Method for large-scale preparation of polyimide-based porous carbon spheres by using liquid nitrogen rotary freezing method
The preparation of polyimide-based porous carbon spheres by liquid nitrogen rotary freezing solves the problems of high cost and environmental burden of existing porous carbon sphere preparation methods, and realizes low-cost and environmentally friendly preparation of porous carbon spheres with good pore structure and high specific surface area, which is suitable for large-scale production.
Patent Information
- Application Number
- CN202511032164.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-25
- Publication Date
- 2025-11-21
AI Technical Summary
Existing methods for preparing porous carbon spheres suffer from problems such as cumbersome processes, high costs, heavy environmental burden, difficulty in achieving large-scale stable preparation, and difficulty in precisely controlling the hierarchical pore structure.
A liquid nitrogen rotary freezing method was adopted, in which droplets were rotated and shaped in liquid nitrogen and then frozen to form spherical particles. Polyimide-based porous carbon spheres were prepared by combining freeze drying and stepwise carbonization. Polyimide acid, triethylamine and biomass starch were used as raw materials. The process conditions were controlled to achieve the large-scale preparation of spherical porous carbon spheres.
A low-cost, low-energy-consumption, and environmentally friendly method for preparing porous carbon spheres has been achieved. These spheres have a high sphericity, a good three-dimensional cross-linked pore structure, and a large specific surface area, making them suitable for large-scale production.
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Figure CN120987296A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of porous carbon material preparation technology, and in particular to a spherical porous carbon and its large-scale preparation method and application. Technical Background
[0002] Traditional carbon materials (such as activated carbon and graphite) mostly have disordered or single-pore structures, making it difficult to meet the precise control requirements for mass transport, active site exposure, and interfacial interactions in complex scenarios. Porous carbon spheres, however, can achieve multiple functional integrations of "rapid mass transfer, efficient adsorption, and electron transport" through the synergistic effect of hierarchical pores. Due to their high specific surface area, tunable pore structure (micropore-mesopore-macropore hierarchy), excellent electrical conductivity, and chemical stability, porous carbon materials have shown significant application potential in energy storage and conversion, catalysis, environmental remediation, and biomedicine in recent years, becoming one of the research hotspots in materials science and chemistry. Among them, porous carbon spheres, as a type of porous carbon material with a regular spherical morphology, exhibit unique potential in supercapacitors, lithium-ion batteries, catalyst supports, and thermal energy storage due to their highly uniform particle size distribution, controllable three-dimensional network structure, and surface active sites. Compared to traditional amorphous or bulk carbon materials, the spherical structure of porous carbon spheres gives them better fluidity (facilitating uniform filling), lower interfacial impedance (promoting charge transport), and higher structural stability (resisting volume changes during cycling). In recent years, they have become an important branch of porous carbon material research.
[0003] Compared to other forms of porous carbon materials, such as powders, bulk materials, or porous carbon fibers, porous carbon spheres offer numerous advantages. ① Structural controllability and functionality: By adjusting synthesis conditions (such as template type, carbon source type, and reaction temperature), porous carbon spheres with controllable specific surface area, pore volume, and pore size distribution can be designed and prepared to meet the needs of mass transfer, adsorption, or ion intercalation in different scenarios; ② Mass transfer and kinetic optimization: The absence of sharp edges in spherical particles reduces frictional resistance between particles, making it easier to form a uniform and dense porous medium during filling, significantly improving the diffusion efficiency of substances within the material; simultaneously, the hierarchical pore structure (micropores provide high specific surface area, while mesopores / macropores construct rapid transport channels) can synergistically optimize transport kinetics; ③ Engineering adaptability: The spherical morphology endows the material with excellent flowability and mechanical stability, facilitating large-scale processing and reducing agglomeration, making it suitable for a wider range of applications.
