A method for preparing carbon nanotube microspheres by carbonizing waste polyolefins

Abstract

The present invention belongs to the technical field of waste polyolefin carbonization and discloses a method for preparing carbon nanotube microspheres by carbonizing waste polyolefins, comprising the following steps: (1) physically stirring and mixing the waste polyolefins with spherical nickel hydroxide particles and metal halides to obtain a uniformly mixed mixture; (2) carbonizing the mixture at 550°C to 950°C, and then acid-washing and purifying the product to obtain the carbon nanotube microspheres. The present invention improves the overall process flow, reaction participants, carbonization reaction conditions, etc., and adopts a nickel-based catalyst combined carbonization strategy to achieve controllable carbonization of waste polyolefins, and in situ grows carbon nanotube microspheres rich in micropores, mesopores, and macropores from top to bottom. The present invention realizes the upgraded chemical recycling and reuse of waste polyolefins and the efficient preparation of high-value-added carbon nanotube microspheres with specific morphologies, effectively solving the problem of recycling and reuse of urban and industrial waste polyolefins.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbonization of waste polyolefins, and more specifically, relates to a method for preparing carbon nanotube microspheres by carbonizing waste polyolefins. The method can achieve controllable carbonization and prepare carbon nanotube microspheres with controllable morphology and rich in micropores, mesopores and macropores by in situ growth from bottom to top. Background Art

[0002] Among numerous one-dimensional nanomaterials, carbon nanotubes (CNTs) have attracted significant attention due to their remarkable properties, including large surface area, high conductivity, strong mechanical strength, and ease of functionalization. They are widely used in electronic devices, environmental applications, and biological applications. However, due to their unique structure, CNTs suffer from drawbacks such as poor dispersibility, difficulty in transportation, and inconvenience in use. In recent years, the self-assembly of CNTs has attracted widespread research attention. The morphology of carbon materials significantly influences their application performance, therefore, designing carbon nanomaterials with specific morphologies is of great significance.

[0003] Carbon nanotube microspheres are spherical aggregates assembled from carbon nanotubes. The template method is a common method for self-assembly of carbon nanotubes into carbon nanospheres. Specifically, polystyrene, polymethyl methacrylate, silica, or other materials are used as templates to complete the self-assembly process through electrostatic interaction. The template is then removed by washing with an organic solvent, calcining at high temperature, and purifying with hydrofluoric acid (Jiahua Shi, Zhiyong Chen, Yujun Qin, Zhi-Xin Guo, Multiwalled Carbon Nanotube Microspheres from Layer-by-Layer Assembly and Calcination, The Journal of Physical Chemistry C 2008, 112, 11617-11622; Mingxue Tang, Yujun Qin, Youyou Wang, Zhi-Xin Guo, Hollow Carbon Nanotube Microspheres and Hemimicrospheres, The Journal of Physical Chemistry C, 2009, 113, 1666-1671). The template method usually requires a long processing time (more than 24 hours), harsh template removal conditions (such as hydrofluoric acid is highly corrosive), and complex steps (all requiring 2 to 3 steps). Some researchers have also prepared carbon nanotube microspheres through template-free methods, such as surfactants with cationic, anionic, and nonionic charges interacting with the carboxyl groups on the surface of carbon nanotubes to entangle them, thereby obtaining carbon nanotube microspheres (Mahvash Zuberi, Debra M. Sherman, Youngnam Cho, Carbon Nanotube Microspheres Produced by Surfactant-Mediated Aggregation, The Journal of Physical Chemistry C, 2011, 115, 3881-3887). The disadvantage of this method is that the prepared carbon nanotube microspheres are of different sizes and the size cannot be controlled.Microbubble assembly is also a method for preparing carbon nanotube microspheres, and its process is mainly to accurately control the size of the bubble by microfluid flow rate, and prepare stable carbon nanotube bubble balls (HyunMin Jun, Min Jun Oh, Jun Hyuk Lee, Pil J. Yoo, Microfluidic Synthesis of Carbon Nanotube-Networked Solid-Shelled Bubbles, Langmuir, 2020, 36, 948-955) with uniform size and shape. However, the stability of the bubble is generally poor. The common feature of the preparation method of the above carbon nanotube microspheres is that carbon nanotube materials are first prepared, and then formed to prepare carbon nanotubes of specific macroscopic morphology (such as spherical).

