosively refining micron-sized droplets. Catalyst particles refined through secondary atomization possess a larger specific surface area and improved dispersion, providing more active sites and thus improving the efficiency of the catalytic reaction. Furthermore, uniform dispersion ensures even distribution of the catalyst throughout the reaction system, resulting in a more complete and stable reaction.

[0023] Furthermore, in the above-mentioned method of supercritical nitrogen dispersion of catalyst, the particle size of the micron-sized droplets produced by the primary atomization is 10-50 μm, and the ultrasonic cavitation effect causes the droplets to be explosively refined to a particle size of 200-500 nm.

[0024] Furthermore, in the above-mentioned method of supercritical nitrogen dispersion of the catalyst, the reactor is an ASME-certified explosion-proof reactor with a design pressure of ≥30 MPa.

[0025] Catalyst preparation under a supercritical nitrogen atmosphere involves high pressures and temperatures within the reactor, posing certain safety risks. ASME-certified explosion-proof reactors offer excellent explosion-proof performance and a high design pressure, capable of withstanding the pressure and impact forces generated during the reaction, ensuring a safe and reliable production process. A design pressure of ≥30 MPa meets the pressure requirements of the reactor during heating and pressurization, ensuring a stable reaction pressure environment, which is beneficial for catalyst preparation and performance stability.

[0026] Furthermore, after the above-mentioned method of supercritical nitrogen dispersion of the catalyst is completed, the reactor needs to be depressurized step by step to normal pressure before being opened, and the depressurization rate is ≤1 MPa / min.

[0027] Gradual pressure relief and controlled pressure relief rate can avoid damage to equipment caused by sudden pressure changes in the reactor, and can also prevent harm to operators caused by the shock caused by sudden pressure drop.

[0028] Compared with the prior art, the present invention has the following beneficial effects: The method for supercritical nitrogen catalyst dispersion disclosed in the present invention is rationally designed. Through the synergistic effect of a supercritical nitrogen environment and two-stage atomization, molecular-level dispersion can be achieved, breaking the aggregation trend between catalyst particles caused by van der Waals forces. A mesh nozzle preliminarily atomizes the catalyst solution into micron-sized droplets, providing a basis for subsequent secondary atomization. Ultrasonic waves utilize the acoustic cavitation effect to generate a local high-temperature and high-pressure environment, further refining the micron-sized droplets. A smaller particle size means that the catalyst has a larger specific surface area, which can provide more active sites, thereby improving the efficiency of the catalytic reaction and providing support for the controllable growth of high-quality SWCNTs. The method has broad application prospects. DETAILED DESCRIPTION

[0029] The following examples 1 and 2 are combined with specific experimental data to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The following Example 1 provides a method for supercritical dispersion of a catalyst using nitrogen.

[0030] Example 1 The method for supercritical nitrogen dispersion of a catalyst in Example 1 comprises the following steps: S1: dissolving the catalyst in a solvent to prepare a catalyst solution; S2: Introduce high-purity nitrogen (99.999%) into the reactor (ASME-certified explosion-proof reactor, design pressure ≥30 MPa) and replace it three times to ensure that the oxygen content is <5 ppm; S3: The reactor is heated to 200-250°C and pressurized to 10-15 MPa (to maintain a supercritical nitrogen state). Supercritical nitrogen is continuously introduced at a flow rate of 5-10 L / min to form a supercritical nitrogen environment. S4: The catalyst solution is first injected into a mesh nozzle (aperture size 10 μm) via a high-pressure plunger pump (pressure 20 MPa) for primary atomization to produce micron-sized primary droplets (10-50 μm); S5: The primary droplets are then sprayed into the supercritical nitrogen environment of the reactor for secondary atomization and immediately enter an ultrasonic field (frequency 20 kHz, power density 100 W / cm²). The ultrasonic cavitation effect causes the primary droplets to explosively refine to 200-500 nm. The supercritical nitrogen gas instantly extracts the solvent from the catalyst solution, generating solid catalyst nanoparticles.

[0031] As shown in Table 1, compared with the traditional air flow conveying method, this embodiment 1 has the following advantages: Table 1 index This embodiment 1 Traditional air flow conveying method Average catalyst particle size 200~500 nm 1~5μm Pipe diameter distribution 0.8~1.2 nm (narrow distribution) 1~2 nm (broad distribution) Energy consumption Reduce by 20~30% Baseline value The following Example 2 provides a process for preparing single-walled carbon nanotubes using a nitrogen supercritical dispersed catalyst.

