Method for producing carbon nanotubes

Abstract

The present disclosure relates to a production method of carbon nanotubes, taking catalytic diesel as raw material, selecting a suitable catalyst to sequentially react in two-stage fluidized bed reactors in series, realizing cleaning and high value-added utilization of catalytic diesel, and efficiently, low-cost and continuously preparing high-quality carbon nanotube products, and having good industrial application prospect.

Description

Technical Field

[0001] This disclosure relates to a method for producing carbon nanotubes. Background Technology

[0002] Carbon nanotubes are widely used in catalyst supports, adsorbent materials, and energy storage due to their excellent electrical conductivity, chemical stability, high mechanical strength, and large specific surface area. Current technologies typically use high-purity hydrocarbons (such as propylene) or alcohols as carbon sources to prepare carbon nanotubes in reactors with good flowability. However, the high cost of high-purity carbon sources limits the large-scale, low-cost preparation of carbon nanotubes.

[0003] In the petroleum refining industry, the production scale of gasoline and diesel far exceeds that of olefins and aromatics, making their prices more easily controlled. Catalytic diesel, with its low hydrogen-to-carbon ratio, is difficult to convert into other chemical media and contains high levels of sulfur and nitrogen impurities, making it a component that is not easily utilized in the petrochemical refining chain. Driven by the need for new energy utilization, it is necessary to develop technologies for processing catalytic diesel into high-value-added products. However, the high sulfur and nitrogen content of catalytic diesel often leads to catalyst poisoning or alters the catalyst's melting point, and generates large amounts of catalyst lumps, resulting in low production efficiency and affecting the quality of carbon nanotube products. Summary of the Invention

[0004] The purpose of this disclosure is to provide a method for producing carbon nanotubes, enabling the efficient preparation of high-quality carbon nanotube products.

[0005] To achieve the above objectives, this disclosure provides a method for producing carbon nanotubes, the method comprising: The catalytic diesel fuel is brought into contact with the first catalyst in the first fluidized bed reactor to carry out a desulfurization and denitrification reaction, and the gaseous products are collected. The gaseous product is brought into contact with a second catalyst in a second fluidized bed reactor to carry out a pyrolysis reaction, yielding pyrolysis gas and a solid product containing carbon nanotubes. The first catalyst is a metal oxide particle, and the second catalyst is a metal-supported catalyst.

[0006] Optionally, the catalytic diesel oil has a distillation range of 200~300℃, a sulfur content of 100~10000 mg / kg, and a nitrogen content of 20~2000 mg / kg.

[0007] Optionally, the first catalyst comprises at least one selected from iron oxide, nickel oxide, cobalt oxide, molybdenum oxide, tungsten oxide, zinc oxide, and manganese oxide; and / or, The particle size of the first catalyst is 50~350μm, and the mesoporous pore volume of the first catalyst accounts for 50~90% of the total pore volume.

[0008] Optionally, the second catalyst comprises a support, an active metal, and an additive, wherein, based on the dry weight of the second catalyst, the content of the active metal is 1-15% by weight, the content of the additive is 1-3% by weight, wherein the support comprises at least one selected from alumina, silicon oxide, and magnesium oxide, the active metal comprises at least one selected from iron, cobalt, and nickel, and the additive comprises molybdenum and / or tungsten; and / or, The particle size of the second catalyst is 1~200μm.

[0009] Optionally, the weight ratio of the catalytic diesel oil, the first catalyst, and the second catalyst is 1:(0.2~5):(0.2~3). Preferably, when the hydrogen content of the pyrolysis gas exceeds a first preset threshold and the purity of the carbon nanotubes exceeds a second preset threshold, the second catalyst is added to the second fluidized bed reactor at a first rate; when the hydrogen content of the pyrolysis gas is lower than a third preset threshold or the purity of the carbon nanotubes is lower than a fourth preset threshold, the second catalyst is added to the second fluidized bed reactor at a second rate; the first rate is lower than the second rate.

[0010] Optionally, the method further includes: The catalytic diesel fuel is carried by a carrier gas into the first fluidized bed reactor to carry out the desulfurization and denitrification reaction; Preferably, the flow rate of the carrier gas is 0.02~0.1m / s.

[0011] Optionally, the method further includes: The pyrolysis gas is used to preheat the catalytic diesel and / or as the carrier gas to carry the catalytic diesel.

[0012] Optionally, the method further includes: The sulfur content of the gaseous product is detected, and when the sulfur content of the gaseous product exceeds a first threshold, the first catalyst in the first fluidized bed reactor is replaced with a fresh catalyst; and / or, The sulfur content of the pyrolysis gas is detected, and when the sulfur content of the pyrolysis gas exceeds a second threshold, the solid product is drawn out of the second fluidized bed reactor.

[0013] Optionally, the first threshold is 50 ppm; and / or, the second threshold is 5 ppm.

[0014] Optionally, the conditions for the desulfurization and denitrification reaction include: a temperature of 300~450℃ and a time of 2~14h; and / or, The conditions for the pyrolysis reaction include: a temperature of 700~950℃ and a time of 2~14h.

[0015] Optionally, the solid product is an aggregate of a second catalyst and carbon nanotubes, the particle size of the aggregate being 30 μm to 30 mm. The method further includes: breaking the solid product to obtain carbon nanotubes. Preferably, the diameter of the carbon nanotubes is in the range of 8~25nm.

