A method for preparing arrayed carbon nanotubes using LNG as a carbon source

Abstract

This invention provides a method for preparing arrayed carbon nanotubes (CNTs) using LNG as a carbon source, which is low-cost, has a high production rate, and produces high-quality products. It utilizes a layered compound as a support, an ion-exchange catalyst prepared with iron and nickel as active materials, and liquefied natural gas (LNG) as the carbon source for catalytic cracking to prepare CNTs. The method includes the following steps: S1: support acid washing; S2: catalyst preparation; S3: LNG cracking.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube preparation technology, specifically a method for preparing arrayed carbon nanotubes using LNG as a carbon source. Background Technology

[0002] Carbon nanotubes (CNTs) are one-dimensional quantum materials with a unique structure. They are lightweight, have a perfectly connected hexagonal structure, and possess excellent optical, thermal, acoustic, mechanical, electrical, and chemical properties. Due to their excellent electrical conductivity, carbon nanotubes are currently widely used in lithium-ion batteries and also show great promise for applications in sodium-ion batteries.

[0003] Carbon nanotubes (CNTs) can be classified into entangled CNTs and arrayed CNTs according to their aggregation state. Generally, CNTs grown on disordered catalysts exhibit a certain agglomeration structure, severe entanglement, and disordered arrangement, which adversely affects subsequent dispersion and other processing. However, under certain conditions, CNTs can exhibit ordered orientation and achieve parallel arrangement, which is known as arrayed CNTs. Currently, commercially available carbon nanotubes are mainly prepared by chemical vapor deposition (CVD), in which the carbon source is an important component. Propylene is currently the main carbon source that can be industrially used to prepare arrayed CNTs. For example, patent CN115805076A, "Catalyst and its preparation method, arrayed carbon nanotubes and their preparation method," discloses a method for preparing a catalyst precursor by dissolving a soluble active component, a soluble support component containing a support element, and a soluble complexing agent in water, followed by high-temperature calcination at 500-900℃ for 10 min-4 h, and using propylene as a carbon source for catalytic cracking to prepare arrayed CNTs. Patent CN 114632521 A, "Preparation Method of Vermiculite-Based Catalyst and Carbon Nanotube Preparation Method, and Catalyst and Carbon Nanotubes Prepared Therefrom," discloses a catalyst prepared by ion exchange using pretreated vermiculite as a support and ferric nitrate, aluminum nitrate, magnesium nitrate, ammonium heptamolybdate, and citric acid as active materials, and uses propylene as a carbon source to prepare arrayed CNTs. The arrayed CNTs in this patent exhibit a relatively low rate of cracking. There are also reports using ethylene as a carbon source, such as patent CN111247094 A, "Controlled Height Carbon Nanotube Array," which discloses a method for preparing highly controllable arrayed CNTs using layered minerals as a support, soaked in an active solution of Fe, Co, and Ni, followed by calcination, and using ethylene as a carbon source. Its loading method is an over-impregnation method, and the mass of active material adsorbed on the support cannot be precisely controlled, leading to unstable CNT rates; this patent does not address the rate of ethylene cracking by the prepared catalyst.

[0004] The above technologies all use the annual price of propylene or ethylene as the carbon source to prepare carbon nanotubes. However, the current market prices of propylene and ethylene are high, resulting in high production costs for carbon nanotubes, and the production rates are low or unstable. Currently, commercially available array CNTs have long array lengths and large specific surface areas (>200m²). 2 The viscosity of the nickel nanotubes produced is relatively low, which is detrimental to the dispersion of the conductive slurry and results in a high viscosity. Furthermore, carbon nanotubes prepared using nickel as the active catalyst are generally coarse (approximately 30-100 nm in diameter). Therefore, the current production quality of carbon nanotubes is also relatively low. Summary of the Invention

[0005] To address the shortcomings of existing methods for preparing arrayed carbon nanotubes, such as high cost, low or unstable production rate, and low production quality, this invention provides a method for preparing arrayed carbon nanotubes using LNG as a carbon source, which is low in cost, has a high production rate, and produces high quality.