[0004] Waste polyolefin is a carbon source with extremely rich carbon content. For example, the carbon content of polyolefin is 87.5%, which has great "carbon recovery" value. The inventor's research group has used "combined catalytic carbonization" and "template carbonization" to prepare carbon nanomaterials such as carbon nanotubes and carbon nanoflakes from waste polyolefins as carbon sources (Jiang Gong, Jingdong Feng, Jie Liu, Zhiwei Jiang, Xuecheng Chen, Ewa Mijowska, Xin Wen, Tao Tang, Catalytic Carbonization of Polypropylene into Cup-Stacked Carbon Nanotubes with High Performances in Adsorption of Heavy Metallic Ions and Organic Dyes, Chemical Engineering Journal 2014, 248, 27-40; Jiang Gong, Jie Liu, Xin Wen, Zhiwei Jiang, Xuecheng Chen, Ewa Mijowska, Tao Tang, Upcycling Waste Polypropylene into Graphene Flakes on Organically-Modified Montmorillonite, Industrial & Engineering Chemistry Research 2014, 53, 4173-4181). Carbonization pretreatment uses an internal mixer to mix the raw materials. The carbon materials prepared by this method still face difficulties in transportation and use.

[0005] In summary, at present, the preparation of carbon nanotube microspheres mostly comes from the secondary processing of carbon nanotubes. This method is cumbersome, and carbon nanotubes are mostly prepared by vapor deposition, which is costly. Using waste polyolefins as a carbon source to prepare high-value-added carbon nanomaterials is a new way of chemical upgrading and recycling. The controllable carbonization of waste polyolefins to prepare carbon nanotubes has attracted the attention of more and more researchers, but the regulation of the macroscopic morphology of carbon nanotubes has not been achieved, which directly affects the application performance of carbon nanotubes. Therefore, there is an urgent need for a simple and low-cost method to prepare carbon nanotube microspheres with specific morphology, so as to further improve the performance of carbon nanotubes on the original basis and realize "turning waste into treasure". Summary of the Invention

[0006] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a method for preparing carbon nanotube microspheres by carbonizing waste polyolefins, wherein by improving the overall process flow, reaction participants, carbonization reaction conditions, etc., a nickel-based catalyst combined carbonization strategy is adopted to achieve controllable carbonization of waste polyolefins, and carbon nanotube microspheres rich in micropores, mesopores and macropores are grown in situ from top to bottom. The present invention has the advantages of cheap and easy carbon source and simple preparation method, and realizes the upgraded chemical recycling and reuse of waste polyolefins and the efficient preparation of high-value-added carbon nanotube microspheres with specific morphology. This method effectively solves the problem of recycling and reuse of urban and industrial waste polyolefins, and provides a new way for the recycling and reuse of large amounts of waste polyolefins.

[0007] To achieve the above object, according to the present invention, a method for preparing carbon nanotube microspheres by carbonizing waste polyolefins is provided, characterized in that it comprises the following steps:

[0008] (1) physically stirring and mixing waste polyolefin, spherical nickel hydroxide particles and metal halide to obtain a uniformly mixed polyolefin-nickel hydroxide-metal halide mixture;

[0009] (2) The polyolefin-nickel hydroxide-metal halide mixture obtained in step (1) is carbonized in an air atmosphere at 550-950° C. for 3-20 min, and the carbonized product is then acid-washed and purified to obtain carbon nanotube microspheres.