[0016] By using the above technical solution as raw material, and selecting a suitable catalyst to carry out the reaction sequentially in a two-stage fluidized bed reactor in series, the clean and high-value-added utilization of catalytic diesel is realized. High-quality carbon nanotube products can be prepared efficiently, at low cost, and continuously, and have good prospects for industrial application.

[0017] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic flowchart of a specific embodiment of the carbon nanotube production method disclosed herein.

[0019] Figure 2 This is a schematic diagram of the system structure and process used in Comparative Example 1.

[0020] Explanation of reference numerals in the attached figures 1—First fluidized bed reactor; 2—Second fluidized bed reactor; 3—First fluidized bed feed inlet; 4—First fluidized bed gaseous product outlet; 5—First fluidized bed fresh catalyst inlet; 6—First fluidized bed solid product outlet; 7—Second fluidized bed gas inlet; 8—Second fluidized bed pyrolysis gas outlet; 9—Second fluidized bed fresh catalyst inlet; 10—Second fluidized bed solid product outlet. Detailed Implementation

[0021] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0022] This disclosure provides a method for producing carbon nanotubes, with reference to... Figure 1 The method includes the following steps S1~S2: S1. The catalytic diesel oil is brought into contact with the first catalyst in the first fluidized bed reactor 1 to carry out a desulfurization and denitrification reaction, and the gaseous products are collected. According to this disclosure, the catalytic diesel refers to a heavy distillate oil obtained from the catalytic cracking process in the petroleum refining process. Its distillation range can be 200~300℃, and it is particularly suitable for catalytic diesel with high sulfur and nitrogen content. Specifically, the sulfur content of the catalytic diesel can be 100~10000 mg / kg, preferably 150~500 ppm, and the nitrogen content can be 20~2000 mg / kg, preferably 300~1500 mg / kg.

[0023] In the first fluidized bed reactor 1, organic sulfur and organic nitrogen in catalytic diesel oil undergo an oxidation reaction in the presence of a first catalyst to generate sulfides and nitrides, yielding desulfurized and denitrified gaseous products. The first catalyst is composed of metal oxide particles, which exhibit high desulfurization and denitrification activity and catalytic efficiency, facilitating the preparation of high-value-added products under low energy consumption conditions. The first catalyst has suitable particle size and mesoporous pore volume; specifically, the particle size can be 50-350 μm, preferably 100-200 μm; the mesoporous pore volume of the first catalyst accounts for 50-90% of the total pore volume, preferably 60-80%, specifically, the mesoporous pore volume of the first catalyst can be 0.25-0.55 cm³. 3 / g, with a total pore volume of 0.5~0.8cm³. 3 / g. Further, the first catalyst may include at least one of iron oxide, nickel oxide, cobalt oxide, molybdenum oxide, tungsten oxide, zinc oxide, and manganese oxide, preferably at least one of iron oxide, nickel oxide, tungsten oxide, and zinc oxide.

[0024] The weight ratio of the catalytic diesel to the first catalyst can be 1:(0.2~5), preferably 1:(0.5~1.5). The conditions for the desulfurization and denitrification reaction can include: a temperature of 300~450℃, preferably 300~400℃; and a time of 2~14h, preferably 6~14h.

[0025] In one embodiment, the first fluidized bed reactor 1 may have a first fluidized bed feed inlet 3, a first fluidized bed gaseous product outlet 4, and a first fluidized bed fresh catalyst inlet 5; wherein the first fluidized bed feed inlet 3 is used to introduce catalytic diesel, the first fluidized bed gaseous product outlet 4 is used to extract gaseous products, and the first fluidized bed fresh catalyst inlet 5 is used to introduce fresh first catalyst.

[0026] Further, this step may also include: carrying the catalytic diesel fuel into the first fluidized bed reactor 1 via a carrier gas to carry out the desulfurization and denitrification reaction. In this case, the first fluidized bed feed inlet 3 can be located at the bottom of the first fluidized bed reactor 1, the first fluidized bed gaseous product outlet 4 can be located at the top of the first fluidized bed reactor 1, and the first fluidized bed fresh catalyst inlet 5 can be located at the upper part of the first fluidized bed reactor 1. Thus, the mixture of catalytic diesel fuel and carrier gas can enter the first fluidized bed reactor 1 from bottom to top, and the first catalyst, flowing from top to bottom, can be in a suspended fluidized state when it contacts the first carrier gas carrying the catalytic diesel fuel, which is beneficial for improving the contact reaction efficiency. The carrier gas may include at least one of nitrogen (N2), hydrogen (H2), and methane (CH4). Furthermore, by reasonably controlling the flow rate of the carrier gas, it is beneficial to avoid metal oxide particles being carried into the second fluidized bed reactor 2. Specifically, the flow rate of the carrier gas can be 0.02~0.5 m / s, preferably 0.08~0.2 m / s.

[0027] According to this disclosure, the components of the gaseous product may include hydrogen, methane and other hydrocarbon gases. Specifically, the hydrogen content in the gaseous product may be 1 to 10% by volume, the methane content may be 10 to 20% by volume, and the content of other hydrocarbon gases may be 70 to 85% by volume.