[0006] A method for preparing arrayed carbon nanotubes using LNG as a carbon source is characterized by: using a layered compound as a support, preparing a catalyst via ion exchange with iron and nickel as active materials, and catalytically cracking liquefied natural gas (LNG) as a carbon source to prepare arrayed CNTs, comprising the following steps:

[0007] S1: Carrier pickling; Carrier pickling includes the following steps:

[0008] A1: Weigh the layered compound and place it in a beaker, add dilute nitric acid solution and stir;

[0009] A2: Heat the beaker and keep the temperature constant to carry out the reaction, and obtain the acid-washed carrier;

[0010] A3: Filter or centrifuge the pickling carrier, wash it with deionized water until it is weakly acidic or neutral, and continue to filter or centrifuge to maintain the water content of the pickling carrier.

[0011] S2: Catalyst preparation; The method for catalyst preparation includes the following steps:

[0012] B1: Weigh out a soluble metal salt and dissolve it in deionized water to form an active metal solution A;

[0013] B2: Weigh out the auxiliary metal salt and dissolve it in deionized water to form solution B;

[0014] B3: Continue stirring solution A, add solution B to solution A, and continue stirring until the solution is clear and transparent, then label it solution C;

[0015] B4: Weigh the acid-washed carrier and place it in a high-pressure reactor. Add the solution C and stir until it is uniform. Then place it in a resistance furnace and heat it up. Exhaust the steam until a slight yellow smoke is emitted. Stop the reaction to form a catalyst precursor.

[0016] B5: Remove the catalyst precursor from the high-pressure reactor and calcine the catalyst precursor at high temperature to obtain a crude catalyst.

[0017] B6: The target catalyst is obtained by sieving the crude catalyst.

[0018] S3: LNG cracking; The method of LNG cracking includes the following steps:

[0019] C1: Weigh the target catalyst for later use;

[0020] C2: Heat the fluidized bed reactor and introduce N2 to remove residual oxygen from the reactor.

[0021] C3: Add the catalyst to the reactor, seal the fluidized bed reactor, and after the temperature inside the fluidized bed reactor stabilizes, introduce reducing gas to carry out the reduction reaction;

[0022] C4: Switch to cracked gas for cracking reaction;

[0023] C5: After the reaction is complete, stop heating, introduce N2 to replace the cracked gas until the temperature drops to room temperature, and then obtain array CNTs.

[0024] Its further features are:

[0025] In A1, the layered compound includes at least one or any combination of vermiculite, mica, saponite, or montmorillonite, and the concentration of the dilute nitric acid solution is 0.5-0.8 mol / L;

[0026] In step A2, the heating beaker is heated to 70-80℃ and kept constant for 0.5-3 hours; in step A3, the water content of the pickling carrier is kept between 56% and 70%.

[0027] In B1, the soluble metal salt includes soluble nickel salt, soluble iron salt, and soluble aluminum salt; the soluble nickel salt includes at least one or any combination of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the soluble iron salt includes at least one or any combination of ferric nitrate, ferric acetate, ferric chloride, and ferric sulfate; the soluble aluminum salt includes at least one or any combination of aluminum nitrate, aluminum chloride, and aluminum sulfate; the concentration of the soluble nickel salt is 1.0-2.5 mol / L, the concentration of the soluble iron salt is 1.0-2.5 mol / L, and the concentration of the soluble aluminum salt is 0.5-1.0 mol / L.

[0028] In B2, the auxiliary metal salt includes at least one or any combination of ammonium molybdate, ammonium metatungstate, lanthanum nitrate, or ammonium metavanadate, and the molar ratio of the total auxiliary metal to the active metal is between 0.01 and 0.15.

[0029] In B4, the mass ratio of the pickling carrier to the solution C is 1:3-5, and the temperature of the resistance furnace is 600-700℃; zirconium beads are added inside the high-pressure reactor to prevent boiling over during heating; the mass ratio of the zirconium beads to the carrier is 1:20.

[0030] When the batch size for preparing the target catalyst is less than 10 kg, the following steps are included before B5:

[0031] B5': After the high-pressure reactor has cooled to room temperature, remove the catalyst precursor from the high-pressure reactor and place it in a halogen moisture analyzer for moisture testing. The moisture content should be controlled between 15-25%.

[0032] In B6, the catalyst precursor is calcined at 400-700℃ for 2-8 hours, and the particle size of the target catalyst obtained after sieving is 60-120 mesh; the catalyst with a particle size greater than 120 mesh obtained after sieving is used for LNG cracking in a moving fixed bed.