[0010] As a further preferred embodiment of the present invention, in step (1), the physical stirring and mixing is specifically carried out by using a glass rod for stirring for 3 to 10 minutes; preferably, the stirring is carried out in a crucible.

[0011] As a further preferred embodiment of the present invention, in step (1), the diameter of the spherical nickel hydroxide particles is less than 10 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 8 to 15 μm;

[0012] Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 11 to 20 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 15 to 30 μm;

[0013] Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 21 to 30 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 35 to 50 μm;

[0014] Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 31 to 40 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 45 to 55 μm;

[0015] Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 41 to 50 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 50 to 80 μm.

[0016] As a further preferred embodiment of the present invention, in step (1), the metal halide is selected from manganese chloride, nickel chloride, ferric chloride, ferrous chloride, cuprous chloride, and cuprous bromide.

[0017] As a further preferred embodiment of the present invention, in step (1), the mass ratio of the waste polyolefin to the spherical nickel hydroxide particles is 1:0.05-0.4; the mass ratio of the waste polyolefin to the metal halide is 1:0.005-0.1.

[0018] As a further preference of the present invention, in step (1), the waste polyolefin is selected from waste low-density polyethylene, waste high-density polyethylene, waste isotactic polypropylene, waste atactic polypropylene, waste syndiotactic polypropylene, waste polybutene, and waste polyisobutylene.

[0019] As a further preference of the present invention, in the step (2), the acid washing purification is performed by using a 0.5 to 1 mol / L dilute hydrochloric acid solution and soaking and washing for 12 to 24 hours.

[0020] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0021] (1) The present invention mixes three raw materials, namely, waste polyolefin, nickel hydroxide, and metal halide, by simple physical stirring (for example, thorough manual stirring and uniform mixing in a crucible), thereby well maintaining the original morphology of the spherical aggregates of nickel hydroxide nanoparticles, and then performs controllable carbonization on this basis to obtain carbon nanotube microspheres with a macroscopic specific morphology.

[0022] During the treatment process of the present invention, polyolefins are first degraded into small-molecule hydrocarbons and aromatic compounds under the action of a metal halide (degradation catalyst). Subsequently, under the action of a nickel-based catalyst, nickel hydroxide (carbon-forming catalyst), the degradation products undergo further dehydrogenation, cyclization, aromatization, and other reactions, gradually growing into carbon nanotubes. Simultaneously, physical stirring and mixing preserve the spherical morphology of the nickel hydroxide catalyst, allowing the carbon nanotubes to grow from top to bottom in situ into carbon nanotube microspheres. During the carbonization reaction, as the polyolefin degrades and the degradation products undergo a series of crosslinking, cyclization, and aromatization reactions to construct a carbon material skeleton, the carbon nanotubes begin to grow directly on the surface of the nickel-based catalyst (that is, the nickel catalyst is at the end of the carbon nanotubes), thereby producing carbon nanotube microspheres with controllable morphology and rich in micropores, mesopores, and macropores through in situ growth from bottom to top.

[0023] Compared with the reported controlled carbonization of waste polyolefins to prepare carbon nanotubes, the present invention does not require the complex step of mixing in an internal mixer, and happens to retain the original morphology of the catalyst (in the method of the present invention, the raw material spherical nickel hydroxide particles act as a catalyst on the one hand, and on the other hand, can affect the size of the microsphere products), and accordingly obtains carbon nanotube microspheres, effectively solving the problem that carbon nanotubes are difficult to use directly.

[0024] (2) The present invention mixes the raw material mixture evenly and then carbonizes it in a muffle furnace at 550°C to 950°C, thereby preparing carbon nanotube microspheres with controllable morphology and uniform size in one step. The method of the present invention can control the size of the microsphere product by using nickel catalysts of different sizes according to actual needs, and has the characteristic of controllable size. Compared with the reported secondary processing methods such as "template method" and "microbubble assembly", the present invention only requires a one-step carbonization process to efficiently prepare carbon nanotube microspheres by in-situ growth from bottom to top, with a yield of up to 80wt%. The preparation time of carbon nanotube microspheres is significantly shortened, the preparation cost is saved, and a new strategy for the preparation of carbon nanotube microspheres is provided.