[0028] In one specific embodiment, to improve the quality of the carbon nanotube product, this step may further include: detecting the sulfur content of the gaseous product; when the sulfur content of the gaseous product exceeds a first threshold, replacing the reacted first catalyst in the first fluidized bed reactor 1 with a fresh catalyst. In this case, the first fluidized bed reactor 1 may also have a first fluidized bed solid product outlet 6 for discharging the reacted first catalyst; this first fluidized bed solid product outlet 6 may be located at the lower part of the first fluidized bed reactor 1. The first threshold can be adjusted according to actual production needs; for example, the first threshold may be 50 ppm.

[0029] S2. The gaseous product is brought into contact with the second catalyst in the second fluidized bed reactor 2 to carry out a pyrolysis reaction, thereby obtaining pyrolysis gas and a solid product containing carbon nanotubes. In the second fluidized bed reactor 2, the gaseous products from the first fluidized bed reactor 1 undergo thermal decomposition in the presence of a second catalyst, whereby the carbon source can be deposited on the surface of the second catalyst and grown into carbon nanotubes. The second catalyst is a metal-supported catalyst. Furthermore, the second catalyst has a small particle size; specifically, the particle size of the second catalyst can be 1~200 μm, preferably 50~100 μm.

[0030] In one specific embodiment, the second catalyst may include a support, an active metal, and an additive; based on the dry weight of the second catalyst, the content of the active metal may be 1-15% by weight, and the content of the additive may be 1-3% by weight; wherein, the support may include at least one of alumina, silicon oxide, and magnesium oxide, the active metal may include at least one of iron, cobalt, and nickel, and the additive may include molybdenum and / or tungsten. The second catalyst can be prepared by a co-precipitation method. For example, the preparation steps of the second catalyst may include: (1) calculating the weight ratio of the corresponding support, active metal salt, and additive metal salt according to the target weight ratio of each metal in the catalyst; (2) dissolving the weighed solid in deionized water and mixing it evenly to prepare a solution, stirring it thoroughly at a certain temperature for a certain time to obtain a precipitate; (3) filtering, washing, drying, calcining, and pulverizing the stirred solution.

[0031] Furthermore, the second catalyst can be added to the second fluidized bed reactor all at once, or the addition method of the second catalyst can be adjusted according to the degree of the pyrolysis reaction and / or the quality of the carbon nanotube product. In one specific embodiment, the second catalyst can be added to the second fluidized bed reactor in batches at varying rates. For example, when the hydrogen content of the pyrolysis gas exceeds a first preset threshold (e.g., 90% by volume) and the purity of the carbon nanotube product exceeds a second preset threshold (e.g., 92%), the second catalyst is added to the second fluidized bed reactor at a first rate; when the hydrogen content of the pyrolysis gas is lower than a third preset threshold (e.g., 80% by volume), or the purity of the carbon nanotube product is lower than a fourth preset threshold (e.g., 85%), the second catalyst is added to the second fluidized bed reactor at a second rate; the first rate is lower than the second rate. Specifically, the first rate can be 0.5~1.0 kg / h, and the second rate can be 1.5~2.5 kg / h; thus, by dynamically adjusting the addition rate of the second catalyst, the pyrolysis reaction can always be kept in an optimal state, which helps to improve the yield and quality of carbon nanotubes. The weight ratio of the catalytic diesel to the second catalyst can be 1:(0.2~3), preferably 1:(0.3~1). The conditions for the pyrolysis reaction can include: a temperature of 700~950℃, preferably 700~850℃; and a time of 2~14h, preferably 6~14h.

[0032] In one embodiment, the second fluidized bed reactor 2 may have a second fluidized bed gas inlet 7, a second fluidized bed pyrolysis gas outlet 8, a second fluidized bed fresh catalyst inlet 9, and a second fluidized bed solid product outlet 10. The second fluidized bed gas inlet 7 is connected to the first fluidized bed gaseous product outlet 4 via a pipeline for introducing gaseous products; the second fluidized bed pyrolysis gas outlet 8 is used to extract pyrolysis gas; the second fluidized bed fresh catalyst inlet 9 is used to introduce fresh second catalyst; and the second fluidized bed solid product outlet 10 is used to extract the solid product after the reaction. Further, the second fluidized bed gas inlet 7 may be located at the bottom of the second fluidized bed reactor 2, the second fluidized bed pyrolysis gas outlet 8 may be located at the top of the second fluidized bed reactor 2, the second fluidized bed fresh catalyst inlet 9 may be located at the upper part of the second fluidized bed reactor 2, and the second fluidized bed solid product outlet 10 may be located at the lower part of the second fluidized bed reactor 2. This allows the upward-flowing gaseous product to fully contact the downward-flowing second catalyst, which is beneficial for improving reaction efficiency.

[0033] The pyrolysis gas may include hydrogen, methane, and a small amount of sulfur-containing hydrocarbon gases. Specifically, the hydrogen content in the pyrolysis gas may be 50-99% by volume, the methane content may be 1-50% by volume, and the content of other hydrocarbon gases may be 0-5% by volume. In one specific embodiment, to improve the purity of the carbon nanotube product, this step may further include: detecting the sulfur content of the pyrolysis gas; when the sulfur content of the pyrolysis gas exceeds a second threshold, the solid-phase product is withdrawn from the second fluidized bed reactor 2. To achieve continuous production, a freshener may be added to the second fluidized bed reactor 2 when the solid-phase product is withdrawn. The second threshold may be adjusted according to production needs; for example, the second threshold may be 5 ppm.