[0033] In C2, the fluidized bed reactor is heated to 650-700℃, and 300L / h N2 is introduced for 4-6 minutes; in C3, the reducing gas includes a mixture of 270L / h N2 and 30L / h H2, and the reduction reaction time is 0-20 minutes; in C4, the pyrolysis gas includes a mixture of 210L / h LNG and 60L / h H2, and the pyrolysis reaction time is 0.5-2 hours.

[0034] Using the method described above, LNG prices are lower than those of propylene and ethylene, thus reducing raw material costs for CNT arrays prepared using LNG as a carbon source. The auxiliary metal salt can form a co-solution with the active metal in the catalyst during the LNG pyrolysis reaction, which helps reduce the catalyst particle size, improves the distribution of the active metal on the support, and reduces the agglomeration of active metal nickel-iron particles, thereby activating the catalyst and improving the production rate and quality of carbon nanotubes. Acid washing of the support can etch impurities within the support, thereby improving the support's ability to support the catalyst and ensuring a high production rate. The mass ratio of the acid-washed support to the C solution is 1:3-5, which can prevent the agglomeration of active metal particles from increasing and reducing the catalyst's pyrolysis performance, further improving the production rate and quality of carbon nanotubes. When preparing the catalyst precursor, the reaction is stopped when a slight yellow smoke appears as the steam is discharged from the reactor. This phenomenon indicates the presence of a catalyst precursor with the appropriate water content for this invention. This provides a convenient way to quickly control the water content of the catalyst precursor, especially suitable for large-scale catalyst preparation. It eliminates the need to measure the water content of the catalyst precursor, saving time, equipment, and labor costs, and further ensuring high production rates and low costs. Target catalysts with particle sizes of 60-120 mesh are used to crack LNG to produce carbon nanotubes in a fluidized bed, while catalysts with particle sizes larger than 120 mesh can be used to crack LNG to produce carbon nanotubes in a moving fixed bed, fully utilizing catalysts of various particle sizes to reduce catalyst preparation costs. Attached Figure Description

[0035] Figure 1 These are TEM images from Example 1 with an average tube diameter of 11 nm;

[0036] Figure 2 These are SEM images from Example 1 with an average tube diameter of 11 nm;

[0037] Figure 3 These are TEM images from Example 5 with an average tube diameter of 13.7 nm. Detailed Implementation

[0038] This invention provides a method for preparing arrayed carbon nanotubes using LNG as a carbon source. The method utilizes a layered compound as a support, iron and nickel as active materials to prepare a catalyst via ion exchange, and LNG is used as a carbon source for catalytic cracking to prepare arrayed CNTs. The method includes the following steps:

[0039] S1: Carrier pickling; Carrier pickling includes the following steps:

[0040] A1: Weigh the layered compound and place it in a beaker, add a dilute nitric acid solution with a concentration of 0.5-0.8 mol / L and stir; the layered compound includes at least one or any combination of vermiculite, mica, saponite or montmorillonite;

[0041] A2: Heat the beaker to 70-80℃ and maintain the temperature for 0.5-3 hours to allow the reaction to proceed.

[0042] A3: After the reaction is complete, the acid-washed carrier is filtered or centrifuged, and washed with deionized water until it is weakly acidic or neutral. Continue to filter or centrifuge until the water content of the acid-washed carrier is maintained between 56% and 70%.

[0043] In this step, when the concentration of dilute nitric acid is below 56%, the etching of impurities inside the layered compound is insufficient, and the H in the nitric acid... + With Mg contained in layered compounds 2+ Al 3+ Ca 2+ The reduced plasma exchange capacity leads to a decrease in the performance of subsequent catalysts for LNG cracking; when the concentration of dilute nitric acid is higher than 70%, it is easy to cause the collapse of the internal layered structure of the layered compound, resulting in the loss of a large number of metal cations, which is not conducive to the preparation of subsequent catalysts.