[0032] Example 2 The process for preparing single-walled carbon nanotubes using a nitrogen supercritical dispersed catalyst in Example 1 comprises the following steps: S1: Dissolve a metal salt (e.g., Fe(NO3)3 or CoMoO4) in an ethanol / water mixture (volume ratio 4:1) to control the metal ion concentration to 0.05–0.2 mol / L. Add a sulfur-containing compound (e.g., thiophene) to the solution at a concentration of 50–200 ppm. Stir magnetically for 30 minutes, mix thoroughly, and filter through a 0.22 μm filter membrane to prepare a precursor solution. S2: Introduce high-purity nitrogen (99.999%) into the reactor (ASME-certified explosion-proof reactor, design pressure ≥30 MPa) and replace it three times to ensure that the oxygen content is <5 ppm; S3: The reactor is heated to 200-250°C and pressurized to 10-15 MPa (to maintain a supercritical nitrogen state). Supercritical nitrogen is continuously introduced at a flow rate of 5-10 L / min to form a supercritical nitrogen environment. S4: The catalyst solution is first injected into a mesh nozzle (aperture size 10 μm) via a high-pressure plunger pump (pressure 20 MPa) for primary atomization to produce micron-sized primary droplets (10-50 μm); S5: The primary droplets are then sprayed into the supercritical nitrogen environment of the reactor for secondary atomization. Immediately, they enter an ultrasonic field (frequency 20 kHz, power density 100 W / cm²). The ultrasonic cavitation effect explosively refines the primary droplets to 200-500 nm. The supercritical nitrogen gas instantly extracts the solvent from the catalyst solution, generating solid catalyst nanoparticles. S6: A mixture of solid catalyst nanoparticles and supercritical nitrogen is introduced into the CVD reaction zone at a temperature of 800-900°C. A carbon source gas (e.g., CH4 / CO) is simultaneously introduced at a flow rate of 100-200 sccm for a growth time of 10-30 min to produce SWCNTs with a large aspect ratio (length > 10 μm). S7: The reaction exhaust gas passes through a high-temperature ceramic filter membrane (pore size 0.1 μm) to intercept the SWCNT product; S8: The SWCNT product was immersed in a 3 M HNO3 solution and refluxed at 85°C for 2 h; centrifuged, then washed with deionized water several times until neutral, and vacuum dried at 60°C for 12 h to obtain SWCNT with a purity of >90%.

[0033] In summary, the present invention provides a method for supercritical nitrogen dispersion of catalysts, which achieves catalyst nano-sizing through suppression of agglomeration in a supercritical nitrogen environment and double-stage atomization, breaking through the difficulty of traditional catalyst dispersion and providing a standardized process for the controllable preparation of high-performance SWCNTs.

[0034] The present invention has many specific application paths, and the above is only a preferred embodiment of the present invention. It should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, several improvements can be made without departing from the principles of the present invention, and these improvements should also be considered as the scope of protection of the present invention.

Claims

1. A method for supercritical nitrogen dispersion of a catalyst, characterized in that: The steps include: S1: dissolving the catalyst in a solvent to prepare a catalyst solution; S2: Introduce high-purity nitrogen into the reactor and replace it 2 to 5 times to ensure that the oxygen content is < 5 ppm; S3: The reactor is heated to 200-250°C, pressurized to 10-15 MPa, and supercritical nitrogen is continuously introduced to form a supercritical nitrogen environment; S4: The catalyst solution is first injected into the mesh nozzle through a high-pressure plunger pump for primary atomization to produce micron-sized primary droplets; S5: The primary droplets are then sprayed into the supercritical nitrogen environment of the reactor for secondary atomization. At the same time, ultrasound synergizes and the ultrasonic cavitation effect causes the primary droplets to be explosively refined. The supercritical nitrogen instantly extracts the solvent in the catalyst solution to generate solid catalyst nanoparticles.

2. The method for supercritical nitrogen dispersion catalyst according to claim 1, characterized in that: In the S2, the purity of the high-purity nitrogen is 99.999%.

3. The method for supercritical nitrogen dispersion catalyst according to claim 1, characterized in that: In S3, the flow rate of supercritical nitrogen is 5-10 L / min.

4. The method for supercritical nitrogen dispersion catalyst according to claim 1, characterized in that: In the above-mentioned S4, the pressure of the high-pressure plunger pump is 10-30 MPa, and the aperture of the mesh nozzle is 1-20 μm.

5. The method for supercritical nitrogen dispersion catalyst according to claim 1, characterized in that: In the S5, the frequency of ultrasound is 10-30 kHz, and the power density is 50-200 W / cm².

6. The method for supercritical nitrogen dispersion catalyst according to claim 1, characterized in that: The micron-sized droplets produced by the primary atomization have a particle size of 10-50 μm, and the ultrasonic cavitation effect causes the droplets to be explosively refined to a particle size of 200-500 nm.

7. The method for supercritical nitrogen dispersion catalyst according to claim 1, characterized in that: The reactor is an ASME-certified explosion-proof reactor with a design pressure ≥ 30 MPa.

8. The method for supercritical nitrogen dispersion catalyst according to claim 1, characterized in that: After completion, the reactor must be depressurized step by step to normal pressure before it can be opened, and the depressurization rate should be ≤1 MPa / min.