[0004] Despite significant progress in the research of porous carbon spheres and the development of several relatively mature preparation methods, each method has its drawbacks. Template methods are currently the most commonly used for porous carbon sphere preparation, including hard template methods and soft template methods. However, the preparation process involves numerous operations such as template synthesis, precursor impregnation, high-temperature carbonization, and template removal, making it cumbersome, costly, and environmentally burdensome, and difficult to achieve large-scale stable preparation. Hydrothermal / solvothermal methods directly generate porous carbon spheres through the hydrolysis, condensation, and carbonization of precursors under high temperature and pressure conditions. The process is relatively simple but energy-intensive (typically requiring 180-300℃). Large-scale scaling presents challenges in temperature / pressure control and safety risks. Chemical vapor deposition (CVD) uses carbon-containing gases as precursors, achieving carbon deposition through catalytic cracking on the catalyst surface, and can prepare high-purity, low-defect porous carbon spheres. However, this method requires noble metal or metal oxide catalysts, and the precursors are mostly volatile organic compounds, posing problems of high toxicity and significant pollution; simultaneously, the equipment investment and operating costs are high, making it difficult to meet the needs of low-cost industrial-scale preparation. Self-assembly, driven by non-covalent intermolecular interactions, allows carbon precursors to assemble into spheres, theoretically enabling green and mild preparation under suitable conditions. However, this method places extremely high demands on the molecular design of the raw materials, and the self-assembly process is significantly affected by kinetic factors such as solvent polarity and stirring rate, easily leading to a wide porosity distribution and limited specific surface area in the product. Furthermore, some self-assembled carbon spheres lack sufficient mechanical strength and are prone to pulverization failure in practical applications. In summary, developing a simple, low-cost, environmentally friendly method for preparing porous carbon spheres with precisely controllable hierarchical pore structures remains a key scientific and technological challenge that urgently needs to be addressed in this field. Summary of the Invention
[0005] Purpose of the invention: In view of the above-mentioned shortcomings of the existing technology, the purpose of the present invention is to provide a method for large-scale preparation of polyimide-based porous carbon spheres using liquid nitrogen rotary freezing, which can produce spherical porous carbon materials with well-developed pores and high specific surface area.
[0006] Technical Solution: The present invention discloses a method for large-scale preparation of polyimide-based porous carbon spheres using liquid nitrogen rotary freezing. This method requires only three key and simple steps: liquid nitrogen rotary freezing, freeze-drying, and stepwise carbonization. The liquid nitrogen rotary freezing method involves dropping droplets into liquid nitrogen at room temperature. Upon contact with the liquid nitrogen, the temperature difference causes the nitrogen to rapidly evaporate. The resulting nitrogen gas suspends the droplets on the surface of the liquid nitrogen, causing them to rotate, shape, and freeze into spherical particles.
[0007] Includes the following steps:
[0008] (1) Mix polyimide powder with water and stir, then add triethylamine dropwise and stir until dissolved to obtain an aqueous solution of polyimide salt.
[0009] (2) Add biomass starch slowly in portions to the polyimide aqueous solution, stir until completely hydrated and dissolved, let stand to remove bubbles, and obtain a viscous precursor aqueous solution.
[0010] (3) The precursor aqueous solution is slowly dripped into liquid nitrogen, and the droplets are rotated and shaped on the surface of liquid nitrogen and then frozen to form spherical particles;
[0011] (4) Vacuum freeze-dry the spherical particles to obtain a polyimide-based porous carbon sphere precursor;
[0012] (5) The polyimide-based porous carbon sphere precursor is subjected to polyimide amidation at a lower temperature and then carbonized at a high temperature to obtain polyimide-based porous carbon spheres.
[0013] Further, in step (1), the mass ratio of polyimide acid to triethylamine is 1:(0.4-0.8); the concentration of polyimide acid in the polyimide aqueous solution is 4-8 wt%, the stirring speed is 300-600 rpm, and the stirring time is 10-15 h. In step (2), the biomass starch is one or more of chitosan, xanthan gum, and guar gum. The mass ratio of polyimide aqueous solution to biomass starch is 100:(0.8-2.0); the stirring speed is 600-1000 rpm, the stirring time is 12-20 h, and the mixture is allowed to stand for 6-10 h to remove bubbles. In step (3), the precursor aqueous solution is slowly dripped into liquid nitrogen using a syringe. The syringe needle is a stainless steel flat-tipped needle, model 16-23G, with an inner diameter of 0.36-1.2 mm. The size of the extruded droplets can be adjusted by controlling the inner diameter of the needle, thereby controlling the diameter of the polyimide-based porous carbon spheres. The dripping speed is such that the droplet drop interval is >1s. In step (4), the vacuum freeze-drying temperature is below -10℃, and the vacuum freeze-drying time is 2-3 days. In step (5), the atmosphere for polyimide amidation and carbonization is an inert gas atmosphere, and the inert gas is argon or nitrogen. Polyimide amidation is carried out by heating to 200-400℃ at 3-6℃ / min and holding for more than 3 hours; carbonization is carried out by heating to 500-700℃ at 2-5℃ / min and holding for more than 3 hours.