[0034] In one embodiment, the step may further include: using the pyrolysis gas to preheat the catalytic diesel and / or using it as the carrier gas described above to carry the catalytic diesel into the first fluidized bed reactor 1, thereby reducing the external heating or carrier gas requirements, further improving energy utilization efficiency, and reducing overall operating costs.

[0035] The solid product is a mixture of a second catalyst and carbon nanotubes, and the mixture is in agglomerated form with a particle size of 30 μm to 30 mm, preferably 50 μm to 2 mm. Specifically, the solid product is an aggregate of the second catalyst and carbon nanotubes.

[0036] In one specific embodiment, the method may further include the following step S3: S3. The solid product is crushed to obtain carbon nanotubes.

[0037] By physically crushing the solid-phase product, carbon nanotubes on the surface of the second catalyst are detached, achieving efficient separation of the catalyst from the high-value-added product. This process not only obtains high-quality carbon nanotubes but also helps maintain the particle uniformity and activity of the second catalyst, further enabling catalyst recycling. The crushing can be carried out in a grinding device under conditions including a temperature of 20~300℃ and a time of 0.1~3h.

[0038] The carbon nanotubes prepared by the method disclosed herein have suitable diameter characteristics and uniform morphology. Specifically, the diameter of the carbon nanotubes can range from 8 to 25 nm, the length can range from 3 to 10 μm, and the specific surface area can range from 100 to 350 m². 2 / g, in particular, the carbon nanotubes have high conductivity, specifically 5000~1000000 S / m, and have important application prospects in the fields of high-performance electronic devices, energy storage materials and nanocomposite materials.

[0039] This disclosure utilizes catalytic diesel as raw material, sequentially carrying out desulfurization, denitrification, and pyrolysis reactions in a two-stage fluidized bed reactor to prepare high-quality carbon nanotubes, achieving clean and high-value-added utilization of catalytic diesel. Due to the high temperature of the pyrolysis reaction, the desulfurization and denitrification reaction conditions can be flexibly adjusted, providing favorable conditions for in-depth reaction control, significantly improving desulfurization and denitrification efficiency, effectively increasing the catalyst's tolerance to catalytic diesel, reducing catalyst deactivation, and improving energy utilization efficiency. This enables efficient, low-cost, continuous, and high-purity carbon nanotube production, suitable for industrial applications and possessing excellent prospects for widespread adoption.

[0040] The present disclosure will be described in detail below through examples, but it is not intended to limit the present disclosure.

[0041] In this embodiment, the method for detecting the component content of the gaseous products of the first fluidized bed reactor 1 and the pyrolysis gas of the second fluidized bed reactor 2 is gas chromatography.

[0042] Example 1 This embodiment uses, as follows: Figure 1 The system shown is used to prepare carbon nanotubes from catalytic diesel fuel. The catalytic diesel fuel has a distillation temperature range of 210–300 °C (at atmospheric pressure), a sulfur content of 5000 mg / kg, and a nitrogen content of 1000 mg / kg. The primary catalyst is zinc oxide with a particle size range of 50–200 μm and a mesopore volume of 0.4 cm³. 3 / g, total pore volume is 0.6cm³ 3 / g, mesoporous pore volume accounts for 67% of the total pore volume; the active metal of the second catalyst is 15% by weight iron, the auxiliary agent is 1.5% by weight molybdenum, the support is alumina, the particle size range is 1~100μm, and the weight ratio of catalytic diesel, the first catalyst and the second catalyst is 1:1:1.

[0043] The first catalyst is added to the first fluidized bed reactor 1 through the first fluidized bed fresh catalyst inlet 5, and the second catalyst is added to the second fluidized bed reactor 2 through the second fluidized bed fresh catalyst inlet 9. Carrier gas (50% N2, 50% CH4) and catalytic diesel are introduced through the first fluidized bed feed inlet 3. The first catalyst is in a suspended fluidized state and reacts at 350℃ for 6 hours. The organic sulfur and organic nitrogen in the catalytic diesel react with the metal oxide particles, and most of them are removed. The generated gaseous product is led out through the first fluidized bed gaseous product outlet 4. The sulfur content in the gaseous product is detected. When the sulfur content exceeds 50 ppm, the reacted metal oxide particles are discharged from the first fluidized bed solid product outlet 6, and fresh metal oxide particles are added through the first fluidized bed fresh catalyst inlet 5. The gas velocity of the carrier gas is controlled at 0.06 m / s to prevent the metal oxide particles from exiting through the first fluidized bed gaseous product outlet 4 with the gas. The gaseous products are introduced into the second fluidized bed reactor 2 through the second fluidized bed gas inlet 7 and pyrolyzed at 800℃ for 6 hours on the second catalyst. The pyrolysis gas (mainly methane and hydrogen) is drawn out through the second fluidized bed pyrolysis gas outlet 8. When the sulfur content of the pyrolysis gas exceeds 5 ppm, the solid products after the reaction (agglomerates of carbon nanotubes and the second catalyst, with particle sizes of 100 μm to 1 mm) are discharged from the second fluidized bed solid product outlet 10, and fresh catalyst is added through the second fluidized bed fresh catalyst inlet 9. The second fluidized bed reactor 2 is equipped with a second catalyst replenishment tank, and the opening of the corresponding delivery valve can be adjusted according to the following speed requirements: when the hydrogen content of the pyrolysis gas exceeds 90% by volume and the purity of the carbon nanotubes exceeds 92%, the addition rate of the second catalyst is 1.0 kg / h; when the hydrogen content of the pyrolysis gas is less than 80% by volume or the purity of the carbon nanotubes is less than 85%, the addition rate of the second catalyst is 1.5 kg / h. Part of the pyrolysis gas was used for preheating catalytic diesel, and part of it was pressurized and used as carrier gas in the first fluidized bed reactor 1. The solid products were crushed at 200°C for 1 hour to obtain carbon nanotubes.