[0025] In summary, the present invention adopts a "combined carbonization strategy" and a simple physical stirring strategy to convert waste polyolefins into carbon nanotube microspheres with a specific morphology, thereby realizing the upgraded chemical recycling and reuse of waste polyolefins, improving the application performance of carbon nanotubes, and broadening their application scope. The present invention controllably carbonizes waste polyolefins to prepare carbon nanotube microspheres with a specific macroscopic morphology and a high specific surface area, and proposes a new strategy for the upgraded chemical recycling of waste polyolefins, which contributes to the sustainable development strategy and provides a new approach for the recycling of large amounts of urban and industrial waste polyolefins. While effectively solving the problem of recycling and reuse of urban and industrial waste polyolefins, it prepares carbon nanotube microspheres with high added value and high performance, which have broad application prospects in electrochemical devices such as supercapacitors and lithium-ion batteries, and have high environmental, economic, and social effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Scanning electron micrograph of purified carbon nanotube microspheres.

[0027] Figure 2 The optical microscope images and scanning electron microscope images of nickel hydroxide catalyst at different magnifications are shown; Figure 2 a in the figure is an optical microscope image of nickel hydroxide catalyst. Figure 2 b and Figure 2 c is a scanning electron microscope image of nickel hydroxide catalyst. Figure 2 Figure d is a scanning electron micrograph of purified carbon nanotube microspheres.

[0028] Figure 3 The optical microscope images of nickel hydroxide catalyst at different magnifications and the scanning electron microscope images of prepared unpurified carbon nanotube microspheres at different magnifications are shown; wherein, Figure 3 a and Figure 3 b is an optical microscope image of nickel hydroxide catalyst. Figure 3 c and Figure 3 Figure d is a scanning electron micrograph of the prepared unpurified carbon nanotube microspheres.

[0029] Figure 4 The following are scanning electron microscope images of unpurified carbon nanotube microspheres prepared at different magnifications, photos of carbonized carbon nanotube microspheres, and X-ray diffraction patterns of purified carbon nanotube microspheres; Figure 4 a and Figure 4 Scanning electron micrograph of unpurified carbon nanotube microspheres prepared in b. Figure 4 The c in the figure is a photo of carbonized carbon nanotube microspheres (before separation from the crucible). Figure 4 d in the figure is the X-ray diffraction pattern of the purified carbon nanotube microspheres.

[0030] Figure 5 The nitrogen adsorption and desorption curves and pore size distribution diagram of the purified carbon nanotube microspheres are shown in FIG. Figure 5 a in the figure is the nitrogen adsorption and desorption curve of the purified carbon nanotube microspheres. Figure 5 b in FIG is the pore size distribution diagram of the purified carbon nanotube microspheres.

[0031] Figure 6 is the X-ray diffraction pattern of the purified carbon nanotube microspheres.

[0032] Figure 7 This is a high-resolution transmission electron micrograph of carbon nanotube microspheres after acid washing and purification.

[0033] Figure 8 Scanning electron micrographs of the prepared unpurified carbon nanotubes at different magnifications. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0035] In general, based on the method of the present invention, waste polyolefins can be first physically mixed with spherical nickel hydroxide catalysts and metal halides, and then the mixture is placed in a crucible and carbonized in a muffle furnace at 550°C to 950°C for 3 to 20 minutes. After post-treatment such as washing and purification, carbon nanotube microspheres can be obtained.

[0036] The nickel hydroxide used in the following examples is a spherical aggregate of nickel hydroxide nanoparticles, all of which have a spherical microscopic morphology, but with different size distribution ranges (ie, diameter intervals).

[0037] The carbonization treatments in the following examples were all carried out under air atmosphere.