[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention uses only polyimide acid, triethylamine, biomass starch and water as raw materials, and prepares spherical polyimide-based porous carbon sphere precursor particles by liquid nitrogen rotary freezing method, and then freeze-drying and stepwise carbonization to obtain polyimide-based porous carbon spheres. The overall process is simple, the raw material cost is low, and it is low-carbon, environmentally friendly and pollution-free, which greatly reduces the preparation cost. (2) The polyimide-based porous carbon spheres prepared by the present invention have controllable particle size, high sphericity, sphericity rate of more than 90%, and good three-dimensional cross-linked pore structure and large specific surface area. The preparation method is simple to operate, low in energy consumption, and can be prepared on a large scale. Moreover, it has significant advantages in resource utilization and environmental protection, which is in line with the concept of sustainable development. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the preparation process of the polyimide-based porous carbon spheres of the present invention;
[0016] Figure 2 An optical photograph of the polyimide-based porous carbon spheres prepared in Example 1;
[0017] Figure 3 This is a SEM image of the overall appearance of the polyimide-based porous carbon spheres prepared in Example 1;
[0018] Figure 4 This is a SEM image of the internal cross-section of the polyimide-based porous carbon spheres prepared in Example 1;
[0019] Figure 5 The nitrogen adsorption-desorption isotherm and pore size distribution diagram of the polyimide-based porous carbon spheres prepared in Example 1 are shown.
[0020] Figure 6 This is a SEM image of the overall appearance of the polyimide-based porous carbon spheres prepared in Example 2;
[0021] Figure 7 This is a SEM image of the overall appearance of the polyimide-based porous carbon spheres prepared in Example 3;
[0022] Figure 8 This is a SEM image of the overall appearance of the polyimide-based porous carbon spheres prepared in Example 4. Detailed Implementation
[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings.
[0024] Example 1
[0025] (1) Mix polyimide powder and water at a mass ratio of 5:95, and then add triethylamine dropwise at a mass ratio of 1:0.52 to polyimide powder. Stir with magnetic stirring at a speed of 500 rpm for 12 hours to obtain a 5% wt polyimide salt aqueous solution.
[0026] (2) According to the mass ratio of polyimide aqueous solution and guar gum of 100:1, guar gum powder was slowly added to the polyimide aqueous solution in portions. The mixture was stirred at 800 rpm for 15 hours to completely hydrate and dissolve the mixture. After standing at room temperature for 8 hours to remove bubbles, a viscous precursor aqueous solution was obtained.
[0027] (3) Use a 30mL syringe to draw an appropriate amount of precursor aqueous solution, and use a precision injection pump to control the precursor aqueous solution to drip evenly into a thermostatic container containing liquid nitrogen at a falling speed of one drop per second through a stainless steel flat-head needle (0.5mm inner diameter) of model 21G. The droplets rotate on the surface of the liquid nitrogen to form spherical particles.
[0028] (4) The spherical particle product was then separated and placed at -10℃ for vacuum freeze-drying for 2 days to obtain polyimide-based porous carbon sphere precursor.
[0029] (5) The polyimide-based porous carbon sphere precursor was placed in a tube furnace at room temperature and heated to 300°C at a rate of 5°C / min under a N2 atmosphere, and held for 3 hours to complete the amidation of the polyimide. Then, the temperature was increased to 600°C at a rate of 5°C / min and held for 3 hours to complete the carbonization of the particles, finally obtaining polyimide-based porous carbon spheres. The preparation process is as follows: Figure 1 As shown, the optical photographs of the obtained polyimide-based porous carbon spheres are as follows: Figure 2 As shown.
[0030] The polyimide-based porous carbon spheres prepared in Example 1 were characterized using scanning electron microscopy, and the results are as follows: Figures 3-4 As shown. By Figure 3 As can be seen, the polyimide-based porous carbon spheres extruded using a 21G stainless steel flat-tipped needle in Example 1 have a standard spherical structure and a particle size of approximately 1.5 mm. Figure 4 Thus, the polyimide-based porous carbon spheres extruded using a stainless steel flat-head needle of model 21G in Example 1 have a three-dimensional cross-linked porous structure in their internal cross-section.
[0031] The specific surface area and pore size distribution of the polyimide-based porous carbon spheres prepared in Example 1 were tested, and the test results are as follows: Figure 5 As shown, the BET specific surface area of the prepared polyimide-based porous carbon spheres is 447.9 m². 2 ·g -1
[0032] Example 2
[0033] The experimental procedure was the same as in Example 1, except that a 19G stainless steel flat-head needle (0.5mm inner diameter) was used instead of a 21G stainless steel flat-head needle (0.67mm inner diameter), while other conditions remained unchanged. Finally, polyimide-based porous carbon spheres were obtained.