[0044] The diameter characteristics of carbon nanotubes were detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the specific surface area was detected by physical adsorption (BET) method, the purity was detected by thermogravimetric analysis (TG), and the conductivity was detected by four-probe method. The results are listed in Table 1.

[0045] Example 2 This embodiment uses, as follows: Figure 1The system shown is used to prepare carbon nanotubes from catalytic diesel fuel. The catalytic diesel fuel has a distillation temperature range of 200–300 °C (at atmospheric pressure), a sulfur content of 500 mg / kg, and a nitrogen content of 1000 mg / kg. The first catalyst is zinc oxide and nickel oxide (weight ratio 3:7), with a particle size range of 150–200 μm and a mesopore volume of 0.5 cm³. 3 / g, total pore volume is 0.7cm³ 3 / g, mesoporous pore volume accounts for 71% of the total pore volume; the active metal of the second catalyst is 10% by weight iron, the auxiliary agent is 1% by weight molybdenum, the support is alumina, the particle size range is 50~70μm, and the weight ratio of catalytic diesel, the first catalyst and the second catalyst is 1:1:0.5.

[0046] The first catalyst is added to the first fluidized bed reactor 1 through the first fluidized bed fresh catalyst inlet 5, and the second catalyst is added to the second fluidized bed reactor 2 through the second fluidized bed fresh catalyst inlet 9. Carrier gas (50% H2, 50% CH4) and catalytic diesel are introduced through the first fluidized bed feed inlet 3. The first catalyst is in a suspended fluidized state and reacts at 350℃ for 8 hours. The organic sulfur and organic nitrogen in the catalytic diesel react with the metal oxide particles, and most of them are removed. The generated gaseous product is led out through the first fluidized bed gaseous product outlet 4. The sulfur content in the gaseous product is detected. When the sulfur content exceeds 50 ppm, the reacted metal oxide particles are discharged from the first fluidized bed solid product outlet 6, and fresh metal oxide particles are added through the first fluidized bed fresh catalyst inlet 5. The gas velocity of the carrier gas is controlled at 0.09 m / s to prevent the metal oxide particles from exiting through the first fluidized bed gaseous product outlet 4 with the gas. The gaseous products are introduced into the second fluidized bed reactor 2 through the second fluidized bed gas inlet 7 and pyrolyzed at 750°C for 6 hours on the second catalyst. The pyrolysis gas (mainly methane and hydrogen) is drawn out through the second fluidized bed pyrolysis gas outlet 8. When the sulfur content of the pyrolysis gas exceeds 5 ppm, the solid products after the reaction (agglomerates of carbon nanotubes and the second catalyst, with particle sizes of 50 μm to 0.8 mm) are discharged from the second fluidized bed solid product outlet 10, and fresh catalyst is added through the second fluidized bed fresh catalyst inlet 9. The second fluidized bed reactor 2 is equipped with a second catalyst replenishment tank, and the opening of the corresponding delivery valve can be adjusted according to the following speed requirements: when the hydrogen content of the pyrolysis gas exceeds 90% by volume and the purity of the carbon nanotubes exceeds 92%, the addition rate of the second catalyst is 1.0 kg / h; when the hydrogen content of the pyrolysis gas is less than 80% by volume or the purity of the carbon nanotubes is less than 85%, the addition rate of the second catalyst is 1.5 kg / h. Part of the pyrolysis gas was used for preheating catalytic diesel, and part was pressurized and used as carrier gas in the first fluidized bed reactor 1. The solid products were crushed at 50°C for 1 hour to obtain carbon nanotubes.

[0047] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1.

[0048] Example 3 This embodiment uses, as follows: Figure 1 The system shown is used to prepare carbon nanotubes from catalytic diesel fuel. The catalytic diesel fuel has a distillation temperature range of 230–300 °C (at atmospheric pressure), a sulfur content of 8000 mg / kg, and a nitrogen content of 1800 mg / kg. The first catalyst is zinc oxide and iron oxide (weight ratio 2:8), with a particle size range of 50–200 μm and a mesopore volume of 0.35 cm³. 3 / g, total pore volume is 0.5cm³ 3 / g, mesoporous pore volume accounts for 70% of the total pore volume; the active metal of the second catalyst is 2% nickel by weight, the auxiliary agent is 1% tungsten by weight, the support is silicon oxide, the particle size range is 50~150μm, and the weight ratio of catalytic diesel, the first catalyst and the second catalyst is 1:1.5:1.5.