[0044] S2: Catalyst preparation; catalyst preparation includes the following steps:

[0045] B1: Weigh out a soluble metal salt and dissolve it in deionized water to form an active metal solution A; the soluble metal salt includes soluble nickel salt, soluble iron salt, and soluble aluminum salt; the soluble nickel salt includes at least one or any combination of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the soluble iron salt includes at least one or any combination of ferric nitrate, ferric acetate, ferric chloride, and ferric sulfate; the soluble aluminum salt includes at least one or any combination of aluminum nitrate, aluminum chloride, and aluminum sulfate; the concentration of the soluble nickel salt is 1.0-2.5 mol / L, the concentration of the soluble iron salt is 1.0-2.5 mol / L, and the concentration of the soluble aluminum salt is 0.5-1.0 mol / L;

[0046] B2: Weigh out the auxiliary metal salt and dissolve it in deionized water to form solution B; In B2, the auxiliary metal salt includes at least one or any combination of ammonium molybdate, ammonium metatungstate, lanthanum nitrate or ammonium metavanadate, and the molar ratio of the total auxiliary metal to the active metal is between 0.01 and 0.15.

[0047] In the catalytic cracking of LNG, auxiliary metal salts mainly play a role in activating the catalyst. These auxiliary metal salts typically have high melting points, above 2000℃. They can form a eutectic with the active metal in the catalyst, which helps reduce the catalyst particle size, improves the distribution of the active metal on the support, and reduces the agglomeration of active metal nickel-iron particles. When the molar ratio of the total auxiliary metal to the active metal is less than 0.01, the auxiliary metal, due to its low content, cannot effectively assist in catalyst activation. When the molar ratio of the total auxiliary metal to the active metal is greater than 0.15, the auxiliary metal, due to its high content, competes with the active metal for reactive sites. Since the auxiliary metal itself has little or no activity, this leads to a reduction in the active sites of the catalyst and a decrease in its ability to crack carbon sources.

[0048] B3: Continuously stir solution A, add solution B to solution A, and continue stirring until the solution is clear and transparent, and label it as solution C; when the additive solution is added to the metal active solution, the catalytic cracking rate of the catalyst can be increased, and the catalyst cracking performance is improved by 15% compared with the addition of the metal active solution to the additive solution.

[0049] B4: Weigh the pickling carrier and place it in a high-pressure reactor. Add a small amount of 3mm zirconium beads inside the reactor to prevent boiling over during heating. The mass ratio of zirconium beads to carrier is 1:20. Add solution C and stir evenly. Then place it in a resistance furnace at 600-700℃ to raise the temperature. Exhaust steam until a slight yellow smoke is emitted, then stop the reaction.

[0050] The mass ratio of the acid-washed support to the solution C is 1:3-5. When the mass ratio of the acid-washed support to the solution C is less than 1, the ion exchange time between the support and the solution is too short, resulting in some active metals not completely entering the interior of the support and accumulating on the surface of the support. During the subsequent roasting process, this leads to the agglomeration and enlargement of active metal particles, reducing the catalyst's cracking performance. When the mass ratio of the acid-washed support to the solution C is greater than 3.5, on the one hand, the active metal content is too high, and the agglomeration phenomenon will also occur on the support surface. On the other hand, due to the increase in the amount of solution, the catalyst preparation time increases, and the required heating energy increases accordingly, which increases the catalyst preparation cost.

[0051] The reaction is stopped when a slight yellow smoke is emitted, as the water vapor in the reactor has been largely removed at this stage, and the ion exchange process between the active material and the support in the solution has been completed. The slight yellow smoke indicates that a small amount of nitrate has decomposed inside the catalyst, producing nitrogen oxides (yellow smoke). Continuing to heat will cause the metal nitrate to decompose, producing a large amount of nitrogen oxides. Furthermore, the occurrence of this phenomenon is precisely when a catalyst precursor with the appropriate water content for this invention is obtained. This provides a convenient way to quickly control the water content of the catalyst precursor, especially suitable for preparing large batches of catalysts with a mass greater than 10 kg, where step B5' can be omitted.

[0052] B5': After the high-pressure reactor has cooled to room temperature, remove the catalyst precursor from the high-pressure reactor and place it in a halogen moisture analyzer for moisture testing. The moisture content should be controlled between 15-25%.

[0053] B5: Remove the catalyst precursor from the high-pressure reactor and calcine the catalyst precursor at 400-700℃ for 2-8 hours to obtain the crude catalyst.

[0054] The catalyst precursor was chosen to be a relatively loose carrier inside the reactor, rather than the part of the reactor wall in contact with the carrier. The main reason is that the part of the reactor wall in contact with the carrier is prone to agglomeration under high temperature conditions, which leads to inaccurate moisture measurement. At the same time, the performance of the catalyst in this part of the reactor is poor in cracking LNG.