[0034] The polyimide-based porous carbon spheres prepared in Example 2 were characterized using scanning electron microscopy, and the results are as follows: Figure 6 As shown. By Figure 6 It can be seen that the polyimide-based porous carbon spheres extruded using a 19G stainless steel flat-tipped needle in Example 2 have a standard spherical structure and a particle size of approximately 1.9 mm. This demonstrates that the size of the droplets can be controlled by adjusting the inner diameter of the stainless steel flat-tipped needle, thereby regulating the particle size of the polyimide-based porous carbon spheres. Further experiments showed that by controlling the inner diameter of the stainless steel flat-tipped needle from 0.36 to 1.2 mm, the particle size of the polyimide-based porous carbon spheres can be controlled from 1.0 to 2.5 mm. Within this particle size range, the spherical structure is standard, and the internal structure exhibits a three-dimensional cross-linked porous structure.
[0035] Example 3
[0036] The experimental procedure was the same as in Example 1, except that chitosan was used to replace guar gum, while other conditions remained unchanged, and polyimide-based porous carbon spheres were finally obtained.
[0037] The polyimide-based porous carbon spheres prepared in Example 3 were characterized using scanning electron microscopy, and the results are as follows: Figure 7 As shown. By Figure 7 It can be seen that replacing guar gum with biomass starch chitosan does not affect the spherical structure of the prepared polyimide-based porous carbon spheres.
[0038] Example 4
[0039] The experimental procedure was the same as in Example 1, except that the mass ratio of polyimide acid aqueous solution to guar gum was increased to 100:2, while other conditions remained unchanged, and finally polyimide-based porous carbon spheres were obtained.
[0040] The polyimide-based porous carbon spheres prepared in Example 4 were characterized using scanning electron microscopy, and the results are as follows: Figure 8 As shown. By Figure 8 It can be seen that increasing the proportion of guar gum will increase the viscosity of the precursor aqueous solution, which will hinder the rotation and freezing of the droplets when extruding and dripping liquid nitrogen using a precision injection pump, thus affecting the spherical structure of the prepared polyimide-based porous carbon spheres.
Claims
1. A method for large-scale preparation of polyimide-based porous carbon spheres using liquid nitrogen rotary freezing, characterized in that, Includes the following steps: (1) Mix polyimide powder with water and stir, then add triethylamine dropwise and stir until dissolved to obtain an aqueous solution of polyimide salt. (2) Add biomass starch slowly in portions to the polyimide aqueous solution, stir until completely hydrated and dissolved, let stand to remove bubbles, and obtain a viscous precursor aqueous solution. (3) The precursor aqueous solution is slowly dripped into liquid nitrogen, and the droplets are rotated and shaped on the surface of liquid nitrogen and then frozen to form spherical particles; (4) Vacuum freeze-dry the spherical particles to obtain a polyimide-based porous carbon sphere precursor; (5) The polyimide-based porous carbon sphere precursor is subjected to polyimide amidation at a lower temperature and then carbonized at a high temperature to obtain polyimide-based porous carbon spheres.
2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of polyimide acid to triethylamine is 1:(0.4-0.8), and the concentration of polyimide acid in the polyimide acid aqueous solution is 4-8 wt%.
3. The preparation method according to claim 1, characterized in that, In step (1), the stirring speed is 300-600 rpm and the stirring time is 10-15 h.
4. The preparation method according to claim 1, characterized in that, In step (2), the biomass starch is one or more of chitosan, xanthan gum, and guar gum.
5. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of polyimide aqueous solution to biomass starch is 100:(0.8~2.0); the stirring speed is 600~1000 rpm, the stirring time is 12~20h, and the mixture is allowed to stand for 6~10h to remove bubbles.
6. The preparation method according to claim 1, characterized in that, In step (3), the precursor aqueous solution is slowly dripped into liquid nitrogen drop by drop using a syringe. The syringe needle is a stainless steel flat-tipped needle, model 16-23G, with an inner diameter of 0.36 to 1.2 mm.
7. The preparation method according to claim 1, characterized in that, In step (3), the dripping speed is such that the droplet falling interval is >1s.
8. The preparation method according to claim 1, characterized in that, In step (4), the temperature for vacuum freeze drying is below -10℃, and the time for vacuum freeze drying is 2 to 3 days.
9. The preparation method according to claim 1, characterized in that, In step (5), the atmosphere for the amidation and carbonization of polyimide is an inert gas atmosphere, and the inert gas is argon or nitrogen.
10. The preparation method according to claim 1, characterized in that, In step (5), the polyimide amidation is carried out by heating at 3-6℃ / min to 200-400℃ and holding for more than 3 hours; the carbonization is carried out by heating at 2-5℃ / min to 500-700℃ and holding for more than 3 hours.