A method for preparing a catalyst for synthesizing carbon nanotubes and a method for preparing carbon nanotubes

Abstract

The application provides a preparation method of a catalyst for synthesizing carbon nanotubes and a preparation method of carbon nanotubes. The preparation method of the catalyst comprises respectively arranging a precursor solution, a combustion improver solution and a surfactant solution; sequentially adding the combustion improver solution and the precursor solution into the surfactant solution, aging, and calcining to obtain the catalyst. The active component precursor and the combustion improver are sequentially mixed with the surfactant, and through the adjustment of the PH and the temperature in different stages in the mixing process, the catalyst product obtained has few components, simple preparation process, high selectivity, high yield, can effectively reduce the cost of the carbon nanotubes, has very good economic value, and can improve the product quality of the carbon nanotubes and relieve the cost, equipment investment and environmental pressure.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon nanotube preparation, and in particular relates to a method for preparing a catalyst for carbon nanotube synthesis and a method for preparing carbon nanotubes. Background Art

[0002] The main methods for producing carbon nanotubes include arc discharge, laser evaporation, chemical vapor deposition, and polymerization synthesis. Arc discharge and other techniques require relatively high reaction temperatures and high process requirements. Chemical vapor deposition, however, offers simpler processes and equipment, lower costs, and controllable carbon nanotube growth, making it an alternative to arc discharge and laser evaporation methods for semi-industrial and industrial production, meeting industrial demand for carbon nanotube materials. However, its operating temperature typically ranges from 850-1100°C, and many substrate materials cannot withstand the high temperatures of CVD.

[0003] Moreover, in the process of preparing carbon nanotubes using chemical vapor deposition, the key is to choose a suitable catalyst. The composition, fineness, and physical and chemical properties of the catalyst will affect the structure and performance of the carbon nanotubes. The existing catalysts are mostly iron-based catalysts, and the conversion rate and yield of the carbon nanotubes produced are relatively low.

[0004] Currently, the production methods for carbon nanotube catalysts mainly use co-precipitation or hydrothermal methods, supplemented by calcination to obtain the target catalyst. The above methods are complex, cause high wastewater discharge, and have long production cycles.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing a catalyst for synthesizing carbon nanotubes and a method for preparing carbon nanotubes, so as to solve the above problems.

[0007] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing a catalyst for synthesizing carbon nanotubes, comprising:

[0009] respectively preparing a precursor solution, a combustion-supporting agent solution and a surfactant solution;

[0010] The combustion-supporting agent solution and the precursor solution are sequentially added to the surfactant solution, aged, and calcined to obtain the catalyst.

[0011] Optionally, the precursor includes one or more of cobalt nitrate, magnesium nitrate, aluminum nitrate, manganese nitrate, nickel nitrate, iron nitrate or ammonium nitrate.

[0012] Optionally, the combustion aid includes citric acid and / or glucose.

[0013] Furthermore, the mass ratio of the precursor to the combustion aid is 1:(1-3).

[0014] Optionally, the surfactant comprises a fluorine-containing ion surfactant.

[0015] Preferably, the fluorine-containing ionic surfactant comprises a perfluorinated cationic surfactant.

[0016] More preferably, the perfluorocationic surfactant includes an amine salt type and / or a quaternary ammonium salt type surfactant.

[0017] Furthermore, when preparing the surfactant solution, the system temperature is controlled at 50-95° C. under stirring conditions. Preferably, the stirring speed is 30±10 r / min, and the temperature is controlled at 60-90° C.

[0018] Preferably, when the combustion improver solution is added to the surfactant solution, the pH value is adjusted to 5-7;

[0019] More preferably, when the combustion improver solution is added to the surfactant solution, the pH value is adjusted to 5-6.

[0020] Preferably, when the combustion improver solution is added to the surfactant solution, the system solution is kept stable by continuously stirring and controlling the feeding rate to prevent the solution from locally agglomerating into lumps.

[0021] Furthermore, after the precursor solution is added to the surfactant solution, the pH value is adjusted to 7-11 for aging. Preferably, the pH value is adjusted to 8-9 for aging.

[0022] Furthermore, the aging time is 20-60 minutes. Preferably, the aging temperature is controlled at 70-90°C and the aging time is 30-50 minutes.

[0023] Furthermore, the calcination temperature is 150-350°C and the calcination time is 20-60 minutes. Preferably, the calcination temperature is 150-300°C.

[0024] The present invention also provides a method for preparing carbon nanotubes, and the catalyst used is the catalyst prepared by the preparation method.