[0055] The target catalyst has a particle size of 60-120 mesh. Too large or too small a particle size is not conducive to fluidized bed production. Other catalysts larger than 120 mesh can be used to crack LNG in a moving fixed bed. The resulting carbon nanotubes have the same performance, making full use of the catalyst to reduce the catalyst preparation cost.

[0056] B6: The target catalyst is obtained by sieving the crude catalyst. The target catalyst has a particle size of 60-120 mesh. Particle sizes that are too large or too small are detrimental to fluidized bed production. Catalysts larger than 120 mesh can be used to crack LNG in a moving fixed bed. The resulting carbon nanotubes have the same performance, thus fully utilizing the catalyst to reduce its preparation cost. The technology of using 120-mesh catalyst to crack LNG in a moving fixed bed is existing technology and will not be elaborated upon here.

[0057] S3: LNG cracking; LNG cracking includes the following steps:

[0058] C1: Weigh 1.0g of the target catalyst for later use;

[0059] C2: Heat the fluidized bed reactor to 650-700℃ and introduce 300L / h N2 for about 5 minutes to remove residual oxygen in the quartz reactor;

[0060] C3: The target catalyst is then added to the reactor, the reactor is sealed, and after the temperature inside the reactor stabilizes, reducing gas is introduced for reduction for 0-20 minutes; the reducing gas includes a mixture of 270 L / h N2 and 30 L / h H2.

[0061] C4: Switching to cracked gas cracking reaction time is 0.5-2h; cracked gas includes a mixture of 210L / h LNG and 60L / h H2.

[0062] C5: After the reaction is complete, stop heating, introduce N2 to replace the cracked gas until the temperature drops to room temperature, and then obtain array CNTs.

[0063] Example 1

[0064] S1: Carrier pickling;

[0065] A1: Weigh 500g of vermiculite into a 2000mL beaker, add 1L of 0.5mol / L dilute nitric acid solution and stir. Heat the beaker to 75℃ and maintain the temperature for 2 hours. After the reaction is complete, filter or centrifuge the carrier and wash it with deionized water until it is weakly acidic or neutral. Continue filtration until the water content of the carrier is maintained between 60% and 70%.

[0066] Catalyst preparation;

[0067] B1 Weigh 140.4g of nickel nitrate hexahydrate, 180g of ferric nitrate nonhydrate and 85.4g of aluminum nitrate nonhydrate into a 1L beaker containing 260ml of deionized water, and stir continuously until dissolved into a transparent solution, which is labeled as active metal solution A;

[0068] B2 Weigh 15g of ammonium molybdate and dissolve it in 170ml of deionized water to form solution B;

[0069] B3. Continue stirring solution A, add solution B to solution A, and continue stirring until the solution is clear and transparent. Label this solution C.

[0070] B4 Weigh 200g of the pickled carrier and place it in a high-pressure reactor. Add solution C and stir until homogeneous. Then place it in a resistance furnace at 650℃ and heat it up. Exhaust steam until yellow smoke is emitted, then stop the reaction.

[0071] B5 After the high-pressure reactor has cooled to room temperature, remove the catalyst precursor from the high-pressure reactor and place it in a halogen moisture analyzer for moisture testing.

[0072] B6 calcined the above catalyst precursor at 500°C for 5 hours and then sieved it using 60-mesh and 120-mesh sieves to obtain the target catalyst.

[0073] Cracking LNG;

[0074] C1: Weigh 1.0g of the target catalyst for later use.

[0075] C2: Heat the fluidized bed reactor to 680℃ and introduce 300L / h N2 for 5min to remove residual oxygen in the fluidized bed reactor.

[0076] C3: Add the catalyst to the fluidized bed reactor, seal the fluidized bed reactor, and after the temperature inside the reactor stabilizes, introduce reducing gas (270L / h N2 and 30L / h H2 mixture) for 0 min of reduction;

[0077] C4: Switch to cracked gas (210L / h LNG and 60L / h H2 mixture) with a cracking reaction time of 1 hour.

[0078] C5: After the reaction is complete, stop heating, introduce N2 to replace the cracked gas until the temperature drops to room temperature, and then obtain array CNTs.

[0079] Example 2 uses the same preparation method as Example 1, except that ammonium molybdate is replaced with ammonium metatungstate in the catalyst preparation.