[0049] The first catalyst is added to the first fluidized bed reactor 1 through the first fluidized bed fresh catalyst inlet 5, and the second catalyst is added to the second fluidized bed reactor 2 through the second fluidized bed fresh catalyst inlet 9. Carrier gas (100% CH4) and catalytic diesel are introduced through the first fluidized bed feed inlet 3. The first catalyst is in a suspended fluidized state and reacts at 420℃ for 8 hours. The organic sulfur and organic nitrogen in the catalytic diesel react with the metal oxide particles, and most of them are removed. The generated gaseous product is led out through the first fluidized bed gaseous product outlet 4. The sulfur content in the gaseous product is detected. When the sulfur content exceeds 50 ppm, the reacted metal oxide particles are discharged from the first fluidized bed solid product outlet 6, and fresh metal oxide particles are added through the first fluidized bed fresh catalyst inlet 5. The gas velocity of the carrier gas is controlled at 0.1 m / s to prevent the metal oxide particles from exiting through the first fluidized bed gaseous product outlet 4 with the gas. The gaseous products are introduced into the second fluidized bed reactor 2 through the second fluidized bed gas inlet 7 and pyrolyzed at 900°C for 8 hours on the second catalyst. The pyrolysis gas (mainly methane and hydrogen) is drawn out through the second fluidized bed pyrolysis gas outlet 8. When the sulfur content of the pyrolysis gas exceeds 5 ppm, the solid products after the reaction (agglomerates of carbon nanotubes and the second catalyst, with particle sizes of 120 μm to 1 mm) are discharged from the second fluidized bed solid product outlet 10, and fresh catalyst is added through the second fluidized bed fresh catalyst inlet 9. The second fluidized bed reactor 2 is equipped with a second catalyst replenishment tank, and the opening of the corresponding delivery valve can be adjusted according to the following speed requirements: when the hydrogen content of the pyrolysis gas exceeds 90% by volume and the purity of the carbon nanotubes exceeds 92%, the addition rate of the second catalyst is 1.0 kg / h; when the hydrogen content of the pyrolysis gas is less than 80% by volume or the purity of the carbon nanotubes is less than 85%, the addition rate of the second catalyst is 2.0 kg / h. Part of the pyrolysis gas was used for preheating catalytic diesel, and part of it was pressurized and used as carrier gas in the first fluidized bed reactor 1. The solid products were crushed at 80°C for 1.5 h to obtain carbon nanotubes.

[0050] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1.

[0051] Example 4 This embodiment uses, as follows: Figure 1 The system shown is used to prepare carbon nanotubes from catalytic diesel fuel. The catalytic diesel fuel has a distillation temperature range of 200–300 °C (at atmospheric pressure), a sulfur content of 100 mg / kg, and a nitrogen content of 200 mg / kg. The first catalyst consists of manganese oxide, zinc oxide, and molybdenum oxide (weight ratio 5:2:3), with a particle size range of 150–300 μm and a mesopore volume of 0.45 cm³. 3 / g, total pore volume is 0.65cm³ 3 / g, mesoporous pore volume accounts for 69% of the total pore volume; the active metal of the second catalyst is 5% iron by weight, the auxiliary agent is 1% molybdenum by weight, the support is silicon oxide, the particle size range is 1~200μm, and the weight ratio of catalytic diesel, the first catalyst and the second catalyst is 1:0.8:1.2.

[0052] The first catalyst is added to the first fluidized bed reactor 1 through the first fluidized bed fresh catalyst inlet 5, and the second catalyst is added to the second fluidized bed reactor 2 through the second fluidized bed fresh catalyst inlet 9. Carrier gas (80% N2, 20% H2) and catalytic diesel are introduced through the first fluidized bed feed inlet 3. The first catalyst is in a suspended fluidized state and reacts at 400℃ for 12 hours. The organic sulfur and organic nitrogen in the catalytic diesel react with the metal oxide particles, and most of them are removed. The generated gaseous product is led out through the first fluidized bed gaseous product outlet 4. The sulfur content in the gaseous product is detected. When the sulfur content is greater than 50 ppm, the reacted metal oxide particles are discharged from the first fluidized bed solid product outlet 6, and fresh metal oxide particles are added through the first fluidized bed fresh catalyst inlet 5. The gas velocity of the carrier gas is controlled at 0.08 m / s to prevent the metal oxide particles from exiting through the first fluidized bed gaseous product outlet 4 with the gas. The gaseous products are introduced into the second fluidized bed reactor 2 through the second fluidized bed gas inlet 7 and pyrolyzed at 700℃ for 12 hours on the second catalyst. The pyrolysis gas (mainly methane and hydrogen) is drawn out through the second fluidized bed pyrolysis gas outlet 8. When the sulfur content of the pyrolysis gas exceeds 5 ppm, the solid products after the reaction (agglomerates of carbon nanotubes and the second catalyst, with particle sizes of 150 μm to 2 mm) are discharged from the second fluidized bed solid product outlet 10, and fresh catalyst is added through the second fluidized bed fresh catalyst inlet 9. The second fluidized bed reactor 2 is equipped with a second catalyst replenishment tank, and the opening of the corresponding delivery valve can be adjusted according to the following speed requirements: when the hydrogen content of the pyrolysis gas exceeds 90% by volume and the purity of the carbon nanotubes exceeds 92%, the addition rate of the second catalyst is 0.5 kg / h; when the hydrogen content of the pyrolysis gas is less than 80% by volume or the purity of the carbon nanotubes is less than 85%, the addition rate of the second catalyst is 1.5 kg / h. Part of the pyrolysis gas was used for preheating catalytic diesel, and part of it was pressurized and used as carrier gas in the first fluidized bed reactor 1. The solid products were crushed at 100°C for 1 hour to obtain carbon nanotubes.