[0038] Example 1

[0039] (1) Weigh 5 g of low-density polyethylene, 1 g of nickel hydroxide (diameter 41-50 μm), and 0.25 g of cuprous chloride.

[0040] (2) The polyethylene, nickel hydroxide, and cuprous chloride in step (1) are placed in a crucible and thoroughly stirred and mixed (specifically, manually stirred with a glass rod for 8 minutes) to obtain a polyethylene-nickel hydroxide-cuprous chloride mixture, which is then placed in a muffle furnace for high-temperature carbonization at a temperature of 600° C. for 15 minutes.

[0041] (3) After the crucible is cooled naturally, the product is added to 50 mL of 1 mol / L hydrochloric acid solution and soaked for 12 h. After washing, drying and other post-treatment processes, the yield of carbon nanotube microspheres is weighed and calculated to be 68 wt%.

[0042] Figure 1 The scanning electron micrograph of the carbon nanotube microspheres after acid washing and purification shows that the size of the carbon nanotube microspheres is 50 to 80 μm, the diameter of the carbon nanotubes is 20 to 30 nm, and the length is 1 to 5 μm.

[0043] Example 2

[0044] (1) Weigh 5 g of high-density polyethylene, 0.5 g of nickel hydroxide (diameter 21-30 μm), and 0.05 g of nickel chloride.

[0045] (2) The polyethylene, nickel hydroxide, and nickel chloride in step (1) are placed in a crucible and thoroughly stirred and mixed (specifically, manually stirred with a glass rod for 3 minutes) to obtain a polyethylene-nickel hydroxide-nickel chloride mixture, which is then placed in a muffle furnace for high-temperature carbonization at a carbonization temperature of 650° C. for 10 minutes.

[0046] (3) After the crucible was cooled naturally, the product was added to 50 mL of a 1 mol / L hydrochloric acid solution and soaked for 12 h. After washing, drying, and other post-treatment processes, the carbon nanotube microspheres were weighed and calculated to have a yield of 70 wt%. The size of the carbon nanotube microspheres was 35 to 45 μm, the diameter of the carbon nanotubes was 5 to 15 nm, and the length was 5 to 10 μm.

[0047] Figure 2 a in the figure is an optical microscope image of nickel hydroxide catalyst. Figure 2 b and Figure 2 Figure c is a scanning electron microscope image of nickel hydroxide catalyst. Figure 2 Figure d is a scanning electron micrograph of purified carbon nanotube microspheres. Figure 2 The bar chart inset shows the size distribution of the raw nickel hydroxide particles in the range of 21 to 30 μm. The first bar corresponds to [20, 21) μm, the second bar corresponds to [21, 22) μm, the third bar corresponds to [22, 23) μm, the fourth bar corresponds to [23, 24) μm, the fifth bar corresponds to [24, 25) μm, the sixth bar corresponds to [25, 26) μm, the seventh bar corresponds to [26, 27) μm, the eighth bar corresponds to [27, 28) μm, the ninth bar corresponds to [28, 29) μm, and the tenth bar corresponds to [29, 30) μm. It is not difficult to see that the diameter of the raw nickel hydroxide particles is mainly concentrated in the range of 24 to 30 μm. From the optical microscope image of the catalyst, it can be seen that the catalyst morphology is spherical and the size is approximately 21 to 30 μm. The scanning electron micrograph of the catalyst shows that the microstructure of the spherical nickel hydroxide is lamellar. The scanning electron micrograph of the carbon nanotube spheres shows that the size of the carbon nanotube microspheres is 35 to 45 μm.

[0048] Example 3

[0049] (1) Weigh 10 g of isotactic polypropylene, 0.5 g of nickel hydroxide (diameter 11-20 μm), and 0.05 g of ferric chloride.