[0080] Example 3 uses the same preparation method as Example 1, except that ammonium molybdate in the catalyst preparation is replaced with lanthanum nitrate.

[0081] Example 4 uses the same preparation method as Example 1, except that ammonium molybdate is replaced with ammonium metavanadate in the catalyst preparation.

[0082] Example 5 was prepared in the same manner as Example 1, except that the masses of nickel nitrate hexahydrate, ferric nitrate nonahydrate, and aluminum nitrate nonahydrate in the catalyst preparation were changed to 190.5g, 195.5g, and 95g, respectively.

[0083] Example 6: 5g of polyvinylpyrrolidone (PVP) and 375g of N-methylpyrrolidone were added to 1 liter of dispersant and dispersed at 2000 rpm. After uniform dispersion, 1500g of zirconium beads and 20g of carbon nanotubes prepared in Example 1 were added, and stirring was continued at high speed (4000 rpm) for 5.5 hours. Test samples were then taken out every 30 minutes for testing. Using the Hergmann scale, when the discharge viscosity was less than 10 micrometers, the discharge viscosity of the slurry was measured at 25°C using a Brookfield viscometer. The above-dispersed carbon nanotube slurry was used to fabricate a lithium-ion cathode electrode. A mixed metal oxide (NCM) of Li(NiCoMn)O2 was used as the cathode material. A cathode slurry containing NCM, carbon nanotubes, PVP, and polyvinylidene fluoride (PVDF) was prepared by mixing appropriate amounts of NCM, carbon nanotube slurry, and PVDF together with N-methylpyrrolidone in a high-speed mixer. A slurry coating was scraped onto Al foil using a doctor blade, followed by drying and compression shearing for subsequent measurements. The final carbon nanotube slurry had a solids content of 6.51%, an output viscosity of 130 mPa·s, a viscosity of 1208 mPa·s after one week, and a viscosity of 5700 mPa·s after four months. The resistivity of the electrode sheet prepared using NCM as the cathode material was 5.39 Ω·cm.

[0084] The same preparation method was used for Comparative Example 1 as for the Example, except that the reduction time for LNG cracking by the catalyst was 10 min.

[0085] Comparative Example 2 was prepared in the same manner as the Example, except that active metal solution A was added to solution B during the catalyst preparation process.

[0086] Table 1 Summary of carbon nanotube data from the examples of carbon nanotube preparation

[0087]

[0088] Detailed Explanation Figure 1 This indicates that the carbon nanotubes prepared by the nickel-iron catalyst of the present invention have a relatively small diameter, with an average diameter of 11 nm, and more than half of them have a diameter of less than 10 nm. Figure 2 This indicates that the carbon nanotubes prepared by the catalyst of this invention are grown vertically, with tube lengths between 20-50 μm. Figure 3 This indicates that increasing the nickel content in the catalyst will increase the average diameter of the resulting carbon nanotubes.

[0089] From Table 1, Figure 1 , Figure 2 , Figure 3 It is known that the carbon source of the array CNTs prepared by this invention is low in cost, has a high carbon yield (>20), good dispersibility, good tube diameter uniformity (average tube diameter is about 11nm), moderate array tube length (20-50μm), low specific surface area (150-200m2 / g), moderate tap density (0.03-0.06g / cm3), and good conductivity (powder resistivity is between 10-20mΩ·cm). The resulting high solids slurry has low viscosity and extremely high production quality.