[0025] Furthermore, the carbon nanotube preparation method is to place the catalyst in a reactor, raise the temperature to 600-800° C., introduce propane as a carbon source at a rate of 30-50 m 3 / h, and react for 3-6 hours to obtain the carbon nanotube.

[0026] Compared to existing technologies, this invention sequentially mixes the active component precursor and combustion aid with a surfactant. By adjusting the pH and temperature at different stages during the mixing process, the resulting catalyst product has fewer components, a simple preparation process, high selectivity, and a high yield. This effectively reduces the cost of carbon nanotubes and offers excellent economic value. While improving the quality of the carbon nanotube product, it also reduces costs, equipment investment, and environmental pressures.

[0027] The carbon nanotubes prepared by using the catalyst and the method of the present invention have a diameter of about 5-50 nm, a powder conductivity of about 4000-15000 S / m, and a growth rate of about 15-120 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 This is a morphology of the carbon nanotubes prepared using the catalyst prepared in Example 1 of the present invention;

[0030] Figure 2 This is a morphology of the carbon nanotubes prepared using the catalyst prepared in Example 2 of the present invention;

[0031] Figure 3 This is a morphology of the carbon nanotubes prepared using the catalyst prepared in Example 3 of the present invention;

[0032] Figure 4 This is a morphology of the carbon nanotubes prepared using the catalyst prepared in Example 4 of the present invention;

[0033] Figure 5 This is a morphology of the carbon nanotubes prepared using the catalyst prepared in Example 5 of the present invention;

[0034] Figure 6 This is a morphology of the carbon nanotubes prepared using the catalyst prepared in Comparative Example 1;

[0035] Figure 7 This is a morphology diagram of the carbon nanotubes prepared using the catalyst prepared in Comparative Example 2. DETAILED DESCRIPTION

[0036] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0037] Embodiment 1

[0038] A preparation method of a catalyst for synthesizing carbon nanotubes, and the specific steps are as follows:

[0039] S1: 10 parts of cobalt nitrate, 3 parts of iron nitrate and 2 parts of copper nitrate are taken as precursors and dissolved in deionized water to prepare a precursor solution A according to the mole fraction;

[0040] S2: citric acid is weighed and dissolved in deionized water to prepare a combustion improver solution B according to the mass ratio of the precursor to citric acid being 1:2;

[0041] S3: deionized water is added to a reaction kettle, and perfluoro cationic surfactant is weighed and added to the reaction kettle according to the mass ratio of the precursor to the perfluoro cationic surfactant being 1:0.05, and the temperature is controlled at 75℃ under the condition of stirring at a speed of 30±10 r / min to prepare a surfactant solution C;

[0042] S4: the combustion improver solution B is added into the reaction kettle at a uniform speed, and stirred at a speed of 30±10 r / min, and the dropping speed is adjusted to keep the system solution stable by observing the solution dropping in the kettle;

[0043] S5: after the combustion improver solution B is added, the precursor solution A is started to be added, and the dropping speed is adjusted as in step S4, and after the addition is completed, the pH value is adjusted to 8, and the temperature is controlled at 80℃ for aging for 40 min;

[0044] S6: the aged material is taken out and calcined at 230℃ to obtain a catalyst primary product;

[0045] S7: the catalyst primary product obtained in S6 is ground into fine powder.

[0046] A preparation method of carbon nanotubes, the catalyst obtained in step S7 is placed in a reactor, heated to 650℃, and propane is introduced as a carbon source at a rate of 40 m 3 / h, and reacted for 3 h to obtain carbon nanotubes; the appearance morphology diagram is shown in Figure 1 .

[0047] Embodiment 2

[0048] A method for preparing a catalyst for carbon nanotube synthesis, comprising the following steps:

[0049] S1: 11 parts of cobalt nitrate, 3 parts of ferric nitrate, and 1 part of copper nitrate were dissolved in deionized water to prepare precursor solution A.

[0050] S2: Glucose was weighed and dissolved in deionized water at a mass ratio of 1:2 to prepare combustion aid solution B;

[0051] S3: Deionized water was added to the reactor. The mass ratio of the precursor to the perfluorocationic surfactant was 1:0.1. The perfluorocationic surfactant was weighed and added to the reactor. The temperature was controlled at 80°C under stirring at a rate of 30±10 r / min to prepare surfactant solution C.