[0050] (2) The polypropylene, nickel hydroxide, and ferric chloride in step (1) are placed in a crucible and stirred thoroughly (specifically, manually stirred with a glass rod for 10 minutes) to obtain a polypropylene-nickel hydroxide-ferric chloride mixture, which is then placed in a muffle furnace for high-temperature carbonization at a carbonization temperature of 550° C. for 20 minutes.

[0051] (3) After the crucible is cooled naturally, the product is added to 50 mL of a 0.5 mol / L hydrochloric acid solution and soaked for 12 h. After washing, drying, and other post-treatment processes, the carbon nanotube microspheres are weighed and calculated to yield 65 wt %. The carbon nanotube microspheres have a size of 20 to 30 μm, the carbon nanotubes are 1 to 5 μm long, and the carbon nanotubes have a diameter of 5 to 10 nm.

[0052] Figure 3 a and Figure 3 b is an optical microscope image of nickel hydroxide catalyst. Figure 3 c and Figure 3 Figure d is a scanning electron micrograph of the prepared unpurified carbon nanotube microspheres. Figure 3 The bar chart inset shows the size distribution of the raw nickel hydroxide particles in the range of 11 to 20 μm. The first bar corresponds to [10, 11) μm, the second bar corresponds to [11, 12) μm, the third bar corresponds to [12, 13) μm, the fourth bar corresponds to [13, 14) μm, the fifth bar corresponds to [14, 15) μm, the sixth bar corresponds to [15, 16) μm, the seventh bar corresponds to [16, 17) μm, the eighth bar corresponds to [17, 18) μm, the ninth bar corresponds to [18, 19) μm, and the tenth bar corresponds to [19, 20) μm. It is not difficult to see that the diameter of the raw nickel hydroxide particles is mainly concentrated in the range of 16 to 20 μm. The scanning electron micrograph shows that the carbon nanotube microspheres are 25 μm in size, the carbon nanotubes are 1 to 5 μm long, and the carbon nanotubes are 5 to 10 nm in diameter. And, because Figure 3 The bright spot in d is the Ni aggregation part. It can be seen that during the reaction, the nickel catalyst is at the end of the carbon tube, that is, the carbon nanotube starts to grow directly on the surface of the nickel-based catalyst, and the preparation process is in situ growth from bottom to top.

[0053] Example 4

[0054] (1) Weigh 10 g of random polypropylene, 3 g of nickel hydroxide (diameter 21-30 μm), and 0.8 g of ferrous chloride.

[0055] (2) The polypropylene, nickel hydroxide, and ferrous chloride in step (1) are placed in a crucible and stirred thoroughly (specifically, manually stirred with a glass rod for 8 minutes) to obtain a polypropylene-nickel hydroxide-ferrous chloride mixture, which is then placed in a muffle furnace for high-temperature carbonization at a carbonization temperature of 700° C. for 5 minutes.

[0056] (3) After the crucible has cooled naturally, the product is added to 50 mL of a 1 mol / L hydrochloric acid solution and soaked for 24 h. After washing, drying, and other post-treatment processes, the carbon nanotube microspheres are weighed and calculated to yield 70 wt %. The carbon nanotube microspheres have a size of 40 to 50 μm, and the carbon nanotubes are 1 to 5 μm long and 5 to 20 nm in diameter.

[0057] Figure 4 a and Figure 4 Scanning electron micrograph of unpurified carbon nanotube microspheres prepared in b. Figure 4 The c in the figure is a photo of carbonized carbon nanotube microspheres. Figure 4 The d in the figure represents the X-ray diffraction pattern of the unpurified carbon nanotube microspheres. Scanning electron micrographs reveal that the carbon nanotube microspheres are 50 μm in size, with carbon nanotubes 1 to 5 μm long and 5 to 20 nm in diameter. The X-ray diffraction pattern confirms the lattice structure of the carbon nanotube microspheres, and the characteristic absorption peaks of elemental nickel (i.e., 2θ = 44.5°, corresponding to Ni(111); 2θ = 51.8°, corresponding to Ni(200)) indicate that the catalyst has been converted to elemental nickel after carbonization.