Claims

1. A method for preparing arrayed carbon nanotubes using LNG as a carbon source, characterized in that: Based on layered compounds as a support, a catalyst is prepared by ion exchange using iron and nickel as active materials, and array CNTs are prepared by catalytic cracking of liquefied natural gas (LNG) as a carbon source. The process includes the following steps: S1: Carrier pickling; Carrier pickling includes the following steps: A1: Weigh the layered compound and place it in a beaker, add dilute nitric acid solution and stir; A2: Heat the beaker and keep the temperature constant to carry out the reaction, and obtain the acid-washed carrier; A3: Filter or centrifuge the pickling carrier, wash it with deionized water until it is weakly acidic or neutral, and continue to filter or centrifuge to maintain the water content of the pickling carrier. S2: Catalyst preparation; The method for catalyst preparation includes the following steps: B1: Weigh out a soluble metal salt and dissolve it in deionized water to form an active metal solution A; B2: Weigh out the auxiliary metal salt and dissolve it in deionized water to form solution B; B3: Continue stirring solution A, add solution B to solution A, and continue stirring until the solution is clear and transparent, then label it solution C; B4: Weigh the acid-washed carrier and place it in a high-pressure reactor. Add the solution C and stir until it is uniform. Then place it in a resistance furnace and heat it up. Exhaust the steam until a slight yellow smoke is emitted. Stop the reaction to form a catalyst precursor. B5: Remove the catalyst precursor from the high-pressure reactor and calcine the catalyst precursor at high temperature to obtain a crude catalyst. B6: The target catalyst is obtained by sieving the crude catalyst. S3: LNG cracking; The method of LNG cracking includes the following steps: C1: Weigh the target catalyst for later use; C2: Heat the fluidized bed reactor and introduce N2 to remove residual oxygen from the reactor. C3: Add the catalyst to the reactor, seal the fluidized bed reactor, and after the temperature inside the fluidized bed reactor stabilizes, introduce reducing gas to carry out the reduction reaction; C4: Switch to cracked gas for cracking reaction; C5: After the reaction is complete, stop heating, introduce N2 to replace the cracking gas until the temperature drops to room temperature to obtain array CNTs; In A1, the layered compound includes at least one or any combination of vermiculite, mica, saponite, or montmorillonite, and the concentration of the dilute nitric acid solution is 0.5-0.8 mol / L; in A3, the water content of the pickling carrier is maintained between 56% and 70%; in B1, the soluble metal salt includes soluble nickel salt, soluble iron salt, and soluble aluminum salt; in B2, the auxiliary metal salt includes at least one or any combination of ammonium molybdate, ammonium metatungstate, lanthanum nitrate, or ammonium metavanadate, and the molar ratio of the total auxiliary metal to the active metal is between 0.01 and 0.

15.

2. The method for preparing arrayed carbon nanotubes using LNG as a carbon source according to claim 1, characterized in that: In A2, the heating beaker is heated to 70-80℃ and kept at a constant temperature for 0.5-3 hours.

3. The method for preparing arrayed carbon nanotubes using LNG as a carbon source according to claim 1, characterized in that: The soluble nickel salt includes at least one or any combination of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate; the soluble iron salt includes at least one or any combination of ferric nitrate, ferric acetate, ferric chloride, and ferric sulfate; the soluble aluminum salt includes at least one or any combination of aluminum nitrate, aluminum chloride, and aluminum sulfate; the concentration of the soluble metallic nickel salt is 1.0-2.5 mol / L, the concentration of the soluble metallic iron salt is 1.0-2.5 mol / L, and the concentration of the soluble metallic aluminum salt is 0.5-1.0 mol / L.

4. The method for preparing arrayed carbon nanotubes using LNG as a carbon source according to claim 1, characterized in that: In B4, the mass ratio of the pickling carrier to the solution C is 1:3-5, and the temperature of the resistance furnace is 600-700℃; zirconium beads are added inside the high-pressure reactor to prevent boiling over during heating. The mass ratio of the zirconium beads to the carrier is 1:

20.

5. The method for preparing arrayed carbon nanotubes using LNG as a carbon source according to claim 1, characterized in that: When the batch size for preparing the target catalyst is less than 10 kg, the following steps are included before B5: B5': After the high-pressure reactor has cooled to room temperature, remove the catalyst precursor from the high-pressure reactor and place it in a halogen moisture analyzer for moisture testing. The moisture content should be controlled between 15-25%.

6. The method for preparing arrayed carbon nanotubes using LNG as a carbon source according to claim 1, characterized in that: In B5, the catalyst precursor is calcined at 400-700℃ for 2-8 hours. In B6, the target catalyst obtained after sieving has a particle size of 60-120 mesh. The catalyst with a particle size greater than 120 mesh obtained after sieving is used for LNG cracking in a moving fixed bed.

7. The method for preparing arrayed carbon nanotubes using LNG as a carbon source according to claim 1, characterized in that: In C2, the fluidized bed reactor is heated to 650-700℃ and N2 is introduced at a rate of 300L / h for 4-6 minutes. In C3, the reducing gas comprises a mixture of 270 L / h N2 and 30 L / h H2, and the reduction reaction time is 0-20 min; in C4, the cracking gas comprises a mixture of 210 L / h LNG and 60 L / h H2, and the cracking reaction time is 0.5-2 h.

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