[0052] S4: First, add the combustion-supporting agent solution B dropwise into the reactor at a uniform speed, stir at a rate of 30±10r / min, observe the solution dropwise addition in the reactor through the observation hole, and adjust the dropwise addition speed to keep the system solution stable;

[0053] S5: After the addition of the combustion-supporting agent solution B is completed, the precursor solution A is started to be added dropwise, and the dropping speed is adjusted as in step S4. After the addition is completed, the pH value is adjusted to 7, and the temperature is controlled at 80°C for aging for 50 minutes;

[0054] S6: taking out the aged material and calcining it at 280°C to obtain a primary catalyst;

[0055] S7: Grind the catalyst obtained in S6 into fine powder.

[0056] A method for preparing carbon nanotubes, wherein the catalyst obtained in step S7 is placed in a reactor, heated to 750°C, and heated at 50m 3 Propane was introduced as a carbon source at a rate of / h and the reaction was continued for 5h to obtain carbon nanotubes; the appearance morphology thereof is shown in the figure below. Figure 2 shown.

[0057] Example 3

[0058] A method for preparing a catalyst for carbon nanotube synthesis, comprising the following steps:

[0059] S1: 9 parts of cobalt nitrate, 4 parts of ferric nitrate, and 2 parts of copper nitrate were dissolved in deionized water to prepare precursor solution A.

[0060] S2: According to the mass ratio of precursor to citric acid of 1:3, citric acid was weighed and dissolved in deionized water to prepare combustion aid solution B;

[0061] S3: Add deionized water into the reactor, and add the perfluorocationic surfactant into the reactor according to the mass ratio of the precursor to the perfluorocationic surfactant of 1:0.01. Stir at a speed of 30±10 r / min, and control the temperature at 55°C to prepare a surfactant solution C;

[0062] S4: First, add the combustion-supporting agent solution B into the reactor at a constant speed, and stir at a speed of 30±10 r / min. Observe the solution dropping in the reactor through the observation hole, and adjust the dropping speed to keep the system solution stable.

[0063] S5: After the addition of the combustion-supporting agent solution B is completed, start to add the precursor solution A, and adjust the dropping speed as in step S4. After the addition is completed, adjust the pH value to 9, and control the temperature at 80°C for aging for 20 min.

[0064] S6: Take out the aged material, and calcine it at 150°C to obtain a catalyst product.

[0065] S7: Grind the catalyst product obtained in S6 into a fine powder.

[0066] A method for preparing carbon nanotubes is provided. The catalyst obtained in step S7 is placed in a reactor, heated to 600°C, and propane is introduced into the reactor at a rate of 30 m3 / h as a carbon source. The reaction is carried out for 5 h to obtain carbon nanotubes. The appearance and morphology of the carbon nanotubes are shown in Figure 3 .

[0067] Example 4

[0068] The difference between the method for preparing the catalyst and that in Example 1 is that, in step S4, the pH value in the reactor is adjusted to 6 before the combustion-supporting agent solution B is added into the reactor at a constant speed.

[0069] The method for preparing carbon nanotubes is the same as that in Example 1. The appearance and morphology of the carbon nanotubes are shown in Figure 4 .

[0070] Example 5

[0071] The difference between the method for preparing the catalyst and that in Example 2 is that, in step S4, the pH value in the reactor is adjusted to 6 before the combustion-supporting agent solution B is added into the reactor at a constant speed.

[0072] The method for preparing carbon nanotubes is the same as that in Example 2. The appearance and morphology of the carbon nanotubes are shown in Figure 5 .

[0073] Comparative Example 1

[0074] The difference between the method for preparing the catalyst and that in Example 1 is that, in step S3, deionized water is directly added into the reactor, and no surfactant is added.

[0075] The preparation method of carbon nanotubes is the same as that of Example 1, and the appearance morphology thereof is shown in FIG. Figure 6 shown.

[0076] Comparative Example 2

[0077] The method for preparing the catalyst is different from that of Example 1 in that, in step S5, after the precursor solution A is added dropwise, the pH value is not adjusted.

[0078] The preparation method of carbon nanotubes is the same as that of Example 1, and the appearance morphology thereof is shown in FIG. Figure 7 shown.

[0079] The carbon nanotubes prepared in the examples and comparative examples were subjected to performance tests in accordance with the following standards: GB / T 26826-2011 - Measurement of carbon nanotube diameter; GB / T 33243-2016 - Nanotechnology - Characterization of multi-walled carbon nanotubes; GB / T 32871-2016 - Characterization of single-walled carbon nanotubes by Raman spectroscopy; and GB / T 37152-2018 - Nanotechnology - Carbon nanotube materials - Sheet resistance. The test results are shown in Table 1.