[0058] Example 5

[0059] (1) Weigh 8 g of polybutene, 3.2 g of nickel hydroxide (diameter <10 μm), and 0.8 g of manganese chloride.

[0060] (2) The polybutene, nickel hydroxide, and manganese chloride in step (1) were placed in a crucible and thoroughly stirred and mixed (specifically, manually stirred with a glass rod for 7 minutes) to obtain a polybutene-nickel hydroxide-manganese chloride mixture, which was then placed in a muffle furnace for high-temperature carbonization at a temperature of 900° C. for 3 minutes.

[0061] (3) After the crucible has cooled naturally, the product is added to 50 mL of a 1 mol / L hydrochloric acid solution and soaked for 24 h. After washing, drying, and other post-treatment processes, the carbon nanotube microspheres are weighed and calculated to yield 80 wt %. The size of the carbon nanotube microspheres is 8 to 15 μm, the diameter of the carbon nanotubes is 10 to 30 nm, and the length is 5 to 10 μm.

[0062] Figure 5The nitrogen adsorption and desorption curves and pore size distribution of the carbon nanotube microspheres after acid washing and purification are shown in the figure. From the nitrogen adsorption and desorption curves, it can be seen that there are obvious adsorption and desorption hysteresis loops. The specific surface area of ​​the carbon nanotube microspheres is 350m 2 / g, and carbon nanotube microspheres have a large number of micropores (<2nm), mesopores (2-50nm) and macropores (>50nm).

[0063] Example 6

[0064] (1) Weigh 10 g of polyisobutylene, 2 g of nickel hydroxide (diameter 11-20 μm), and 0.5 g of cuprous bromide.

[0065] (2) The polyisobutylene, nickel hydroxide, and cuprous bromide obtained in step (1) are placed in a crucible and thoroughly stirred and mixed (specifically, manually stirred with a glass rod for 10 minutes) to obtain a polyisobutylene-nickel hydroxide-cuprous bromide mixture, which is then placed in a muffle furnace for high-temperature carbonization at a carbonization temperature of 800° C. for 5 minutes.

[0066] (3) After the crucible was cooled naturally, the product was added to 50 mL of a 1 mol / L hydrochloric acid solution and soaked for 12 h. After washing, drying, and other post-treatment processes, the carbon nanotube microspheres were weighed and calculated to have a yield of 60 wt %. The size of the carbon nanotube microspheres was 15 to 25 μm, the diameter of the carbon nanotubes was 20 to 50 nm, and the length was 5 to 10 μm.

[0067] Figure 6 The X-ray diffraction pattern of the carbon nanotube microspheres after acid washing and purification shows that the characteristic peaks of Ni (2θ=44.5°, 51.8°) have disappeared, indicating that the catalyst has been cleaned.

[0068] Example 7

[0069] (1) Weigh 10 g of high-density polyethylene, 2 g of nickel hydroxide (diameter 31-40 μm), and 0.8 g of ferrous chloride.

[0070] (2) The polyethylene, nickel hydroxide, and ferrous chloride obtained in step (1) are placed in a crucible and thoroughly stirred and mixed (specifically, manually stirred with a glass rod for 8 minutes) to obtain a polyethylene-nickel hydroxide-ferrous chloride mixture, which is then placed in a muffle furnace for high-temperature carbonization at a carbonization temperature of 950° C. for 3 minutes.

[0071] (3) After the crucible is cooled naturally, the product is added to 50 mL of a 1 mol / L hydrochloric acid solution and soaked for 24 h. After washing, drying, and other post-treatment processes, the carbon nanotube microspheres are weighed and calculated to have a yield of 75 wt %. The size of the carbon nanotube microspheres is 45 to 55 μm, the diameter of the carbon nanotubes is 10 to 30 nm, and the length is 1 to 5 μm.