[0053] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1.

[0054] Example 5 This embodiment uses, as follows: Figure 1The system shown is used to prepare carbon nanotubes from catalytic diesel fuel. The catalytic diesel fuel has a distillation temperature range of 200–300 °C (at atmospheric pressure), a sulfur content of 10,000 mg / kg, and a nitrogen content of 2,000 mg / kg. The first catalyst is iron oxide with a particle size range of 50–100 μm and a mesopore volume of 0.3 cm³. 3 / g, total pore volume is 0.5cm³ 3 / g, with mesoporous pore volume accounting for 60% of the total pore volume; the active metal of the second catalyst is 5% iron by weight, the auxiliary agent is 3% molybdenum by weight, the support is magnesium oxide, the particle size range is 1~100μm, and the weight ratio of catalytic diesel, the first catalyst and the second catalyst is 1:1.2:1.5.

[0055] The first catalyst is added to the first fluidized bed reactor 1 through the first fluidized bed fresh catalyst inlet 5, and the second catalyst is added to the second fluidized bed reactor 2 through the second fluidized bed fresh catalyst inlet 9. Carrier gas (100% H2) and catalytic diesel are introduced through the first fluidized bed feed inlet 3. The first catalyst is in a suspended fluidized state and reacts at 450℃ for 2 hours. The organic sulfur and organic nitrogen in the catalytic diesel react with the metal oxide particles, and most of them are removed. The generated gaseous product is led out through the first fluidized bed gaseous product outlet 4. The sulfur content in the gaseous product is detected. When the sulfur content exceeds 50 ppm, the reacted metal oxide particles are discharged from the first fluidized bed solid product outlet 6, and fresh metal oxide particles are added through the first fluidized bed fresh catalyst inlet 5. The gas velocity of the carrier gas is controlled at 0.05 m / s to prevent the metal oxide particles from exiting through the first fluidized bed gaseous product outlet 4 with the gas. The gaseous products are introduced into the second fluidized bed reactor 2 through the second fluidized bed gas inlet 7 and pyrolyzed at 950°C for 2 hours on the second catalyst. The pyrolysis gases (mainly methane and hydrogen) are exited through the second fluidized bed pyrolysis gas outlet 8. When the sulfur content of the pyrolysis gases exceeds 5 ppm, the solid products after the reaction (agglomerates of carbon nanotubes and the second catalyst, with particle sizes of 150 μm to 2 mm) are discharged from the second fluidized bed solid product outlet 10, and fresh catalyst is added through the second fluidized bed fresh catalyst inlet 9. The second fluidized bed reactor 2 is equipped with a second catalyst replenishment tank, and the addition rate of the second catalyst is stable at 1.0 kg / h. Part of the pyrolysis gas is used for preheating catalytic diesel, and part is pressurized and used as carrier gas in the first fluidized bed reactor 1. The solid products are crushed at 150°C for 0.5 hours to obtain carbon nanotubes.

[0056] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1.

[0057] Comparative Example 1 Adopting such Figure 2The system shown includes a thermal cracking downward fluidized bed A, a catalytic cracking upward fluidized bed B, a heat exchanger C-1, a desulfurization and denitrification unit C-2, and a separation unit C-3. The catalytic diesel and catalyst are the same as in Example 1.

[0058] Catalytic diesel is fed into a downward-flowing fluidized bed A for thermal cracking through inlet 15. At 800℃ and 0.8MPa, the residence time is controlled at 16s, and the diesel is cracked into hard carbon, C1-C10 hydrocarbons, hydrogen, hydrogen sulfide and ammonia.

[0059] The aforementioned gaseous and solid products exit fluidized bed A from pyrolysis product outlet 16 and enter catalytic pyrolysis upward fluidized bed B via pyrolysis product inlet 17. A small amount of solid enters the solid dilute phase region 18 along with the gas. They then continue upward, entering cyclone separator 19. After gas-solid separation, the solid returns to the bottom of catalytic pyrolysis upward fluidized bed B.

[0060] After exiting the catalytic cracking upward fluidized bed B through mixed gas outlet 20, the gas enters heat exchanger C-1 through mixed gas inlet 21. After being heated to 480℃, the gas exits heat exchanger C-1 through heat exchange gas outlet 22, and then enters desulfurization and denitrification unit C-2 through heat exchange gas inlet 23. Using conventional techniques (such as water washing and acid-base neutralization), all sulfur and nitrogen are removed. The gas then exits through desulfurization and denitrification gas outlet 24, and then enters separation unit C-3 through desulfurization and denitrification gas inlet 25 for hydrogen and hydrocarbon separation. The purified hydrogen, separated using conventional techniques (such as pressure swing adsorption), exits through hydrogen outlet 26, and the target product hydrogen is collected.

[0061] The separated light hydrocarbon gas exits the separation unit C-3 through light hydrocarbon gas outlet 27, then enters the heat exchange unit C-1 through light hydrocarbon gas inlet 28 and is heated to 450°C. After exiting the heat exchange unit C-1 through light hydrocarbon gas outlet 29, it is recycled back to light hydrocarbon gas inlet 30 and enters the catalytic cracking upward fluidized bed B, where it is used as fluidizing gas and reaction medium.