[0080] Table 1 Performance test results of carbon nanotubes prepared in Examples and Comparative Examples

[0081] project Pipe diameter nm Conductivity S / m Specific surface area m 2 / g]] Growth rate Example 1 10～40 >10000 >300 20～60 Example 2 10～40 >10000 >300 20～60 Example 3 20～50 >6000 >200 15～50 Example 4 5～20 >13000 >400 50～120 Example 5 5～20 >12000 >400 50～120 Comparative Example 1 20～60 >8000 >300 20～60 Comparative Example 2 20～50 >6000 >200 20～60

[0082] The test results of carbon nanotubes produced by the catalysts prepared in Examples 1-5 and Comparative Examples 1-2 show that, referring to Table 1 and the attached Figure 1-7 The catalysts prepared by the method provided by the present invention generally show better catalytic performance.

[0083] As can be seen from the performance data of Example 1 and Comparative Example 1, a certain amount of fluorine-containing ion surfactant solution is added during the catalyst production process, the main purpose of which is to enhance the dispersion properties of the precursor and the combustion-supporting agent and to avoid coagulation and aggregation effects during the reaction. In addition, with the help of the good thermal stability of the fluorine-containing ion surfactant, in the reaction and roasting process of the later stage, the metal ions can be more permanently isolated in situ, which is similar to the effect of a water reducer and prevents the agglomeration phenomenon between the hydrated particles. In addition, the in situ isolation effect can also carry out in situ hydrophobization protection to its ions, preventing the catalyst from serious interfacial sintering and aggregation during the roasting process. And then when synthesizing carbon nanotubes, it shows more superior performance, and the carbon nanotubes catalyzed by the catalyst have more outstanding performance.

[0084] The performance data of Example 1 and Comparative Example 2 show that if the pH value is not adjusted after the precursor solution A is added, the catalyst performance will be reduced, resulting in an increase in the diameter of the produced carbon nanotubes, a decrease in conductivity, and a decrease in specific surface area.

[0085] It can be seen from the performance data of Examples 1 and 4 that adjusting the pH value in the reactor to 6 before adding the combustion-supporting agent solution B dropwise into the reactor can effectively improve the efficiency of the added combustion-supporting agent, thereby enhancing the catalyst performance. The diameter of the produced carbon nanotubes reaches the ideal range, the conductivity is increased, the specific surface area is increased, and the maximum production rate reaches 120.

[0086] A similar conclusion can be drawn from the comparison of the performance data of Example 2 and Example 5.

[0087] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of this application, several variations and improvements can be made, which all fall within the scope of protection of this application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing a catalyst for carbon nanotube synthesis, characterized in that: include: respectively preparing a precursor solution, a combustion-supporting agent solution and a surfactant solution; The combustion-supporting agent solution and the precursor solution are sequentially added to the surfactant solution, aged, and calcined to obtain the catalyst; When the combustion-supporting agent solution is added to the surfactant solution, the pH value is adjusted to 5-7; after the precursor solution is added to the surfactant solution, the pH value is adjusted to 7-11 for aging; the aging temperature is controlled at 70-90°C and the aging time is 20-60 minutes; the calcination temperature is 150-350°C and the calcination time is 20-60 minutes; The precursor includes one or more of cobalt nitrate, magnesium nitrate, aluminum nitrate, manganese nitrate, nickel nitrate, iron nitrate or ammonium nitrate; The combustion aid includes citric acid and / or glucose; The surfactant includes a fluorine-containing ion surfactant, and the fluorine-containing ion surfactant includes a perfluorinated cationic surfactant.

2. The preparation method according to claim 1, characterized in that The mass ratio of the precursor to the combustion aid is 1:(1-3).

3. The preparation method according to claim 1, characterized in that When preparing the surfactant solution, the system temperature is controlled to be 50-95° C. under stirring conditions.

4. The preparation method according to claim 3, characterized in that The stirring speed is 30±10 r / min, and the temperature is controlled at 60-90°C.

5. The preparation method according to claim 1, characterized in that When the combustion improver solution is added to the surfactant solution, the pH value is adjusted to 5-6.

6. The preparation method according to claim 1 or 5, characterized in that When the combustion improver solution is added to the surfactant solution, the system solution is kept stable by continuously stirring and controlling the addition rate.

7. The preparation method according to claim 1, characterized in that After the precursor solution is added to the surfactant solution, the pH value is adjusted to 8-9 for aging.

8. A method for preparing carbon nanotubes, characterized in that: The catalyst used is a catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. The method for preparing nanotubes according to claim 8, characterized in that: The method for preparing the carbon nanotubes is to place the catalyst in a fluidized bed reactor, heat it to 600-800°C, and 3 Propane is introduced as a carbon source at a rate of / h to react to obtain the carbon nanotubes.

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