[0072] Figure 7 This is a high-resolution transmission electron micrograph of the carbon nanotube microspheres after acid washing and purification. The high-resolution transmission electron micrograph shows that the carbon nanotubes have a distinct graphite layer structure, and the graphite layer is roughly parallel to the axis.

[0073] Comparative Example 1

[0074] (1) Weigh 10 g of isotactic polypropylene, 0.5 g of nickel hydroxide (diameter 11-20 μm), and 0.05 g of nickel chloride, and stir and mix them in an internal mixer to obtain a polypropylene-nickel hydroxide-nickel chloride mixture.

[0075] (2) The polypropylene-nickel hydroxide-nickel chloride obtained in step (1) is placed in a crucible, and then placed in a muffle furnace for high-temperature carbonization, with the carbonization temperature being 600° C. and the carbonization time being 10 min.

[0076] (3) After the crucible is cooled naturally, the product is added to 50 mL of 1 mol / L hydrochloric acid solution and soaked for 24 h. After post-treatment such as washing and drying, the yield of carbon nanotubes is weighed and calculated to be 65 wt%.

[0077] Figure 8 This is a scanning electron microscope image of the prepared unpurified carbon nanotubes. It can be seen from the image that the prepared carbon nanotubes are not spherical in morphology.

[0078] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing carbon nanotube microspheres by carbonizing waste polyolefins, characterized in that: The following steps are involved: (1) physically stirring and mixing waste polyolefin, spherical nickel hydroxide particles and metal halide to obtain a uniformly mixed polyolefin-nickel hydroxide-metal halide mixture; (2) The polyolefin-nickel hydroxide-metal halide mixture obtained in step (1) is carbonized in an air atmosphere at 550°C to 950°C for 3 to 20 minutes, and the carbonized product is then acid-washed and purified to obtain carbon nanotube microspheres.

2. The method for preparing carbon nanotube microspheres by carbonizing waste polyolefins according to claim 1, wherein: In the step (1), the physical stirring and mixing is specifically carried out by using a glass rod for stirring for 3 to 10 minutes.

3. The method for preparing carbon nanotube microspheres by carbonizing waste polyolefins as claimed in claim 2, characterized in that: In the step (1), the physical stirring and mixing is carried out in a crucible.

4. The method for preparing carbon nanotube microspheres by carbonizing waste polyolefins according to claim 1, wherein: In step (1), the diameter of the spherical nickel hydroxide particles is less than 10 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 8-15 μm; Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 11-20 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 15-30 μm; Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 21-30 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 35-50 μm; Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 31-40 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 45-55 μm; Alternatively, in step (1), the diameter of the spherical nickel hydroxide particles is 41-50 μm; correspondingly, the diameter of the carbon nanotube microspheres obtained in step (2) is 50-80 μm.

5. The method for preparing carbon nanotube microspheres by carbonizing waste polyolefins according to claim 1, wherein: In the step (1), the metal halide is selected from manganese chloride, nickel chloride, ferric chloride, ferrous chloride, cuprous chloride, and cuprous bromide.

6. The method for preparing carbon nanotube microspheres by carbonizing waste polyolefins according to claim 1, wherein: In the step (1), the mass ratio of the waste polyolefin to the spherical nickel hydroxide particles is 1:0.05-0.4; the mass ratio of the waste polyolefin to the metal halide is 1:0.005-0.

1.

7. The method for preparing carbon nanotube microspheres by carbonizing waste polyolefins according to claim 1, wherein: In the step (1), the waste polyolefin is selected from waste low-density polyethylene, waste high-density polyethylene, waste isotactic polypropylene, waste atactic polypropylene, waste syndiotactic polypropylene, waste polybutene, and waste polyisobutylene.

8. The method for preparing carbon nanotube microspheres by carbonizing waste polyolefins according to claim 1, wherein: In the step (2), the acid washing purification is performed by using a 0.5-1 mol / L dilute hydrochloric acid solution and soaking and washing for 12-24 hours.

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