[0062] The catalyst is added to the upward-flowing fluidized bed B of catalytic cracking through catalyst inlet 31. The catalyst mixes with the hard carbon at the bottom and hydrocarbon gases entering through light hydrocarbon gas inlet 30, reaching a temperature of 780°C. The hydrocarbon gases are in contact with the catalyst for 1.2 minutes, cracking to produce carbon nanotubes and hydrogen or a small amount of methane. The generated hydrogen and a small amount of methane combine with the gases (H2, H2S, NH3, and hydrocarbons) entering through cracking product inlet 17, diluting the H2S and ammonia. After controlling the reaction time to 2 hours, the resulting mixture of carbon nanotubes and hard carbon exits the upward-flowing fluidized bed B of catalytic cracking through outlet 32, forming the carbon nanotube product.

[0063] Sulfur-nitrogen-containing oil is continuously fed into the downward fluidized bed A of the thermal cracking process through the inlet 15, and catalyst is fed into the upward fluidized bed B of the catalytic cracking process through the inlet 31 every 8 hours, so that the above process forms a continuous operation.

[0064] The diameter characteristics and other results of the carbon nanotubes prepared in this comparative example are listed in Table 1.

[0065] Table 1

[0066] As can be seen from Table 1, the carbon nanotubes prepared in the examples have higher conductivity and purity, indicating that this disclosure realizes the clean and high-value-added utilization of catalytic diesel and can efficiently prepare high-quality carbon nanotube products.

[0067] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0068] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0069] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for producing carbon nanotubes, characterized in that, The method includes: The catalytic diesel fuel is brought into contact with the first catalyst in the first fluidized bed reactor to carry out a desulfurization and denitrification reaction, and the gaseous products are collected. The gaseous product is brought into contact with a second catalyst in a second fluidized bed reactor to carry out a pyrolysis reaction, yielding pyrolysis gas and a solid product containing carbon nanotubes. The first catalyst is a metal oxide particle, and the second catalyst is a metal-supported catalyst.

2. The method according to claim 1, wherein, The catalytic diesel oil has a distillation temperature range of 200~300℃, a sulfur content of 100~10000 mg / kg, and a nitrogen content of 20~2000 mg / kg.

3. The method according to claim 1, wherein, The first catalyst includes at least one of iron oxide, nickel oxide, cobalt oxide, molybdenum oxide, tungsten oxide, zinc oxide, and manganese oxide; The particle size of the first catalyst is 50~350μm, and the mesoporous pore volume of the first catalyst accounts for 50~90% of the total pore volume.

4. The method according to claim 1, wherein, The second catalyst comprises a support, an active metal, and an additive. Based on the dry weight of the second catalyst, the content of the active metal is 1-15% by weight, and the content of the additive is 1-3% by weight. The support comprises at least one of alumina, silicon oxide, and magnesium oxide. The active metal comprises at least one of iron, cobalt, and nickel. The additive comprises molybdenum and / or tungsten. The particle size of the second catalyst is 1~200μm.

5. The method according to claim 1, wherein, The weight ratio of the catalytic diesel, the first catalyst, and the second catalyst is 1:(0.2~5):(0.2~3). Preferably, when the hydrogen content of the pyrolysis gas exceeds a first preset threshold and the purity of the carbon nanotubes exceeds a first preset threshold, the second catalyst is added to the second fluidized bed reactor at a first rate; when the hydrogen content of the pyrolysis gas is lower than a third preset threshold or the purity of the carbon nanotubes is lower than a fourth preset threshold, the second catalyst is added to the second fluidized bed reactor at a second rate; the first rate is lower than the second rate.

6. The method according to claim 1, wherein, The method also includes: The catalytic diesel fuel is carried by a carrier gas into the first fluidized bed reactor to carry out the desulfurization and denitrification reaction; Preferably, the flow rate of the carrier gas is 0.02~0.1m / s.

7. The method according to claim 6, wherein, The method also includes: The pyrolysis gas is used to preheat the catalytic diesel and / or as the carrier gas to carry the catalytic diesel.

8. The method according to claim 1, wherein, The method also includes: The sulfur content of the gaseous product is detected, and when the sulfur content of the gaseous product exceeds a first threshold, the first catalyst in the first fluidized bed reactor is replaced with a freshener. The sulfur content of the pyrolysis gas is detected, and when the sulfur content of the pyrolysis gas exceeds a second threshold, the solid product is drawn out of the second fluidized bed reactor.

9. The method according to claim 8, wherein, The first threshold is 50 ppm; the second threshold is 5 ppm.

10. The method according to claim 1, wherein, The conditions for the desulfurization and denitrification reaction include: a temperature of 300~450℃ and a time of 2~14h; The conditions for the pyrolysis reaction include: a temperature of 700~950℃ and a time of 2~14h.

11. The method according to claim 1, wherein, The solid product is an aggregate of a second catalyst and carbon nanotubes, and the particle size of the aggregate is 30 μm to 30 mm. The method further includes: breaking the solid product to obtain carbon nanotubes. Preferably, the diameter of the carbon nanotubes is in the range of 8~25nm.

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